Analysis of Dynamic Fracture Compliance Based on Poroelastic Theory - Part II: Results of Numerical and Experimental Tests

NASA Astrophysics Data System (ADS)

Wang, Ding; Ding, Pin-bo; Ba, Jing

2018-03-01

In Part I, a dynamic fracture compliance model (DFCM) was derived based on the poroelastic theory. The normal compliance of fractures is frequency-dependent and closely associated with the connectivity of porous media. In this paper, we first compare the DFCM with previous fractured media theories in the literature in a full frequency range. Furthermore, experimental tests are performed on synthetic rock specimens, and the DFCM is compared with the experimental data in the ultrasonic frequency band. Synthetic rock specimens saturated with water have more realistic mineral compositions and pore structures relative to previous works in comparison with natural reservoir rocks. The fracture/pore geometrical and physical parameters can be controlled to replicate approximately those of natural rocks. P- and S-wave anisotropy characteristics with different fracture and pore properties are calculated and numerical results are compared with experimental data. Although the measurement frequency is relatively high, the results of DFCM are appropriate for explaining the experimental data. The characteristic frequency of fluid pressure equilibration calculated based on the specimen parameters is not substantially less than the measurement frequency. In the dynamic fracture model, the wave-induced fluid flow behavior is an important factor for the fracture-wave interaction process, which differs from the models at the high-frequency limits, for instance, Hudson's un-relaxed model.

Effect of hydro mechanical coupling on natural fracture network formation in sedimentary basins

NASA Astrophysics Data System (ADS)

Ouraga, Zady; Guy, Nicolas; Pouya, Amade

2018-05-01

In sedimentary basin context, numerous phenomena, depending on the geological time span, can result in natural fracture network formation. In this paper, fracture network and dynamic fracture spacing triggered by significant sedimentation rate are studied considering mode I fracture propagation using a coupled hydro-mechanical numerical methods. The focus is put on synthetic geological structure under a constant sedimentation rate on its top. This model contains vertical fracture network initially closed and homogeneously distributed. The fractures are modelled with cohesive zone model undergoing damage and the flow is described by Poiseuille's law. The effect of the behaviour of the rock is studied and the analysis leads to a pattern of fracture network and fracture spacing in the geological layer.

Laplace-SGBEM analysis of the dynamic stress intensity factors and the dynamic T-stress for the interaction between a crack and auxetic inclusions

NASA Astrophysics Data System (ADS)

Kwon, Kibum

A dynamic analysis of the interaction between a crack and an auxetic (negative Poisson ratio)/non-auxetic inclusion is presented. The two most important fracture parameters, namely the stress intensity factors and the T-stress are analyzed by using the symmetric Galerkin boundary element method in the Laplace domain for three different models of crack-inclusion interaction. To investigate the effects of auxetic inclusions on the fracture behavior of composites reinforced by this new type of material, comparisons of the dynamic stress intensity factors and the dynamic T-stress are made between the use of auxetic inclusions as opposed to the use of traditional inclusions. Furthermore, the technique presented in this research can be employed to analyze for the interaction between a crack and a cluster of auxetic/non-auxetic inclusions. Results from the latter models can be employed in crack growth analysis in auxetic-fiber-reinforced composites.

Decision Making in the Management of Extracapsular Fractures of the Proximal Femur - is the Dynamic Hip Screw the Prevailing Gold Standard?

PubMed

Jacob, Joshua; Desai, Ankit; Trompeter, Alex

2017-01-01

Currently, approximately half of all hip fractures are extracapsular, with an incidence as high as 50 in 100,000 in some countries. The common classification systems fail to explain the logistics of fracture classification and whether they all behave in the same manner. The Muller AO classification system is a useful platform to delineate stable and unstable fractures. The Dynamic hip screw (DHS) however, has remained the 'gold standard' implant of choice for application in all extracapsular fractures. The DHS relies on the integrity and strength of the lateral femoral wall as well as the postero-medial fragment. An analysis of several studies indicates significant improvements in design and techniques to ensure a better outcome with intramedullary nails. This article reviews the historical trends that helped to evolve the DHS implant as well as discussing if the surgeon should remain content with this implant. We suggest that the gold standard surgical management of extracapsular fractures can, and should, evolve.

In-vitro development of a temporal abutment screw to protect osseointegration in immediate loaded implants

PubMed Central

2015-01-01

PURPOSE In this study, a temporal abutment fixation screw, designed to fracture in a controlled way upon application of an occlusal force sufficient to produce critical micromotion was developed. The purpose of the screw was to protect the osseointegration of immediate loaded single implants. MATERIALS AND METHODS Seven different screw prototypes were examined by fixing titanium abutments to 112 Mozo-Grau external hexagon implants (MG Osseous®; Mozo-Grau, S.A., Valladolid, Spain). Fracture strength was tested at 30° in two subgroups per screw: one under dynamic loading and the other without prior dynamic loading. Dynamic loading was performed in a single-axis chewing simulator using 150,000 load cycles at 50 N. After normal distribution of obtained data was verified by Kolmogorov-Smirnov test, fracture resistance between samples submitted and not submitted to dynamic loading was compared by the use of Student's t-test. Comparison of fracture resistance among different screw designs was performed by the use of one-way analysis of variance. Confidence interval was set at 95%. RESULTS Fractures occurred in all screws, allowing easy retrieval. Screw Prototypes 2, 5 and 6 failed during dynamic loading and exhibited statistically significant differences from the other prototypes. CONCLUSION Prototypes 2, 5 and 6 may offer a useful protective mechanism during occlusal overload in immediate loaded implants. PMID:25932315

Biomechanical investigation of naso-orbitoethmoid trauma by finite element analysis.

PubMed

Huempfner-Hierl, Heike; Schaller, Andreas; Hemprich, Alexander; Hierl, Thomas

2014-11-01

Naso-orbitoethmoid fractures account for 5% of all facial fractures. We used data derived from a white 34-year-old man to make a transient dynamic finite element model, which consisted of about 740 000 elements, to simulate fist-like impacts to this anatomically complex area. Finite element analysis showed a pattern of von Mises stresses beyond the yield criterion of bone that corresponded with fractures commonly seen clinically. Finite element models can be used to simulate injuries to the human skull, and provide information about the pathogenesis of different types of fracture. Copyright © 2014 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.

Video analysis of the biomechanics of a bicycle accident resulting in significant facial fractures.

PubMed

Syed, Shameer H; Willing, Ryan; Jenkyn, Thomas R; Yazdani, Arjang

2013-11-01

This study aimed to use video analysis techniques to determine the velocity, impact force, angle of impact, and impulse to fracture involved in a video-recorded bicycle accident resulting in facial fractures. Computed tomographic images of the resulting facial injury are presented for correlation with data and calculations. To our knowledge, such an analysis of an actual recorded trauma has not been reported in the literature. A video recording of the accident was split into frames and analyzed using an image editing program. Measurements of velocity and angle of impact were obtained from this analysis, and the force of impact and impulse were calculated using the inverse dynamic method with connected rigid body segments. These results were then correlated with the actual fracture pattern found on computed tomographic imaging of the subject's face. There was an impact velocity of 6.25 m/s, impact angles of 14 and 6.3 degrees of neck extension and axial rotation, respectively, an impact force of 1910.4 N, and an impulse to fracture of 47.8 Ns. These physical parameters resulted in clinically significant bilateral mid-facial Le Fort II and III pattern fractures. These data confer further understanding of the biomechanics of bicycle-related accidents by correlating an actual clinical outcome with the kinematic and dynamic parameters involved in the accident itself and yielding a concrete evidence of the velocity, force, and impulse necessary to cause clinically significant facial trauma. These findings can aid in the design of protective equipment for bicycle riders to help avoid this type of injury.

Fractographic Analysis of a Split Tooth Presenting Radiographically as a Horizontal Root Fracture in an Unrestored Mandibular Second Molar.

PubMed

Krishnan, Unni; Moule, Alex; Michael, Shaji; Swain, Michael

2018-02-01

Spontaneously catastrophic fracture of intact unrestored molar teeth is not common. Nevertheless, cracks do occur that progress apically, resulting in the complete splitting of the tooth and root. This report describes a catastrophic fracture that occurred in an unrestored mandibular second molar resulting in a previously unreported combination of a longitudinal and horizontal root fracture, appearing radiographically as a single horizontal root fracture. Tooth fragments were examined clinically, stereoscopically, and by scanning electron microscopy. Fractographic analysis was used to investigate the dynamics involved in fracture initiation, structural resistances encountered during progression of the fracture, and reasons for direction changes culminating in the unusual radiographic appearance. The uniqueness of this report is that it describes fractographic evidence of factors contributing to the initiation and progression of an in vivo crack. It shows fracture markings that are evidence of the energy dissipation mechanisms. The topographic location of these markings confirmed that cracks occur in vivo in stages with different rates of progression. This analysis helps to explain why split teeth are uncommon and highlights some of the multitude of factors that have to coincide for a tooth to catastrophically fracture. The report describes the mechanism of fracture and should stimulate clinicians and researchers to investigate cracking of teeth by undertaking fractographic analysis of extracted cracked teeth. Copyright © 2017 American Association of Endodontists. All rights reserved.

Numerical Analysis in Fracture Mechanics.

DTIC Science & Technology

1983-01-20

pressuriza- tion has also been solved [66] by the HEMP code. The advantage of such supercode, however, lies in its ability to analyze elastic- plastic ...analyzing the elasto-dynamic and elastic- plastic dynamic states In fracturing 2- and 3-D prob’ems. The use of a super finite difference code to study...the finite difference elastic- plastic result of Jacobs in 1950 [2J which was followed by others In the 1960’s [3 - 5). Swedlow et al [6], on the other a

Investigation of the Fracture Behavior of Scaled HY-130 Weldments

DTIC Science & Technology

1990-06-01

RESULTS OF EPFM ANALYSIS OF TFREE-POINT BEND SPECIMENS OF DIFFERENT SIZES ........... D-48 xi NAVSWC TR 90-360 TABLES 1 RESULTS OF DYNAMIC FRACTURE...characterize the critical loading needed to cause fracture of the welded joint. An example of such a measure of severity applicable to structures with...weldments. Application of the approach to two titanium alloys and the results of that hwvestigation will be presented in another report. The next four

On the physics of unstable infiltration, seepage, and gravity drainage in partially saturated tuffs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Faybishenko, B.; Bodvarsson, G.S.; Salve, R.

2002-04-01

To improve understanding of the physics of dynamic instabilities in unsaturated flow processes within the Paintbrush nonwelded unit (PTn) and the middle nonlithophysal portion of the Tonopah Spring welded tuff unit (TSw) of Yucca Mountain, we analyzed data from a series of infiltration tests carried out at two sites (Alcove 4 and Alcove 6) in the Exploratory Studies Facility, using analytical and empirical functions. The analysis of infiltration rates measured at both sites showed three temporal scales of infiltration rate: (1) a macro-scale trend of overall decreasing flow, (2) a meso-scale trend of fast and slow motion exhibiting three-stage variationsmore » of the flow rate (decreasing, increasing, and [again] decreasing flow rate, as observed in soils in the presence of entrapped air), and (3) micro-scale (high frequency) fluctuations. Infiltration tests in the nonwelded unit at Alcove 4 indicate that this unit may effectively dampen episodic fast infiltration events; however, well-known Kostyakov, Horton, and Philip equations do not satisfactorily describe the observed trends of the infiltration rate. Instead, a Weibull distribution model can most accurately describe experimentally determined time trends of the infiltration rate. Infiltration tests in highly permeable, fractured, welded tuff at Alcove 6 indicate that the infiltration rate exhibits pulsation, which may have been caused by multiple threshold effects and water-air redistribution between fractures and matrix. The empirical relationships between the extrinsic seepage from fractures, matrix imbibition, and gravity drainage versus the infiltration rate, as well as scaling and self-similarity for the leading edge of the water front are the hallmark of the nonlinear dynamic processes in water flow under episodic infiltration through fractured tuff. Based on the analysis of experimental data, we propose a conceptual model of a dynamic fracture flow and fracture-matrix interaction in fractured tuff, incorporating the time dependent processes of water redistribution in the fracture-matrix system.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, Shih-Jung

Dynamic strength of the High Flux Isotope Reactor (HFIR) vessel to resist hypothetical accidents is analyzed by using the method of fracture mechanics. Vessel critical stresses are estimated by applying dynamic pressure pulses of a range of magnitudes and pulse-durations. The pulses versus time functions are assumed to be step functions. The probability of vessel fracture is then calculated by assuming a distribution of possible surface cracks of different crack depths. The probability distribution function for the crack depths is based on the form that is recommended by the Marshall report. The toughness of the vessel steel used in themore » analysis is based on the projected and embrittled value after 10 effective full power years from 1986. From the study made by Cheverton, Merkle and Nanstad, the weakest point on the vessel for fracture evaluation is known to be located within the region surrounding the tangential beam tube HB3. The increase in the probability of fracture is obtained as an extension of the result from that report for the regular operating condition to include conditions of higher dynamic pressures due to accident loadings. The increase in the probability of vessel fracture is plotted for a range of hoop stresses to indicate the vessel strength against hypothetical accident conditions.« less

Visualization and Hierarchical Analysis of Flow in Discrete Fracture Network Models

NASA Astrophysics Data System (ADS)

Aldrich, G. A.; Gable, C. W.; Painter, S. L.; Makedonska, N.; Hamann, B.; Woodring, J.

2013-12-01

Flow and transport in low permeability fractured rock is primary in interconnected fracture networks. Prediction and characterization of flow and transport in fractured rock has important implications in underground repositories for hazardous materials (eg. nuclear and chemical waste), contaminant migration and remediation, groundwater resource management, and hydrocarbon extraction. We have developed methods to explicitly model flow in discrete fracture networks and track flow paths using passive particle tracking algorithms. Visualization and analysis of particle trajectory through the fracture network is important to understanding fracture connectivity, flow patterns, potential contaminant pathways and fast paths through the network. However, occlusion due to the large number of highly tessellated and intersecting fracture polygons preclude the effective use of traditional visualization methods. We would also like quantitative analysis methods to characterize the trajectory of a large number of particle paths. We have solved these problems by defining a hierarchal flow network representing the topology of particle flow through the fracture network. This approach allows us to analyses the flow and the dynamics of the system as a whole. We are able to easily query the flow network, and use paint-and-link style framework to filter the fracture geometry and particle traces based on the flow analytics. This allows us to greatly reduce occlusion while emphasizing salient features such as the principal transport pathways. Examples are shown that demonstrate the methodology and highlight how use of this new method allows quantitative analysis and characterization of flow and transport in a number of representative fracture networks.

Finite Element Modeling of Non-linear Coupled Interacting Fault System

NASA Astrophysics Data System (ADS)

Xing, H. L.; Zhang, J.; Wyborn, D.

2009-04-01

PANDAS - Parallel Adaptive static/dynamic Nonlinear Deformation Analysis System - a novel supercomputer simulation tool is developed for simulating the highly non-linear coupled geomechanical-fluid flow-thermal systems involving heterogeneously fractured geomaterials. PANDAS includes the following key components: Pandas/Pre, ESyS_Crustal, Pandas/Thermo, Pandas/Fluid and Pandas/Post as detailed in the following: • Pandas/Pre is developed to visualise the microseismicity events recorded during the hydraulic stimulation process to further evaluate the fracture location and evolution and geological setting of a certain reservoir, and then generate the mesh by it and/or other commercial graphics software (such as Patran) for the further finite element analysis of various cases; The Delaunay algorithm is applied as a suitable method for mesh generation using such a point set; • ESyS_Crustal is a finite element code developed for the interacting fault system simulation, which employs the adaptive static/dynamic algorithm to simulate the dynamics and evolution of interacting fault systems and processes that are relevant on short to mediate time scales in which several dynamic phenomena related with stick-slip instability along the faults need to be taken into account, i.e. (a). slow quasi-static stress accumulation, (b) rapid dynamic rupture, (c) wave propagation and (d) corresponding stress redistribution due to the energy release along the multiple fault boundaries; those are needed to better describe ruputure/microseimicity/earthquake related phenomena with applications in earthquake forecasting, hazard quantification, exploration, and environmental problems. It has been verified with various available experimental results[1-3]; • Pandas/Thermo is a finite element method based module for the thermal analysis of the fractured porous media; the temperature distribution is calculated from the heat transfer induced by the thermal boundary conditions without/with the coupled fluid effects and the geomechanical energy conversion for the pure/coupled thermal analysis. • Pandas/Fluid is a finite element method based module for simulating the fluid flow in the fractured porous media; the fluid flow velocity and pressure are calculated from energy equilibrium equations without/together with the coupling effects of the thermal and solid rock deformation for an independent/coupled fluid flow analysis; • Pandas/Post is to visualise the simulation results through the integration of VTK and/or Patran. All the above modules can be used independently/together to simulate individual/coupled phenomena (such as interacting fault system dynamics, heat flow and fluid flow) without/with coupling effects. PANDAS has been applied to the following issues: • visualisation of the microseismic events to monitor and determine where/how the underground rupture proceeds during a hydraulic stimulation, to generate the mesh using the recorded data for determining the domain of the ruptured zone and to evaluate the material parameters (i.e. the permeability) for the further numerical analysis; • interacting fault system simulation to determine the relevant complicated dynamic rupture process. • geomechanical-fluid flow coupling analysis to investigate the interactions between fluid flow and deformation in the fractured porous media under different loading conditions. • thermo-fluid flow coupling analysis of a fractured geothermal reservoir system. PANDAS will be further developed for a multiscale simulation of multiphase dynamic behaviour for a certain fractured geothermal reservoir. More details and additional application examples will be given during the presentation. References [1] Xing, H. L., Makinouchi, A. and Mora, P. (2007). Finite element modeling of interacting fault system, Physics of the Earth and Planetary Interiors, 163, 106-121.doi:10.1016/j.pepi.2007.05.006 [2] Xing, H. L., Mora, P., Makinouchi, A. (2006). An unified friction description and its application to simulation of frictional instability using finite element method. Philosophy Magazine, 86, 3453-3475 [3] Xing, H. L., Mora, P.(2006). Construction of an intraplate fault system model of South Australia, and simulation tool for the iSERVO institute seed project.. Pure and Applied Geophysics. 163, 2297-2316. DOI 10.1007/s00024-006-0127-x

Penetration analysis of projectile with inclined concrete target

NASA Astrophysics Data System (ADS)

Kim, S. B.; Kim, H. W.; Yoo, Y. H.

2015-09-01

This paper presents numerical analysis result of projectile penetration with concrete target. We applied dynamic material properties of 4340 steels, aluminium and explosive for projectile body. Dynamic material properties were measured with static tensile testing machine and Hopkinson pressure bar tests. Moreover, we used three concrete damage models included in LS-DYNA 3D, such as SOIL_CONCRETE, CSCM (cap model with smooth interaction) and CONCRETE_DAMAGE (K&C concrete) models. Strain rate effect for concrete material is important to predict the fracture deformation and shape of concrete, and penetration depth for projectiles. CONCRETE_DAMAGE model with strain rate effect also applied to penetration analysis. Analysis result with CSCM model shows good agreement with penetration experimental data. The projectile trace and fracture shapes of concrete target were compared with experimental data.

Decision Making in the Management of Extracapsular Fractures of the Proximal Femur – is the Dynamic Hip Screw the Prevailing Gold Standard?

PubMed Central

Jacob, Joshua; Desai, Ankit; Trompeter, Alex

2017-01-01

Currently, approximately half of all hip fractures are extracapsular, with an incidence as high as 50 in 100,000 in some countries. The common classification systems fail to explain the logistics of fracture classification and whether they all behave in the same manner. The Muller AO classification system is a useful platform to delineate stable and unstable fractures. The Dynamic hip screw (DHS) however, has remained the ‘gold standard’ implant of choice for application in all extracapsular fractures. The DHS relies on the integrity and strength of the lateral femoral wall as well as the postero-medial fragment. An analysis of several studies indicates significant improvements in design and techniques to ensure a better outcome with intramedullary nails. This article reviews the historical trends that helped to evolve the DHS implant as well as discussing if the surgeon should remain content with this implant. We suggest that the gold standard surgical management of extracapsular fractures can, and should, evolve. PMID:29290858

Nonequilibrium capillarity effects in multiphase flow through small volume fractured porous media

NASA Astrophysics Data System (ADS)

Tang, M.; Zhan, H.; Lu, S.

2017-12-01

Analyzing and understanding the capillary pressure curves in fractured porous media is a crucial subject in a number of industrial applications, such as crude oil recovery in the fractured reservoir, CO2 sequestration in fractured brine aquifers and shale gas development. Many studies have observed the significant nonequilibrium capillarity effects in multiphase flow through porous media and proposed that conventional equilibrium capillary pressure may not accurately describe transient two-phase flow behavior under dynamical conditions. To date, only several laboratory experiments and numerical models have been conducted into investigating the characteristic of nonequilibrium capillary pressure in unfractured porous media, a clear picture of the effects of fractures on the dynamic capillary pressure in fractured porous media remains elusive. In this study, four digital porous models were built based on CT image data from ZEISS Xradia 520 Versa CT scanning, a series of direct simulations of multiphase flow in fractured porous media were carried out based on lattice Boltzmann method and three-dimensional porous models. The results show that both the aperture and orientation of the fractures have significant effects on the nonequilibrium capillary pressure coefficients and multiphase flow behaviors. The nonequilibrium capillary pressure coefficients in fractured porous media are one to two orders of magnitude lower than unfractured porous media. This study presents a new direct simulation based methodology for the detailed analysis of nonequilibrium capillary pressure in fractured porous media.

Dynamic Tensile Properties of Iron and Steels for a Wide Range of Strain Rates and Strain

NASA Astrophysics Data System (ADS)

Kojima, Nobusato; Hayashi, Hiroyuki; Yamamoto, Terumi; Mimura, Koji; Tanimura, Shinji

The tensile stress-strain curves of iron and a variety of steels, covering a wide range of strength level, over a wide strain rate range on the order of 10-3 ~ 103 s-1, were obtained systematically by using the Sensing Block Type High Speed Material Testing System (SBTS, Saginomiya). Through intensive analysis of these results, the strain rate sensitivity of the flow stress for the large strain region, including the viscous term at high strain rates, the true fracture strength and the true fracture strain were cleared for the material group of the ferrous metals. These systematical data may be useful to develop a practical constitutive model for computer codes, including a fracture criterion for simulations of the dynamic behavior in crash worthiness studies and of work-pieces subjected to dynamic plastic working for a wide strain rate range.

Nonlinear quasi-static finite element simulations predict in vitro strength of human proximal femora assessed in a dynamic sideways fall setup.

PubMed

Varga, Peter; Schwiedrzik, Jakob; Zysset, Philippe K; Fliri-Hofmann, Ladina; Widmer, Daniel; Gueorguiev, Boyko; Blauth, Michael; Windolf, Markus

2016-04-01

Osteoporotic proximal femur fractures are caused by low energy trauma, typically when falling on the hip from standing height. Finite element simulations, widely used to predict the fracture load of femora in fall, usually include neither mass-related inertial effects, nor the viscous part of bone׳s material behavior. The aim of this study was to elucidate if quasi-static non-linear homogenized finite element analyses can predict in vitro mechanical properties of proximal femora assessed in dynamic drop tower experiments. The case-specific numerical models of 13 femora predicted the strength (R(2)=0.84, SEE=540N, 16.2%), stiffness (R(2)=0.82, SEE=233N/mm, 18.0%) and fracture energy (R(2)=0.72, SEE=3.85J, 39.6%); and provided fair qualitative matches with the fracture patterns. The influence of material anisotropy was negligible for all predictions. These results suggest that quasi-static homogenized finite element analysis may be used to predict mechanical properties of proximal femora in the dynamic sideways fall situation. Copyright © 2015 Elsevier Ltd. All rights reserved.

Influence of Microstructural Disorder and Wavefield in Dynamic Fracture

NASA Astrophysics Data System (ADS)

Alizee, D.; Bonamy, D.

2017-12-01

Dynamic fracture and its instabilities have been widely studied but the influence of the finite sample size and subsequent 3D aspects are generally neglected. However, a sample of a few centimeter is a waveguide for the elastodynamic field emitted by the propagating crack front (from 100kHz to a few GHz): It excites the sample's free oscillations (or normal modes), and creates a fluctuating landscape of elastic energy. This may be seen as an effective noise, with an amplitude proportional to the frequency of a given mode, which can reach the same order of magnitude as that of the fracture toughness (In PMMA: 103 J.m-2 for f ˜ MHz). We designed an experiment to evidence this effect in a homogeneous brittle material (PMMA) and subsequently to characterize the possible coupling between the fracture front and its wavefield. Dynamic cracks are driven by means of a wedge splitting geometry which allow us to modulate, over a wide range, the velocity of the crack tip. Spatial geometry and frequency content of the emitted wavefield are modulated by adjusting the geometry of the sample and the loading conditions. Hints of the wavefield are looked in the high-frequency fluctuations of the crack speed, measured on both sides of the specimen via a state-of-the art potential drop method. Fractography and statistical analysis of the post-mortem fracture surfaces are used to characterize the mesoscale/microstructure scale response of the crack front to the wavefield. Experiments performed in PMMA will finally be compared to others performed on heterogeneous materials with controlled defects size (40 - 500µm). This study will permit (i) to shed light on the key role of elastic wavefield in dynamic fracture, and how those are selected by the sample geometry and microstructure and finally and (ii) to give some leads on how to account for these effects by adapting the paradigm of interface growth model to the case of dynamic fracture.

Influence of different manufacturing methods on the cyclic fatigue of rotary nickel-titanium endodontic instruments.

PubMed

Rodrigues, Renata C V; Lopes, Hélio P; Elias, Carlos N; Amaral, Georgiana; Vieira, Victor T L; De Martin, Alexandre S

2011-11-01

The aim of this study was to evaluate, by static and dynamic cyclic fatigue tests, the number of cycles to fracture (NCF) 2 types of rotary NiTi instruments: Twisted File (SybronEndo, Orange, CA), which is manufactured by a proprietary twisting process, and RaCe files (FKG Dentaire, La Chaux-de-Fonds, Switzerland), which are manufactured by grinding. Twenty Twisted Files (TFs) and 20 RaCe files #25/.006 taper instruments were allowed to rotate freely in an artificial curved canal at 310 rpm in a static or a dynamic model until fracture occurred. Measurements of the fractured fragments showed that fracture occurred at the point of maximum flexure in the midpoint of the curved segment. The NCF was significantly lower for RaCe instruments compared with TFs. The NCF was also lower for instruments subjected to the static test compared with the dynamic model in both groups. Scanning electron microscopic analysis revealed ductile morphologic characteristics on the fractured surfaces of all instruments and no plastic deformation in their helical shafts. Rotary NiTi endodontic instruments manufactured by twisting present greater resistance to cyclic fatigue compared with instruments manufactured by grinding. The fracture mode observed in all instruments was of the ductile type. Copyright © 2011 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

PREFACE: International Symposium on Dynamic Deformation and Fracture of Advanced Materials (D2FAM 2013)

NASA Astrophysics Data System (ADS)

Silberschmidt, Vadim V.

2013-07-01

Intensification of manufacturing processes and expansion of usability envelopes of modern components and structures in many cases result in dynamic loading regimes that cannot be resented adequately employing quasi-static formulations of respective problems of solid mechanics. Specific features of dynamic deformation, damage and fracture processes are linked to various factors, most important among them being: a transient character of load application; complex scenarios of propagation, attenuation and reflection of stress waves in real materials, components and structures; strain-rate sensitivity of materials properties; various thermo-mechanical regimes. All these factors make both experimental characterisation and theoretical (analytical and numerical) analysis of dynamic deformation and fracture rather challenging; for instance, besides dealing with a spatial realisation of these processes, their evolution with time should be also accounted for. To meet these challenges, an International Symposium on Dynamic Deformation and Fracture of Advanced Materials D2FAM 2013 was held on 9-11 September 2013 in Loughborough, UK. Its aim was to bring together specialists in mechanics of materials, applied mathematics, physics, continuum mechanics, materials science as well as various areas of engineering to discuss advances in experimental and theoretical analysis, and numerical simulations of dynamic mechanical phenomena. Some 50 papers presented at the Symposium by researchers from 12 countries covered various topics including: high-strain-rate loading and deformation; dynamic fracture; impact and blast loading; high-speed penetration; impact fatigue; damping properties of advanced materials; thermomechanics of dynamic loading; stress waves in micro-structured materials; simulation of failure mechanisms and damage accumulation; processes in materials under dynamic loading; a response of components and structures to harsh environment. The materials discussed at D2FAM 2013 ranged from traditional ones such as metals, alloys, polymers and composites to advanced and emerging materials, such as foams, cellular materials and metallic glasses, as well as bio-materials. Within the framework of the Symposium, a Special Session 'Parametric Resonance, Vibro-impact and Related Phenomena' was organised by partners of the FP7 IAPP project PARM-2: 'Vibro-impact machines based on parametric resonance: Concepts, mathematical modelling, experimental verification and implementation.' The Session focused on the topics, directly related to the project: excitation, stabilization, control and applications of parametric resonance (PR); multiple degrees of freedom of PR-excited systems; basic principles of PR-based macro and micro tools; design and technological aspects of PR-based machines; vibro-assisted machining; fatigue under high-amplitude vibro-impact conditions and corresponding optimal design; localisation near defects in dynamic response of elastic lattices and structures; dispersive waves and dynamic fracture in non-uniform lattice systems; thermally induced surface-breaking cracks, etc. This issue presents a selection of research papers presented at the International Symposium on Dynamic Deformation and Fracture of Advanced Materials D2FAM 2013. The Symposium Organisers would like to acknowledge its sponsors: Institute of Physics, International Centre of Vibro-Impact Systems and Marie Curie Action: Industry-Academia Partnerships and Pathways of the Seventh Framework Programme (FP7) of the European Commission (PARM-2 consortium). The PARM-2 consortium sponsored twenty scholarships for early-stage researchers to participate in this Symposium.

Influence of mechanical rock properties and fracture healing rate on crustal fluid flow dynamics

NASA Astrophysics Data System (ADS)

Sachau, Till; Bons, Paul; Gomez-Rivas, Enrique; Koehn, Daniel; de Riese, Tamara

2016-04-01

Fluid flow in the Earth's crust is very slow over extended periods of time, during which it occurs within the connected pore space of rocks. If the fluid production rate exceeds a certain threshold, matrix permeability alone is insufficient to drain the fluid volume and fluid pressure builds up, thereby reducing the effective stress supported by the rock matrix. Hydraulic fractures form once the effective pressure exceeds the tensile strength of the rock matrix and act subsequently as highly effective fluid conduits. Once local fluid pressure is sufficiently low again, flow ceases and fractures begin to heal. Since fluid flow is controlled by the alternation of fracture permeability and matrix permeability, the flow rate in the system is strongly discontinuous and occurs in intermittent pulses. Resulting hydraulic fracture networks are largely self-organized: opening and subsequent healing of hydraulic fractures depends on the local fluid pressure and on the time-span between fluid pulses. We simulate this process with a computer model and describe the resulting dynamics statistically. Special interest is given to a) the spatially and temporally discontinuous formation and closure of fractures and fracture networks and b) the total flow rate over time. The computer model consists of a crustal-scale dual-porosity setup. Control parameters are the pressure- and time-dependent fracture healing rate, and the strength and the permeability of the intact rock. Statistical analysis involves determination of the multifractal properties and of the power spectral density of the temporal development of the total drainage rate and hydraulic fractures. References Bons, P. D. (2001). The formation of large quartz veins by rapid ascent of fluids in mobile hydrofractures. Tectonophysics, 336, 1-17. Miller, S. a., & Nur, A. (2000). Permeability as a toggle switch in fluid-controlled crustal processes. Earth and Planetary Science Letters, 183(1-2), 133-146. Sachau, T., Bons, P. D., & Gomez-Rivas, E. (2015). Transport efficiency and dynamics of hydraulic fracture networks. Frontiers in Physics, 3.

Cracks dynamics under tensional stress - a DEM approach

NASA Astrophysics Data System (ADS)

Debski, Wojciech; Klejment, Piotr; Kosmala, Alicja; Foltyn, Natalia; Szpindler, Maciej

2017-04-01

Breaking and fragmentation of solid materials is an extremely complex process involving scales ranging from an atomic scale (breaking inter-atomic bounds) up to thousands of kilometers in case of catastrophic earthquakes (in energy scale it ranges from single eV up to 1024 J). Such a large scale span of breaking processes opens lot of questions like, for example, scaling of breaking processes, existence of factors controlling final size of broken area, existence of precursors, dynamics of fragmentation, to name a few. The classical approach to study breaking process at seismological scales, i.e., physical processes in earthquake foci, is essentially based on two factors: seismic data (mostly) and the continuum mechanics (including the linear fracture mechanics). Such approach has been gratefully successful in developing kinematic (first) and dynamic (recently) models of seismic rupture and explaining many of earthquake features observed all around the globe. However, such approach will sooner or latter face a limitation due to a limited information content of seismic data and inherit limitations of the fracture mechanics principles. A way of avoiding this expected limitation is turning an attention towards a well established in physics method of computational simulations - a powerful branch of contemporary physics. In this presentation we discuss preliminary results of analysis of fracturing dynamics under external tensional forces using the Discrete Element Method approach. We demonstrate that even under a very simplified tensional conditions, the fragmentation dynamics is a very complex process, including multi-fracturing, spontaneous fracture generation and healing, etc. We also emphasis a role of material heterogeneity on the fragmentation process.

[Stress test and clinical application of the minimal-invasive dynamic hip screw].

PubMed

Tong, Song-Lin; Chen, Jian-Lie; Lu, Wen-Jie; Pan, Zhi-Jun; Wang, Yi-Jin

2008-05-01

To recognize the effect of minimal-invasive dynamic hip screw (MIDHS) on the treatment of intertrochanteric fracture of the hip by biomechanical test and preliminary clinical application. Ten artifical made intertrochanteric fractures of femoral specimen from five cadavers were divided into two groups randomly. The fractures in first group were fixed by MIDHS and other group were fixed by dynamic hip (DHS). Biomechanical characteristics of two different devices were compared with the biomechanical character of load-straining, load-displacing, rigidity and strength of femur by statistic analysis. According to the Harris evaluation, healing effect of intertrochanteric fractures was evaluated clinically on the 15 cases. Straining changes of MIDHS were 14% and 11% less than that of DHS on the tensile side and the pressure side respectively; Sinking and horizontal displacement, were 19% and 22% less than that of DHS respectivly. But external and internal stress intensity,axial and bending rigidity were all higher than that of DHS, they were 12%, 11%, 19% and 37%. Maximal destroyed twisting moment (15%) and average twisting rigidity (15%) were both higher than that of DHS, but twisting angle was 18% less. Under the force, of 1 800 N, the open angle of the fracture on transverse section was 2.28 degrees,while the DHS's was 3.60 degrees . The data above were significant differences statistically (P < 0.01). The average Harris score of the 15 cases with intertrochanteric fractures treated by MIDHS was 91, excellent and good rate was 92.7%, without complications of internal fixation failure,postoperative infection and so on. The design of minimal-invasive dynamic hip screw is reasonable and effective against rotating, shearing and varus stress force of the fracture, and it provides possibility of implanting the internal fixation with minimal incision. So it is an ideal internal fixation device for the treatment of intertrochanteric fractures.

Analysis of Fragmentation During Dynamic Loading: Investigations in the Ries Impact Crater, Germany

NASA Astrophysics Data System (ADS)

Weimer, D.; Hergarten, S.; Kenkmann, T.

2015-09-01

We tested three methods to quantify fragmentation of rocks during dynamic loading and found a trend of decreasing fracture density with increasing distance from crater center. Fragmentation attenuation rates in the near- and far-field are different.

Development and Advanced Analysis of Dynamic and Static Casing Strain Monitoring to Characterize the Orientation and Dimensions of Hydraulic Fractures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bruno, Michael; Ramos, Juan; Lao, Kang

Horizontal wells combined with multi-stage hydraulic fracturing have been applied to significantly increase production from low permeability formations, contributing to expanded total US production of oil and gas. Not all applications are successful, however. Field observations indicate that poorly designed or placed fracture stages in horizontal wells can result in significant well casing deformation and damage. In some instances, early fracture stages have deformed the casing enough so that it is not possible to drill out plugs in order to complete subsequent fracture stages. Improved fracture characterization techniques are required to identify potential problems early in the development of themore » field. Over the past decade, several new technologies have been presented as alternatives to characterize the fracture geometry for unconventional reservoirs. Monitoring dynamic casing strain and deformation during hydraulic fracturing represents one of these new techniques. The objective of this research is to evaluate dynamic and static strains imposed on a well casing by single and multiple stage fractures, and to use that information in combination with numerical inversion techniques to estimate fracture characteristics such as length, orientation and post treatment opening. GeoMechanics Technologies, working in cooperation with the Department of Energy, Small Business Innovation Research through DOE SBIR Grant No: DE-SC-0017746, is conducting a research project to complete an advanced analysis of dynamic and static casing strain monitoring to characterize the orientation and dimensions of hydraulic fractures. This report describes our literature review and technical approach. The following conclusions summarize our review and simulation results to date: A literature review was performed related to the fundamental theoretical and analytical developments of stress and strain imposed by hydraulic fracturing along casing completions and deformation monitoring techniques. Analytical solutions have been developed to understand the mechanisms responsible for casing deformation induced by hydraulic fracturing operations. After reviewing a range of casing deformation techniques, including fiber optic sensors, borehole ultrasonic tools and electromagnetic tools, we can state that challenges in deployment, data acquisition and interpretation must still be overcome to ensure successful application of strain measurement and inversion techniques to characterize hydraulic fractures in the field. Numerical models were developed to analyze induced strain along casing, cement and formation interfaces. The location of the monitoring sensor around the completion, mechanical properties of the cement and its condition in the annular space can impact the strain measurement. Field data from fiber optic sensors were evaluated to compare against numerical models. A reasonable match for the fracture height characterization was obtained. Discrepancies in the strain magnitude between the field data and the numerical model was observed and can be caused by temperature effects, the cement condition in the well and the perturbation at the surface during injection. To avoid damage in the fiber optic cable during the perforation (e.g. when setting up multi stage HF scenarios), oriented perforation technologies are suggested. This issue was evidenced in the analyzed field data, where it was not possible to obtain strain measurement below the top of the perforation. This presented a limitation to characterize the entire fracture geometry. The comparison results from numerical modeling and field data for fracture characterization shows that the proposed methodology should be validated with alternative field demonstration techniques using measurements in an offset observation well to monitor and measure the induced strain. We propose to expand on this research in Phase II with a further study of multi-fracture characterization and field demonstration for horizontal wells.« less

A chaotic-dynamical conceptual model to describe fluid flow and contaminant transport in a fractured vadose zone. 1997 progress report and presentations at the annual meeting, Ernest Orlando Lawrence Berkeley National Laboratory, December 3--4, 1997

DOE Office of Scientific and Technical Information (OSTI.GOV)

Faybishenko, B.; Doughty, C.; Geller, J.

1998-07-01

Understanding subsurface flow and transport processes is critical for effective assessment, decision-making, and remediation activities for contaminated sites. However, for fluid flow and contaminant transport through fractured vadose zones, traditional hydrogeological approaches are often found to be inadequate. In this project, the authors examine flow and transport through a fractured vadose zone as a deterministic chaotic dynamical process, and develop a model of it in these terms. Initially, the authors examine separately the geometric model of fractured rock and the flow dynamics model needed to describe chaotic behavior. Ultimately they will put the geometry and flow dynamics together to developmore » a chaotic-dynamical model of flow and transport in a fractured vadose zone. They investigate water flow and contaminant transport on several scales, ranging from small-scale laboratory experiments in fracture replicas and fractured cores, to field experiments conducted in a single exposed fracture at a basalt outcrop, and finally to a ponded infiltration test using a pond of 7 by 8 m. In the field experiments, they measure the time-variation of water flux, moisture content, and hydraulic head at various locations, as well as the total inflow rate to the subsurface. Such variations reflect the changes in the geometry and physics of water flow that display chaotic behavior, which they try to reconstruct using the data obtained. In the analysis of experimental data, a chaotic model can be used to predict the long-term bounds on fluid flow and transport behavior, known as the attractor of the system, and to examine the limits of short-term predictability within these bounds. This approach is especially well suited to the need for short-term predictions to support remediation decisions and long-term bounding studies. View-graphs from ten presentations made at the annual meeting held December 3--4, 1997 are included in an appendix to this report.« less

Measurements of radiated elastic wave energy from dynamic tensile cracks

NASA Technical Reports Server (NTRS)

Boler, Frances M.

1990-01-01

The role of fracture-velocity, microstructure, and fracture-energy barriers in elastic wave radiation during a dynamic fracture was investigated in experiments in which dynamic tensile cracks of two fracture cofigurations of double cantilever beam geometry were propagating in glass samples. The first, referred to as primary fracture, consisted of fractures of intact glass specimens; the second configuration, referred to as secondary fracture, consisted of a refracture of primary fracture specimens which were rebonded with an intermittent pattern of adhesive to produce variations in fracture surface energy along the crack path. For primary fracture cases, measurable elastic waves were generated in 31 percent of the 16 fracture events observed; the condition for radiation of measurable waves appears to be a local abrupt change in the fracture path direction, such as occurs when the fracture intersects a surface flaw. For secondary fractures, 100 percent of events showed measurable elastic waves; in these fractures, the ratio of radiated elastic wave energy in the measured component to fracture surface energy was 10 times greater than for primary fracture.

Self organized spatio-temporal structure within the fractured Vadose Zone: The influence of dynamic overloading at fracture intersections

NASA Astrophysics Data System (ADS)

LaViolette, Randall A.; Glass, Robert J.

2004-09-01

Under low flow conditions (where gravity and capillary forces dominate) within an unsaturated fracture network, fracture intersections act as capillary barriers to integrate flow from above and then release it as a pulse below. Water exiting a fracture intersection is often thought to enter the single connected fracture with the lowest invasion pressure. When the accumulated volume varies between intersections, the smaller volume intersections can be overloaded to cause all of the available fractures exiting an intersection to flow. We included the dynamic overloading process at fracture intersections within our previously discussed model where intersections were modeled as tipping buckets connected within a two-dimensional diamond lattice. With dynamic overloading, the flow behavior transitioned smoothly from diverging to converging flow with increasing overload parameter, as a consequence of a heterogeneous field, and they impose a dynamic structure where additional pathways activate or deactivate in time.

Inverse Dynamics Model for the Ankle Joint with Applications in Tibia Malleolus Fracture

NASA Astrophysics Data System (ADS)

Budescu, E.; Merticaru, E.; Chirazi, M.

The paper presents a biomechanical model of the ankle joint, in order to determine the force and the torque of reaction into the articulation, through inverse dynamic analysis, in various stages of the gait. Thus, knowing the acceleration of the foot and the reaction force between foot and ground during the gait, determined by experimental measurement, there was calculated, for five different positions of the foot, the joint reaction forces, on the basis of dynamic balance equations. The values numerically determined were compared with the admissible forces appearing in the technical systems of osteosynthesis of tibia malleolus fracture, in order to emphasize the motion restrictions during bone healing.

Porous media fracturing dynamics: stepwise crack advancement and fluid pressure oscillations

NASA Astrophysics Data System (ADS)

Cao, Toan D.; Hussain, Fazle; Schrefler, Bernhard A.

2018-02-01

We present new results explaining why fracturing in saturated porous media is not smooth and continuous but is a distinct stepwise process concomitant with fluid pressure oscillations. All exact solutions and almost all numerical models yield smooth fracture advancement and fluid pressure evolution, while recent experimental results, mainly from the oil industry, observation from geophysics and a very few numerical results for the quasi-static case indeed reveal the stepwise phenomenon. We summarize first these new experiments and these few numerical solutions for the quasi-static case. Both mechanical loading and pressure driven fractures are considered because their behaviours differ in the direction of the pressure jumps. Then we explore stepwise crack tip advancement and pressure fluctuations in dynamic fracturing with a hydro-mechanical model of porous media based on the Hybrid Mixture Theory. Full dynamic analyses of examples dealing with both hydraulic fracturing and mechanical loading are presented. The stepwise fracture advancement is confirmed in the dynamic setting as well as in the pressure fluctuations, but there are substantial differences in the frequency contents of the pressure waves in the two loading cases. Comparison between the quasi-static and fully dynamic solutions reveals that the dynamic response gives much more information such as the type of pressure oscillations and related frequencies and should be applied whenever there is a doubt about inertia forces playing a role - the case in most fracturing events. In the absence of direct relevant dynamic tests on saturated media some experimental results on dynamic fracture in dry materials, a fast hydraulic fracturing test and observations from geophysics confirm qualitatively the obtained results such as the type of pressure oscillations and the substantial difference in the behaviour under the two loading cases.

On Subsurface Fracture Opening and Closure

NASA Astrophysics Data System (ADS)

Wang, Y.

2016-12-01

Mechanistic understanding of fracture opening and closure in geologic media is of significant importance to nature resource extraction and waste management, such as geothermal energy extraction, oil/gas production, radioactive waste disposal, and carbon sequestration and storage). A dynamic model for subsurface fracture opening and closure has been formulated. The model explicitly accounts for the stress concentration around individual aperture channels and the stress-activated mineral dissolution and precipitation. A preliminary model analysis has demonstrated the importance of the stress-activated dissolution mechanism in the evolution of fracture aperture in a stressed geologic medium. The model provides a reasonable explanation for some key features of fracture opening and closure observed in laboratory experiments, including a spontaneous switch from a net permeability reduction to a net permeability increase with no changes in a limestone fracture experiment.

Dynamic finite element analysis and moving particle simulation of human enamel on a microscale.

PubMed

Yamaguchi, Satoshi; Coelho, Paulo G; Thompson, Van P; Tovar, Nick; Yamauchi, Junpei; Imazato, Satoshi

2014-12-01

The study of biomechanics of deformation and fracture of hard biological tissues involving organic matrix remains a challenge as variations in mechanical properties and fracture mode may have time-dependency. Finite element analysis (FEA) has been widely used but the shortcomings of FEA such as the long computation time owing to re-meshing in simulating fracture mechanics have warranted the development of alternative computational methods with higher throughput. The aim of this study was to compare dynamic two-dimensional FEA and moving particle simulation (MPS) when assuming a plane strain condition in the modeling of human enamel on a reduced scale. Two-dimensional models with the same geometry were developed for MPS and FEA and tested in tension generated with a single step of displacement. The displacement, velocity, pressure, and stress levels were compared and Spearman׳s rank-correlation coefficients R were calculated (p<0.001). The MPS and FEA were significantly correlated for displacement, velocity, pressure, and Y-stress. The MPS may be further developed as an alternative approach without mesh generation to simulate deformation and fracture phenomena of dental and potentially other hard tissues with complex microstructure. Copyright © 2014 Elsevier Ltd. All rights reserved.

Continuum Damage Modeling for Dynamic Fracture Toughness of Metal Matrix Composites

NASA Astrophysics Data System (ADS)

Lee, Intaek; Ochi, Yasuo; Bae, Sungin; Song, Jungil

Short fiber reinforced metal-matrix composites (MMCs) have widely adopted as structural materials and many experimental researches have been performed to study fracture toughness of it. Fracture toughness is often referred as the plane strain(maximum constraint) fracture toughness KIc determined by the well-established standard test method, such as ASTM E399. But the application for dynamic fracture toughness KId has not been popular yet, because of reliance in capturing the crack propagating time. This paper deals with dynamic fracture toughness testing and simulation using finite element method to evaluate fracture behaviors of MMCs manufactured by squeeze casting process when material combination is varied with the type of reinforcement (appearance, size), volume fraction and combination of reinforcements, and the matrix alloy. The instrumented Charphy impact test was used for KId determination and continuum damage model embedded in commercial FE program is used to investigate the dynamic fracture toughness with the influence of elasto-visco-plastic constitutive relation of quasi-brittle fracture that is typical examples of ceramics and some fibre reinforced composites. With Compared results between experimental method and FE simulation, the determination process for KId is presented. FE simulation coupled with continuum damage model is emphasized single shot simulation can predict the dynamic fracture toughness, KId and real time evolution of that directly.

Based on records of Three Gorge Telemetric Seismic Network to analyze Vibration process of micro fracture of rock landslide

NASA Astrophysics Data System (ADS)

WANG, Q.

2017-12-01

Used the finite element analysis software GeoStudio to establish vibration analysis model of Qianjiangping landslide, which locates at the Three Gorges Reservoir area. In QUAKE/W module, we chosen proper Dynamic elasticity modulus and Poisson's ratio of soil layer and rock stratum. When loading, we selected the waveform data record of Three Gorge Telemetric Seismic Network as input ground motion, which includes five rupture events recorded of Lujiashan seismic station. In dynamic simulating, we mainly focused on sliding process when the earthquake date record was applied. The simulation result shows that Qianjiangping landslide wasn't not only affected by its own static force, but also experienced the dynamic process of micro fracture-creep-slip rupture-creep-slip.it provides a new approach for the early warning feasibility of rock landslide in future research.

Challenges of biological sample preparation for SIMS imaging of elements and molecules at subcellular resolution

NASA Astrophysics Data System (ADS)

Chandra, Subhash

2008-12-01

Secondary ion mass spectrometry (SIMS) based imaging techniques capable of subcellular resolution characterization of elements and molecules are becoming valuable tools in many areas of biology and medicine. Due to high vacuum requirements of SIMS, the live cells cannot be analyzed directly in the instrument. The sample preparation, therefore, plays a critical role in preserving the native chemical composition for SIMS analysis. This work focuses on the evaluation of frozen-hydrated and frozen freeze-dried sample preparations for SIMS studies of cultured cells with a CAMECA IMS-3f dynamic SIMS ion microscope instrument capable of producing SIMS images with a spatial resolution of 500 nm. The sandwich freeze-fracture method was used for fracturing the cells. The complimentary fracture planes in the plasma membrane were characterized by field-emission secondary electron microscopy (FESEM) in the frozen-hydrated state. The cells fractured at the dorsal surface were used for SIMS analysis. The frozen-hydrated SIMS analysis of individual cells under dynamic primary ion beam (O 2+) revealed local secondary ion signal enhancements correlated with the water image signals of 19(H 3O) +. A preferential removal of water from the frozen cell matrix in the Z-axis was also observed. These complications render the frozen-hydrated sample type less desirable for subcellular dynamic SIMS studies. The freeze-drying of frozen-hydrated cells, either inside the instrument or externally in a freeze-drier, allowed SIMS imaging of subcellular chemical composition. Morphological evaluations of fractured freeze-dried cells with SEM and confocal laser scanning microscopy (CLSM) revealed well-preserved mitochondria, Golgi apparatus, and stress fibers. SIMS analysis of fractured freeze-dried cells revealed well-preserved chemical composition of even the most highly diffusible ions like K + and Na + in physiologically relevant concentrations. The high K-low Na signature in individual cells provided a rule-of-thumb criterion for the validation of sample preparation. The fractured freeze-dried cells allowed 3-D SIMS imaging and localization of 13C 15N labeled molecules and therapeutic drugs containing an elemental tag. Examples are shown to demonstrate that both diffusible elements and molecules are prone to artifact-induced relocation at subcellular scale if the sample preparation is compromised. The sample preparation is problem dependent and may vary widely between the diverse sample types of biological systems and the type of instrument used for SIMS analysis. The sample preparation, however, must be validated so that SIMS can be applied with confidence in biology and medicine.

Fracture Behavior of High-Nitrogen Austenitic Stainless Steel Under Continuous Cooling: Physical Simulation of Free-Surface Cracking of Heavy Forgings

NASA Astrophysics Data System (ADS)

Wang, Zhenhua; Xue, Hongpeng; Fu, Wantang

2018-03-01

18Mn18Cr0.6N steel was tension tested at 0.001 s-1 to fracture from 1473 K to 1363 K (1200 °C to 1090 °C, fracture temperature) at a cooling rate of 0.4 Ks-1. For comparison, specimens were tension tested at temperatures of 1473 K and 1363 K (1200 °C and 1090 °C). The microstructure near the fracture surface was examined using electron backscatter diffraction analysis. The lowest hot ductility was observed under continuous cooling and was attributed to the suppression of dynamic recrystallization nucleation.

Spontaneous imbibition in fractal tortuous micro-nano pores considering dynamic contact angle and slip effect: phase portrait analysis and analytical solutions.

PubMed

Li, Caoxiong; Shen, Yinghao; Ge, Hongkui; Zhang, Yanjun; Liu, Tao

2018-03-02

Shales have abundant micro-nano pores. Meanwhile, a considerable amount of fracturing liquid is imbibed spontaneously in the hydraulic fracturing process. The spontaneous imbibition in tortuous micro-nano pores is special to shale, and dynamic contact angle and slippage are two important characteristics. In this work, we mainly investigate spontaneous imbibition considering dynamic contact angle and slip effect in fractal tortuous capillaries. We introduce phase portrait analysis to analyse the dynamic state and stability of imbibition. Moreover, analytical solutions to the imbibition equation are derived under special situations, and the solutions are verified by published data. Finally, we discuss the influences of slip length, dynamic contact angle and gravity on spontaneous imbibition. The analysis shows that phase portrait is an ideal tool for analysing spontaneous imbibition because it can evaluate the process without solving the complex governing ordinary differential equations. Moreover, dynamic contact angle and slip effect play an important role in fluid imbibition in fractal tortuous capillaries. Neglecting slip effect in micro-nano pores apparently underestimates imbibition capability, and ignoring variations in contact angle causes inaccuracy in predicting imbibition speed at the initial stage of the process. Finally, gravity is one of the factors that control the stabilisation of the imbibition process.

Dynamic Response in Transient Stress-Field Behavior Induced by Hydraulic Fracturing

NASA Astrophysics Data System (ADS)

Jenkins, Andrew

Hydraulic fracturing is a technique which is used to exploit geologic features and subsurface properties in an effort to increase production in low-permeability formations. The process of hydraulic fracturing provides a greater surface contact area between the producing formation and the wellbore and thus increases the amount of recoverable hydrocarbons from within the reservoir. The use of this stimulation technique has brought on massive applause from the industry due to its widespread success and effectiveness, however the dynamic processes that take part in the development of hydraulic fractures is a relatively new area of research with respect to the massive scale operations that are seen today. The process of hydraulic fracturing relies upon understanding and exploiting the in-situ stress distribution throughout the area of study. These in-situ stress conditions are responsible for directing fracture orientation and propagation paths throughout the period of injection. The relative magnitude of these principle stresses is key in developing a successful stimulation plan. In horizontal well plan development the interpretation of stress within the reservoir is required for determining the azimuth of the horizontal well path. These horizontal laterals are typically oriented in a manner such that the well path lies parallel to the minimum horizontal stress. This allows for vertical fractures to develop transversely to the wellbore, or normal to the least principle stress without the theoretical possibility of fractures overlapping, creating the most efficient use of the fluid energy during injection. The orientation and magnitude of these in-situ stress fields however can be dynamic, controlled by the subsequent fracture propagation and redistribution of the surrounding stresses. That is, that as the fracture propagates throughout the reservoir, the relative stress fields surrounding the fractures may see a shift and deviate from their original direction or magnitude. These types of shifts are of great concern because they can impact subsequent fracture development causing non-uniform fracture propagation and the potential overlapping of fracture paths as they extend from the wellbore at the point of injection. The dynamics of stress variation that occur with respect to hydraulic fracturing is a somewhat new area of study. In order to accomplish the goals of this thesis and continue future research in this area a new transient model has been developed in order to asses these dynamic systems and determine their influence on fracture behavior. This applies the use of a fully coupled finite element method in 2-D using linear elastic fracture mechanics which is then expanded using displacement discontinuity to a cohesive zone model in 3-D. A static boundary element model was also used to determine stress fields surrounding static, predetermined fracture geometries. These models have been verified against analytical solutions for simple cases and are now being applied to more detailed case studies and analysis. These models have been briefly discussed throughout this thesis in order to give insight on their current capabilities and application as well as their future potential within this area of research. The majority of this work introduces transient stress field prediction to cases of single and multiple hydraulic fractures. The static assessment of these stresses is determined for verification of results to those found in publication which leads into these transient stress field variations. A new method has been developed and applied to the stress state prediction for the first time in a transient fracture model which is partly based upon a critical distance theory. These dynamic interactions can provide useful insight to pertinent issues within the petroleum and natural gas industry such as those to hydraulic fracturing fluid loss and induced seismic events, as well as to applications of efficiency and optimization of the stimulation treatment plan.

Dynamic Fracture Behavior of Plastic-Bonded Explosives

NASA Astrophysics Data System (ADS)

Fu, Hua; Li, Jun-Ling; Tan, Duo-Wang; Ifp, Caep Team

2011-06-01

Plastic-Bonded Explosives (PBX) are used as important energetic materials in nuclear or conventional weapons. Arms Warhead in the service process and the ballistic phase, may experience complex process such as long pulse and higher loading, compresson, tension and reciprocating compression - tension, friction with the projectile shell, which would lead to explosive deformation and fracture.And the dynamic deformation and fracture behavior of PBX subsequently affect reaction characteristics and initiation mechanism in explosives, then having influence on explosives safety. The dynamic fracure behavior of PBX are generally complex and not well studied or understood. In this paper, the dynamic fracture of explosives are conducted using a Kolsky bar. The Brazilian test, also known as a indirect tensile test or splitting test, is chosen as the test method. Tensile strength under different strain rates are obtained using quartz crystal embedded in rod end. The dynamic deformation and fracture process are captured in real-time by high-speed digital camera, and the displacement and strain fields distribution before specimen fracture are obtained by digital correlation method. Considering the non-uniform microstructure of explosives,the dynamic fracture behavior of explosive are simulated by discrete element method, the simulation results can reproduce the deformation and fracture process in Brazilian test using a maximum tensile strain criterion.

An Effective Modal Approach to the Dynamic Evaluation of Fracture Toughness of Quasi-Brittle Materials

NASA Astrophysics Data System (ADS)

Ferreira, L. E. T.; Vareda, L. V.; Hanai, J. B.; Sousa, J. L. A. O.; Silva, A. I.

2017-05-01

A modal dynamic analysis is used as the tool to evaluate the fracture toughness of concrete from the results of notched-through beam tests. The dimensionless functions describing the relation between the frequencies and specimen geometry used for identifying the variation in the natural frequency as a function of crack depth is first determined for a 150 × 150 × 500-mm notched-through specimen. The frequency decrease resulting from the propagating crack is modeled through a modal/fracture mechanics approach, leading to determination of an effective crack length. This length, obtained numerically, is used to evaluate the fracture toughness of concrete, the critical crack mouth opening displacements, and the brittleness index proposed. The methodology is applied to tests performed on high-strength concrete specimens. The frequency response for each specimen is evaluated before and after each crack propagation step. The methodology is then validated by comparison with results from the application of other methodologies described in the literature and suggested by RILEM.

Partitioning dynamics of unsaturated flows in fractured porous media: Laboratory studies and three-dimensional multi-scale smoothed particle hydrodynamics simulations of gravity-driven flow in fractures

NASA Astrophysics Data System (ADS)

Kordilla, J.; Bresinsky, L. T.; Shigorina, E.; Noffz, T.; Dentz, M.; Sauter, M.; Tartakovsky, A. M.

2017-12-01

Preferential flow dynamics in unsaturated fractures remain a challenging topic on various scales. On pore- and fracture-scales the highly erratic gravity-driven flow dynamics often provoke a strong deviation from classical volume-effective approaches. Against the common notion that flow in fractures (or macropores) can only occur under equilibrium conditions, i.e., if the surrounding porous matrix is fully saturated and capillary pressures are high enough to allow filling of the fracture void space, arrival times suggest the existence of rapid preferential flow along fractures, fracture networks, and fault zones, even if the matrix is not fully saturated. Modeling such flows requires efficient numerical techniques to cover various flow-relevant physics, such as surface tension, static and dynamic contact angles, free-surface (multi-phase) interface dynamics, and formation of singularities. Here we demonstrate the importance of such flow modes on the partitioning dynamics at simple fracture intersections, with a combination of laboratory experiments, analytical solutions and numerical simulations using our newly developed massively parallel smoothed particle hydrodynamics (SPH) code. Flow modes heavily influence the "bypass" behavior of water flowing along a fracture junction. Flows favoring the formation of droplets exhibit a much stronger bypass capacity compared to rivulet flows, where nearly the whole fluid mass is initially stored within the horizontal fracture. This behavior is demonstrated for a multi-inlet laboratory setup where the inlet-specific flow rate is chosen so that either a droplet or rivulet flow persists. The effect of fluid buffering within the horizontal fracture is presented in terms of dimensionless fracture inflow so that characteristic scaling regimes can be recovered. For both cases (rivulets and droplets), flow within the horizontal fracture transitions into a Washburn regime until a critical threshold is reached and the bypass efficiency increases. For rivulet flows, the initial filling of the horizontal fracture is described by classical plug flow. Meanwhile, for droplet flows, a size-dependent partitioning behavior is observed, and the filling of the fracture takes longer.

Time-dependent fracture probability of bilayer, lithium-disilicate-based, glass-ceramic, molar crowns as a function of core/veneer thickness ratio and load orientation.

PubMed

Anusavice, Kenneth J; Jadaan, Osama M; Esquivel-Upshaw, Josephine F

2013-11-01

Recent reports on bilayer ceramic crown prostheses suggest that fractures of the veneering ceramic represent the most common reason for prosthesis failure. The aims of this study were to test the hypotheses that: (1) an increase in core ceramic/veneer ceramic thickness ratio for a crown thickness of 1.6mm reduces the time-dependent fracture probability (Pf) of bilayer crowns with a lithium-disilicate-based glass-ceramic core, and (2) oblique loading, within the central fossa, increases Pf for 1.6-mm-thick crowns compared with vertical loading. Time-dependent fracture probabilities were calculated for 1.6-mm-thick, veneered lithium-disilicate-based glass-ceramic molar crowns as a function of core/veneer thickness ratio and load orientation in the central fossa area. Time-dependent fracture probability analyses were computed by CARES/Life software and finite element analysis, using dynamic fatigue strength data for monolithic discs of a lithium-disilicate glass-ceramic core (Empress 2), and ceramic veneer (Empress 2 Veneer Ceramic). Predicted fracture probabilities (Pf) for centrally loaded 1.6-mm-thick bilayer crowns over periods of 1, 5, and 10 years are 1.2%, 2.7%, and 3.5%, respectively, for a core/veneer thickness ratio of 1.0 (0.8mm/0.8mm), and 2.5%, 5.1%, and 7.0%, respectively, for a core/veneer thickness ratio of 0.33 (0.4mm/1.2mm). CARES/Life results support the proposed crown design and load orientation hypotheses. The application of dynamic fatigue data, finite element stress analysis, and CARES/Life analysis represent an optimal approach to optimize fixed dental prosthesis designs produced from dental ceramics and to predict time-dependent fracture probabilities of ceramic-based fixed dental prostheses that can minimize the risk for clinical failures. Copyright © 2013 Academy of Dental Materials. All rights reserved.

Time-dependent fracture probability of bilayer, lithium-disilicate-based glass-ceramic molar crowns as a function of core/veneer thickness ratio and load orientation

PubMed Central

Anusavice, Kenneth J.; Jadaan, Osama M.; Esquivel–Upshaw, Josephine

2013-01-01

Recent reports on bilayer ceramic crown prostheses suggest that fractures of the veneering ceramic represent the most common reason for prosthesis failure. Objective The aims of this study were to test the hypotheses that: (1) an increase in core ceramic/veneer ceramic thickness ratio for a crown thickness of 1.6 mm reduces the time-dependent fracture probability (Pf) of bilayer crowns with a lithium-disilicate-based glass-ceramic core, and (2) oblique loading, within the central fossa, increases Pf for 1.6-mm-thick crowns compared with vertical loading. Materials and methods Time-dependent fracture probabilities were calculated for 1.6-mm-thick, veneered lithium-disilicate-based glass-ceramic molar crowns as a function of core/veneer thickness ratio and load orientation in the central fossa area. Time-dependent fracture probability analyses were computed by CARES/Life software and finite element analysis, using dynamic fatigue strength data for monolithic discs of a lithium-disilicate glass-ceramic core (Empress 2), and ceramic veneer (Empress 2 Veneer Ceramic). Results Predicted fracture probabilities (Pf) for centrally-loaded 1,6-mm-thick bilayer crowns over periods of 1, 5, and 10 years are 1.2%, 2.7%, and 3.5%, respectively, for a core/veneer thickness ratio of 1.0 (0.8 mm/0.8 mm), and 2.5%, 5.1%, and 7.0%, respectively, for a core/veneer thickness ratio of 0.33 (0.4 mm/1.2 mm). Conclusion CARES/Life results support the proposed crown design and load orientation hypotheses. Significance The application of dynamic fatigue data, finite element stress analysis, and CARES/Life analysis represent an optimal approach to optimize fixed dental prosthesis designs produced from dental ceramics and to predict time-dependent fracture probabilities of ceramic-based fixed dental prostheses that can minimize the risk for clinical failures. PMID:24060349

Dynamic fracture mechanics analysis for an edge delamination crack

NASA Technical Reports Server (NTRS)

Rizzi, Stephen A.; Doyle, James F.

1994-01-01

A global/local analysis is applied to the problem of a panel with an edge delamination crack subject to an impulse loading to ascertain the dynamic J integral. The approach uses the spectral element method to obtain the global dynamic response and local resultants to obtain the J integral. The variation of J integral along the crack front is shown. The crack behavior is mixed mode (Mode 2 and Mode 3), but is dominated by the Mode 2 behavior.

Analysis of foot structure in athletes sustaining proximal fifth metatarsal stress fracture.

PubMed

Hetsroni, Iftach; Nyska, Meir; Ben-Sira, David; Mann, Gideon; Segal, Ofer; Maoz, Guy; Ayalon, Moshe

2010-03-01

In the past, several studies provided anecdotal descriptions of high-arched feet in individuals sustaining proximal fifth metatarsal stress fractures. This relationship has never been supported by scientific evidence. Our objective was to examine whether athletes who sustained this injury had an exceptional static foot structure or dynamic loading pattern. Ten injured professional soccer players who regained full professional activity following a unilateral proximal fifth metatarsal stress fracture and ten control soccer players were examined. Independent variables included static evaluation of foot and arch structure, followed by dynamic plantar foot pressure evaluation. Each variable was compared between injured, contra-lateral uninjured, and control feet. Static measurements of foot and arch structure did not reveal differences among the groups. However, plantar pressure evaluation revealed relative unloading of the fourth metatarsal in injured and uninjured limbs of injured athletes compared with control, while the fifth metatarsal revealed pressure reduction only in the injured limbs of injured athletes. Athletes who sustained proximal fifth metatarsal stress fracture were not characterized by an exceptional static foot structure. Dynamically, lateral metatarsal unloading during stance may either play a role in the pathogenesis of the injury, or alternately represent an adaptive process. Footwear fabrication for previously injured athletes should not categorically address cushioning properties designed for high-arch feet, but rather focus on individual dynamic evaluation of forefoot loading, with less attention applied to static foot and arch characteristics.

Static and dynamic strain energy release rates in toughened thermosetting composite laminates

NASA Technical Reports Server (NTRS)

Cairns, Douglas S.

1992-01-01

In this work, the static and dynamic fracture properties of several thermosetting resin based composite laminates are presented. Two classes of materials are explored. These are homogeneous, thermosetting resins and toughened, multi-phase, thermosetting resin systems. Multi-phase resin materials have shown enhancement over homogenous materials with respect to damage resistance. The development of new dynamic tests are presented for composite laminates based on Width Tapered Double Cantilevered Beam (WTDCB) for Mode 1 fracture and the End Notched Flexure (ENF) specimen. The WTDCB sample was loaded via a low inertia, pneumatic cylinder to produce rapid cross-head displacements. A high rate, piezo-electric load cell and an accelerometer were mounted on the specimen. A digital oscilloscope was used for data acquisition. Typical static and dynamic load versus displacement plots are presented. The ENF specimen was impacted in three point bending with an instrumented impact tower. Fracture initiation and propagation energies under static and dynamic conditions were determined analytically and experimentally. The test results for Mode 1 fracture are relatively insensitive to strain rate effects for the laminates tested in this study. The test results from Mode 2 fracture indicate that the toughened systems provide superior fracture initiation and higher resistance to propagation under dynamic conditions. While the static fracture properties of the homogeneous systems may be relatively high, the apparent Mode 2 dynamic critical strain energy release rate drops significantly. The results indicate that static Mode 2 fracture testing is inadequate for determining the fracture performance of composite structures subjected to conditions such as low velocity impact. A good correlation between the basic Mode 2 dynamic fracture properties and the performance is a combined material/structural Compression After Impact (CAI) test is found. These results underscore the importance of examining rate-dependent behavior for determining the longevity of structures manufactured from composite materials.

Graphene and its elemental analogue: A molecular dynamics view of fracture phenomenon

NASA Astrophysics Data System (ADS)

Rakib, Tawfiqur; Mojumder, Satyajit; Das, Sourav; Saha, Sourav; Motalab, Mohammad

2017-06-01

Graphene and some graphene like two dimensional materials; hexagonal boron nitride (hBN) and silicene have unique mechanical properties which severely limit the suitability of conventional theories used for common brittle and ductile materials to predict the fracture response of these materials. This study revealed the fracture response of graphene, hBN and silicene nanosheets under different tiny crack lengths by molecular dynamics (MD) simulations using LAMMPS. The useful strength of these two dimensional materials are determined by their fracture toughness. Our study shows a comparative analysis of mechanical properties among the elemental analogues of graphene and suggested that hBN can be a good substitute for graphene in terms of mechanical properties. We have also found that the pre-cracked sheets fail in brittle manner and their failure is governed by the strength of the atomic bonds at the crack tip. The MD prediction of fracture toughness shows significant difference with the fracture toughness determined by Griffth's theory of brittle failure which restricts the applicability of Griffith's criterion for these materials in case of nano-cracks. Moreover, the strengths measured in armchair and zigzag directions of nanosheets of these materials implied that the bonds in armchair direction have the stronger capability to resist crack propagation compared to zigzag direction.

On the dynamic behavior of mineralized tissues

NASA Astrophysics Data System (ADS)

Kulin, Robb Michael

Mineralized tissues, such as bone and antler, are complex hierarchical materials that have adapted over millennia to optimize strength and fracture resistance for their in vivo applications. As a structural support, skeletal bone primarily acts as a rigid framework that is resistant to fracture, and able to repair damage and adapt to sustained loads during its lifetime. Antler is typically deciduous and subjected to large bending moments and violent impacts during its annual cycle. To date, extensive characterization of the quasi-static mechanical properties of these materials has been performed. However, very little has been done to characterize their dynamic properties, despite the fact that the majority of failures in these materials occur under impact loads. Here, an in depth analysis of the dynamic mechanical behavior of these two materials is presented, using equine bone obtained post-mortem from donors ranging in age from 6 months to 28 years, and antler from the North American Elk. Specimens were tested under compressive strain rates of 10-3, 100, and 103 sec-1 in order to investigate their strain rate dependent compressive response. Fracture toughness experiments were performed using a four-point bending geometry on single and double-notch specimens in order to measure fracture toughness, as well as observe differences in crack propagation between dynamic (˜2x105 MPa˙m1/2/s) and quasi-static (˜0.25 MPa˙m1/2/s) loading rates. After testing, specimens were analyzed using a combination of optical, electron and confocal microscopy. Results indicated that the mechanical response of these materials is highly dependent on loading rate. Decreasing quasi-static fracture toughness is observed with age in bone specimens, while dynamic specimens show no age trends, yet universally decreased fracture toughness compared to those tested quasi-statically. For the first time, rising R-curve behavior in bone was also shown to exist under both quasi-static and dynamic loading. Antler demonstrated itself to be extremely resistant to impact loading, often requiring multiple impacts to fracture a specimen. Microscopy observations of deformation and crack propagation mechanisms indicate that differences in mechanical behavior between bone and antler, and at varying strain rates, are the result of subtle differences in bulk composition and active microstructural toughening mechanisms.

Multiscale Modeling for the Analysis for Grain-Scale Fracture Within Aluminum Microstructures

NASA Technical Reports Server (NTRS)

Glaessgen, Edward H.; Phillips, Dawn R.; Yamakov, Vesselin; Saether, Erik

2005-01-01

Multiscale modeling methods for the analysis of metallic microstructures are discussed. Both molecular dynamics and the finite element method are used to analyze crack propagation and stress distribution in a nanoscale aluminum bicrystal model subjected to hydrostatic loading. Quantitative similarity is observed between the results from the two very different analysis methods. A bilinear traction-displacement relationship that may be embedded into cohesive zone finite elements is extracted from the nanoscale molecular dynamics results.

A Nonlocal Peridynamic Plasticity Model for the Dynamic Flow and Fracture of Concrete.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vogler, Tracy; Lammi, Christopher James

A nonlocal, ordinary peridynamic constitutive model is formulated to numerically simulate the pressure-dependent flow and fracture of heterogeneous, quasi-brittle ma- terials, such as concrete. Classical mechanics and traditional computational modeling methods do not accurately model the distributed fracture observed within this family of materials. The peridynamic horizon, or range of influence, provides a characteristic length to the continuum and limits localization of fracture. Scaling laws are derived to relate the parameters of peridynamic constitutive model to the parameters of the classical Drucker-Prager plasticity model. Thermodynamic analysis of associated and non-associated plastic flow is performed. An implicit integration algorithm is formu-more » lated to calculate the accumulated plastic bond extension and force state. The gov- erning equations are linearized and the simulation of the quasi-static compression of a cylinder is compared to the classical theory. A dissipation-based peridynamic bond failure criteria is implemented to model fracture and the splitting of a concrete cylinder is numerically simulated. Finally, calculation of the impact and spallation of a con- crete structure is performed to assess the suitability of the material and failure models for simulating concrete during dynamic loadings. The peridynamic model is found to accurately simulate the inelastic deformation and fracture behavior of concrete during compression, splitting, and dynamically induced spall. The work expands the types of materials that can be modeled using peridynamics. A multi-scale methodology for simulating concrete to be used in conjunction with the plasticity model is presented. The work was funded by LDRD 158806.« less

An efficient quasi-3D particle tracking-based approach for transport through fractures with application to dynamic dispersion calculation.

PubMed

Wang, Lichun; Cardenas, M Bayani

2015-08-01

The quantitative study of transport through fractured media has continued for many decades, but has often been constrained by observational and computational challenges. Here, we developed an efficient quasi-3D random walk particle tracking (RWPT) algorithm to simulate solute transport through natural fractures based on a 2D flow field generated from the modified local cubic law (MLCL). As a reference, we also modeled the actual breakthrough curves (BTCs) through direct simulations with the 3D advection-diffusion equation (ADE) and Navier-Stokes equations. The RWPT algorithm along with the MLCL accurately reproduced the actual BTCs calculated with the 3D ADE. The BTCs exhibited non-Fickian behavior, including early arrival and long tails. Using the spatial information of particle trajectories, we further analyzed the dynamic dispersion process through moment analysis. From this, asymptotic time scales were determined for solute dispersion to distinguish non-Fickian from Fickian regimes. This analysis illustrates the advantage and benefit of using an efficient combination of flow modeling and RWPT. Copyright © 2015 Elsevier B.V. All rights reserved.

Determination of Dynamic Fracture Toughness Properties of Rail Steels

DOT National Transportation Integrated Search

1987-11-01

Motivated by the occurrence of a long-running rail web fracture in service, dynamic fracture mechanics research was undertaken to (1) quantify the crack driving force due to the residual stresses induced by roller straightening operations, (2) determ...

Analysis of crevasse patterns on Helheim and Kangerdlugssuaq Glaciers in Greenland

NASA Astrophysics Data System (ADS)

Udell, K.; Walker, C. C.; Schmidt, B. E.

2017-12-01

As a tidewater glacier flows through a valley, it accumulates fractures that provide qualitative information on how glacier thickness, climate forcing, and areas of compression and extension conspire within the ice. These fracture patterns remain and evolve on the glacier, and rapid changes in the pattern can be indicative of a transition in the movement of the glacier. Not only can the fractures provide qualitative information about a glacier, they can also provide quantitative information that allows for the calculation of the stress field and dynamics that the ice experiences. Helheim and Kangerdlugssuaq both terminate in the ocean, potentially providing information on the transition from solid glacier to mélange, which is an important but not well understood process. Using satellite imagery, we traced surface crevasses present along each glacier for available images between 2001-2016 using geospatial software QGIS. We also qualitatively tracked any surface melt ponds present, and monitored for large fractures or regions of the terminus that appeared to be susceptible to or currently calving. With the trace maps, we will use spatial analysis techniques to allow us to quantify the visible patterns and compare the information from year to year and glacier to glacier. Once we can quantitatively describe fracture density in different areas of the glacier, we will also be able to better describe the transition within the glacier from solid mass to highly-fractured and collapsing. Having this data for each glacier allows for comparisons to be made within regions of individual glaciers as well as between glaciers. Using this information, we can answer questions about the relationship between density and pattern of fractures to the stability of the terminus, the stresses that drive glacial fractures, and what effects climate has on glacier dynamics and calving. Preliminary observations include the increasing prevalence of melt ponds beginning in 2004 as well as the retreat of the terminus during the same period. More recently the location of the terminus has remained relatively constant. Overall, understanding the processes of glacial fracturing has implications for both better understanding climate change and analyzing ice fracturing on other planetary bodies such as Europa.

Crack stability in a representative piping system under combined inertial and seismic/dynamic displacement-controlled stresses. Subtask 1.3 final report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scott, P.; Olson, R.; Wilkowski, O.G.

1997-06-01

This report presents the results from Subtask 1.3 of the International Piping Integrity Research Group (IPIRG) program. The objective of Subtask 1.3 is to develop data to assess analysis methodologies for characterizing the fracture behavior of circumferentially cracked pipe in a representative piping system under combined inertial and displacement-controlled stresses. A unique experimental facility was designed and constructed. The piping system evaluated is an expansion loop with over 30 meters of 16-inch diameter Schedule 100 pipe. The experimental facility is equipped with special hardware to ensure system boundary conditions could be appropriately modeled. The test matrix involved one uncracked andmore » five cracked dynamic pipe-system experiments. The uncracked experiment was conducted to evaluate piping system damping and natural frequency characteristics. The cracked-pipe experiments evaluated the fracture behavior, pipe system response, and stability characteristics of five different materials. All cracked-pipe experiments were conducted at PWR conditions. Material characterization efforts provided tensile and fracture toughness properties of the different pipe materials at various strain rates and temperatures. Results from all pipe-system experiments and material characterization efforts are presented. Results of fracture mechanics analyses, dynamic finite element stress analyses, and stability analyses are presented and compared with experimental results.« less

Baseflow recession analysis in a large shale play: Climate variability and anthropogenic alterations mask effects of hydraulic fracturing

NASA Astrophysics Data System (ADS)

Arciniega-Esparza, Saúl; Breña-Naranjo, Jose Agustín; Hernández-Espriú, Antonio; Pedrozo-Acuña, Adrián; Scanlon, Bridget R.; Nicot, Jean Philippe; Young, Michael H.; Wolaver, Brad D.; Alcocer-Yamanaka, Victor Hugo

2017-10-01

Water resources development and landscape alteration exert marked impacts on water-cycle dynamics, including areas subjected to hydraulic fracturing (HF) for exploitation of unconventional oil and gas resources found in shale or tight sandstones. Here we apply a conceptual framework for linking baseflow analysis to changes in water demands from different sectors (e.g. oil/gas extraction, irrigation, and municipal consumption) and climatic variability in the semiarid Eagle Ford play in Texas, USA. We hypothesize that, in water-limited regions, baseflow (Qb) changes are partly due (along with climate variability) to groundwater abstraction. For a more realistic assessment, the analysis was conducted in two different sets of unregulated catchments, located outside and inside the Eagle Ford play. Three periods were considered in the analysis related to HF activities: pre-development (1980-2000), moderate (2001-2008) and intensive (2009-2015) periods. Results indicate that in the Eagle Ford play region, temporal changes in baseflow cannot be directly related to the increase in hydraulic fracturing. Instead, substantial baseflow declines during the intensive period of hydraulic fracturing represent the aggregated effects from the combination of: (1) a historical exceptional drought during 2011-2012; (2) increased groundwater-based irrigation; and (3) an intensive hydraulic fracturing activity.

Dynamic fracture instability of tough bulk metallic glass

NASA Astrophysics Data System (ADS)

Meng, J. X.; Ling, Z.; Jiang, M. Q.; Zhang, H. S.; Dai, L. H.

2008-04-01

We report the observations of a clear fractographic evolution from vein pattern, dimple structure, and then to periodic corrugation structure, followed by microbranching pattern, along the crack propagation direction in the dynamic fracture of a tough Zr41.2Ti13.8Cu12.5Ni10Be22.5 (Vit.1) bulk metallic glass (BMGs) under high-velocity plate impact. A model based on fracture surface energy dissipation and void growth is proposed to characterize this fracture pattern transition. We find that once the dynamic crack propagation velocity reaches a critical fraction of Rayleigh wave speed, the crack instability occurs; hence, crack microbranching goes ahead. Furthermore, the correlation between the critical velocity of amorphous materials and their intrinsic strength such as Young's modulus is uncovered. The results may shed new insight into dynamic fracture instability for BMGs.

Fractography used with lifetime prediction tests on commercial grades of alumina and silicon carbide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuebler, J.; Woodtli, J.; Berroth, K.

1996-12-31

Fractographic investigations were conducted on alumina and {alpha}-SSiC bend bars from a round robin test comparing a static and a dynamic lifetime test method. The investigations revealed that not all fracture origins found on {alpha}-SSiC specimens had contact with the ambient medium and therefore the dynamic lifetime tests did not measure the materials` behaviour under stress in water. In addition to the conventional SEM fractography an alternate technique, using an auto focus scanning laser profilometer was applied for characterizing the fractures. This tool is very promising for fractography because of the ability to handle topographic data by imaging procedures andmore » fractal analysis.« less

Duplex stainless steel fracture surface analysis using X-ray fractography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rajanna, K.; Pathiraj, B.; Kolster, B.H.

1997-02-01

The fatigue fracture surface of a duplex stainless steel was analyzed using x-ray fractography. A lower than average austenite content was observed at the fracture surface due to the transformation of austenite into deformation-induced martensite. The influence of fatigue cycling on the transformation was confined to a depth of about 30 {micro}m below the fracture surface. X-ray analyses of both the ferrite-martensite and the austenite phases indicated residual stresses ({sigma}{sub r}) increasing with depth from the fracture surface and reaching a maximum some tens of microns below the fracture surface. The lower {sigma}{sub r} observed at the fracture surface hasmore » been attributed to the stress relaxation effects caused by the new fracture surfaces created in the crack growth process. The observed decrease in full width at half maximum (FWHM) in the ferrite-martensite phase was presumed to be due to the dynamic recovery effect that was likely to occur within the material close to the crack tip as a consequence of fatigue cycling.« less

Acoustic emission from a growing crack

NASA Technical Reports Server (NTRS)

Jacobs, Laurence J.

1989-01-01

An analytical method is being developed to determine the signature of an acoustic emission waveform from a growing crack and the results of this analysis are compared to experimentally obtained values. Within the assumptions of linear elastic fracture mechanics, a two dimensional model is developed to examine a semi-infinite crack that, after propagating with a constant velocity, suddenly stops. The analytical model employs an integral equation method for the analysis of problems of dynamic fracture mechanics. The experimental procedure uses an interferometric apparatus that makes very localized absolute measurements with very high fidelity and without acoustically loading the specimen.

Evolution of a fracture network in an elastic medium with internal fluid generation and expulsion

NASA Astrophysics Data System (ADS)

Kobchenko, Maya; Hafver, Andreas; Jettestuen, Espen; Renard, François; Galland, Olivier; Jamtveit, Bjørn; Meakin, Paul; Dysthe, Dag Kristian

2014-11-01

A simple and reproducible analog experiment was used to simulate fracture formation in a low-permeability elastic solid during internal fluid/gas production, with the objective of developing a better understanding of the mechanisms that control the dynamics of fracturing, fracture opening and closing, and fluid transport. In the experiment, nucleation, propagation, and coalescence of fractures within an elastic gelatin matrix, confined in a Hele-Shaw cell, occurred due to CO2 production via fermentation of sugar, and it was monitored by optical means. We first quantified how a fracture network develops, and then how intermittent fluid transport is controlled by the dynamics of opening and closing of fractures. The gas escape dynamics exhibited three characteristic behaviors: (1) Quasiperiodic release of gas with a characteristic frequency that depends on the gas production rate but not on the system size. (2) A 1 /f power spectrum for the fluctuations in the total open fracture area over an intermediate range of frequencies (f ), which we attribute to collective effects caused by interaction between fractures in the drainage network. (3) A 1 /f2 power spectrum was observed at high frequencies, which can be explained by the characteristic behavior of single fractures.

Effects of age and loading rate on equine cortical bone failure.

PubMed

Kulin, Robb M; Jiang, Fengchun; Vecchio, Kenneth S

2011-01-01

Although clinical bone fractures occur predominantly under impact loading (as occurs during sporting accidents, falls, high-speed impacts or other catastrophic events), experimentally validated studies on the dynamic fracture behavior of bone, at the loading rates associated with such events, remain limited. In this study, a series of tests were performed on femoral specimens obtained post-mortem from equine donors ranging in age from 6 months to 28 years. Fracture toughness and compressive tests were performed under both quasi-static and dynamic loading conditions in order to determine the effects of loading rate and age on the mechanical behavior of the cortical bone. Fracture toughness experiments were performed using a four-point bending geometry on single and double-notch specimens in order to measure fracture toughness, as well as observe differences in crack initiation between dynamic and quasi-static experiments. Compressive properties were measured on bone loaded parallel and transverse to the osteonal growth direction. Fracture propagation was then analyzed using scanning electron and scanning confocal microscopy to observe the effects of microstructural toughening mechanisms at different strain rates. Specimens from each horse were also analyzed for dry, wet and mineral densities, as well as weight percent mineral, in order to investigate possible influences of composition on mechanical behavior. Results indicate that bone has a higher compressive strength, but lower fracture toughness when tested dynamically as compared to quasi-static experiments. Fracture toughness also tends to decrease with age when measured quasi-statically, but shows little change with age under dynamic loading conditions, where brittle "cleavage-like" fracture behavior dominates. Copyright © 2010 Elsevier Ltd. All rights reserved.

A discrete-element model for viscoelastic deformation and fracture of glacial ice

NASA Astrophysics Data System (ADS)

Riikilä, T. I.; Tallinen, T.; Åström, J.; Timonen, J.

2015-10-01

A discrete-element model was developed to study the behavior of viscoelastic materials that are allowed to fracture. Applicable to many materials, the main objective of this analysis was to develop a model specifically for ice dynamics. A realistic model of glacial ice must include elasticity, brittle fracture and slow viscous deformations. Here the model is described in detail and tested with several benchmark simulations. The model was used to simulate various ice-specific applications with resulting flow rates that were compatible with Glen's law, and produced under fragmentation fragment-size distributions that agreed with the known analytical and experimental results.

Simulating Hydraulic Fracturing: Failure in soft versus hard rocks

NASA Astrophysics Data System (ADS)

Aleksans, J.; Koehn, D.; Toussaint, R.

2017-12-01

In this contribution we discuss the dynamic development of hydraulic fractures, their evolution and the resulting seismicity during fluid injection in a coupled numerical model. The model describes coupling between a solid that can fracture dynamically and a compressible fluid that can push back at the rock and open fractures. With a series of numerical simulations we show how the fracture pattern and seismicity change depending on changes in depth, injection rate, Young's Modulus and breaking strength. Our simulations indicate that the Young's Modulus has the largest influence on the fracture dynamics and also the related seismicity. Simulations of rocks with a Young's modulus smaller than 10 GPa show dominant mode I failure and a growth of fracture aperture with a decrease in Young's modulus. Simulations of rocks with a higher Young's modulus than 10 GPa show fractures with a constant aperture and fracture growth that is mainly governed by a growth in crack length and an increasing amount of mode II failure. We propose that two distinct failure regimes are observed in the simulations, above 10 GPa rocks break with a constant critical stress intensity factor whereas below 10 GPa they break reaching a critical cohesion, i.e. a critical tensile strength. These results are very important for the prediction of fracture dynamics and seismicity during fluid injection, especially since we see a transition from one failure regime to another at around 10 GPa, a Young's modulus that lies in the middle of possible values for natural shale rocks.

Coseismic Damage Generation in Fault Zones by Successive High Strain Rate Loading Experiments

NASA Astrophysics Data System (ADS)

Aben, F. M.; Doan, M. L.; Renard, F.; Toussaint, R.; Reuschlé, T.; Gratier, J. P.

2014-12-01

Damage zones of active faults control both resistance to rupture and transport properties of the fault. Hence, knowing the rock damage's origin is important to constrain its properties. Here we study experimentally the damage generated by a succession of dynamic loadings, a process mimicking the stress history of a rock sample located next to an active fault. A propagating rupture generates high frequency stress perturbations next to its tip. This dynamic loading creates pervasive damage (pulverization), as multiple fractures initiate and grow simultaneously. Previous single loading experiments have shown a strain rate threshold for pulverization. Here, we focus on conditions below this threshold and the dynamic peak stress to constrain: 1) if there is dynamic fracturing at these conditions and 2) if successive loadings (cumulative seismic events) result in pervasive fracturing, effectively reducing the pulverization threshold to milder conditions. Monzonite samples were dynamically loaded (strain rate > 50 s-1) several times below the dynamic peak strength, using a Split Hopkinson Pressure Bar apparatus. Several quasi-static experiments were conducted as well (strain rate < 10-5-s). Samples loaded up to stresses above the quasi-static uniaxial compressive strength (qsUCS) systematically fragmented or pulverized after four successive loadings. We measured several damage proxies (P-wave velocity, porosity), that show a systematic increase in damage with each load. In addition, micro-computed tomography acquisition on several damage samples revealed the growth of a pervasive fracture network between ensuing loadings. Samples loaded dynamically below the qsUCS failed along one fracture after a variable amount of loadings and damage proxies do not show any a systematic trend. Our conclusions is that milder dynamic loading conditions, below the dynamic peak strength, result in pervasive dynamic fracturing. Also, successive loadings effectively lower the pulverization threshold of the rock. However, the peak loading stress must exceed the qsUCS of the rock, otherwise quasi-static fracturing occurs. Pulverized rocks found in the field are therefore witnesses of previous large earthquakes.

Verification of nonlinear dynamic structural test results by combined image processing and acoustic analysis

NASA Astrophysics Data System (ADS)

Tene, Yair; Tene, Noam; Tene, G.

1993-08-01

An interactive data fusion methodology of video, audio, and nonlinear structural dynamic analysis for potential application in forensic engineering is presented. The methodology was developed and successfully demonstrated in the analysis of heavy transportable bridge collapse during preparation for testing. Multiple bridge elements failures were identified after the collapse, including fracture, cracks and rupture of high performance structural materials. Videotape recording by hand held camcorder was the only source of information about the collapse sequence. The interactive data fusion methodology resulted in extracting relevant information form the videotape and from dynamic nonlinear structural analysis, leading to full account of the sequence of events during the bridge collapse.

The microbiota of traumatic, open fracture wounds is associated with mechanism of injury.

PubMed

Bartow-McKenney, Casey; Hannigan, Geoffrey D; Horwinski, Joseph; Hesketh, Patrick; Horan, Annamarie D; Mehta, Samir; Grice, Elizabeth A

2018-05-26

Open fractures are characterized by disruption of the skin and soft tissue, which allows for microbial contamination and colonization. Preventing infection-related complications of open fractures and other acute wounds remains an evolving challenge due to an incomplete understanding of how microbial colonization and contamination influence healing and outcomes. Culture-independent molecular methods are now widely used to study human-associated microbial communities without introducing culture biases. Using such approaches, the objectives of this study were to 1) define the long-term temporal microbial community dynamics of open fracture wounds and 2) examine microbial community dynamics with respect to clinical and demographic factors. Fifty-two subjects with traumatic open fracture wounds (32 blunt and 20 penetrating injuries) were enrolled prospectively and sampled longitudinally from presentation to the emergency department and at each subsequent inpatient or outpatient encounter. Specimens were collected from both the wound center and adjacent skin. Culture-independent sequencing of the 16S ribosomal RNA gene was employed to identify and characterize microbiota. Upon presentation to the emergency department and time points immediately following, sample collection site (wound or adjacent skin) was the most defining feature discriminating microbial profiles. Microbial composition of adjacent skin and wound center converged over time. Mechanism of injury most strongly defined the microbiota after initial convergence. Further analysis controlling for race, gender, and age revealed that mechanism of injury remained a significant discriminating feature throughout the continuum of care. We conclude that the microbial communities associated with open fracture wounds are dynamic in nature until eventual convergence with the adjacent skin community during healing, with mechanism of injury as an important feature affecting both diversity and composition of the microbiota. A more complete understanding of the factors influencing microbial contamination and/or colonization in open fractures is a critical foundation for identifying markers indicative of outcome and deciphering their respective contributions to healing and/or complication. This article is protected by copyright. All rights reserved. © 2018 by the Wound Healing Society.

Damage and fracture in fabric-reinforced composites under quasi-static and dynamic bending

NASA Astrophysics Data System (ADS)

Ullah, H.; Harland, A. R.; Silberschmidt, V. V.

2013-07-01

Fabric-reinforced polymer composites used in sports products can be exposed to different in-service conditions such as large deformations caused by quasi-static and dynamic loading. Composite materials subjected to such bending loads can demonstrate various damage modes - matrix cracking, delamination and, ultimately, fabric fracture. Damage evolution in composites affects both their in-service properties and performance that can deteriorate with time. Such behaviour needs adequate means of analysis and investigation, the main approaches being experimental characterisation and non-destructive examination of internal damage in composite laminates. This research deals with a deformation behaviour and damage in carbon fabric-reinforced polymer (CFRP) laminates caused by quasi-static and dynamic bending. Experimental tests were carried out to characterise the behaviour of a CFRP material under large-deflection bending, first in quasi-static and then in dynamic conditions. Izod-type impact bending tests were performed on un-notched specimens of CFRP using a Resil impactor to assess the transient response and energy absorbing capability of the material. X-ray micro computed tomography (micro-CT) was used to analyse various damage modes in the tested specimens. X-ray tomographs revealed that through-thickness matrix cracking, inter-ply and intra-ply delamination such as tow debonding, and fabric fracture were the prominent damage modes both in quasi-static and dynamic test specimens. However, the inter-ply damage was localised at impact location in dynamically tested specimens, whereas in the quasi-static specimens, it spread almost over the entire interface.

Factors influencing short-term outcomes for older patients accessing emergency departments after a fall: The role of fall dynamics.

PubMed

Trevisan, Caterina; Di Gregorio, Patrizia; Debiasi, Eugenio; Pedrotti, Martina; La Guardia, Mario; Manzato, Enzo; Sergi, Giuseppe; March, Albert

2017-10-01

While the relevance of falls in raising the risk of fractures, hospitalization and disability in older age is well recognized, the factors influencing the onset of fractures and the need for ward admission after a fall have yet to be fully elucidated. We investigated which factors and fall dynamics were mainly associated with fall-related injuries and hospitalization among elderly persons accessing the Emergency Department (ED) following a fall. The study involved 2144 older subjects who accessed the ED after a fall. Data on the fall´s nature and related injuries, ward admissions, history of falls, dementia, and medical therapies were examined for all patients. Considering dynamics, we distinguished accidental falls (due to interaction with environmental hazards while in motion) and falls from standing (secondary to syncope, lipothymia, drop attack, or vertigo). The overall prevalence of fractures in our population did not differ significantly with advancing age, though hip fractures were more common in the oldest, and upper limb fractures in the youngest patients. Falls from standing were associated with polypharmacy and with higher ward admission rate despite a lower fractures´ prevalence than accidental falls. The chances of fall-related fractures were more than fourfold as high for accidental dynamics (OR=4.05, 95%CI:3.10-5.29, p<0.0001). Ward admission was associated with polypharmacy, dementia, anticoagulants´ use and fall-related fractures (OR=6.84, 95%CI:5.45-8.58, p<0.0001), while it correlated inversely with accidental fall dynamics. Outcomes of falls in older age depend not only on any fall-related injuries, but also on factors such as polypharmacy, cognitive status and fall dynamics. Copyright © 2017 Elsevier B.V. All rights reserved.

Review of fatigue and fracture research at NASA Langley Research Center

NASA Technical Reports Server (NTRS)

Everett, Richard A., Jr.

1988-01-01

Most dynamic components in helicopters are designed with a safe-life constant-amplitude testing approach that has not changed in many years. In contrast, the fatigue methodology in other industries has advanced significantly in the last two decades. Recent research at the NASA Langley Research Center and the U.S. Army Aerostructures Directorate at Langley are reviewed relative to fatigue and fracture design methodology for metallic components. Most of the Langley research was directed towards the damage tolerance design approach, but some work was done that is applicable to the safe-life approach. In the areas of testing, damage tolerance concepts are concentrating on the small-crack effect in crack growth and measurement of crack opening stresses. Tests were conducted to determine the effects of a machining scratch on the fatigue life of a high strength steel. In the area of analysis, work was concentrated on developing a crack closure model that will predict fatigue life under spectrum loading for several different metal alloys including a high strength steel that is often used in the dynamic components of helicopters. Work is also continuing in developing a three-dimensional, finite-element stress analysis for cracked and uncracked isotropic and anisotropic structures. A numerical technique for solving simultaneous equations called the multigrid method is being pursued to enhance the solution schemes in both the finite-element analysis and the boundary element analysis. Finally, a fracture mechanics project involving an elastic-plastic finite element analysis of J-resistance curve is also being pursued.

Advanced Hydraulic Fracturing Technology for Unconventional Tight Gas Reservoirs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stephen Holditch; A. Daniel Hill; D. Zhu

2007-06-19

The objectives of this project are to develop and test new techniques for creating extensive, conductive hydraulic fractures in unconventional tight gas reservoirs by statistically assessing the productivity achieved in hundreds of field treatments with a variety of current fracturing practices ranging from 'water fracs' to conventional gel fracture treatments; by laboratory measurements of the conductivity created with high rate proppant fracturing using an entirely new conductivity test - the 'dynamic fracture conductivity test'; and by developing design models to implement the optimal fracture treatments determined from the field assessment and the laboratory measurements. One of the tasks of thismore » project is to create an 'advisor' or expert system for completion, production and stimulation of tight gas reservoirs. A central part of this study is an extensive survey of the productivity of hundreds of tight gas wells that have been hydraulically fractured. We have been doing an extensive literature search of the SPE eLibrary, DOE, Gas Technology Institute (GTI), Bureau of Economic Geology and IHS Energy, for publicly available technical reports about procedures of drilling, completion and production of the tight gas wells. We have downloaded numerous papers and read and summarized the information to build a database that will contain field treatment data, organized by geographic location, and hydraulic fracture treatment design data, organized by the treatment type. We have conducted experimental study on 'dynamic fracture conductivity' created when proppant slurries are pumped into hydraulic fractures in tight gas sands. Unlike conventional fracture conductivity tests in which proppant is loaded into the fracture artificially; we pump proppant/frac fluid slurries into a fracture cell, dynamically placing the proppant just as it occurs in the field. From such tests, we expect to gain new insights into some of the critical issues in tight gas fracturing, in particular the roles of gel damage, polymer loading (water-frac versus gel frac), and proppant concentration on the created fracture conductivity. To achieve this objective, we have designed the experimental apparatus to conduct the dynamic fracture conductivity tests. The experimental apparatus has been built and some preliminary tests have been conducted to test the apparatus.« less

Evaluation of fracture toughness and mechanical properties of ternary thiol-ene-methacrylate systems as resin matrix for dental restorative composites.

PubMed

Beigi, Saeed; Yeganeh, Hamid; Atai, Mohammad

2013-07-01

Study and evaluation of fracture toughness, flexural and dynamic mechanical properties, and crosslink density of ternary thiol-ene-methacrylate systems and comparison with corresponding conventional methacrylate system were considered in the present study. Urethane tetra allyl ether monomer (UTAE) was synthesized as ene monomer. Different formulations were prepared based on combination of UTAE, BisGMA/TEGDMA and a tetrathiol monomer (PETMP). The photocuring reaction was conducted under visible light using BD/CQ combination as photoinitiator system. Mechanical properties were evaluated via measuring flexural strength, flexural modulus and fracture toughness. Scanning electron microscopy (SEM) was utilized to study the morphology of the fractured specimen's cross section. Viscoelastic properties of the samples were also determined by dynamic mechanical thermal analysis (DMTA). The same study was performed on a conventional methacrylate system. The data were analyzed and compared by ANOVA and Tukey HSD tests (significance level=0.05). The results showed improvement in fracture toughness of the specimens containing thiol-ene moieties. DMTA revealed a lower glass transition temperature and more homogenous structure for thiol-ene containing specimens in comparison to the system containing merely methacrylate monomer. The flexural modulus and flexural strength of the specimens with higher thiol-ene content were lower than the neat methacrylate system. The SEM micrographs of the fractured surface of specimens with higher methacrylate content were smooth and mirror-like (shiny) which represent brittle fracture. The thiol-ene-methacrylate system can be used as resin matrix of dental composites with enhanced fracture toughness in comparison to the methacrylate analogous. Copyright © 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Biomechanical analysis of four different fixations for the posterolateral shearing tibial plateau fracture.

PubMed

Zhang, Wei; Luo, Cong-Feng; Putnis, Sven; Sun, Hui; Zeng, Zhi-Min; Zeng, Bing-Fang

2012-03-01

The posterolateral shearing tibial plateau fracture is uncommon in the literature, however with the increased usage of computer tomography (CT), the incidence of these fractures is no longer as low as previously thought. Few studies have concentrated on this fracture, least of all using a biomechanical model. The purpose of this study was to compare and analyse the biomechanical characteristics of four different types of internal fixation to stabilise the posterolateral shearing tibial plateau fracture. Forty synthetic tibiae (Synbone, right) simulated the posterolateral shearing fracture models and these were randomly assigned into four groups; Group A was fixed with two anterolateral lag screws, Group B with an anteromedial Limited Contact Dynamic Compression Plate (LC-DCP), Group C with a lateral locking plate, and Group D with a posterolateral buttress plate. Vertical displacement of the posterolateral fragment was measured using three different strengths of axial loading force, and finally loaded until fixation failure. It was concluded that the posterolateral buttress plate is biomechanically the strongest fixation method for the posterolateral shearing tibial plateau fracture. Copyright © 2011 Elsevier B.V. All rights reserved.

Preliminary analysis of force-torque measurements for robot-assisted fracture surgery.

PubMed

Georgilas, Ioannis; Dagnino, Giulio; Tarassoli, Payam; Atkins, Roger; Dogramadzi, Sanja

2015-08-01

Our group at Bristol Robotics Laboratory has been working on a new robotic system for fracture surgery that has been previously reported [1]. The robotic system is being developed for distal femur fractures and features a robot that manipulates the small fracture fragments through small percutaneous incisions and a robot that re-aligns the long bones. The robots controller design relies on accurate and bounded force and position parameters for which we require real surgical data. This paper reports preliminary findings of forces and torques applied during bone and soft tissue manipulation in typical orthopaedic surgery procedures. Using customised orthopaedic surgical tools we have collected data from a range of orthopaedic surgical procedures at Bristol Royal Infirmary, UK. Maximum forces and torques encountered during fracture manipulation which involved proximal femur and soft tissue distraction around it and reduction of neck of femur fractures have been recorded and further analysed in conjunction with accompanying image recordings. Using this data we are establishing a set of technical requirements for creating safe and dynamically stable minimally invasive robot-assisted fracture surgery (RAFS) systems.

Rupture Dynamics and Scaling Behavior of Hydraulically Stimulated Micro-Earthquakes in a Shale Reservoir

NASA Astrophysics Data System (ADS)

Viegas, G. F.; Urbancic, T.; Baig, A. M.

2014-12-01

In hydraulic fracturing completion programs fluids are injected under pressure into fractured rock formations to open escape pathways for trapped hydrocarbons along pre-existing and newly generated fractures. To characterize the failure process, we estimate static and dynamic source and rupture parameters, such as dynamic and static stress drop, radiated energy, seismic efficiency, failure modes, failure plane orientations and dimensions, and rupture velocity to investigate the rupture dynamics and scaling relations of micro-earthquakes induced during a hydraulic fracturing shale completion program in NE British Columbia, Canada. The relationships between the different parameters combined with the in-situ stress field and rock properties provide valuable information on the rupture process giving insights into the generation and development of the fracture network. Approximately 30,000 micro-earthquakes were recorded using three multi-sensor arrays of high frequency geophones temporarily placed close to the treatment area at reservoir depth (~2km). On average the events have low radiated energy, low dynamic stress and low seismic efficiency, consistent with the obtained slow rupture velocities. Events fail in overshoot mode (slip weakening failure model), with fluids lubricating faults and decreasing friction resistance. Events occurring in deeper formations tend to have faster rupture velocities and are more efficient in radiating energy. Variations in rupture velocity tend to correlate with variation in depth, fault azimuth and elapsed time, reflecting a dominance of the local stress field over other factors. Several regions with different characteristic failure modes are identifiable based on coherent stress drop, seismic efficiency, rupture velocities and fracture orientations. Variations of source parameters with rock rheology and hydro-fracture fluids are also observed. Our results suggest that the spatial and temporal distribution of events with similar characteristic rupture behaviors can be used to determine reservoir geophysical properties, constrain reservoir geo-mechanical models, classify dynamic rupture processes for fracture models and improve fracture treatment designs.

Dynamic fracture responses of alumina and two ceramic composites

NASA Technical Reports Server (NTRS)

Yang, Kwan-Ho; Kobayashi, Albert S.

1990-01-01

A hybrid experimental-numerical procedure was used to characterize the dynamic fracture response of Al2O3 and TiB2-particulate/SiC-matrix and SiC-whisker/Al2O3-matrix composites. Unlike metals and polymers, dynamic arrest stress intensity factors (SIFs) did not exist in the monolithic ceramics and the two ceramic composites considered. Thus a running crack in these materials cannot be arrested by lowering the driving force, i.e., the dynamic SIF. Fractography study of the alumina specimens showed that the area of transgranular failure varied from about 3 percent to about 16 percent for rapid crack extensions in statically and impact loaded specimens, respectively. The influence of kinematic constraints which enforces transgranular flat crack extension, despite the higher fracture energy of transgranular fracture, is discussed.

Response of Metals and Metallic Structures to Dynamic Loading

DTIC Science & Technology

1978-05-01

materials for service by testing under high rates of loading. Impact tests such as the Charpy test, the drop-weight tear test, and the dynamic tear...have clearly shown this for precracked charpy specimens and for the drop-weight tear test. Hence, there is a strong need for additional dynamic...dynamic fracture resistance ( Charpy , dynamic-tear, drop-weight tear test, etc.), normally assures that fracture in dynamically loaded structures is

Experimental investigation of heat transport through single synthetic fractures

NASA Astrophysics Data System (ADS)

Pastore, Nicola; Cherubini, Claudia; Giasi, Concetta I.; Redondo, Jose M.

2017-04-01

In fractured geothermal reservoirs, heat transport is highly influenced by the presence of the fractures, so appropriate knowledge of heat behaviour in fractured porous media is essential for accurate prediction of the energy extraction in geothermal reservoirs. The present study focuses on the study of heat transport within single synthetic fractures. In particular manner several tests have been carried out in order to explore the role of fracture roughness, aperture variability and the fracture-matrix ratio on the heat transport dynamics. The Synfrac program together with a 3d printer have been used to build several fracture planes having different geometrical characteristics that have been moulded to generate concrete porous fractured blocks. The tests regard the observation of the thermal breakthrough curves obtained through a continuous flow injection in correspondence of eight thermocouples located uniformly on the fractured blocks. The physical model developed permits to reproduce and understand adequately some features of heat transport dynamics in fractured media. The results give emphasis on the errors of the assumptions commonly used in heat transport modelling.

Damage Mechanisms and Controlled Crack Propagation in a Hot Pressed Silicon Nitride Ceramic. Ph.D. Thesis - Northwestern Univ., 1993

NASA Technical Reports Server (NTRS)

Calomino, Anthony Martin

1994-01-01

The subcritical growth of cracks from pre-existing flaws in ceramics can severely affect the structural reliability of a material. The ability to directly observe subcritical crack growth and rigorously analyze its influence on fracture behavior is important for an accurate assessment of material performance. A Mode I fracture specimen and loading method has been developed which permits the observation of stable, subcritical crack extension in monolithic and toughened ceramics. The test specimen and procedure has demonstrated its ability to generate and stably propagate sharp, through-thickness cracks in brittle high modulus materials. Crack growth for an aluminum oxide ceramic was observed to be continuously stable throughout testing. Conversely, the fracture behavior of a silicon nitride ceramic exhibited crack growth as a series of subcritical extensions which are interrupted by dynamic propagation. Dynamic initiation and arrest fracture resistance measurements for the silicon nitride averaged 67 and 48 J/sq m, respectively. The dynamic initiation event was observed to be sudden and explosive. Increments of subcritical crack growth contributed to a 40 percent increase in fracture resistance before dynamic initiation. Subcritical crack growth visibly marked the fracture surface with an increase in surface roughness. Increments of subcritical crack growth loosen ceramic material near the fracture surface and the fracture debris is easily removed by a replication technique. Fracture debris is viewed as evidence that both crack bridging and subsurface microcracking may be some of the mechanisms contributing to the increase in fracture resistance. A Statistical Fracture Mechanics model specifically developed to address subcritical crack growth and fracture reliability is used together with a damaged zone of material at the crack tip to model experimental results. A Monte Carlo simulation of the actual experiments was used to establish a set of modeling input parameters. It was demonstrated that a single critical parameter does not characterize the conditions required for dynamic initiation. Experimental measurements for critical crack lengths, and the energy release rates exhibit significant scatter. The resulting output of the model produces good agreement with both the average values and scatter of experimental measurements.

Dynamic Y stent fractures in crescentic tracheobronchomalacia.

PubMed

Popilevsky, Frida; Al-Ajam, Mohammad R; Ly, Vanthanh; Sanchez, Lisette Delgado; Cutaia, Michael

2012-07-01

Endobronchial stents have been used occasionally to treat benign conditions such as tracheobronchomalacia (TBM). This report describes a unique case of a patient with crescentic TBM in whom Dynamic Y stent was placed on 2 separate occasions to control symptoms and resulted in identical posterior wall stent fractures within a year of stent placement, both times. A silicone Y stent was substituted for the dynamic stent, and it has been effective in controlling symptoms for 9 months without complications. A literature review of cases of fractured Dynamic Y stents is made and factors affecting the choice of stent type for crescentic TBM are explored.

Dynamic Fracture Toughness Evaluation by Measurement of CTOD (Crack Tip Opening Displacement).

DTIC Science & Technology

1988-03-15

fracture toughness of structural steels were reported by Shoemaker and Rolfe [1]; these and similar results are also presented in the text by Rolfe and...8217 MPaV/-m/s. Following the dynamic tests of Shoemaker and Rolfe , extensions of the familiar ASTM E-399 static fracture toughness tests were examined. This...s.V.: **.4* .4 5, -~ 5 5 - 𔃿 .4.4 References [1] Shoemaker, A.K. and Rolfe , S.T., "The Static and Dynamic Low-Temperature Crack-Toughness

Dynamic tensile stress-strain characteristics of carbon/epoxy laminated composites in through-thickness direction

NASA Astrophysics Data System (ADS)

Nakai, Kenji; Yokoyama, Takashi

2015-09-01

The effect of strain rate up to approximately ɛ˙ = 102/s on the tensile stress-strain properties of unidirectional and cross-ply carbon/epoxy laminated composites in the through-thickness direction is investigated. Waisted cylindrical specimens machined out of the laminated composites in the through-thickness direction are used in both static and dynamic tests. The dynamic tensile stress-strain curves up to fracture are determined using the split Hopkinson bar (SHB). The low and intermediate strain-rate tensile stress-strain relations up to fracture are measured on an Instron 5500R testing machine. It is demonstrated that the ultimate tensile strength and absorbed energy up to fracture increase significantly, while the fracture strain decreases slightly with increasing strain rate. Macro- and micro-scopic examinations reveal a marked difference in the fracture surfaces between the static and dynamic tension specimens.

Investigation of strength characteristics of aluminum alloy under dynamic tension

NASA Astrophysics Data System (ADS)

Evstifeev, A. D.

2018-04-01

The study presents the results of experimental-theoretical analysis for aluminum alloy subjected to static and dynamic tension on samples of different types. The material was tested under initial coarse-grained (CG) and in ultrafine-grained (UFG) condition. The time dependence of the tensile strength is calculated using an incubation time fracture criterion based on a set of fixed constants of the material.

Joint Use of ERT, Tracer, and Numerical Techniques to Image Preferential Flow Paths in a Fractured Granite Aquifer

NASA Astrophysics Data System (ADS)

Sanaga, S.; Vijay, S.; Kbvn, P.; Peddinti, S. R.; P S L, S.

2017-12-01

Fractured geologic media poses formidable challenges to hydrogeologists due of the strenuous mapping of fracture-matrix system and quantification of flow and transport processes. In this research, we demonstrated the efficacy of tracer-ERT studies coupled with numerical simulations to delineate preferential flow paths in a fractured granite aquifer of Deccan traps in India. A series of natural gradient saline tracer experiments were conducted from a depth window of 18 to 22 m in an injection well located inside the IIT Hyderabad campus. Tracer migration was monitored in a time-lapse mode using two cross-sectional surface ERT profiles placed in the direction of flow gradient. Dynamic changes in sub-surface electrical properties inferred via resistivity anomalies were used to highlight preferential flow paths of the study area. ERT-derived tracer breakthrough curves were in agreement with geochemical sample measurements (R2=0.74). Fracture geometry and hydraulic properties derived from ERT and pumping tests were then used to evaluate two mathematical conceptualizations that are relevant to fractured aquifers. Results of numerical analysis conclude that a dual continuum model that combines matrix and fracture systems through a flow exchange term has outperformed equivalent continuum model in reproducing tracer concentrations at the monitoring wells (evident by decrease in RMSE from 199 mg/l to 65 mg/l). A sensitivity analysis of the model parameters reveals that spatial variability in hydraulic conductivity, local-scale dispersion, and flow exchange at fracture-matrix interface have a profound effect on model simulations. Keywords: saline tracer, ERT, fractured granite, groundwater, preferential flow, numerical simulation

Measurement of fracture properties of concrete at high strain rates

PubMed Central

Cendón, D. A.; Sánchez-Gálvez, V.; Gálvez, F.

2017-01-01

An analysis of the spalling technique of concrete bars using the modified Hopkinson bar was carried out. A new experimental configuration is proposed adding some variations to previous works. An increased length for concrete specimens was chosen and finite-element analysis was used for designing a conic projectile to obtain a suitable triangular impulse wave. The aim of this initial work is to establish an experimental framework which allows a simple and direct analysis of concrete subjected to high strain rates. The efforts and configuration of these primary tests, as well as the selected geometry and dimensions for the different elements, have been focused to achieve a simple way of identifying the fracture position and so the tensile strength of tested specimens. This dynamic tensile strength can be easily compared with previous values published in literature giving an idea of the accuracy of the method and technique proposed and the possibility to extend it in a near future to obtain other mechanical properties such as the fracture energy. The tests were instrumented with strain gauges, accelerometers and high-speed camera in order to validate the results by different ways. Results of the dynamic tensile strength of the tested concrete are presented. This article is part of the themed issue ‘Experimental testing and modelling of brittle materials at high strain rates’. PMID:27956510

Fluctuations of global energy release and crackling in nominally brittle heterogeneous fracture.

PubMed

Barés, J; Hattali, M L; Dalmas, D; Bonamy, D

2014-12-31

The temporal evolution of mechanical energy and spatially averaged crack speed are both monitored in slowly fracturing artificial rocks. Both signals display an irregular burstlike dynamics, with power-law distributed fluctuations spanning a broad range of scales. Yet, the elastic power released at each time step is proportional to the global velocity all along the process, which enables defining a material-constant fracture energy. We characterize the intermittent dynamics by computing the burst statistics. This latter displays the scale-free features signature of crackling dynamics, in qualitative but not quantitative agreement with the depinning interface models derived for fracture problems. The possible sources of discrepancies are pointed out and discussed.

Lattice Boltzmann simulation of CO2 reactive transport in network fractured media

NASA Astrophysics Data System (ADS)

Tian, Zhiwei; Wang, Junye

2017-08-01

Carbon dioxide (CO2) geological sequestration plays an important role in mitigating CO2 emissions for climate change. Understanding interactions of the injected CO2 with network fractures and hydrocarbons is key for optimizing and controlling CO2 geological sequestration and evaluating its risks to ground water. However, there is a well-known, difficult process in simulating the dynamic interaction of fracture-matrix, such as dynamic change of matrix porosity, unsaturated processes in rock matrix, and effect of rock mineral properties. In this paper, we develop an explicit model of the fracture-matrix interactions using multilayer bounce-back treatment as a first attempt to simulate CO2 reactive transport in network fractured media through coupling the Dardis's LBM porous model for a new interface treatment. Two kinds of typical fracture networks in porous media are simulated: straight cross network fractures and interleaving network fractures. The reaction rate and porosity distribution are illustrated and well-matched patterns are found. The species concentration distribution and evolution with time steps are also analyzed and compared with different transport properties. The results demonstrate the capability of this model to investigate the complex processes of CO2 geological injection and reactive transport in network fractured media, such as dynamic change of matrix porosity.

Late postoperative analysis of the tip-apex distance (TAD) in pertrochanteric fractures: is there an accommodation of the implant within the bone?

PubMed

Aihara, Leandro Jun; Nanni, Rafael Augusto; Carvalho, Marina Sousa; Zamboni, Caio; Durigan, Jorge R; Hungria Neto, José S; Mercadante, Marcelo T; Christian, Ralph W; Hungria, José O S

2017-10-01

This study measured the tip-apex distance (TAD) values in the immediate postoperative period and following weight-bearing and fracture impaction in patients undergoing osteosynthesis with dynamic hip screw and cephalomedullary nail. To correlate the Baumgaertner index in the immediate postoperative period with values obtained after impaction of the fracture with the accommodation of the cephalic implant in the femoral head. Radiographic TAD measurements were taken with AGFA-VIEW ® of 82 patients with a mean age of 72 years with pertrochanteric fractures who were operated on and the fracture fixed with DHS- Synthes ® , TFN-Synthes ® , or Gamma Nail III-Stryker ® in the immediate postoperative period, and following weight-bearing and fracture impaction (mean 3-8 weeks after surgery). The overall average TAD decreased from 20.3mm to 18.2mm. Regardless of the instability of the fracture, the age of the patient or the implant used, TAD decreased between the immediate postoperative period and following fracture impaction. The osteosynthesis of pertrochanteric fractures was associated with important accommodation of the cephalic implant in the femoral head with decreased TAD values after weight-bearing. © 2017 Elsevier Ltd. All rights reserved.

Nano-scale zero valent iron transport in a variable aperture dolomite fracture and a glass fracture

NASA Astrophysics Data System (ADS)

Mondal, P.; Sleep, B. E.; Cui, Z.; Zhou, Z.

2014-12-01

Experiments and numerical simulations are being performed to understand the transport behavior of carboxymethyl cellulose polymer stabilized nano-scale zero valent iron (nZVI) in a variable aperture dolomite rock fracture and a variable aperture glass replica of a fractured slate. The rock fracture was prepared by artificially inducing a fracture in a dolomite block along a stylolite, and the glass fracture was prepared by creating molds with melted glass on two opposing sides of a fractured slate rock block. Both of the fractures were 0.28 m in length and 0.21 m in width. Equivalent hydraulic apertures are about 110 microns for the rock fracture and 250 microns for the glass replica fracture. Sodium bromide and lissamine green B (LGB) serve as conservative tracers in the rock fracture and glass replica fracture, respectively. A dark box set-up with a light source and digital camera is being used to visualize the LGB and CMC-nZVI movement in the glass fracture. Experiments are being performed to determine the effects of water specific discharge and CMC concentration on nZVI transport in the fractures. Transmission electron microscopy, dynamic light scattering, and UV-visual spectrophotometry were performed to determine the stability and characteristics of the CMC-nZVI mixture. The transport of bromide, LGB, CMC, and CMC-nZVI in both fractures is being evaluated through analysis of the effluent concentrations. Time-lapse images are also being captured for the glass fracture. Bromide, LGB, and CMC recoveries have exceeded 95% in both fractures. Significant channeling has been observed in the fractures for CMC transport due to viscous effects.

Dynamic analysis of a needle insertion for soft materials: Arbitrary Lagrangian-Eulerian-based three-dimensional finite element analysis.

PubMed

Yamaguchi, Satoshi; Tsutsui, Kihei; Satake, Koji; Morikawa, Shigehiro; Shirai, Yoshiaki; Tanaka, Hiromi T

2014-10-01

Our goal was to develop a three-dimensional finite element model that enables dynamic analysis of needle insertion for soft materials. To demonstrate large deformation and fracture, we used the arbitrary Lagrangian-Eulerian (ALE) method for fluid analysis. We performed ALE-based finite element analysis for 3% agar gel and three types of copper needle with bevel tips. To evaluate simulation results, we compared the needle deflection and insertion force with corresponding experimental results acquired with a uniaxial manipulator. We studied the shear stress distribution of agar gel on various time scales. For 30°, 45°, and 60°, differences in deflections of each needle between both sets of results were 2.424, 2.981, and 3.737mm, respectively. For the insertion force, there was no significant difference for mismatching area error (p<0.05) between simulation and experimental results. Our results have the potential to be a stepping stone to develop pre-operative surgical planning to estimate an optimal needle insertion path for MR image-guided microwave coagulation therapy and for analyzing large deformation and fracture in biological tissues. Copyright © 2014 Elsevier Ltd. All rights reserved.

Dynamic Fracture Initiation Toughness at Elevated Temperatures With Application to the New Generation of Titanium Aluminide Alloys. Chapter 8

NASA Technical Reports Server (NTRS)

Shazly, Mostafa; Prakash, Vikas; Draper, Susan; Shukla, Arun (Editor)

2006-01-01

Recently, a new generation of titanium aluminide alloy, named Gamma-Met PX, has been developed with better rolling and post-rolling characteristics. I'revious work on this alloy has shown the material to have higher strengths at room and elevated temperatures when compared with other gamma titanium aluminides. In particular, this new alloy has shown increased ductility at elevated temperatures under both quasi-static and high strain rate uniaxial compressive loading. However, its high strain rate tensile ductility at room and elevated temperatures is limited to approx. 1%. In the present chapter, results of a study to investigate the effects of loading rate and test temperature on the dynamic fracture initiation toughness in Gamma-Met PX are presented. Modified split Hopkinson pressure bar was used along with high-speed photography to determine the crack initiation time. Three-point bend dynamic fracture experiments were conducted at impact speeds of approx. 1 m/s and tests temperatures of up-to 1200 C. The results show that thc dynamic fracture initiation toughness decreases with increasing test temperatures beyond 600 C. Furthermore, thc effect of long time high temperature air exposure on the fracture toughness was investigated. The dynamic fracture initiation toughness was found to decrease with increasing exposure time. The reasons behind this drop are analyzed and discussed.

The Shock and Vibration Digest. Volume 16, Number 3

DTIC Science & Technology

1984-03-01

Fluid-induced Statistical Energy Analysis Method excitation, Wind tunnel testing V.R. Miller and L.L. Faulkner Flight Dynamics Lab., Air Force...84475 wall by the statistical energy analysis (SEA) method. The fuselage structure is represented as a series of curved, iso- Probabilistic Fracture...heavy are demonstrated in three-dimensional form. floor, a statistical energy analysis (SEA) model is presented. Only structural systems (i.e., no

Conformal dynamics of precursors to fracture

NASA Astrophysics Data System (ADS)

Barra, F.; Herrera, M.; Procaccia, I.

2003-09-01

An exact integro-differential equation for the conformal map from the unit circle to the boundary of an evolving cavity in a stressed 2-dimensional solid is derived. This equation provides an accurate description of the dynamics of precursors to fracture when surface diffusion is important. The solution predicts the creation of sharp grooves that eventually lead to material failure via rapid fracture. Solutions of the new equation are demonstrated for the dynamics of an elliptical cavity and the stability of a circular cavity under biaxial stress, including the effects of surface stress.

Prevalence of overweight in children with bone fractures: a case control study.

PubMed

Valerio, Giuliana; Gallè, Francesca; Mancusi, Caterina; Di Onofrio, Valeria; Guida, Pasquale; Tramontano, Antonino; Ruotolo, Edoardo; Liguori, Giorgio

2012-10-22

Children's fractures have been enlisted among orthopaedics complaints of childhood obesity. Unhealthy lifestyle behaviours may contribute to increased risk. This study described the prevalence of overweight/obesity in children and adolescents reporting a recent fracture in relation to gender, dynamic of trauma, and site of fracture. Four-hundred-forty-nine children and adolescents with fracture and 130 fracture-free controls were recruited from a large children's hospital. The interaction between overweight and gender, dynamic of trauma, site of fracture was explored. Sports participation, television viewing, and calcium intake were also investigated. Overweight/obesity rate was increased in girls with fracture either at the upper or the lower limb (p= 0.004), while it was increased only in boys with fracture at the lower limb (p <0.02). Overweight/obesity rate did not differ between groups with low or moderate trauma. TV viewing ≥ 2 hrs was more frequent in children with fractures than controls (61.5% vs 34.5%, p =0.015) in the overweight/obese group. The increased prevalence of overweight/obesity in children with fractures is related to gender and site of fracture. Higher levels of sedentary behaviours characterize overweight children reporting fractures.

Prevalence of overweight in children with bone fractures: a case control study

PubMed Central

2012-01-01

Background Children's fractures have been enlisted among orthopaedics complaints of childhood obesity. Unhealthy lifestyle behaviours may contribute to increased risk. This study described the prevalence of overweight/obesity in children and adolescents reporting a recent fracture in relation to gender, dynamic of trauma, and site of fracture. Methods Four-hundred-forty-nine children and adolescents with fracture and 130 fracture-free controls were recruited from a large children’s hospital. The interaction between overweight and gender, dynamic of trauma, site of fracture was explored. Sports participation, television viewing, and calcium intake were also investigated. Results Overweight/obesity rate was increased in girls with fracture either at the upper or the lower limb (p= 0.004), while it was increased only in boys with fracture at the lower limb (p <0.02). Overweight/obesity rate did not differ between groups with low or moderate trauma. TV viewing ≥ 2 hrs was more frequent in children with fractures than controls (61.5% vs 34.5%, p =0.015) in the overweight/obese group. Conclusions The increased prevalence of overweight/obesity in children with fractures is related to gender and site of fracture. Higher levels of sedentary behaviours characterize overweight children reporting fractures. PMID:23088687

Does the continuum theory of dynamic fracture work?

NASA Astrophysics Data System (ADS)

Kessler, David A.; Levine, Herbert

2003-09-01

We investigate the validity of the linear elastic fracture mechanics approach to dynamic fracture. We first test the predictions in a lattice simulation, using a formula of Eshelby for the time-dependent stress intensity factor. Excellent agreement with the theory is found. We then use the same method to analyze the experiment of Sharon and Fineberg. The data here are not consistent with the theoretical expectation.

Lateral and posterior dynamic bending of the mid-shaft femur: fracture risk curves for the adult population.

PubMed

Kennedy, Eric A; Hurst, William J; Stitzel, Joel D; Cormier, Joseph M; Hansen, Gail A; Smith, Eric P; Duma, Stefan M

2004-11-01

The purpose of this study was to develop injury risk functions for dynamic bending of the human femur in the lateral-to-medial and posterior-to-anterior loading directions. A total of 45 experiments were performed on human cadaver femurs using a dynamic three-point drop test setup. An impactor of 9.8 kg was dropped from 2.2 m for an impact velocity of 5 m/s. Five-axis load cells measured the impactor and support loads, while an in situ strain gage measured the failure strain and subsequent strain rate. All 45 tests resulted in mid-shaft femur fractures with comminuted wedge and oblique fractures as the most common fracture patterns. In the lateral-to-medial bending tests the reaction loads were 4180 +/- 764 N, and the impactor loads were 4780 +/- 792 N. In the posterior-to-anterior bending tests the reaction loads were 3780 +/- 930 N, and the impactor loads were 4310 +/- 1040 N. The difference between the sum of the reaction forces and the applied load is due to inertial effects. The reaction loads were used to estimate the mid-shaft bending moments at failure since there was insufficient data to include the inertial effects in the calculations. The resulting moments are conservative estimates (lower bounds) of the mid-shaft bending moments at failure and are appropriate for use in the assessment of knee restraints and pedestrian impacts with ATD measurements. Regression analysis was used to identify significant parameters, and parametric survival analysis was used to estimate risk functions. Femur cross-sectional area, area moment of inertia (I), maximum distance to the neutral axis (c), I/c, occupant gender, and occupant mass are shown to be significant predictors of fracture tolerance, while no significant difference is shown for loading direction, bone mineral density, leg aspect and age. Risk functions are presented for femur cross-sectional area and I/c as they offer the highest correlation to peak bending moment. The risk function that utilizes the most highly correlated (R2 = 0.82) and significant (p = 0.0001) variable, cross-sectional area, predicts a 50 percent risk of femur fracture of 240 Nm, 395 Nm, and 562 Nm for equivalent cross-sectional area of the 5(th) percentile female, 50(th) percentile male, and 95(th) percentile male respectively.

Elevated temperature mechanical behavior of monolithic and SiC whisker-reinforced silicon nitrides

NASA Technical Reports Server (NTRS)

Salem, Jonathan A.; Choi, Sung R.; Sanders, William A.; Fox, Dennis S.

1991-01-01

The mechanical behavior of a 30 volume percent SiC whisker reinforced silicon nitride and a similar monolithic silicon nitride were measured at several temperatures. Measurements included strength, fracture toughness, crack growth resistance, dynamic fatigue susceptibility, post oxidation strength, and creep rate. Strength controlling defects were determined with fractographic analysis. The addition of SiC whiskers to silicon nitride did not substantially improve the strength, fracture toughness, or crack growth resistance. However, the fatigue resistance, post oxidation strength, and creep resistance were diminished by the whisker addition.

Comparison of fracture resistance and fracture characterization of bilayered zirconia/fluorapatite and monolithic lithium disilicate all ceramic crowns.

PubMed

Altamimi, Abdulaziz M; Tripodakis, Aris Petros; Eliades, George; Hirayama, Hiroshi

2014-01-01

To compare the fracture resistance between bilayered zirconia/ fluorapatite and monolithic lithium disilicate heat-pressed crowns and characterize the mode of fracture failure. Thirty crown samples were sequentially fitted on a mandibular right first molar metal replica of an ivory prepared molar tooth. The crown specimens were divided in three groups (A, B, and C; n = 10 for each group). Group A consisted of bilayered zirconia/fluorhapatite pressed-over crowns with standard design crown copings (0.7 mm uniform thickness), Group B of bilayered zirconia/fluorhapatite with anatomical design crown copings, and Group C of lithium disilicate monolithic crowns. The samples were then dynamically loaded under water for 100,000 cycles with a profile of 250 N maximum load at 1,000 N/s rate and 2.0 Hz frequency. Loading was performed with a steel ball (5 mm in diameter) coming into contact with the test crown, loading to maximum, holding for 0.2 s, unloading and lifting off 0.5 mm. The samples were then fractured under static loading, in order to determine the ultimate crown strength. Analysis of the recorded fracture load values was carried out with one-way analysis of variance (ANOVA) followed by Tukey tests. Fractured specimens were examined by stereomicroscopy and scanning electron microscopy. The fracture loads measured were (N, means and standard deviations): Group A: 561.87 (72.63), Group B: 1,014.16 (70.18) and Group C: 1,360.63 (77.95). All mean differences were statistically significant (P < 0.001). Catastrophic fractures occurred in Group C, whereas mainly veneer fractures were observed in Groups A and B. In the present study, the heat-pressed monolithic lithium-disilicate crowns showed more fracture resistance than zirconia/fluorapatite pressed-over crowns. Within the bilayered groups, the anatomical zirconia coping design presented increased ceramic fracture resistance.

Assessment of the role of cross section on fatigue resistance of rotary files when used in reciprocation.

PubMed

Sekar, Vadhana; Kumar, Ranjith; Nandini, Suresh; Ballal, Suma; Velmurugan, Natanasabapathy

2016-01-01

The purpose of this study was to assess the role of cross section on cyclic fatigue resistance of One Shape, Revo-S SU, and Mtwo rotary files in continuous rotation and reciprocating motion in dynamic testing model. A total of 90 new rotary One Shape, Revo-S SU, and Mtwo files (ISO size 25, taper 0.06, length 25 mm) were subjected to continuous rotation or reciprocating motion. A cyclic fatigue testing device was fabricated with 60° angle of curvature and 5 mm radius. The dynamic testing of these files was performed using an electric motor which permitted the reproduction of pecking motion. All instruments were rotated or reciprocated until fracture occurred. The time taken for each instrument to fracture was recorded. All the fractured files were analyzed under a scanning electron microscope (SEM) to detect the mode of fracture. Statistical analysis was performed using one-way ANOVA, followed by Tukey's honestly significant difference post hoc test. The time taken for instruments in reciprocating motion to fail under cyclic loading was significantly longer when compared with groups in continuous rotary motion. There was a statistically significant difference between Mtwo rotary and the other two groups in both continuous and reciprocating motion. One Shape rotary files recorded significantly longer duration to fracture resistance when compared with Revo-S SU files in both continuous and reciprocating motion. SEM observations showed that the instruments of all groups had undergone a ductile mode of fracture. Reciprocating motion improved the cyclic fatigue resistance of all tested groups.

Assessment of the role of cross section on fatigue resistance of rotary files when used in reciprocation

PubMed Central

Sekar, Vadhana; Kumar, Ranjith; Nandini, Suresh; Ballal, Suma; Velmurugan, Natanasabapathy

2016-01-01

Objective: The purpose of this study was to assess the role of cross section on cyclic fatigue resistance of One Shape, Revo-S SU, and Mtwo rotary files in continuous rotation and reciprocating motion in dynamic testing model. Materials and Methods: A total of 90 new rotary One Shape, Revo-S SU, and Mtwo files (ISO size 25, taper 0.06, length 25 mm) were subjected to continuous rotation or reciprocating motion. A cyclic fatigue testing device was fabricated with 60° angle of curvature and 5 mm radius. The dynamic testing of these files was performed using an electric motor which permitted the reproduction of pecking motion. All instruments were rotated or reciprocated until fracture occurred. The time taken for each instrument to fracture was recorded. All the fractured files were analyzed under a scanning electron microscope (SEM) to detect the mode of fracture. Statistical analysis was performed using one-way ANOVA, followed by Tukey's honestly significant difference post hoc test. Results: The time taken for instruments in reciprocating motion to fail under cyclic loading was significantly longer when compared with groups in continuous rotary motion. There was a statistically significant difference between Mtwo rotary and the other two groups in both continuous and reciprocating motion. One Shape rotary files recorded significantly longer duration to fracture resistance when compared with Revo-S SU files in both continuous and reciprocating motion. SEM observations showed that the instruments of all groups had undergone a ductile mode of fracture. Conclusion: Reciprocating motion improved the cyclic fatigue resistance of all tested groups. PMID:28042272

Intraoperative CT in the assessment of posterior wall acetabular fracture stability.

PubMed

Cunningham, Brian; Jackson, Kelly; Ortega, Gil

2014-04-01

Posterior wall acetabular fractures that involve 10% to 40% of the posterior wall may or may not require an open reduction and internal fixation. Dynamic stress examination of the acetabular fracture under fluoroscopy has been used as an intraoperative method to assess joint stability. The aim of this study was to demonstrate the value of intraoperative ISO computed tomography (CT) examination using the Siemens ISO-C imaging system (Siemens Corp, Malvern, Pennsylvania) in the assessment of posterior wall acetabular fracture stability during stress examination under anesthesia. In 5 posterior wall acetabular fractures, standard fluoroscopic images (including anteroposterior pelvis and Judet radiographs) with dynamic stress examinations were compared with the ISO-C CT imaging system to assess posterior wall fracture stability during stress examination. After review of standard intraoperative fluoroscopic images under dynamic stress examination, all 5 cases appeared to demonstrate posterior wall stability; however, when the intraoperative images from the ISO-C CT imaging system demonstrated that 1 case showed fracture instability of the posterior wall segment during stress examination, open reduction and internal fixation was performed. The use of intraoperative ISO CT imaging has shown an initial improvement in the surgeon's ability to assess the intraoperative stability of posterior wall acetabular fractures during stress examination when compared with standard fluoroscopic images. Copyright 2014, SLACK Incorporated.

Dynamic fracture network around faults: implications for earthquake ruptures, ground motion and energy budget

NASA Astrophysics Data System (ADS)

Okubo, K.; Bhat, H. S.; Rougier, E.; Lei, Z.; Knight, E. E.; Klinger, Y.

2017-12-01

Numerous studies have suggested that spontaneous earthquake ruptures can dynamically induce failure in secondary fracture network, regarded as damage zone around faults. The feedbacks of such fracture network play a crucial role in earthquake rupture, its radiated wave field and the total energy budget. A novel numerical modeling tool based on the combined finite-discrete element method (FDEM), which accounts for the main rupture propagation and nucleation/propagation of secondary cracks, was used to quantify the evolution of the fracture network and evaluate its effects on the main rupture and its associated radiation. The simulations were performed with the FDEM-based software tool, Hybrid Optimization Software Suite (HOSSedu) developed by Los Alamos National Laboratory. We first modeled an earthquake rupture on a planar strike-slip fault surrounded by a brittle medium where secondary cracks can be nucleated/activated by the earthquake rupture. We show that the secondary cracks are dynamically generated dominantly on the extensional side of the fault, mainly behind the rupture front, and it forms an intricate network of fractures in the damage zone. The rupture velocity thereby significantly decreases, by 10 to 20 percent, while the supershear transition length increases in comparison to the one with purely elastic medium. It is also observed that the high-frequency component (10 to 100 Hz) of the near-field ground acceleration is enhanced by the dynamically activated fracture network, consistent with field observations. We then conducted the case study in depth with various sets of initial stress state, and friction properties, to investigate the evolution of damage zone. We show that the width of damage zone decreases in depth, forming "flower-like" structure as the characteristic slip distance in linear slip-weakening law, or the fracture energy on the fault, is kept constant with depth. Finally, we compared the fracture energy on the fault to the energy absorbed by the secondary fracture network to better understand the earthquake energy budget. We conclude that the secondary fracture network plays an important role on the dynamic earthquake rupture, its radiated wave field and the overall energy budget.

Multiphase fluid-solid coupled analysis of shock-bubble-stone interaction in shockwave lithotripsy.

PubMed

Wang, Kevin G

2017-10-01

A novel multiphase fluid-solid-coupled computational framework is applied to investigate the interaction of a kidney stone immersed in liquid with a lithotripsy shock wave (LSW) and a gas bubble near the stone. The main objective is to elucidate the effects of a bubble in the shock path to the elastic and fracture behaviors of the stone. The computational framework couples a finite volume 2-phase computational fluid dynamics solver with a finite element computational solid dynamics solver. The surface of the stone is represented as a dynamic embedded boundary in the computational fluid dynamics solver. The evolution of the bubble surface is captured by solving the level set equation. The interface conditions at the surfaces of the stone and the bubble are enforced through the construction and solution of local fluid-solid and 2-fluid Riemann problems. This computational framework is first verified for 3 example problems including a 1D multimaterial Riemann problem, a 3D shock-stone interaction problem, and a 3D shock-bubble interaction problem. Next, a series of shock-bubble-stone-coupled simulations are presented. This study suggests that the dynamic response of a bubble to LSW varies dramatically depending on its initial size. Bubbles with an initial radius smaller than a threshold collapse within 1 μs after the passage of LSW, whereas larger bubbles do not. For a typical LSW generated by an electrohydraulic lithotripter (p max  = 35.0MPa, p min  =- 10.1MPa), this threshold is approximately 0.12mm. Moreover, this study suggests that a noncollapsing bubble imposes a negative effect on stone fracture as it shields part of the LSW from the stone. On the other hand, a collapsing bubble may promote fracture on the proximal surface of the stone, yet hinder fracture from stone interior. Copyright © 2016 John Wiley & Sons, Ltd.

Dynamic Fracture Properties of Rocks Subjected to Static Pre-load Using Notched Semi-circular Bend Method

NASA Astrophysics Data System (ADS)

Chen, Rong; Li, Kang; Xia, Kaiwen; Lin, Yuliang; Yao, Wei; Lu, Fangyun

2016-10-01

A dynamic load superposed on a static pre-load is a key problem in deep underground rock engineering projects. Based on a modified split Hopkinson pressure bar test system, the notched semi-circular bend (NSCB) method is selected to investigate the fracture initiation toughness of rocks subjected to pre-load. In this study, a two-dimensional ANSYS finite element simulation model is developed to calculate the dimensionless stress intensity factor. Three groups of NSCB specimen are tested under a pre-load of 0, 37 and 74 % of the maximum static load and with the loading rate ranging from 0 to 60 GPa m1/2 s-1. The results show that under a given pre-load, the fracture initiation toughness of rock increases with the loading rate, resembling the typical rate dependence of materials. Furthermore, the dynamic rock fracture toughness decreases with the static pre-load at a given loading rate. The total fracture toughness, defined as the sum of the dynamic fracture toughness and initial stress intensity factor calculated from the pre-load, increases with the pre-load at a given loading rate. An empirical equation is used to represent the effect of loading rate and pre-load force, and the results show that this equation can depict the trend of the experimental data.

Experimental Study of Slabbing and Rockburst Induced by True-Triaxial Unloading and Local Dynamic Disturbance

NASA Astrophysics Data System (ADS)

Du, Kun; Tao, Ming; Li, Xi-bing; Zhou, Jian

2016-09-01

Slabbing/spalling and rockburst are unconventional types of failure of hard rocks under conditions of unloading and various dynamic loads in environments with high and complex initial stresses. In this study, the failure behaviors of different rock types (granite, red sandstone, and cement mortar) were investigated using a novel testing system coupled to true-triaxial static loads and local dynamic disturbances. An acoustic emission system and a high-speed camera were used to record the real-time fracturing processes. The true-triaxial unloading test results indicate that slabbing occurred in the granite and sandstone, whereas the cement mortar underwent shear failure. Under local dynamically disturbed loading, none of the specimens displayed obvious fracturing at low-amplitude local dynamic loading; however, the degree of rock failure increased as the local dynamic loading amplitude increased. The cement mortar displayed no failure during testing, showing a considerable load-carrying capacity after testing. The sandstone underwent a relatively stable fracturing process, whereas violent rockbursts occurred in the granite specimen. The fracturing process does not appear to depend on the direction of local dynamic loading, and the acoustic emission count rate during rock fragmentation shows that similar crack evolution occurred under the two test scenarios (true-triaxial unloading and local dynamically disturbed loading).

Tuning Fractures With Dynamic Data

NASA Astrophysics Data System (ADS)

Yao, Mengbi; Chang, Haibin; Li, Xiang; Zhang, Dongxiao

2018-02-01

Flow in fractured porous media is crucial for production of oil/gas reservoirs and exploitation of geothermal energy. Flow behaviors in such media are mainly dictated by the distribution of fractures. Measuring and inferring the distribution of fractures is subject to large uncertainty, which, in turn, leads to great uncertainty in the prediction of flow behaviors. Inverse modeling with dynamic data may assist to constrain fracture distributions, thus reducing the uncertainty of flow prediction. However, inverse modeling for flow in fractured reservoirs is challenging, owing to the discrete and non-Gaussian distribution of fractures, as well as strong nonlinearity in the relationship between flow responses and model parameters. In this work, building upon a series of recent advances, an inverse modeling approach is proposed to efficiently update the flow model to match the dynamic data while retaining geological realism in the distribution of fractures. In the approach, the Hough-transform method is employed to parameterize non-Gaussian fracture fields with continuous parameter fields, thus rendering desirable properties required by many inverse modeling methods. In addition, a recently developed forward simulation method, the embedded discrete fracture method (EDFM), is utilized to model the fractures. The EDFM maintains computational efficiency while preserving the ability to capture the geometrical details of fractures because the matrix is discretized as structured grid, while the fractures being handled as planes are inserted into the matrix grids. The combination of Hough representation of fractures with the EDFM makes it possible to tune the fractures (through updating their existence, location, orientation, length, and other properties) without requiring either unstructured grids or regridding during updating. Such a treatment is amenable to numerous inverse modeling approaches, such as the iterative inverse modeling method employed in this study, which is capable of dealing with strongly nonlinear problems. A series of numerical case studies with increasing complexity are set up to examine the performance of the proposed approach.

Strain rate effects on fracture behavior of Austempered Ductile Irons

NASA Astrophysics Data System (ADS)

Ruggiero, Andrew; Bonora, Nicola; Gentile, Domenico; Iannitti, Gianluca; Testa, Gabriel; Hörnqvist Colliander, Magnus; Masaggia, Stefano; Vettore, Federico

2017-06-01

Austempered Ductile Irons (ADIs), combining high strength, good ductility and low density, are candidates to be a suitable alternative to high-strength steels. Nevertheless, the concern about a low ductility under dynamic loads often leads designers to exclude cast irons for structural applications. However, results from dynamic tensile tests contradict this perception showing larger failure strain with respect to quasistatic data. The fracture behaviour of ADIs depends on damage mechanisms occurring in the spheroids of graphite, in the matrix and at their interface, with the matrix (ausferrite) consisting of acicular ferrite in carbon-enriched austenite. Here, a detailed microstructural analysis was performed on the ADI 1050-6 deformed under different conditions of strain rates, temperatures, and states of stress. Beside the smooth specimens used for uniaxial tensile tests, round notched bars to evaluate the ductility reduction with increasing stress triaxiality and tophat geometries to evaluate the propensity to shear localization and the associated microstructural alterations were tested. The aim of the work is to link the mechanical and fracture behavior of ADIs to the load condition through the microstructural modifications that occur for the corresponding deformation path.

On the Processing of Spalling Experiments. Part II: Identification of Concrete Fracture Energy in Dynamic Tension

NASA Astrophysics Data System (ADS)

Lukić, Bratislav B.; Saletti, Dominique; Forquin, Pascal

2017-12-01

This paper presents a second part of the study aimed at investigating the fracture behavior of concrete under high strain rate tensile loading. The experimental method together with the identified stress-strain response of three tests conducted on ordinary concrete have been presented in the paper entitled Part I (Forquin and Lukić in Journal of Dynamic Behavior of Materials, 2017. https://doi.org/10.1007/s40870-017-0135-1). In the present paper, Part II, the investigation is extended towards directly determining the specific fracture energy of each observed fracture zone by visualizing the dynamic cracking process with a temporal resolution of 1 µs. Having access to temporal displacement fields of the sample surface, it is possible to identify the fracture opening displacement (FOD) and the fracture opening velocity of any principle (open) and secondary (closed) fracture at each measurement instance, that may or may not lead to complete physical failure of the sample. Finally, the local Stress-FOD curves were obtained for each observed fracture zone, opposed to previous works where indirect measurements were used. The obtained results indicated a much lower specific fracture energy compared to the results often found in the literature. Furthermore, numerical simulations were performed with a damage law to evaluate the validity of the proposed experimental data processing and compare it to the most often used one in the previous works. The results showed that the present method can reliably predict the specific fracture energy needed to open one macro-fracture and suggested that indirect measurement techniques can lead to an overestimate of specific fracture energy due to the stringent assumption of linear elasticity up-to the peak and the inability of having access to the real post-peak change of axial stress.

Early Functional Treatment of Proximal Phalanx Fractures in Children: A Case Series Study.

PubMed

Bohr, Stefan; Mammadli, Toghrul

2018-05-23

The objective of this study was to assess proper indications a nonsurgical treatment regime for pediatric fractures of the proximal phalanx based on principles of early functional treatment. A case series (evidence level 4) of 30 pediatric patients with fractures of the proximal phalanx were treated nonsurgically using protective dynamic splinting techniques and fiberglass casting material. Assessments were performed clinically and by x-ray within 4 to 8 weeks of commencement of treatment. Outcome measures included Disabilities of the Arm, Shoulder, and Hand score questionnaire as well as fingertip palm distance (cm) and dynamic pain interval assessments. All fractures healed without any clinically apparent bony deformities. Disabilities of the Arm, Shoulder, and Hand scores were of 25.17 ± 5.29 (mean ± SD), which indicated good functional results usually within 2 weeks of removal of dynamic splints. Fingertip palm distance measurements at endpoints were of 0.17 ± 0.27 cm (mean ± SD), which indicated an almost free range of finger motion. Absence of pain perception under active finger motion (dynamic pain interval) was noted at 14.10 ± 6.79 days (mean ± SD). Well-established criteria for surgical treatment of phalangeal fractures exist. However, in our experience, a majority of pediatric fractures of the proximal phalanx can be safely treated nonsurgically with dynamic splinting along with shorter intervals of immobilization of the affected fingers and faster restoration of overall hand function compared to surgical treatment.

Biomechanical analysis of fixation of middle third fractures of the clavicle.

PubMed

Drosdowech, Darren S; Manwell, Stuart E E; Ferreira, Louis M; Goel, Danny P; Faber, Kenneth J; Johnson, James A

2011-01-01

This biomechanical study compares four different techniques of fixation of middle third clavicular fractures. Twenty fresh-frozen clavicles were randomized into four groups. Each group used a different fixation device (3.5 Synthes reconstruction plate, 3.5 Synthes limited contact dynamic compression plate, 3.5 Synthes locking compression plate, and 4.5 DePuy Rockwood clavicular pin). All constructs were mechanically tested in bending and torque modes both with and without a simulated inferior cortical defect. Bending load to failure was also conducted. The four groups were compared using an analysis of variance test. The plate constructs were stiffer than the pin during both pure bending and torque loads with or without an inferior cortical defect. Bending load to failure with an inferior cortical defect revealed that the reconstruction plate was weaker compared with the other three groups. The limited contact and locking plates were stiffer than the reconstruction plate but demonstrated statistical significance only with the cortical defect. As hypothesized, the 3.5 limited contact dynamic compression plate and 3.5 locking compression plate demonstrated the greatest resistance to bending and torque loads, especially in the presence of simulated comminution of a middle third clavicular fracture. The reconstruction plate demonstrated lower stiffness and strength values compared with the other plates, especially with a cortical defect, whereas the pin showed poor resistance to bending and torque loads in all modes of testing. This information may help surgeons to choose the most appropriate method of fixation when treating fractures of the middle third of the clavicle.

High Strain Rate Testing of Rocks using a Split-Hopkinson-Pressure Bar

NASA Astrophysics Data System (ADS)

Zwiessler, Ruprecht; Kenkmann, Thomas; Poelchau, Michael; Nau, Siegfried; Hess, Sebastian

2016-04-01

Dynamic mechanical testing of rocks is important to define the onset of rate dependency of brittle failure. The strain rate dependency occurs through the propagation velocity limit (Rayleigh wave speed) of cracks and their reduced ability to coalesce, which, in turn, significantly increases the strength of the rock. We use a newly developed pressurized air driven Split-Hopkinson-Pressure Bar (SHPB), that is specifically designed for the investigation of high strain rate testing of rocks, consisting of several 10 to 50 cm long strikers and bar components of 50 mm in diameter and 2.5 meters in length each. The whole set up, composed of striker, incident- and transmission bar is available in aluminum, titanium and maraging steel to minimize the acoustic impedance contrast, determined by the change of density and speed of sound, to the specific rock of investigation. Dynamic mechanical parameters are obtained in compression as well as in spallation configuration, covering a wide spectrum from intermediate to high strain rates (100-103 s-1). In SHPB experiments [1] one-dimensional longitudinal compressive pulses of diverse shapes and lengths - formed with pulse shapers - are used to generate a variety of loading histories under 1D states of stress in cylindrical rock samples, in order to measure the respective stress-strain response at specific strain rates. Subsequent microstructural analysis of the deformed samples is aimed at quantification fracture orientation, fracture pattern, fracture density, and fracture surface properties as a function of the loading rate. Linking mechanical and microstructural data to natural dynamic deformation processes has relevance for the understanding of earthquakes, landslides, impacts, and has several rock engineering applications. For instance, experiments on dynamic fragmentation help to unravel super-shear rupture events that pervasively pulverize rocks up to several hundred meters from the fault core [2, 3, 4]. The dynamic, strain rate dependent behavior with strongly increasing strength and changing fracturing process has not been consequently considered in modeling of geo-hazards such as earthquakes, rock falls, landslides or even meteorite impacts [5]. Incorporation of dynamic material data therefore will contribute to improvements of forecast models and the understanding of fast geodynamic processes. References [1] Zhang, Q. B. & Zhao, J. (2013). A Review of Dynamic Experimental Techniques and Mechanical Behaviour of Rock Materials. Rock Mech Rock Eng. DOI 10.1007/s00603-013-0463-y [2] Doan, M. L., & Gary, G. (2009). Rock pulverization at high strain rate near the San Andreas fault. Nature Geosci., 2, 709-712. [3] Reches, Z. E., & Dewers, T. A. (2005). Gouge formation by dynamic pulverization during earthquake rupture. Earth Planet. Sci. Lett., 235, 361-374. [4] Fondriest, M., Aretusini, S., Di Toro, G., & Smith, S. A. (2015). Fracturing and rock pulverization along an exhumed seismogenic fault zone in dolostones: The Foiana Fault Zone (Southern Alps, Italy). Tectonophys.654, 56-74. [5] Kenkmann, T., Poelchau, M. H., & Wulf, G. (2014). Structural Geology of impact craters. J. .Struct. Geol., 62, 156-182.

Digital diagnosis and treatment of mandibular condylar fractures based on Extensible Neuro imaging Archive Toolkit (XNAT)

PubMed Central

Ren, Jiayin; He, Mingyun; Huang, Yongqing; Tian, WeiDong; Tang, Wei

2018-01-01

Objectives The treatment of condylar fractures has long been controversial. In this paper, we established a database for accurate measurement, storage, management and analysis of patients’ data, in order to help determine the best treatment plan. Methods First of all, the diagnosis and treatment database was established based on XNAT, including 339 cases of condylar fractures and their related information. Then image segmentation, registration and three-dimensional (3D) measurement were used to measure and analyze the condyle shapes. Statistical analysis was used to analyze the anatomical structure changes of condyle and the surrounding tissues at different stages before and after treatment. The processes of condylar fracture reestablishment at different stages were also dynamically monitored. Finally, based on all these information, the digital diagnosis and treatment plans for condylar fractures were developed. Results For the patients less than 18 years old with no significant dislocation, surgical treatment and conservative treatment were equally effective for intracapsular fracture, and had no significant difference for neck and basal fractures. For patients above 18 years old, there was no significant difference between the two treatment methods for intracapsular fractures; but for condylar neck and basal fractures, surgical treatment was better than conservative treatment. When condylar fracture shift angle was greater than 11 degrees, and mandibular ramus height reduction was greater than 4mm, the patients felt the strongest pain, and their mouths opening was severely restricted. There were 170 surgical cases with condylar fracture shift angel greater than 11 degrees, and 118 of them (69.4%) had good prognosis, 52 of them (30.6%) had complications such as limited mouth opening. There were 173 surgical cases with mandibular ramus height reduction more than 4mm, and 112 of them (64.7%) had good prognosis, 61 of them (35.3%) had complications such as limited mouth opening. Conclusions The establishment of XNAT condylar fracture database is helpful for establishing a digital diagnosis and treatment workflow for mandibular condylar fractures, providing new theoretical foundation and application basis for diagnosis and treatment of condylar fractures. PMID:29432477

Dynamic locked plating for fixation of distal femur fractures using near- cortical over-drilling: Preliminary results of a prospective observational study.

PubMed

Galal, Sherif

2017-01-01

Nonunion after locked plating of distal femur fractures is not uncommon. Authors wanted to assess if "Dynamic" locked plating using near-cortex over-Drilling technique would provide a mechanical environment the promotes callus formation, thereby avoiding non-union encountered when applying locked plates with the conventional method. This study was conducted at an academic Level 1 Trauma Center. This is a prospective study conducted from November 2015 to November 2016. Follow-up was 10 months on average (ranging from 8 to 12 months). The study included 20 patients with 20 fractures (13 males, 7 females). The average patients' age was 41.2 years (18-64 years). According to the Müller AO classification of distal femur fractures (33A-C) there were 15 cases with extra-articular fractures (AO 33A), 5 patients with intra-articular fractures (AO 33C). Dynamic Locked plating using near-cortical over-drilling technique was done for all patients. Two blinded observers assessed callus score on 6-week radiographs using a 4-point ordinal scale. A 2-tailed t -test. Two-way mixed intra-class correlation testing was performed to determine reliability of the callus measurements by the 2 observers. All patients achieved union, time to union was 13.4 weeks on average (range form 8-24 weeks). Delayed union was observed in 2 patients. The average callus score for fractures was 1.8 (SD 0.6). All fractures united in alignment except 1 fracture which united in valgus malalignment, the deformity was appreciated in the postoperative radiographs. No wound related complications, no loss of reduction, no catastrophic implant failure or screw breakage were detected. Dynamic locked plating using near-cortex over-drilling is a simple technique that uses standard locked plates that promotes callus formation when used for fixing distal femur fractures.

Implications of fractured Arctic perennial ice cover on thermodynamic and dynamic sea ice processes

NASA Astrophysics Data System (ADS)

Asplin, Matthew G.; Scharien, Randall; Else, Brent; Howell, Stephen; Barber, David G.; Papakyriakou, Tim; Prinsenberg, Simon

2014-04-01

Decline of the Arctic summer minimum sea ice extent is characterized by large expanses of open water in the Siberian, Laptev, Chukchi, and Beaufort Seas, and introduces large fetch distances in the Arctic Ocean. Long waves can propagate deep into the pack ice, thereby causing flexural swell and failure of the sea ice. This process shifts the floe size diameter distribution smaller, increases floe surface area, and thereby affects sea ice dynamic and thermodynamic processes. The results of Radarsat-2 imagery analysis show that a flexural fracture event which occurred in the Beaufort Sea region on 6 September 2009 affected ˜40,000 km2. Open water fractional area in the area affected initially decreased from 3.7% to 2.7%, but later increased to ˜20% following wind-forced divergence of the ice pack. Energy available for lateral melting was assessed by estimating the change in energy entrainment from longwave and shortwave radiation in the mixed-layer of the ocean following flexural fracture. 11.54 MJ m-2 of additional energy for lateral melting of ice floes was identified in affected areas. The impact of this process in future Arctic sea ice melt seasons was assessed using estimations of earlier occurrences of fracture during the melt season, and is discussed in context with ocean heat fluxes, atmospheric mixing of the ocean mixed layer, and declining sea ice cover. We conclude that this process is an important positive feedback to Arctic sea ice loss, and timing of initiation is critical in how it affects sea ice thermodynamic and dynamic processes.

Snap, Crackle, Pop: Dilational fault breccias record seismic slip below the brittle-plastic transition

NASA Astrophysics Data System (ADS)

Melosh, Ben L.; Rowe, Christie D.; Smit, Louis; Groenewald, Conrad; Lambert, Christopher W.; Macey, Paul

2014-10-01

Off-fault dynamic tensile cracks form behind an earthquake rupture front with distinct orientation and spacing. These cracks explode the wall rock and create breccias, which we hypothesize will preserve a unique fingerprint of dynamic rupture. Identification of these characteristic breccias may enable a new tool for identifying paleoseismic slip surfaces in the rock record. Using previous experimental and theoretical predictions, we develop a field-based model of dynamic dilational breccia formation. Experimental studies find that secondary tensile fracture networks comprise closely spaced fractures at angles of 70-90° from a slip surface, as well as fractures that branch at angles of ∼ 30 ° from a primary mode I fracture. The Pofadder Shear Zone, in Namibia and South Africa, preserves breccias formed in the brittle-ductile transition zone displaying fracture patterns consistent with those described above. Fracture spacing is approximately two orders of magnitude less than predicted by quasi-static models. Breccias are clast-supported, monomict and can display an abrupt transition from fracture network crackle breccia to mosaic breccia textures. Brecciation occurs by the intersection of off-fault dynamic fractures and wall rock fabric; this is in contrast to previous models of fluid pressure gradient-driven failure ;implosion breccias;. This mechanism tends to form many similar sized clasts with particle size distributions that may not display self-similarity; where self-similarity is observed the distributions have relatively low D-values of 1.47 ± 0.37, similar to other studies of dynamic processes. We measure slip distances at dilational breccia stepovers, estimating earthquake magnitudes between Mw 2.8-5.8 and associated rupture lengths of 0.023-3.3 km. The small calculated rupture dimensions, in combination with our geologic observations, suggest that some earthquakes nucleated within the quartz-plastic transitional zone and potentially record deep seismic slip.

Futurepath: The Story of Research and Technology at NASA Lewis Research Center. Structures for Flight Propulsion, ARC Sprayed Monotape, National Aero-Space Plane

NASA Technical Reports Server (NTRS)

1989-01-01

The story of research and technology at NASA Lewis Research Center's Structures Division is presented. The job and designs of the Structures Division needed for flight propulsion is described including structural mechanics, structural dynamics, fatigue, and fracture. The video briefly explains why properties of metals used in structural mechanics need to be tested. Examples of tests and simulations used in structural dynamics (bodies in motion) are briefly described. Destructive and non-destructive fatigue/fracture analysis is also described. The arc sprayed monotape (a composite material) is explained, as are the programs in which monotape plays a roll. Finally, the National Aero-Space Plane (NASP or x-30) is introduced, including the material development and metal matrix as well as how NASP will reduce costs for NASA.

A review on recent contribution of meshfree methods to structure and fracture mechanics applications.

PubMed

Daxini, S D; Prajapati, J M

2014-01-01

Meshfree methods are viewed as next generation computational techniques. With evident limitations of conventional grid based methods, like FEM, in dealing with problems of fracture mechanics, large deformation, and simulation of manufacturing processes, meshfree methods have gained much attention by researchers. A number of meshfree methods have been proposed till now for analyzing complex problems in various fields of engineering. Present work attempts to review recent developments and some earlier applications of well-known meshfree methods like EFG and MLPG to various types of structure mechanics and fracture mechanics applications like bending, buckling, free vibration analysis, sensitivity analysis and topology optimization, single and mixed mode crack problems, fatigue crack growth, and dynamic crack analysis and some typical applications like vibration of cracked structures, thermoelastic crack problems, and failure transition in impact problems. Due to complex nature of meshfree shape functions and evaluation of integrals in domain, meshless methods are computationally expensive as compared to conventional mesh based methods. Some improved versions of original meshfree methods and other techniques suggested by researchers to improve computational efficiency of meshfree methods are also reviewed here.

Seismic Characterizations of Fractures: Dynamic Diagnostics

NASA Astrophysics Data System (ADS)

Pyrak-Nolte, L. J.

2017-12-01

Fracture geometry controls fluid flow in a fracture, affects mechanical stability and influences energy partitioning that affects wave scattering. Our ability to detect and monitor fracture evolution is controlled by the frequency of the signal used to probe a fracture system, i.e. frequency selects the scales. No matter the frequency chosen, some set of discontinuities will be optimal for detection because different wavelengths sample different subsets of fractures. The select subset of fractures is based on the stiffness of the fractures which in turn is linked to fluid flow. A goal is obtaining information from scales outside the optimal detection regime. Fracture geometry trajectories are a potential approach to drive a fracture system across observation scales, i.e. moving systems between effective medium and scattering regimes. Dynamic trajectories (such as perturbing stress, fluid pressure, chemical alteration, etc.) can be used to perturb fracture geometry to enhance scattering or give rise to discrete modes that are intimately related to the micro-structural evolution of a fracture. However, identification of these signal features will require methods for identifying these micro-structural signatures in complicated scattered fields. Acknowledgment: This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Geosciences Research Program under Award Number (DE-FG02-09ER16022).

Flow and fracture behavior of aluminum alloy 6082-T6 at different tensile strain rates and triaxialities.

PubMed

Chen, Xuanzhen; Peng, Yong; Peng, Shan; Yao, Song; Chen, Chao; Xu, Ping

2017-01-01

This study aims to investigate the flow and fracture behavior of aluminum alloy 6082-T6 (AA6082-T6) at different strain rates and triaxialities. Two groups of Charpy impact tests were carried out to further investigate its dynamic impact fracture property. A series of tensile tests and numerical simulations based on finite element analysis (FEA) were performed. Experimental data on smooth specimens under various strain rates ranging from 0.0001~3400 s-1 shows that AA6082-T6 is rather insensitive to strain rates in general. However, clear rate sensitivity was observed in the range of 0.001~1 s-1 while such a characteristic is counteracted by the adiabatic heating of specimens under high strain rates. A Johnson-Cook constitutive model was proposed based on tensile tests at different strain rates. In this study, the average stress triaxiality and equivalent plastic strain at facture obtained from numerical simulations were used for the calibration of J-C fracture model. Both of the J-C constitutive model and fracture model were employed in numerical simulations and the results was compared with experimental results. The calibrated J-C fracture model exhibits higher accuracy than the J-C fracture model obtained by the common method in predicting the fracture behavior of AA6082-T6. Finally, the Scanning Electron Microscope (SEM) of fractured specimens with different initial stress triaxialities were analyzed. The magnified fractographs indicate that high initial stress triaxiality likely results in dimple fracture.

Predicting the dynamic fracture of steel via a non-local strain-energy density failure criterion.

DOT National Transportation Integrated Search

2014-06-01

Predicting the onset of fracture in a material subjected to dynamic loading conditions has typically been heavily mesh-dependent, and often must be specifically calibrated for each geometric design. This can lead to costly models and even : costlier ...

Dynamic fracture toughness of ASME SA508 Class 2a ASME SA533 grade A Class 2 base and heat affected zone material and applicable weld metals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Logsdon, W.A.; Begley, J.A.; Gottshall, C.L.

1978-03-01

The ASME Boiler and Pressure Vessel Code, Section III, Article G-2000, requires that dynamic fracture toughness data be developed for materials with specified minimum yield strengths greater than 50 ksi to provide verification and utilization of the ASME specified minimum reference toughness K/sub IR/ curve. In order to qualify ASME SA508 Class 2a and ASME SA533 Grade A Class 2 pressure vessel steels (minimum yield strengths equal 65 kip/in./sup 2/ and 70 kip/in./sup 2/, respectively) per this requirement, dynamic fracture toughness tests were performed on these materials. All dynamic fracture toughness values of SA508 Class 2a base and HAZ material,more » SA533 Grade A Class 2 base and HAZ material, and applicable weld metals exceeded the ASME specified minimum reference toughness K/sub IR/ curve.« less

Reinforcement of a PMMA resin for interim fixed prostheses with silica nanoparticles.

PubMed

Topouzi, Marianthi; Kontonasaki, Eleana; Bikiaris, Dimitrios; Papadopoulou, Lambrini; Paraskevopoulos, Konstantinos M; Koidis, Petros

2017-05-01

Fractures in long span provisional/interim restorations are a common complication. Adequate fracture toughness is necessary to resist occlusal forces and crack propagation, so these restorations should be constructed with materials of improved mechanical properties. The aim of this study was to investigate the possible reinforcement of neat silica nanoparticles and trietoxyvinylsilane-modified silica nanoparticles in a PMMA resin for fixed interim restorations. Composite PMMA-Silica nanoparticles powders were mixed with PMMA liquid and compact bar shaped specimens were fabricated according to the British standard BS EN ISO 127337:2005. The single-edge notched method was used to evaluate fracture toughness (three-point bending test), while the dynamic thermomechanical properties (Storage Modulus, Loss Modulus, tanδ) of a series of nanocomposites with different amounts of nanoparticles (0.25%, 0.50%, 0.75%, 1% w.t.) were evaluated. Statistical analysis was performed and the statistically significant level was set to p<0.05. The fracture toughness of all experimental composites was remarkably higher compared to control. There was a tendency to decrease of fracture toughness, by increasing the concentration of the filler. No statistically significant differences were detected among the modified/unmodified silica nanoparticles. Dynamic mechanical properties were also affected. By increasing the silica nanoparticles content an increase in Storage Modulus was recorded, while Glass Transition Temperature was shifted at higher temperatures. Under the limitations of this in-vitro study, it can be suggested that both neat silica nanoparticles and trietoxyvinylsilane-modified silica nanoparticles, especially at low concentrations, may enhance the overall performance of fixed interim prostheses, as can effectively increase the fracture toughness, the elastic modulus and the Glass Transition Temperature of PMMA resins used in fixed provisional restorations. Copyright © 2017 Elsevier Ltd. All rights reserved.

Flow Mode Dependent Partitioning Processes of Preferential Flow Dynamics in Unsaturated Fractures - Findings From Analogue Percolation Experiments

NASA Astrophysics Data System (ADS)

Kordilla, J.; Noffz, T.; Dentz, M.; Sauter, M.

2017-12-01

To assess the vulnerability of an aquifer system it is of utmost importance to recognize the high potential for a rapid mass transport offered by ow through unsaturated fracture networks. Numerical models have to reproduce complex effects of gravity-driven flow dynamics to generate accurate predictions of flow and transport. However, the non-linear characteristics of free surface flow dynamics and partitioning behaviour at unsaturated fracture intersections often exceed the capacity of classical volume-effective modelling approaches. Laboratory experiments that manage to isolate single aspects of the mass partitioning process can enhance the understanding of underlying dynamics, which ultimately influence travel time distributions on multiple scales. Our analogue fracture network consists of synthetic cubes with dimensions of 20 x 20 x 20 cm creating simple geometries of a single or a cascade of consecutive horizontal fractures. Gravity-driven free surface flow (droplets; rivulets) is established via a high precision multichannel dispenser at flow rates ranging from 1.5 to 4.5 ml/min. Single-inlet experiments show the influence of variable flow rate, atmospheric pressure and temperature on the stability of flow modes and allow to delineate a droplet and rivulet regime. The transition between these regimes exhibits mixed flow characteristics. In addition, multi-inlet setups with constant total infow rates decrease the variance induced by erratic free-surface flow dynamics. We investigate the impacts of variable aperture widths, horizontal offsets of vertical fracture surfaces, and alternating injection methods for both flow regimes. Normalized fracture inflow rates allow to demonstrate and compare the effects of variable geometric features. Firstly, the fracture filling can be described by plug flow. At later stages it transitions into a Washburn-type flow, which we compare to an analytical solution for the case of rivulet flow. Observations show a considerably higher bypass effciency of droplet flow. This behaviour may not be recovered by plug flow but also transitions into a Washburn stage. Furthermore, we study the effect of additional cubes, i.e. increasing amount of horizontal fractures, on the bulk arrival times and associated importance of flow mode dependent partitioning processes.

Expression of TGF-β in Fractures Fixed by Nitinol Swan-like Memory Compressive Connectors

NASA Astrophysics Data System (ADS)

Li, M.; Zhang, C. C.; Xu, S. G.; Fu, Q. G.

2011-07-01

In this article, the effect of internal fixation of a Nitinol swan-like memory compressive connector (SMC) on the temporal expression of transforming growth factor-β (TGF-β) at fracture sites is evaluated. Specimens were collected from 35 New Zealand rabbits modeled for bilateral humeral fracture fixed with either SMC or stainless dynamic compression plate (DCP). Five rabbits each were killed at day 1, 3, 7, 14, 21, 28, and 56. The local positive staining potency, positive area ratio, and positive index of TGF-β were measured using an immunohistochemistry approach (EnVision) in combination with a computerized image analysis system. TGF-β staining was seen in mesenchymal cells, osteoblasts, chondrocytes, and in the extracellular matrix of fractures fixed in both the SMC and the DCP samples without a significant difference in staining at both the early stages (days 1 and 3) and day 56. A higher TGF-β content was observed in the fractures fixed with SMC when compared to that of DCP from day 7 to 28. As a conclusion, TGF-β is highly expressed in fractures fixed with SMC during chondrogenesis stage and entochondrostosis stage. Finally, the mechanism of how SMC promoting synthesis and secretion of TGF-β in the process of fracture healing has been discussed.

Biomechanical effect of the configuration of screw hole style on locking plate fixation in proximal humerus fracture with a simulated gap: A finite element analysis.

PubMed

Zhang, Ya-Kui; Wei, Hung-Wen; Lin, Kang-Ping; Chen, Wen-Chuan; Tsai, Cheng-Lun; Lin, Kun-Jhih

2016-06-01

Locking plate fixation for proximal humeral fractures is a commonly used device. Recently, plate breakages were continuously reported that the implants all have a mixture of holes allowing placement of both locking and non-locking screws (so-called combi plates). In commercialized proximal humeral plates, there still are two screw hole styles included "locking and dynamic holes separated" and "locking hole only" configurations. It is important to understand the biomechanical effect of different screw hole style on the stress distribution in bone plate. Finite element method was employed to conduct a computational investigation. Three proximal humeral plate models with different screw hole configurations were reconstructed depended upon an identical commercialized implant. A three-dimensional model of a humerus was created using process of thresholding based on the grayscale values of the CT scanning of an intact humerus. A "virtual" subcapital osteotomy was performed. Simulations were performed under an increasing axial load. The von Mises stresses around the screw holes of the plate shaft, the construct stiffness and the directional displacement within the fracture gap were calculated for comparison. The mean value of the peak von Mises stresses around the screw holes in the plate shaft was the highest for combi hole design while it was smallest for the locking and dynamic holes separated design. The stiffness of the plate-bone construct was 15% higher in the locking screw only design (132.6N/mm) compared with the combi design (115.0N/mm), and it was 4% higher than the combi design for the locking and dynamic holes separated design (119.5N/mm). The displacement within the fracture gap was greatest in the combi hole design, whereas it was smallest for the locking hole only design. The computed results provide a possible explanation for the breakages of combi plates revealed in clinical reports. The locking and dynamic holes separated design may be a better configuration to reduce the risk of plate fracture. Copyright © 2016 Elsevier Ltd. All rights reserved.

Geotechnical Site Investigation Using S-waves with Implications for Ground Motion Analysis

NASA Astrophysics Data System (ADS)

Hassan, Bilal; Butt, Stephen D.; Hurich, Charles A.

2017-12-01

Evaluation results of shear wave attenuation-based ground motion restricted by fracture orientation and rheology, from among those of an extended experimental study, are presented herein. The issues of competence of fractured bedrock dynamically disturbed multilaterally are assessed. Disturbance is primarily modelled by Sh and Sv stimulation, given fracture orientation, while subjected to direct fracture stress regime conditions varying in time. Hence, directionalities of polarisation and stress are taken into consideration simultaneously following simple site-specific non-erodetic approach. Comparison of spectral curves and spectral ratio curves of attenuation with respect to variations of direction and stress emphasise the amplification of the `seismic response' in one direction compared to the other, i.e. vertical vs. horizontal, in terms of weighing possibilities of or predicting structural integrity against failure. The composite analyses of multiple spectral curves not only enable determination of the orientation of the fracture set/s in space but also allow inferring the nature of more amplified response perpendicular to the crack surface compared to that of a response parallel to the crack surface.

Dynamic Stabilization of Simple Fractures With Active Plates Delivers Stronger Healing Than Conventional Compression Plating

PubMed Central

Tsai, Stanley; Bliven, Emily K.; von Rechenberg, Brigitte; Kindt, Philipp; Augat, Peter; Henschel, Julia; Fitzpatrick, Daniel C.; Madey, Steven M.

2017-01-01

Objectives: Active plates dynamize a fracture by elastic suspension of screw holes within the plate. We hypothesized that dynamic stabilization with active plates delivers stronger healing relative to standard compression plating. Methods: Twelve sheep were randomized to receive either a standard compression plate (CP) or an active plate (ACTIVE) for stabilization of an anatomically reduced tibial osteotomy. In the CP group, absolute stabilization was pursued by interfragmentary compression with 6 cortical screws. In the ACTIVE group, dynamic stabilization after bony apposition was achieved with 6 elastically suspended locking screws. Fracture healing was analyzed weekly on radiographs. After sacrifice 9 weeks postsurgery, the torsional strength of healed tibiae and contralateral tibiae was measured. Finally, computed tomography was used to assess fracture patterns and healing modes. Results: Healing in both groups included periosteal callus formation. ACTIVE specimens had almost 6 times more callus area by week 9 (P < 0.001) than CP specimens. ACTIVE specimens recovered on average 64% of their native strength by week 9, and were over twice as strong as CP specimens, which recovered 24% of their native strength (P = 0.008). Microcomputed tomography demonstrated that compression plating induced a combination of primary bone healing and gap healing. Active plating consistently stimulated biological bone healing by periosteal callus formation. Conclusions: Compared with compression plating, dynamic stabilization of simple fractures with active plates delivers significantly stronger healing. PMID:27861456

Effect of Unsaturated Flow Modes on Partitioning Dynamics of Gravity-Driven Flow at a Simple Fracture Intersection: Laboratory Study and Three-Dimensional Smoothed Particle Hydrodynamics Simulations

NASA Astrophysics Data System (ADS)

Kordilla, Jannes; Noffz, Torsten; Dentz, Marco; Geyer, Tobias; Tartakovsky, Alexandre M.

2017-11-01

In this work, we study gravity-driven flow of water in the presence of air on a synthetic surface intersected by a horizontal fracture and investigate the importance of droplet and rivulet flow modes on the partitioning behavior at the fracture intersection. We present laboratory experiments, three-dimensional smoothed particle hydrodynamics (SPH) simulations using a heavily parallelized code, and a theoretical analysis. The flow-rate-dependent mode switching from droplets to rivulets is observed in experiments and reproduced by the SPH model, and the transition ranges agree in SPH simulations and laboratory experiments. We show that flow modes heavily influence the "bypass" behavior of water flowing along a fracture junction. Flows favoring the formation of droplets exhibit a much stronger bypass capacity compared to rivulet flows, where nearly the whole fluid mass is initially stored within the horizontal fracture. The effect of fluid buffering within the horizontal fracture is presented in terms of dimensionless fracture inflow so that characteristic scaling regimes can be recovered. For both cases (rivulets and droplets), the flow within the horizontal fracture transitions into a Washburn regime until a critical threshold is reached and the bypass efficiency increases. For rivulet flows, the initial filling of the horizontal fracture is described by classical plug flow. Meanwhile, for droplet flows, a size-dependent partitioning behavior is observed, and the filling of the fracture takes longer. For the case of rivulet flow, we provide an analytical solution that demonstrates the existence of classical Washburn flow within the horizontal fracture.

Molecular-dynamic study of the influence of temperature on the process of metallic nanocrystals fracture

NASA Astrophysics Data System (ADS)

Demianenko, A. M.; Golovnev, I. F.; Golovneva, E. I.

2017-10-01

The behavior of the fracture processes of a metal nanostructure under deformation in the temperature range 0-550 K was investigated by the molecular dynamics method. An ideal copper crystal was used as a sample in the form of a rectangular parallelepiped with the number of crystalline cells nx = 50, ny = nz = 5 along the corresponding axes. The deformation was carried out by uniaxial stretching of the sample between two clamps (movable and fixed) with a constant speed. The stretching rate varied from 50 to 500 m/s. To describe the interatomic interaction, the Voter many-body EAM potential was used. The effect of temperature on macro characteristics of fracture (the fracture place, the number of fragments formed, the stress on the clamps), and also on the kinetic characteristics (fracture rate, time of formation of maximum stress values on the clamps, mass transfer phenomena and formation of the fracture neck) were revealed.

Attempting to bridge the gap between laboratory and seismic estimates of fracture energy

USGS Publications Warehouse

McGarr, A.; Fletcher, Joe B.; Beeler, N.M.

2004-01-01

To investigate the behavior of the fracture energy associated with expanding the rupture zone of an earthquake, we have used the results of a large-scale, biaxial stick-slip friction experiment to set the parameters of an equivalent dynamic rupture model. This model is determined by matching the fault slip, the static stress drop and the apparent stress. After confirming that the fracture energy associated with this model earthquake is in reasonable agreement with corresponding laboratory values, we can use it to determine fracture energies for earthquakes as functions of stress drop, rupture velocity and fault slip. If we take account of the state of stress at seismogenic depths, the model extrapolation to larger fault slips yields fracture energies that agree with independent estimates by others based on dynamic rupture models for large earthquakes. For fixed stress drop and rupture speed, the fracture energy scales linearly with fault slip.

Dynamic Mechanical Properties and Fracture Surface Morphologies of Core-Shell Rubber (CSR) Toughened Epoxy at Liquid Nitrogen (Ln2) Temperatures

NASA Technical Reports Server (NTRS)

Wang, J.; Magee, D.; Schneider, J. A.

2009-01-01

The dynamic mechanical properties and fracture surface morphologies were evaluated for a commercial epoxy resin toughened with two types of core-shell rubber (CSR) toughening agents (Kane Ace(Registered TradeMark) MX130 and MX960). The impact resistance (R) was evaluated by the resulting breaking energy measured in Charpy impact tests conducted on an instrumented drop tower. The resulting fracture surface morphologies were examined using Scanning Electron Microscopy (SEM). Fractographic observations of the CSR toughened epoxy tested at ambient temperature, showed a fracture as characterized by slender dendrite textures with large voids. The increasing number of dendrites and decreasing size of scale-like texture with more CSR particles corresponded with increased R. As the temperature decreased to Liquid Nitrogen (LN 2), the fracture surfaces showed a fracture characterized by a rough, torn texture containing many river markings and deep furrows.

The corrosion fatigue fractography of Ti-24Al-11Nb

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Y.; Wang, Y.B.; Chu, W.Y.

1994-03-01

Many researchers have studied the fracture behaviors and fractography of the Ti-24Al-11Nb alloy. While hydrogen induced delayed fracture could occur in this titanium aluminide in hydrogen gas at temperatures above 300[degree]C, there was no obvious difference in fractography of the alloy in hydrogen or air. The fractography of stress corrosion cracking in a solution was also similar to that of overloaded fracture in air. The recent work showed that hydrogen induced delayed fracture for a notched sample could occur during dynamic cathodic charging at the temperature. There were a lot of small dimples on the fracture surface near the notchmore » tip when K[sub I] neared the threshold k[sub IH]. This differed from that of an overloaded fracture. The fractography of corrosion fatigue in methanol or during dynamic charging for the Ti-24Al-11Nb alloy was studied in this paper.« less

A revisit to high-rate mode-II fracture characterization of composites with Kolsky bar techniques.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, Wei-Yang; Song, Bo; Jin, Huiqing

2010-03-01

Nowadays composite materials have been extensively utilized in many military and industrial applications. For example, the newest Boeing 787 uses 50% composite (mostly carbon fiber reinforced plastic) in production. However, the weak delamination strength of fiber reinforced composites, when subjected to external impact such as ballistic impact, has been always potential serious threats to the safety of passengers. Dynamic fracture toughness is a critical indicator of the performance from delamination in such impact events. Quasi-static experimental techniques for fracture toughness have been well developed. For example, end notched flexure (ENF) technique, which is illustrated in Fig. 1, has become amore » typical method to determined mode-II fracture toughness for composites under quasi-static loading conditions. However, dynamic fracture characterization of composites has been challenging. This has resulted in conflictive and confusing conclusions in regard to strain rate effects on fracture toughness of composites.« less

Imaging hydraulic fractures at Median Tectonic Line, Japan using multiply generated and scattered tube waves in a shallow VSP experiment

NASA Astrophysics Data System (ADS)

Minato, Shohei; Ghose, Ranajit; Tsuji, Takeshi; Ikeda, Michiharu; Onishi, Kozo

2016-04-01

Tube waves are low frequency guided waves that propagate along a fluid-filled borehole. The analysis of tube waves is a promising approach to image and characterize hydraulic fractures intersecting a borehole. It exploits tube waves generated by an external seismic wavefield which compresses fractures and injects fluid into the borehole. It also utilizes the attenuation of tube waves due to fluid exchange between the fracture and the borehole, which creates scattered waves (reflection and transmission). Conventional approaches consider tube waves due to a single fracture. However, when the spacing between multiple fractures is short relative to the wavelength of the tube waves, the generated and scattered tube waves interfere with each other, making it difficult to isolate the effect of a single fracture. The analysis of closely spaced fractures is important in highly fractured areas, such as a fault zone. In this study, we explore the possibility of prediction and utilization of generated and scattered tube waves due to multiple fractures. We derive a new integral equation of the full tube wavefield using 1D wavefield representation theory incorporating nonwelded interfaces. We adapt the recent developments in modeling tube wave generation/scattering at a fracture. In these models, a fracture is represented as a parallel wall or a thin poloelastic layer. This allowed us to consider the effects of a dynamic fracture aperture with fracture compliances and the permeability. The representation also leads to a new imaging method for the hydraulic fractures, using multiply-generated and scattered tube waves. This is achieved by applying an inverse operator to the observed tube waves, which focuses the tube waves to the depth where they are generated and/or scattered. The inverse operator is constructed by a tube wave Green's function with a known propagation velocity. The Median Tectonic Line (MTL) is the most significant fault in Japan, extending NE-SW for over 1000 km across the Japanese Islands. We observed multiple tube waves in a P-wave VSP experiment in a 250 m deep, vertical borehole located on the MTL at Shikoku, Japan. The borehole televiewer and the core studies show that below 40 m depth, the Sambagawa metamorphic rocks contain highly fractured zones which consist of more than 100 open fractures and more than 30 cataclasites. We predict the full tube wavefield using the values of fracture depth and thickness known from the borehole televiewer. We model the open fractures as parallel-wall fractures and the cataclasites as thin poroelastic layers. Furthermore, we estimate the depth of the hydraulic fractures by applying the inverse operator. The results show that the tube waves could be generated and scattered at these permeable structures. Our preliminary results also indicate the possibility that the effect of the open fractures is more dominant in the generation and scattering of tube waves than that of the cataclasites in this field. The formulation and the results presented in this study and the following discussion will be useful in analysis of tube waves in highly fractured zones, in order to localize and characterize hydraulic fractures.

Method for detecting moment connection fracture using high-frequency transients in recorded accelerations

USGS Publications Warehouse

Rodgers, J.E.; Elebi, M.

2011-01-01

The 1994 Northridge earthquake caused brittle fractures in steel moment frame building connections, despite causing little visible building damage in most cases. Future strong earthquakes are likely to cause similar damage to the many un-retrofitted pre-Northridge buildings in the western US and elsewhere. Without obvious permanent building deformation, costly intrusive inspections are currently the only way to determine if major fracture damage that compromises building safety has occurred. Building instrumentation has the potential to provide engineers and owners with timely information on fracture occurrence. Structural dynamics theory predicts and scale model experiments have demonstrated that sudden, large changes in structure properties caused by moment connection fractures will cause transient dynamic response. A method is proposed for detecting the building-wide level of connection fracture damage, based on observing high-frequency, fracture-induced transient dynamic responses in strong motion accelerograms. High-frequency transients are short (<1 s), sudden-onset waveforms with frequency content above 25 Hz that are visually apparent in recorded accelerations. Strong motion data and damage information from intrusive inspections collected from 24 sparsely instrumented buildings following the 1994 Northridge earthquake are used to evaluate the proposed method. The method's overall success rate for this data set is 67%, but this rate varies significantly with damage level. The method performs reasonably well in detecting significant fracture damage and in identifying cases with no damage, but fails in cases with few fractures. Combining the method with other damage indicators and removing records with excessive noise improves the ability to detect the level of damage. ?? 2010 Elsevier B.V. All rights reserved.

Valgus osteotomy and repositioning and fixation with a dynamic hip screw and a 135º single-angled barrel plate for un-united and neglected femoral neck fractures.

PubMed

Gupta, Sameer; Kukreja, Sunil; Singh, Vivek

2014-04-01

To review the outcome of 60 patients who underwent valgus subtrochanteric osteotomy and its repositioning for un-united and neglected femoral neck fractures. 60 patients (mean age, 35 years) underwent valgus subtrochanteric osteotomy and repositioning of the osteotomy and fixation with a dynamic hip screw and a 135° single-angled barrel plate for closed un-united femoral neck fractures after failed internal fixation (n=27) or neglected (>3 weeks) fractures (n=33). The most common fracture type was transcervical (n=48), followed by subcapital (n=6) and basal (n=6). All patients had displaced femoral neck fractures (Garden types 3 and 4). According to the Pauwel angle, 45 fractures were type 2 (30º-70º) and 15 were type 3 (>70º). Patients were followed up for a mean of 3.5 (range, 2-7.5) years. The mean Pauwel angle of the fracture was corrected from 65° (range, 50°-89°) to 26° (range, 25°-28°). Bone union was achieved in 56 patients after a mean of 3.9 (range, 3-5.5) months. The mean Harris hip score improved from 65 to 87.5. Outcome was excellent in 30 patients, good in 24, and poor in 6. Four of the patients developed avascular necrosis; 2 of whom nonetheless achieved a good outcome. Valgus osteotomy and repositioning and fixation with a dynamic hip screw and a 135° single-angled barrel plate was effective treatment for un-united and neglected femoral neck fractures.

The Second International Piping Integrity Research Group (IPIRG-2) program. Final report, October 1991--April 1996

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hopper, A.; Wilowski, G.; Scott, P.

1997-03-01

The IPIRG-2 program was an international group program managed by the US NRC and funded by organizations from 15 nations. The emphasis of the IPIRG-2 program was the development of data to verify fracture analyses for cracked pipes and fittings subjected to dynamic/cyclic load histories typical of seismic events. The scope included: (1) the study of more complex dynamic/cyclic load histories, i.e., multi-frequency, variable amplitude, simulated seismic excitations, than those considered in the IPIRG-1 program, (2) crack sizes more typical of those considered in Leak-Before-Break (LBB) and in-service flaw evaluations, (3) through-wall-cracked pipe experiments which can be used to validatemore » LBB-type fracture analyses, (4) cracks in and around pipe fittings, such as elbows, and (5) laboratory specimen and separate effect pipe experiments to provide better insight into the effects of dynamic and cyclic load histories. Also undertaken were an uncertainty analysis to identify the issues most important for LBB or in-service flaw evaluations, updating computer codes and databases, the development and conduct of a series of round-robin analyses, and analyst`s group meetings to provide a forum for nuclear piping experts from around the world to exchange information on the subject of pipe fracture technology. 17 refs., 104 figs., 41 tabs.« less

Dynamic characterisation of the specific surface area for fracture networks

NASA Astrophysics Data System (ADS)

Cvetkovic, V.

2017-12-01

One important application of chemical transport is geological disposal of high-level nuclear waste for which crystalline rock is a prime candidate for instance in Scandinavia. Interconnected heterogeneous fractures of sparsely fractured rock such as granite, act as conduits for transport of dissolved tracers. Fluid flow is known to be highly channelized in such rocks. Channels imply narrow flow paths, adjacent to essentially stagnant water in the fracture and/or the rock matrix. Tracers are transported along channelised flow paths and retained by minerals and/or stagnant water, depending on their sorption properties; this mechanism is critical for rocks to act as a barrier and ultimately provide safety for a geological repository. The sorbing tracers are retained by diffusion and sorption on mineral surfaces, whereas non-sorbing tracers can be retained only by diffusion into stagnant water of fractures. The retention and transport properties of a sparsely fractured rock will primarily depend on the specific surface area (SSA) of the fracture network which is determined by the heterogeneous structure and flow. The main challenge when characterising SSA on the field-scale is its dependence on the flow dynamics. We first define SSA as a physical quantity and clarify its importance for chemical transport. A methodology for dynamic characterisation of SSA in fracture networks is proposed that relies on three sets of data: i) Flow rate data as obtained by a flow logging procedure; ii) transmissivity data as obtained by pumping tests; iii) fracture network data as obtained from outcrop and geophysical observations. The proposed methodology utilises these data directly as well as indirectly through flow and particle tracking simulations in three-dimensional discrete fracture networks. The methodology is exemplified using specific data from the Swedish site Laxemar. The potential impact of uncertainties is of particular significance and is illustrated for radionuclide attenuation. Effects of internal fracture heterogeneity vs fracture network heterogeneity, and of rock deformation, on the statistical properties of SSA are briefly discussed.

An analytical model for pressure of volume fractured tight oil reservoir with horizontal well

NASA Astrophysics Data System (ADS)

Feng, Qihong; Dou, Kaiwen; Zhang, Xianmin; Xing, Xiangdong; Xia, Tian

2017-05-01

The property of tight oil reservoir is worse than common reservoir that we usually seen before, the porosity and permeability is low, the diffusion is very complex. Therefore, the ordinary depletion method is useless here. The volume fracture breaks through the conventional EOR mechanism, which set the target by amplifying the contact area of fracture and reservoir so as to improving the production of every single well. In order to forecast the production effectively, we use the traditional dual-porosity model, build an analytical model for production of volume fractured tight oil reservoir with horizontal well, and get the analytical solution in Laplace domain. Then we construct the log-log plot of dimensionless pressure and time by stiffest conversion. After that, we discuss the influential factors of pressure. Several factors like cross flow, skin factors and threshold pressure gradient was analyzed in the article. This model provides a useful method for tight oil production forecast and it has certain guiding significance for the production capacity prediction and dynamic analysis.

Laboratory experimental investigation of heat transport in fractured media

NASA Astrophysics Data System (ADS)

Cherubini, Claudia; Pastore, Nicola; Giasi, Concetta I.; Allegretti, Nicoletta Maria

2017-01-01

Low enthalpy geothermal energy is a renewable resource that is still underexploited nowadays in relation to its potential for development in society worldwide. Most of its applications have already been investigated, such as heating and cooling of private and public buildings, road defrosting, cooling of industrial processes, food drying systems or desalination. Geothermal power development is a long, risky and expensive process. It basically consists of successive development stages aimed at locating the resources (exploration), confirming the power generating capacity of the reservoir (confirmation) and building the power plant and associated structures (site development). Different factors intervene in influencing the length, difficulty and materials required for these phases, thereby affecting their cost. One of the major limitations related to the installation of low enthalpy geothermal power plants regards the initial development steps that are risky and the upfront capital costs that are huge. Most of the total cost of geothermal power is related to the reimbursement of invested capital and associated returns. In order to increase the optimal efficiency of installations which use groundwater as a geothermal resource, flow and heat transport dynamics in aquifers need to be well characterized. Especially in fractured rock aquifers these processes represent critical elements that are not well known. Therefore there is a tendency to oversize geothermal plants. In the literature there are very few studies on heat transport, especially on fractured media. This study is aimed at deepening the understanding of this topic through heat transport experiments in fractured networks and their interpretation. Heat transfer tests have been carried out on the experimental apparatus previously employed to perform flow and tracer transport experiments, which has been modified in order to analyze heat transport dynamics in a network of fractures. In order to model the obtained thermal breakthrough curves, the Explicit Network Model (ENM) has been used, which is based on an adaptation of Tang's solution for the transport of the solutes in a semi-infinite single fracture embedded in a porous matrix. Parameter estimation, time moment analysis, tailing character and other dimensionless parameters have permitted a better understanding of the dynamics of heat transport and the efficiency of heat exchange between the fractures and the matrix. The results have been compared with the previous experimental studies on solute transport.

Fractography applied to investigations of cores, outcrops, and fractured reservoirs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kulander, B.

1995-11-01

Fractography focuses investigations on the topography of fracture surfaces. This topography is composed of fractographic features produced by changing stress magnitudes and directions along the advancing crack tip. Fractographic features commonly useful in core and outcrop analysis include the origin, twist hackle, inclusion hackle, and rib marks. These structures develop during brittle failure by Mode I loading at the crack tip and act together to form a hackle plume. Fractographic components throughout the plume record the dynamic history of fracture development. Components show, to the limit of visual scale, the principal stress directions, as well as relative stress magnitudes andmore » propagation velocities, that existed at the advancing fracture front. This information contributes to more meaningful conclusions in fracture investigations. In core studies, fractography aids identification of induced and natural fractures. Induced fractures and fractographic features show distinct geometry with that of the core and reflect the effects of the core boundary, in-situ stresses, drilling stresses, and rock anisotropies. Certain drilling- and coring-induced fractures possess orientations and fractographic features that suggest the direction of minimum in-situ stress and that this direction may change abruptly within the drilled volume of rock. Cored natural fractures generally originated away from the bit and possess fractographic features that bear no geometerical relationship to core parameters. Abrupt changes of natural fracture strike and development of twist hackle suggest locally complex paleostress distributions. A combined knowledge of in-situ stress and natural fracture trends is useful in predicting reservoir permeability. In outcrop, fractographic features, including abutting relationships between joints, more readily depict order of development, intrastratum distribution of fracturing stress, and size for joints in any set.« less

Dynamic fuzzy modeling of storm water infiltration in urban fractured aquifers

USGS Publications Warehouse

Hong, Y.-S.; Rosen, Michael R.; Reeves, R.R.

2002-01-01

In an urban fractured-rock aquifer in the Mt. Eden area of Auckland, New Zealand, disposal of storm water is via "soakholes" drilled directly into the top of the fractured basalt rock. The dynamic response of the groundwater level due to the storm water infiltration shows characteristics of a strongly time-varying system. A dynamic fuzzy modeling approach, which is based on multiple local models that are weighted using fuzzy membership functions, has been developed to identify and predict groundwater level fluctuations caused by storm water infiltration. The dynamic fuzzy model is initialized by the fuzzy clustering algorithm and optimized by the gradient-descent algorithm in order to effectively derive the multiple local models-each of which is associated with a locally valid model that represents the groundwater level state as a response to different intensities of rainfall events. The results have shown that even if the number of fuzzy local models derived is small, the fuzzy modeling approach developed provides good prediction results despite the highly time-varying nature of this urban fractured-rock aquifer system. Further, it allows interpretable representations of the dynamic behavior of the groundwater system due to storm water infiltration.

Finite Element Analysis of Aluminum Honeycombs Subjected to Dynamic Indentation and Compression Loads

PubMed Central

Ashab, A.S.M. Ayman; Ruan, Dong; Lu, Guoxing; Bhuiyan, Arafat A.

2016-01-01

The mechanical behavior of aluminum hexagonal honeycombs subjected to out-of-plane dynamic indentation and compression loads has been investigated numerically using ANSYS/LS-DYNA in this paper. The finite element (FE) models have been verified by previous experimental results in terms of deformation pattern, stress-strain curve, and energy dissipation. The verified FE models have then been used in comprehensive numerical analysis of different aluminum honeycombs. Plateau stress, σpl, and dissipated energy (EI for indentation and EC for compression) have been calculated at different strain rates ranging from 102 to 104 s−1. The effects of strain rate and t/l ratio on the plateau stress, dissipated energy, and tearing energy have been discussed. An empirical formula is proposed to describe the relationship between the tearing energy per unit fracture area, relative density, and strain rate for honeycombs. Moreover, it has been found that a generic formula can be used to describe the relationship between tearing energy per unit fracture area and relative density for both aluminum honeycombs and foams. PMID:28773288

Camera-tracking gaming control device for evaluation of active wrist flexion and extension.

PubMed

Shefer Eini, Dalit; Ratzon, Navah Z; Rizzo, Albert A; Yeh, Shih-Ching; Lange, Belinda; Yaffe, Batia; Daich, Alexander; Weiss, Patrice L; Kizony, Rachel

Cross sectional. Measuring wrist range of motion (ROM) is an essential procedure in hand therapy clinics. To test the reliability and validity of a dynamic ROM assessment, the Camera Wrist Tracker (CWT). Wrist flexion and extension ROM of 15 patients with distal radius fractures and 15 matched controls were assessed with the CWT and with a universal goniometer. One-way model intraclass correlation coefficient analysis indicated high test-retest reliability for extension (ICC = 0.92) and moderate reliability for flexion (ICC = 0.49). Standard error for extension was 2.45° and for flexion was 4.07°. Repeated-measures analysis revealed a significant main effect for group; ROM was greater in the control group (F[1, 28] = 47.35; P < .001). The concurrent validity of the CWT was partially supported. The results indicate that the CWT may provide highly reliable scores for dynamic wrist extension ROM, and moderately reliable scores for flexion, in people recovering from a distal radius fracture. N/A. Copyright © 2016 Hanley & Belfus. Published by Elsevier Inc. All rights reserved.

Relationships of bone characteristics in MYO9B deficient femurs.

PubMed

Kim, Do-Gyoon; Jeong, Yong-Hoon; McMichael, Brooke K; Bähler, Martin; Bodnyk, Kyle; Sedlar, Ryan; Lee, Beth S

2018-08-01

The objective of this study was to examine relationships among a variety of bone characteristics, including volumetric, mineral density, geometric, dynamic mechanical analysis, and static fracture mechanical properties. As MYO9B is an unconventional myosin in bone cells responsible for normal skeletal growth, bone characteristics of wild-type (WT), heterozygous (HET), and MYO9B knockout (KO) mice groups were compared as an animal model to express different bone quantity and quality. Forty-five sex-matched 12-week-old mice were used in this study. After euthanization, femurs were isolated and scanned using microcomputed tomography (micro-CT) to assess bone volumetric, tissue mineral density (TMD), and geometric parameters. Then, a non-destructive dynamic mechanical analysis (DMA) was performed by applying oscillatory bending displacement on the femur. Finally, the same femur was subject to static fracture testing. KO group had significantly lower length, bone mineral density (BMD), bone mass and volume, dynamic and static stiffness, and strength than WT and HET groups (p < 0.019). On the other hand, TMD parameters of KO group were comparable with those of WT group. HET group showed volumetric, geometric, and mechanical properties similar to WT group, but had lower TMD (p < 0.014). Non-destructive micro-CT and DMA parameters had significant positive correlations with strength (p < 0.015) without combined effect of groups and sex on the correlations (p > 0.077). This comprehensive characterization provides a better understanding of interactive behavior between the tissue- and organ-level of the same femur. The current findings elucidate that MYO9B is responsible for controlling bone volume to determine the growth rate and fracture risk of bone. Copyright © 2018 Elsevier Ltd. All rights reserved.

Finite-element analysis of dynamic fracture

NASA Technical Reports Server (NTRS)

Aberson, J. A.; Anderson, J. M.; King, W. W.

1976-01-01

Applications of the finite element method to the two dimensional elastodynamics of cracked structures are presented. Stress intensity factors are computed for two problems involving stationary cracks. The first serves as a vehicle for discussing lumped-mass and consistent-mass characterizations of inertia. In the second problem, the behavior of a photoelastic dynamic tear test specimen is determined for the time prior to crack propagation. Some results of a finite element simulation of rapid crack propagation in an infinite body are discussed.

Dynamic fatigue of a lithia-alumina-silica glass-ceramic

NASA Technical Reports Server (NTRS)

Tucker, Dennis S.

1990-01-01

A dynamic fatigue study was performed on a Li2O-Al2O3-SiO2 glass-ceramic in order to assess its susceptibility to delayed failure. Fracture mechanics techniques were used to analyze the results for the purpose of making lifetime predictions for optical elements made from this material. The material has reasonably good resistance (N = 20) to stress corrosion in ambient conditions. Analysis also indicated the elements should survive applied stresses incurred during grinding and polishing operations.

Numerical analysis of projectile impact in woven texile structures

NASA Technical Reports Server (NTRS)

Roylance, D.

1977-01-01

Computer codes were developed for simulating the dynamic fracture and viscoelastic constitutive response due to stress wave interaction and reflections caused by ballistic impact on woven textiles. The method, which was developed for use in the design and analysis of protection devices for personnel armor, has potential for use in studies of rotor blade burst containment at high velocity. Alterations in coding required for burst containment problems are discussed.

Anomaly in the dynamic strength of austenitic stainless steel 12Cr19Ni10Ti under shock wave loading

NASA Astrophysics Data System (ADS)

Garkushin, G. V.; Kanel, G. I.; Razorenov, S. V.; Savinykh, A. S.

2017-07-01

Measurement results for the shock wave compression profiles of 12Cr19Ni10Ti steel and its dynamic strength in the strain rate range 105-106 s-1 are presented. The protracted viscous character of the spall fracture is revealed. With the previously obtained data taken into account, the measurement results are described by a polynomial relation, which can be used to construct the fracture kinetics. On the lower boundary of the range, the resistance to spall fracture is close to the value of the true strength of the material under standard low-rate strain conditions; on the upper boundary, the spall strength is more than twice greater than this quantity. An increase in the temperature results in a decrease in both the dynamic limit of elasticity and the spall fracture strength of steel. The most interesting result is the anomaly in the dependence of the spall fracture strength on the duration of the shock wave compression pulse, which is related to the formation of deformation martensite near the growing discontinuities.

Effect of Intracoronal Depth of Teeth Restored with Endocrowns on Fracture Resistance: In Vitro and 3-dimensional Finite Element Analysis.

PubMed

Dartora, Nereu Roque; de Conto Ferreira, Michele Bertoluzi; Moris, Izabela Cristina Maurício; Brazão, Elisabeth Helena; Spazin, Aloísio Oro; Sousa-Neto, Manoel Damião; Silva-Sousa, Yara Terezinha; Gomes, Erica Alves

2018-07-01

Endodontically treated teeth have an increased risk of biomechanical failure because of significant loss of tooth structure. The biomechanical behavior of endodontically treated teeth restored was evaluated using different extensions of endocrowns inside the pulp chamber by in vitro and 3-dimensional finite element analysis (FEA). Thirty mandibular human molars were endodontically treated. Standardized endocrown preparations were performed, and the teeth were randomly divided into 3 groups (n = 10) according to different endocrown extensions inside the pulp chamber: G-5 mm, a 5-mm extension; G-3 mm, a 3-mm extension; and G-1 mm, a 1-mm extension. After adhesive cementation, all specimens were subjected to thermocycling and dynamic loading. The survival specimens were subjected to fracture resistance testing at a crosshead speed of 1 mm/min in a universal testing machine. All fractured specimens were subjected to fractography. Data were analyzed by 1-way analysis of variance and the Tukey post hoc test (P < .05). Stress distribution patterns in each group were analyzed using FEA. Qualitative analyses were performed according to the von Mises criterion. After dynamic loading, a survival rate of 100% was observed in all groups. For static loading, statistically significant differences among the groups were observed (P < .05) (G-5 mm = 2008.61 N, G-3 mm = 1795.41 N, and G-1 mm = 1268.12 N). Fractography showed a higher frequency of compression curls for G-5 mm and G-3 mm than for G-1 mm. FEA explained the results of fracture strength testing and fractography. Greater extension of endocrowns inside the pulp chamber provided better mechanical performance. Copyright © 2018 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

Flow and fracture behavior of aluminum alloy 6082-T6 at different tensile strain rates and triaxialities

PubMed Central

Chen, Xuanzhen; Peng, Shan; Yao, Song; Chen, Chao; Xu, Ping

2017-01-01

This study aims to investigate the flow and fracture behavior of aluminum alloy 6082-T6 (AA6082-T6) at different strain rates and triaxialities. Two groups of Charpy impact tests were carried out to further investigate its dynamic impact fracture property. A series of tensile tests and numerical simulations based on finite element analysis (FEA) were performed. Experimental data on smooth specimens under various strain rates ranging from 0.0001~3400 s-1 shows that AA6082-T6 is rather insensitive to strain rates in general. However, clear rate sensitivity was observed in the range of 0.001~1 s-1 while such a characteristic is counteracted by the adiabatic heating of specimens under high strain rates. A Johnson-Cook constitutive model was proposed based on tensile tests at different strain rates. In this study, the average stress triaxiality and equivalent plastic strain at facture obtained from numerical simulations were used for the calibration of J-C fracture model. Both of the J-C constitutive model and fracture model were employed in numerical simulations and the results was compared with experimental results. The calibrated J-C fracture model exhibits higher accuracy than the J-C fracture model obtained by the common method in predicting the fracture behavior of AA6082-T6. Finally, the Scanning Electron Microscope (SEM) of fractured specimens with different initial stress triaxialities were analyzed. The magnified fractographs indicate that high initial stress triaxiality likely results in dimple fracture. PMID:28759617

A comparison of two reciprocating instruments using bending stress and cyclic fatigue tests.

PubMed

Scelza, Pantaleo; Harry, Davidowicz; Silva, Licinio Esmeraldo da; Barbosa, Igor Bastos; Scelza, Miriam Zaccaro

2015-01-01

The aim of this study was to comparatively evaluate the bending resistance at 45º, the static and dynamic cyclic fatigue life, and the fracture type of the WaveOne (Dentsply Maillefer, Ballaigues, Switzerland) 25-08 and Reciproc (VDW, Munich, Germany) 25-08 instruments. A total of 60 nickel-titanium (NiTi) instruments (30 Reciproc and 30 WaveOne) from three different lots, each of which was 25 mm in length, were tested. The bending resistance was evaluated through the results of a cantilever-bending test conducted using a universal testing machine. Static and dynamic cyclic fatigue testing was conducted using a custom-made device. For the static and dynamic tests, a cast Ni-Cr-Mo-Ti alloy metal block with an artificial canal measuring 1.77 mm in diameter and 20.00 mm in total length was used. A scanning electron microscope was used to determine the type of fracture. Statistical analyses were performed on the results. The WaveOne instrument was less flexible than the Reciproc (p < 0.05). The Reciproc instrument showed better resistance in the static and dynamic cyclic fatigue tests (p < 0.05). The transverse cross-section and geometry of the instruments were important factors in their resistance to bending and cyclic fracture. Both of the instruments showed ductile-type fracture characteristics. It can be concluded that the Reciproc 25-08 instrument was more resistant to static and dynamic cyclic fatigue than the WaveOne 25-08 instrument, while the WaveOne 25-08 instrument was less flexible. Bending and resistance to cyclic fracture were influenced by the instruments' geometries and transverse cross-sections. Both of the instruments showed ductile-type fracture characteristics.

Condylar buttress plate versus fixed angle condylar blade plate versus dynamic condylar screw for supracondylar intra-articular distal femoral fractures.

PubMed

Petsatodis, George; Chatzisymeon, Apostolos; Antonarakos, Petros; Givissis, Panagiotis; Papadopoulos, Pericles; Christodoulou, Anastasios

2010-04-01

To compare outcomes of 3 fixation techniques for intra-articular distal femoral fractures. Records of 59 men and 49 women aged 16 to 80 (mean, 47) years who underwent internal fixation for 116 type-C (complete intra-articular) distal femoral fractures were retrospectively reviewed. According to the AO classification, 25 fractures were type C1 (23 closed and 2 open), 71 type C2 (69 closed and 2 open), and 20 type C3 (16 closed and 4 open). Based on implant availability at the time, all surgeries were performed by a single surgeon using a condylar buttress plate (n=38), a fixed angle (95 degrees) condylar blade plate (n=24), or a dynamic condylar screw (n=54). The mean follow-up period was 11 (range, 4-19) years. At the latest follow-up, functional outcome was classified according to Schatzker and Lambert criteria. Functional outcomes were excellent in 64 (55%) of the fractures, good in 37 (32%), moderate in 9 (8%), and poor in 6 (5%). Outcomes in patients treated by the dynamic condylar screw were significantly superior to those treated by the condylar buttress plate (p=0.016) or condylar blade plate (p=0.001). Good-to-excellent results were achieved in 96% vs 84% vs 71% of these patients, respectively. Complication rates were lower in the dynamic condylar screw group than the other 2 groups (pseudarthrosis, 5% vs 11% vs 25%; varus deformity, 4% vs 26% vs 25%; knee stiffness, 0% vs 5% vs 8%, respectively). No implant failure was encountered. Dynamic condylar screw fixation for distal femoral fractures achieves better functional outcomes and lower complication rates.

Fluid-driven Fractures and Backflow in a Multilayered Elastic Matrix

NASA Astrophysics Data System (ADS)

Smiddy, Samuel; Lai, Ching-Yao; Stone, Howard

2016-11-01

We study the dynamics when pressurized fluid is injected at a constant flow rate into a multi-layered elastic matrix. In particular, we report experiments of such crack propagation as a function of orientation and distance from the contact of the layers. Subsequently we study the shape and propagation of the fluid along the contact of layers as well as volume of fluid remaining in the matrix once the injection pressure is released and "flowback" occurs. The experiments presented here may mimic the interaction between hydraulic fractures and pre-existing fractures and the dynamics of flowback in hydraulic fracturing. Study made possible by the Andlinger Center for Energy and the Environment and the Fred Fox Fund.

Mechanisms of fracture of ring samples made of FCC metals on loading with magnetic-pulse method

NASA Astrophysics Data System (ADS)

Morozov, Viktor; Kats, Victor; Savenkov, Georgiy; Lukin, Anton

2018-05-01

Results of study of deformation and fracture of ring-shaped samples made of thin strips of cuprum, aluminum and steel in wide range of loading velocity are presented. Three developed by us schemes of magnetic-pulse method are used for the samples loading. The method of samples fracture with the high electrical resistance (e.g. steel) is proposed. Crack velocity at the sample fracture is estimated. Fracture surfaces are inspected. Mechanisms of dynamic fracture of the sample arere discussed.

Free-Surface flow dynamics and its effect on travel time distribution in unsaturated fractured zones - findings from analogue percolation experiments

NASA Astrophysics Data System (ADS)

Noffz, Torsten; Kordilla, Jannes; Dentz, Marco; Sauter, Martin

2017-04-01

Flow in unsaturated fracture networks constitutes a high potential for rapid mass transport and can therefore possibly contributes to the vulnerability of aquifer systems. Numerical models are generally used to predict flow and transport and have to reproduce various complex effects of gravity-driven flow dynamics. However, many classical volume-effective modelling approaches often do not grasp the non-linear free surface flow dynamics and partitioning behaviour at fracture intersections in unsaturated fracture networks. Better process understanding can be obtained by laboratory experiments, that isolate single aspects of the mass partitioning process, which influence travel time distributions and allow possible cross-scale applications. We present a series of percolation experiments investigating partitioning dynamics of unsaturated multiphase flow at an individual horizontal fracture intersection. A high precision multichannel dispenser is used to establish gravity-driven free surface flow on a smooth and vertical PMMA (poly(methyl methacrylate)) surface at rates ranging from 1.5 to 4.5 mL/min to obtain various flow modes (droplets; rivulets). Cubes with dimensions 20 x 20 x 20 cm are used to create a set of simple geometries. A digital balance provides continuous real-time cumulative mass bypassing the network. The influence of variable flow rate, atmospheric pressure and temperature on the stability of flow modes is shown in single-inlet experiments. Droplet and rivulet flow are delineated and a transition zone exhibiting mixed flow modes can be determined. Furthermore, multi-inlet setups with constant total inflow rates are used to reduce variance and the effect of erratic free-surface flow dynamics. Investigated parameters include: variable aperture widths df, horizontal offsets dv of the vertical fracture surface and alternating injection methods for both droplet and rivulet flow. Repetitive structures with several horizontal fractures extend arrival times but also complexity and variance. Finally, impacts of variable geometric features and flow modes on partitioning dynamics are highlighted by normalized fracture inflow rates. For higher flow rates, i.e. rivulet flows dominates, the effectiveness of filling horizontal fractures strongly increases. We demonstrate that the filling can be described by plug flow, which transitions into a Washburn-type flow at later times, and derive an analytical solution for the case of rivulet flows. Droplet flow dominated flow experiments exhibit a high bypass efficiency, which cannot be described by plug-flow, however, they also transition into a Washburn stage.

Dynamic Torsional and Cyclic Fracture Behavior of ProFile Rotary Instruments at Continuous or Reciprocating Rotation as Visualized with High-speed Digital Video Imaging.

PubMed

Tokita, Daisuke; Ebihara, Arata; Miyara, Kana; Okiji, Takashi

2017-08-01

This study examined the dynamic fracture behavior of nickel-titanium rotary instruments in torsional or cyclic loading at continuous or reciprocating rotation by means of high-speed digital video imaging. The ProFile instruments (size 30, 0.06 taper; Dentsply Maillefer, Ballaigues, Switzerland) were categorized into 4 groups (n = 7 in each group) as follows: torsional/continuous (TC), torsional/reciprocating (TR), cyclic/continuous (CC), and cyclic/reciprocating (CR). Torsional loading was performed by rotating the instruments by holding the tip with a vise. For cyclic loading, a custom-made device with a 38° curvature was used. Dynamic fracture behavior was observed with a high-speed camera. The time to fracture was recorded, and the fractured surface was examined with scanning electron microscopy. The TC group initially exhibited necking of the file followed by the development of an initial crack line. The TR group demonstrated opening and closing of a crack according to its rotation in the cutting and noncutting directions, respectively. The CC group separated without any detectable signs of deformation. In the CR group, initial crack formation was recognized in 5 of 7 samples. The reciprocating rotation exhibited a longer time to fracture in both torsional and cyclic fatigue testing (P < .05). The scanning electron microscopic images showed a severely deformed surface in the TR group. The dynamic fracture behavior of NiTi rotary instruments, as visualized with high-speed digital video imaging, varied between the different modes of rotation and different fatigue testing. Reciprocating rotation induced a slower crack propagation and conferred higher fatigue resistance than continuous rotation in both torsional and cyclic loads. Copyright © 2017 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

Less-invasive stabilization of rib fractures by intramedullary fixation: a biomechanical evaluation.

PubMed

Bottlang, Michael; Helzel, Inga; Long, William; Fitzpatrick, Daniel; Madey, Steven

2010-05-01

This study evaluated intramedullary fixation of rib fractures with Kirschner wires and novel ribs splints. We hypothesized that rib splints can provide equivalent fixation strength while avoiding complications associated with Kirschner wires, namely wire migration and cutout. The durability, strength, and failure modes of rib fracture fixation with Kirschner wires and rib splints were evaluated in 22 paired human ribs. First, intact ribs were loaded to failure to determine their strength. After fracture fixation with Kirschner wires and rib splints, fixation constructs were dynamically loaded to 360,000 cycles at five times the respiratory load to determine their durability. Finally, constructs were loaded to failure to determine residual strength and failure modes. All constructs sustained dynamic loading without failure. Dynamic loading caused three times more subsidence in Kirschner wire constructs (1.2 mm +/- 1.4 mm) than in rib splint constructs (0.4 mm +/- 0.2 mm, p = 0.09). After dynamic loading, rib splint constructs remained 48% stronger than Kirschner wire constructs (p = 0.001). Five of 11 Kirschner wire constructs failed catastrophically by cutting through the medial cortex, leading to complete loss of stability and wire migration through the lateral cortex. The remaining six constructs failed by wire bending. Rib splint constructs failed by development of fracture lines along the superior and interior cortices. No splint construct failed catastrophically, and all splint constructs retained functional reduction and fixation. Because of their superior strength and absence of catastrophic failure mode, rib splints can serve as an attractive alternative to Kirschner wires for intramedullary stabilization of rib fractures, especially in the case of posterior rib fractures where access for plating is limited.

Randomised controlled trial of the sliding hip screw versus X-Bolt Dynamic Hip Plating System for the fixation of trochanteric fractures of the hip in adults: a protocol study for WHiTE 4 (WHiTE4).

PubMed

Griffin, Xavier L; Achten, Juul; Sones, William; Cook, Jonathan; Costa, Matthew L

2018-01-26

Sliding hip screw fixation is well established in the treatment of trochanteric fractures of the hip. The X-Bolt Dynamic Hip Plating System builds on the successful design features of the sliding hip screw but differs in the nature of the fixation in the femoral head. A randomised pilot study suggested that the X-bolt Dynamic Hip Plating System might provide similar health-related quality of life while reducing the risk of revision surgery when compared with the sliding hip screw. This is the protocol for a multicentre randomised trial of sliding hip screw versus X-Bolt Dynamic Hip Plating System for patients 60 years and over treated for a trochanteric fracture of the hip. Multicentre, multisurgeon, parallel, two-arm, randomised controlled trial. Patients aged 60 years and older with a trochanteric hip fracture are potentially eligible. Participants will be randomly allocated on a 1:1 basis to either sliding hip screw or X-Bolt Dynamic Hip Plating System. Otherwise, all care will be in accordance with National Institute for Health and Care Excellence guidance. A minimum of 1128 patients will be recruited to obtain 90% power to detect a 0.075-point difference in EuroQol-5D health-related quality of life at 4 months postrandomisation. Secondary outcomes include mortality, residential status, revision surgery and radiographic measures. The treatment effect will be estimated using a two-sided t-test adjusted for age, gender and cognitive impairment based on an intention-to-treat analysis. National Research Ethics Committee approved this study on 5 February 2016 (16/WM/0001). The study is sponsored by the University of Oxford and funded through an investigator initiated grant by X-Bolt Orthopaedics. A manuscript for a high-impact peer-reviewed journal will be prepared, and the results will be disseminated to patients through local mechanisms at participating centres. ISRCTN92825709. © Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2018. All rights reserved. No commercial use is permitted unless otherwise expressly granted.

The Influence of Fracturing Fluids on Fracturing Processes: A Comparison Between Water, Oil and SC-CO2

NASA Astrophysics Data System (ADS)

Wang, Jiehao; Elsworth, Derek; Wu, Yu; Liu, Jishan; Zhu, Wancheng; Liu, Yu

2018-01-01

Conventional water-based fracturing treatments may not work well for many shale gas reservoirs. This is due to the fact that shale gas formations are much more sensitive to water because of the significant capillary effects and the potentially high contents of swelling clay, each of which may result in the impairment of productivity. As an alternative to water-based fluids, gaseous stimulants not only avoid this potential impairment in productivity, but also conserve water as a resource and may sequester greenhouse gases underground. However, experimental observations have shown that different fracturing fluids yield variations in the induced fracture. During the hydraulic fracturing process, fracturing fluids will penetrate into the borehole wall, and the evolution of the fracture(s) then results from the coupled phenomena of fluid flow, solid deformation and damage. To represent this, coupled models of rock damage mechanics and fluid flow for both slightly compressible fluids and CO2 are presented. We investigate the fracturing processes driven by pressurization of three kinds of fluids: water, viscous oil and supercritical CO2. Simulation results indicate that SC-CO2-based fracturing indeed has a lower breakdown pressure, as observed in experiments, and may develop fractures with greater complexity than those developed with water-based and oil-based fracturing. We explore the relation between the breakdown pressure to both the dynamic viscosity and the interfacial tension of the fracturing fluids. Modeling demonstrates an increase in the breakdown pressure with an increase both in the dynamic viscosity and in the interfacial tension, consistent with experimental observations.

Proceedings of the International Symposium on Dynamics of Fluids in Fractured Rocks: Concepts and Recent Advances

DOE Office of Scientific and Technical Information (OSTI.GOV)

Faybishenko, B.

1999-02-01

This publication contains extended abstracts of papers presented at the International Symposium ''Dynamics of Fluids in Fractured Rocks: Concepts and Recent Advances'' held at Ernest Orlando Lawrence Berkeley National Laboratory on February 10-12, 1999. This Symposium is organized in Honor of the 80th Birthday of Paul A. Witherspoon, who initiated some of the early investigations on flow and transport in fractured rocks at the University of California, Berkeley, and at Lawrence Berkeley National Laboratory. He is a key figure in the development of basic concepts, modeling, and field measurements of fluid flow and contaminant transport in fractured rock systems. Themore » technical problems of assessing fluid flow, radionuclide transport, site characterization, modeling, and performance assessment in fractured rocks remain the most challenging aspects of subsurface flow and transport investigations. An understanding of these important aspects of hydrogeology is needed to assess disposal of nu clear wastes, development of geothermal resources, production of oil and gas resources, and remediation of contaminated sites. These Proceedings of more than 100 papers from 12 countries discuss recent scientific and practical developments and the status of our understanding of fluid flow and radionuclide transport in fractured rocks. The main topics of the papers are: Theoretical studies of fluid flow in fractured rocks; Multi-phase flow and reactive chemical transport in fractured rocks; Fracture/matrix interactions; Hydrogeological and transport testing; Fracture flow models; Vadose zone studies; Isotopic studies of flow in fractured systems; Fractures in geothermal systems; Remediation and colloid transport in fractured systems; and Nuclear waste disposal in fractured rocks.« less

Dynamic mechanical characterization of aluminum: analysis of strain-rate-dependent behavior

NASA Astrophysics Data System (ADS)

Rahmat, Meysam

2018-05-01

A significant number of materials show different mechanical behavior under dynamic loads compared to quasi-static (Salvado et al. in Prog. Mater. Sci. 88:186-231, 2017). Therefore, a comprehensive study of material dynamic behavior is essential for applications in which dynamic loads are dominant (Li et al. in J. Mater. Process. Technol. 255:373-386, 2018). In this work, aluminum 6061-T6, as an example of ductile alloys with numerous applications including in the aerospace industry, has been studied under quasi-static and dynamic tensile tests with strain rates of up to 156 s^{-1}. Dogbone specimens were designed, instrumented and tested with a high speed servo-hydraulic load frame, and the results were validated with the literature. It was observed that at a strain rate of 156 s^{-1} the yield and ultimate strength increased by 31% and 33% from their quasi-static values, respectively. Moreover, the failure elongation and fracture energy per unit volume also increased by 18% and 52%, respectively. A Johnson-Cook model was used to capture the behavior of the material at different strain rates, and a modified version of this model was presented to enhance the capabilities of the original model, especially in predicting material properties close to the failure point. Finally, the fracture surfaces of specimens tested under quasi-static and dynamic loads were compared and conclusions about the differences were drawn.

Comparison of the Lag Screw Placements for the Treatment of Stable and Unstable Intertrochanteric Femoral Fractures regarding Trabecular Bone Failure.

PubMed

Celik, Talip; Mutlu, Ibrahim; Ozkan, Arif; Kisioglu, Yasin

2016-01-01

Background. In this study, the cut-out risk of Dynamic Hip Screw (DHS) was investigated in nine different positions of the lag screw for two fracture types by using Finite Element Analysis (FEA). Methods. Two types of fractures (31-A1.1 and A2.1 in AO classification) were generated in the femur model obtained from Computerized Tomography images. The DHS model was placed into the fractured femur model in nine different positions. Tip-Apex Distances were measured using SolidWorks. In FEA, the force applied to the femoral head was determined according to the maximum value being observed during walking. Results. The highest volume percentage exceeding the yield strength of trabecular bone was obtained in posterior-inferior region in both fracture types. The best placement region for the lag screw was found in the middle of both fracture types. There are compatible results between Tip-Apex Distances and the cut-out risk except for posterior-superior and superior region of 31-A2.1 fracture type. Conclusion. The position of the lag screw affects the risk of cut-out significantly. Also, Tip-Apex Distance is a good predictor of the cut-out risk. All in all, we can supposedly say that the density distribution of the trabecular bone is a more efficient factor compared to the positions of lag screw in the cut-out risk.

A primer on selecting grain boundary sets for comparison of interfacial fracture properties in molecular dynamics simulations

DOE PAGES

Dingreville, Remi; Aksoy, Doruk; Spearot, Douglas E.

2017-08-21

In this study, all grain boundaries are not equal in their predisposition for fracture due to the complex coupling between lattice geometry, interfacial structure, and mechanical properties. The ability to understand these relationships is crucial to engineer materials resilient to grain boundary fracture. Here, a methodology is presented to isolate the role of grain boundary structure on interfacial fracture properties, such as the tensile strength and work of separation, using atomistic simulations. Instead of constructing sets of grain boundary models within the misorientation/structure space by simply varying the misorientation angle around a fixed misorientation axis, the proposed method creates setsmore » of grain boundary models by means of isocurves associated with important fracture-related properties of the adjoining lattices. Such properties may include anisotropic elastic moduli, the Schmid factor for primary slip, and the propensity for simultaneous slip on multiple slip systems. This approach eliminates the effect of lattice properties from the comparative analysis of interfacial fracture properties and thus enables the identification of structure-property relationships for grain boundaries. As an example, this methodology is implemented to study crack propagation along Ni grain boundaries. Segregated H is used as a means to emphasize differences in the selected grain boundary structures while keeping lattice properties fixed.« less

Biomechanical analysis of posteromedial tibial plateau split fracture fixation.

PubMed

Zeng, Zhi-Min; Luo, Cong-Feng; Putnis, Sven; Zeng, Bing-Fang

2011-01-01

The purpose of this study was to compare the biomechanical strength of four different fixation methods for a posteromedial tibial plateau split fracture. Twenty-eight tibial plateau fractures were simulated using right-sided synthetic tibiae models. Each fracture model was randomly instrumented with one of the four following constructs, anteroposterior lag-screws, an anteromedial limited contact dynamic compression plate (LC-DCP), a lateral locking plate, or a posterior T-shaped buttress plate. Vertical subsidence of the posteromedial fragment was measured from 500 N to 1500 N during biomechanical testing, the maximum load to failure was also determined. It was found that the posterior T-shaped buttress plate allowed the least subsidence of the posteromedial fragment and produced the highest mean failure load than each of the other three constructs (P=0.00). There was no statistical significant difference between using lag screws or an anteromedial LC-DCP construct for the vertical subsidence at a 1500 N load and the load to failure (P>0.05). This study showed that a posterior-based buttress technique is biomechanically the most stable in-vitro fixation method for posteromedial split tibial plateau fractures, with AP screws and anteromedial-based LC-DCP are not as stable for this type of fracture. Copyright © 2010 Elsevier B.V. All rights reserved.

A primer on selecting grain boundary sets for comparison of interfacial fracture properties in molecular dynamics simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dingreville, Remi; Aksoy, Doruk; Spearot, Douglas E.

In this study, all grain boundaries are not equal in their predisposition for fracture due to the complex coupling between lattice geometry, interfacial structure, and mechanical properties. The ability to understand these relationships is crucial to engineer materials resilient to grain boundary fracture. Here, a methodology is presented to isolate the role of grain boundary structure on interfacial fracture properties, such as the tensile strength and work of separation, using atomistic simulations. Instead of constructing sets of grain boundary models within the misorientation/structure space by simply varying the misorientation angle around a fixed misorientation axis, the proposed method creates setsmore » of grain boundary models by means of isocurves associated with important fracture-related properties of the adjoining lattices. Such properties may include anisotropic elastic moduli, the Schmid factor for primary slip, and the propensity for simultaneous slip on multiple slip systems. This approach eliminates the effect of lattice properties from the comparative analysis of interfacial fracture properties and thus enables the identification of structure-property relationships for grain boundaries. As an example, this methodology is implemented to study crack propagation along Ni grain boundaries. Segregated H is used as a means to emphasize differences in the selected grain boundary structures while keeping lattice properties fixed.« less

Effect of milling on particle shape and surface energy heterogeneity of needle-shaped crystals.

PubMed

Ho, Raimundo; Naderi, Majid; Heng, Jerry Y Y; Williams, Daryl R; Thielmann, Frank; Bouza, Peter; Keith, Adam R; Thiele, Greg; Burnett, Daniel J

2012-10-01

Milling and micronization of particles are routinely employed in the pharmaceutical industry to obtain small particles with desired particle size characteristics. The aim of this study is to demonstrate that particle shape is an important factor affecting the fracture mechanism in milling. Needle-shaped crystals of the β polymorph of D-mannitol were prepared from recrystallization in water. A portion of the recrystallized materials was ball-milled. Unmilled and milled sieved fractions of recrystallized D-mannitol were analyzed by dynamic image analysis (DIA) and inverse gas chromatography (IGC) at finite concentration to explain the breakage/fracture behavior. In the process of ball-milling, D-mannitol preferentially fractured along their shortest axis, exposing (011) plane with increased hydrophilicity and increased bounding rectangular aspect ratio. This is in contrary to attachment energy modeling which predicts a fracture mechanism across the (010) plane with increased hydrophobicity, and small change in particle shape. Crystal size, and more importantly, crystal shape and facet-specific mechanical properties, can dictate the fracture/cleavage behavior of organic crystalline materials. Thorough understanding of the crystal slip systems, combining attachment energy prediction with particle shape and surface characterization using DIA and IGC, are important in understanding fracture behavior of organic crystalline solids in milling and micronization.

The role of the titanium functionally dynamic bridging plate for the treatment of the atrophic mandible fractures.

PubMed

Hachleitner, Johannes; Enzinger, Simon; Brandtner, Christian; Gaggl, Alexander

2014-07-01

The role of the titanium functionally dynamic bridging plate (TFDBP) in the fracture treatment of the severely atrophic mandible was assessed retrospectively. In 28 consecutive patients with fractures of a severely atrophic mandible fixation was carried out with TFDBPs. Twenty-one patients with 27 fractures were included in the study and then followed up for complications and the progress of fracture healing for 17 months postoperatively on average. There was only one case that required plate removal. All patients showed bone healing 3 months after surgery. The mental nerve sensation improved in 12 out of 23 fractures that had presented with nerve function disturbance. Every patient who had dentures prior to sustaining the fracture was able to return to denture wearing 3 weeks after surgery. No major complications occurred. A high proportion of bone healing with a low complication rate was observed with the use of TFDBPs in the treatment of severely atrophic mandible fractures. The TFDBP is an excellent alternative to conventional plating of the severely atrophic mandible. Copyright © 2013 European Association for Cranio-Maxillo-Facial Surgery. Published by Elsevier Ltd. All rights reserved.

J-R fracture characteristics of ferritic steels for RPVs and RCS piping of nuclear power plants

NASA Astrophysics Data System (ADS)

Yoon, Ji-Hyun; Lee, Bong-Sang; Hong, Jun-Hwa

2001-10-01

J-R fracture resistance tests have been performed on 3 heats of SA508-Gr.3 nuclear reactor pressure vessel (RPV) steel as well as 2 heats of SA516-Gr.70 and a heat of SA508-Gr.1a steels for nuclear reactor coolant system (RCS) piping. For the latter two steels, dynamic in addition to static J-R fracture resistances were investigated. From the test results of the SA508-Gr.3 steels, the J-R fracture resistance was superior in the following order: Si-killing steel, modified VCD steel and VCD steel. Microstructural analyses were carried out to correlate J-R fracture resistances with microstructural characteristics. According to the test results for SA508-Gr.1a and SA516-Gr.70 steels, all of the tested steels showed steep drops in fracture resistance at certain temperature and loading rate combinations. One heat of SA516-Gr.70 steel was very sensitive to dynamic strain aging and its fracture resistance was significantly low. It was concluded that microstructural and chemical factors affect the J-R fracture and DSA characteristics of SA516-Gr.70 steels.

Fundamental aspects in the quantitative ultrasonic determination of fracture toughness: General equations

NASA Technical Reports Server (NTRS)

Fu, L. S.

1981-01-01

The problem of establishing a theoretical groundwork for experimentally-found correlations between ultrasonic and fracture toughness factors in polycrystalline metals is discussed. It is noted that the link between these material properties and ultrasonic factors are the microstructural parameters that interact with stress wave propagation during deformation and fracture. The dynamic response of material inhomogeneities and the strains and displacements they undergo under incident stress waves are considered. Dynamic strains and displacements inside and outside scatterers are treated. The underlying approach, the formulation and governing equations for the eigenstrains, and the determination of the energy due to the presence of inhomogeneities are presented. The stress wave interaction problem is presented in terms of the dynamic eigenstrain concept.

Tensile strength of Fe-Ni and Mg-Al nanocomposites: Molecular dynamic simulations

NASA Astrophysics Data System (ADS)

Pogorelko, V. V.; Mayer, A. E.

2018-01-01

In this work, molecular dynamic simulations of the tensile strength of Fe-Ni and Mg-Al nanocomposites in the conditions of high-rate uniaxial tension were carried out. Two different mechanisms of fracture were identified. In the case of nickel inclusion in iron matrix, the fracture begins on the interface between the inclusion and the matrix, a formed void penetrates both into the inclusion and into the matrix; presence of inclusion reduces the tensile strength. In the case of aluminum inclusion in magnesium matrix, fracture takes place into magnesium matrix and does not touch the inclusion; presence of inclusion has practically no effect on the tensile strength. Molecular dynamic simulations were carried out in a wide range of strain rates and temperatures.

Mesoscale Fracture Analysis of Multiphase Cementitious Composites Using Peridynamics

PubMed Central

Yaghoobi, Amin; Chorzepa, Mi G.; Kim, S. Sonny; Durham, Stephan A.

2017-01-01

Concrete is a complex heterogeneous material, and thus, it is important to develop numerical modeling methods to enhance the prediction accuracy of the fracture mechanism. In this study, a two-dimensional mesoscale model is developed using a non-ordinary state-based peridynamic (NOSBPD) method. Fracture in a concrete cube specimen subjected to pure tension is studied. The presence of heterogeneous materials consisting of coarse aggregates, interfacial transition zones, air voids and cementitious matrix is characterized as particle points in a two-dimensional mesoscale model. Coarse aggregates and voids are generated using uniform probability distributions, while a statistical study is provided to comprise the effect of random distributions of constituent materials. In obtaining the steady-state response, an incremental and iterative solver is adopted for the dynamic relaxation method. Load-displacement curves and damage patterns are compared with available experimental and finite element analysis (FEA) results. Although the proposed model uses much simpler material damage models and discretization schemes, the load-displacement curves show no difference from the FEA results. Furthermore, no mesh refinement is necessary, as fracture is inherently characterized by bond breakages. Finally, a sensitivity study is conducted to understand the effect of aggregate volume fraction and porosity on the load capacity of the proposed mesoscale model. PMID:28772518

Numerical Simulation and Experimental Validation of Failure Caused by Vibration of a Fan

NASA Astrophysics Data System (ADS)

Zhou, Qiang; Han, Wu; Feng, Jianmei; Jia, Xiaohan; Peng, Xueyuan

2017-08-01

This paper presents the root cause analysis of an unexpected fracture occurred on the blades of a motor fan used in a natural gas reciprocating compressor unit. A finite element model was established to investigate the natural frequencies and modal shapes of the fan, and a modal test was performed to verify the numerical results. It was indicated that the numerical results agreed well with experimental data. The third order natural frequency was close to the six times excitation frequency, and the corresponding modal shape was the combination of bending and torsional vibration, which consequently contributed to low-order resonance and fracture failure of the fan. The torsional moment obtained by a torsional vibration analysis of the compressor shaft system was exerted on the numerical model of the fan to evaluate the dynamic stress response of the fan. The results showed that the stress concentration regions on the numerical model were consistent with the location of fractures on the fan. Based on the numerical simulation and experimental validation, some recommendations were given to improve the reliability of the motor fan.

Application of ERT, Saline Tracer and Numerical Studies to Delineate Preferential Paths in Fractured Granites.

PubMed

Sreeparvathy, Vijay; Kambhammettu, B V N P; Peddinti, Srinivasa Rao; Sarada, P S L

2018-03-22

Accurate quantification of in situ heterogeneity and flow processes through fractured geologic media remains elusive for hydrogeologists due to the complexity in fracture characterization and its multiscale behavior. In this research, we demonstrated the efficacy of tracer-electrical resistivity tomography (ERT) experiments combined with numerical simulations to characterize heterogeneity and delineate preferential flow paths in a fractured granite aquifer. A series of natural gradient saline tracer experiments were conducted from a depth window of 18 to 22 m in an injection well (IW) located inside the Indian Institute of Technology Hyderabad campus. Tracer migration was monitored in a time-lapse mode using two cross-sectional surface ERT profiles placed in the direction of flow gradient. ERT data quality was improved by considering stacking, reciprocal measurements, resolution indicators, and geophysical logs. Dynamic changes in subsurface electrical properties inferred via resistivity anomalies were used to highlight preferential flow paths of the study area. Temporal changes in electrical resistivity and tracer concentration were monitored along the vertical in an observation well located at 48 m to the east of the IW. ERT-derived tracer breakthrough curves were in agreement with geochemical sample measurements. Fracture geometry and hydraulic properties derived from ERT and pumping tests were further used to evaluate two mathematical conceptualizations that are relevant to fractured aquifers. Results of numerical analysis conclude that dual continuum model that combines matrix and fracture systems through a flow exchange term has outperformed equivalent continuum model in reproducing tracer concentrations at the monitoring wells (evident by a decrease in RMSE from 199 to 65 mg/L). A sensitivity analysis on model simulations conclude that spatial variability in hydraulic conductivity, local-scale dispersion, and flow exchange at fracture-matrix interface have a profound effect on model simulations. © 2018, National Ground Water Association.

Influence of long-time stress relief treatments on the dynamic fracture toughness properties of ASME SA508 C1 2a and ASME SA533 GR B C12 pressure vessel steels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Logsdon, W.A.

1982-03-01

Dynamic fracture toughness tests were performed on materials which had been subjected to one of three long-time post weld type stress relief heat treatments: 48 hours at 1000/degree/F (538/degree/C), 24 hours at 1125/degree/F (607/degree/C), and 48 hours at 1125/degree/F (607/degree/C). Linear elastic K/sub Id/ results were obtained at low temperatures while J-integral techniques were utilized to evaluate dynamic fracture toughness over the transition and upper shelf temperature ranges. Tensile, Charpy impact, and drop weight nil-ductility transition tests as well as room temperature, air environment fatigue crack growth rate tests (SA508 Cl 2a only) were also performed. The fracture toughness ofmore » both materials exceeded the ASME specified minimum reference toughness K/sub IR/ curve. 17 refs.« less

Microscopic Observation of the Side Surface of Dynamically-Tensile-Fractured 6061-T6 and 2219-T87 Aluminum Alloys with Pre-Fatigue

NASA Astrophysics Data System (ADS)

Itabashi, Masaaki; Nakajima, Shigeru; Fukuda, Hiroshi

After unexpected failure of metallic structure, microscopic investigation will be performed. Generally, such an investigation is limited to search striation pattern with a SEM (scanning electron microscope). But, when the cause of the failure was not severe repeated stress, this investigation is ineffective. In this paper, new microscopic observation technique is proposed to detect low cycle fatigue-impact tensile loading history. Al alloys, 6061-T6 and 2219-T87, were fractured in dynamic tension, after severe pre-fatigue. The side surface of the fractured specimens was observed with a SEM. Neighboring fractured surface, many opened cracks on the side surface have been generated. For each specimen, the number of the cracks was counted together with information of individual sizes and geometric features. For 6061-T6 alloy specimen with the pre-fatigue, the number of the cracks is greater than that for the specimen without the pre-fatigue. For 2219-T87 alloy, the same tendency can be found after a certain screening of the crack counting. Therefore, the crack counting technique may be useful to detect the existence of the pre-fatigue from the dynamically fractured specimen surface.

Intermittent stick-slip dynamics during the peeling of an adhesive tape from a roller.

PubMed

Cortet, Pierre-Philippe; Dalbe, Marie-Julie; Guerra, Claudia; Cohen, Caroline; Ciccotti, Matteo; Santucci, Stéphane; Vanel, Loïc

2013-02-01

We study experimentally the fracture dynamics during the peeling at a constant velocity of a roller adhesive tape mounted on a freely rotating pulley. Thanks to a high speed camera, we measure, in an intermediate range of peeling velocities, high frequency oscillations between phases of slow and rapid propagation of the peeling fracture. This so-called stick-slip regime is well known as the consequence of a decreasing fracture energy of the adhesive in a certain range of peeling velocity coupled to the elasticity of the peeled tape. Simultaneously with stick slip, we observe low frequency oscillations of the adhesive roller angular velocity which are the consequence of a pendular instability of the roller submitted to the peeling force. The stick-slip dynamics is shown to become intermittent due to these slow pendular oscillations which produce a quasistatic oscillation of the peeling angle while keeping constant the peeling fracture velocity (averaged over each stick-slip cycle). The observed correlation between the mean peeling angle and the stick-slip amplitude questions the validity of the usually admitted independence with the peeling angle of the fracture energy of adhesives.

The effect of a microscale fracture on dynamic capillary pressure of two-phase flow in porous media

NASA Astrophysics Data System (ADS)

Tang, Mingming; Lu, Shuangfang; Zhan, Hongbin; Wenqjie, Guo; Ma, Huifang

2018-03-01

Dynamic capillary pressure (DCP) effects, which is vital for predicting multiphase flow behavior in porous media, refers to the injection rate dependence capillary pressure observed during non-equilibrium displacement experiments. However, a clear picture of the effects of microscale fractures on DCP remains elusive. This study quantified the effects of microscale fractures on DCP and simulated pore-scale force and saturation change in fractured porous media using the multiphase lattice Boltzmann method (LBM). Eighteen simulation cases were carried out to calculate DCP as a function of wetting phase saturation. The effects of viscosity ratio and fracture orientation, aperture and length on DCP and DCP coefficient τ were investigated, where τ refers to the ratio of the difference of DCP and static capillary pressure (SCP) over the rate of wetting-phase saturation change versus time. Significant differences in τ values were observed between unfractured and fractured porous media. The τ values of fractured porous media were 1.1  × 104 Pa ms to 5.68 × 105 Pa ms, which were one or two orders of magnitude lower than those of unfractured porous media with a value of 4 × 106 Pa. ms. A horizontal fracture had greater effects on DCP and τ than a vertical fracture, given the same fracture aperture and length. This study suggested that a microscale fracture might result in large magnitude changes in DCP for two-phase flow.

Three-dimensional characterization of microporosity and permeability in fault zones hosted in heterolithic succession

NASA Astrophysics Data System (ADS)

Riegel, H. B.; Zambrano, M.; Jablonska, D.; Emanuele, T.; Agosta, F.; Mattioni, L.; Rustichelli, A.

2017-12-01

The hydraulic properties of fault zones depend upon the individual contributions of the damage zone and the fault core. In the case of the damage zone, it is generally characterized by means of fracture analysis and modelling implementing multiple approaches, for instance the discrete fracture network model, the continuum model, and the channel network model. Conversely, the fault core is more difficult to characterize because it is normally composed of fine grain material generated by friction and wear. If the dimensions of the fault core allows it, the porosity and permeability are normally studied by means of laboratory analysis or in the other case by two dimensional microporosity analysis and in situ measurements of permeability (e.g. micro-permeameter). In this study, a combined approach consisting of fracture modeling, three-dimensional microporosity analysis, and computational fluid dynamics was applied to characterize the hydraulic properties of fault zones. The studied fault zones crosscut a well-cemented heterolithic succession (sandstone and mudstones) and may vary in terms of fault core thickness and composition, fracture properties, kinematics (normal or strike-slip), and displacement. These characteristics produce various splay and fault core behavior. The alternation of sandstone and mudstone layers is responsible for the concurrent occurrence of brittle (fractures) and ductile (clay smearing) deformation. When these alternating layers are faulted, they produce corresponding fault cores which act as conduits or barriers for fluid migration. When analyzing damage zones, accurate field and data acquisition and stochastic modeling was used to determine the hydraulic properties of the rock volume, in relation to the surrounding, undamaged host rock. In the fault cores, the three-dimensional pore network quantitative analysis based on X-ray microtomography images includes porosity, pore connectivity, and specific surface area. In addition, images were used to perform computational fluid simulation (Lattice-Boltzmann multi relaxation time method) and estimate the permeability. These results will be useful for understanding the deformation process and hydraulic properties across meter-scale damage zones.

Dynamic Fixation of Humeral Shaft Fractures Using Active Locking Plates: A Prospective Observational Study.

PubMed

Madey, Steven M; Tsai, Stanley; Fitzpatrick, Daniel C; Earley, Kathleen; Lutsch, Michael; Bottlang, Michael

2017-01-01

Rigid locked plating constructs can suppress fracture healing by inhibiting interfragmentary motion required to stimulate natural bone healing by callus formation. Dynamic fixation with active locking plates reduces construct stiffness, enables controlled interfragmentary motion, and has been shown to induce faster and stronger bone healing in vivo compared to rigid locking plates. This prospective observational study represents the first clinical use of active locking plates. It documents our early clinical experience with active plates for stabilization of humeral shaft fractures to assess their durability and understand potential complications. Eleven consecutive patients with humeral shaft fractures (AO/OTA types 12 A-C) were prospectively enrolled at a level I and a level II trauma center. Fractures were stabilized by using active locking plates without supplemental bone graft or bone morphogenic proteins. The screw holes of active locking plates are elastically suspended in elastomer envelopes inside the plate, enabling up to 1.5 mm of controlled interfragmentary motion. Progression of fracture healing and integrity of implant fixation was assessed radiographically at 3, 6, 12, and 24 weeks post surgery. Patient-reported functional outcome measures were obtained at 6, 12, and 24 weeks post surgery. The primary endpoint of this study was plate durability in absence of plate bending or breakage, or failure of the elastically suspended locking hole mechanism. Secondary endpoints included fracture healing, complications requiring revision surgery, and functional outcome scores. The eleven patients had six simple AO/ OTA type 12A fractures, three wedge type 12B fractures, and two comminuted type 12C fracture, including one open fracture. All active locking plates endured the 6-month loading period without any signs of fatigue or failure. Ten of eleven fractures healed at 10.9 ± 5.2 weeks, as evident by bridging callus and pain-free function. One fracture required revision surgery 37 weeks post surgery due to late fixation failure at the screwbone interface in the presence of a atrophic delayed union. The average Disability of the Arm, Shoulder and Hand (DASH) score improved from 31 ± 22 at week 6 to 13 ± 15 by week 24, approaching that of the normal, healthy population (DASH = 10.1). By week 12, the difference between Constant shoulder scores, expressed as the difference between the affected and contralateral arm (8 ± 8), was considered excellent. By week 24, the SF-12 physical health score (44 ± 9) and mental health score (48 ± 11) approached the mean value of 50 that represents the norm for the general U.S. population. Absence of failure of the plate and locking holes suggests that dynamic fixation of humeral shaft fractures with active plates provides safe and effective fixation. Moreover, early callus bridging and excellent functional outcome scores suggest that dynamic fixation with active locking plates may promote increased fracture healing over standard locked plating.

Non-local damage rheology and size effect

NASA Astrophysics Data System (ADS)

Lyakhovsky, V.

2011-12-01

We study scaling relations controlling the onset of transiently-accelerating fracturing and transition to dynamic rupture propagation in a non-local damage rheology model. The size effect is caused principally by growth of a fracture process zone, involving stress redistribution and energy release associated with a large fracture. This implies that rupture nucleation and transition to dynamic propagation are inherently scale-dependent processes. Linear elastic fracture mechanics (LEFM) and local damage mechanics are formulated in terms of dimensionless strain components and thus do not allow introducing any space scaling, except linear relations between fracture length and displacements. Generalization of Weibull theory provides scaling relations between stress and crack length at the onset of failure. A powerful extension of the LEFM formulation is the displacement-weakening model which postulates that yielding is complete when the crack wall displacement exceeds some critical value or slip-weakening distance Dc at which a transition to kinetic friction is complete. Scaling relations controlling the transition to dynamic rupture propagation in slip-weakening formulation are widely accepted in earthquake physics. Strong micro-crack interaction in a process zone may be accounted for by adopting either integral or gradient type non-local damage models. We formulate a gradient-type model with free energy depending on the scalar damage parameter and its spatial derivative. The damage-gradient term leads to structural stresses in the constitutive stress-strain relations and a damage diffusion term in the kinetic equation for damage evolution. The damage diffusion eliminates the singular localization predicted by local models. The finite width of the localization zone provides a fundamental length scale that allows numerical simulations with the model to achieve the continuum limit. A diffusive term in the damage evolution gives rise to additional damage diffusive time scale associated with the structural length scale. The ratio between two time scales associated with damage accumulation and diffusion, the damage diffusivity ratio, reflects the role of the diffusion-controlled delocalization. We demonstrate that localized fracturing occurs at the damage diffusivity ratio below certain critical value leading to a linear scaling between stress and crack length compatible with size effect for failures at crack initiation. A subseuqent quasi-static fracture growth is self-similar with increasing size of the process zone proportional to the fracture length. At a certain stage, controlled by dynamic weakening, the self-similarity breaks down and crack velocity significantly deviates from that predicted by the quasi-static regime, the size of the process zone decreases, and the rate of crack growth ceases to be controlled by the rate of damage increase. Furthermore, the crack speed approaches that predicted by the elasto-dynamic equation. The non-local damage rheology model predicts that the nucleation size of the dynamic fracture scales with fault zone thickness distance of the stress interraction.

Design of high temperature ceramic components against fast fracture and time-dependent failure using cares/life

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jadaan, O.M.; Powers, L.M.; Nemeth, N.N.

1995-08-01

A probabilistic design methodology which predicts the fast fracture and time-dependent failure behavior of thermomechanically loaded ceramic components is discussed using the CARES/LIFE integrated design computer program. Slow crack growth (SCG) is assumed to be the mechanism responsible for delayed failure behavior. Inert strength and dynamic fatigue data obtained from testing coupon specimens (O-ring and C-ring specimens) are initially used to calculate the fast fracture and SCG material parameters as a function of temperature using the parameter estimation techniques available with the CARES/LIFE code. Finite element analysis (FEA) is used to compute the stress distributions for the tube as amore » function of applied pressure. Knowing the stress and temperature distributions and the fast fracture and SCG material parameters, the life time for a given tube can be computed. A stress-failure probability-time to failure (SPT) diagram is subsequently constructed for these tubes. Such a diagram can be used by design engineers to estimate the time to failure at a given failure probability level for a component subjected to a given thermomechanical load.« less

Molecular dynamics simulations of intergranular fracture in UO2 with nine empirical interatomic potentials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yongfeng Zhang; Paul C Millett; Michael R Tonks

The intergranular fracture behavior of UO2 was studied using molecular dynamics simulations with a bicrystal model. The anisotropic fracture behavior due to the different grain boundary characters was investigated with the View the MathML source symmetrical tilt S5 and the View the MathML source symmetrical tilt S3 ({1 1 1} twin) grain boundaries. Nine interatomic potentials, seven rigid-ion plus two core–shell ones, were utilized to elucidate possible potential dependence. Initiating from a notch, crack propagation along grain boundaries was observed for most potentials. The S3 boundary was found to be more prone to fracture than the S5 one, indicated bymore » a lower energy release rate associated with the former. However, some potential dependence was identified on the existence of transient plastic deformation at crack tips, and the results were discussed regarding the relevant material properties including the excess energies of metastable phases and the critical energy release rate for intergranular fracture. In general, local plasticity at crack tips was observed in fracture simulations with potentials that predict low excess energies for metastable phases and high critical energy release rates for intergranular fracture.« less

Symptomatic relevance of intravertebral cleft in patients with osteoporotic vertebral fracture.

PubMed

Kawaguchi, Satoshi; Horigome, Keiko; Yajima, Hideki; Oda, Takashi; Kii, Yuichiro; Ida, Kazunori; Yoshimoto, Mitsunori; Iba, Kousuke; Takebayashi, Tsuneo; Yamashita, Toshihiko

2010-08-01

The present study was designed to determine clinical and radiographic characteristics of unhealed osteoporotic vertebral fractures (OVFs) and the role of fracture mobility and an intravertebral cleft in the regulation of pain symptoms in patients with an OVF. Patients who had persistent low-back pain for 3 months or longer and a collapsed thoracic or lumbar vertebra that had an intervertebral cleft and abnormal mobility were referred to as having unhealed OVFs. Twenty-four patients with an unhealed OVF and 30 patients with an acute OVF were compared with regard to several clinical and radiographic features including the presence of an intravertebral fluid sign. Subsequently, the extent of dynamic mobility of the fractured vertebra was analyzed for correlation with the patients' age, duration of symptoms, back pain visual analog scale (VAS) score, and performance status. Finally, in cases of unhealed OVFs, the subgroup of patients with positive fluid signs was compared with the subgroup of patients with negative fluid signs. Patients with an unhealed OVF were more likely to have a crush-type fracture, shorter vertebral height of the fractured vertebra, and a fracture with a positive fluid sign than those with an acute OVF. The extent of dynamic mobility of the vertebra correlated significantly with the VAS score in patients with an unhealed OVF. In addition, a significant correlation with the extent of dynamic vertebral mobility with performance status was seen in patients with an unhealed OVF and those with an acute OVF. Of the 24 patients with an unhealed OVF, 14 had a positive fluid sign in the affected vertebra. Patients with a positive fluid sign exhibited a statistically significantly greater extent of dynamic vertebral mobility, a higher VAS score, a higher performance status grade, and a greater likelihood of having a crush-type fracture than those with a negative fluid sign. All but 1 patient with an unhealed OVF and a positive fluid sign had an Eastern Cooperative Oncology Group Performance Status Grade 3 or 4 (bedridden most or all of the time). In sharp contrast, all 10 patients with an unhealed OVF and a negative fluid sign were Grade 1 or 2. Unhealed OVFs form a group of fractures that are distinct from acute OVFs regarding radiographic morphometry and contents of the intravertebral cleft. Dynamic vertebral mobility serves as a primal pain determinant in patients with an unhealed OVF and potentially in those with an acute OVF. Fluid accumulation in the intravertebral cleft of unhealed OVFs likely reflects long-term bedridden positioning of the patients in daily activity.

Symposium II: Mechanochemistry in Materials Science, MRS Fall Meeting, Nov 30-Dec 4, 2009, Boston, MA

DTIC Science & Technology

2010-09-02

Dynamic Mechanical Analysis (DMA). The fracture behavior of the mechanophore-linked polymer is also examined through the Double Cleavage Drilled ...multinary complex structures. Structural, microstructural, and chemical characterizations were explored by metrological tools to support this...simple hydrocarbons in order to quantitatively define structure-property relationships for reacting materials under shock compression. Embedded gauge

A Policy Analysis of Child Care Subsidies: Increasing Quality, Access, and Affordability

ERIC Educational Resources Information Center

Moodie-Dyer, Amber

2011-01-01

Changing family dynamics over the past four decades, including rises in the numbers of working mothers and single-parent families, have created an increased need for affordable child care. Government response to this need has involved a number of stop-and-start policy approaches, which have led to a fractured child care system that makes it…

Comminution of solids caused by kinetic energy of high shear strain rate, with implications for impact, shock, and shale fracturing.

PubMed

Bazant, Zdenek P; Caner, Ferhun C

2013-11-26

Although there exists a vast literature on the dynamic comminution or fragmentation of rocks, concrete, metals, and ceramics, none of the known models suffices for macroscopic dynamic finite element analysis. This paper outlines the basic idea of the macroscopic model. Unlike static fracture, in which the driving force is the release of strain energy, here the essential idea is that the driving force of comminution under high-rate compression is the release of the local kinetic energy of shear strain rate. The density of this energy at strain rates >1,000/s is found to exceed the maximum possible strain energy density by orders of magnitude, making the strain energy irrelevant. It is shown that particle size is proportional to the -2/3 power of the shear strain rate and the 2/3 power of the interface fracture energy or interface shear stress, and that the comminution process is macroscopically equivalent to an apparent shear viscosity that is proportional (at constant interface stress) to the -1/3 power of this rate. A dimensionless indicator of the comminution intensity is formulated. The theory was inspired by noting that the local kinetic energy of shear strain rate plays a role analogous to the local kinetic energy of eddies in turbulent flow.

Dynamic deformation and fracture of single crystal silicon: Fracture modes, damage laws, and anisotropy

DOE PAGES

Huang, J. Y.; E, J. C.; Huang, J. W.; ...

2016-05-25

Impact fracture of single-crystal Si is critical to long-term reliability of electronic devices and solar cells for its wide use as components or substrates in semiconductor industry. Single-crystal Si is loaded along two different crystallographic directions with a split Hopkinson pressure bar integrated with an in situ x-ray imaging and diffraction system. Bulk stress histories are measured, simultaneously with x-ray phase contrast imaging (XPCI) and Laue diffraction. Damage evolution is quantified with grayscale maps from XPCI. Single-crystal Si exhibits pronounced anisotropy in fracture modes, and thus fracture strengths and damage evolution. For loading along [11¯ 0] and viewing along [001],more » (1¯1¯0)[11¯ 0] cleavage is activated and induces horizontal primary cracks followed by perpendicular wing cracks. However, for loading along [011¯] and viewing along [111], random nucleation and growth of shear and tensile-splitting crack networks lead to catastrophic failure of materials with no cleavage. The primary-wing crack mode leads to a lower characteristic fracture strength due to predamage, but a more concentrated strength distribution, i.e., a higher Weibull modulus, compared to the second loading case. Furthermore, the sequential primary cracking, wing cracking and wing-crack coalescence processes result in a gradual increase of damage with time, deviating from theoretical predictions. Particle size and aspect ratios of fragments are discussed with postmortem fragment analysis, which verifies fracture modes observed in XPCI.« less

Comparison of the Lag Screw Placements for the Treatment of Stable and Unstable Intertrochanteric Femoral Fractures regarding Trabecular Bone Failure

PubMed Central

Mutlu, Ibrahim; Ozkan, Arif; Kisioglu, Yasin

2016-01-01

Background. In this study, the cut-out risk of Dynamic Hip Screw (DHS) was investigated in nine different positions of the lag screw for two fracture types by using Finite Element Analysis (FEA). Methods. Two types of fractures (31-A1.1 and A2.1 in AO classification) were generated in the femur model obtained from Computerized Tomography images. The DHS model was placed into the fractured femur model in nine different positions. Tip-Apex Distances were measured using SolidWorks. In FEA, the force applied to the femoral head was determined according to the maximum value being observed during walking. Results. The highest volume percentage exceeding the yield strength of trabecular bone was obtained in posterior-inferior region in both fracture types. The best placement region for the lag screw was found in the middle of both fracture types. There are compatible results between Tip-Apex Distances and the cut-out risk except for posterior-superior and superior region of 31-A2.1 fracture type. Conclusion. The position of the lag screw affects the risk of cut-out significantly. Also, Tip-Apex Distance is a good predictor of the cut-out risk. All in all, we can supposedly say that the density distribution of the trabecular bone is a more efficient factor compared to the positions of lag screw in the cut-out risk. PMID:27995133

Integrated Modeling and Experiments to Characterize Coupled Thermo-hydro-geomechanical-chemical processes in Hydraulic Fracturing

NASA Astrophysics Data System (ADS)

Viswanathan, H. S.; Carey, J. W.; Karra, S.; Porter, M. L.; Rougier, E.; Kang, Q.; Makedonska, N.; Hyman, J.; Jimenez Martinez, J.; Frash, L.; Chen, L.

2015-12-01

Hydraulic fracturing phenomena involve fluid-solid interactions embedded within coupled thermo-hydro-mechanical-chemical (THMC) processes over scales from microns to tens of meters. Feedbacks between processes result in complex dynamics that must be unraveled if one is to predict and, in the case of unconventional resources, facilitate fracture propagation, fluid flow, and interfacial transport processes. The proposed work is part of a broader class of complex systems involving coupled fluid flow and fractures that are critical to subsurface energy issues, such as shale oil, geothermal, carbon sequestration, and nuclear waste disposal. We use unique LANL microfluidic and triaxial core flood experiments integrated with state-of-the-art numerical simulation to reveal the fundamental dynamics of fracture-fluid interactions to characterize the key coupled processes that impact hydrocarbon production. We are also comparing CO2-based fracturing and aqueous fluids to enhance production, greatly reduce waste water, while simultaneously sequestering CO2. We will show pore, core and reservoir scale simulations/experiments that investigate the contolling mechanisms that control hydrocarbon production.

Does plate type influence the clinical outcomes and implant removal in midclavicular fractures fixed with 2.7-mm anteroinferior plates? A retrospective cohort study

PubMed Central

2014-01-01

Background The purpose of this study was to evaluate surgical healing rates, implant failure, implant removal, and the need for surgical revision with regards to plate type in midshaft clavicle fractures fixed with 2.7-mm anteroinferior plates utilizing modern plating techniques. Methods This retrospective exploratory cohort review took place at a level I teaching trauma center and a single large private practice office. A total of 155 skeletally mature individuals with 156 midshaft clavicle fractures between March 2002 and March 2012 were included in the final results. Fractures were identified by mechanism of injury and classified based on OTA/AO criteria. All fractures were fixed with 2.7-mm anteroinferior plates. Primary outcome measurements included implant failure, malunion, nonunion, and implant removal. Secondary outcome measurements included pain with the visual analog scale and range of motion. Statistically significant testing was set at 0.05, and testing was performed using chi-square, Fisher’s exact, Mann–Whitney U, and Kruskall-Wallis. Results Implant failure occurred more often in reconstruction plates as compared to dynamic compression plates (p = 0.029). Malunions and nonunions occurred more often in fractures fixed with reconstruction plates as compared to dynamic compression plates, but it was not statistically significant. Implant removal attributed to irritation or implant prominence was observed in 14 patients. Statistically significant levels of pain were seen in patients requiring implant removal (p = 0.001) but were not associated with the plate type. Conclusions Anteroinferior clavicular fracture fixation with 2.7-mm dynamic compression plates results in excellent healing rates with low removal rates in accordance with the published literature. Given higher rates of failure, 2.7-mm reconstruction plates should be discouraged in comparison to stiffer and more reliable 2.7-mm dynamic compression plates. PMID:24993508

Improvement in Fatigue Performance of Aluminium Alloy Welded Joints by Laser Shock Peening in a Dynamic Strain Aging Temperature Regime.

PubMed

Su, Chun; Zhou, Jianzhong; Meng, Xiankai; Huang, Shu

2016-09-26

As a new treatment process after welding, the process parameters of laser shock peening (LSP) in dynamic strain aging (DSA) temperature regimes can be precisely controlled, and the process is a non-contact one. The effects of LSP at elevated temperatures on the distribution of the surface residual stress of AA6061-T6 welded joints were investigated by using X-ray diffraction technology with the sin² ϕ method and Abaqus software. The fatigue life of the welded joints was estimated by performing tensile fatigue tests. The microstructural evolution in surface and fatigue fractures of the welded joints was presented by means of surface integrity and fracture surface testing. In the DSA temperature regime of AA6061-T6 welded joints, the residual compressive stress was distributed more stably than that of LSP at room temperature. The thermal corrosion resistance and fatigue properties of the welded joints were also improved. The experimental results and numerical analysis were in mutual agreement.

Improvement in Fatigue Performance of Aluminium Alloy Welded Joints by Laser Shock Peening in a Dynamic Strain Aging Temperature Regime

PubMed Central

Su, Chun; Zhou, Jianzhong; Meng, Xiankai; Huang, Shu

2016-01-01

As a new treatment process after welding, the process parameters of laser shock peening (LSP) in dynamic strain aging (DSA) temperature regimes can be precisely controlled, and the process is a non-contact one. The effects of LSP at elevated temperatures on the distribution of the surface residual stress of AA6061-T6 welded joints were investigated by using X-ray diffraction technology with the sin2ϕ method and Abaqus software. The fatigue life of the welded joints was estimated by performing tensile fatigue tests. The microstructural evolution in surface and fatigue fractures of the welded joints was presented by means of surface integrity and fracture surface testing. In the DSA temperature regime of AA6061-T6 welded joints, the residual compressive stress was distributed more stably than that of LSP at room temperature. The thermal corrosion resistance and fatigue properties of the welded joints were also improved. The experimental results and numerical analysis were in mutual agreement. PMID:28773920

Identification of an urban fractured-rock aquifer dynamics using an evolutionary self-organizing modelling

NASA Astrophysics Data System (ADS)

Hong, Yoon-Seok; Rosen, Michael R.

2002-03-01

An urban fractured-rock aquifer system, where disposal of storm water is via 'soak holes' drilled directly into the top of fractured-rock basalt, has a highly dynamic nature where theories or knowledge to generate the model are still incomplete and insufficient. Therefore, formulating an accurate mechanistic model, usually based on first principles (physical and chemical laws, mass balance, and diffusion and transport, etc.), requires time- and money-consuming tasks. Instead of a human developing the mechanistic-based model, this paper presents an approach to automatic model evolution in genetic programming (GP) to model dynamic behaviour of groundwater level fluctuations affected by storm water infiltration. This GP evolves mathematical models automatically that have an understandable structure using function tree representation by methods of natural selection ('survival of the fittest') through genetic operators (reproduction, crossover, and mutation). The simulation results have shown that GP is not only capable of predicting the groundwater level fluctuation due to storm water infiltration but also provides insight into the dynamic behaviour of a partially known urban fractured-rock aquifer system by allowing knowledge extraction of the evolved models. Our results show that GP can work as a cost-effective modelling tool, enabling us to create prototype models quickly and inexpensively and assists us in developing accurate models in less time, even if we have limited experience and incomplete knowledge for an urban fractured-rock aquifer system affected by storm water infiltration.

Groundwater mixing at fracture intersections triggers massive iron-rich microbial mats

NASA Astrophysics Data System (ADS)

Bochet, O.; Le Borgne, T.; Bethencourt, L.; Aquilina, L.; Dufresne, A.; Pédrot, M.; Farasin, J.; Abbott, B. W.; Labasque, T.; Chatton, E.; Lavenant, N.; Petton, C.

2017-12-01

While most freshwater on Earth resides and flows in groundwater systems, these deep subsurface environments are often assumed to have little biogeochemical activity compared to surface environments. Here we report a massive microbial mat of iron-oxidizing bacteria, flourishing 60 meters below the surface, far below the mixing zone where most microbial activity is believed to occur. The abundance of microtubular structures in the mat hinted at the prevalence of of Leptothrix ochracea, but metagenomic analysis revealed a diverse consortium of iron-oxidizing bacteria dominated by unknown members of the Gallionellaceae family. This deep biogeochemical hot spot formed at the intersection of bedrock fractures, which maintain redox gradients by mixing water with different residence times and chemical compositions. Using measured fracture properties and hydrological conditions we developed a quantitative model to simulate the reactive zone where such deep hot spots could occur. While seasonal fluctuations are generally thought to decrease with depth, we found that meter-scale changes in water table level moved the depth of the reactive zone hundreds of meters because the microaerophilic threshold for ironoxidizers is highly sensitive to changes in mixing rates at fracture intersections. These results demonstrate that dynamic microbial communities can be sustained deep below the surface in bedrock fractures. Given the ubiquity of fractures at multiple scales in Earth's subsurface, such deep hot spots may strongly influence global biogeochemical cycles.

Comparing slow and fast rupture in laboratory experiments

NASA Astrophysics Data System (ADS)

Aben, F. M.; Brantut, N.; David, E.; Mitchell, T. M.

2017-12-01

During the brittle failure of rock, elastically stored energy is converted into a localized fracture plane and surrounding fracture damage, seismic radiation, and thermal energy. However, the partitioning of energy might vary with the rate of elastic energy release during failure. Here, we present the results of controlled (slow) and dynamic (fast) rupture experiments on dry Lanhélin granite and Westerly granite samples, performed under triaxial stress conditions at confining pressures of 50 and 100 MPa. During the tests, we measured sample shortening, axial load and local strains (with 2 pairs of strain gauges glued directly onto the sample). In addition, acoustic emissions (AEs) and changes in seismic velocities were monitored. The AE rate was used as an indicator to manually control the axial load on the sample to stabilize rupture in the quasi-static failure experiments. For the dynamic rupture experiments a constant strain rate of 10-5 s-1 was applied until sample failure. A third experiment, labeled semi-controlled rupture, involved controlled rupture up to a point where the rupture became unstable and the remaining elastic energy was released dynamically. All experiments were concluded after a macroscopic fracture had developed across the whole sample and frictional sliding commenced. Post-mortem samples were epoxied, cut and polished to reveal the macroscopic fracture and the surrounding damage zone. The samples failed with average rupture velocities varying from 5x10-6 m/s up to >> 0.1 m/s. The analyses of AE locations on the slow ruptures reveal that within Westerly granite samples - with a smaller grain size - fracture planes are disbanded in favor of other planes when a geometrical irregularity is encountered. For the coarser grained Lanhélin granite a single fracture plane is always formed, although irregularities are recognized as well. The semi-controlled experiments show that for both rock types the rupture can become unstable in response to these irregularities. In Westerly granite, slow rupture experiments tend to produce complex fracture patterns while during the dynamic rupture experiments secondary rupture planes are not formed. These findings show that grain or flaw size, flaw distribution, and rupture speed strongly influence fracture localization and propagation.

Dynamic osteosynthesis by modified Kuntscher nail for the treatment of tibial diaphyseal fractures.

PubMed

Gadegone, Wasudeo M; Salphale, Yogesh S

2009-04-01

We evaluated a series of diaphyseal fractures of the tibia using low-cost, Indian-made modified Kuntscher nail (Daga nail) with the provision of distal locking screw for the management of the tibial diaphyseal fractures. One hundred and fifty one consecutive patients with diaphyseal fractures of tibia with 151 fractures who were treated by Daga nail were enrolled. One of the patients who had died because of cancer, and the two patients who were lost to follow-up at 3 months were excluded from the study.Therefore data of 148 patients with one hundred and fortyeight fractures is described. One hundred twenty closed fractures, 20 open Grade I fractures, and eight open Grade II fractures as per Gustilo and Anderson classification were included in this study. One hundred fourteen men and 34 women, with a mean age of 38.4 years, were studied. The result were analysed for Surgical time, duration of hospitalisation, union time, union rate, complication rate, functional recovery and crutch walking time. The fractures were followed at least until the time of solid union. The follow-up period averaged 15 months (range, 6-26 months). Union occurred in 140 cases (94.6%). The mean time to union was 13 weeks for closed fractures,17.8 weeks for Grade I open fractures, and 21.6 weeks for Grade II open fractures. Compartment syndrome occurred in two patients. Superficial infection occurred in five cases of Grade I and II compound fractures. Three closed fractures and one case of Grade I compound fracture required bone grafting for delayed union. Two cases of Grade II compound fracture with nonunion required revision surgery and bone grafting. Twelve cases resulted in acceptable malalignment due to operative technical error. In four cases, the distal screw breakage was seen, but none of these complications interfered with fracture healing. Recovery of joint motion was essentially normal in those patients without knee or ankle injury. Unreamed distally locked dynamic tibial nailing (modified Kuntscher nail/Daga nail) can produce excellent clinical results for diaphyseal tibial fractures. It has the advantages of technical simplicity, minimal cost, user-friendly instrumentation, and a short learning curve.

Impact of Microorganisms on Unsatured Flow within Fractures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Daphne L. Stoner; Robert D. Stedtfeld; Tina L. Tyler

An experiment is described in which a groundwater bacterium, Sphingomonas sp., influenced the dynamics of unsaturated flow at a fracture intersection. A washed cell suspension increased by three-fold the length of time that water pooled at the fracture intersection. On the other hand, the addition of growth substrates resulted in cell growth and the conversion from intermittent to continuous flow behavior at the fracture intersection. The results suggest that microbial properties and processes need to be included with other important variables for understanding unsaturated flow in fractured geomatrices.

Prediction of Ductile Fracture Behaviors for 42CrMo Steel at Elevated Temperatures

NASA Astrophysics Data System (ADS)

Lin, Y. C.; Liu, Yan-Xing; Liu, Ge; Chen, Ming-Song; Huang, Yuan-Chun

2015-01-01

The ductile fracture behaviors of 42CrMo steel are studied by hot tensile tests with the deformation temperature range of 1123-1373 K and strain rate range of 0.0001-0.1 s-1. Effects of deformation temperature and strain rate on the flow stress and fracture strain of the studied steel are discussed in detail. Based on the experimental results, a ductile damage model is established to describe the combined effects of deformation temperature and strain rate on the ductile fracture behaviors of 42CrMo steel. It is found that the flow stress first increases to a peak value and then decreases, showing an obvious dynamic softening. This is mainly attributed to the dynamic recrystallization and material intrinsic damage during the hot tensile deformation. The established damage model is verified by hot forging experiments and finite element simulations. Comparisons between the predicted and experimental results indicate that the established ductile damage model is capable of predicting the fracture behaviors of 42CrMo steel during hot forging.

Aging and loading rate effects on the mechanical behavior of equine bone

NASA Astrophysics Data System (ADS)

Kulin, Robb M.; Jiang, Fengchun; Vecchio, Kenneth S.

2008-06-01

Whether due to a sporting accident, high-speed impact, fall, or other catastrophic event, the majority of clinical bone fractures occur under dynamic loading conditions. However, although extensive research has been performed on the quasi-static fracture and mechanical behavior of bone to date, few high-quality studies on the fracture behavior of bone at high strain rates have been performed. Therefore, many questions remain regarding the material behavior, including not only the loading-rate-dependent response of bone, but also how this response varies with age. In this study, tests were performed on equine femoral bone taken post-mortem from donors 6 months to 28 years of age. Quasi-static and dynamic tests were performed to determine the fracture toughness and compressive mechanical behavior as a function of age at varying loading rates. Fracture paths were then analyzed using scanning confocal and scanning-electron microscopy techniques to assess the role of various microstructural features on toughening mechanisms.

Prospective analysis of magnetic resonance imaging accuracy in diagnosing traumatic injuries of the posterior ligamentous complex of the thoracolumbar spine.

PubMed

Pizones, Javier; Sánchez-Mariscal, Felisa; Zúñiga, Lorenzo; Álvarez, Patricia; Izquierdo, Enrique

2013-04-20

Prospective cohort study. To study magnetic resonance imaging (MRI) accuracy in diagnosing posterior ligamentous complex (PLC) damage, when applying the new dichotomic instability criteria in a prospective cohort of patients with vertebral fracture. Recent studies dispute MRI accuracy to diagnose PLC injuries. They analyze the complex based on 3 categories (intact/indeterminate/rupture), including the indeterminate in the ruptured group (measurement bias) in the accuracy analysis. Moreover, fractures with conservative treatment (selection bias) are not included. Both facts reduce the specificity. A recent study has proposed new criteria where posterior instability is determined with supraspinous ligament (SSL) rupture. Prospective study of patients with acute thoracolumbar fracture, using radiography and MRI (FS-T2-w/short-tau inversion-recovery sequences). 1. The integrity (ruptured/unruptured) of each isolated component of the PLC (facet capsules, interspinous ligament, SSL, and ligamentum flavum) was assessed via MRI and surgical findings. 2. PLC integrity as a whole was assessed, adopting the new dichotomic stability criteria from previous studies. In the MR images, PLC is considered ruptured when the SSL is found discontinued, and intact when not (this excludes the "indeterminate" category). In surgically treated fractures, PLC stability as a whole was assessed dynamically (ruptured/unruptured). In conservative fractures, PLC stability was assessed according to change in vertebral kyphosis measured with the local kyphotic angle at 2-year follow-up (ruptured if difference is > 5°/unruptured if difference is < 5°).3. Comparative analysis among findings provided MRI accuracy in diagnosing PLC damage. Fifty-eight vertebral fractures were studied (38 surgical, 20 conservative), of which 50% were in males; average age, 40.4 years. MRI sensitivity for injury diagnosis of each isolated PLC component varied between 92.3% (interspinous ligament) and 100% (ligamentum flavum). Specificity varied between 52% (facet capsules) and 100% (SSL). PLC integrity sensitivity and specificity as a whole were 91% and 100%, respectively. Adopting the new stability criteria, MRI accuracy in PLC injury diagnosis increases. Specificity is increased (true positives) both in isolated component analysis and PLC as a whole.

Dislocation dynamics modelling of the ductile-brittle-transition

NASA Astrophysics Data System (ADS)

Hennecke, Thomas; Hähner, Peter

2009-07-01

Many materials like silicon, tungsten or ferritic steels show a transition between high temperature ductile fracture with stable crack grow and high deformation energy absorption and low temperature brittle fracture in an unstable and low deformation mode, the ductile-brittle-transition. Especially in steels, the temperature transition is accompanied by a strong increase of the measured fracture toughness over a certain temperature range and strong scatter in the toughness data in this transition regime. The change in fracture modes is affected by dynamic interactions between dislocations and the inhomogeneous stress fields of notches and small cracks. In the present work a dislocation dynamics model for the ductile-brittle-transition is proposed, which takes those interactions into account. The model can explain an increase with temperature of apparent toughness in the quasi-brittle regime and different levels of scatter in the different temperature regimes. Furthermore it can predict changing failure sites in materials with heterogeneous microstructure. Based on the model, the effects of crack tip blunting, stress state, external strain rate and irradiation-induced changes in the plastic flow properties can be discussed.

Dynamic Yielding and Spall Behavior of Commercially Pure Grade 4 Titanium

NASA Astrophysics Data System (ADS)

Thadhani, Naresh; Whelchel, R. L.; Sanders, Tom; Mehkote, D. S.; Iyer, K. A.; Georgia Instiutute of Technology Collaboration; Johns Hopkins University, Applied Physics Labortaory Collaboration

2015-06-01

The dynamic yielding and fracture (spalling) of commercially pure (grade 4) titanium are investigated using symmetric plate impact experiments over a peak stress range of 5.6 GPa to 12.5 GPa, using the 80-mm single-stage gas-gun. VISAR rear free surface velocity profiles display both a Hugoniot elastic limit (HEL) and a velocity pullback, which are indicative of dynamic compressive yielding and tensile fracture (spalling), respectively. The HEL values appear to show a slight decrease with peak stress from 2.2 GPa to 2.0 GPa along with a corresponding increase in twinning observed in recovered impacted samples. The spall strength on the other hand increases with peak stress from a value of 3.3 GPa to 3.8 GPa and shows a good power law fit with the decompression strain rate. The differing responses in dynamic yield and fracture behavior suggest that void nucleation may be the dominant mechanism affecting the spall strength of grade 4 titanium.

Effects of {10-12} Twins on Dynamic Torsional Properties of Extruded AZ31 Magnesium Alloy

NASA Astrophysics Data System (ADS)

Lee, Jong Un; Song, Seok Weon; Kim, Yongjin; Kim, Sang-Hoon; Kim, Ye Jin; Park, Sung Hyuk

2018-03-01

Effects of initial twins on dynamic torsional properties of extruded AZ31 alloy were investigated by introducing {10-12} twins into it through precompression to 3 and 6% strains along the extrusion direction and performing torsional testing at a strain rate of 1.4 × 103 s-1 using a torsional Kolsky bar system. The as-extruded sample without twins showed higher dynamic torsional properties than the precompressed samples with many initial twins; the maximum shear strength and fracture shear strain decreased with increasing amount of initial twins. In the as-extruded sample, twinning occurred vigorously throughout the gage section of the tubular specimen during high-strain-rate torsional tests, resulting in heavily deformed morphology, many macrocracks, and rough fractured surfaces. The increased amount of initial twins suppressed the twinning behavior and localized the applied torsional deformation; this resulted in an almost unchanged sample shape, no secondary cracks, and a flat fracture plane, thereby deteriorating the dynamic torsional properties of the extruded alloy.

Water Inrush Analysis of the Longmen Mountain Tunnel Based on a 3D Simulation of the Discrete Fracture Network

NASA Astrophysics Data System (ADS)

Xiong, Ziming; Wang, Mingyang; Shi, ShaoShuai; Xia, YuanPu; Lu, Hao; Bu, Lin

2017-12-01

The construction of tunnels and underground engineering in China has developed rapidly in recent years in both the number and the length of tunnels. However, with the development of tunnel construction technology, risk assessment of the tunnels has become increasingly important. Water inrush is one of the most important causes of engineering accidents worldwide, resulting in considerable economic and environmental losses. Accordingly, water inrush prediction is important for ensuring the safety of tunnel construction. Therefore, in this study, we constructed a three-dimensional discrete network fracture model using the Monte Carlo method first with the basic data from the engineering geological map of the Longmen Mountain area, the location of the Longmen Mountain tunnel. Subsequently, we transformed the discrete fracture networks into a pipe network model. Next, the DEM of the study area was analysed and a submerged analysis was conducted to determine the water storage area. Finally, we attempted to predict the water inrush along the Longmen Mountain tunnel based on the Darcy flow equation. Based on the contrast of water inrush between the proposed approach, groundwater dynamics and precipitation infiltration method, we conclude the following: the water inflow determined using the groundwater dynamics simulation results are basically consistent with those in the D2K91+020 to D2K110+150 mileage. Specifically, in the D2K91+020 to D2K94+060, D2K96+440 to D2K98+100 and other sections of the tunnel, the simulated and measured results are in close agreement and show that this method is effective. In general, we can predict the water inflow in the area of the Longmen Mountain tunnel based on the existing fracture joint parameters and the hydrogeological data of the Longmen Mountain area, providing a water inrush simulation and guiding the tunnel excavation and construction stages.

A Fracture Mechanics Approach to Thermal Shock Investigation in Alumina-Based Refractory

NASA Astrophysics Data System (ADS)

Volkov-Husović, T.; Heinemann, R. Jančić; Mitraković, D.

2008-02-01

The thermal shock behavior of large grain size, alumina-based refractories was investigated experimentally using a standard water quench test. A mathematical model was employed to simulate the thermal stability behavior. Behavior of the samples under repeated thermal shock was monitored using ultrasonic measurements of dynamic Young's modulus. Image analysis was used to observe the extent of surface degradation. Analysis of the obtained results for the behavior of large grain size samples under conditions of rapid temperature changes is given.

Moisture desorption in mechanically masticated fuels: effects of particle fracturing and fuelbed compaction

Treesearch

Jesse K. Kreye; J.Morgan Varner; Eric E. Knapp

2012-01-01

Mechanical mastication is increasingly used as a wildland fuel treatment, reducing standing trees and shrubs to compacted fuelbeds of fractured woody fuels. One major shortcoming in our understanding of these fuelbeds is how particle fracturing influences moisture gain or loss, a primary determinant of fire behaviour. To better understand fuel moisture dynamics, we...

Reactivation of a Propped Hydraulic Fracture

NASA Astrophysics Data System (ADS)

Sarvaramini, E.; Garagash, D.

2014-12-01

The problem of massive fluid injection into a pre-existing fracture has many applications in petroleum industry including underground liquid waste disposal and waterflooding to increase recovery from a hydrocarbon reservoir. Understanding the conditions leading to the re-activation of pre-existing fractures and ensuing propagation is critical for a successful injection project design, and it may also help to mitigate potential environmental hazards, such as contamination of underground aquifers and induced seismicity. The problem of injection of a low viscosity fluid into a permeable formation can be distinguished from conventional hydraulic fracture by the mechanism of fluid leak-off. In conventional fracturing, high viscosity and cake building properties of injected fluid limit leak-off to a 1-D boundary layer incasing the crack. In the case of injection of low viscosity fluid into a fracture, leak-off and related pore fluid diffusion will take place over wider range of scales, from 1-D to 2 or 3-D. We consider a pre-existing stationary propped hydraulic fracture with constrained height into which a fluid is injected under constant flow rate. Although the net effective stress on the crack is initially compressive, the proppant keeps the crack open. It is worthwhile to note that during injection and related pressurization of a propped crack, the fracture breakdown is to be achieved prior to the fracture re-opening. Therefore, the effect of the change of the propped fracture storage on the pressurization dynamics can be neglected. The objective of this work is to study the transient pressurization and the onset of the propagation for a propped fracture. To the end, we formulate and solve a general problem of injection into a fracture accounting for viscous dissipation (i.e. non-uniform pressure distribution). We quantify how the fracture breakdown condition depends upon the rock and fluid properties, the in-situ stress and the fluid injection rate. We also establish a criterion when the assumption of negligible viscous dissipation is justified. The obtained solution is also transportable to the production well test analysis of a fractured well (Cinco et al., SPE 1978).

Thermal Fatigue and Fracture Behavior of Ceramic Thermal Barrier Coatings

NASA Technical Reports Server (NTRS)

Zhu, Dong-Ming; Choi, Sung R.; Miller, Robert A.

2001-01-01

Thermal fatigue and fracture behavior of plasma-sprayed ceramic thermal barrier coatings has been investigated under high heat flux and thermal cyclic conditions. The coating crack propagation is studied under laser heat flux cyclic thermal loading, and is correlated with dynamic fatigue and strength test results. The coating stress response and inelasticity, fatigue and creep interactions, and interface damage mechanisms during dynamic thermal fatigue processes are emphasized.

Deformation and fracture of explosion-welded Ti/Al plates: A synchrotron-based study

DOE Office of Scientific and Technical Information (OSTI.GOV)

E, J. C.; Huang, J. Y.; Bie, B. X.

Here, explosion-welded Ti/Al plates are characterized with energy dispersive spectroscopy and x-ray computed tomography, and exhibit smooth, well-jointed, interface. We perform dynamic and quasi-static uniaxial tension experiments on Ti/Al with the loading direction either perpendicular or parallel to the Ti/Al interface, using a mini split Hopkinson tension bar and a material testing system in conjunction with time-resolved synchrotron x-ray imaging. X-ray imaging and strain-field mapping reveal different deformation mechanisms responsible for anisotropic bulk-scale responses, including yield strength, ductility and rate sensitivity. Deformation and fracture are achieved predominantly in Al layer for perpendicular loading, but both Ti and Al layers asmore » well as the interface play a role for parallel loading. The rate sensitivity of Ti/Al follows those of the constituent metals. For perpendicular loading, single deformation band develops in Al layer under quasi-static loading, while multiple deformation bands nucleate simultaneously under dynamic loading, leading to a higher dynamic fracture strain. For parallel loading, the interface impedes the growth of deformation and results in increased ductility of Ti/Al under quasi-static loading, while interface fracture occurs under dynamic loading due to the disparity in Poisson's contraction.« less

Deformation and fracture of explosion-welded Ti/Al plates: A synchrotron-based study

DOE PAGES

E, J. C.; Huang, J. Y.; Bie, B. X.; ...

2016-08-02

Here, explosion-welded Ti/Al plates are characterized with energy dispersive spectroscopy and x-ray computed tomography, and exhibit smooth, well-jointed, interface. We perform dynamic and quasi-static uniaxial tension experiments on Ti/Al with the loading direction either perpendicular or parallel to the Ti/Al interface, using a mini split Hopkinson tension bar and a material testing system in conjunction with time-resolved synchrotron x-ray imaging. X-ray imaging and strain-field mapping reveal different deformation mechanisms responsible for anisotropic bulk-scale responses, including yield strength, ductility and rate sensitivity. Deformation and fracture are achieved predominantly in Al layer for perpendicular loading, but both Ti and Al layers asmore » well as the interface play a role for parallel loading. The rate sensitivity of Ti/Al follows those of the constituent metals. For perpendicular loading, single deformation band develops in Al layer under quasi-static loading, while multiple deformation bands nucleate simultaneously under dynamic loading, leading to a higher dynamic fracture strain. For parallel loading, the interface impedes the growth of deformation and results in increased ductility of Ti/Al under quasi-static loading, while interface fracture occurs under dynamic loading due to the disparity in Poisson's contraction.« less

Studying Petrophysical and Geomechanical Properties of Utica Point-Pleasant Shale and its Variations Across the Northern Appalachian Basin

NASA Astrophysics Data System (ADS)

Raziperchikolaee, S.; Kelley, M. E.; Burchwell, A.

2017-12-01

Understanding petrophysical and geomechanical parameters of shale formations and their variations across the basin are necessary to optimize the design of a hydraulic fracturing program aimed at enhancing long term oil/gas production from unconventional wells. Dipole sonic logging data (compressional-wave and shear-wave slowness) from multiple wells across the study area, coupled with formation bulk density log data, were used to calculate dynamic elastic parameters, including shear modulus, bulk modulus, Poisson's ratio, and Young's modulus for the shale formations. The individual-well data were aggregated into a single histogram for each parameter to gain an understanding of the variation in the properties (including brittleness) of the Utica Point-Pleasant formations across the entire study area. A crossplot of the compressional velocity and bulk density and a crossplot between the compressional velocity, the shear velocity, and depth of the measurement were used for a high level petrophysical characterization of the Utica Point-Pleasant. Detailed interpretation of drilling induced fractures recorded in image logs, and an analysis of shear wave anisotropy using multi-receiver sonic logs were also performed. Orientation of drilling induced fractures was measured to determine the maximum horizontal stress azimuth. Also, an analysis of shear wave anisotropy to predict stress anisotropy around the wellbore was performed to determine the direction of maximum horizontal stress. Our study shows how the detailed interpretation of borehole breakouts, drilling induced fractures, and sonic wave data can be used to reduce uncertainty and produce a better hydraulic fracturing design in the Utica Point Pleasant formations across the northern Appalachian Basin region of Ohio.

Modal and thermal analysis of Les Arches unstable rock column (Vercors massif, French Alps)

NASA Astrophysics Data System (ADS)

Bottelin, P.; Lévy, C.; Baillet, L.; Jongmans, D.; Guéguen, P.

2013-08-01

A potentially unstable limestone column (˜1000 m3, Vercors, French Alps) delineated by an open rear fracture was continuously instrumented with two three-component seismic sensors from mid-May 2009 to mid-October 2011. Spectral analysis of seismic noise allowed several resonance frequencies to be determined, ranging from 6 to 21 Hz. The frequency domain decomposition (FDD) technique was applied to the ambient vibrations recorded on the top of the rock column. Three vibration modes were identified at 6, 7.5 and 9 Hz, describing the upper part of corresponding modal shapes. Finite element numerical modelling of the column dynamic response confirmed that the first two modes are bending modes perpendicular and parallel to the fracture, respectively, while the third one corresponds to torsion. Seismic noise monitoring also pointed out that resonance frequencies fluctuate with time, under thermomechanical control. For seasonal cycles, changes in frequency are due to the variations of the bulk elastic properties with temperature. At daily scale, increase in fundamental frequency with temperature has been interpreted as resulting from the rock expansion inducing a closure of the rear fracture rock bridges, hence stiffening the contact between the column and the rock mass. Conversely, the rock contraction induces a fracture opening and a decrease in resonance frequency. In winter, when the temperature drops below 0 °C, a dramatic increase in fundamental frequency is observed from 6 Hz to more than 25 Hz, resulting from ice formation in the fracture. During spring, the resonance frequency gradually diminishes with ice melting to reach the value measured before winter.

Finite Element Analysis of Absorbable Sheath to Prevent Stress Shielding of Tibial Interlocking Intramedullary Nail

NASA Astrophysics Data System (ADS)

Dong, Yansheng; Wang, Yongqing; Dong, Limin; Jia, Peng; Lu, Fengcheng

2017-07-01

The nail with absorbable sheath (AS nail) is designed to reduce the stress shielding effect of internal fixation with interlocking intramedullary nail. In order to verify its feasibility, two types of the finite element models of internal fixation of tibia with the AS nail and the common metal nail (CM nail) are established using the Softwares of Mimics, Geomagic, SolidWorks and ANSYS according to the CT scanning data of tibia. The result of the finite element analysis shows that the AS nail has great advantages compared with the CM nail in reducing the stress shielding effect in different periods of fracture healing. The conclusion is that the AS nail can realize the static fixation to the dynamic fixation from the early to the later automatically to shorten the time of fracture healing, which also provides a new technique to the interlocking intramedullary nail.

On the breakup of tectonic plates by polar wandering

NASA Technical Reports Server (NTRS)

Liu, H. S.

1973-01-01

The observed boundary system of the major tectonic plates on the surface of the earth lends fresh support to the hypothesis of polar wandering. A dynamic model of the outer shell of the earth under the influence of polar shift is developed. The analysis falls into two parts: (1) deriving equations for stresses caused by polar shifting; and (2) deducing the pattern according to which the fracture of the shell can be expected. For stress analysis, the theory of plates and shells is the dominant feature of this model. In order to determine the fracture pattern, the existence of a mathematical theorem of plasticity is recalled: it says that the plastic flow begins to occur when a function in terms of the differences of the three principal stresses surpasses a certain critical value. By introducing the figures for the geophysical constants, this model generates stresses which could produce an initial break in the lithosphere.

Three-Dimensional Smoothed Particle Hydrodynamics Modeling of Preferential Flow Dynamics at Fracture Intersections on a High-Performance Computing Platform

NASA Astrophysics Data System (ADS)

Kordilla, J.; Bresinsky, L. T.

2017-12-01

The physical mechanisms that govern preferential flow dynamics in unsaturated fractured rock formations are complex and not well understood. Fracture intersections may act as an integrator of unsaturated flow, leading to temporal delay, intermittent flow and partitioning dynamics. In this work, a three-dimensional Pairwise-Force Smoothed Particle Hydrodynamics (PF-SPH) model is being applied in order to simulate gravity-driven multiphase flow at synthetic fracture intersections. SPH, as a meshless Lagrangian method, is particularly suitable for modeling deformable interfaces, such as three-phase contact dynamics of droplets, rivulets and free-surface films. The static and dynamic contact angle can be recognized as the most important parameter of gravity-driven free-surface flow. In SPH, surface tension and adhesion naturally emerges from the implemented pairwise fluid-fluid (sff) and solid-fluid (ssf) interaction force. The model was calibrated to a contact angle of 65°, which corresponds to the wetting properties of water on Poly(methyl methacrylate). The accuracy of the SPH simulations were validated against an analytical solution of Poiseuille flow between two parallel plates and against laboratory experiments. Using the SPH model, the complex flow mode transitions from droplet to rivulet flow of an experimental study were reproduced. Additionally, laboratory dimensionless scaling experiments of water droplets were successfully replicated in SPH. Finally, SPH simulations were used to investigate the partitioning dynamics of single droplets into synthetic horizontal fractures with various apertures (Δdf = 0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0 mm) and offsets (Δdoff = -1.5, -1.0, -0.5, 0, 1.0, 2.0, 3.0 mm). Fluid masses were measured in the domains R1, R2 and R3. The perfect conditions of ideally smooth surfaces and the SPH inherent advantage of particle tracking allow the recognition of small scale partitioning mechanisms and its importance for bulk flow behavior.

Metachronous bilateral subtrochanteric fracture of femur in an osteopetrotic bone: A case report with technical note.

PubMed

Kumar, Dharmendra; Jain, Vijay Kumar; Lal, Hitesh; Arya, Rajinder Kumar; Sinha, Skand

2012-12-01

Osteopetrosis is a rare inherited skeletal disorder characterized by increased density. The increased fragility of such dense bone results in a greater incidence of fractures, especially around hip and proximal femur. The surgical treatment of such fractures is difficult due to hard but brittle structure of bone. Herein we report a case of bilateral subtrochanteric fracture in an osteopetrotic patient. It was fixed using a dynamic hip screw with plate.

Dynamic and cyclic fatigue of engine-driven rotary nickel-titanium endodontic instruments.

PubMed

Haïkel, Y; Serfaty, R; Bateman, G; Senger, B; Allemann, C

1999-06-01

The absence of adequate testing standards for engine-driven nickel-titanium (NiTi) instruments necessitates further study of these instruments in all areas. This study examined three groups of engine-driven rotary NiTi endodontic instruments (Profile, Hero, and Quantec) and assessed the times for dynamic fracture in relation to the radius of curvature to which the instruments were subjected during preparation, with the instrument diameter determined by size and taper and the mode by which the fracture occurred. Ten instruments were randomly selected representing each size and taper for each group and for each radius of curvature: 600 in total. The instruments were rotated at 350 rpm and introduced into a tempered steel curve that simulated a canal. Two radii of curvature of canals were used: 5 and 10 mm. Time at fracture was noted for all files, and the fracture faces of each file were analyzed with scanning electron microscopy. Radius of curvature was found to be the most significant factor in determining the fatigue resistance of the files. As radius of curvature decreased, fracture time decreased. Taper of files was found to be significant in determining fracture time. As diameter increased, fracture time decreased. In all cases, fracture was found to be of a ductile nature, thus implicating cyclic fatigue as a major cause of failure and necessitating further analyses and setting of standards in this area.

Observed source parameters for dynamic rupture with non-uniform initial stressand relatively high fracture energy

USGS Publications Warehouse

Beeler, Nicholas M.; Kilgore, Brian D.; McGarr, Arthur F.; Fletcher, Jon Peter B.; Evans, John R.; Steven R. Baker,

2012-01-01

We have conducted dynamic rupture propagation experiments to establish the relations between in-source stress drop, fracture energy and the resulting particle velocity during slip of an unconfined 2 m long laboratory fault at normal stresses between 4 and 8 MPa. To produce high fracture energy in the source we use a rough fault that has a large slip weakening distance. An artifact of the high fracture energy is that the nucleation zone is large such that precursory slip reduces fault strength over a large fraction of the total fault length prior to dynamic rupture, making the initial stress non-uniform. Shear stress, particle velocity, fault slip and acceleration were recorded coseismically at multiple locations along strike and at small fault-normal distances. Stress drop increases weakly with normal stress. Average slip rate depends linearly on the fault strength loss and on static stress drop, both with a nonzero intercept. A minimum fracture energy of 1.8 J/m2 and a linear slip weakening distance of 33 μm are inferred from the intercept. The large slip weakening distance also affects the average slip rate which is reduced by in-source energy dissipation from on-fault fracture energy.Because of the low normal stress and small per event slip (∼86 μm), no thermal weakening such as melting or pore fluid pressurization occurs in these experiments. Despite the relatively high fracture energy, and the very low heat production, energy partitioning during these laboratory earthquakes is very similar to typical earthquake source properties. The product of fracture energy and fault area is larger than the radiated energy. Seismic efficiency is low at ∼2%. The ratio of apparent stress to static stress drop is ∼27%, consistent with measured overshoot. The fracture efficiency is ∼33%. The static and dynamic stress drops when extrapolated to crustal stresses are 2–7.3 MPa and in the range of typical earthquake stress drops. As the relatively high fracture energy reduces the slip velocities in these experiments, the extrapolated average particle velocities for crustal stresses are 0.18–0.6 m/s. That these experiments are consistent with typical earthquake source properties suggests, albeit indirectly, that thermal weakening mechanisms such as thermal pressurization and melting which lead to near complete stress drops, dominate earthquake source properties only for exceptional events unless crustal stresses are low.

The First Static and Dynamic Analysis of 3-D Printed Sintered Ceramics for Body Armor Applications

DTIC Science & Technology

2016-09-01

evaluate sintered alumina tiles produced by 3-D printing methodology. This report examines the static and quasi -static parameters (including density...Figures iv List of Tables iv Acknowledgments v 1. Introduction 1 2. Processing and Experimental Procedures 1 3. Results and Discussion 7 4...6 Fig. 8 Experimental setup for recording fracture .............................................7 Fig. 9 Rod projectile

A biomechanical comparison of conventional dynamic compression plates and string-of-pearls™ locking plates using cantilever bending in a canine Ilial fracture model.

PubMed

Kenzig, Allison R; Butler, James R; Priddy, Lauren B; Lacy, Kristen R; Elder, Steven H

2017-07-13

Fracture of the ilium is common orthopedic injury that often requires surgical stabilization in canine patients. Of the various methods of surgical stabilization available, application of a lateral bone plate to the ilium is the most common method of fixation. Many plating options are available, each having its own advantages and disadvantages. The purpose of this study was to evaluate the biomechanical properties of a 3.5 mm String-of-Pearls™ plate and a 3.5 mm dynamic compression plate in a cadaveric canine ilial fracture model. Hemipelves were tested in cantilever bending to failure and construct stiffness, yield load, displacement at yield, ultimate load, and mode of failure were compared. The mean stiffness of dynamic compression plate (116 ± 47 N/mm) and String-of-Pearls™ plate (107 ± 18 N/mm) constructs, mean yield load of dynamic compression plate (793 ± 333 N) and String-of-Pearls™ plate (860 ± 207 N) constructs, mean displacement at yield of dynamic compression plate (8.6 ± 3.0 mm) and String-of-Pearls™ plate (10.2 ± 2.8 mm) constructs, and ultimate load at failure of dynamic compression plate (936 ± 320 N) and String-of-Pearls™ plate (939 ± 191 N) constructs were not significantly different. No differences were found between constructs with respect to mode of failure. No significant biomechanical differences were found between String-of-Pearls™ plate and dynamic compression plate constructs in this simplified cadaveric canine ilial fracture model.

Biomechanical fatigue analysis of an advanced new carbon fiber/flax/epoxy plate for bone fracture repair using conventional fatigue tests and thermography.

PubMed

Bagheri, Zahra S; El Sawi, Ihab; Bougherara, Habiba; Zdero, Radovan

2014-07-01

The current study is part of an ongoing research program to develop an advanced new carbon fiber/flax/epoxy (CF/flax/epoxy) hybrid composite with a “sandwich structure” as a substitute for metallic materials for orthopedic long bone fracture plate applications. The purpose of this study was to assess the fatigue properties of this composite, since cyclic loading is one of the main types of loads carried by a femur fracture plate during normal daily activities. Conventional fatigue testing, thermographic analysis, and scanning electron microscopy (SEM) were used to analyze the damage progress that occurred during fatigue loading. Fatigue strength obtained using thermography analysis (51% of ultimate tensile strength) was confirmed using the conventional fatigue test (50–55% of ultimate tensile strength). The dynamic modulus (E⁎) was found to stay almost constant at 47 GPa versus the number of cycles, which can be related to the contribution of both flax/epoxy and CF/epoxy laminae to the stiffness of the composite. SEM images showed solid bonding at the CF/epoxy and flax/epoxy laminae, with a crack density of only 0.48% for the plate loaded for 2 million cycles. The current composite plate showed much higher fatigue strength than the main loads experienced by a typical patient during cyclic activities; thus, it may be a potential candidate for bone fracture plate applications. Moreover, the fatigue strength from thermographic analysis was the same as that obtained by the conventional fatigue tests, thus demonstrating its potential use as an alternate tool to rapidly evaluate fatigue strength of composite biomaterials.

Biomechanical fatigue analysis of an advanced new carbon fiber/flax/epoxy plate for bone fracture repair using conventional fatigue tests and thermography.

PubMed

Bagheri, Zahra S; El Sawi, Ihab; Bougherara, Habiba; Zdero, Radovan

2014-07-01

The current study is part of an ongoing research program to develop an advanced new carbon fiber/flax/epoxy (CF/flax/epoxy) hybrid composite with a "sandwich structure" as a substitute for metallic materials for orthopedic long bone fracture plate applications. The purpose of this study was to assess the fatigue properties of this composite, since cyclic loading is one of the main types of loads carried by a femur fracture plate during normal daily activities. Conventional fatigue testing, thermographic analysis, and scanning electron microscopy (SEM) were used to analyze the damage progress that occurred during fatigue loading. Fatigue strength obtained using thermography analysis (51% of ultimate tensile strength) was confirmed using the conventional fatigue test (50-55% of ultimate tensile strength). The dynamic modulus (E(⁎)) was found to stay almost constant at 47GPa versus the number of cycles, which can be related to the contribution of both flax/epoxy and CF/epoxy laminae to the stiffness of the composite. SEM images showed solid bonding at the CF/epoxy and flax/epoxy laminae, with a crack density of only 0.48% for the plate loaded for 2 million cycles. The current composite plate showed much higher fatigue strength than the main loads experienced by a typical patient during cyclic activities; thus, it may be a potential candidate for bone fracture plate applications. Moreover, the fatigue strength from thermographic analysis was the same as that obtained by the conventional fatigue tests, thus demonstrating its potential use as an alternate tool to rapidly evaluate fatigue strength of composite biomaterials. Copyright © 2014 Elsevier Ltd. All rights reserved.

Rate & Microstructure Influence on Fracture of WC-Co/Ni Composites

NASA Astrophysics Data System (ADS)

Lamberson, Leslie

2017-06-01

Tungsten carbide metal matrix composites contain ceramic grains of tungsten carbide within a binder of cobalt (Co) or nickel (Ni), allowing the material to have advantageous properties of both metals and ceramics including higher resistance to fracture than most structural ceramics, and higher resistance to permanent deformation than most engineering metals. Due to these performance advantages, WC composites are of interest in drilling, manufacturing tools, and defense penetrator applications, to name a few. Under quasi-static conditions, these hardmetals have been shown to generally exhibit an increase in fracture toughness with an increase in mean free path in the binder phase, and an increase in hardness and wear resistance with a decrease in WC grain size; yet relatively little is known in regards to their dynamic response. Here we present the fracture behavior of WC metal matrix composites under three extreme loading conditions: (1) a single-strike acceleration loading to characterize classical dynamic crack tip energetics via stress intensity factors (SIFs) (2) the impact fatigue, or sub-catastrophic repetitive strikes to failure, and (3) the dynamic crack interactions with normal impact over 1 km/s using an in-house combustionless two-stage light-gas gun. All investigations are conducted using ultra high-speed imaging with full-field measurements from digital image correlation (DIC), and post-mortem scanning electron microscopy. Preliminary results for (1) show that the dynamic fracture toughness increases by a factor of 1.22 to 1.65 over quasi-static, regardless of the binder or grain size investigated. Supported by the American Chemical Society Petroleum Research Fund No. 55860-ND10.

Fatigue Behavior of a Box-Type Welded Structure of Hydraulic Support Used in Coal Mine

PubMed Central

Zhao, Xiaohui; Li, Fuyong; Liu, Yu; Fan, Yanjun

2015-01-01

Hydraulic support is the main supporting equipment of the coal mining systems, and they are usually subjected to fatigue failure under the high dynamic load. The fracture positions are generally at welded joints where there is a serious stress concentration. In order to investigate and further improve the fatigue strength of hydraulic support, the present work first located the possible position where fatigue failure occurs through finite element analysis, and then fatigue tests were carried out on the different forms of welded joints for the dangerous parts. Finally, Fatigue strength-life (S-N) curves and fracture mechanism were studied. This research will provide a theoretical reference for the fatigue design of welded structures for hydraulic support. PMID:28793586

From brittle to ductile fracture in disordered materials.

PubMed

Picallo, Clara B; López, Juan M; Zapperi, Stefano; Alava, Mikko J

2010-10-08

We introduce a lattice model able to describe damage and yielding in heterogeneous materials ranging from brittle to ductile ones. Ductile fracture surfaces, obtained when the system breaks once the strain is completely localized, are shown to correspond to minimum energy surfaces. The similarity of the resulting fracture paths to the limits of brittle fracture or minimum energy surfaces is quantified. The model exhibits a smooth transition from brittleness to ductility. The dynamics of yielding exhibits avalanches with a power-law distribution.

Numerical stability analysis of two-dimensional solute transport along a discrete fracture in a porous rock matrix

NASA Astrophysics Data System (ADS)

Watanabe, Norihiro; Kolditz, Olaf

2015-07-01

This work reports numerical stability conditions in two-dimensional solute transport simulations including discrete fractures surrounded by an impermeable rock matrix. We use an advective-dispersive problem described in Tang et al. (1981) and examine the stability of the Crank-Nicolson Galerkin finite element method (CN-GFEM). The stability conditions are analyzed in terms of the spatial discretization length perpendicular to the fracture, the flow velocity, the diffusion coefficient, the matrix porosity, the fracture aperture, and the fracture longitudinal dispersivity. In addition, we verify applicability of the recently developed finite element method-flux corrected transport (FEM-FCT) method by Kuzmin () to suppress oscillations in the hybrid system, with a comparison to the commonly utilized Streamline Upwinding/Petrov-Galerkin (SUPG) method. Major findings of this study are (1) the mesh von Neumann number (Fo) ≥ 0.373 must be satisfied to avoid undershooting in the matrix, (2) in addition to an upper bound, the Courant number also has a lower bound in the fracture in cases of low dispersivity, and (3) the FEM-FCT method can effectively suppress the oscillations in both the fracture and the matrix. The results imply that, in cases of low dispersivity, prerefinement of a numerical mesh is not sufficient to avoid the instability in the hybrid system if a problem involves evolutionary flow fields and dynamic material parameters. Applying the FEM-FCT method to such problems is recommended if negative concentrations cannot be tolerated and computing time is not a strong issue.

The relative contributions of non-enzymatic glycation and cortical porosity on the fracture toughness of aging bone

PubMed Central

Tang, S.Y.; Vashishth, D.

2010-01-01

The risk of fracture increases with age due to the decline of bone mass and bone quality. One of the age-related changes in bone quality occurs through the formation and accumulation of advanced glycation end-products (AGEs) due to non-enzymatic glycation (NEG). However as a number of other changes including increased porosity occur with age and affect bone fragility, the relative contribution of AGEs on the fracture resistance of aging bone is unknown. Using a high-resolution nonlinear finite element model that incorporate cohesive elements and micro-computed tomography-based 3d meshes, we investigated the contribution of AGEs and cortical porosity on the fracture toughness of human bone. The results show that NEG caused a 52% reduction in propagation fracture toughness (R-curve slope). The combined effects of porosity and AGEs resulted in an 88% reduction in propagation toughness. These findings are consistent with previous experimental results. The model captured the age-related changes in the R-curve toughening by incorporating bone quantity and bone quality changes, and these simulations demonstrate the ability of the cohesive models to account for the irreversible dynamic crack growth processes affected by the changes in post-yield material behavior. By decoupling the matrix-level effects due to NEG and intracortical porosity, we are able to directly determine the effects of NEG on fracture toughness. The outcome of this study suggests that it may be important to include the age-related changes in the material level properties by using finite element analysis towards the prediction of fracture risk. PMID:21056419

CARES/PC - CERAMICS ANALYSIS AND RELIABILITY EVALUATION OF STRUCTURES

NASA Technical Reports Server (NTRS)

Szatmary, S. A.

1994-01-01

The beneficial properties of structural ceramics include their high-temperature strength, light weight, hardness, and corrosion and oxidation resistance. For advanced heat engines, ceramics have demonstrated functional abilities at temperatures well beyond the operational limits of metals. This is offset by the fact that ceramic materials tend to be brittle. When a load is applied, their lack of significant plastic deformation causes the material to crack at microscopic flaws, destroying the component. CARES/PC performs statistical analysis of data obtained from the fracture of simple, uniaxial tensile or flexural specimens and estimates the Weibull and Batdorf material parameters from this data. CARES/PC is a subset of the program CARES (COSMIC program number LEW-15168) which calculates the fast-fracture reliability or failure probability of ceramic components utilizing the Batdorf and Weibull models to describe the effects of multi-axial stress states on material strength. CARES additionally requires that the ceramic structure be modeled by a finite element program such as MSC/NASTRAN or ANSYS. The more limited CARES/PC does not perform fast-fracture reliability estimation of components. CARES/PC estimates ceramic material properties from uniaxial tensile or from three- and four-point bend bar data. In general, the parameters are obtained from the fracture stresses of many specimens (30 or more are recommended) whose geometry and loading configurations are held constant. Parameter estimation can be performed for single or multiple failure modes by using the least-squares analysis or the maximum likelihood method. Kolmogorov-Smirnov and Anderson-Darling goodness-of-fit tests measure the accuracy of the hypothesis that the fracture data comes from a population with a distribution specified by the estimated Weibull parameters. Ninety-percent confidence intervals on the Weibull parameters and the unbiased value of the shape parameter for complete samples are provided when the maximum likelihood technique is used. CARES/PC is written and compiled with the Microsoft FORTRAN v5.0 compiler using the VAX FORTRAN extensions and dynamic array allocation supported by this compiler for the IBM/MS-DOS or OS/2 operating systems. The dynamic array allocation routines allow the user to match the number of fracture sets and test specimens to the memory available. Machine requirements include IBM PC compatibles with optional math coprocessor. Program output is designed to fit 80-column format printers. Executables for both DOS and OS/2 are provided. CARES/PC is distributed on one 5.25 inch 360K MS-DOS format diskette in compressed format. The expansion tool PKUNZIP.EXE is supplied on the diskette. CARES/PC was developed in 1990. IBM PC and OS/2 are trademarks of International Business Machines. MS-DOS and MS OS/2 are trademarks of Microsoft Corporation. VAX is a trademark of Digital Equipment Corporation.

Distal tibial pilon fractures (AO/OTA type B, and C) treated with the external skeletal and minimal internal fixation method.

PubMed

Milenković, Sasa; Mitković, Milorad; Micić, Ivan; Mladenović, Desimir; Najman, Stevo; Trajanović, Miroslav; Manić, Miodrag; Mitković, Milan

2013-09-01

Distal tibial pilon fractures include extra-articular fractures of the tibial metaphysis and the more severe intra-articular tibial pilon fractures. There is no universal method for treating distal tibial pilon fractures. These fractures are treated by means of open reduction, internal fixation (ORIF) and external skeletal fixation. The high rate of soft-tissue complications associated with primary ORIF of pilon fractures led to the use of external skeletal fixation, with limited internal fixation as an alternative technique for definitive management. The aim of this study was to estimate efficacy of distal tibial pilon fratures treatment using the external skeletal and minimal internal fixation method. We presented a series of 31 operated patients with tibial pilon fractures. The patients were operated on using the method of external skeletal fixation with a minimal internal fixation. According to the AO/OTA classification, 17 patients had type B fracture and 14 patients type C fractures. The rigid external skeletal fixation was transformed into a dynamic external skeletal fixation 6 weeks post-surgery. This retrospective study involved 31 patients with tibial pilon fractures, average age 41.81 (from 21 to 60) years. The average follow-up was 21.86 (from 12 to 48) months. The percentage of union was 90.32%, nonunion 3.22% and malunion 6.45%. The mean to fracture union was 14 (range 12-20) weeks. There were 4 (12.19%) infections around the pins of the external skeletal fixator and one (3.22%) deep infections. The ankle joint arthrosis as a late complication appeared in 4 (12.90%) patients. All arthroses appeared in patients who had type C fractures. The final functional results based on the AOFAS score were excellent in 51.61%, good in 32.25%, average in 12.90% and bad in 3.22% of the patients. External skeletal fixation and minimal internal fixation of distal tibial pilon fractures is a good method for treating all types of inta-articular pilon fractures. In fractures types B and C dynamic external skeletal fixation allows early mobility in the ankle joint.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Parab, Niranjan D.; Hudspeth, Matthew; Claus, Ben

Granular materials are widely used to resist impact and blast. Under these dynamic loadings, the constituent particles in the granular system fracture. To study the fracture mechanisms in brittle particles under dynamic compressive loading, a high speed X-ray phase contrast imaging setup was synchronized with a Kolsky bar apparatus. Controlled compressive loading was applied on two contacting particles using the Kolsky bar apparatus and fracture process was captured using the high speed X-ray imaging setup. Five different particles were investigated: soda-lime glass, polycrystalline silica (silicon dioxide), polycrystalline silicon, barium titanate glass, and yttrium stabilized zirconia. For both soda lime glassmore » and polycrystalline silica particles, one of the particles fragmented explosively, thus breaking into many small pieces. For Silicon and barium titanate glass particles, a finite number of cracks were observed in one of the particles causing it to fracture. For yttrium stabilized zirconia particles, a single meridonial crack developed in one of the particles, breaking it into two parts.« less

Scale dependency of fracture energy and estimates thereof via dynamic rupture solutions with strong thermal weakening

NASA Astrophysics Data System (ADS)

Viesca, R. C.; Garagash, D.

2013-12-01

Seismological estimates of fracture energy show a scaling with the total slip of an earthquake [e.g., Abercrombie and Rice, GJI 2005]. Potential sources for this scale dependency are coseismic fault strength reductions that continue with increasing slip or an increasing amount of off-fault inelastic deformation with dynamic rupture propagation [e.g., Andrews, JGR 2005; Rice, JGR 2006]. Here, we investigate the former mechanism by solving for the slip dependence of fracture energy at the crack tip of a dynamically propagating rupture in which weakening takes place by strong reductions of friction via flash heating of asperity contacts and thermal pressurization of pore fluid leading to reductions in effective normal stress. Laboratory measurements of small characteristic slip evolution distances for friction (~10 μm at low slip rates of μm-mm/s, possibly up to 1 mm for slip rates near 0.1 m/s) [e.g., Marone and Kilgore, Nature 1993; Kohli et al., JGR 2011] imply that flash weakening of friction occurs at small slips before any significant thermal pressurization and may thus have a negligible contribution to the total fracture energy [Brantut and Rice, GRL 2011; Garagash, AGU 2011]. The subsequent manner of weakening under thermal pressurization (the dominant contributor to fracture energy) spans a range of behavior from the deformation of a finite-thickness shear zone in which diffusion is negligible (i.e., undrained-adiabatic) to that in which large-scale diffusion obscures the existence of a thin shear zone and thermal pressurization effectively occurs by the heating of slip on a plane. Separating the contribution of flash heating, the dynamic rupture solutions reduce to a problem with a single parameter, which is the ratio of the undrained-adiabatic slip-weakening distance (δc) to the characteristic slip-on-a-plane slip-weakening distance (L*). However, for any value of the parameter, there are two end-member scalings of the fracture energy: for small slip, the undrained-adiabatic behavior expectedly results in fracture energy scaling as G ~ δ^2, and for large slip (where TP approaches slip on a plane) we find that G ~ δ^(2/3). This last result is a slight correction to estimates made assuming a constant, kinematically imposed slip rate and slip-on-a-plane TP resulting in G ~ δ^(1/2) [Rice, JGR 2006]. We compile fracture energy estimates of both continental and subduction zone earthquakes. In doing so, we incorporate independent estimates of fault prestress to distinguish fracture energy G from the parameter G' defined by Abercrombie and Rice [2005], which represents the energetic quantity that is most directly inferred following seismological estimates of radiated energy, seismic moment and source radius. We find that the dynamic rupture solutions (which account for the variable manner of thermal pressurization and result in a self-consistent slip rate history) allow for a close match of the estimated fracture energy over several orders of total event slip, further supporting the proposed explanation that fracture energy scaling may largely be attributed to a fault strength that weakens gradually with slip, and additionally, the potential prevalence of thermal pressurization.

Analysis of the influence of dynamic phenomena on the fracture of a reinforced concrete beam under quasistatic loading (computations and experiment)

NASA Astrophysics Data System (ADS)

Bykov, A. A.; Matveenko, V. P.; Serovaev, G. S.; Shardakov, I. N.; Shestakov, A. P.

2015-07-01

Construction of numerical models which reliably describe the processes of crack formation and development in reinforced concrete permit estimating the bearing capacity and structural strength of any structural element without using expensive full-scale experiments. In the present paper, an example of four-point bending of a rectangular beam is used to consider a finite-element model of concrete fracture. The results obtained by quasistatic calculations and by solving the problem with inertia forces taken into account are compared. The kinetic energy contribution to the total mechanical energy of the system at the crack origination moment, which is greater than 30%, is estimated to justify the expediency of taking the inertia forces into account. The crack distribution characters obtained numerically and observed experimentally are compared. It is shown that the leading role in the evolution of the crack formation process is played by the mechanism of fracture of bonds between the reinforcing elements and the concrete.

The Development of Directional Decohesion Finite Elements for Multiscale Failure Analysis of Metallic Polycrystals

NASA Technical Reports Server (NTRS)

Saether, Erik; Glaessgen, Edward H.

2009-01-01

Atomistic simulations of intergranular fracture have indicated that grain-scale crack growth in polycrystalline metals can be direction dependent. At these material length scales, the atomic environment greatly influences the nature of intergranular crack propagation, through either brittle or ductile mechanisms, that are a function of adjacent grain orientation and direction of crack propagation. Methods have been developed to obtain cohesive zone models (CZM) directly from molecular dynamics simulations. These CZMs may be incorporated into decohesion finite element formulations to simulate fracture at larger length scales. A new directional decohesion element is presented that calculates the direction of Mode I opening and incorporates a material criterion for dislocation emission based on the local crystallographic environment to automatically select the CZM that best represents crack growth. The simulation of fracture in 2-D and 3-D aluminum polycrystals is used to illustrate the effect of parameterized CZMs and the effectiveness of directional decohesion finite elements.

Advances and trends in structures and dynamics; Proceedings of the Symposium, Washington, DC, October 22-25, 1984

NASA Technical Reports Server (NTRS)

Noor, A. K. (Editor); Hayduk, R. J. (Editor)

1985-01-01

Among the topics discussed are developments in structural engineering hardware and software, computation for fracture mechanics, trends in numerical analysis and parallel algorithms, mechanics of materials, advances in finite element methods, composite materials and structures, determinations of random motion and dynamic response, optimization theory, automotive tire modeling methods and contact problems, the damping and control of aircraft structures, and advanced structural applications. Specific topics covered include structural design expert systems, the evaluation of finite element system architectures, systolic arrays for finite element analyses, nonlinear finite element computations, hierarchical boundary elements, adaptive substructuring techniques in elastoplastic finite element analyses, automatic tracking of crack propagation, a theory of rate-dependent plasticity, the torsional stability of nonlinear eccentric structures, a computation method for fluid-structure interaction, the seismic analysis of three-dimensional soil-structure interaction, a stress analysis for a composite sandwich panel, toughness criterion identification for unidirectional composite laminates, the modeling of submerged cable dynamics, and damping synthesis for flexible spacecraft structures.

Low-intensity pulsed ultrasound stimulation promotes osteoblast differentiation through hedgehog signaling.

PubMed

Matsumoto, Kenichi; Shimo, Tsuyoshi; Kurio, Naito; Okui, Tatsuo; Ibaragi, Soichiro; Kunisada, Yuki; Obata, Kyoichi; Masui, Masanori; Pai, Pang; Horikiri, Yuu; Yamanaka, Nobuyuki; Takigawa, Masaharu; Sasaki, Akira

2018-06-01

Low-intensity pulsed ultrasound (LIPUS) has been used as an adjunct to fracture healing therapies, but the mechanisms underlying its action are not known. We reported that sonic hedgehog (SHH) signaling was activated in osteoblasts at the dynamic remodeling site of a bone fracture. Mechanical stimulation is a crucial factor in bone remodeling, and it is related to the primary cilia as a sensor of hedgehog signaling. Here we observed that LIPUS promoted callus formation in accord with Gli2-positive cells after 14 days at the mouse femur fractured site compared with a control group. An immunofluorescence analysis showed that the numbers of primary cilia and cilia/osterix double-positive osteoblasts were increased at the fracture site by LIPUS. LIPUS stimulated not only the number and the length of primary cilia, but also the levels of ciliated protein, Ift88 mRNA, and SHH, Gli1, and Gli2 in MC3T3-E1 cells. Further experiments revealed that LIPUS stimulated osteogenic differentiation in the presence of smoothened agonist (SAG) treatment. These results indicate that LIPUS stimulates osteogenic differentiation and the maturation of osteoblasts by a primary cilium-mediated activation of hedgehog signaling. © 2017 Wiley Periodicals, Inc.

Femur loading in feet-first fall experiments using an anthropomorphic test device.

PubMed

Thompson, Angela; Bertocci, Gina; Smalley, Craig

2018-03-31

Femur fractures are a common orthopedic injury in young children. Falls account for a large portion of accidental femur fractures in young children, but there is also a high prevalence of femur fractures in child abuse, with falls often provided as false histories. Objective information regarding fracture potential in short distance fall scenarios may aid in assessing whether a child's injuries are the result of abuse or an accidental fall. Knowledge of femur loading is the first step towards understanding likelihood of fracture in a fall. Characterize femur loading during feet-first free falls using a surrogate representing a 12-month-old child. The femur and hip joint of a surrogate representing a 12-month-old were modified to improve biofidelity and measure femur loading; 6-axis load cells were integrated into the proximal and distal femur. Femur modification was based upon CT imaging of cadaveric femurs in children 10-14 months of age. Using the modified 12-month-old surrogate, feet-first free falls from 69 cm and 119 cm heights onto padded carpet and linoleum were conducted to assess fall dynamics and determine femur loading. Femur compression, bending moment, shear and torsional moment were measured for each fall. Fall dynamics differed across fall heights, but did not substantially differ by impact surface type. Significant differences were found in all loading conditions across fall heights, while only compression and bending loads differed between carpet and linoleum surfaces. Maximum compression, bending, torsion and shear occurred in 119 cm falls and were 572 N, 23 N-m, 11 N-m and 281 N, respectively. Fall dynamics play an important role in the biomechanical assessment of falls. Fall height was found to influence both fall dynamics and femur loading, while impact surface affected only compression and bending in feet-first falls; fall dynamics did not differ across carpet and linoleum. Improved pediatric thresholds are necessary to predict likelihood of fracture, but morphologically accurate representation of the lower extremity, along with accurate characterization of loading in falls are a crucial first step. Copyright © 2018 Elsevier Ltd and Faculty of Forensic and Legal Medicine. All rights reserved.

A pore-scale study of fracture dynamics in rock using X-ray micro-CT under ambient freeze-thaw cycling.

PubMed

De Kock, Tim; Boone, Marijn A; De Schryver, Thomas; Van Stappen, Jeroen; Derluyn, Hannelore; Masschaele, Bert; De Schutter, Geert; Cnudde, Veerle

2015-03-03

Freeze-thaw cycling stresses many environments which include porous media such as soil, rock and concrete. Climate change can expose new regions and subject others to a changing freeze-thaw frequency. Therefore, understanding and predicting the effect of freeze-thaw cycles is important in environmental science, the built environment and cultural heritage preservation. In this paper, we explore the possibilities of state-of-the-art micro-CT in studying the pore scale dynamics related to freezing and thawing. The experiments show the development of a fracture network in a porous limestone when cooling to -9.7 °C, at which an exothermal temperature peak is a proxy for ice crystallization. The dynamics of the fracture network are visualized with a time frame of 80 s. Theoretical assumptions predict that crystallization in these experiments occurs in pores of 6-20.1 nm under transient conditions. Here, the crystallization-induced stress exceeds rock strength when the local crystal fraction in the pores is 4.3%. The location of fractures is strongly related to preferential water uptake paths and rock texture, which are visually identified. Laboratory, continuous X-ray micro-CT scanning opens new perspectives for the pore-scale study of ice crystallization in porous media as well as for environmental processes related to freeze-thaw fracturing.

Impact Damage and Strain Rate Effects for Toughened Epoxy Composite Structures

NASA Technical Reports Server (NTRS)

Chamis, Christos C.; Minnetyan, Levon

2006-01-01

Structural integrity of composite systems under dynamic impact loading is investigated herein. The GENOA virtual testing software environment is used to implement the effects of dynamic loading on fracture progression and damage tolerance. Combinations of graphite and glass fibers with a toughened epoxy matrix are investigated. The effect of a ceramic coating for the absorption of impact energy is also included. Impact and post impact simulations include verification and prediction of (1) Load and Impact Energy, (2) Impact Damage Size, (3) Maximum Impact Peak Load, (4) Residual Strength, (5) Maximum Displacement, (6) Contribution of Failure Modes to Failure Mechanisms, (7) Prediction of Impact Load Versus Time, and (8) Damage, and Fracture Pattern. A computer model is utilized for the assessment of structural response, progressive fracture, and defect/damage tolerance characteristics. Results show the damage progression sequence and the changes in the structural response characteristics due to dynamic impact. The fundamental premise of computational simulation is that the complete evaluation of composite fracture requires an assessment of ply and subply level damage/fracture processes as the structure is subjected to loads. Simulation results for the graphite/epoxy composite were compared with the impact and tension failure test data, correlation and verification was obtained that included: (1) impact energy, (2) damage size, (3) maximum impact peak load, (4) residual strength, (5) maximum displacement, and (6) failure mechanisms of the composite structure.

Comminution of solids caused by kinetic energy of high shear strain rate, with implications for impact, shock, and shale fracturing

PubMed Central

Bažant, Zdeněk P.; Caner, Ferhun C.

2013-01-01

Although there exists a vast literature on the dynamic comminution or fragmentation of rocks, concrete, metals, and ceramics, none of the known models suffices for macroscopic dynamic finite element analysis. This paper outlines the basic idea of the macroscopic model. Unlike static fracture, in which the driving force is the release of strain energy, here the essential idea is that the driving force of comminution under high-rate compression is the release of the local kinetic energy of shear strain rate. The density of this energy at strain rates >1,000/s is found to exceed the maximum possible strain energy density by orders of magnitude, making the strain energy irrelevant. It is shown that particle size is proportional to the −2/3 power of the shear strain rate and the 2/3 power of the interface fracture energy or interface shear stress, and that the comminution process is macroscopically equivalent to an apparent shear viscosity that is proportional (at constant interface stress) to the −1/3 power of this rate. A dimensionless indicator of the comminution intensity is formulated. The theory was inspired by noting that the local kinetic energy of shear strain rate plays a role analogous to the local kinetic energy of eddies in turbulent flow. PMID:24218624

Comparison of explicit finite element and mechanical simulation of the proximal femur during dynamic drop-tower testing.

PubMed

Ariza, O; Gilchrist, S; Widmer, R P; Guy, P; Ferguson, S J; Cripton, P A; Helgason, B

2015-01-21

Current screening techniques based on areal bone mineral density (aBMD) measurements are unable to identify the majority of people who sustain hip fractures. Biomechanical examination of such events may help determine what predisposes a hip to be susceptible to fracture. Recently, drop-tower simulations of in-vitro sideways falls have allowed the study of the mechanical response of the proximal human femur at realistic impact speeds. This technique has created an opportunity to validate explicit finite element (FE) models against dynamic test data. This study compared the outcomes of 15 human femoral specimens fractured using a drop tower with complementary specimen-specific explicit FE analysis. Correlation coefficient and root mean square error (RMSE) were found to be moderate for whole bone stiffness comparison (R(2)=0.3476 and 22.85% respectively). No correlation was found between experimentally and computationally predicted peak force, however, energy absorption comparison produced moderate correlation and RMSE (R(2)=0.4781 and 29.14% respectively). By comparing predicted strain maps to high speed video data we demonstrated the ability of the FE models to detect vulnerable portions of the bones. Based on our observations, we conclude that there exists a need to extend the current apparent level material models for bone to cover higher strain rates than previously tested experimentally. Copyright © 2014 Elsevier Ltd. All rights reserved.

Modeling the fracture of ice sheets on parallel computers.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Waisman, Haim; Bell, Robin; Keyes, David

2010-03-01

The objective of this project is to investigate the complex fracture of ice and understand its role within larger ice sheet simulations and global climate change. At the present time, ice fracture is not explicitly considered within ice sheet models due in part to large computational costs associated with the accurate modeling of this complex phenomena. However, fracture not only plays an extremely important role in regional behavior but also influences ice dynamics over much larger zones in ways that are currently not well understood. Dramatic illustrations of fracture-induced phenomena most notably include the recent collapse of ice shelves inmore » Antarctica (e.g. partial collapse of the Wilkins shelf in March of 2008 and the diminishing extent of the Larsen B shelf from 1998 to 2002). Other fracture examples include ice calving (fracture of icebergs) which is presently approximated in simplistic ways within ice sheet models, and the draining of supraglacial lakes through a complex network of cracks, a so called ice sheet plumbing system, that is believed to cause accelerated ice sheet flows due essentially to lubrication of the contact surface with the ground. These dramatic changes are emblematic of the ongoing change in the Earth's polar regions and highlight the important role of fracturing ice. To model ice fracture, a simulation capability will be designed centered around extended finite elements and solved by specialized multigrid methods on parallel computers. In addition, appropriate dynamic load balancing techniques will be employed to ensure an approximate equal amount of work for each processor.« less

Biomechanical Concepts for Fracture Fixation

PubMed Central

Bottlang, Michael; Schemitsch, Christine E.; Nauth, Aaron; Routt, Milton; Egol, Kenneth; Cook, Gillian E.; Schemitsch, Emil H.

2015-01-01

Application of the correct fixation construct is critical for fracture healing and long-term stability; however, it is a complex issue with numerous significant factors. This review describes a number of common fracture types, and evaluates their currently available fracture fixation constructs. In the setting of complex elbow instability, stable fixation or radial head replacement with an appropriately sized implant in conjunction with ligamentous repair is required to restore stability. For unstable sacral fractures, “standard” iliosacral screw fixation is not sufficient for fractures with vertical or multiplanar instabilities. Periprosthetic femur fractures, in particular Vancouver B1 fractures, have increased stability when using 90/90 fixation versus a single locking plate. Far Cortical Locking combines the concept of dynamization with locked plating in order to achieve superior healing of a distal femur fracture. Finally, there is no ideal construct for syndesmotic fracture stabilization; however, these fractures should be fixed using a device that allows for sufficient motion in the syndesmosis. In general, orthopaedic surgeons should select a fracture fixation construct that restores stability and promotes healing at the fracture site, while reducing the potential for fixation failure. PMID:26584263

A Microfluidics Study to Quantify the Impact of Microfracture Properties on Two-Phase Flow in Tight Rocks

NASA Astrophysics Data System (ADS)

Mehmani, A.; Kelly, S. A.; Torres-Verdin, C.; Balhoff, M.

2017-12-01

Microfluidics provides the opportunity for controlled experiments of immiscible fluid dynamics in quasi two-dimensional permeable media and allows their direct observation. We leverage microfluidics to investigate the impact of microfracture properties on water imbibition and drainage in a porous matrix. In the context of this work, microfractures are defined as apertures or preferential flow paths formed along planes of weakness, such as between two different rock fabrics. Patterns of pseudo-microfractures with orientations from parallel and perpendicular to fluid flow as well as variations in their connectivity were fabricated in glass micromodels; surface roughness of the micromodels was also varied utilizing a new method. Light microscopy and image analysis were used to quantify transient front advancement and trapped non-wetting phase saturation during imbibition as well as residual wetting phase saturation and its spatial distribution following drainage. Our experiments enable the assessment of quantitative relationships between fluid invasion rate and residual phase distributions as functions of microfracture network properties. Ultimately, the wide variety of microfluidic experiments performed in this study provide valuable insight into two-phase fluid dynamics in microfracture/matrix networks, the extent of fracture fluid invasion, and the saturation of trapped phases. In reservoir description, the geometries of subsurface fractures are often difficult to ascertain, but the distribution of rock types in a zone, from highly laminated to homogenous, can be reliably assessed with core data and well logs. Assuming that microcracks are functions of lamination planes (thin beds), then a priori predictions of the effect of microcracks on two-phase fluid flow across various geological conditions can possibly be upscaled via effective lamination properties. Such upscaling can significantly reduce the uncertainties associated with subsurface operations, including reservoir production, carbon storage and sequestration, and hazardous waste sequestration. A reliable prediction of capillary trapping, for instance, can determine the fracture fluid saturation subsequent to hydraulic fracturing of unconventional formations or the efficacy of water flooding in fractured reservoirs.

Fundamental considerations in dynamic fracture in nuclear materials

NASA Astrophysics Data System (ADS)

Cady, Carl; Eastwood, David; Bourne, Neil; Pei, Ruizhi; Mummery, Paul; Rau, Christoph

2017-06-01

The structural integrity of components used in nuclear power plants is the biggest concern of operators. A diverse range of materials, loading, prior histories and environmental conditions, leads to a complex operating environment. An experimental technique has been developed to characterize brittle materials and using linear elastic fracture mechanics, has given accurate measurements of the fracture toughness of materials. X-ray measurements were used to track the crack front as a function of loading parameters as well as determine the crack surface area as loads increased. This X-ray tomographic study of dynamic fracture in beryllium indicates the onset of damage within the target as load is increased. Similarly, measurements on nuclear graphite were conducted to evaluate the technique. This new, quantitative information obtained using the X-ray techniques has shown application in other materials. These materials exhibited a range of brittle and ductile responses that will test our modelling schemes for fracture. Further visualization of crack front advance and the correlated strain fields that are generated during the experiment for the two distinct deformation processes provide a vital step in validating new multiscale predicative modelling.

The Dynamic Tensile Behavior of Railway Wheel Steel at High Strain Rates

NASA Astrophysics Data System (ADS)

Jing, Lin; Han, Liangliang; Zhao, Longmao; Zhang, Ying

2016-11-01

The dynamic tensile tests on D1 railway wheel steel at high strain rates were conducted using a split Hopkinson tensile bar (SHTB) apparatus, compared to quasi-static tests. Three different types of specimens, which were machined from three different positions (i.e., the rim, web and hub) of a railway wheel, were prepared and examined. The rim specimens were checked to have a higher yield stress and ultimate tensile strength than those web and hub specimens under both quasi-static and dynamic loadings, and the railway wheel steel was demonstrated to be strain rate dependent in dynamic tension. The dynamic tensile fracture surfaces of all the wheel steel specimens are cup-cone-shaped morphology on a macroscopic scale and with the quasi-ductile fracture features on the microscopic scale.

Models for Ductile and Brittle Fracture for Two-Dimensional Wave Propagation Calculations

DTIC Science & Technology

1975-02-01

bainite , and retained austenlte. Fracture toughness testing by Hickey indicated that the United States Steel material was slightly tougher...CLASSIFICATION OF THIS PACEfWh«! Data Bnitnd) ’ ductile model). Rolled homogeneous steel XAR30 was characterized statically and dynamically...1145 aluminum, Armco iron, and XAR30 armor steel . The fracture models were found to function satisfactorily. It is concluded that the

Correlations of microstructure with dynamic and quasi-static fracture in a plain carbon steel

NASA Astrophysics Data System (ADS)

Couque, H.; Asaro, R. J.; Duffy, J.; Lee, S. H.

1988-09-01

An investigation was conducted into the effects of temperature, loading rate, and various micro-structural parameters on the initiation of plane strain fracture of a plain carbon AISI 1020 steel. Ferrite and prior austenite grain sizes were chosen as the principal microstructural features to be in-vestigated. The microstructural variations were accomplished by changing the austenitizing tempera-ture and by altering the cooling rate during normalization. Fracture toughness tests were conducted using precracked notched round bars loaded in tension to produce two stress intensity rates, viz., K 1 = 1 MPa √m s-1 and K 1 = 2 × 106 MPa √m s-1. In addition, Charpy impact tests along with quasistatic and high rate plasticity tests were conducted. The plasticity tests were done in torsion at shear strain rates ofoverline γ = 5.0 × 10^{ - 4} s^{ - 1 } and overline γ = 1.5 × 10^{3 } s^{ - 1} . Testing temperatures covered the range from -150 °C to 150 °C which encompassed fracture initiation modes involving transgranular cleavage to fully ductile fracture. Micromechanical processes involved in void and cleavage micro-crack formation were identified and quantified. For these purposes notched round tensile tests and subsequent metallographic observations along with TEM and SEM observations of the plane strain fracture toughness specimens were performed. The experimental results and quantitative micro-modeling using simple fracture models provide a means of correlating both quasistatic and dynamic fracture toughness with microstructures.

Dynamic Fracture in Brittle Materials

DTIC Science & Technology

2006-02-01

Stress analysis in oxidation problems usually follows the approach of introducing a known eigenstrain in the constitutive equation for elastic stress...deformation behavior in the oxide. The eigenstrain is assumed to be independent of time and position; it is the strain that would be observed in an...imaginary stress-free phase transformation. The total strain of the oxide is the sum of elastic strain and this eigenstrain . As shown in [13], the principal

Dynamic fracture of tantalum under extreme tensile stress.

PubMed

Albertazzi, Bruno; Ozaki, Norimasa; Zhakhovsky, Vasily; Faenov, Anatoly; Habara, Hideaki; Harmand, Marion; Hartley, Nicholas; Ilnitsky, Denis; Inogamov, Nail; Inubushi, Yuichi; Ishikawa, Tetsuya; Katayama, Tetsuo; Koyama, Takahisa; Koenig, Michel; Krygier, Andrew; Matsuoka, Takeshi; Matsuyama, Satoshi; McBride, Emma; Migdal, Kirill Petrovich; Morard, Guillaume; Ohashi, Haruhiko; Okuchi, Takuo; Pikuz, Tatiana; Purevjav, Narangoo; Sakata, Osami; Sano, Yasuhisa; Sato, Tomoko; Sekine, Toshimori; Seto, Yusuke; Takahashi, Kenjiro; Tanaka, Kazuo; Tange, Yoshinori; Togashi, Tadashi; Tono, Kensuke; Umeda, Yuhei; Vinci, Tommaso; Yabashi, Makina; Yabuuchi, Toshinori; Yamauchi, Kazuto; Yumoto, Hirokatsu; Kodama, Ryosuke

2017-06-01

The understanding of fracture phenomena of a material at extremely high strain rates is a key issue for a wide variety of scientific research ranging from applied science and technological developments to fundamental science such as laser-matter interaction and geology. Despite its interest, its study relies on a fine multiscale description, in between the atomic scale and macroscopic processes, so far only achievable by large-scale atomic simulations. Direct ultrafast real-time monitoring of dynamic fracture (spallation) at the atomic lattice scale with picosecond time resolution was beyond the reach of experimental techniques. We show that the coupling between a high-power optical laser pump pulse and a femtosecond x-ray probe pulse generated by an x-ray free electron laser allows detection of the lattice dynamics in a tantalum foil at an ultrahigh strain rate of [Formula: see text] ~2 × 10 8 to 3.5 × 10 8 s -1 . A maximal density drop of 8 to 10%, associated with the onset of spallation at a spall strength of ~17 GPa, was directly measured using x-ray diffraction. The experimental results of density evolution agree well with large-scale atomistic simulations of shock wave propagation and fracture of the sample. Our experimental technique opens a new pathway to the investigation of ultrahigh strain-rate phenomena in materials at the atomic scale, including high-speed crack dynamics and stress-induced solid-solid phase transitions.

Dynamic fracture of tantalum under extreme tensile stress

PubMed Central

Albertazzi, Bruno; Ozaki, Norimasa; Zhakhovsky, Vasily; Faenov, Anatoly; Habara, Hideaki; Harmand, Marion; Hartley, Nicholas; Ilnitsky, Denis; Inogamov, Nail; Inubushi, Yuichi; Ishikawa, Tetsuya; Katayama, Tetsuo; Koyama, Takahisa; Koenig, Michel; Krygier, Andrew; Matsuoka, Takeshi; Matsuyama, Satoshi; McBride, Emma; Migdal, Kirill Petrovich; Morard, Guillaume; Ohashi, Haruhiko; Okuchi, Takuo; Pikuz, Tatiana; Purevjav, Narangoo; Sakata, Osami; Sano, Yasuhisa; Sato, Tomoko; Sekine, Toshimori; Seto, Yusuke; Takahashi, Kenjiro; Tanaka, Kazuo; Tange, Yoshinori; Togashi, Tadashi; Tono, Kensuke; Umeda, Yuhei; Vinci, Tommaso; Yabashi, Makina; Yabuuchi, Toshinori; Yamauchi, Kazuto; Yumoto, Hirokatsu; Kodama, Ryosuke

2017-01-01

The understanding of fracture phenomena of a material at extremely high strain rates is a key issue for a wide variety of scientific research ranging from applied science and technological developments to fundamental science such as laser-matter interaction and geology. Despite its interest, its study relies on a fine multiscale description, in between the atomic scale and macroscopic processes, so far only achievable by large-scale atomic simulations. Direct ultrafast real-time monitoring of dynamic fracture (spallation) at the atomic lattice scale with picosecond time resolution was beyond the reach of experimental techniques. We show that the coupling between a high-power optical laser pump pulse and a femtosecond x-ray probe pulse generated by an x-ray free electron laser allows detection of the lattice dynamics in a tantalum foil at an ultrahigh strain rate of ε. ~2 × 108 to 3.5 × 108 s−1. A maximal density drop of 8 to 10%, associated with the onset of spallation at a spall strength of ~17 GPa, was directly measured using x-ray diffraction. The experimental results of density evolution agree well with large-scale atomistic simulations of shock wave propagation and fracture of the sample. Our experimental technique opens a new pathway to the investigation of ultrahigh strain-rate phenomena in materials at the atomic scale, including high-speed crack dynamics and stress-induced solid-solid phase transitions. PMID:28630909

Biomechanical Comparison of Superior Versus Anterior Plate Position for Fixation of Distal Clavicular Fractures: A New Model.

PubMed

Wilkerson, James; Paryavi, Ebrahim; Kim, Hyunchul; Murthi, Anand; Pensy, Raymond A

2017-01-01

Although most clavicular fractures are amenable to nonoperative management, metadiaphyseal fractures are considerably more complex, with rates of suboptimal healing as high as 75% when treated nonoperatively. The poor results are ascribed to the deforming forces on the distal clavicle from the surrounding muscles and the weight of the arm. It recently has been noted that some operative fixations of these fractures are also failing when a standard superiorly placed plate is used. We hypothesized that anterior plating, when compared with superior plating, improves the strength and durability of the construct by redirecting the axis of the major deforming force across rather than in line with the screws of the construct. Six pairs of fresh-frozen human cadaveric clavicles with the scapula attached by the coracoclavicular ligaments were osteotomized just medial to the ligaments and plated with a standard 3.5-mm limited-contact dynamic compression plate. Specimens were potted and mounted on a materials testing system machine, preserving the anatomic relationship of the clavicle and scapula. They were then loaded through the coracoclavicular ligaments to mimic the weight of the arm pulling inferiorly. Each specimen was loaded with 375 N at 1 Hz for 2000 cycles. Sequential loading was then applied at 25-N intervals until failure. Statistical analysis was performed using a Wilcoxon signed-rank test. The superiorly plated specimens failed after fewer cycles and with lower force than the anteriorly plated specimens. The median number of cycles to failure was 2082 for anterior plated specimens and 50 for superiorly plated (P = 0.028). The median load to failure was 587.5 N in the anterior group and 375 N in the superior group (P = 0.035). The median stiffness was 46.13 N/mm for anterior and 40.45 N/mm for superior (P = 0.375) plates. Anteriorly plated distal third clavicular fractures have superior strength and durability compared with fractures plated superiorly when using a physician-contoured, 3.5-mm, limited-contact, dynamic compression plate in this cadaver model.

Predictions and Experimental Microstructural Characterization of High Strain Rate Failure Modes in Layered Aluminum Composites

NASA Astrophysics Data System (ADS)

Khanikar, Prasenjit

Different aluminum alloys can be combined, as composites, for tailored dynamic applications. Most investigations pertaining to metallic alloy layered composites, however, have been based on quasi-static approaches. The dynamic failure of layered metallic composites, therefore, needs to be characterized in terms of strength, toughness, and fracture response. A dislocation-density based crystalline plasticity formulation, finite-element techniques, rational crystallographic orientation relations and a new fracture methodology were used to predict the failure modes associated with the high strain rate behavior of aluminum layered composites. Two alloy layers, a high strength alloy, aluminum 2195, and an aluminum alloy 2139, with high toughness, were modeled with representative microstructures that included precipitates, dispersed particles, and different grain boundary (GB) distributions. The new fracture methodology, based on an overlap method and phantom nodes, is used with a fracture criteria specialized for fracture on different cleavage planes. One of the objectives of this investigation, therefore, was to determine the optimal arrangements of the 2139 and 2195 aluminum alloys for a metallic layered composite that would combine strength, toughness and fracture resistance for high strain-rate applications. Different layer arrangements were investigated for high strain-rate applications, and the optimal arrangement was with the high toughness 2139 layer on the bottom, which provided extensive shear strain localization, and the high strength 2195 layer on the top for high strength resistance. The layer thickness of the bottom high toughness layer also affected the bending behavior of the roll-boned interface and the potential delamination of the layers. Shear strain localization, dynamic cracking and delamination were the mutually competing failure mechanisms for the layered metallic composite, and control of these failure modes can be optimized for high strain-rate applications. The second major objective of this investigation was the use of recently developed dynamic fracture formulations to model and analyze the crack nucleation and propagation of aluminum layered composites subjected to high strain rate loading conditions and how microstructural effects, such as precipitates, dispersed particles, and GB orientations affect failure evolution. This dynamic fracture approach is used to investigate crack nucleation and crack growth as a function of the different microstructural characteristics of each alloy in layered composites with and without pre-existing cracks. The zigzag nature of the crack paths were mainly due to the microstructural features, such as precipitates and dispersed particles distributions and orientations ahead of the crack front, and it underscored the capabilities of the fracture methodology. The evolution of dislocation density and the formation of localized shear slip contributed to the blunting of the propagating crack. Extensive geometrical and thermal softening due to the localized plastic slip also affected crack path orientations and directions. These softening mechanisms resulted in the switching of cleavage planes, which affected crack path orientations. Interface delamination can also have an important role in the failure and toughening of the layered composites. Different scenarios of delamination were investigated, such as planar crack growth and crack penetration into the layers. The presence of brittle surface oxide platelets in the interface region also significantly influenced the interface delamination process. Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) and Optical Microscopy (OM) characterization provided further physical insights and validation of the predictive capabilities. The inherent microstructural features of each alloy play a significant role in the dynamic fracture, shear strain localization, and interface delamination of the layered metallic composite. These microstructural features, such as precipitates, dispersed particles, and GB orientations and distributions can be optimized for desired behavior of metallic composites.

Spartan Release Engagement Mechanism (REM) stress and fracture analysis

NASA Technical Reports Server (NTRS)

Marlowe, D. S.; West, E. J.

1984-01-01

The revised stress and fracture analysis of the Spartan REM hardware for current load conditions and mass properties is presented. The stress analysis was performed using a NASTRAN math model of the Spartan REM adapter, base, and payload. Appendix A contains the material properties, loads, and stress analysis of the hardware. The computer output and model description are in Appendix B. Factors of safety used in the stress analysis were 1.4 on tested items and 2.0 on all other items. Fracture analysis of the items considered fracture critical was accomplished using the MSFC Crack Growth Analysis code. Loads and stresses were obtaind from the stress analysis. The fracture analysis notes are located in Appendix A and the computer output in Appendix B. All items analyzed met design and fracture criteria.

The Effect of Geographic Proximity to Unconventional Oil and Gas Development on Public Support for Hydraulic Fracturing.

PubMed

Boudet, Hilary S; Zanocco, Chad M; Howe, Peter D; Clarke, Christopher E

2018-04-10

With the rapid growth of unconventional oil and natural gas development transforming the U.S. economic and physical landscape, social scientists have increasingly explored the spatial dynamics of public support for this issue-that is, whether people closer to unconventional oil and gas development are more supportive or more opposed. While theoretical frameworks like construal-level theory and the "Not in My Backyard" (or NIMBY) moniker provide insight into these spatial dynamics, case studies in specific locations experiencing energy development reveal substantial variation in community responses. Larger-scale studies exploring the link between proximity and support have been hampered by data quality and availability. We draw on a unique data set that includes geo-coded data from national surveys (nine waves; n = 19,098) and high-resolution well location data to explore the relationship between proximity and both familiarity with and support for hydraulic fracturing. We use two different measures of proximity-respondent distance to the nearest well and the density of wells within a certain radius of the respondent's location. We find that both types of proximity to new development are linked to more familiarity with hydraulic fracturing, even after controlling for various individual and contextual factors, but only distance-based proximity is linked to more support for the practice. When significant, these relationships are similar to or exceed the effects of race, income, gender, and age. We discuss the implications of these findings for effective risk communication as well as the importance of incorporating spatial analysis into public opinion research on perceptions of energy development. © 2018 Society for Risk Analysis.

Cyclic fatigue resistance of R-Pilot, WaveOne Gold Glider, and ProGlider glide path instruments.

PubMed

Keskin, Cangül; İnan, Uğur; Demiral, Murat; Keleş, Ali

2018-02-17

The aim of the present study was to compare the cyclic fatigue resistance of R-Pilot (VDW; Munich, Germany) with ProGlider (Denstply Sirona; Ballaigues, Switzerland) and WaveOne Gold Glider (Denstply Sirona; Ballaigues, Switzerland) glide path instruments. R-Pilot, ProGlider, and WaveOne Gold Glider instruments were collected (n = 15) and tested in a dynamic cyclic fatigue test device, which has an artificial canal with 60° angle of curvature and a 5-mm radius of curvature. All instruments were operated until fracture occurred, and both time to fracture (TF) and the lengths of the fractured fragments were recorded. Mean and standard deviations of TF and fragment length were calculated for each reciprocating system. TF data and fractured fragment length data were subjected to one-way ANOVA and post-hoc Tukey tests (P < 0.05). Also a Weibull analysis was performed on TF data. The cyclic fatigue resistance values of the WaveOne Gold Glider and R-Pilot were significantly higher than those of the ProGlider (P < 0.05), with no significant difference between them (P > 0.05). Weibull analysis revealed that WaveOne Gold Glider showed the highest predicted TF value for 99% survival rate, which was followed by R-Pilot and ProGlider. Regarding the length of the fractured tips, there were no significant differences among the instruments (P > 0.05). The reciprocating WaveOne Gold Glider and R-Pilot instruments had significantly higher cyclic fatigue resistance than rotary ProGlider instruments. This study reported that novel reciprocating glide path instruments exhibited higher cyclic fatigue resistance than rotating glide path instrument.

Quantitative Characterisation of Fracturing Around the Damage Zone Surrounding New Zealand's Alpine Fault Using X-ray CT Scans of DFDP-1 Core

NASA Astrophysics Data System (ADS)

Williams, J. N.; Toy, V.; Massiot, C.; Mcnamara, D. D.; Wang, T.

2015-12-01

X-ray computer tomography (CT) scans of core recovered from the first phase of the Deep Fault Drilling Project (DFDP-1) through the Alpine Fault provide an excellent opportunity to analyse brittle deformation around the fault. In particular, assessment can be made of the heavily fractured protolith constituting the damage zone. Damage zone structures are divided into two types that result from two distinct processes: (1) "off fault damage" formed by stress changes induced by the passage of a seismic rupture and (2) "off fault deformation" that represent structures, which accommodate strain around the fault that was not localised on the principal slip zone (PSZ). The distribution of these damage zones structures within CT scans of the recovered core was measured along a scanline parallel to the core axis and assessed using a weighted moving average technique to account for orientation bias. The results of this analysis reveal that within the part of the fault rocks sampled by DFDP-1 there is no increase in density of these structures towards the PSZ. This is in agreement with independent analysis using Borehole Televiewer Data of the DFDP-1B borehole. Instead, we consider the density of these structures to be controlled to the first order by lithology, which modulates the mechanical properties of the fault rocks such as its frictional strength and cohesion. Comparisons of fracture density to p-wave velocities obtained from wireline logs indicate they are independent of each other, therefore, for the cores sampled in this study fractures impart no influence on the elastic properties of the rock. This is consistent with the observation from core that the majority of fractures are cemented. We consider how this might influence future rupture dynamics.

Fatigue Analysis of the Piston Rod in a Kaplan Turbine Based on Crack Propagation under Unsteady Hydraulic Loads

NASA Astrophysics Data System (ADS)

Liu, X.; Y Luo, Y.; Wang, Z. W.

2014-03-01

As an important component of the blade-control system in Kaplan turbines, piston rods are subjected to fluctuating forces transferred by the turbines blades from hydraulic pressure oscillations. Damage due to unsteady hydraulic loads might generate unexpected down time and high repair cost. In one running hydropower plant, the fracture failure of the piston rod was found twice at the same location. With the transient dynamic analysis, the retainer ring structure of the piston rod existed a relative high stress concentration. This predicted position of the stress concentration agreed well with the actual fracture position in the plant. However, the local strain approach was not able to explain why this position broke frequently. Since traditional structural fatigue analyses use a local stress strain approach to assess structural integrity, do not consider the effect of flaws which can significantly degrade structural life. Using linear elastic fracture mechanism (LEFM) approaches that include the effect of flaws is becoming common practice in many industries. In this research, a case involving a small semi-ellipse crack was taken into account at the stress concentration area, crack growth progress was calculated by FEM. The relationship between crack length and remaining life was obtained. The crack propagation path approximately agreed with the actual fracture section. The results showed that presence of the crack had significantly changed the local stress and strain distributions of the piston rod compared with non-flaw assumption.

Determination of Fracture Patterns in Glass and Glassy Polymers.

PubMed

Baca, Allison C; Thornton, John I; Tulleners, Frederic A

2016-01-01

The study of fractures of glass, glassy-type materials, and plastic has long been of interest to the forensic community. The focus of this interest has been the use of glass and polymer fractures to associate items of evidence under the assumption that each fracture is different. Generally, it is well-accepted that deviations exist; however, the emphasis has been on classifying and predicting fracture rather than determining that each fracture is different. This study documented the controlled fracture patterns of 60 glass panes, 60 glass bottles, and 60 plastic tail light lens covers using both dynamic impact and static pressure methods under closely controlled conditions. Each pattern was intercompared, and based on the limited specimens tested in this study, the results illustrate that the fracture patterns are different. Further repetitive studies, under controlled conditions, will be needed to provide more statistical significance to the theory that each fracture forms a nonreproducible fracture pattern. © 2015 American Academy of Forensic Sciences.

Groundwater recharge dynamics in unsaturated fractured chalk: a case study

NASA Astrophysics Data System (ADS)

Cherubini, Claudia; Pastore, Nicola; Giasi, Concetta I.; Allegretti, Nicolaetta M.

2016-04-01

The heterogeneity of the unsaturated zone controls its hydraulic response to rainfall and the extent to which pollutants are delayed or attenuated before reaching groundwater. It plays therefore a very important role in the recharge of aquifers and the transfer of pollutants because of the presence of temporary storage zones and preferential flows. A better knowledge of the physical processes in the unsaturated zone would allow an improved assessment of the natural recharge in a heterogeneous aquifer and of its vulnerability to surface-applied pollution. The case study regards the role of the thick unsaturated zone of the Cretaceous chalk aquifer in Picardy (North of France) that controls the hydraulic response to rainfall. In the North Paris Basin, much of the recharge must pass through a regional chalk bed that is composed of a porous matrix with embedded fractures. Different types of conceptual models have been formulated to explain infiltration and recharge processes in the unsaturated fractured rock. The present study analyses the episodic recharge in fractured Chalk aquifer using the kinematic diffusion theory to predict water table fluctuation in response to rainfall. From an analysis of the data, there is the evidence of 1) a seasonal behavior characterized by a constant increase in the water level during the winter/spring period and a recession period, 2) a series of episodic behaviors during the summer/autumn. Kinematic diffusion models are useful for predict preferential fluxes and dynamic conditions. The presented approach conceptualizes the unsaturated flow as a combination of 1) diffusive flow refers to the idealized portion of the pore space of the medium within the flow rate is driven essentially by local gradient of potential; 2) preferential flow by which water moves across macroscopic distances through conduits of macropore length.

Assessment of structural, thermal, and mechanical properties of portlandite through molecular dynamics simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hajilar, Shahin, E-mail: shajilar@iastate.edu; Shafei, Behrouz, E-mail: shafei@iastate.edu

The structural, thermal, and mechanical properties of portlandite, the primary solid phase of ordinary hydrated cement paste, are investigated using the molecular dynamics method. To understand the effects of temperature on the structural properties of portlandite, the coefficients of thermal expansion of portlandite are determined in the current study and validated with what reported from the experimental tests. The atomic structure of portlandite equilibrated at various temperatures is then subjected to uniaxial tensile strains in the three orthogonal directions and the stress-strain curves are developed. Based on the obtained results, the effect of the direction of straining on the mechanicalmore » properties of portlandite is investigated in detail. Structural damage analysis is performed to reveal the failure mechanisms in different directions. The energies of the fractured surfaces are calculated in different directions and compared to those of the ideal surfaces available in the literature. The key mechanical properties, including tensile strength, Young's modulus, and fracture strain, are extracted from the stress-strain curves. The sensitivity of the obtained mechanical properties to temperature and strain rate is then explored in a systematic way. This leads to valuable information on how the structural and mechanical properties of portlandite are affected under various exposure conditions and loading rates. - Graphical abstract: Fracture mechanism of portlandite under uniaxial strain in the z-direction. - Highlights: • The structural, thermal, and mechanical properties of portlandite are investigated. • The coefficients of thermal expansion are determined. • The stress-strain relationships are studied in three orthogonal directions. • The effects of temperature and strain rate on mechanical properties are examined. • The plastic energy required for fracture in the crystalline structure is reported.« less

Dynamic toughness in elastic nonlinear viscous solids

NASA Astrophysics Data System (ADS)

Tang, S.; Guo, T. F.; Cheng, L.

2009-02-01

This work addresses the interrelationship among dissipative mechanisms—material separation in the fracture process zone (FPZ), nonelastic deformation in the surrounding background material and kinetic energy—and how they affect the macroscopic dynamic fracture toughness as well as the limiting crack speed in strain rate sensitive materials. To this end, a micromechanics-based model for void growth in a nonlinear viscous solid is incorporated into a microporous strip of cell elements that forms the FPZ. The latter is surrounded by background material described by conventional constitutive relations. In the first part of the paper, the background material is assumed to be purely elastic. Here, the computed dynamic fracture toughness is a convex function of crack velocity. In the second part, the background material as well as the FPZ are described by similar rate-sensitivity parameters. Voids grow in the strain rate strengthened FPZ as the crack velocity increases. Consequently, the work of separation increases. By contrast, the inelastic dissipation in the background material appears to be a concave function of crack velocity. At the lower crack velocity regime, where dissipation in the background material is dominant, toughness decreases as crack velocity increases. At high crack velocities, inelastic deformation enhanced by the inertial force can cause a sharp increase in toughness. Here, the computed toughness increases rapidly with crack velocity. There exist regimes where the toughness is a non-monotonic function of the crack velocity. Two length scales—the width of the FPZ and the ratio of the shear wave speed to the reference strain rate—can be shown to strongly affect the dynamic fracture toughness. Our computational simulations can predict experimental data for fracture toughness vs. crack velocity reported in several studies for amorphous polymeric materials.

Fracture toughness and crack growth of Zerodur

NASA Technical Reports Server (NTRS)

Viens, Michael J.

1990-01-01

The fracture toughness and crack growth parameters of Zerodur, a low expansion glass ceramic material, were determined. The fracture toughness was determined using indentation techniques and was found to be 0.9 MPa x m(sup 1/2). The crack growth parameters were determined using indented biaxial specimens subjected to static and dynamic loading in an aqueous environment. The crack growth parameters n and 1n(B) were found to be 30.7 and -6.837, respectively. The crack growth parameters were also determined using indented biaxial specimens subjected to dynamic loading in an ambient 50 percent relative humidity environment. The crack growth parameters n and 1n(B) at 50 percent relative humidity were found to be 59.3 and -17.51, respectively.

Molecular-dynamics Simulation-based Cohesive Zone Representation of Intergranular Fracture Processes in Aluminum

NASA Technical Reports Server (NTRS)

Yamakov, Vesselin I.; Saether, Erik; Phillips, Dawn R.; Glaessgen, Edward H.

2006-01-01

A traction-displacement relationship that may be embedded into a cohesive zone model for microscale problems of intergranular fracture is extracted from atomistic molecular-dynamics simulations. A molecular-dynamics model for crack propagation under steady-state conditions is developed to analyze intergranular fracture along a flat 99 [1 1 0] symmetric tilt grain boundary in aluminum. Under hydrostatic tensile load, the simulation reveals asymmetric crack propagation in the two opposite directions along the grain boundary. In one direction, the crack propagates in a brittle manner by cleavage with very little or no dislocation emission, and in the other direction, the propagation is ductile through the mechanism of deformation twinning. This behavior is consistent with the Rice criterion for cleavage vs. dislocation blunting transition at the crack tip. The preference for twinning to dislocation slip is in agreement with the predictions of the Tadmor and Hai criterion. A comparison with finite element calculations shows that while the stress field around the brittle crack tip follows the expected elastic solution for the given boundary conditions of the model, the stress field around the twinning crack tip has a strong plastic contribution. Through the definition of a Cohesive-Zone-Volume-Element an atomistic analog to a continuum cohesive zone model element - the results from the molecular-dynamics simulation are recast to obtain an average continuum traction-displacement relationship to represent cohesive zone interaction along a characteristic length of the grain boundary interface for the cases of ductile and brittle decohesion. Keywords: Crack-tip plasticity; Cohesive zone model; Grain boundary decohesion; Intergranular fracture; Molecular-dynamics simulation

Effect of Pulse Shape on Spall Strength

NASA Astrophysics Data System (ADS)

Smirnov, V. I.; Petrov, Yu. V.

2018-03-01

This paper analyzes the effect of the time-dependent shape of a load pulse on the spall strength of materials. Within the framework of a classical one-dimensional scheme, triangular pulses with signal rise and decay portions and with no signal rise portions considered. Calculation results for the threshold characteristics of fracture for rail steel are given. The possibility of optimization of fracture by selecting a loading time with the use of an introduced characteristic of dynamic strength (pulse fracture capacity) is demonstrated. The study is carried out using a structure-time fracture criterion.

Surgical correction of severe strabismus and enophthalmos secondary to zygomatic arch fracture in a dog.

PubMed

Konrade, Kricket A; Clode, Alison B; Michau, Tammy M; Roe, Simon C; Trumpatori, Brian J; Krug, William V; Gilger, Brian C

2009-01-01

A grossly displaced segmental zygomatic arch fracture with marked ventro-lateral deviation of the left globe was diagnosed in a 3-month-old male German Shepherd dog following a bite injury. The fracture was approached via a modified lateral orbitotomy and a fragment of the lacrimal bone removed. The rostral portion of the fracture was stabilized with a 5-hole 2.0 dynamic compression plate bone plate. The surgical correction achieved sufficient skeletal fixation for proper anatomical reduction of the globe and excellent cosmetic and functional outcomes.

Treatment dynamics of newly marketed drugs and implications for comparative effectiveness research.

PubMed

Gagne, Joshua J; Bykov, Katsiaryna; Willke, Richard J; Kahler, Kristijan H; Subedi, Prasun; Schneeweiss, Sebastian

2013-01-01

Clinicians and payers require rapid comparative effectiveness (CE) evidence generation to inform decisions for new drugs. We empirically assessed treatment dynamics of newly marked drugs and their implications for conducting CE research. We used claims data to evaluate five drug-outcome pairs: 1) raloxifene (vs. alendronate) and fracture; 2) risedronate (vs. alendronate) and fracture; 3) simvastatin plus ezetimibe fixed-dose combination (simvastatin + ezetimibe) (vs. simvastatin alone) and cardiovascular events; 4) rofecoxib (vs. nonselective nonsteroidal anti-inflammatory drugs [ns-NSAIDs]) and myocardial infarction; and 5) rofecoxib (vs. ns-NSAIDS) and gastrointestinal bleed. We examined utilization dynamics in the early marketing period, including evolving utilization patterns, outcome risk among those treated with new versus established drugs, and prior treatment patterns that may indicate treatment resistance or intolerance. We addressed these challenges by replicating active CE monitoring with sequential matched cohort analysis. Patients initiating new drugs were more likely to have used other drugs for the same indication in the past, but the majority of patients in all new drug cohorts were treatment naive (82.0% overall). Patients initiating rofecoxib had higher predicted baseline risk of gastrointestinal bleed than did patients initiating ns-NSAIDs. Patients initiating risedronate and alendronate had similar predicted baseline risks of fracture, while those initiating raloxifene and simvastatin + ezetimibe had lower risks of outcomes of interest relative to their comparators. Prospective monitoring yielded results consistent with expectation for each example. Many challenges to assessing the CE of new drugs are borne out in empirical data. Attention to these challenges can yield valid CE results. Copyright © 2013, International Society for Pharmacoeconomics and Outcomes Research (ISPOR). Published by Elsevier Inc.

The research on delayed fracture behavior of high-strength bolts in steel structure

NASA Astrophysics Data System (ADS)

Li, Guo dong; Li, Nan

2017-07-01

High-strength bolts have been widely used in power plants. However, the high-strength bolts which being employed in pumping station, steel structure and pipeline anti-whip structure have been found delayed fracture for many times in a power plant, this will affect the reliability of steel fracture and bring blow risk caused by falling objects. The high-strength bolt with delayed fracture was carried out fracture analysis, metallurgical analysis, chemical analysis, mechanical analysis, as well as bolts installation analysis, it can be comprehensively confirmed that the direct cause of high-strength bolts delayed fracture is the stress corrosion, and the root cause of high-strength bolts delayed fracture should be the improper installation at the initial and the imperfect routine anti-corrosion maintenance.

Characteristics of bone turnover in the long bone metaphysis fractured patients with normal or low Bone Mineral Density (BMD).

PubMed

Wölfl, Christoph; Schweppenhäuser, Daniela; Gühring, Thorsten; Takur, Caner; Höner, Bernd; Kneser, Ulrich; Grützner, Paul Alfred; Kolios, Leila

2014-01-01

The incidence of osteoporotic fractures increases as our population ages. Until now, the exact biochemical processes that occur during the healing of metaphyseal fractures remain unclear. Diagnostic instruments that allow a dynamic insight into the fracture healing process are as yet unavailable. In the present matched pair analysis, we study the time course of the osteoanabolic markers bone specific alkaline phosphatase (BAP) and transforming growth factor β1 (TGFβ1), as well as the osteocatabolic markers crosslinked C-telopeptide of type-I-collagen (β-CTX) and serum band 5 tartrate-resistant acid phosphatase (TRAP5b), during the healing of fractures that have a low level of bone mineral density (BMD) compared with fractures that have a normal BMD. Between March 2007 and February 2009, 30 patients aged older than 50 years who suffered a metaphyseal fracture were included in our study. BMDs were verified by dual energy Xray absorptiometry (DXEA) scans. The levels of BTMs were examined over an 8-week period. Osteoanabolic BAP levels in those with low levels of BMD were significantly different from the BAP levels in those with normal BMD. BAP levels in the former group increased constantly, whereas the latter group showed an initial strong decrease in BAP followed by slowly rising values. Osteocatabolic β-CTX increased in the bone of the normal BMD group constantly, whereas these levels decreased significantly in the bone of the group with low BMD from the first week. TRAP5b was significantly reduced in the low level BMD group. With this work, we conduct first insights into the molecular biology of the fracture healing process in patients with low levels of BMD that explains the mechanism of its fracture healing. The results may be one reason for the reduced healing qualities in bones with low BMD.

Dynamic Behavior and Optimization of Advanced Armor Ceramics: January-December 2011 Annual Report

DTIC Science & Technology

2015-03-01

however, under conventional methods of processing. To develop plasticity in ceramic like SiC, new fracture mechanisms and interesting behaviors need...and new fracture mechanisms . These improvements, in turn, could offer the potential for improved ballistic performance. Co-precipitation has been...experiments, the following deformed fragments were recovered for extensive SEM and TEM study.  A fracture mechanism map has been constructed in

Second hip fractures at Chiang Mai University Hospital.

PubMed

Wongtriratanachai, Prasit; Chiewchantanakit, Siripong; Vaseenon, Tanawat; Rojanasthien, Sattaya; Leerapun, Taninnit

2015-02-01

Hip fractures are a major public health problem. Patients who have suffered a hip fracture have an increased risk of a subsequent hip fracture. This study examines the incidence ofsecondhip fractures and attempts to identify underlying risk factors. To examine the incidence ofsecond hip fractures in osteoporotic patients at Chiang Mai University Hospital and to identify risk factors related to second hip fractures. A retrospective review was conducted of all low-energy mechanism hip fracture patients admitted during 2008 and 2009. Analysis of second hip fractures was conducted using survival analysis and logistic regression analysis. A total of 191 patients were observed for 391.68 person-years (mean 2.05 person-years per patient). Among that group, nine second hip fractures were identified, an overall incidence rate of 0.023 second fractures per person-year. Second hip fractures tended to occur within the first year following an initial hip fracture. There were no significant differences related to either gender or comorbid medical conditions. Logistic regression analysis revealed that increased risk of a second hip fracture was associated with age (highest between 80 to 89 years) and patients who were not treated for osteoporosis following their initial fracture. The incidence of second hip fractures at Chiang Mai University Hospital was 0.023 per person-year Careful follow-up of older patients, especially those over 80, and treatment ofosteoporosis with bisphosphonate plus vitamin D and calcium supplements was correlated with a reduction in the incidence of second hip fractures.

Electromagnetic Measurements in an Active Oilfield Environment

NASA Astrophysics Data System (ADS)

Weiss, C. J.; Aur, K. A.; Schramm, K. A.; Aldridge, D. F.; O'rourke, W. T.

2016-12-01

An important issue in oilfield development is mapping fracture distributions (either natural or man-made) controlling subsurface fluid flow. Although microseismic monitoring has been successful in constraining fracture system geometry and dynamics, accurate interpretation of microseismic data can be confounded by factors such as complex or poorly-understood velocity distributions, reactivation of previously unknown faults and fractures, and the problem of relating flow patterns to the cloud of hypocenter locations. For the particular problem of hydrocarbon production, the question of which fractures remain sufficiently "open" to allow economical fluid extraction is critical. As a supplement to microseismic analysis, we are investigating a novel electromagnetic (EM) technique for detecting and mapping hydraulic fractures in a hydrocarbon or geothermal reservoir by introducing an electrically conductive contrast agent into the fracturing fluid. In the field experiment presented here, a proppant-filled fracture zone is illuminated by a large engineered antenna consisting of an insulated current-carrying cable, grounded to `Earth' near the wellhead, and grounded at the other end to the steel-cased borehole near the target. Time-lapse measurements of horizontal electric field are subsequently made on Earth's surface to map the change in subsurface conductivity due to proppant emplacement. As predicted by 3D numerical modelling, observed differences in electric field values are very small. While these numbers are above the noise floor of electric field sensors, pervasive anthropogenic EM noise and regional-scale magnetotelluric signals make extraction of the differences from the observed time series especially difficult. We present field-acquired data on ambient EM noise in an active oilfield environment and demonstrate techniques for extracting the difference signal due to proppant emplacement. These techniques include classical spectral methods along with estimation of time-domain Green's function by regularized, linear least squares methods.

Complex Fluids and Hydraulic Fracturing.

PubMed

Barbati, Alexander C; Desroches, Jean; Robisson, Agathe; McKinley, Gareth H

2016-06-07

Nearly 70 years old, hydraulic fracturing is a core technique for stimulating hydrocarbon production in a majority of oil and gas reservoirs. Complex fluids are implemented in nearly every step of the fracturing process, most significantly to generate and sustain fractures and transport and distribute proppant particles during and following fluid injection. An extremely wide range of complex fluids are used: naturally occurring polysaccharide and synthetic polymer solutions, aqueous physical and chemical gels, organic gels, micellar surfactant solutions, emulsions, and foams. These fluids are loaded over a wide range of concentrations with particles of varying sizes and aspect ratios and are subjected to extreme mechanical and environmental conditions. We describe the settings of hydraulic fracturing (framed by geology), fracturing mechanics and physics, and the critical role that non-Newtonian fluid dynamics and complex fluids play in the hydraulic fracturing process.

Physical simulation study on the hydraulic fracture propagation of coalbed methane well

NASA Astrophysics Data System (ADS)

Wu, Caifang; Zhang, Xiaoyang; Wang, Meng; Zhou, Longgang; Jiang, Wei

2018-03-01

As the most widely used technique to modify reservoirs in the exploitation of unconventional natural gas, hydraulic fracturing could effectively raise the production of CBM wells. To study the propagation rules of hydraulic fractures, analyze the fracture morphology, and obtain the controlling factors, a physical simulation experiment was conducted with a tri-axial hydraulic fracturing test system. In this experiment, the fracturing sample - including the roof, the floor, and the surrounding rock - was prepared from coal and similar materials, and the whole fracturing process was monitored by an acoustic emission instrument. The results demonstrated that the number of hydraulic fractures in coal is considerably higher than that observed in other parts, and the fracture morphology was complex. Vertical fractures were interwoven with horizontal fractures, forming a connected network. With the injection of fracturing fluid, a new hydraulic fracture was produced and it extended along the preexisting fractures. The fracture propagation was a discontinuous, dynamic process. Furthermore, in-situ stress plays a key role in fracture propagation, causing the fractures to extend in a direction perpendicular to the minimum principal stress. To a certain extent, the different mechanical properties of the coal and the other components inhibited the vertical propagation of hydraulic fractures. Nonetheless, the vertical stress and the interfacial property are the major factors to influence the formation of the "T" shaped and "工" shaped fractures.

NASGRO(registered trademark): Fracture Mechanics and Fatigue Crack Growth Analysis Software

NASA Technical Reports Server (NTRS)

Forman, Royce; Shivakumar, V.; Mettu, Sambi; Beek, Joachim; Williams, Leonard; Yeh, Feng; McClung, Craig; Cardinal, Joe

2004-01-01

This viewgraph presentation describes NASGRO, which is a fracture mechanics and fatigue crack growth analysis software package that is used to reduce risk of fracture in Space Shuttles. The contents include: 1) Consequences of Fracture; 2) NASA Fracture Control Requirements; 3) NASGRO Reduces Risk; 4) NASGRO Use Inside NASA; 5) NASGRO Components: Crack Growth Module; 6) NASGRO Components:Material Property Module; 7) Typical NASGRO analysis: Crack growth or component life calculation; and 8) NASGRO Sample Application: Orbiter feedline flowliner crack analysis.

Molecular dynamics simulation of propagating cracks

NASA Technical Reports Server (NTRS)

Mullins, M.

1982-01-01

Steady state crack propagation is investigated numerically using a model consisting of 236 free atoms in two (010) planes of bcc alpha iron. The continuum region is modeled using the finite element method with 175 nodes and 288 elements. The model shows clear (010) plane fracture to the edge of the discrete region at moderate loads. Analysis of the results obtained indicates that models of this type can provide realistic simulation of steady state crack propagation.

Incorporating Scale-Dependent Fracture Stiffness for Improved Reservoir Performance Prediction

NASA Astrophysics Data System (ADS)

Crawford, B. R.; Tsenn, M. C.; Homburg, J. M.; Stehle, R. C.; Freysteinson, J. A.; Reese, W. C.

2017-12-01

We present a novel technique for predicting dynamic fracture network response to production-driven changes in effective stress, with the potential for optimizing depletion planning and improving recovery prediction in stress-sensitive naturally fractured reservoirs. A key component of the method involves laboratory geomechanics testing of single fractures in order to develop a unique scaling relationship between fracture normal stiffness and initial mechanical aperture. Details of the workflow are as follows: tensile, opening mode fractures are created in a variety of low matrix permeability rocks with initial, unstressed apertures in the micrometer to millimeter range, as determined from image analyses of X-ray CT scans; subsequent hydrostatic compression of these fractured samples with synchronous radial strain and flow measurement indicates that both mechanical and hydraulic aperture reduction varies linearly with the natural logarithm of effective normal stress; these stress-sensitive single-fracture laboratory observations are then upscaled to networks with fracture populations displaying frequency-length and length-aperture scaling laws commonly exhibited by natural fracture arrays; functional relationships between reservoir pressure reduction and fracture network porosity, compressibility and directional permeabilities as generated by such discrete fracture network modeling are then exported to the reservoir simulator for improved naturally fractured reservoir performance prediction.

Surgical repair of femoral fractures in New World camelids: five cases (1996-2003).

PubMed

Shoemaker, R W; Wilson, D G

2007-04-01

Five New World camelids were admitted to the Western College of Veterinary Medicine between 1996 and 2003 for evaluation of femoral fractures. There were three alpacas and two llamas. Four of the animals were female and three were less than 3 months of age. Fracture configurations consisted of distal physeal fractures (three), a comminuted diaphyseal/metaphyseal fracture, and a transverse diaphyseal fracture. Fractures were diagnosed with a combination of physical examination and radiographs in all cases. All five fractures were repaired with internal fixation and three animals were discharged from the hospital with fractures that healed. One cria underwent successful internal fixation but died from pulmonary oedema during recovery from anaesthesia. Postoperative complications were rare and limited to inadequate fracture stability in one alpaca and prolonged recovery to weight bearing in another. One llama with a comminuted metaphyseal fracture, repaired with a 4.5 mm dynamic compression plate, subsequently had catastrophic failure of the bone 17 days after surgery. Overall the clients were pleased with the outcome of discharged animals. Although femoral fractures are considered rare, they pose a unique opportunity for the large animal veterinarian to successfully achieve fracture union with the aid of internal fixation.

Gas Flow Tightly Coupled to Elastoplastic Geomechanics for Tight- and Shale-Gas Reservoirs: Material Failure and Enhanced Permeability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Jihoon; Moridis, George J.

We investigate coupled flow and geomechanics in gas production from extremely low permeability reservoirs such as tight and shale gas reservoirs, using dynamic porosity and permeability during numerical simulation. In particular, we take the intrinsic permeability as a step function of the status of material failure, and the permeability is updated every time step. We consider gas reservoirs with the vertical and horizontal primary fractures, employing the single and dynamic double porosity (dual continuum) models. We modify the multiple porosity constitutive relations for modeling the double porous continua for flow and geomechanics. The numerical results indicate that production of gasmore » causes redistribution of the effective stress fields, increasing the effective shear stress and resulting in plasticity. Shear failure occurs not only near the fracture tips but also away from the primary fractures, which indicates generation of secondary fractures. These secondary fractures increase the permeability significantly, and change the flow pattern, which in turn causes a change in distribution of geomechanical variables. From various numerical tests, we find that shear failure is enhanced by a large pressure drop at the production well, high Biot's coefficient, low frictional and dilation angles. Smaller spacing between the horizontal wells also contributes to faster secondary fracturing. When the dynamic double porosity model is used, we observe a faster evolution of the enhanced permeability areas than that obtained from the single porosity model, mainly due to a higher permeability of the fractures in the double porosity model. These complicated physics for stress sensitive reservoirs cannot properly be captured by the uncoupled or flow-only simulation, and thus tightly coupled flow and geomechanical models are highly recommended to accurately describe the reservoir behavior during gas production in tight and shale gas reservoirs and to smartly design production scenarios.« less

Gas Flow Tightly Coupled to Elastoplastic Geomechanics for Tight- and Shale-Gas Reservoirs: Material Failure and Enhanced Permeability

DOE PAGES

Kim, Jihoon; Moridis, George J.

2014-12-01

We investigate coupled flow and geomechanics in gas production from extremely low permeability reservoirs such as tight and shale gas reservoirs, using dynamic porosity and permeability during numerical simulation. In particular, we take the intrinsic permeability as a step function of the status of material failure, and the permeability is updated every time step. We consider gas reservoirs with the vertical and horizontal primary fractures, employing the single and dynamic double porosity (dual continuum) models. We modify the multiple porosity constitutive relations for modeling the double porous continua for flow and geomechanics. The numerical results indicate that production of gasmore » causes redistribution of the effective stress fields, increasing the effective shear stress and resulting in plasticity. Shear failure occurs not only near the fracture tips but also away from the primary fractures, which indicates generation of secondary fractures. These secondary fractures increase the permeability significantly, and change the flow pattern, which in turn causes a change in distribution of geomechanical variables. From various numerical tests, we find that shear failure is enhanced by a large pressure drop at the production well, high Biot's coefficient, low frictional and dilation angles. Smaller spacing between the horizontal wells also contributes to faster secondary fracturing. When the dynamic double porosity model is used, we observe a faster evolution of the enhanced permeability areas than that obtained from the single porosity model, mainly due to a higher permeability of the fractures in the double porosity model. These complicated physics for stress sensitive reservoirs cannot properly be captured by the uncoupled or flow-only simulation, and thus tightly coupled flow and geomechanical models are highly recommended to accurately describe the reservoir behavior during gas production in tight and shale gas reservoirs and to smartly design production scenarios.« less

Design and implementation of a novel mechanical testing system for cellular solids.

PubMed

Nazarian, Ara; Stauber, Martin; Müller, Ralph

2005-05-01

Cellular solids constitute an important class of engineering materials encompassing both man-made and natural constructs. Materials such as wood, cork, coral, and cancellous bone are examples of cellular solids. The structural analysis of cellular solid failure has been limited to 2D sections to illustrate global fracture patterns. Due to the inherent destructiveness of 2D methods, dynamic assessment of fracture progression has not been possible. Image-guided failure assessment (IGFA), a noninvasive technique to analyze 3D progressive bone failure, has been developed utilizing stepwise microcompression in combination with time-lapsed microcomputed tomographic imaging (microCT). This method allows for the assessment of fracture progression in the plastic region, where much of the structural deformation/energy absorption is encountered in a cellular solid. Therefore, the goal of this project was to design and fabricate a novel micromechanical testing system to validate the effectiveness of the stepwise IGFA technique compared to classical continuous mechanical testing, using a variety of engineered and natural cellular solids. In our analysis, we found stepwise compression to be a valid approach for IGFA with high precision and accuracy comparable to classical continuous testing. Therefore, this approach complements the conventional mechanical testing methods by providing visual insight into the failure propagation mechanisms of cellular solids. (c) 2005 Wiley Periodicals, Inc.

Processing, thermal and mechanical behaviour of PEI/MWCNT/carbon fiber nanostructured laminate

NASA Astrophysics Data System (ADS)

Santos, L. F. P.; Ribeiro, B.; Hein, L. R. O.; Botelho, E. C.; Costa, M. L.

2017-11-01

In this work, nanostructured composites of polyetherimide (PEI) with addition of functionalized multiwall carbon nanotube (MWCNT) were processed via solution mixing. After processing, these nanocomposites were evaluated by thermogravimetry (TGA), dynamic-mechanical analysis (DMA), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Subsequently, the nanocomposite was processed with carbon fibers by using hot compression molding. In order to evaluate interlaminar fracture strength, the processed laminates were mechanically evaluated by interlaminar shear strength (ILSS) and compression shear test (CST). Also, the Weibull distribution was employed to help in the statistical treatment of the data obtained from the mechanical tests. With regards to the fracture of the specimens, optical microscopy was used for the evaluation of the material. The addition of 1 wt% of MWCNT in the polymer matrix increased both thermal stability and viscoelastic behavior of the material. These improvements positively impacted the mechanical properties, generating a 16% and 58% increase in the short-beam strength and apparent interlaminar shear, respectively. In addition, it can be verified from morphological analysis of the fracture a change in the failure mode of the laminate by the incorporation of MWCNT. This behavior can be proven from CST test where there was no presence of the shear force by compression.

Faults and Fractures in the Subseafloor Environment tell a Different Story than They do at the Seafloor

NASA Astrophysics Data System (ADS)

Hayman, N. W.

2018-05-01

Planetary studies can benefit from a lesson learned in the research of Mid-Ocean Ridges, wherein the subsurface view of faulting and fracturing contrasts with surface observations, important for the dynamics and chemistry of hydrothermal systems.

Plate versus intramedullary fixation of two-part and multifragmentary displaced midshaft clavicle fractures - a long-term analysis.

PubMed

Chan, Gareth; Korac, Zelimir; Miletic, Matija; Vidovic, Dinko; Phadnis, Joideep; Bakota, Bore

2017-11-01

Surgical fixation of displaced midshaft clavicle fractures is predominantly achieved with intramedullary (IM) or plate fixation. Both techniques have potential pitfalls: plate fixation involves greater periosteal stripping and protuberance of the implant, whereas IM fixation may be associated with implant-related complications, such as migration or skin irritation, which may lead to further surgery for implant removal. The aim of this study was to compare these two methods in simple (Robinson 2b.1) and multifragmentary (Robinson 2b.2) displaced midshaft clavicle fractures. A total of 133 consecutive patients who underwent surgical fixation for a displaced midshaft clavicle fracture with either IM fixation using a 2.5-mm Kirschner wire or plate fixation using an 8-hole Dynamic Compression Plate (DCP) were retrospectively reviewed. Follow-up was a minimum of 1 year. The patients were allocated into two injury groups: displaced simple 2-part fractures (64 IM vs. 16 DCP) and displaced multifragmentary fractures (27 IM vs. 26 DCP). The major observed outcome measures were: infection rate, non-union rate, reoperation rate and postoperative range of motion (ROM). Rates of non-union for displaced 2-part fractures were 2/64 (3.13%) with IM fixation and 0/16 (0.00%) with plate fixation (p = 0.477). For displaced multifragmentary fractures, rates of non-union were 2/27 (7.41%) with IM fixation and 0/26 (0.00%) with plate fixation (p = 0.161). No significant difference was observed between the two fixation modalities in patient-reported time to regain ROM on the injured side for displaced 2-part fractures (p = 0.129) and displaced multifragmentary fractures (p = 0.070). Deep infection rate was zero (p = 1.000) overall in the study, and reoperation rate for IM and plate fixation, respectively, was 3.13% and 6.25% in the Robinson 2b.1 group (p = 0.559) and 7.41% and 7.69% in the Robinson 2b.2 group (p = 0.969). IM fixation of displaced midshaft clavicle fractures (Robinson 2b.1) has an equivalent non-union rate to plate fixation and similarly low complication and reoperation rates. For displaced midshaft multifragmentary clavicle fractures (Robinson 2b.2), the higher non-union rates observed with IM fixation leads us to recommend consideration of plate fixation for Robinson 2b.2 fractures. © 2017 Elsevier Ltd. All rights reserved.

Dynamic fracture of tantalum under extreme tensile stress

DOE PAGES

Albertazzi, Bruno; Ozaki, Norimasa; Zhakhovsky, Vasily; ...

2017-06-02

The understanding of fracture phenomena of a material at extremely high strain rates is a key issue for a wide variety of scientific research ranging from applied science and technological developments to fundamental science such as laser-matter interaction and geology. Despite its interest, its study relies on a fine multiscale description, in between the atomic scale and macroscopic processes, so far only achievable by large-scale atomic simulations. Direct ultrafast real-time monitoring of dynamic fracture (spallation) at the atomic lattice scale with picosecond time resolution was beyond the reach of experimental techniques. We show that the coupling between a high-power opticalmore » laser pump pulse and a femtosecond x-ray probe pulse generated by an x-ray free electron laser allows detection of the lattice dynamics in a tantalum foil at an ultrahigh strain rate of Embedded Image ~2 × 10 8 to 3.5 × 10 8 s -1. A maximal density drop of 8 to 10%, associated with the onset of spallation at a spall strength of ~17 GPa, was directly measured using x-ray diffraction. The experimental results of density evolution agree well with large-scale atomistic simulations of shock wave propagation and fracture of the sample. Our experimental technique opens a new pathway to the investigation of ultrahigh strain-rate phenomena in materials at the atomic scale, including high-speed crack dynamics and stress-induced solid-solid phase transitions.« less

Fractures of the growing mandible.

PubMed

Kushner, George M; Tiwana, Paul S

2009-03-01

Oral and maxillofacial surgeons must constantly weigh the risks of surgical intervention for pediatric mandible fractures against the wonderful healing capacity of children. The majority of pediatric mandibular fractures can be managed with closed techniques using short periods of maxillomandibular fixation or training elastics alone. Generally, the use of plate- and screw-type internal fixation is reserved for difficult fractures. This article details general and special considerations for this surgery including: craniofacial growth & development, surgical anatomy, epidemiology evaluation, various fractures, the role rigid internal fixation and the Risdon cable in pediatric maxillofacial trauma. It concludes with suggestions concerning long-term follow-up care in light of the mobility, insurance obstacles, and family dynamics facing the patient population.

Real frequency of ordinary and atypical sub-trochanteric and diaphyseal fractures in France based on X-rays and medical file analysis.

PubMed

Beaudouin-Bazire, Constance; Dalmas, Noémie; Bourgeois, Julie; Babinet, Antoine; Anract, Philippe; Chantelot, Christophe; Farizon, Frédéric; Chopin, Florence; Briot, Karine; Roux, Christian; Cortet, Bernard; Thomas, Thierry

2013-03-01

Atypical sub-trochanteric and femoral shaft fractures have been reported in patients treated with bisphosphonates. Their incidence has been determined from registered data analysis using international codes. Therefore, the aim of our study was to estimate the real frequency of typical and atypical sub-trochanteric or diaphyseal fractures, based on radiological and clinical data compared to registered data. In the registers of three large French University Hospitals, patients identified with International Classification of Diseases, 10th Revision diagnosis codes for sub-trochanteric or diaphyseal fracture were selected. Frequencies of ordinary and atypical fractures were calculated after both registered data, radiological and clinical files analysis. Among the 4592 patients hospitalized for a femoral fracture over 5 years, 574 were identified to have had a sub-trochanteric or femoral shaft fracture. 47.7% of the sub-trochanteric and femoral shaft fractures were misclassified, predominantly in the sub-trochanteric fractures subset. 12 patients had an atypical fracture (4% of the sub-trochanteric and femoral shaft fractures) and 11 fractures presented radiological features of atypical fractures, whereas clinical files analysis revealed they were pathological or traumatic fractures. Atypical fractures frequency is very low. Because of their low frequency and the unreliability of registered databases, the risk of atypical fractures is very difficult to estimate retrospectively. A prospective study is needed to clarify the risk factors associated with these fractures. Copyright © 2012 Société française de rhumatologie. Published by Elsevier SAS. All rights reserved.

Numerical investigations of rib fracture failure models in different dynamic loading conditions.

PubMed

Wang, Fang; Yang, Jikuang; Miller, Karol; Li, Guibing; Joldes, Grand R; Doyle, Barry; Wittek, Adam

2016-01-01

Rib fracture is one of the most common thoracic injuries in vehicle traffic accidents that can result in fatalities associated with seriously injured internal organs. A failure model is critical when modelling rib fracture to predict such injuries. Different rib failure models have been proposed in prediction of thorax injuries. However, the biofidelity of the fracture failure models when varying the loading conditions and the effects of a rib fracture failure model on prediction of thoracic injuries have been studied only to a limited extent. Therefore, this study aimed to investigate the effects of three rib failure models on prediction of thoracic injuries using a previously validated finite element model of the human thorax. The performance and biofidelity of each rib failure model were first evaluated by modelling rib responses to different loading conditions in two experimental configurations: (1) the three-point bending on the specimen taken from rib and (2) the anterior-posterior dynamic loading to an entire bony part of the rib. Furthermore, the simulation of the rib failure behaviour in the frontal impact to an entire thorax was conducted at varying velocities and the effects of the failure models were analysed with respect to the severity of rib cage damages. Simulation results demonstrated that the responses of the thorax model are similar to the general trends of the rib fracture responses reported in the experimental literature. However, they also indicated that the accuracy of the rib fracture prediction using a given failure model varies for different loading conditions.

Analysis of the Effects of Surface Pitting and Wear on the Vibrations of a Gear Transmission System

NASA Technical Reports Server (NTRS)

Choy, F. K.; Polyshchuk, V.; Zakrajsek, J. J.; Handschuh, R. F.; Townsend, D. P.

1994-01-01

A comprehensive procedure to simulate and analyze the vibrations in a gear transmission system with surface pitting, 'wear' and partial tooth fracture of the gear teeth is presented. An analytical model was developed where the effects of surface pitting and wear of the gear tooth were simulated by phase and magnitude changes in the gear mesh stiffness. Changes in the gear mesh stiffness were incorporated into each gear-shaft model during the global dynamic simulation of the system. The overall dynamics of the system were evaluated by solving for the transient dynamics of each shaft system simultaneously with the vibration of the gearbox structure. In order to reduce the number of degrees-of-freedom in the system, a modal synthesis procedure was used in the global transient dynamic analysis of the overall transmission system. An FFT procedure was used to transform the averaged time signal into the frequency domain for signature analysis. In addition, the Wigner-Ville distribution was also introduced to examine the gear vibration in the joint time frequency domain for vibration pattern recognition. Experimental results obtained from a gear fatigue test rig at NASA Lewis Research Center were used to evaluate the analytical model.

Field-gradient partitioning for fracture and frictional contact in the material point method: Field-gradient partitioning for fracture and frictional contact in the material point method [Fracture and frictional contact in material point method using damage-field gradients for velocity-field partitioning

DOE Office of Scientific and Technical Information (OSTI.GOV)

Homel, Michael A.; Herbold, Eric B.

Contact and fracture in the material point method require grid-scale enrichment or partitioning of material into distinct velocity fields to allow for displacement or velocity discontinuities at a material interface. We present a new method which a kernel-based damage field is constructed from the particle data. The gradient of this field is used to dynamically repartition the material into contact pairs at each node. Our approach avoids the need to construct and evolve explicit cracks or contact surfaces and is therefore well suited to problems involving complex 3-D fracture with crack branching and coalescence. A straightforward extension of this approachmore » permits frictional ‘self-contact’ between surfaces that are initially part of a single velocity field, enabling more accurate simulation of granular flow, porous compaction, fragmentation, and comminution of brittle materials. Finally, numerical simulations of self contact and dynamic crack propagation are presented to demonstrate the accuracy of the approach.« less

Field-gradient partitioning for fracture and frictional contact in the material point method: Field-gradient partitioning for fracture and frictional contact in the material point method [Fracture and frictional contact in material point method using damage-field gradients for velocity-field partitioning

DOE PAGES

Homel, Michael A.; Herbold, Eric B.

2016-08-15

Contact and fracture in the material point method require grid-scale enrichment or partitioning of material into distinct velocity fields to allow for displacement or velocity discontinuities at a material interface. We present a new method which a kernel-based damage field is constructed from the particle data. The gradient of this field is used to dynamically repartition the material into contact pairs at each node. Our approach avoids the need to construct and evolve explicit cracks or contact surfaces and is therefore well suited to problems involving complex 3-D fracture with crack branching and coalescence. A straightforward extension of this approachmore » permits frictional ‘self-contact’ between surfaces that are initially part of a single velocity field, enabling more accurate simulation of granular flow, porous compaction, fragmentation, and comminution of brittle materials. Finally, numerical simulations of self contact and dynamic crack propagation are presented to demonstrate the accuracy of the approach.« less

Mathematical modeling of the crack growth in linear elastic isotropic materials by conventional fracture mechanics approaches and by molecular dynamics method: crack propagation direction angle under mixed mode loading

NASA Astrophysics Data System (ADS)

Stepanova, Larisa; Bronnikov, Sergej

2018-03-01

The crack growth directional angles in the isotropic linear elastic plane with the central crack under mixed-mode loading conditions for the full range of the mixity parameter are found. Two fracture criteria of traditional linear fracture mechanics (maximum tangential stress and minimum strain energy density criteria) are used. Atomistic simulations of the central crack growth process in an infinite plane medium under mixed-mode loading using Large-scale Molecular Massively Parallel Simulator (LAMMPS), a classical molecular dynamics code, are performed. The inter-atomic potential used in this investigation is Embedded Atom Method (EAM) potential. The plane specimens with initial central crack were subjected to Mixed-Mode loadings. The simulation cell contains 400000 atoms. The crack propagation direction angles under different values of the mixity parameter in a wide range of values from pure tensile loading to pure shear loading in a wide diapason of temperatures (from 0.1 К to 800 К) are obtained and analyzed. It is shown that the crack propagation direction angles obtained by molecular dynamics method coincide with the crack propagation direction angles given by the multi-parameter fracture criteria based on the strain energy density and the multi-parameter description of the crack-tip fields.

Utilization of fractography in the evaluations of high temperature dynamic fatigue experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Breder, K.; Tennery, V.J.; Mroz, T.J.

1996-12-31

The slow crack growth properties of six structural ceramics were measured by dynamic fatigue in air and inert atmospheres over a range of elevated temperatures. The material response varied from no strength degradation as a function of stress and environment to significant strength degradation by slow crack growth (SCG) and by a combination of SCG and creep. The fractographic investigation showed that SCG was evidenced by growth of isolated cracks and often by an intergranular fracture mode, while creep was evidenced by accumulated damage such as void formation and opening of the microstructure at grain boundaries and triple junctions. Formore » the materials in which the strength was unaffected by the stress and environment, the fracture surfaces were essentially indistinguishable from the inert fracture surfaces.« less

Utilization of fractography in the evaluation of high temperature dynamic fatigue experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Breder, K.; Wereszczak, A.A.; Tennery, V.J.

1995-12-31

The slow crack growth properties of six structural ceramics were measured by dynamic fatigue in air and inert atmospheres over a range of elevated temperatures. The material response varied from no strength degradation as a function of stress and environment to significant strength degradation by slow crack growth (SCG) and by a combination of SCG and creep. The fractographic investigation showed that SCG was evidenced by growth of isolated cracks and often by an intergranular fracture mode, while creep was evidenced by accumulated damage such as void formation and opening of the microstructure at grain boundaries and triple junctions. Formore » the materials in which the strength was unaffected by the stress and environment, the fracture surfaces were essentially indistinguishable from the inert fracture surfaces.« less

A multi-scale experimental and simulation approach for fractured subsurface systems

NASA Astrophysics Data System (ADS)

Viswanathan, H. S.; Carey, J. W.; Frash, L.; Karra, S.; Hyman, J.; Kang, Q.; Rougier, E.; Srinivasan, G.

2017-12-01

Fractured systems play an important role in numerous subsurface applications including hydraulic fracturing, carbon sequestration, geothermal energy and underground nuclear test detection. Fractures that range in scale from microns to meters and their structure control the behavior of these systems which provide over 85% of our energy and 50% of US drinking water. Determining the key mechanisms in subsurface fractured systems has been impeded due to the lack of sophisticated experimental methods to measure fracture aperture and connectivity, multiphase permeability, and chemical exchange capacities at the high temperature, pressure, and stresses present in the subsurface. In this study, we developed and use microfluidic and triaxial core flood experiments required to reveal the fundamental dynamics of fracture-fluid interactions. In addition we have developed high fidelity fracture propagation and discrete fracture network flow models to simulate these fractured systems. We also have developed reduced order models of these fracture simulators in order to conduct uncertainty quantification for these systems. We demonstrate an integrated experimental/modeling approach that allows for a comprehensive characterization of fractured systems and develop models that can be used to optimize the reservoir operating conditions over a range of subsurface conditions.

High-Speed Observations of Dynamic Fracture Propagation in Solids and Their Implications in Earthquake Rupture Dynamics

NASA Astrophysics Data System (ADS)

Uenishi, Koji

2016-04-01

This contribution outlines our experimental observations of seismicity-related fast fracture (rupture) propagation in solids utilising high-speed analog and digital photography (maximum frame rate 1,000,000 frames per second) over the last two decades. Dynamic fracture may be triggered or initiated in the monolithic or layered seismic models by detonation of micro explosives, a projectile launched by a gun, laser pulses and electric discharge impulses, etc. First, we have investigated strike-slip rupture along planes of weakness in transparent photoelastic (birefringent) materials at a laboratory scale and shown (at that time) extraordinarily fast rupture propagation in a bi-material system and its possible effect on the generation of large strong motion in the limited narrow areas in the Kobe region on the occasion of the 1995 Hyogo-ken Nanbu, Japan, earthquake (Uenishi Ph.D. thesis 1997, Uenishi et al. BSSA 1999). In this series of experiments, we have also modelled shallow dip-slip earthquakes and indicated a possible origin of the asymmetric ground motion in the hanging and foot-walls. In the photoelastic photographs, we have found the unique dynamic wave interaction and generation of specific shear and interface waves numerically predicted by Uenishi and Madariaga (Eos 2005), and considered as a case study the seismic motion associated with the 2014 Nagano-ken Hokubu (Kamishiro Fault), Japan, dip-slip earthquake (Uenishi EFA 2015). Second, we have experimentally shown that even in a monolithic material, rupture speed may exceed the local shear wave speed if we employ hyperelasically behaving materials like natural rubber (balloons) (Uenishi Eos 2006, Uenishi ICF 2009, Uenishi Trans. JSME A 2012) but fracture in typical monolithic thin fluid films (e.g. soap bubbles, which may be treated as a solid material) propagates at an ordinary subsonic (sub-Rayleigh) speed (Uenishi et al. SSJ 2006). More recent investigation handling three-dimensional rupture propagation in monolithic brittle materials (e.g. ice spheres, concrete blocks in the field) has repeatedly indicated some specific (rather simple and smooth) fracture patterns even without the existence of distinct planes of weakness, which may help in understanding how the dynamic fracture propagation is controlled in three-dimensional brittle solids like Earth's crust (Uenishi et al. Con. Buld. Mat. 2010, 2014, JSME 2013).

Rock fracture skeleton tracing by image processing and quantitative analysis by geometry features

NASA Astrophysics Data System (ADS)

Liang, Yanjie

2016-06-01

In rock engineering, fracture measurement is important for many applications. This paper proposes a novel method for rock fracture skeleton tracing and analyzing. As for skeleton localizing, the curvilinear fractures are multiscale enhanced based on a Hessian matrix, after image binarization, and clutters are post-processed by image analysis; subsequently, the fracture skeleton is extracted via ridge detection combined with a distance transform and thinning algorithm, after which gap sewing and burrs removal repair the skeleton. In regard to skeleton analyzing, the roughness and distribution of a fracture network are respectively described by the fractal dimensions D s and D b; the intersection and fragmentation of a fracture network are respectively characterized by the average number of ends and junctions per fracture N average and the average length per fracture L average. Three rock fracture surfaces are analyzed for experiments and the results verify that both the fracture tracing accuracy and the analysis feasibility are satisfactory using the new method.

Distal tibial fractures and non-unions treated with shortened intramedullary nail.

PubMed

Megas, P; Zouboulis, P; Papadopoulos, A X; Karageorgos, A; Lambiris, E

2003-01-01

We reviewed 18 patients, 14 with acute fractures and four with non-union of the distal tibia, treated between 1990 and 2001 with a shortened, reamed intramedullary nail. The mean follow-up was 38 (8-144) months. The fractures united at an average of 16 (12-18) weeks and the non-unions at 20 (12-30) weeks. Two patients required nail dynamization. No limb shortening nor material failures were seen. All patients returned to normal daily activities. Although technically demanding, intramedullary nailing for distal tibial fractures and non-unions with a shortened nail represents a safe and reliable method.

Complementary hydro-mechanical coupled finite/discrete element and microseismic modelling to predict hydraulic fracture propagation in tight shale reservoirs

NASA Astrophysics Data System (ADS)

Profit, Matthew; Dutko, Martin; Yu, Jianguo; Cole, Sarah; Angus, Doug; Baird, Alan

2016-04-01

This paper presents a novel approach to predict the propagation of hydraulic fractures in tight shale reservoirs. Many hydraulic fracture modelling schemes assume that the fracture direction is pre-seeded in the problem domain discretisation. This is a severe limitation as the reservoir often contains large numbers of pre-existing fractures that strongly influence the direction of the propagating fracture. To circumvent these shortcomings, a new fracture modelling treatment is proposed where the introduction of discrete fracture surfaces is based on new and dynamically updated geometrical entities rather than the topology of the underlying spatial discretisation. Hydraulic fracturing is an inherently coupled engineering problem with interactions between fluid flow and fracturing when the stress state of the reservoir rock attains a failure criterion. This work follows a staggered hydro-mechanical coupled finite/discrete element approach to capture the key interplay between fluid pressure and fracture growth. In field practice, the fracture growth is hidden from the design engineer and microseismicity is often used to infer hydraulic fracture lengths and directions. Microseismic output can also be computed from changes of the effective stress in the geomechanical model and compared against field microseismicity. A number of hydraulic fracture numerical examples are presented to illustrate the new technology.

Laboratory testing on infiltration in single synthetic fractures

NASA Astrophysics Data System (ADS)

Cherubini, Claudia; Pastore, Nicola; Li, Jiawei; Giasi, Concetta I.; Li, Ling

2017-04-01

An understanding of infiltration phenomena in unsaturated rock fractures is extremely important in many branches of engineering for numerous reasons. Sectors such as the oil, gas and water industries are regularly interacting with water seepage through rock fractures, yet the understanding of the mechanics and behaviour associated with this sort of flow is still incomplete. An apparatus has been set up to test infiltration in single synthetic fractures in both dry and wet conditions. To simulate the two fracture planes, concrete fractures have been moulded from 3D printed fractures with varying geometrical configurations, in order to analyse the influence of aperture and roughness on infiltration. Water flows through the single fractures by means of a hydraulic system composed by an upstream and a downstream reservoir, the latter being subdivided into five equal sections in order to measure the flow rate in each part to detect zones of preferential flow. The fractures have been set at various angles of inclination to investigate the effect of this parameter on infiltration dynamics. The results obtained identified that altering certain fracture parameters and conditions produces relevant effects on the infiltration process through the fractures. The main variables influencing the formation of preferential flow are: the inclination angle of the fracture, the saturation level of the fracture and the mismatch wavelength of the fracture.

Three-dimensional fracture instability of a displacement-weakening planar interface under locally peaked nonuniform loading

NASA Astrophysics Data System (ADS)

Uenishi, Koji

2018-06-01

We consider stability of fracture on a three-dimensional planar interface subjected to a loading stress that is locally peaked spatially, the level of which increases quasi-statically in time. Similar to the earlier study on the two-dimensional case (Uenishi and Rice, 2003; Rice and Uenishi, 2010), as the loading stress increases, a crack, or a region of displacement discontinuity (opening gap in tension or slip for shear fracture), develops on the interface where the stress is presumed to decrease according to a displacement-weakening constitutive relation. Upon reaching the instability point at which no further quasi-static solution for the extension of the crack on the interface exists, dynamic fracture follows. For the investigation of this instability point, we employ a dimensional analysis as well as an energy approach that gives a Rayleigh-Ritz approximation for the dependence of crack size and maximum displacement discontinuity on the level and quadratic shape of the loading stress distribution. We show that, if the linear displacement-weakening law is applied and the crack may be assumed of an elliptical form, the critical crack size at instability is independent of the curvature of the loading stress distribution and it is of the same order for all two- and three-dimensional cases.

A smoothed particle hydrodynamics model for droplet and film flow on smooth and rough fracture surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kordilla, Jannes; Tartakovsky, Alexandre M.; Geyer, Tobias

2013-09-01

Flow on fracture surfaces has been identified by many authors as an important flow process in unsaturated fractured rock formations. Given the complexity of flow dynamics on such small scales, robust numerical methods have to be employed in order to capture the highly dynamic interfaces and flow intermittency. In this work we present microscale free-surface flow simulations using a three-dimensional multiphase Smoothed Particle Hydrodynamics (SPH) code. Pairwise solid-fluid and fluid-fluid interaction forces are used to control the wetting behavior and cover a wide range of static and transient contact angles as well as Reynolds numbers encountered in droplet flow onmore » rock surfaces. We validate our model via comparison with existing empirical and semi-analyical solutions for droplet flow. We use the model to investigate the occurence of adsorbed trailing films of droplets under various flow conditions and its importance for the flow dynamics when films and droplets coexist. We show that flow velocities are higher on prewetted surfaces covered by a thin film which is qualitatively attributed to the enhanced dynamic wetting and dewetting at the trailing and advancing contact line.« less

Nonlinear dynamics in flow through unsaturated fractured-porous media: Status and perspectives

DOE Office of Scientific and Technical Information (OSTI.GOV)

Faybishenko, Boris

2002-11-27

The need has long been recognized to improve predictions of flow and transport in partially saturated heterogeneous soils and fractured rock of the vadose zone for many practical applications, such as remediation of contaminated sites, nuclear waste disposal in geological formations, and climate predictions. Until recently, flow and transport processes in heterogeneous subsurface media with oscillating irregularities were assumed to be random and were not analyzed using methods of nonlinear dynamics. The goals of this paper are to review the theoretical concepts, present the results, and provide perspectives on investigations of flow and transport in unsaturated heterogeneous soils and fracturedmore » rock, using the methods of nonlinear dynamics and deterministic chaos. The results of laboratory and field investigations indicate that the nonlinear dynamics of flow and transport processes in unsaturated soils and fractured rocks arise from the dynamic feedback and competition between various nonlinear physical processes along with complex geometry of flow paths. Although direct measurements of variables characterizing the individual flow processes are not technically feasible, their cumulative effect can be characterized by analyzing time series data using the models and methods of nonlinear dynamics and chaos. Identifying flow through soil or rock as a nonlinear dynamical system is important for developing appropriate short- and long-time predictive models, evaluating prediction uncertainty, assessing the spatial distribution of flow characteristics from time series data, and improving chemical transport simulations. Inferring the nature of flow processes through the methods of nonlinear dynamics could become widely used in different areas of the earth sciences.« less

Ideas, properties, and standards of fracture repositioning with osteopathy in traditional Mongolian medicine in China.

PubMed

Wang, Mei; Wang, Hongxia; Zhao, Namula

2015-02-01

To explore the unique ideas, properties, and standards of fracture repositioning with osteopathy in traditional Mongolian medicine in China. Based on the natural life concept of "integration of universe and man", osteopathy in traditional Mongolian medicine in China uses the modern principles and methods of physiology, psychology, and biomechanics. Against this background, we explored the unique ideas, properties, and stan- dards of fracture repositioning in traditional Mongolian medicine. Fracture treatment with osteopathy in traditional Mongolian medicine in China is based on (a) the ideas of natural, sealed, self and dynamic repositioning of fractures; (b) the properties of structural continuity and functional completeness; (c) the standards of "integration of movement and stillness" and "force to force". The unique ideas, properties, and standards of fracture repositioning with osteopathy in traditional Mongolian medicine in China have resulted in the widespread use of such techniques and represents the future direction of the development of fracture repositioning.

Postmenopausal women with osteopenia and a healed wrist fracture have reduced physical function and quality of life compared to a matched, healthy control group with no fracture

PubMed Central

2014-01-01

Background Fractures lead to reduced physical function and quality of life (QOL), but little is known about postmenopausal women with osteopenia and a healed wrist fracture. The purpose was to evaluate physical function in terms of quadriceps strength, dynamic balance, physical capacity and QOL in postmenopausal women with osteopenia and a healed wrist fracture compared to a matched, healthy control group with no previous fracture. Methods Eighteen postmenopausal women with osteopenia (patients) (mean age 59.1 years, range 54 – 65) and a healed wrist fracture were matched to 18 healthy control subjects on age (mean age 58.5 years, range 51 – 65), height, weight and body mass index (BMI). We measured quadriceps strength at 60°/sec and at 180°/sec with Biodex 6000, dynamic balance with the Four Square Step Test (FSST), physical capacity with the six-minute walk test (6MWT) followed by the Borg’s scale (BS), and QOL with the Short Form 36 (SF-36), bone mineral density (BMD) with dual x-ray absorptiometry (DXA) and physical activity level with the Physical Activity Scale for the Elderly. Results The patients had 17.6% lower quadriceps strength at 60°/sec (p = 0.025) at left limb and 18.5% at 180°/sec (p = 0.016) at right limb, and 21% lower at 180°/sec (p = 0.010) at left limb compared to the controls. Impaired performance for the patients was found with 2.4 seconds (p = 0.002) on the FSST, 74 metres (p < 0.001) on the 6MWT, and 1.4 points (p = 0.003) on the BS compared to the controls. The patients scored lower on the sub-scales on the SF-36 role limitations-physical (p = 0.014), bodily pain (p = 0.025) and vitality (p = 0.015) compared to the controls. Conclusions The patients with osteopenia and a healed wrist fracture scored significantly lower on quadriceps strength, dynamic balance, physical capacity and QOL compared to the matched controls. Greater focus should be put on this patient group in terms of rehabilitation and early prevention of subsequent fractures. PMID:25086601

Geometric Analysis of Vein Fracture Networks From the Awibengkok Core, Indonesia

NASA Astrophysics Data System (ADS)

Khatwa, A.; Bruhn, R. L.; Brown, S. R.

2003-12-01

Fracture network systems within rocks are important features for the transportation and remediation of hazardous waste, oil and gas production, geothermal energy extraction and the formation of vein fillings and ore deposits. A variety of methods, including computational and laboratory modeling have been employed to further understand the dynamic nature of fractures and fracture systems (e.g. Ebel and Brown, this session). To substantiate these studies, it is also necessary to analyze the characteristics and morphology of naturally occurring vein systems. The Awibengkok core from a geothermal system in West Java, Indonesia provided an excellent opportunity to study geometric and petrologic characteristics of vein systems in volcanic rock. Vein minerals included chlorite, calcite, quartz, zeolites and sulphides. To obtain geometric data on the veins, we employed a neural net image processing technique to analyze high-resolution digital photography of the veins. We trained a neural net processor to map the extent of the vein using RGB pixel training classes. The resulting classification image was then converted to a binary image file and processed through a MatLab program that we designed to calculate vein geometric statistics, including aperture and roughness. We also performed detailed petrographic and microscopic geometric analysis on the veins to determine the history of mineralization and fracturing. We found that multi-phase mineralization due to chemical dissolution and re-precipitation as well as mechanical fracturing was a common feature in many of the veins and that it had a significant role for interpreting vein tortuosity and history of permeability. We used our micro- and macro-scale observations to construct four hypothetical permeability models that compliment the numerical and laboratory modeled data reported by Ebel and Brown. In each model, permeability changes, and in most cases fluctuates, differently over time as the tortuosity and aperture of veins are affected by the precipitation, dissolution, and re-precipitation of minerals, and also by mechanical fracturing. In all of our cases we interpret a first-phase mineral dissolution stage where permeability gradually declines as the vein is blocked by inward growing minerals. Hereafter, permeability may briefly increase with the onset of internal fracturing within the vein or by a phase of mineral dissolution opening up new pathways for fluid flow. Eventually we infer that permeability will decline again as second stage minerals are deposited in the fluid flow pathways.

Influence of fracture network physical properties on stability criteria of density-driven flow in a dual-porosity system

NASA Astrophysics Data System (ADS)

Hassanzadeh, H.; Jafari Raad, S. M.

2017-12-01

Linear stability analysis is conducted to study the onset of buoyancy-driven convection involved in solubility trapping of CO2 into deep fractured aquifers. In this study, the effect of fracture network physical properties on the stability criteria in a brine-rich fractured porous layer is investigated using dual porosity concept for both single and variable matrix block size distributions. Linear stability analysis results show that both fracture interporosity flow and fracture storativity factors play an important role in the stability behavior of the system. It is shown that a diffusive boundary layer under the gravity field in a fractured rock with lower fracture storativity and/or higher fracture interporosity flow coefficient is more stable. We present scaling relations that relate the onset of convective instability in fractured aquifers. These findings improve our understanding of buoyancy driven flow in fractured aquifers and are particularly important in estimation of potential storage capacity, risk assessment, and storage sites characterization and screening.Keywords: CO2 sequestration; fractured rock; buoyancy-driven convection; stability analysis

Fracture Mechanics Analysis of LH2 Feed Line Flow Liners

NASA Technical Reports Server (NTRS)

James, Mark A.; Dawicke, David S.; Brzowski, Matthew B.; Raju, Ivatury S.; Elliott, Kenny B.; Harris, Charles E.

2006-01-01

Inspections of the Space Shuttle Main Engine revealed fatigue cracks growing from slots in the flow liner of the liquid hydrogen (LH2) feed lines. During flight, the flow liners experience complex loading induced by flow of LH2 and the resonance characteristics of the structure. The flow liners are made of Inconel 718 and had previously not been considered a fracture critical component. However, fatigue failure of a flow liner could have catastrophic effect on the Shuttle engines. A fracture mechanics study was performed to determine if a damage tolerance approach to life management was possible and to determine the sensitivity to the load spectra, material properties, and crack size. The load spectra were derived separately from ground tests and material properties were obtained from coupon tests. The stress-intensity factors for the fatigue cracks were determined from a shell-dynamics approach that simulated the dominant resonant frequencies. Life predictions were obtained using the NASGRO life prediction code. The results indicated that adequate life could not be demonstrated for initial crack lengths of the size that could be detected by traditional NDE techniques.

Research on Fracture of Aluminum Foil in Microscale Laser Peen Forming

NASA Astrophysics Data System (ADS)

Zheng, Chao; Sun, Sheng; Liu, Jing; Ji, Zhong

2010-06-01

A novel numerical method for dynamic fracture in microscale laser peen forming (μLPF) of aluminum foils was presented and the role of the die diameter on fracture behavior at the ultra high strain rate was investigated via both experimental and numerical methods. μLPF is a process in which the plastic deformation is generated through laser-induced shock wave and compressive residual stresses can be imparted to improve the fatigue life of micro parts. During μLPF, the pressure exerted on the target is higher than 1 GPa and the strain rate is greater than 106s-1, so the mechanical behavior of materials in this dynamic process is very different from that under static or quasi-static conditions. In the present study, the finite element method with grain and grain boundary elements was used to analyze the μLPF process of aluminum foils with a thickness of 60 μm. The onset and propagation of crack were simulated in this way that the specified nodes were tied together until the equivalent plastic strain exceeded a certain value. Under a given value of plastic strain, the influence of die diameters of 0.6, 1.0, and 1.6 mm on the fracture mode of the material was predicted. A series of experiments were carried out to verify the numerical model. The geometrical morphologies of fracture regions were observed via optical microscope and scan electron microscope. In results from both experiments and simulations, the size of the die diameter affects the location of the fracture: (I) Fracture appeared at the entrance of the die for die diameters of 0.6 and 1.0 mm. (II) Fracture occurred near the centre of the formed dome for 1.6 mm die diameter. The generation mechanism of two fracture modes was explained. This work provides a preliminary insight into the fracture behavior of materials under the ultra high strain rate and lays the ground work for more in-depth simulations in the future study.

Probing Dynamics in Granular Media of Contrasting Geometries via X-Ray Phase Contrast Imaging and PDV

NASA Astrophysics Data System (ADS)

Crum, Ryan; Pagan, Darren; Lind, Jon; Homel, Michael; Hurley, Ryan; Herbold, Eric; Akin, Minta

Granular systems are ubiquitous in our everyday world and play a central role in many dynamic scientific problems including mine blasting, projectile penetration, astrophysical collisions, explosions, and dynamic compaction. An understanding of granular media's behavior under various loading conditions is an ongoing scientific grand challenge. This is partly due to the intricate interplay between material properties, loading conditions, grain geometry, and grain connectivity. Previous dynamic studies in granular media predominantly utilize the macro-scale analyses VISAR or PDV, diagnostics that are not sensitive to the many degrees of freedom and their interactions, focusing instead on their aggregate effect. Results of a macro-scale analysis leave the principal interactions of these degrees of freedom too entangled to elucidate. To isolate the significance of grain geometry, this study probes various geometries of granular media subjected to gas gun generated waves via in-situ X-ray analysis. Analyses include evaluating displacement fields, grain fracture, inter- and intra-granular densification, and wave front motion. Phase Contrast Imaging (PCI) and PDV analyses feed directly into our concurrent meso-scale granular media modeling efforts to enhance our predictive capabilities.

An air brake model for longitudinal train dynamics studies

NASA Astrophysics Data System (ADS)

Wei, Wei; Hu, Yang; Wu, Qing; Zhao, Xubao; Zhang, Jun; Zhang, Yuan

2017-04-01

Experience of heavy haul train operation shows that heavy haul train fatigue fracture of coupler and its related components, even the accidents are caused by excessive coupler force. The most economical and effective method to study on train longitudinal impulse by reducing the coupler force is simulation method. The characteristics of train air brake system is an important excitation source for the study of longitudinal impulse. It is very difficult to obtain the braking characteristic by the test method, a better way to get the input parameters of the excitation source in the train longitudinal dynamics is modelling the train air brake system. In this paper, the air brake system model of integrated system of air brake and longitudinal dynamics is introduced. This introduce is focus on the locomotive automatic brake valve and vehicle distribution valve model, and the comparative analysis of the simulation and test results of the braking system is given. It is proved that the model can predict the characteristics of train braking system. This method provides a good solution for the excitation source of longitudinal dynamic analysis system.

Fracture modes in notched angleplied composite laminates

NASA Technical Reports Server (NTRS)

Irvine, T. B.; Ginty, C. A.

1984-01-01

The Composite Durability Structural Analysis (CODSTRAN) computer code is used to determine composite fracture. Fracture modes in solid and notched, unidirectional and angleplied graphite/epoxy composites were determined by using CODSTRAN. Experimental verification included both nondestructive (ultrasonic C-Scanning) and destructive (scanning electron microscopy) techniques. The fracture modes were found to be a function of ply orientations and whether the composite is notched or unnotched. Delaminations caused by stress concentrations around notch tips were also determined. Results indicate that the composite mechanics, structural analysis, laminate analysis, and fracture criteria modules embedded in CODSTRAN are valid for determining composite fracture modes.

Fundamentals of microcrack nucleation mechanics

NASA Technical Reports Server (NTRS)

Fu, L. S.; Sheu, Y. C.; Co, C. M.; Zhong, W. F.; Shen, H. D.

1985-01-01

A foundation for ultrasonic evaluation of microcrack nucleation mechanics is identified in order to establish a basis for correlations between plane strain fracture toughness and ultrasonic factors through the interaction of elastic waves with material microstructures. Since microcracking is the origin of (brittle) fracture, it is appropriate to consider the role of stress waves in the dynamics of microcracking. Therefore, the following topics are discussed: (1) microstress distributions with typical microstructural defects located in the stress field; (2) elastic wave scattering from various idealized defects; and (3) dynamic effective-properties of media with randomly distributed inhomogeneities.

Simulation of spallation life of metals in relation to operating stresses in the nanosecond loading time range

NASA Astrophysics Data System (ADS)

Makarov, P. V.; Bakeev, R. A.

2015-10-01

Spall fracture of materials is still the only means for investigation of the material life and mechanisms of its fracture in the micro-, nano-, and picosecond time ranges of tensile loading. The phenomenological model based on the concepts of multiscale fracture of materials as nonlinear dynamic systems is shown to satisfactorily describe their life in the given range. The model is employed for the calculation of spallation life.

Etude hydromecanique d'une fracture en cisaillement sous contrainte normale constante

NASA Astrophysics Data System (ADS)

Lamontagne, Eric

This research study deals with the effects of shear direction and injection flow rate on the flow directional anisotropy for a given normal stress. It presents experimental works on hydromechanical shear behaviour of a fracture under constant normal stress conditions that permits the characterisation of the intrinsic hydraulic transmissivity in relation with the directional anisotropy of the roughness morphology on the fracture surfaces. Tests were performed on mortar replicas of a natural fracture so that the fracture roughness and void space geometry were kept the same for each test. The experimental work program was performed through direct shear tests on the fracture replicas in four shear directions under four constant normal stress levels. The application of the normal stress was followed by several injections of fluid under constant flow rate. Then, for each defined shear displacement, several injections of fluid were done at different flow rate but under constant flow rate. The test results show that: (1) for the whole shear tests, the global intrinsic transmissivity is included within an enveloping zone of about one order of size. The transmissivity curves within the enveloping zone has a particularity to increase about two orders of size in the first millimetre of shear displacement and subsequently stabilised rapidly; (2) the highest dilatancy do not correspond necessarily with the highest intrinsic transmissivity so that, the behaviour of the global intrinsic transmissivity is not directly proportional to the fracture dilatancy during shear; (3) after the peak shear stress, the divergence is more marked between the global intrinsic transmissivity curves at various flow rate; (4) after peak shear strength and the beginning of asperity degradation, the gradual passage to residual friction shear behaviour causes a directional flow anisotropy and a reorientation of the flow chenalisation direction sub perpendicularly to the shear direction; (5) the anisotropy is not to develop equally between the two sense in the perpendicular direction to shear direction. In order to characterise the dynamics of the flow pattern in the fracture, a statistical analysis of the surfaces morphology of the fracture and the casting of void space geometry were performed before and after shear. A statistical analysis of asperity heights, on the global scale of the fracture surfaces, permits to characterise the fracture morphology and put in evidence a large morphological structure on which are superposed smaller asperities of variable dimensions. This large dimension structure generate a higher level landing occupying more than half of the fracture area. The study of the surfaces morphology of the fracture, performed with the geostatistical mean asperity heights variogram by direction before shearing, show the presence of two entangled morphologic structure families (28 and 15 mm). This same study done after shearing shows that the asperity degradation seems associated with the reduction of the global intrinsic transmissivity of the fracture. Finally, the void spaces morphology evaluated by casting techniques, during the shear tests, has permitted to verify the contacts evolution with the increasing shear displacement and visualised flow chenalisation during fracture shearing.

Fracture hydromechanical response measured by fiber optic distributed acoustic sensing at milliHertz frequencies

NASA Astrophysics Data System (ADS)

Becker, M. W.; Ciervo, C.; Cole, M.; Coleman, T.; Mondanos, M.

2017-07-01

A new method of measuring dynamic strain in boreholes was used to record fracture displacement in response to head oscillation. Fiber optic distributed acoustic sensing (DAS) was used to measure strain at mHz frequencies, rather than the Hz to kHz frequencies typical for seismic and acoustic monitoring. Fiber optic cable was mechanically coupled to the wall of a borehole drilled into fractured crystalline bedrock. Oscillating hydraulic signals were applied at a companion borehole 30 m away. The DAS instrument measured fracture displacement at frequencies of less than 1 mHz and amplitudes of less than 1 nm, in response to fluid pressure changes of less 20 Pa (2 mm H2O). Displacement was linearly related to the log of effective stress, a relationship typically explained by the effect of self-affine fracture roughness on fracture closure. These results imply that fracture roughness affects closure even when displacement is a million times smaller than the fracture aperture.

Mechanical properties of kinked silicon nanowires

NASA Astrophysics Data System (ADS)

Jing, Yuhang; Zhang, Chuan; Liu, Yingzhi; Guo, Licheng; Meng, Qingyuan

2015-04-01

Molecular dynamics simulations are used to investigate the mechanical properties of KSiNWs. Our results show that KSiNWs have a much larger fracture strain compared to straight SiNWs. The effects of the periodic length of KSiNWs with symmetric arms and the arm length of the KSiNW with asymmetric arms on the mechanical properties of KSiNWs are studied. The fracture stress of KSiNWs decrease as the periodic length increases. However, the fracture strain of KSiNWs is not dependent on the short periodic length and the fracture strain of KSiNWs will abruptly increase to very large value and then vary slightly as the periodic length increases. In addition, the fracture stress is not dependent on arm length while the fracture strain monotonically increases as the arm length increases. We also investigate the fracture process of KSiNWs. The results in this paper suggest that the KSiNWs with larger fracture strain can be a promising anode materials in high performance Li-ion batteries.

The Analysis of Crack Growth Initiation, Propagation, and Arrest in Flawed Ship Structures Subjected to Dynamic Loading

DTIC Science & Technology

1984-08-10

most current efforts in EPFM are focused on the application of the J-resistance curve to predict crack initiation and fracture instability. However...element code FRACDYN, which has since been used to solve a variety of problems related to the Navy, NRC, and several industrial applications . Of...that this parameter remains constant during elastic-plastic stable crack growth--see Reference (9). This fact, together with its ease of application

Dynamic Locked Plating of Distal Femur Fractures.

PubMed

Linn, Michael S; McAndrew, Christopher M; Prusaczyk, Beth; Brimmo, Olubusola; Ricci, William M; Gardner, Michael J

2015-10-01

Nonunion after locked bridge plating of comminuted distal femur fractures is not uncommon. "Dynamic" locked plating may create an improved mechanical environment, thereby achieving higher union rates than standard locked plating constructs. Academic Level 1 Trauma Center. Twenty-eight patients with comminuted supracondylar femur fractures treated with either dynamic or standard locked plating. Dynamic plating was achieved using an overdrilling technique of the near cortex to allow for a 0.5-mm "halo" around the screw shaft at the near cortex. Standard locked plating was done based on manufacturer's suggested technique. The patients treated with dynamic plating were matched 1:1 with those treated with standard locked plating based on OTA classification and working length. Three blinded observers made callus measurements on 6-week radiographs using a 4-point ordinal scale. The results were analyzed using a 2-tailed t test and 2-way intraclass correlations. The dynamic plating group had significantly greater callus (2.0; SD, 0.7) compared with the control group (1.3: SD, 0.8, P = 0.048) with substantial agreement amongst observers in both consistency (0.724) and absolute score (0.734). With dynamic plating group, 1 patient failed to unite, versus three in the control group (P = 0.59). The dynamic group had a mean change in coronal plane alignment of 0.5 degrees (SD, 2.6) compared with 0.6 (SD, 3.0) for the control group (P = 0.9) without fixation failure in either group. Overdrilling the near cortex in metaphyseal bridge plating can be adapted to standard implants to create a dynamic construct and increase axial motion. This technique seems to be safe and leads to increased callus formation, which may decrease nonunion rates seen with standard locked plating. Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Study of sex differences in the association between hip fracture risk and body parameters by DXA-based biomechanical modeling.

PubMed

Nasiri, Masoud; Luo, Yunhua

2016-09-01

There is controversy about whether or not body parameters affect hip fracture in men and women in the same way. In addition, although bone mineral density (BMD) is currently the most important single discriminator of hip fracture, it is unclear if BMD alone is equally effective for men and women. The objective of this study was to quantify and compare the associations of hip fracture risk with BMD and body parameters in men and women using our recently developed two-level biomechanical model that combines a whole-body dynamics model with a proximal-femur finite element model. Sideways fall induced impact force of 130 Chinese clinical cases, including 50 males and 80 females, were determined by subject-specific dynamics modeling. Then, a DXA-based finite element model was used to simulate the femur bone under the fall-induced loading conditions and calculate the hip fracture risk. Body weight, body height, body mass index, trochanteric soft tissue thickness, and hip bone mineral density were determined for each subject and their associations with impact force and hip fracture risk were quantified. Results showed that the association between impact force and hip fracture risk was not strong enough in both men (r=-0.31,p<0.05) and women (r=0.42,p<0.001) to consider the force as a sole indicator of hip fracture risk. The correlation between hip BMD and hip fracture risk in men (r=-0.83,p<0.001) was notably stronger than that in women (r=-0.68,p<0.001). Increased body mass index was not a protective factor against hip fracture in men (r=-0.13,p>0.05), but it can be considered as a protective factor among women (r=-0.28,p<0.05). In contrast to men, trochanteric soft tissue thickness can be considered as a protective factor against hip fracture in women (r=-0.50,p<0.001). This study suggested that the biomechanical risk/protective factors for hip fracture are sex-specific. Therefore, the effect of body parameters should be considered differently for men and women in hip fracture risk assessment tools. These findings support further exploration of sex-specific preventive and protective measurements to reduce the incidence of hip fractures. Copyright © 2016 Elsevier Inc. All rights reserved.

Individual risk factors for deep infection and compromised fracture healing after intramedullary nailing of tibial shaft fractures: a single centre experience of 480 patients.

PubMed

Metsemakers, W-J; Handojo, K; Reynders, P; Sermon, A; Vanderschot, P; Nijs, S

2015-04-01

Despite modern advances in the treatment of tibial shaft fractures, complications including nonunion, malunion, and infection remain relatively frequent. A better understanding of these injuries and its complications could lead to prevention rather than treatment strategies. A retrospective study was performed to identify risk factors for deep infection and compromised fracture healing after intramedullary nailing (IMN) of tibial shaft fractures. Between January 2000 and January 2012, 480 consecutive patients with 486 tibial shaft fractures were enrolled in the study. Statistical analysis was performed to determine predictors of deep infection and compromised fracture healing. Compromised fracture healing was subdivided in delayed union and nonunion. The following independent variables were selected for analysis: age, sex, smoking, obesity, diabetes, American Society of Anaesthesiologists (ASA) classification, polytrauma, fracture type, open fractures, Gustilo type, primary external fixation (EF), time to nailing (TTN) and reaming. As primary statistical evaluation we performed a univariate analysis, followed by a multiple logistic regression model. Univariate regression analysis revealed similar risk factors for delayed union and nonunion, including fracture type, open fractures and Gustilo type. Factors affecting the occurrence of deep infection in this model were primary EF, a prolonged TTN, open fractures and Gustilo type. Multiple logistic regression analysis revealed polytrauma as the single risk factor for nonunion. With respect to delayed union, no risk factors could be identified. In the same statistical model, deep infection was correlated with primary EF. The purpose of this study was to evaluate risk factors of poor outcome after IMN of tibial shaft fractures. The univariate regression analysis showed that the nature of complications after tibial shaft nailing could be multifactorial. This was not confirmed in a multiple logistic regression model, which only revealed polytrauma and primary EF as risk factors for nonunion and deep infection, respectively. Future strategies should focus on prevention in high-risk populations such as polytrauma patients treated with EF. Copyright © 2014 Elsevier Ltd. All rights reserved.

Guidelines for Proof Test Analysis

NASA Technical Reports Server (NTRS)

Chell, G. G.; McClung, R. C.; Kuhlman, C. J.; Russell, D. A.; Garr, K.; Donnelly, B.

1999-01-01

These guidelines integrate state-of-the-art elastic-plastic fracture mechanics (EPFM) and proof test implementation issues into a comprehensive proof test analysis procedure in the form of a road map which identifies the types of data, fracture mechanics based parameters, and calculations needed to perform flaw screening and minimum proof load analyses of fracture critical components. Worked examples are presented to illustrate the application of the road map to proof test analysis. The state-of-the art fracture technology employed in these guidelines is based on the EPFM parameter, J, and a pictorial representation of a J fracture analysis, called the failure assessment diagram (FAD) approach. The recommended fracture technology is validated using finite element J results, and laboratory and hardware fracture test results on the nickel-based superalloy Inconel 718, the aluminum alloy 2024-T3511, and ferritic pressure vessel steels. In all cases the laboratory specimens and hardware failed by ductile mechanisms. Advanced proof test analyses involving probability analysis and multiple-cycle proof testing (MCPT) are addressed. Finally, recommendations are provided on how to account for the effects of the proof test overload on subsequent service fatigue and fracture behaviors.

Numerical simulation of damage evolution for ductile materials and mechanical properties study

NASA Astrophysics Data System (ADS)

El Amri, A.; Hanafi, I.; Haddou, M. E. Y.; Khamlichi, A.

2015-12-01

This paper presents results of a numerical modelling of ductile fracture and failure of elements made of 5182H111 aluminium alloys subjected to dynamic traction. The analysis was performed using Johnson-Cook model based on ABAQUS software. The modelling difficulty related to prediction of ductile fracture mainly arises because there is a tremendous span of length scales from the structural problem to the micro-mechanics problem governing the material separation process. This study has been used the experimental results to calibrate a simple crack propagation criteria for shell elements of which one has often been used in practical analyses. The performance of the proposed model is in general good and it is believed that the presented results and experimental-numerical calibration procedure can be of use in practical finite-element simulations.

Proton-pump inhibitors and risk of fractures: an update meta-analysis.

PubMed

Zhou, B; Huang, Y; Li, H; Sun, W; Liu, J

2016-01-01

To identify the relationship between proton-pump inhibitors (PPIs) and the risk of fracture, we conducted an update meta-analysis of observational studies. Results showed that PPI use was associated with a modestly increased risk of hip, spine, and any-site fracture. Many studies have investigated the association of proton-pump inhibitors (PPIs) with fracture risk, but the results have been inconsistent. To evaluate this question, we performed a meta-analysis of relevant observational studies. A systematic literature search up to February 2015 was performed in PubMed. We combined relative risks (RRs) for fractures using random-effects models and conducted subgroup and stratified analyses. Eighteen studies involving a total of 244,109 fracture cases were included in this meta-analysis. Pooled analysis showed that PPI use could moderately increase the risk of hip fracture [RR = 1.26, 95 % confidence intervals (CIs) 1.16–1.36]. There was statistically significant heterogeneity among studies (p < 0.001; I 2 = 71.9 %). After limiting to cohort studies, there was also a moderate increase in hip fracture risk without evidence of study heterogeneity. Pooling revealed that short-term use (<1 year) and longer use (>1 year) were similarly associated with increased risk of hip fracture. Furthermore, a moderately increased risk of spine (RR = 1.58, 95 % CI 1.38–1.82) and any-site fracture (RR = 1.33, 95 % CI 1.15–1.54) was also found among PPI users. In this update meta-analysis of observational studies, PPI use modestly increased the risk of hip, spine, and any-site fracture, but no evidence of duration effect in subgroup analysis.

Development of test methodology for dynamic mechanical analysis instrumentation

NASA Technical Reports Server (NTRS)

Allen, V. R.

1982-01-01

Dynamic mechanical analysis instrumentation was used for the development of specific test methodology in the determination of engineering parameters of selected materials, esp. plastics and elastomers, over a broad range of temperature with selected environment. The methodology for routine procedures was established with specific attention given to sample geometry, sample size, and mounting techniques. The basic software of the duPont 1090 thermal analyzer was used for data reduction which simplify the theoretical interpretation. Clamps were developed which allowed 'relative' damping during the cure cycle to be measured for the fiber-glass supported resin. The correlation of fracture energy 'toughness' (or impact strength) with the low temperature (glassy) relaxation responses for a 'rubber-modified' epoxy system was negative in result because the low-temperature dispersion mode (-80 C) of the modifier coincided with that of the epoxy matrix, making quantitative comparison unrealistic.

Failure processes in soft and quasi-brittle materials with nonhomogeneous microstructures

NASA Astrophysics Data System (ADS)

Spring, Daniel W.

Material failure pervades the fields of materials science and engineering; it occurs at various scales and in various contexts. Understanding the mechanisms by which a material fails can lead to advancements in the way we design and build the world around us. For example, in structural engineering, understanding the fracture of concrete and steel can lead to improved structural systems and safer designs; in geological engineering, understanding the fracture of rock can lead to increased efficiency in oil and gas extraction; and in biological engineering, understanding the fracture of bone can lead to improvements in the design of bio-composites and medical implants. In this thesis, we numerically investigate a wide spectrum of failure behavior; in soft and quasi-brittle materials with nonhomogeneous microstructures considering a statistical distribution of material properties. The first topic we investigate considers the influence of interfacial interactions on the macroscopic constitutive response of particle reinforced elastomers. When a particle is embedded into an elastomer, the polymer chains in the elastomer tend to adsorb (or anchor) onto the surface of the particle; creating a region in the vicinity of each particle (often referred to as an interphase) with distinct properties from those in the bulk elastomer. This interphasial region has been known to exist for many decades, but is primarily omitted in computational investigations of such composites. In this thesis, we present an investigation into the influence of interphases on the macroscopic constitutive response of particle filled elastomers undergoing large deformations. In addition, at large deformations, a localized region of failure tends to accumulate around inclusions. To capture this localized region of failure (often referred to as interfacial debonding), we use cohesive zone elements which follow the Park-Paulino-Roesler traction-separation relation. To account for friction, we present a new, coupled cohesive-friction relation and detail its formulation and implementation. In the process of this investigation, we developed a small library of cohesive elements for use with a commercially available finite element analysis software package. Additionally, in this thesis, we present a series of methods for reducing mesh dependency in two-dimensional dynamic cohesive fracture simulations of quasi-brittle materials. In this setting, cracks are only permitted to propagate along element facets, thus a poorly designed discretization of the problem domain can introduce artifacts into the fracture behavior. To reduce mesh induced artifacts, we consider unstructured polygonal finite elements. A randomly-seeded polygonal mesh leads to an isotropic discretization of the problem domain, which does not bias the direction of crack propagation. However, polygonal meshes tend to limit the possible directions a crack may travel at each node, making this discretization a poor candidate for dynamic cohesive fracture simulations. To alleviate this problem, we propose two new topological operators. The first operator we propose is adaptive element-splitting, and the second is adaptive mesh refinement. Both operators are designed to improve the ability of unstructured polygonal meshes to capture crack patterns in dynamic cohesive fracture simulations. However, we demonstrate that element-splitting is more suited to pervasive fracture problems, whereas, adaptive refinement is more suited to problems exhibiting a dominant crack. Finally, we investigate the use of geometric and constitutive design features to regularize pervasive fragmentation behavior in three-dimensions. Throughout pervasive fracture simulations, many cracks initiate, propagate, branch and coalesce simultaneously. Because of the cohesive element method's unique framework, this behavior can be captured in a regularized manner. In this investigation, unstructuring techniques are used to introduce randomness into a numerical model. The behavior of quasi-brittle materials undergoing pervasive fracture and fragmentation is then examined using three examples. The examples are selected to investigate some of the significant factors influencing pervasive fracture and fragmentation behavior; including, geometric features, loading conditions, and material gradation.

Natural fracture systems studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lorenz, J.C.; Warpinski, N.R.

The objectives of this program are (1) to develop a basinal-analysis methodology for natural fracture exploration and exploitation, and (2) to determine the important characteristics of natural fracture systems for use in completion, stimulation, and production operations. Natural-fracture basinal analysis begins with studies of fractures in outcrop, core and logs in order to determine the type of fracturing and the relationship of the fractures to the lithologic environment. Of particular interest are the regional fracture systems that are pervasive in western US tight sand basins. A Methodology for applying this analysis is being developed, with the goal of providing amore » structure for rationally characterizing natural fracture systems basin-wide. Such basin-wide characterizations can then be expanded and supplemented locally, at sites where production may be favorable. Initial application of this analysis is to the Piceance basin where there is a wealth of data from the Multiwell Experiment (MWX), DOE cooperative wells, and other basin studies conducted by Sandia, CER Corporation, and the USGS (Lorenz and Finley, 1989, Lorenz et aI., 1989, and Spencer and Keighin, 1984). Such a basinal approach has been capable of explaining the fracture characteristics found throughout the southern part of the Piceance basin and along the Grand Hogback.« less

Fracture strength of all-ceramic lithium disilicate and porcelain-fused-to-metal bridges for molar replacement after dynamic loading.

PubMed

Chitmongkolsuk, Somsak; Heydecke, Guido; Stappert, Christian; Strub, Joerg R

2002-03-01

The replacement of missing posterior teeth using all-ceramic bridges remains a challenge. This study compares the fracture resistance of all-ceramic 3-unit bridges for the replacement of first molars to conventional porcelain-fused-to-metal bridges. Human premolars and molars were used to create two test groups and one control group of 16 specimens each. To simulate clinical parameters, the specimens were exposed to cyclic fatigue loading in an artificial mouth with simultaneous thermocycling. All samples were thereafter exposed to fracture strength testing. Porcelain-fused-to-metal bridges showed significantly higher fracture strengths than all-ceramic bridges. However, the fracture strength of the all-ceramic bridges was higher than peak physiological chewing forces.

[Intramedullary nailing of the tibia with the expert tibia nail].

PubMed

Hansen, Matthias; El Attal, René; Blum, Jochen; Blauth, Michael; Rommens, Pol Maria

2009-12-01

Restoration of axis, length, and rotation of the lower leg. Sufficient primary stability of the osteosynthesis for functional aftercare. Early functional aftercare to maintain joint mobility. Good bony healing in closed and open fractures. All closed and open fractures of the tibia and complete lower leg fractures (AO 42). Certain extraarticular fractures of the proximal and distal tibia (AO 41 A2/A3; AO 43 A1/A2/A3). Segmental fractures of the tibia. Certain intraarticular fractures of the tibia with use of additional implants (AO 41 C1/C2; AO 43 C1/C2). Stabilization during and after segmental bone transport or callus distraction of the tibia. Patients in poor general condition (e.g., bedridden). Flexion of the knee of less than 90 degrees . Infection in the nail's insertion area. Infection of the tibial cavity. Complex articular fractures of the proximal or distal tibia with joint depression. Closed reduction of the fracture. If necessary, use of reduction clamps through additional stab incisions or open surgical procedures. In some cases, additional osteosynthesis procedures are necessary (e.g., screws). Positioning of the patient may be performed on a radiolucent table or a traction table. Opening of the proximal tibia in line with the medullary canal. Cannulated or noncannulated insertion of the Expert Tibia Nail((R)) with or without reaming of the medullary canal depending on the fracture type and soft-tissue condition. Control of axis, length, and rotation. Distal interlocking with the radiolucent drill and proximal interlocking with the targeting device. Immediate mobilization of ankle joint and knee joint. Depending on the type of fracture, mobilization with 20 kg partial weight bearing or pain-dependent full weight bearing with crutches. X-ray control 6 weeks postoperatively and increased weight bearing depending on the fracture status. In a prospective, international multicentric study, 181 patients with 186 fractures were included between July 2004 and May 2005. 57 of these fractures (30.7%) initially were graded open, 15 of them grade I, 32 grade II, and ten grade III. Most of the fractures (36%) were shaft fractures. After 1 year, 146 patients (81%) could be evaluated clinically and radiologically. The overall pseudarthrosis rate was 12.2% (18.2% for open and 9.7% for closed fractures). The risk for secondary operations or revisions (including dynamization of the nail) was 18.8%. Without consideration of dynamization procedures, revisions were necessary in only 5.4% of all patients. The risk for varus, valgus or antecurvation malalignment of more than 5 degrees in any plane on radiologic long leg views was 4.3% for shaft fractures, 1.5% for distal fractures, and 13.6% for proximal fractures. The implant-specific risk for bolt breakage was 3.2%.

Analysis of Vertebral Bone Strength, Fracture Pattern, and Fracture Location: A Validation Study Using a Computed Tomography-Based Nonlinear Finite Element Analysis

PubMed Central

Imai, Kazuhiro

2015-01-01

Finite element analysis (FEA) is an advanced computer technique of structural stress analysis developed in engineering mechanics. Because the compressive behavior of vertebral bone shows nonlinear behavior, a nonlinear FEA should be utilized to analyze the clinical vertebral fracture. In this article, a computed tomography-based nonlinear FEA (CT/FEA) to analyze the vertebral bone strength, fracture pattern, and fracture location is introduced. The accuracy of the CT/FEA was validated by performing experimental mechanical testing with human cadaveric specimens. Vertebral bone strength and the minimum principal strain at the vertebral surface were accurately analyzed using the CT/FEA. The experimental fracture pattern and fracture location were also accurately simulated. Optimization of the element size was performed by assessing the accuracy of the CT/FEA, and the optimum element size was assumed to be 2 mm. It is expected that the CT/FEA will be valuable in analyzing vertebral fracture risk and assessing therapeutic effects on osteoporosis. PMID:26029476

Crack propagation and arrest in pressurized containers

NASA Technical Reports Server (NTRS)

Erdogan, F.; Delale, F.; Owczarek, J. A.

1976-01-01

The problem of crack propagation and arrest in a finite volume cylindrical container filled with pressurized gas is considered. It is assumed that the cylinder contains a symmetrically located longitudinal part-through crack with a relatively small net ligament. The net ligament suddenly ruptures initiating the process of fracture propagation and depressurization in the cylinder. Thus the problem is a coupled gas dynamics and solid mechanics problem the exact formulation of which does not seem to be possible. The problem is reduced to a proper initial value problem by introducing a dynamic fracture criterion which relates the crack acceleration to the difference between a load factor and the corresponding strength parameter. The results indicate that generally in gas filled cylinders fracture arrest is not possible unless the material behaves in a ductile manner and the container is relatively long.

Dynamic tensile fracture of mortar at ultra-high strain-rates

NASA Astrophysics Data System (ADS)

Erzar, B.; Buzaud, E.; Chanal, P.-Y.

2013-12-01

During the lifetime of a structure, concrete and mortar may be exposed to highly dynamic loadings, such as impact or explosion. The dynamic fracture at high loading rates needs to be well understood to allow an accurate modeling of this kind of event. In this work, a pulsed-power generator has been employed to conduct spalling tests on mortar samples at strain-rates ranging from 2 × 104 to 4 × 104 s-1. The ramp loading allowed identifying the strain-rate anytime during the test. A power law has been proposed to fit properly the rate-sensitivity of tensile strength of this cementitious material over a wide range of strain-rate. Moreover, a specimen has been recovered damaged but unbroken. Micro-computed tomography has been employed to study the characteristics of the damage pattern provoked by the dynamic tensile loading.

Applications and benefits of technology in naturally fractured, low permeability reservoirs with special emphasis on results from GRI`s devonian shale and berea sand research in the appalachian basin

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jochen, J.E.; Hopkins, C.W.

1993-12-31

;Contents: Naturally fractured reservoir description; Geologic considerations; Shale-specific log model; Stress profiles; Berea reasearch; Benefits analysis; Summary of technologies; Novel well test methods; Natural fracture identification; Reverse drilling; Production data analysis; Fracture treatment quality control; Novel core analysis methods; and Shale well cleanouts.

Universal Linear Scaling of Permeability and Time for Heterogeneous Fracture Dissolution

NASA Astrophysics Data System (ADS)

Wang, L.; Cardenas, M. B.

2017-12-01

Fractures are dynamically changing over geological time scale due to mechanical deformation and chemical reactions. However, the latter mechanism remains poorly understood with respect to the expanding fracture, which leads to a positively coupled flow and reactive transport processes, i.e., as a fracture expands, so does its permeability (k) and thus flow and reactive transport processes. To unravel this coupling, we consider a self-enhancing process that leads to fracture expansion caused by acidic fluid, i.e., CO2-saturated brine dissolving calcite fracture. We rigorously derive a theory, for the first time, showing that fracture permeability increases linearly with time [Wang and Cardenas, 2017]. To validate this theory, we resort to the direct simulation that solves the Navier-Stokes and Advection-Diffusion equations with a moving mesh according to the dynamic dissolution process in two-dimensional (2D) fractures. We find that k slowly increases first until the dissolution front breakthrough the outbound when we observe a rapid k increase, i.e., the linear time-dependence of k occurs. The theory agrees well with numerical observations across a broad range of Peclet and Damkohler numbers through homogeneous and heterogeneous 2D fractures. Moreover, the theory of linear scaling relationship between k and time matches well with experimental observations of three-dimensional (3D) fractures' dissolution. To further attest to our theory's universality for 3D heterogeneous fractures across a broad range of roughness and correlation length of aperture field, we develop a depth-averaged model that simulates the process-based reactive transport. The simulation results show that, regardless of a wide variety of dissolution patterns such as the presence of dissolution fingers and preferential dissolution paths, the linear scaling relationship between k and time holds. Our theory sheds light on predicting permeability evolution in many geological settings when the self-enhancing process is relevant. References: Wang, L., and M. B. Cardenas (2017), Linear permeability evolution of expanding conduits due to feedback between flow and fast phase change, Geophys. Res. Lett., 44(9), 4116-4123, doi: 10.1002/2017gl073161.

Extending Topological Approaches to Microseismic-Derived 3D Fracture Networks

NASA Astrophysics Data System (ADS)

Urbancic, T.; Bosman, K.; Baig, A.; Ardakani, E. P.

2017-12-01

Fracture topology is important for determining the fluid-flow characteristics of a fracture network. In most unconventional petroleum applications, flow through subsurface fracture networks is the primary source of production, as matrix permeability is often in the nanodarcy range. Typical models of reservoir discrete fracture networks (DFNs) are constructed using fracture orientation and average spacing, without consideration of how the connectivity of the fracture network aids the percolation of hydrocarbons back to the wellbore. Topological approaches to DFN characterization have been developed and extensively used in analysis of outcrop data and aerial photography. Such study of the surface expression of fracture networks is straight-forward, and the physical form of the observed fractures is directly reflected in the parameters used to describe the topology. However, this analysis largely ignores the three-dimensional nature of natural fracture networks, which is difficult to define accurately in geological studies. SMTI analysis of microseismic event distributions can produce DFNs, where each event is represented by a penny-shaped crack with radius and orientation determined from the frequency content of the waveforms and assessment of the slip instability of the potential fracture planes, respectively. Analysis of the geometric relationships between a set of fractures can provide details of intersections between fractures, and thus the topological characteristics of the fracture network. Extension of existing 2D topology approaches to 3D fracture networks is non-trivial. In the 2D case, a fracture intersection is a single point (node), and branches connect adjacent nodes along fractures. For the 3D case, intersection "nodes" become lines, and connecting nodes to find branches becomes more complicated. There are several parameters defined in 2D topology to quantify the connectivity of the fracture network. Equivalent quantities must be defined and calibrated for the 3D case to provide a meaningful measurement of fracture network connectivity. We have developed an approach to analyze the topology of 3D fracture networks derived from microseismic moment tensors. We illustrate the utility of the approach with applications to example datasets from hydraulic fracturing completions.

A parametric study of the dynamic failure of energetic composites

NASA Astrophysics Data System (ADS)

Tanasoiu, Bogdan; Koslowski, Marisol

2017-09-01

Heating by frictional sliding of cracks is often considered to be one of the most important causes of localized melting and ignition in solid explosives. Furthermore, recent high speed X-ray phase contrast experiments on energetic composites under dynamic compression [Parab et al., Appl. Phys. Lett. 109(13) (2016)] show that most fracture events appear inside the particles. Initial cracks develop in regions where particles are close, and widespread fragmentation is observed in the interior of the particles as the stress waves propagate through the sample. However, most simulations have focused on interface debonding of energetic composites and, in general, do not include fracture of the particles explicitly. A phase field damage approach is used to model the dynamic response of a system of cyclotetramethylene-tetranitramine particles embedded in a Sylgard matrix. The simulations show several damage mechanisms observed in the experiments. The effects of the energy release rate and the initial crack distribution on the energy dissipation due to fracture are studied. The numerical results confirm that initial cracks play an important role in the evolution of damage, energy dissipation and consequently, the formation of hot-spots.

Microstructure dependence of dynamic fracture and yielding in aluminum and an aluminum alloy at strain rates of 2 × 106 s-1 and faster

NASA Astrophysics Data System (ADS)

Dalton, D. A.; Worthington, D. L.; Sherek, P. A.; Pedrazas, N. A.; Quevedo, H. J.; Bernstein, A. C.; Rambo, P.; Schwarz, J.; Edens, A.; Geissel, M.; Smith, I. C.; Taleff, E. M.; Ditmire, T.

2011-11-01

Experiments investigating fracture and resistance to plastic deformation at fast strain rates (>106 s-1) were performed via laser ablation on thin sheets of aluminum and aluminum alloys. Single crystal high purity aluminum (Al-HP) and a single crystal 1100 series aluminum alloy (AA1100) were prepared to investigate the role of impurity particles. Specimens of aluminum alloy +3 wt. % Mg (Al+3Mg) at three different grain sizes were also studied to determine the effect of grain size. In the present experiments, high purity aluminum (Al-HP) exhibited the highest spall strength over 1100 series aluminum alloy (AA1100) and Al+3Mg. Fracture characterization and particle analysis revealed that fracture was initiated in the presence of particles associated with impurity content in the AA1100 and at both grain boundaries and particles in Al+3Mg. The Al+3Mg specimens exhibited the greatest resistance to plastic deformation likely resulting from the presence of magnesium atoms. The Al-HP and AA1100, both lacking a strengthening element such as Mg, were found to have the same Hugoniot elastic limit (HEL) stress. Within the single crystal specimens, orientation effects on spall strength and HEL stress appear to be negligible. Although the fracture character shows a trend with grain size, no clear dependence of spall strength and HEL stress on grain size was measured for the Al+3Mg. Hydrodynamic simulations show how various strength and fracture models are insufficient to predict material behavior at fast strain rates, and a revised set of Tuler-Butcher coefficients for spall are proposed.

[Treatment strategy and planning for pilon fractures].

PubMed

Mittlmeier, Thomas; Wichelhaus, Alice

2017-08-01

Pilon fractures are mainly severe and prognostically serious injuries with a high rate of relevant soft tissue involvement. The adequate decision making and choice of treatment in the early phase of trauma are of paramount importance for the final outcome. This essentially encompasses the management of the soft tissue damage, the surgical planning and the differentiated selection of procedures. Most concepts of staged treatment nowadays offer a wide range of options which are integrated into expert-based algorithms. The aim of the present analysis was to display the strategy variations for the treatment of pilon fractures taking into account the advantages and disadvantages of the corresponding treatment concepts. A staged procedure including primary closed reduction employing ligamentotaxis and fixation of the joints of the hindfoot via tibiocalcaneal metatarsal fixation offers a safe basis for consecutive imaging and the selection of specific approaches for definitive reconstruction. A simultaneous reconstruction and fixation of the fibula during the primary intervention are generally not recommended in order to avoid any limitations for subsequent reconstructive procedures. A time frame for definitive reconstruction covers a period of up to 3 weeks after trauma and allows a detailed planning considering the individual dynamics of the soft tissue situation and any logistic requirements. For the choice of the definitive treatment concept a wide range of procedures and implants are available. There are also valid concepts for primary treatment of defined fracture constellations while primary arthrodesis represents a solution in cases of major destruction of the joint surface. Knowledge of the multiple procedural variations for pilon fracture treatment creates the basis to optimize the treatment modalities and to take into account individual parameters of the fracture.

The Effect of Freezing on the Dynamics of Dike Propagation

NASA Astrophysics Data System (ADS)

Tait, S.; Taisne, B.

2007-12-01

When magma-filled cracks propagate close to the Earth's surface, host rock temperature is well below the magma solidus. Solidification and substantial increase in magma viscosity can occur, are most pronounced near the propagating tip and can slow or arrest the progress of the dike. Quantitative analysis is required to predict whether a given dike will reach the surface to erupt and the duration of the precursor sequence. This challenging physical problem mixes elasticity, fracture mechanics, heat transfer and fluid flow with strong rheologic gradients due to cooling. We describe the propagation behaviour of such a hydraulic fracture using a laboratory experimental system of a crack fed by a constant flux of paraffin wax from a source reservoir propagating through gelatin below the solidus of the wax. The most novel behaviour is an intermittent regime in which cracks periodically stop advancing due to solidification, then swell at constant length while enhancing the elastic deformation in the surrounding solid before propagation resumes. We present a physical model of this system, based on different balances between driving and resistive forces: the former are elastic stress and liquid buoyancy, the latter are fracture resistance at the tip and viscous resistance. The fracture is represented as a head, behind the propagating tip, connected to the source by a narrow tail. Freezing of liquid close to the tip is assumed to enhance fracture resistance according to a cooling law, and propagation is assumed to occur only when the stress exerted by the liquid is enough to overcome fracture resistance. Our theoretical model reproduces intermittent propagation with precise behaviour depending on the controlling stress balances, and provides a tool to analyse natural systems.

Probalistic Finite Elements (PFEM) structural dynamics and fracture mechanics

NASA Technical Reports Server (NTRS)

Liu, Wing-Kam; Belytschko, Ted; Mani, A.; Besterfield, G.

1989-01-01

The purpose of this work is to develop computationally efficient methodologies for assessing the effects of randomness in loads, material properties, and other aspects of a problem by a finite element analysis. The resulting group of methods is called probabilistic finite elements (PFEM). The overall objective of this work is to develop methodologies whereby the lifetime of a component can be predicted, accounting for the variability in the material and geometry of the component, the loads, and other aspects of the environment; and the range of response expected in a particular scenario can be presented to the analyst in addition to the response itself. Emphasis has been placed on methods which are not statistical in character; that is, they do not involve Monte Carlo simulations. The reason for this choice of direction is that Monte Carlo simulations of complex nonlinear response require a tremendous amount of computation. The focus of efforts so far has been on nonlinear structural dynamics. However, in the continuation of this project, emphasis will be shifted to probabilistic fracture mechanics so that the effect of randomness in crack geometry and material properties can be studied interactively with the effect of random load and environment.

An analysis of fracture trace patterns in areas of flat-lying sedimentary rocks for the detection of buried geologic structure. [Kansas and Texas

NASA Technical Reports Server (NTRS)

Podwysocki, M. H.

1974-01-01

Two study areas in a cratonic platform underlain by flat-lying sedimentary rocks were analyzed to determine if a quantitative relationship exists between fracture trace patterns and their frequency distributions and subsurface structural closures which might contain petroleum. Fracture trace lengths and frequency (number of fracture traces per unit area) were analyzed by trend surface analysis and length frequency distributions also were compared to a standard Gaussian distribution. Composite rose diagrams of fracture traces were analyzed using a multivariate analysis method which grouped or clustered the rose diagrams and their respective areas on the basis of the behavior of the rays of the rose diagram. Analysis indicates that the lengths of fracture traces are log-normally distributed according to the mapping technique used. Fracture trace frequency appeared higher on the flanks of active structures and lower around passive reef structures. Fracture trace log-mean lengths were shorter over several types of structures, perhaps due to increased fracturing and subsequent erosion. Analysis of rose diagrams using a multivariate technique indicated lithology as the primary control for the lower grouping levels. Groupings at higher levels indicated that areas overlying active structures may be isolated from their neighbors by this technique while passive structures showed no differences which could be isolated.

Lewis Structures Technology, 1988. Volume 3: Structural Integrity Fatigue and Fracture Wind Turbines HOST

NASA Technical Reports Server (NTRS)

1988-01-01

The charter of the Structures Division is to perform and disseminate results of research conducted in support of aerospace engine structures. These results have a wide range of applicability to practioners of structural engineering mechanics beyond the aerospace arena. The specific purpose of the symposium was to familiarize the engineering structures community with the depth and range of research performed by the division and its academic and industrial partners. Sessions covered vibration control, fracture mechanics, ceramic component reliability, parallel computing, nondestructive evaluation, constitutive models and experimental capabilities, dynamic systems, fatigue and damage, wind turbines, hot section technology (HOST), aeroelasticity, structural mechanics codes, computational methods for dynamics, structural optimization, and applications of structural dynamics, and structural mechanics computer codes.

Use of intramedullary fibular strut graft: a novel adjunct to plating in the treatment of osteoporotic humeral shaft nonunion

PubMed Central

Vamsi, K.; Rao, Sharath K.; Gnanadoss, James J.; Pandian, S.

2008-01-01

Humeral shaft fractures respond well to conservative treatment and unite without much problem. Since it is uncommon, there is not much discussion regarding the management of nonunion in the literature, and hence this is a challenge to the treating orthopaedic surgeon. Osteoporosis of the fractured bone and stiffness of the surrounding joints compounds the situation further. The Ilizarov fixator, locking compression plate, and vascularised fibular graft are viable options in this scenario but are technically demanding. We used a fibular strut graft for bridging the fracture site in order to enhance the pull-out strength of the screws of the dynamic compression plate. Six patients in the study had successful uneventful union of the fracture at the last follow-up. The fibula is easy to harvest and produces less graft site morbidity. None of the study patients needed additional iliac crest bone grafting. This is the largest reported series of patients with osteoporotic atrophic nonunion of humerus successfully treated solely using the combination of an intramedullary fibular strut graft and dynamic compression plate. PMID:18563410

Dynamic fracture of sintered Nd-Fe-B magnet under uniaxial compression

NASA Astrophysics Data System (ADS)

Wang, Huanran; Wan, Yin; Chen, Danian; Lei, Guohua; Ren, Chunying

2018-06-01

The dynamic fracture of the Nd-Fe-B magnets under uniaxial compression is investigated using a split Hopkinson pressure bar (SHPB). The surface deformation and fracture processes of the Nd-Fe-B specimens are recorded adopting a high-speed photography (HSP) with digital image correlation (DIC). The load and work applied to the specimens in the SHPB tests are determined with the strain signals of the transmitted and reflected waves. The surface strain distributions of the Nd-Fe-B specimen during the SHPB testing are revealed with DIC. It is shown by the HSP with DIC that when the load is near the maximum, the cracks at some positions on the surface of the expanding Nd-Fe-B specimen are formed and ran along certain directions. The work applied to the specimen per unit volume which corresponds to the maximal load is used to characterize the impact stability of the Nd-Fe-B specimen. The localized fracture strains at some positions on the surface of the expanding specimens at some characteristic times are determined with DIC, which are the projections of the strains onto the DIC plane.

In situ observation of fracture processes in high-strength concretes and limestone using high-speed X-ray phase-contrast imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Parab, Niranjan D.; Guo, Zherui; Hudspeth, Matthew

The mechanical properties and fracture mechanisms of geomaterials and construction materials such as concrete are reported to be dependent on the loading rates. However, the in situ cracking inside such specimens cannot be visualized using traditional optical imaging methods since the materials are opaque. In this study, the in situ sub-surface failure/damage mechanisms in Cor-Tuf (a reactive powder concrete), a high-strength concrete (HSC) and Indiana limestone under dynamic loading were investigated using high-speed synchrotron X-ray phase-contrast imaging. Dynamic compressive loading was applied using a modified Kolsky bar and fracture images were recorded using a synchronized high-speed synchrotron X-ray imaging set-up.more » Three-dimensional synchrotron X-ray tomography was also performed to record the microstructure of the specimens before dynamic loading. In the Cor-Tuf and HSC specimens, two different modes of cracking were observed: straight cracking or angular cracking with respect to the direction of loading. In limestone, cracks followed the grain boundaries and voids, ultimately fracturing the specimen. Cracks in HSC were more tortuous than the cracks in Cor-Tuf specimens. The effects of the microstructure on the observed cracking behaviour are discussed. This article is part of the themed issue ‘Experimental testing and modelling of brittle materials at high strain rates’.« less

Effectiveness of treatment of transtrochanteric fractures with Dynamic Hip Screws using minimally invasive access☆

PubMed Central

de Abreu, Eduardo Lima; Sena, Caroline Brum; Saldanha Rodrigues Filho, Sergio Antonio

2016-01-01

Objective To analyze the short-term results from treating unstable intertrochanteric fractures with Dynamic Hip Screws (DHS), using a minimally invasive route, focusing on the functional aspects and complication and mortality rates of the method. Methods This was a prospective longitudinal study on 140 patients who underwent fixation of transtrochanteric fractures with the DHS system with a lateral minimally invasive access in the hip, between January and December 2013. The patients were evaluated pre and postoperatively (after six months of follow-up) by means of the Parker and Palmer mobility score. Women comprised 65.7% of the sample, and 54.3% of the fractures were on the right side. The patients’ mean age was 80 years, ranging from 60 to 93 years. Results We observed an overall decrease in the mobility score and an increase in the degree of dependence over the short term. However, we encountered only two deaths in the study sample and there were no cases of infection or nonunion. Conclusion Despite the efficacy of the treatment with DHS, with high rates of fracture consolidation and a low mortality rate, we noted that the patients still showed significant functional limitation at the follow-up six months after the operation. PMID:27069880

A scoping review of applications and outcomes of traction orthoses and constructs for the management of intra-articular fractures and fracture dislocations in the hand.

PubMed

Packham, Tara L; Ball, Pamela D; MacDermid, Joy C; Bain, James R; DalCin, Arianna

2016-01-01

Intra-articular hand fractures can have devastating consequences for movement and function. The unique nature of the injury and diverse management strategies are a challenge for conducting trials. To conduct a scoping review of traction constructs for the management of intra-articular hand fractures. We conducted a systematic search of the literature, extracting data on the scope and nature of the evidence for traction constructs. Our search yielded 87 articles addressing 3 traction constructs: (1) static traction (n = 17), (2) dynamic external fixation (n = 53), and (3) dynamic orthoses (n = 17). Active range of motion of the target joint was the most frequently reported outcome. Study designs included 36 cohorts, 21 case series, and 9 case studies: 24% contained only technical information. The current literature addressing traction constructs consists primarily of small and low-quality studies. Evidence synthesis could improve the estimation of range of motion outcomes but would not be able to identify the best treatment. Consensus on classification of fracture patterns, routine use of outcome measures, and randomized trials are needed to compare different traction constructs and inform evidence-based care. Scoping review. N/A. Copyright © 2016 Hanley & Belfus. Published by Elsevier Inc. All rights reserved.

NASA Contractor Report: Guidelines for Proof Test Analysis

NASA Technical Reports Server (NTRS)

Chell, G. G.; McClung, R. C.; Kuhlman, C. J.; Russell, D. A.; Garr, K.; Donnelly, B.

1997-01-01

These Guidelines integrate state-of-the-art Elastic-Plastic Fracture Mechanics (EPFM) and proof test implementation issues into a comprehensive proof test analysis procedure in the form of a Road Map which identifies the types of data, fracture mechanics based parameters, and calculations needed to perform flaw screening and minimum proof load analyses of fracture critical components. Worked examples are presented to illustrate the application of the Road Map to proof test analysis. The state-of-the-art fracture technology employed in these Guidelines is based on the EPFM parameter, J, and a pictorial representation of a J fracture analysis, called the Failure Assessment Diagram (FAD) approach. The recommended fracture technology is validated using finite element J results, and laboratory and hardware fracture test results on the nickel-based superalloy IN-718, the aluminum alloy 2024-T351 1, and ferritic pressure vessel steels. In all cases the laboratory specimens and hardware failed by ductile mechanisms. Advanced proof test analyses involving probability analysis and Multiple Cycle Proof Testing (MCPT) are addressed. Finally, recommendations are provided on to how to account for the effects of the proof test overload on subsequent service fatigue and fracture behaviors.

Fracture overprinting history using Markov chain analysis: Windsor-Kennetcook subbasin, Maritimes Basin, Canada

NASA Astrophysics Data System (ADS)

Snyder, Morgan E.; Waldron, John W. F.

2018-03-01

The deformation history of the Upper Paleozoic Maritimes Basin, Atlantic Canada, can be partially unraveled by examining fractures (joints, veins, and faults) that are well exposed on the shorelines of the macrotidal Bay of Fundy, in subsurface core, and on image logs. Data were collected from coastal outcrops and well core across the Windsor-Kennetcook subbasin, a subbasin in the Maritimes Basin, using the circular scan-line and vertical scan-line methods in outcrop, and FMI Image log analysis of core. We use cross-cutting and abutting relationships between fractures to understand relative timing of fracturing, followed by a statistical test (Markov chain analysis) to separate groups of fractures. This analysis, previously used in sedimentology, was modified to statistically test the randomness of fracture timing relationships. The results of the Markov chain analysis suggest that fracture initiation can be attributed to movement along the Minas Fault Zone, an E-W fault system that bounds the Windsor-Kennetcook subbasin to the north. Four sets of fractures are related to dextral strike slip along the Minas Fault Zone in the late Paleozoic, and four sets are related to sinistral reactivation of the same boundary in the Mesozoic.

Integrated studies into characteristics of physical fields using discontinuous geomedium models under external loading

NASA Astrophysics Data System (ADS)

Usoltseva Vostrikov, OM, VI; Tsoy, PA; Semenov, VN

2018-03-01

The article presents the laboratory study of deformation in artificial layered geomaterial samples down to failure with the simultaneous measurement of stresses, strains, micro-strains and signals of microseismic emission. The analysis of the synchronized experimental data made it possible to determine features of change in the microseismicity parameters and micro-strain fields in the samples depending on the deformation stage, and also to reveal the dynamics of evolution of microfailures and the main fracture zone.

Impact resistance of fiber composites - Energy-absorbing mechanisms and environmental effects

NASA Technical Reports Server (NTRS)

Chamis, C. C.; Sinclair, J. H.

1985-01-01

Energy absorbing mechanisms were identified by several approaches. The energy absorbing mechanisms considered are those in unidirectional composite beams subjected to impact. The approaches used include: mechanic models, statistical models, transient finite element analysis, and simple beam theory. Predicted results are correlated with experimental data from Charpy impact tests. The environmental effects on impact resistance are evaluated. Working definitions for energy absorbing and energy releasing mechanisms are proposed and a dynamic fracture progression is outlined. Possible generalizations to angle-plied laminates are described.

Impact resistance of fiber composites: Energy absorbing mechanisms and environmental effects

NASA Technical Reports Server (NTRS)

Chamis, C. C.; Sinclair, J. H.

1983-01-01

Energy absorbing mechanisms were identified by several approaches. The energy absorbing mechanisms considered are those in unidirectional composite beams subjected to impact. The approaches used include: mechanic models, statistical models, transient finite element analysis, and simple beam theory. Predicted results are correlated with experimental data from Charpy impact tests. The environmental effects on impact resistance are evaluated. Working definitions for energy absorbing and energy releasing mechanisms are proposed and a dynamic fracture progression is outlined. Possible generalizations to angle-plied laminates are described.

Design-Optimization and Material Selection for a Proximal Radius Fracture-Fixation Implant

NASA Astrophysics Data System (ADS)

Grujicic, M.; Xie, X.; Arakere, G.; Grujicic, A.; Wagner, D. W.; Vallejo, A.

2010-11-01

The problem of optimal size, shape, and placement of a proximal radius-fracture fixation-plate is addressed computationally using a combined finite-element/design-optimization procedure. To expand the set of physiological loading conditions experienced by the implant during normal everyday activities of the patient, beyond those typically covered by the pre-clinical implant-evaluation testing procedures, the case of a wheel-chair push exertion is considered. Toward that end, a musculoskeletal multi-body inverse-dynamics analysis is carried out of a human propelling a wheelchair. The results obtained are used as input to a finite-element structural analysis for evaluation of the maximum stress and fatigue life of the parametrically defined implant design. While optimizing the design of the radius-fracture fixation-plate, realistic functional requirements pertaining to the attainment of the required level of the devise safety factor and longevity/lifecycle were considered. It is argued that the type of analyses employed in the present work should be: (a) used to complement the standard experimental pre-clinical implant-evaluation tests (the tests which normally include a limited number of daily-living physiological loading conditions and which rely on single pass/fail outcomes/decisions with respect to a set of lower-bound implant-performance criteria) and (b) integrated early in the implant design and material/manufacturing-route selection process.

In-Situ Ultra Low Frequency Poroelastic Response of a Natural Macro-Fracture

NASA Astrophysics Data System (ADS)

Guglielmi, Y.; Cappa, F.; Rutqvist, J.; Tsang, C.; Gaffet, S.

2008-12-01

The seismic visibility of macro-fractures filled with fluids is a central problem in the exploration of thermo- hydro-mechanical and chemical processes that occur in Earth' s subsurface. Most studies have been concerned (1) with cracks of a small size relative to the seismic wavelength (2) with "core-sized" samples of single macro-fractures. In comparison, in-situ studies of macro-fractures are very rare and no real estimate is made of the relevance of this convenient "core-sized" data to in-situ reservoirs in general. In this study, we present a new experimental approach to in-situ characterize mechanical and hydraulic properties of fractures using the innovative HPPP protocol. This protocol allows simultaneous high-frequency (120.2 Hz) sampling of normal displacement and fluid pressure in a borehole intersecting the fracture. We show preliminary results conducted in a single fracture vertically embedded in a carbonate reservoir that contains 3 sets of macro-fractures with an average 2m spacing. Two HPPP probes were set, spaced one meter vertically in the fracture. Two types of ULF seismic sources are applied: a fluid pressure pulse injected in the fracture and a hammer hit at a point located 5m far from the fracture plane. There is a highly non-linear variation of fracture normal displacement-versus- fluid pressure as a function of frequency, the higher the frequency, the lower the displacement spectral amplitude is. The pressure pulse and the hammer hit allow exploring the fracture poroelastic response in the [0 - 3Hz] frequency range. The fracture plays the role of a "low-pass" filter for fluid pressure waves; only a quasi-static pressure signal being registered at the receiver. The displacement wave propagation is more complex resulting in uncoupled quasi-static-pressure-2Hz-deformation signals at the receiver. For low magnitude seismic sources (low amplitude pulse and seismic wave), the fracture natural resonance is amplified resulting in separate signals power spectral peaks. When fluid pressure is enough increased, hydraulic diffusion takes place at frequencies lower than 1.2 Hz. Poroelastic effects related to static hydraulic diffusion and to wave propagation were described separately using a linear elastic model where the fracture was treated as a displacement discontinuity across which stresses are continuous but displacement are discontinuous. It appears that the dynamic fracture normal stiffness at 2 to 3 Hz is a factor of 2.8 higher than the static stiffness although the fracture displays a high hydraulic aperture of 10-4 m. This surprising result is related to a high heterogeneity of the fracture channel network with a large porosity/permeability contrast that does not allow fluid displacement under dynamic loading. The HPPP approach appears as a possibility to in-situ characterize such fractures static to seismic poroelastic heterogeneous properties.

Edge cracks in nickel and aluminium single crystals: A molecular dynamics study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chandra, Sagar, E-mail: sagarc@barc.gov.in; Chavan, V. M.; Patel, R. J.

A molecular dynamics study of edge cracks in Ni and Al single crystals under mode-I loading conditions is presented. Simulations are performed using embedded-atom method potentials for Ni and Al at a temperature of 0.5 K. The results reveal that Ni and Al show different fracture mechanisms. Overall failure behavior of Ni is brittle, while fracture in Al proceeds through void nucleation and coalescence with a zig-zag pattern of crack growth. The qualitative nature of results is discussed in the context of vacancy-formation energies and surface energies of the two FCC metals.

Onset of density-driven instabilities in fractured aquifers

NASA Astrophysics Data System (ADS)

Jafari Raad, Seyed Mostafa; Hassanzadeh, Hassan

2018-04-01

Linear stability analysis is conducted to study the onset of density-driven convection involved in solubility trapping of C O2 in fractured aquifers. The effect of physical properties of a fracture network on the stability of a diffusive boundary layer in a saturated fractured porous media is investigated using the dual porosity concept. Linear stability analysis results show that both fracture interporosity flow and fracture storativity play an important role in the stability behavior of the system. It is shown that a diffusive boundary layer under the gravity field in fractured porous media with lower fracture storativity and/or higher fracture interporosity flow coefficient is more stable. We present scaling relations for the onset of convective instability in fractured aquifers with single and variable matrix block size distribution. These findings improve our understanding of density-driven flow in fractured aquifers and are important in the estimation of potential storage capacity, risk assessment, and storage site characterization and screening.

Biomechanics of the Upper Extremity in Response to Dynamic Impact Loading Indicative of a Forward Fall: An Experimental and Numerical Investigation

NASA Astrophysics Data System (ADS)

Burkhart, Timothy A.

The distal radius is one of the most common fracture sites in humans, often resulting from a forward fall with more than 60 % of all fractures to the wrist requiring some form of surgical intervention. Although there is a general consensus regarding the risk factors for distal radius fractures resulting from forward falling, prevention of these injuries requires a more thorough understanding of the injury mechanisms. Therefore the overall purpose of this dissertation was to assess the response of the upper extremity to impact loading to improve the understanding of distal radius fracture mechanisms and the effectiveness of joint kinematic strategies for reducing the impact effects. Three main studies were conducted that utilized in vivo, in vitro and numerical techniques. In vitro impact testing of the distal radius revealed that fracture will occur at a mean (SD) resultant impact force and velocity of 2142.1(1228.7) N and 3.4 (0.7) m/s, respectively. Based on the failure data, multi-variate injury criteria models were produced, highlighting the dynamic and multidirectional nature of distal radius fractures The in vitro investigation was also used to develop and validate a finite element model of the distal radius. Dynamic impacts were simulated in LS-DYNARTM and the resulting z-axis force validation metrics (0.23--0.54) suggest that this is a valid model. A comparison of the experimental fracture patterns to those predicted numerically (i.e. von-Mises stress criteria) shows the finite element model is capable of accurately predicting bone failure. Finally, an in vivo fall simulation apparatus was designed and built that was found to reliably (Intraclass Correlation Coefficients > 0.6) apply multi-directional motion and upper extremity impacts indicative of forward falls. This study revealed that, to some extent, individuals are capable of selected an impact strategy that minimizes the significant injury variables that were outlined in the in vitro investigation, with very little instruction. The body of work presented here has the potential to be used to develop distal radius fracture prevention methods in an attempt to improve the health and well being of those individuals currently at the highest risk of sustaining these injuries.

Predicting the Macroscopic Fracture Energy of Epoxy Resins from Atomistic Molecular Simulations

DOE PAGES

Meng, Zhaoxu; Bessa, Miguel A.; Xia, Wenjie; ...

2016-12-06

Predicting the macroscopic fracture energy of highly crosslinked glassy polymers from atomistic simulations is challenging due to the size of the process zone being large in these systems. Here, we present a scale-bridging approach that links atomistic molecular dynamics simulations to macroscopic fracture properties on the basis of a continuum fracture mechanics model for two different epoxy materials. Our approach reveals that the fracture energy of epoxy resins strongly depends on the functionality of epoxy resin and the component ratio between the curing agent (amine) and epoxide. The most intriguing part of our study is that we demonstrate that themore » fracture energy exhibits a maximum value within the range of conversion degrees considered (from 65% to 95%), which can be attributed to the combined effects of structural rigidity and post-yield deformability. Our study provides physical insight into the molecular mechanisms that govern the fracture characteristics of epoxy resins and demonstrates the success of utilizing atomistic molecular simulations towards predicting macroscopic material properties.« less

Predicting the Macroscopic Fracture Energy of Epoxy Resins from Atomistic Molecular Simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meng, Zhaoxu; Bessa, Miguel A.; Xia, Wenjie

Predicting the macroscopic fracture energy of highly crosslinked glassy polymers from atomistic simulations is challenging due to the size of the process zone being large in these systems. Here, we present a scale-bridging approach that links atomistic molecular dynamics simulations to macroscopic fracture properties on the basis of a continuum fracture mechanics model for two different epoxy materials. Our approach reveals that the fracture energy of epoxy resins strongly depends on the functionality of epoxy resin and the component ratio between the curing agent (amine) and epoxide. The most intriguing part of our study is that we demonstrate that themore » fracture energy exhibits a maximum value within the range of conversion degrees considered (from 65% to 95%), which can be attributed to the combined effects of structural rigidity and post-yield deformability. Our study provides physical insight into the molecular mechanisms that govern the fracture characteristics of epoxy resins and demonstrates the success of utilizing atomistic molecular simulations towards predicting macroscopic material properties.« less

Impact Processes in the Solar System

NASA Technical Reports Server (NTRS)

Ahrens, Thomas J.

2004-01-01

Our laboratory has previously conducted impact fracture and dynamic failure tests. Polanskey and Ahrens [1990] mapped the fractures from a series of laboratory craters (Fig. 1) and Ahrens and Rubin [ 1993] inferred that the usually further extending radial cracks resulted from tensional failure during the compression of the shock propagation. The radial spreading induced by the particle velocity field caused the stresses perpendicular to the shock front to become sufficiently large and tensile. This induces "radial fractures." The concentric fractures are attributed to the tensional failure occurring after the initial compressive phase. Upon radial propagation of the stress wave the negative tension behind the stress-wave front caused failure along the quasi-spherical concentric fractures. The near-surface and spall fractures are attributed to the fractures described by Melosh [1984]. These are activated by impact and can launch relatively unshocked samples of planetary surfaces to speeds exceeding escape velocity. In the case of Mars, some of these surface samples presumably become the SNC (Mars) meteorites.

Development of a new semi-analytical model for cross-borehole flow experiments in fractured media

USGS Publications Warehouse

Roubinet, Delphine; Irving, James; Day-Lewis, Frederick D.

2015-01-01

Analysis of borehole flow logs is a valuable technique for identifying the presence of fractures in the subsurface and estimating properties such as fracture connectivity, transmissivity and storativity. However, such estimation requires the development of analytical and/or numerical modeling tools that are well adapted to the complexity of the problem. In this paper, we present a new semi-analytical formulation for cross-borehole flow in fractured media that links transient vertical-flow velocities measured in one or a series of observation wells during hydraulic forcing to the transmissivity and storativity of the fractures intersected by these wells. In comparison with existing models, our approach presents major improvements in terms of computational expense and potential adaptation to a variety of fracture and experimental configurations. After derivation of the formulation, we demonstrate its application in the context of sensitivity analysis for a relatively simple two-fracture synthetic problem, as well as for field-data analysis to investigate fracture connectivity and estimate fracture hydraulic properties. These applications provide important insights regarding (i) the strong sensitivity of fracture property estimates to the overall connectivity of the system; and (ii) the non-uniqueness of the corresponding inverse problem for realistic fracture configurations.

A Hierarchical Approach to Fracture Mechanics

NASA Technical Reports Server (NTRS)

Saether, Erik; Taasan, Shlomo

2004-01-01

Recent research conducted under NASA LaRC's Creativity and Innovation Program has led to the development of an initial approach for a hierarchical fracture mechanics. This methodology unites failure mechanisms occurring at different length scales and provides a framework for a physics-based theory of fracture. At the nanoscale, parametric molecular dynamic simulations are used to compute the energy associated with atomic level failure mechanisms. This information is used in a mesoscale percolation model of defect coalescence to obtain statistics of fracture paths and energies through Monte Carlo simulations. The mathematical structure of predicted crack paths is described using concepts of fractal geometry. The non-integer fractal dimension relates geometric and energy measures between meso- and macroscales. For illustration, a fractal-based continuum strain energy release rate is derived for inter- and transgranular fracture in polycrystalline metals.

Using decision analysis to assess comparative clinical efficacy of surgical treatment of unstable ankle fractures.

PubMed

Michelson, James D

2013-11-01

The development of a robust treatment algorithm for ankle fractures based on well-established stability criteria has been shown to be prognostic with respect to treatment and outcomes. In parallel with the development of improved understanding of the biomechanical rationale of ankle fracture treatment has been an increased emphasis on assessing the effectiveness of medical and surgical interventions. The purpose of this study was to investigate the use of using decision analysis in the assessment of the cost effectiveness of operative treatment of ankle fractures based on the existing clinical data in the literature. Using the data obtained from a previous structured review of the ankle fracture literature, decision analysis trees were constructed using standard software. The decision nodes for the trees were based on ankle fracture stability criteria previously published. The outcomes were assessed by calculated Quality-Adjusted Life Years (QALYs) assigned to achieving normal ankle function, developing posttraumatic arthritis, or sustaining a postoperative infection. Sensitivity analysis was undertaken by varying the patient's age, incidence of arthritis, and incidence or infection. Decision analysis trees captured the essential aspects of clinical decision making in ankle fracture treatment in a clinically useful manner. In general, stable fractures yielded better outcomes with nonoperative treatment, whereas unstable fractures had better outcomes with surgery. These were consistent results over a wide range of postoperative infection rates. Varying the age of the patient did not qualitatively change the results. Between the ages of 30 and 80 years, surgery yielded higher expected QALYs than nonoperative care for unstable fractures, and generated lower QALYs than nonoperative care for stable fractures. Using local cost estimates for operative and nonoperative treatment, the incremental cost of surgery for unstable fractures was less than $40,000 per QALY (the usual cutoff for the determination of cost effectiveness) for patients aged up to 90 years. Decision analysis is a useful methodology in developing treatment guidelines. Numerous previous studies have indicated superior clinical outcomes when unstable ankle fractures underwent operative reduction and stabilization. What has been lacking was an examination of the cost effectiveness of such an approach, particularly in older patients who have fewer expected years of life. In light of the evidence for satisfactory outcomes for surgery of severe ankle fractures in older people, the justification for operative intervention is an obvious question that can be asked in the current increasingly cost-conscious environment. Using a decision-tree decision analysis structured around the stability-based ankle fracture classification system, in conjunction with a relatively simple cost effectiveness analysis, this study was able to demonstrate that surgical treatment of unstable ankle fractures in elderly patients is in fact cost effective. The clinical implication of the present analysis is that these existing treatment protocols for ankle fracture treatment are also cost effective when quality of life outcome measures are taken into account. Economic Level II. See Instructions for Authors for a complete description of levels of evidence.

Bioinformatics and Microarray Analysis of miRNAs in Aged Female Mice Model Implied New Molecular Mechanisms for Impaired Fracture Healing

PubMed Central

He, Bing; Zhang, Zong-Kang; Liu, Jin; He, Yi-Xin; Tang, Tao; Li, Jie; Guo, Bao-Sheng; Lu, Ai-Ping; Zhang, Bao-Ting; Zhang, Ge

2016-01-01

Impaired fracture healing in aged females is still a challenge in clinics. MicroRNAs (miRNAs) play important roles in fracture healing. This study aims to identify the miRNAs that potentially contribute to the impaired fracture healing in aged females. Transverse femoral shaft fractures were created in adult and aged female mice. At post-fracture 0-, 2- and 4-week, the fracture sites were scanned by micro computed tomography to confirm that the fracture healing was impaired in aged female mice and the fracture calluses were collected for miRNA microarray analysis. A total of 53 significantly differentially expressed miRNAs and 5438 miRNA-target gene interactions involved in bone fracture healing were identified. A novel scoring system was designed to analyze the miRNA contribution to impaired fracture healing (RCIFH). Using this method, 11 novel miRNAs were identified to impair fracture healing at 2- or 4-week post-fracture. Thereafter, function analysis of target genes was performed for miRNAs with high RCIFH values. The results showed that high RCIFH miRNAs in aged female mice might impair fracture healing not only by down-regulating angiogenesis-, chondrogenesis-, and osteogenesis-related pathways, but also by up-regulating osteoclastogenesis-related pathway, which implied the essential roles of these high RCIFH miRNAs in impaired fracture healing in aged females, and might promote the discovery of novel therapeutic strategies. PMID:27527150

Surgical Management of Ipsilateral Fracture of the Femur and Tibia in Adults (the Floating Knee): Postoperative Clinical, Radiological, and Functional Outcomes

PubMed Central

2011-01-01

Background This study evaluated the outcomes of surgical management of ipsilateral femoral and tibial fractures in adults. Methods Fifteen patients (13 men, 2 women; mean age, 34.8 years; range, 18 to 65 years) were enrolled in this study. The fractures types were classified according to the classification by Fraser et al. as follows: type I (5), type IIa (3), IIb (4), IIc (3). Femur fractures were treated using locked intramedullary nails, plate-screws, or dynamic condylar screws, and tibia fractures were treated with an external fixator (in open fractures), or plate-screws, and locked intramedullary nailing. The mean follow-up duration was 2.2 years (range, 1.3 to 4 years). Results The extent of bony union according to the Karlstrom criteria was as follows: excellent, 8; good, 4; acceptable, 2; poor, 1. Conclusions The associated injuries and type of fracture (open, intra-articular, comminution) are prognostic factors in a floating knee. The best management of the associated injuries for good final outcome involves intramedullary nailing of both the fractures and postoperative rehabilitation. PMID:21629474

Initial dynamic load estimates during configuration design

NASA Technical Reports Server (NTRS)

Schiff, Daniel

1987-01-01

This analysis includes the structural response to shock and vibration and evaluates the maximum deflections and material stresses and the potential for the occurrence of elastic instability, fatigue and fracture. The required computations are often performed by means of finite element analysis (FEA) computer programs in which the structure is simulated by a finite element model which may contain thousands of elements. The formulation of a finite element model can be time consuming, and substantial additional modeling effort may be necessary if the structure requires significant changes after initial analysis. Rapid methods for obtaining rough estimates of the structural response to shock and vibration are presented for the purpose of providing guidance during the initial mechanical design configuration stage.

Effect of micromorphology of cortical bone tissue on crack propagation under dynamic loading

NASA Astrophysics Data System (ADS)

Wang, Mayao; Gao, Xing; Abdel-Wahab, Adel; Li, Simin; Zimmermann, Elizabeth A.; Riedel, Christoph; Busse, Björn; Silberschmidt, Vadim V.

2015-09-01

Structural integrity of bone tissue plays an important role in daily activities of humans. However, traumatic incidents such as sports injuries, collisions and falls can cause bone fracture, servere pain and mobility loss. In addition, ageing and degenerative bone diseases such as osteoporosis can increase the risk of fracture [1]. As a composite-like material, a cortical bone tissue is capable of tolerating moderate fracture/cracks without complete failure. The key to this is its heterogeneously distributed microstructural constituents providing both intrinsic and extrinsic toughening mechanisms. At micro-scale level, cortical bone can be considered as a four-phase composite material consisting of osteons, Haversian canals, cement lines and interstitial matrix. These microstructural constituents can directly affect local distributions of stresses and strains, and, hence, crack initiation and propagation. Therefore, understanding the effect of micromorphology of cortical bone on crack initiation and propagation, especially under dynamic loading regimes is of great importance for fracture risk evaluation. In this study, random microstructures of a cortical bone tissue were modelled with finite elements for four groups: healthy (control), young age, osteoporosis and bisphosphonate-treated, based on osteonal morphometric parameters measured from microscopic images for these groups. The developed models were loaded under the same dynamic loading conditions, representing a direct impact incident, resulting in progressive crack propagation. An extended finite-element method (X-FEM) was implemented to realize solution-dependent crack propagation within the microstructured cortical bone tissues. The obtained simulation results demonstrate significant differences due to micromorphology of cortical bone, in terms of crack propagation characteristics for different groups, with the young group showing highest fracture resistance and the senior group the lowest.

Comparison of the quasi-static method and the dynamic method for simulating fracture processes in concrete

NASA Astrophysics Data System (ADS)

Liu, J. X.; Deng, S. C.; Liang, N. G.

2008-02-01

Concrete is heterogeneous and usually described as a three-phase material, where matrix, aggregate and interface are distinguished. To take this heterogeneity into consideration, the Generalized Beam (GB) lattice model is adopted. The GB lattice model is much more computationally efficient than the beam lattice model. Numerical procedures of both quasi-static method and dynamic method are developed to simulate fracture processes in uniaxial tensile tests conducted on a concrete panel. Cases of different loading rates are compared with the quasi-static case. It is found that the inertia effect due to load increasing becomes less important and can be ignored with the loading rate decreasing, but the inertia effect due to unstable crack propagation remains considerable no matter how low the loading rate is. Therefore, an unrealistic result will be obtained if a fracture process including unstable cracking is simulated by the quasi-static procedure.

Dynamic tensile fracture of mortar at ultra-high strain-rates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Erzar, B., E-mail: benjamin.erzar@cea.fr; Buzaud, E.; Chanal, P.-Y.

2013-12-28

During the lifetime of a structure, concrete and mortar may be exposed to highly dynamic loadings, such as impact or explosion. The dynamic fracture at high loading rates needs to be well understood to allow an accurate modeling of this kind of event. In this work, a pulsed-power generator has been employed to conduct spalling tests on mortar samples at strain-rates ranging from 2 × 10{sup 4} to 4 × 10{sup 4} s{sup −1}. The ramp loading allowed identifying the strain-rate anytime during the test. A power law has been proposed to fit properly the rate-sensitivity of tensile strength of thismore » cementitious material over a wide range of strain-rate. Moreover, a specimen has been recovered damaged but unbroken. Micro-computed tomography has been employed to study the characteristics of the damage pattern provoked by the dynamic tensile loading.« less

The Applications of Finite Element Analysis in Proximal Humeral Fractures.

PubMed

Ye, Yongyu; You, Wei; Zhu, Weimin; Cui, Jiaming; Chen, Kang; Wang, Daping

2017-01-01

Proximal humeral fractures are common and most challenging, due to the complexity of the glenohumeral joint, especially in the geriatric population with impacted fractures, that the development of implants continues because currently the problems with their fixation are not solved. Pre-, intra-, and postoperative assessments are crucial in management of those patients. Finite element analysis, as one of the valuable tools, has been implemented as an effective and noninvasive method to analyze proximal humeral fractures, providing solid evidence for management of troublesome patients. However, no review article about the applications and effects of finite element analysis in assessing proximal humeral fractures has been reported yet. This review article summarized the applications, contribution, and clinical significance of finite element analysis in assessing proximal humeral fractures. Furthermore, the limitations of finite element analysis, the difficulties of more realistic simulation, and the validation and also the creation of validated FE models were discussed. We concluded that although some advancements in proximal humeral fractures researches have been made by using finite element analysis, utility of this powerful tool for routine clinical management and adequate simulation requires more state-of-the-art studies to provide evidence and bases.

Trabecular Bone Histomorphometry in Humans with Type 1 Diabetes Mellitus

PubMed Central

Armas, Laura A.G.; Akhter, Mohammed P.; Drincic, Andjela; Recker, Robert R.

2011-01-01

Patients with Type 1 Diabetes Mellitus (DM) have markedly increased risk of fracture, but little is known about abnormalities in bone micro-architecture or remodeling properties that might give insight into the pathogenesis of skeletal fragility in these patients. We report here a case-control study comparing bone histomorphometric and micro-CT results from iliac biopsies in 18 otherwise healthy subjects with Type 1 Diabetes Mellitus with those from healthy age- and sex- matched non-diabetic control subjects. Five of the diabetics had histories of low-trauma fracture. Transilial bone biopsies were obtained after tetracycline labeling. The biopsy specimens were fixed, embedded, and scanned using a desktop μCT at 16 micron resolution. They were then sectioned and quantitative histomorphometry was performed as previously described by Recker et al. 1988.[1] Two sections, >250 μm apart, were read from the central part of each biopsy. Overall there were no significant differences between diabetics and controls in histomorphometric or micro-CT measurements. However, fracturing diabetics had structural and dynamic trends different from nonfracturing diabetics by both methods of analysis. In conclusion, Type 1 Diabetes Mellitus does not result in abnormalities in bone histomorphometric or micro-CT variables in the absence of manifest complications from the diabetes. However, diabetics suffering fractures may have defects in their skeletal microarchitecture that may underlie the presence of excess skeletal fragility. PMID:22001578

Trabecular bone histomorphometry in humans with Type 1 Diabetes Mellitus.

PubMed

Armas, Laura A G; Akhter, Mohammed P; Drincic, Andjela; Recker, Robert R

2012-01-01

Patients with Type 1 Diabetes Mellitus (DM) have markedly increased risk of fracture, but little is known about abnormalities in bone microarchitecture or remodeling properties that might give insight into the pathogenesis of skeletal fragility in these patients. We report here a case-control study comparing bone histomorphometric and micro-CT results from iliac biopsies in 18 otherwise healthy subjects with Type 1 Diabetes Mellitus with those from healthy age- and sex-matched non-diabetic control subjects. Five of the diabetics had histories of low-trauma fracture. Transilial bone biopsies were obtained after tetracycline labeling. The biopsy specimens were fixed, embedded, and scanned using a desktop μCT at 16 μm resolution. They were then sectioned and quantitative histomorphometry was performed as previously described by Recker et al. [1]. Two sections, >250 μm apart, were read from the central part of each biopsy. Overall there were no significant differences between diabetics and controls in histomorphometric or micro-CT measurements. However, fracturing diabetics had structural and dynamic trends different from nonfracturing diabetics by both methods of analysis. In conclusion, Type 1 Diabetes Mellitus does not result in abnormalities in bone histomorphometric or micro-CT variables in the absence of manifest complications from the diabetes. However, diabetics suffering fractures may have defects in their skeletal microarchitecture that may underlie the presence of excess skeletal fragility. Copyright © 2011 Elsevier Inc. All rights reserved.

Biomechanical characterisation of osteosyntheses for proximal femur fractures: helical blade versus screw.

PubMed

Al-Munajjed, Amir A; Hammer, Joachim; Mayr, Edgar; Nerlich, Michael; Lenich, Andreas

2008-01-01

Proximal femur fractures are of main concern for elderly and especially osteoporotic patients. Despite advanced implant modifications and surgical techniques, serious mechanical complication rates between 4-18% are found in conventional osteosyntheses of proximal femur fractures. Clinical complications such as the rotation of the femoral head and the cut-out phenomenon of the fracture fixation bolt are often diagnosed during post-operative treatments. Therefore, efforts in new intramedulary techniques focus on the load bearing characteristics of the implant by developing new geometries to improve the implant-tissue interface. The objective of this investigation was to analyse the osteosynthesis/femur head interaction of two commonly used osteosyntheses, one with a helical blade and the other one with a screw design under different loading conditions. For the comparative investigation the helical blade of the Proximal Femur Nail Antirotation was investigated versus the screw system of the Dynamic Hip Screw. After implantation in a femoral head the loads for rotational overwinding of the implants were analysed. Pull-out forces with suppressed rotation were investigated with analysis of the influence of the previous overwinding. All investigations were performed on human femoral heads taken of patients with average age of 70.3+/-11.8. The bone mineral densities of the human specimens were detected by QCT-scans (average BMD: 338.9+/- 61.3$\\frac[\\mathit[mg

Neglected transport equations: extended Rankine-Hugoniot conditions and J -integrals for fracture

NASA Astrophysics Data System (ADS)

Davey, K.; Darvizeh, R.

2016-09-01

Transport equations in integral form are well established for analysis in continuum fluid dynamics but less so for solid mechanics. Four classical continuum mechanics transport equations exist, which describe the transport of mass, momentum, energy and entropy and thus describe the behaviour of density, velocity, temperature and disorder, respectively. However, one transport equation absent from the list is particularly pertinent to solid mechanics and that is a transport equation for movement, from which displacement is described. This paper introduces the fifth transport equation along with a transport equation for mechanical energy and explores some of the corollaries resulting from the existence of these equations. The general applicability of transport equations to discontinuous physics is discussed with particular focus on fracture mechanics. It is well established that bulk properties can be determined from transport equations by application of a control volume methodology. A control volume can be selected to be moving, stationary, mass tracking, part of, or enclosing the whole system domain. The flexibility of transport equations arises from their ability to tolerate discontinuities. It is insightful thus to explore the benefits derived from the displacement and mechanical energy transport equations, which are shown to be beneficial for capturing the physics of fracture arising from a displacement discontinuity. Extended forms of the Rankine-Hugoniot conditions for fracture are established along with extended forms of J -integrals.

Dynamic fracture toughness of cellulose-fiber-reinforced polypropylene : preliminary investigation of microstructural effects

Treesearch

Craig M. Clemons; Daniel F. Caulfield; A. Jeffrey Giacomin

1999-10-01

In this study, the microstructure of injection-molded polypropylene reinforced with cellulose fiber was investigated. Scanning electron microscopy of the fracture surfaces and X-ray diffraction were used to investigate fiber orientation. The polypropylene matrix was removed by solvent extraction, and the lengths of the residual fibers were optically determined. Fiber...

The combined use of heat-pulse flowmeter logging and packer testing for transmissive fracture recognition

NASA Astrophysics Data System (ADS)

Lo, Hung-Chieh; Chen, Po-Jui; Chou, Po-Yi; Hsu, Shih-Meng

2014-06-01

This paper presents an improved borehole prospecting methodology based on a combination of techniques in the hydrogeological characterization of fractured rock aquifers. The approach is demonstrated by on-site tests carried out in the Hoshe Experimental Forest site and the Tailuge National Park, Taiwan. Borehole televiewer logs are used to obtain fracture location and distribution along boreholes. The heat-pulse flow meter log is used to measure vertical velocity flow profiles which can be analyzed to estimate fracture transmissivity and to indicate hydraulic connectivity between fractures. Double-packer hydraulic tests are performed to determine the rock mass transmissivity. The computer program FLASH is used to analyze the data from the flowmeter logs. The FLASH program is confirmed as a useful tool which quantitatively predicts the fracture transmissivity in comparison to the hydraulic properties obtained from packer tests. The location of conductive fractures and their transmissivity is identified, after which the preferential flow paths through the fracture network are precisely delineated from a cross-borehole test. The results provide robust confirmation of the use of combined flowmeter and packer methods in the characterization of fractured-rock aquifers, particularly in reference to the investigation of groundwater resource and contaminant transport dynamics.

Outcome of Repair of Distal Radial and Ulnar Fractures in Dogs Weighing 4 kg or Less Using a 1.5-mm Locking Adaption Plate or 2.0-mm Limited Contact Dynamic Compression Plate.

PubMed

Nelson, Thomas A; Strom, Adam

2017-11-01

Objectives  Retrospective evaluation of repairing distal radial and ulnar fractures in small breed dogs with the Synthes 1.5-mm locking Adaption plate system and compare results in a similar group of patients repaired with the Synthes 2.0-mm limited contact-dynamic compression plate (LC-DCP). Methods  Electronic medical records from one specialty referral centre were reviewed from March 21, 2010, to October 9, 2015, for patients weighing less than or equal to 4 kg that had a distal one-third radial and ulnar fracture repaired with a Synthes 1.5-mm locking adaption plate or Synthes 2.0-mm LC-DCP. Further inclusion criteria included application of the plate to the cranial surface of the radius via open reduction and internal fixation. Results  Six 1.5-mm Adaption plates and 7 2.0-mm LC-DCPs were used to repair 13 distal radial and ulnar fractures in 12 dogs. There were three major complications in the 1.5-mm adaption plate group (one plate fracture, one screw pull-out and one fracture through a distal screw hole) and one major complication in the 2.0-mm LC-DCP group due to a re-fracture. All patients without a complication had good or excellent functional outcome. Clinical Significance  The authors recommend that the 1.5-mm Adaption plate be used only when a 2.0-mm LC-DCP would not allow for a minimum of two screws in the distal segment and at the discretion of the surgeon. Schattauer GmbH Stuttgart.

Surgical treatment of diaphyseal stress fractures of the fifth metatarsal in competitive athletes: long-term follow-up and computerized pedobarographic analysis.

PubMed

Pecina, Marko; Bojanic, Ivan; Smoljanovic, Tomislav; Ivkovic, Alan; Mirkovic, Maja; Jelic, Miroslav

2011-01-01

Proximal diaphyseal stress fractures of the fifth metatarsal are common in athletes. Conservative treatment has been shown to result in high rates of delayed union, nonunion, and refracture, so internal fixation has become the treatment of choice in competitive athletes. Twenty top-level athletes with diaphyseal stress fractures fixed with intramedullary malleolar screws were evaluated. Functional outcome was assessed by American Orthopaedic Foot and Ankle Society midfoot score. Static and dynamic maximum vertical force and peak plantar pressures were evaluated with a computerized pedobarograph. Mean follow-up from surgery to interview was 10.3 years (range, 3.5-19.0 years). Clinical healing was 95%, and there has been one refracture (5%). The mean time from surgery to return to sport was 9 weeks (range, 5-14 weeks). Twelve athletes (60%) returned to a higher level of training, 7 (35%) to the same level, and 1 (5%) to a lower level compared with the level of training before injury. Average American Orthopaedic Foot and Ankle Society midfoot score was 93.8 (range, 85-100). During the computerized pedobarographic evaluations, 18 patients (90%) presented with varus of the metatarsus and the midfoot and 2 (10%) presented with a normal plantigrade foot. Intramedullary malleolar screws can yield reliable and effective healing of fifth metatarsal stress fractures in athletes. Varus of the metatarsus and the midfoot were predisposing factors for stress fractures in this population of competitive athletes, and all were recommended to wear orthoses until their competitive careers were completed.

Reaction-Infiltration Instabilities in Fractured and Porous Rocks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ladd, Anthony

In this project we are developing a multiscale analysis of the evolution of fracture permeability, using numerical simulations and linear stability analysis. Our simulations include fully three-dimensional simulations of the fracture topography, fluid flow, and reactant transport, two-dimensional simulations based on aperture models, and linear stability analysis.

New software for 3D fracture network analysis and visualization

NASA Astrophysics Data System (ADS)

Song, J.; Noh, Y.; Choi, Y.; Um, J.; Hwang, S.

2013-12-01

This study presents new software to perform analysis and visualization of the fracture network system in 3D. The developed software modules for the analysis and visualization, such as BOUNDARY, DISK3D, FNTWK3D, CSECT and BDM, have been developed using Microsoft Visual Basic.NET and Visualization TookKit (VTK) open-source library. Two case studies revealed that each module plays a role in construction of analysis domain, visualization of fracture geometry in 3D, calculation of equivalent pipes, production of cross-section map and management of borehole data, respectively. The developed software for analysis and visualization of the 3D fractured rock mass can be used to tackle the geomechanical problems related to strength, deformability and hydraulic behaviors of the fractured rock masses.

Intrinsic Nano-Ductility of Glasses: The Critical Role of Composition

NASA Astrophysics Data System (ADS)

Wang, Bu; Yu, Yingtian; Lee, Young; Bauchy, Mathieu

2015-02-01

Understanding, predicting and eventually improving the resistance to fracture for silicate materials is of primary importance to design tougher new glasses suitable for advanced applications. However, the fracture mechanism at the atomic level in amorphous silicate materials is still a topic of debate. In particular, there are some controversies about the existence of ductility at the nanoscale during crack propagation. Here, we present simulations of fracture of three archetypical silicate glasses, using molecular dynamics. The simulations clearly show that, depending on their composition, silicate glasses can exhibit different degrees of ductility at the nanoscale. Additionally, we show that the methodology used in the present work can provide realistic predictions of fracture energy and toughness.

Niobrara Discrete Fracture Network: From Outcrop Surveys to Subsurface Reservoir Models

NASA Astrophysics Data System (ADS)

Grechishnikova, Alena

Heterogeneity of an unconventional reservoir is one of the main factors affecting production. Well performance depends on the size and efficiency of the interconnected fracture "plumbing system", as influenced by multistage hydraulic fracturing. A complex, interconnected natural fracture network can significantly increase the size of stimulated reservoir volume, provide additional surface area contact and enhance permeability. In 2013 the Reservoir Characterization Project (RCP) at the Colorado School of Mines began Phase XV to study Niobrara shale reservoir management. Anadarko Petroleum Corporation and RCP jointly acquired time-lapse multicomponent seismic data in Wattenberg Field, Denver Basin. Anadarko also provided RCP with a regional 3D seismic survey and a rich well dataset. The purpose of this study is to characterize the natural fracture patterns occurring in the unconventional Niobrara reservoir and to determine the drivers that influenced fracture trends and distributions. The findings are integrated into a reservoir model though DFN (Discrete Fracture Network) for further prediction of reservoir performance using reservoir simulations. Aiming to better understand the complexity of the natural fracture system I began my fracture analysis work at an active mine site that provides a Niobrara exposure. Access to a "fresh" outcrop surface created a perfect natural laboratory. Ground-based LIDAR and photogrammetry facilitated construction of a geological model and a DFN model for the mine site. The work was carried into subsurface where the information gained served to improve reservoir characterization at a sub-seismic scale and can be used in well planning. I then embarked on a challenging yet essential task of outcrop-to-subsurface data calibration and application to RCP's Wattenberg Field study site. In this research the surface data was proven to be valid for comparative use in the subsurface. The subsurface fracture information was derived from image logs run within the horizontal wellbores and augmented with microseismic data. Limitations of these datasets included the potential to induce biased interpretations; but the data collected during the outcrop study aided in removing the bias. All four fracture sets observed at the quarry were also interpreted in the subsurface; however there was a limitation on statistical validity for one of the four sets due to a low frequency of observed occurrence potentially caused by wellbore orientation. Microseismic data was used for identification of one of the reactivated natural fracture sets. An interesting phenomenon observed in the microseismic data trends was the low frequency of event occurrence within dense populations of open natural fracture swarms suggesting that zones of higher natural fracture intensities are capable of absorbing and transmitting energy resulting in lower levels of microseismicity. Thus currently open natural fractures could be challenging to detect using microseismic. Through this study I identified a significant variability in fracture intensity at a localized scale due to lithological composition and structural features. The complex faulting styles observed at the outcrop were utilized as an analog and verified by horizontal well log data and seismic volume interpretations creating a high resolution structural model for the subsurface. A lithofacies model was developed based on the well log, core, and seismic inversion analysis. These models combined served to accurately distribute fracture intensity information within the geological model for further use in DFN. As a product of this study, a workflow was developed to aid in fracture network model creation allowing for more intelligent decisions to be made during well planning and completion optimization aiming to improve recovery. A high resolution integrated discrete fracture network model serves to advance dynamic reservoir characterization in the subsurface at a sub-seismic scale resulting in improved reservoir characterization.

Diabetes mellitus and risk of hip fractures: a meta-analysis.

PubMed

Fan, Y; Wei, F; Lang, Y; Liu, Y

2016-01-01

This meta-analysis revealed that diabetic adults had a twofold greater risk of hip fractures compared with non-diabetic populations, and this association was more pronounced in type 1 diabetes. The relationship between diabetes mellitus and risk of hip fracture yielded conflicting results. We conducted a meta-analysis to investigate the association between diabetes mellitus and the risk of hip fractures based on observational studies. We conducted a systematic literature search of PubMed and Embase databases through May 2015. We selected cohort and case-control studies providing at least age-adjusted risk ratio (RR) and corresponding 95 % confidence intervals (CI) of hip fractures among diabetic and non-diabetic subjects. Moreover, we pooled the female-to-male RR of hip fractures from studies that reported gender-specific risk estimate in a single study. Twenty-one studies involving 82,293 hip fracture events among 6,995,272 participants were identified. Diabetes mellitus was associated with an increased risk of hip fractures (RR 2.07; 95 % CI 1.83-2.33) in a random effects model. Subgroup analysis indicated that excess risk of hip fracture was more pronounced in type 1 diabetes (RR 5.76; 95 % CI 3.66-9.07) than that in type 2 diabetes (RR 1.34; 95 % CI 1.19-1.51). The pooled female-to-male RR of hip fractures was 1.09 (95 % CI 0.93-1.28). Individuals with diabetes mellitus have an excessive risk of hip fractures, and this relationship is more pronounced in type 1 diabetes. The association between diabetes and hip fracture risk is similar in men and women.

Applying Fractal Dimensions and Energy-Budget Analysis to Characterize Fracturing Processes During Magma Migration and Eruption: 2011-2012 El Hierro (Canary Islands) Submarine Eruption

NASA Astrophysics Data System (ADS)

López, Carmen; Martí, Joan; Abella, Rafael; Tarraga, Marta

2014-07-01

The impossibility of observing magma migration inside the crust obliges us to rely on geophysical data and mathematical modelling to interpret precursors and to forecast volcanic eruptions. Of the geophysical signals that may be recorded before and during an eruption, deformation and seismicity are two of the most relevant as they are directly related to its dynamic. The final phase of the unrest episode that preceded the 2011-2012 eruption on El Hierro (Canary Islands) was characterized by local and accelerated deformation and seismic energy release indicating an increasing fracturing and a migration of the magma. Application of time varying fractal analysis to the seismic data and the characterization of the seismicity pattern and the strain and the stress rates allow us to identify different stages in the source mechanism and to infer the geometry of the path used by the magma and associated fluids to reach the Earth's surface. The results obtained illustrate the relevance of such studies to understanding volcanic unrest and the causes that govern the initiation of volcanic eruptions.

Delamination Modeling of Composites for Improved Crash Analysis

NASA Technical Reports Server (NTRS)

Fleming, David C.

1999-01-01

Finite element crash modeling of composite structures is limited by the inability of current commercial crash codes to accurately model delamination growth. Efforts are made to implement and assess delamination modeling techniques using a current finite element crash code, MSC/DYTRAN. Three methods are evaluated, including a straightforward method based on monitoring forces in elements or constraints representing an interface; a cohesive fracture model proposed in the literature; and the virtual crack closure technique commonly used in fracture mechanics. Results are compared with dynamic double cantilever beam test data from the literature. Examples show that it is possible to accurately model delamination propagation in this case. However, the computational demands required for accurate solution are great and reliable property data may not be available to support general crash modeling efforts. Additional examples are modeled including an impact-loaded beam, damage initiation in laminated crushing specimens, and a scaled aircraft subfloor structures in which composite sandwich structures are used as energy-absorbing elements. These examples illustrate some of the difficulties in modeling delamination as part of a finite element crash analysis.

Development of Fracture Mechanics Maps for Composite Materials. Volume 2.

DTIC Science & Technology

1985-12-01

AD-A169 663 DEP 1/3UR OIOST l uNCL~ss~~n HUCI S I B M 11 1*2 AF,:P,.-TR-?5,-4150 DEVELOPMENT OF FRACTURE MECHANICS MAPS FOR COMPOSITE MATERIALS Dr. H...coIo. Development of N/A N/A N/A N/A Fracture Mechanics Maps for Composite Materials 12. PERSONAL AUTHORISI Editor (Dr. H. W. Bergmann) 13. TYPE OF...GROUP SUB GR. Fiber Reinforced Composites , Dynamic Test, Thermal Cycling, 1I1 04 Quality Control, Static Test, Stress Concentrations 01 03 19

The Features of Fracture Behavior of an Aluminum-Magnesium Alloy AMg6 Under High-Rate Straining

NASA Astrophysics Data System (ADS)

Skripnyak, N. V.

2015-09-01

The results of investigation of fracture dynamics of rolled sheet specimens of an AMg6 alloy are presented for the range of strain rates from 10-3 to 103 s-1. It is found out that the presence of nanostructured surface layers on the thin AMg6 rolled sheets results in improved strength characteristics within the above range of strain rates. A modified model of a deforming medium is proposed to describe the plastic flow and fracture of the AMg6 alloy.

A comparative study of cranial, blunt trauma fractures as seen at medicolegal autopsy and by Computed Tomography

PubMed Central

2009-01-01

Background Computed Tomography (CT) has become a widely used supplement to medico legal autopsies at several forensic institutes. Amongst other things, it has proven to be very valuable in visualising fractures of the cranium. Also CT scan data are being used to create head models for biomechanical trauma analysis by Finite Element Analysis. If CT scan data are to be used for creating individual head models for retrograde trauma analysis in the future we need to ascertain how well cranial fractures are captured by CT scan. The purpose of this study was to compare the diagnostic agreement between CT and autopsy regarding cranial fractures and especially the precision with which cranial fractures are recorded. Methods The autopsy fracture diagnosis was compared to the diagnosis of two CT readings (reconstructed with Multiplanar and Maximum Intensity Projection reconstructions) by registering the fractures on schematic drawings. The extent of the fractures was quantified by merging 3-dimensional datasets from both the autopsy as input by 3D digitizer tracing and CT scan. Results The results showed a good diagnostic agreement regarding fractures localised in the posterior fossa, while the fracture diagnosis in the medial and anterior fossa was difficult at the first CT scan reading. The fracture diagnosis improved during the second CT scan reading. Thus using two different CT reconstructions improved diagnosis in the medial fossa and at the impact points in the cranial vault. However, fracture diagnosis in the anterior and medial fossa and of hairline fractures in general still remained difficult. Conclusion The study showed that the forensically important fracture systems to a large extent were diagnosed on CT images using Multiplanar and Maximum Intensity Projection reconstructions. Difficulties remained in the minute diagnosis of hairline fractures. These inconsistencies need to be resolved in order to use CT scan data of victims for individual head modelling and trauma analysis. PMID:19835570

Progressive Fracture of Composite Structures

NASA Technical Reports Server (NTRS)

Chamis, Christos C.; Minnetyan, Levon

2008-01-01

A new approach is described for evaluating fracture in composite structures. This approach is independent of classical fracture mechanics parameters like fracture toughness. It relies on computational simulation and is programmed in a stand-alone integrated computer code. It is multiscale, multifunctional because it includes composite mechanics for the composite behavior and finite element analysis for predicting the structural response. It contains seven modules; layered composite mechanics (micro, macro, laminate), finite element, updating scheme, local fracture, global fracture, stress based failure modes, and fracture progression. The computer code is called CODSTRAN (Composite Durability Structural ANalysis). It is used in the present paper to evaluate the global fracture of four composite shell problems and one composite built-up structure. Results show that the composite shells and the built-up composite structure global fracture are enhanced when internal pressure is combined with shear loads.

Comparison of the fracture resistances of glass fiber mesh- and metal mesh-reinforced maxillary complete denture under dynamic fatigue loading.

PubMed

Im, So-Min; Huh, Yoon-Hyuk; Cho, Lee-Ra; Park, Chan-Jin

2017-02-01

The aim of this study was to investigate the effect of reinforcing materials on the fracture resistances of glass fiber mesh- and Cr-Co metal mesh-reinforced maxillary complete dentures under fatigue loading. Glass fiber mesh- and Cr-Co mesh-reinforced maxillary complete dentures were fabricated using silicone molds and acrylic resin. A control group was prepared with no reinforcement (n = 15 per group). After fatigue loading was applied using a chewing simulator, fracture resistance was measured by a universal testing machine. The fracture patterns were analyzed and the fractured surfaces were observed by scanning electron microscopy. After cyclic loading, none of the dentures showed cracks or fractures. During fracture resistance testing, all unreinforced dentures experienced complete fracture. The mesh-reinforced dentures primarily showed posterior framework fracture. Deformation of the all-metal framework caused the metal mesh-reinforced denture to exhibit the highest fracture resistance, followed by the glass fiber mesh-reinforced denture ( P <.05) and the control group ( P <.05). The glass fiber mesh-reinforced denture primarily maintained its original shape with unbroken fibers. River line pattern of the control group, dimples and interdendritic fractures of the metal mesh group, and radial fracture lines of the glass fiber group were observed on the fractured surfaces. The glass fiber mesh-reinforced denture exhibits a fracture resistance higher than that of the unreinforced denture, but lower than that of the metal mesh-reinforced denture because of the deformation of the metal mesh. The glass fiber mesh-reinforced denture maintains its shape even after fracture, indicating the possibility of easier repair.

Failure Analysis on Tail Rotor Teeter Pivot Bolt on a Helicopter

NASA Astrophysics Data System (ADS)

Qiang, WANG; Zi-long, DONG

2018-03-01

Tail rotor teeter pivot bolt of a helicopter fractured when in one flight. Failure analysis on the bolt was finished in laboratory. Macroscopic observation of the tailor rotor teeter pivot bolt, macro and microscopic inspection on the fracture surface of the bolt was carried out. Chemical components and metallurgical structure was also carried out. Experiment results showed that fracture mode of the tail rotor teeter pivot bolt is fatigue fracture. Fatigue area is over 80% of the total fracture surface, obvious fatigue band characteristics can be found at the fracture face. According to the results were analyzed from the macroscopic and microcosmic aspects, fracture reasons of the tail rotor teeter pivot bolt were analyzed in detail

Kuhn-Tucker optimization based reliability analysis for probabilistic finite elements

NASA Technical Reports Server (NTRS)

Liu, W. K.; Besterfield, G.; Lawrence, M.; Belytschko, T.

1988-01-01

The fusion of probability finite element method (PFEM) and reliability analysis for fracture mechanics is considered. Reliability analysis with specific application to fracture mechanics is presented, and computational procedures are discussed. Explicit expressions for the optimization procedure with regard to fracture mechanics are given. The results show the PFEM is a very powerful tool in determining the second-moment statistics. The method can determine the probability of failure or fracture subject to randomness in load, material properties and crack length, orientation, and location.

Irradiation embrittlement characterization of the EUROFER 97 material

NASA Astrophysics Data System (ADS)

Kytka, M.; Brumovsky, M.; Falcnik, M.

2011-02-01

The paper summarizes original results of irradiation embrittlement study of EUROFER 97 material that has been proposed as one candidate of structural materials for future fusion energy systems and GEN IV. Test specimens were manufactured from base metal as well as from weld metal and tested in initial unirradiated condition and also after neutron irradiation. Irradiation embrittlement was characterized by testing of toughness properties at transition temperature region - static fracture toughness and dynamic fracture toughness properties, all in sub-size three-point bend specimens (27 × 4 × 3 mm 3). Testing and evaluation was performed in accordance with ASTM and ESIS standards, fracture toughness KJC and KJd data were also evaluated with the "Master curve" approach. Moreover, J- R dependencies were determined and analyzed. The paper compares unirradiated and irradiated properties as well as changes in transition temperature shifts of these material parameters. Discussion about the correlation between static and dynamic properties is also given. Results from irradiation of EUROFER 97 show that this steel - base metal as well as weld metal - is suitable as a structural material for reactor pressure vessels of innovative nuclear systems - fusion energy systems and GEN IV. Transition temperature shifts after neutron irradiation by 2.5 dpa dose show a good agreement in the case of EUROFER 97 base material for both static and dynamic fracture toughness tests. From the results it can be concluded that there is a low sensitivity of weld metal to neutron irradiation embrittlement in comparison with EUROFER 97 base metal.

Dynamic analysis of a geared rotor system considering a slant crack on the shaft

NASA Astrophysics Data System (ADS)

Han, Qinkai; Zhao, Jingshan; Chu, Fulei

2012-12-01

The vibration problems associated with geared systems have been the focus of research in recent years. As the torque is mainly transmitted by the geared system, a slant crack is more likely to appear on the gear shaft. Due to the slant crack and its breathing mechanism, the dynamic behavior of cracked geared system would differ distinctly with that of uncracked system. Relatively less work is reported on slant crack in the geared rotor system during the past research. Thus, the dynamic analysis of a geared rotor-bearing system with a breathing slant crack is performed in the paper. The finite element model of a geared rotor with slant crack is presented. Based on fracture mechanics, the flexibility matrix for the slant crack is derived that accounts for the additional stress intensity factors. Three methods for whirling analysis, parametric instability analysis and steady-state response analysis are introduced. Then, by taking a widely used one-stage geared rotor-bearing system as an example, the whirling frequencies of the equivalent time-invariant system, two types of instability regions and steady-state response under the excitations of unbalance forces and tooth transmission errors, are computed numerically. The effects of crack depth, position and type (transverse or slant) on the system dynamic behaviors are considered in the discussion. The comparative study with slant cracked geared rotor is carried out to explore distinctive features in their modal, parametric instability and frequency response behaviors.

Effect of dynamic hip screw on the treatment of femoral neck fracture in the elderly.

PubMed

Zhao, Wernbo; Liu, Lei; Zhang, Hui; Fang, Yue; Pei, Fuxing; Yang, Tianfu

2014-04-01

To discuss the indications, surgical procedures, and curative effect of dynamic hip screw (DHS) in the treatment of femoral neck fracture in the elderly. A retrospective study was conducted to analyse the clinical data of 42 elderly patients who had been treated for femoral neck fracture with DHS in our department between June 2009 and November 2011. There were 21 males and 21 females with a mean age of 68.5 years (range 60-75 years). According to the Garden Classification, there were 19 cases of type II, 21 cases of type III and 2 cases of type IV fractures. By the Singh Index Classification, there were 3 cases of level 2, 19 cases of level 3 and 20 cases of level 4 fractures. The Harris criterion, complications and function recovery after opera- tion were analysed. The average hospitalization time in 42 patients was 11.2 days (range 7-21 days). All patients were followed up for 12-26 months (mean 18 months). No lung infection, deep venous thrombosis or other complications occurred. Partial backing-out of the screws was found in 2 cases. The internal fixation device was withdrawn after fracture healing. Internal fixation cutting was found in 1 case, and he had a good recovery after total hip arthroplasty. The time for fracture healing ranged from 3-6 months (average 4.5 months). According to Harris criterion, 15 cases were rated as excellent, 24 good, 2 fair and 1 poor. The Harris scale was significantly improved from 30.52±2.71 preoperatively to 86.61±2.53 at 6 months postoperatively (P<0.05). DHS, being minimal invasive, allowing early activity and weight-bearing, is advisable for treatment of elderly patients with femoral neck fracture. In addition, it can avoid complications seen in artificial joint replacement. It is especially suitable for patients with mild osteoporosis.

Comparison of Intertrochanteric Fracture Fixation with Dynamic Hip Screw and Bipolar Hemiarthroplasty Techniques

PubMed Central

Emami, Mohamad; Manafi, Alireza; Hashemi, Behrooz; Nemati, Ali; Safari, Saeed

2013-01-01

Background: At present, there is no consensus on an appropriate treatment modality for intertrochanteric fractures in the elderly with background diseases. The aim of the present study was to compare treatment outcomes of intertrochanteric fractures reduced with dynamic hip screws (DHS) and bipolar hemiarthroplasty in elderly patients with background medical conditions. Methods: In this randomized clinical trial, 60 patients with intertrochanteric fractures, who were 45-60 years old, were randomly divided into DHS and bipolar groups. After treatment, the two groups were compared in relation to complications and mortality rates, functional status using the Harris Hip Score (HHS), range of movement and severity of pain using the visual analogue score (VAS). Results: HHS (86±9 vs. 75±7.6), range of flexion (105±11 degrees vs. 90±17 degrees) and external rotation (35±7 degrees vs. 20±7 degrees) were significantly higher in the bipolar group compared to the DHS group (P<0.05). However, there were no significant differences in pain severity between the two groups. Conclusion: Reduction of intertrochanteric fractures in elderly patients with background medical conditions is more effective and less problematic with the bipolar technique compared to DHS and is better tolerated by patients, because this technique is associated with improvements in functional status and hip joint movement range. PMID:25207277

Modelling of Dynamic Rock Fracture Process with a Rate-Dependent Combined Continuum Damage-Embedded Discontinuity Model Incorporating Microstructure

NASA Astrophysics Data System (ADS)

Saksala, Timo

2016-10-01

This paper deals with numerical modelling of rock fracture under dynamic loading. For this end, a combined continuum damage-embedded discontinuity model is applied in finite element modelling of crack propagation in rock. In this model, the strong loading rate sensitivity of rock is captured by the rate-dependent continuum scalar damage model that controls the pre-peak nonlinear hardening part of rock behaviour. The post-peak exponential softening part of the rock behaviour is governed by the embedded displacement discontinuity model describing the mode I, mode II and mixed mode fracture of rock. Rock heterogeneity is incorporated in the present approach by random description of the rock mineral texture based on the Voronoi tessellation. The model performance is demonstrated in numerical examples where the uniaxial tension and compression tests on rock are simulated. Finally, the dynamic three-point bending test of a semicircular disc is simulated in order to show that the model correctly predicts the strain rate-dependent tensile strengths as well as the failure modes of rock in this test. Special emphasis is laid on modelling the loading rate sensitivity of tensile strength of Laurentian granite.

Modeling of crack growth under mixed-mode loading by a molecular dynamics method and a linear fracture mechanics approach

NASA Astrophysics Data System (ADS)

Stepanova, L. V.

2017-12-01

Atomistic simulations of the central crack growth process in an infinite plane medium under mixed-mode loading using Large-Scale Atomic/Molecular Massively Parallel Simulator (LAMMPS), a classical molecular dynamics code, are performed. The inter-atomic potential used in this investigation is the Embedded Atom Method (EAM) potential. Plane specimens with an initial central crack are subjected to mixed-mode loadings. The simulation cell contains 400,000 atoms. The crack propagation direction angles under different values of the mixity parameter in a wide range of values from pure tensile loading to pure shear loading in a wide range of temperatures (from 0.1 K to 800 K) are obtained and analyzed. It is shown that the crack propagation direction angles obtained by molecular dynamics coincide with the crack propagation direction angles given by the multi-parameter fracture criteria based on the strain energy density and the multi-parameter description of the crack-tip fields. The multi-parameter fracture criteria are based on the multi-parameter stress field description taking into account the higher order terms of the Williams series expansion of the crack tip fields.

Are Locking Constructs in Distal Femoral Fractures Always Best? A Prospective Multicenter Randomized Controlled Trial Comparing the Less Invasive Stabilization System With the Minimally Invasive Dynamic Condylar Screw System.

PubMed

2016-01-01

The purpose of this clinical study is to determine whether the rate of fracture healing and fracture union, repaired with a locked device, will be as good as or better than standard nonlocking bicortical fixation in distal femoral fractures. Institutional review board-approved, multicenter prospective randomized controlled trial. Seven level 1 trauma centers across Canada. Fifty-two patients with distal femoral fractures (AO/OTA 33A1 to 33C2) were enrolled in the randomized trial. Twelve AO/OTA 33C3 fractures were excluded from the randomized trial but followed up as a nonrandomized cohort. Patients were treated through a standardized minimally invasive approach. Fractures were randomized 1:1 to treatment with the locked Less Invasive Stabilization System (LISS; Synthes, Paoli, PA) or the dynamic condylar screw (DCS). The nonrandomized cohort was treated at the surgeon's discretion. Primary outcomes were time to radiological union and number of delayed/nonunions at 12 months. Secondary outcomes were postoperative function and complications. Fifty-two patients were randomized including 34 women and 18 men. The mean age was 59 years. Twenty-eight patients were treated with the LISS and 24 with the DCS. There was no statistically significant difference between the LISS and the DCS in terms of the number of fractures healed, time to union, or functional scores. Complications and revisions were more common in the LISS group. There were 7 reoperations in the LISS group and one in the DCS group. Only 52% of the LISS group healed without intervention by 12 months compared with 91% in the DCS group. There was no advantage to the locking plate design in the management of distal femoral fractures in this study. The higher cost of the locking plates, challenges in technique, and lack of superiority have led the authors to discontinue the use of this lateral unicortical locking device in favor of other devices that allow locked or nonlocked bicortical fixation, articular compression, and bridging of the comminuted fracture segments. The cost-effective treatment for a subgroup or periarticular fractures may be a fixed-angle nonlocked device in patients with reasonable bone quality. Therapeutic Level II. See Instructions for Authors for a complete description of levels of evidence.

The utility of FRAX® in predicting bone fractures in patients with chronic kidney disease on hemodialysis: a two-year prospective multicenter cohort study.

PubMed

Przedlacki, J; Buczyńska-Chyl, J; Koźmiński, P; Niemczyk, E; Wojtaszek, E; Gieglis, E; Żebrowski, P; Podgórzak, A; Wściślak, J; Wieliczko, M; Matuszkiewicz-Rowińska, J

2018-05-01

We assessed the FRAX® method in 718 hemodialyzed patients in estimating increased risk of bone major and hip fractures. Over two prospective years, statistical analysis showed that FRAX® enables a better assessment of bone major fracture risk in these patients than any of its components and other risk factors considered in the analysis. Despite the generally increased risk of bone fractures among patients with end-stage renal disease, no prediction models for identifying individuals at particular risk have been developed to date. The goal of this prospective, multicenter observational study was to assess the usefulness of the FRAX® method in comparison to all its elements considered separately, selected factors associated with renal disease and the history of falls, in estimating increased risk of low-energy major bone and hip fractures in patients undergoing chronic hemodialysis. The study included a total of 1068 hemodialysis patients, who were followed for 2 years, and finally, 718 of them were analyzed. The risk analysis included the Polish version of the FRAX® calculator (without bone mineral density), dialysis vintage, mineral metabolism disorders (serum calcium, phosphate, and parathyroid hormone), and the number of falls during the last year before the study. Over 2 years, low-energy 30 major bone fractures were diagnosed and 13 of hip fractures among them. Area under the curve for FRAX® was 0.76 (95% CI 0.69-0.84) for major fractures and 0.70 (95% CI 0.563-0.832) for hip fractures. The AUC for major bone fractures was significantly higher than for all elements of the FRAX® calculator. In logistic regression analysis FRAX® was the strongest independent risk factor of assessment of the major bone fracture risk. FRAX® enables a better assessment of major bone fracture risk in ESRD patients undergoing hemodialysis than any of its components and other risk factors considered in the analysis.

Semi-analytical model of cross-borehole flow experiments for fractured medium characterization

NASA Astrophysics Data System (ADS)

Roubinet, D.; Irving, J.; Day-Lewis, F. D.

2014-12-01

The study of fractured rocks is extremely important in a wide variety of research fields where the fractures and faults can represent either rapid access to some resource of interest or potential pathways for the migration of contaminants in the subsurface. Identification of their presence and determination of their properties are critical and challenging tasks that have led to numerous fracture characterization methods. Among these methods, cross-borehole flowmeter analysis aims to evaluate fracture connections and hydraulic properties from vertical-flow-velocity measurements conducted in one or more observation boreholes under forced hydraulic conditions. Previous studies have demonstrated that analysis of these data can provide important information on fracture connectivity, transmissivity, and storativity. Estimating these properties requires the development of analytical and/or numerical modeling tools that are well adapted to the complexity of the problem. Quantitative analysis of cross-borehole flowmeter experiments, in particular, requires modeling formulations that: (i) can be adapted to a variety of fracture and experimental configurations; (ii) can take into account interactions between the boreholes because their radii of influence may overlap; and (iii) can be readily cast into an inversion framework that allows for not only the estimation of fracture hydraulic properties, but also an assessment of estimation error. To this end, we present a new semi-analytical formulation for cross-borehole flow in fractured media that links transient vertical-flow velocities measured in one or a series of observation wells during hydraulic forcing to the transmissivity and storativity of the fractures intersected by these wells. Our model addresses the above needs and provides a flexible and computationally efficient semi-analytical framework having strong potential for future adaptation to more complex configurations. The proposed modeling approach is demonstrated in the context of sensitivity analysis for a relatively simple two-fracture synthetic problem, as well as in the context of field-data analysis for fracture connectivity and estimation of corresponding hydraulic properties.

Assessment of the Influence of Fractures on the Dynamics of Coal Seam Fires by Numerical Experiments

NASA Astrophysics Data System (ADS)

Wuttke, Manfred W.; Zeng, Qiang

2016-04-01

Uncontrolled burning coal seam fires still constitute major problems for the coal industry by destroying the resource, a serious hazard for the local people by severe environmental pollution, and a tremendous threat to the global environment by the emission of greenhouse gases and aerosols. In particular when the seams are lying shallow the alteration of the immediate surrounding of the coal seam fire feeds back on the dynamics of the fire. Thermal stress induced fracturing produces direct connections of the fire zone with the atmosphere. This influences the supply with oxygen, the venting of the exhaust gases, and the dissipation of heat. The first two processes are expected to enhance the fire propagation whereas the latter effect should slow it down. With our dedicated coal seam fire code ACME ("Amendable Coal-fire Modeling Exercise") we study these coupled effects of fractures in simulations of typical coal seam fire scenarios based on data from Xinjiang, China. Fractures are predefined as 1D/2D objects in a 2D/3D model geometry and are opened depending on the passage of the heat wave produced by the coal seam fire.

The breakage behaviour of Aspirin under quasi-static indentation and single particle impact loading: effect of crystallographic anisotropy.

PubMed

Olusanmi, D; Roberts, K J; Ghadiri, M; Ding, Y

2011-06-15

The influence of crystallographic structural anisotropy on the breakage behaviour of Aspirin under impact loading is highlighted. Under both quasi-static testing conditions, using nano-indentation, and dynamic impact tests, Aspirin demonstrates clear anisotropy in its slip and fracture behaviour. During nano-indentation on the (100) and (001) faces, cracks were propagated along the [010] direction. While the hardness was found to be comparatively similar for both these faces, it was observed that slip due to plastic deformation occurred more readily on the (100) than the (001) crystal planes suggesting the former as the preferred slip plane. Furthermore, the fracture toughness on the (001) planes was found to be distinctly lower than that of the (100) planes, indicating the former as the preferred cleavage plane. Observations of the crystal morphology of damaged particles after dynamic impact testing showed that both the chipping and fragmentation of Aspirin mostly occurred via cleavage in a manner consistent with the observed fracture behaviour following nano-indentation. This work highlights the importance of cleavage as a dominant factor underpinning the fracture mechanism of Aspirin under both quasi-static and impact loading conditions. Copyright © 2011 Elsevier B.V. All rights reserved.

Early results of a simple distraction dynamic external fixator in management of comminuted intra-articular fractures of base of middle phalanx.

PubMed

Mansha, Muhammad; Miranda, Sanjay

2013-12-01

Treatment for comminuted fracture dislocations of the proximal interphalangeal joint (pilon injuries) remains a challenge. We present our short term results of twelve pilon fracture dislocations treated by closed reduction and application of a distraction dynamic external fixator. The aim of the study was to assess the clinical outcomes and compare them to the original description by Hynes and Giddins. A cohort of 12 consecutive patients with pilon fracture of the proximal interphalangeal joint (comminuted fracture of the base of middle phalanx, longitudinally unstable with joint subluxation), were treated with this method over the study period. Data was collected by an independent observer at last follow-up appointment in the clinic. The outcome measures recorded were; level of residual pain, arc of motion, X-ray appearance, return to work and satisfaction with the procedure. The study group comprises of 7 male and 5 female patients at a mean age of 38.1 years (range 21-70 years). The average range of movement achieved was 13-87° at a mean follow-up of 16.4 weeks (Range 12-42 weeks). Early return to work, good pain relief and high level of patient satisfaction were achieved. No serious complication was noted during this period. We used the construct with slight modification of the original description and we feel this modification may help to reduce the pin site infection. We found the results reproducible and based on our experience we recommend this technique to treat these complex intra-articular fractures of base of middle phalanx.

Fracture Reactivation in Chemically Reactive Rock Systems

NASA Astrophysics Data System (ADS)

Eichhubl, P.; Hooker, J. N.

2013-12-01

Reactivation of existing fractures is a fundamental process of brittle failure that controls the nucleation of earthquake ruptures, propagation and linkage of hydraulic fractures in oil and gas production, and the evolution of fault and fracture networks and thus of fluid and heat transport in the upper crust. At depths below 2-3 km, and frequently shallower, brittle processes of fracture growth, linkage, and reactivation compete with chemical processes of fracture sealing by mineral precipitation, with precipitation rates similar to fracture opening rates. We recently found rates of fracture opening in tectonically quiescent settings of 10-20 μm/m.y., rates similar to euhedral quartz precipitation under these conditions. The tendency of existing partially or completely cemented fractures to reactivate will vary depending on strain rate, mineral precipitation kinetics, strength contrast between host rock and fracture cement, stress conditions, degree of fracture infill, and fracture network geometry. Natural fractures in quartzite of the Cambrian Eriboll Formation, NW Scotland, exhibit a complex history of fracture formation and reactivation, with reactivation involving both repeated crack-seal opening-mode failure and shear failure of fractures that formed in opening mode. Fractures are partially to completely sealed with crack-seal or euhedral quartz cement or quartz cement fragmented by shear reactivation. Degree of cementation controls the tendency of fractures for later shear reactivation, to interact elastically with adjacent open fractures, and their intersection behavior. Using kinematic, dynamic, and diagenetic criteria, we determine the sequence of opening-mode fracture formation and later shear reactivation. We find that sheared fracture systems of similar orientation display spatially varying sense of slip We attribute these inconsistent directions of shear reactivation to 1) a heterogeneous stress field in this highly fractured rock unit and 2) variations in the degree of fracture cement infill in fractures of same orientation, allowing fractures to reactivate at times when adjacent, more cemented fractures remain dormant. The observed interaction of chemical and mechanical fracture growth and sealing processes in this chemically reactive and heavily deformed rock unit results in a complex fracture network geometry not generally observed in less chemically reactive, shallower crustal environments.

Use of antipsychotics increases the risk of fracture: a systematic review and meta-analysis.

PubMed

Lee, S-H; Hsu, W-T; Lai, C-C; Esmaily-Fard, A; Tsai, Y-W; Chiu, C-C; Wang, J; Chang, S-S; Lee, C C

2017-04-01

Our systematic review and meta-analysis of observational studies indicated that the use of antipsychotics was associated with a nearly 1.5-fold increase in the risk of fracture. First-generation antipsychotics (FGAs) appeared to carry a higher risk of fracture than second-generation antipsychotics (SGAs). The risk of fractures associated with the use of antipsychotic medications has inconsistent evidence between different drug classes. A systematic review and meta-analysis was conducted to evaluate whether there is an association between the use of antipsychotic drugs and fractures. Searches were conducted through the PubMed and EMBASE databases to identify observational studies that had reported a quantitative estimate of the association between use of antipsychotics and fractures. The summary risk was derived from random effects meta-analysis. The search yielded 19 observational studies (n = 544,811 participants) with 80,835 fracture cases. Compared with nonuse, use of FGAs was associated with a significantly higher risk for hip fractures (OR 1.67, 95% CI, 1.45-1.93), and use of second generation antipsychotics (SGAs) was associated with an attenuated but still significant risk for hip fractures (OR 1.33, 95% CI, 1.11-1.58). The risk of fractures associated with individual classes of antipsychotic users was heterogeneous, and odds ratios ranged from 1.24 to 2.01. Chlorpromazine was associated with the highest risk (OR 2.01, 95% CI 1.43-2.83), while Risperidone was associated with the lowest risk of fracture (OR 1.24, 95% CI 0.95-1.83). FGA users were at a higher risk of hip fracture than SGA users. Both FGAs and SGAs were associated with an increased risk of fractures, especially among the older population. Therefore, the benefit of the off-label use of antipsychotics in elderly patients should be weighed against any risks for fracture.

Analysis of delamination related fracture processes in composites

NASA Technical Reports Server (NTRS)

Armanios, Erian A.

1988-01-01

Delamination related fracture processes in composite materials are discussed. Thermal and moisture influences on the free-edge delamination of laminated composites, fracture analysis of local delaminations in laminated composites, and strain energy release rates in belts are among the topics covered.

Applications of Automation Methods for Nonlinear Fracture Test Analysis

NASA Technical Reports Server (NTRS)

Allen, Phillip A.; Wells, Douglas N.

2013-01-01

As fracture mechanics material testing evolves, the governing test standards continue to be refined to better reflect the latest understanding of the physics of the fracture processes involved. The traditional format of ASTM fracture testing standards, utilizing equations expressed directly in the text of the standard to assess the experimental result, is self-limiting in the complexity that can be reasonably captured. The use of automated analysis techniques to draw upon a rich, detailed solution database for assessing fracture mechanics tests provides a foundation for a new approach to testing standards that enables routine users to obtain highly reliable assessments of tests involving complex, non-linear fracture behavior. Herein, the case for automating the analysis of tests of surface cracks in tension in the elastic-plastic regime is utilized as an example of how such a database can be generated and implemented for use in the ASTM standards framework. The presented approach forms a bridge between the equation-based fracture testing standards of today and the next generation of standards solving complex problems through analysis automation.

Multiscale Multifunctional Progressive Fracture of Composite Structures

NASA Technical Reports Server (NTRS)

Chamis, C. C.; Minnetyan, L.

2012-01-01

A new approach is described for evaluating fracture in composite structures. This approach is independent of classical fracture mechanics parameters like fracture toughness. It relies on computational simulation and is programmed in a stand-alone integrated computer code. It is multiscale, multifunctional because it includes composite mechanics for the composite behavior and finite element analysis for predicting the structural response. It contains seven modules; layered composite mechanics (micro, macro, laminate), finite element, updating scheme, local fracture, global fracture, stress based failure modes, and fracture progression. The computer code is called CODSTRAN (Composite Durability Structural ANalysis). It is used in the present paper to evaluate the global fracture of four composite shell problems and one composite built-up structure. Results show that the composite shells. Global fracture is enhanced when internal pressure is combined with shear loads. The old reference denotes that nothing has been added to this comprehensive report since then.

FRACOR-software toolbox for deterministic mapping of fracture corridors in oil fields on AutoCAD platform

NASA Astrophysics Data System (ADS)

Ozkaya, Sait I.

2018-03-01

Fracture corridors are interconnected large fractures in a narrow sub vertical tabular array, which usually traverse entire reservoir vertically and extended for several hundreds of meters laterally. Fracture corridors with their huge conductivities constitute an important element of many fractured reservoirs. Unlike small diffuse fractures, actual fracture corridors must be mapped deterministically for simulation or field development purposes. Fracture corridors can be identified and quantified definitely with borehole image logs and well testing. However, there are rarely sufficient image logs or well tests, and it is necessary to utilize various fracture corridor indicators with varying degrees of reliability. Integration of data from many different sources, in turn, requires a platform with powerful editing and layering capability. Available commercial reservoir characterization software packages, with layering and editing capabilities, can be cost intensive. CAD packages are far more affordable and may easily acquire the versatility and power of commercial software packages with addition of a small software toolbox. The objective of this communication is to present FRACOR, a software toolbox which enables deterministic 2D fracture corridor mapping and modeling on AutoCAD platform. The FRACOR toolbox is written in AutoLISPand contains several independent routines to import and integrate available fracture corridor data from an oil field, and export results as text files. The resulting fracture corridor maps consists mainly of fracture corridors with different confidence levels from combination of static and dynamic data and exclusion zones where no fracture corridor can exist. The exported text file of fracture corridors from FRACOR can be imported into an upscaling programs to generate fracture grid for dual porosity simulation or used for field development and well planning.

Development of the T+M coupled flow–geomechanical simulator to describe fracture propagation and coupled flow–thermal–geomechanical processes in tight/shale gas systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Jihoon; Moridis, George J.

2013-10-01

We developed a hydraulic fracturing simulator by coupling a flow simulator to a geomechanics code, namely T+M simulator. Modeling of the vertical fracture development involves continuous updating of the boundary conditions and of the data connectivity, based on the finite element method for geomechanics. The T+M simulator can model the initial fracture development during the hydraulic fracturing operations, after which the domain description changes from single continuum to double or multiple continua in order to rigorously model both flow and geomechanics for fracture-rock matrix systems. The T+H simulator provides two-way coupling between fluid-heat flow and geomechanics, accounting for thermoporomechanics, treatsmore » nonlinear permeability and geomechanical moduli explicitly, and dynamically tracks changes in the fracture(s) and in the pore volume. We also fully accounts for leak-off in all directions during hydraulic fracturing. We first validate the T+M simulator, matching numerical solutions with the analytical solutions for poromechanical effects, static fractures, and fracture propagations. Then, from numerical simulation of various cases of the planar fracture propagation, shear failure can limit the vertical fracture propagation of tensile failure, because of leak-off into the reservoirs. Slow injection causes more leak-off, compared with fast injection, when the same amount of fluid is injected. Changes in initial total stress and contributions of shear effective stress to tensile failure can also affect formation of the fractured areas, and the geomechanical responses are still well-posed.« less

Hydraulic Fracturing Fluid Analysis for Regulatory Parameters - A Progress Report

EPA Pesticide Factsheets

This presentation is a progress report on the analysis of Hydraulic Fracturing Fluids for regulatory compounds outlined in the various US EPA methodologies. Fracturing fluids vary significantly in consistency and viscosity prior to fracturing. Due to the nature of the fluids the analytical challenges will have to be addressed. This presentation also outlines the sampling issues associated with the collection of dissolved gas samples.

Intergranular fracture in UO{sub 2}: derivation of traction-separation law from atomistic simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Yongfeng; Millett, P.C.; Tonks, M.R.

2013-07-01

In this study, the intergranular fracture behavior of UO{sub 2} was studied by molecular dynamics simulations using the Basak potential. In addition, the constitutive traction-separation law was derived from atomistic data using the cohesive-zone model. In the simulations a bicrystal model with the (100) symmetric tilt Σ5 grain boundaries was utilized. Uniaxial tension along the grain boundary normal was applied to simulate Mode-I fracture. The fracture was observed to propagate along the grain boundary by micro-pore nucleation and coalescence, giving an overall intergranular fracture behavior. Phase transformations from the Fluorite to the Rutile and Scrutinyite phases were identified at themore » propagating crack tips. These new phases are metastable and they transformed back to the Fluorite phase at the wake of crack tips as the local stress concentration was relieved by complete cracking. Such transient behavior observed at atomistic scale was found to substantially increase the energy release rate for fracture. Insertion of Xe gas into the initial notch showed minor effect on the overall fracture behavior. (authors)« less

Intergranular fracture in UO2: derivation of traction-separation law from atomistic simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yongfeng Zhang; Paul C Millett; Michael R Tonks

2013-10-01

In this study, the intergranular fracture behavior of UO2 was studied by molecular dynamics simulations using the Basak potential. In addition, the constitutive traction-separation law was derived from atomistic data using the cohesive-zone model. In the simulations a bicrystal model with the (100) symmetric tilt E5 grain boundaries was utilized. Uniaxial tension along the grain boundary normal was applied to simulate Mode-I fracture. The fracture was observed to propagate along the grain boundary by micro-pore nucleation and coalescence, giving an overall intergranular fracture behavior. Phase transformations from the Fluorite to the Rutile and Scrutinyite phases were identified at the propagatingmore » crack tips. These new phases are metastable and they transformed back to the Fluorite phase at the wake of crack tips as the local stress concentration was relieved by complete cracking. Such transient behavior observed at atomistic scale was found to substantially increase the energy release rate for fracture. Insertion of Xe gas into the initial notch showed minor effect on the overall fracture behavior.« less

Theoretical Analysis of the Mechanism of Fracture Network Propagation with Stimulated Reservoir Volume (SRV) Fracturing in Tight Oil Reservoirs.

PubMed

Su, Yuliang; Ren, Long; Meng, Fankun; Xu, Chen; Wang, Wendong

2015-01-01

Stimulated reservoir volume (SRV) fracturing in tight oil reservoirs often induces complex fracture-network growth, which has a fundamentally different formation mechanism from traditional planar bi-winged fracturing. To reveal the mechanism of fracture network propagation, this paper employs a modified displacement discontinuity method (DDM), mechanical mechanism analysis and initiation and propagation criteria for the theoretical model of fracture network propagation and its derivation. A reasonable solution of the theoretical model for a tight oil reservoir is obtained and verified by a numerical discrete method. Through theoretical calculation and computer programming, the variation rules of formation stress fields, hydraulic fracture propagation patterns (FPP) and branch fracture propagation angles and pressures are analyzed. The results show that during the process of fracture propagation, the initial orientation of the principal stress deflects, and the stress fields at the fracture tips change dramatically in the region surrounding the fracture. Whether the ideal fracture network can be produced depends on the geological conditions and on the engineering treatments. This study has both theoretical significance and practical application value by contributing to a better understanding of fracture network propagation mechanisms in unconventional oil/gas reservoirs and to the improvement of the science and design efficiency of reservoir fracturing.

Theoretical Analysis of the Mechanism of Fracture Network Propagation with Stimulated Reservoir Volume (SRV) Fracturing in Tight Oil Reservoirs

PubMed Central

Su, Yuliang; Ren, Long; Meng, Fankun; Xu, Chen; Wang, Wendong

2015-01-01

Stimulated reservoir volume (SRV) fracturing in tight oil reservoirs often induces complex fracture-network growth, which has a fundamentally different formation mechanism from traditional planar bi-winged fracturing. To reveal the mechanism of fracture network propagation, this paper employs a modified displacement discontinuity method (DDM), mechanical mechanism analysis and initiation and propagation criteria for the theoretical model of fracture network propagation and its derivation. A reasonable solution of the theoretical model for a tight oil reservoir is obtained and verified by a numerical discrete method. Through theoretical calculation and computer programming, the variation rules of formation stress fields, hydraulic fracture propagation patterns (FPP) and branch fracture propagation angles and pressures are analyzed. The results show that during the process of fracture propagation, the initial orientation of the principal stress deflects, and the stress fields at the fracture tips change dramatically in the region surrounding the fracture. Whether the ideal fracture network can be produced depends on the geological conditions and on the engineering treatments. This study has both theoretical significance and practical application value by contributing to a better understanding of fracture network propagation mechanisms in unconventional oil/gas reservoirs and to the improvement of the science and design efficiency of reservoir fracturing. PMID:25966285

A study on electromigration-inducing intergranular fracture of fine silver alloy wires

NASA Astrophysics Data System (ADS)

Hsueh, Hao-Wen; Hung, Fei-Yi; Lui, Truan-Sheng

2017-01-01

In this study, Pd-coated Cu, Ag (purity = 4 N), and Ag alloy (Ag-8Au-3Pd) wires were employed to measure the tensile properties during current stressing using the so-called dynamic current tensile (DCT) test. Both the tensile strength and elongation of the wires decreased dramatically in the DCT test, particularly of the Ag-based wires, and the fracture morphology of the Cu-based and Ag-based wires was ductile fracture and intergranular fracture, respectively. Compared to the Cu-based wires, electromigration occurred more easily in the Ag-based wires, and it always generated voids and cracks at the grain boundaries; therefore, the fracture morphology of the Ag-based wires was intergranular fracture owing to the weakened grain boundary. Further, the results indicated that the Ag-based wires could not carry a higher current density than the Cu-based wires, primarily because their extremely low strength and elongation in current stressing might cause serious reliability problems.

Experiments and FEM simulations of fracture behaviors for ADC12 aluminum alloy under impact load

NASA Astrophysics Data System (ADS)

Hu, Yumei; Xiao, Yue; Jin, Xiaoqing; Zheng, Haoran; Zhou, Yinge; Shao, Jinhua

2016-11-01

Using the combination of experiment and simulation, the fracture behavior of the brittle metal named ADC12 aluminum alloy was studied. Five typical experiments were carried out on this material, with responding data collected on different stress states and dynamic strain rates. Fractographs revealed that the morphologies of fractured specimen under several rates showed different results, indicating that the fracture was predominantly a brittle one in nature. Simulations of the fracture processes of those specimens were conducted by Finite Element Method, whilst consistency was observed between simulations and experiments. In simulation, the Johnson- Cook model was chosen to describe the damage development and to predict the failure using parameters determined from those experimental data. Subsequently, an ADC12 engine mount bracket crashing simulation was conducted and the results indicated good agreement with the experiments. The accordance showed that our research can provide an accurate description for the deforming and fracture processes of the studied alloy.

Viscoplastic fracture transition of a biopolymer gel.

PubMed

Frieberg, Bradley R; Garatsa, Ray-Shimry; Jones, Ronald L; Bachert, John O; Crawshaw, Benjamin; Liu, X Michael; Chan, Edwin P

2018-06-13

Physical gels are swollen polymer networks consisting of transient crosslink junctions associated with hydrogen or ionic bonds. Unlike covalently crosslinked gels, these physical crosslinks are reversible thus enabling these materials to display highly tunable and dynamic mechanical properties. In this work, we study the polymer composition effects on the fracture behavior of a gelatin gel, which is a thermoreversible biopolymer gel consisting of denatured collagen chains bridging physical network junctions formed from triple helices. Below the critical volume fraction for chain entanglement, which we confirm via neutron scattering measurements, we find that the fracture behavior is consistent with a viscoplastic type process characterized by hydrodynamic friction of individual polymer chains through the polymer mesh to show that the enhancement in fracture scales inversely with the squared of the mesh size of the gelatin gel network. Above this critical volume fraction, the fracture process can be described by the Lake-Thomas theory that considers fracture as a chain scission process due to chain entanglements.

Fracture and buckling of piezoelectric nanowires subject to an electric field

NASA Astrophysics Data System (ADS)

Zhang, Jin; Wang, Chengyuan; Adhikari, Sondipon

2013-11-01

Fracture and buckling are major failure modes of thin and long nanowires (NWs), which could be affected significantly by an electric field when piezoelectricity is involved in the NWs. This paper aims to examine the issue based on the molecular dynamics simulations, where the gallium nitride (GaN) NWs are taken as an example. The results show that the influence of the electric field is strong for the fracture and the critical buckling strains, detectable for the fracture strength but almost negligible for the critical buckling stress. In addition, the reversed effects are achieved for the fracture and the critical buckling strains. Subsequently, the Timoshenko beam model is utilized to account for the effect of the electric field on the axial buckling of the GaN NWs, where nonlocal effect is observed and characterized by the nonlocal coefficient e0a=1.1 nm. The results show that the fracture and buckling of piezoelectric NWs can be controlled by applying an electric field.

Mechanical properties and fracture behaviour of defective phosphorene nanotubes under uniaxial tension

NASA Astrophysics Data System (ADS)

Liu, Ping; Pei, Qing-Xiang; Huang, Wei; Zhang, Yong-Wei

2017-12-01

The easy formation of vacancy defects and the asymmetry in the two sublayers of phosphorene nanotubes (PNTs) may result in brand new mechanical properties and failure behaviour. Herein, we investigate the mechanical properties and fracture behaviour of defective PNTs under uniaxial tension using molecular dynamics simulations. Our simulation results show that atomic vacancies cause local stress concentration and thus significantly reduce the fracture strength and fracture strain of PNTs. More specifically, a 1% defect concentration is able to reduce the fracture strength and fracture strain by as much as 50% and 66%, respectively. Interestingly, the reduction in the mechanical properties is found to depend on the defect location: a defect located in the outer sublayer has a stronger effect than one located in the inner layer, especially for PNTs with a small diameter. Temperature is also found to strongly influence the mechanical properties of both defect-free and defective PNTs. When the temperature is increased from 0 K to 400 K, the fracture strength and fracture strain of defective PNTs with a defect concentration of 1% are reduced further by 71% and 61%, respectively. These findings are of great importance for the structural design of PNTs as building blocks in nanodevices.

Mixed integer simulation optimization for optimal hydraulic fracturing and production of shale gas fields

NASA Astrophysics Data System (ADS)

Li, J. C.; Gong, B.; Wang, H. G.

2016-08-01

Optimal development of shale gas fields involves designing a most productive fracturing network for hydraulic stimulation processes and operating wells appropriately throughout the production time. A hydraulic fracturing network design-determining well placement, number of fracturing stages, and fracture lengths-is defined by specifying a set of integer ordered blocks to drill wells and create fractures in a discrete shale gas reservoir model. The well control variables such as bottom hole pressures or production rates for well operations are real valued. Shale gas development problems, therefore, can be mathematically formulated with mixed-integer optimization models. A shale gas reservoir simulator is used to evaluate the production performance for a hydraulic fracturing and well control plan. To find the optimal fracturing design and well operation is challenging because the problem is a mixed integer optimization problem and entails computationally expensive reservoir simulation. A dynamic simplex interpolation-based alternate subspace (DSIAS) search method is applied for mixed integer optimization problems associated with shale gas development projects. The optimization performance is demonstrated with the example case of the development of the Barnett Shale field. The optimization results of DSIAS are compared with those of a pattern search algorithm.

Study on fracture identification of shale reservoir based on electrical imaging logging

NASA Astrophysics Data System (ADS)

Yu, Zhou; Lai, Fuqiang; Xu, Lei; Liu, Lin; Yu, Tong; Chen, Junyu; Zhu, Yuantong

2017-05-01

In recent years, shale gas exploration has made important development, access to a major breakthrough, in which the study of mud shale fractures is extremely important. The development of fractures has an important role in the development of gas reservoirs. Based on the core observation and the analysis of laboratory flakes and laboratory materials, this paper divides the lithology of the shale reservoirs of the XX well in Zhanhua Depression. Based on the response of the mudstone fractures in the logging curve, the fracture development and logging Response to the relationship between the conventional logging and electrical imaging logging to identify the fractures in the work, the final completion of the type of fractures in the area to determine and quantify the calculation of fractures. It is concluded that the fracture type of the study area is high and the microstructures are developed from the analysis of the XX wells in Zhanhua Depression. The shape of the fractures can be clearly seen by imaging logging technology to determine its type.

Delayed fixation of displaced bilateral, atraumatic, femoral neck fractures in a patient with pregnancy related osteomalacia.

PubMed

Docker, Charles; Starks, Ian; Wade, Roger; Wynn-Jones, Charles

2011-06-01

We present the case of a woman diagnosed with simultaneous displaced intracapsular femoral neck fractures following the birth of her second child. No traumatic event was identified. Diagnosis was delayed as the cause of her pain was thought to be non-skeletal in origin. Radiological and serological investigations were diagnostic of osteomalacia. Surgical fixation of her fractures was further delayed due to profound hypocalcaemia. Despite the delays, fixation with bilateral dynamic hip screws resulted in union with no evidence of avascular necrosis at 2 years follow-up. We believe this to be the first report of atraumatic bilateral femoral neck fractures and it shows that a good result can be achieved even in the presence of delayed fixation.

Bilateral simultaneous femoral neck and shafts fractures - a case report.

PubMed

Sadeghifar, Amirreza; Saied, Alireza

2014-10-01

Simultaneous fractures of the femoral neck and shaft are not common injuries, though they cannot be considered rare. Herein, we report our experience with a patient with bilateral occurance of this injury. Up to the best of our knowkedge this is the first case reported in literature in which correct diagnosis was made initially. Both femurs were fixed using broad 4.5 mm dynamic compression plate and both necks were fixed using 6.5 mm cannulated screws. Femur fixation on one side was converted to retrograde nailing because of plate failure. Both neck fractures healed uneventfully. In spite of rarity of concomitant fractures of femoral neck and shaft, this injury must be approached carefully demanding especial attention and careful device selection.

[Dynamic magnetotherapy use in comprehensive treatment phlegmons of maxillofacial region and mandible fractures].

PubMed

Lepilin, A V; Raĭgorodckiĭ, Iu M; Nozdrachev, V G; Erokina, N L

2007-01-01

145 patients (60 with phlegmons of submandibular and submental regions, 85--with fractures of mandible) were observed and treated with the use of moving pulse magnetic field (MPMF) produced by special apparatus (AMO-ATOS-E, , Saratov-city), 60 patients with the same pathology were treated by traditional physical methods and served as control. Use of MPMF led to quicker patient recovery: quicker reduction (if compared with traditional physical methods of treatment) of oedema and soft tissue inflammatory infiltration, quicker relief from inflammatory reaction (according to data of cytokinin profile), improvement of tissue blood supply in the region of fractures in patients with mandible fractures. As the result--we had shortening treatment terms of such patients and complication number reduction.

Analysis of impact energy to fracture un-notched charpy specimens made from railroad tank car steel

DOT National Transportation Integrated Search

2007-09-11

This paper describes a nonlinear finite element analysis : (FEA) framework that examines the impact energy to fracture : unnotched Charpy specimens by an oversized, nonstandard : pendulum impactor called the Bulk Fracture Charpy Machine : (BFCM). The...

Fractography and estimates of fracture origin size from fracture mechanics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Quinn, G.D.; Swab, J.J.

1996-12-31

Fracture mechanics should be used routinely in fractographic analyses in order to verify that the correct feature has been identified as the fracture origin. This was highlighted in a recent Versailles Advanced Materials and Standards (VAMAS) fractographic analysis round robin. The practice of using fracture mechanics as an aid to fractographic interpretation is codified in a new ASTM Standard Practice. Conversely, very good estimates for fracture toughness often come from fractographic analysis of strength tested specimens. In many instances however, the calculated flaw size is different from the empirically-measured flaw size. This paper reviews the factors which may cause themore » discrepancies.« less

Scanning electron microscope fractography in failure analysis of steels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wouters, R.; Froyen, L.

1996-04-01

For many failure cases, macroscopic examination of the fracture surface permits discrimination of fatigue fractures from overload fractures. For clarifying fatigue fractures, the practical significance of microfractography is limited to an investigation of the crack initiation areas. Scanning electron microscopy is successfully used in tracing local material abnormalities that act as fatigue crack initiators. The task for the scanning electron microscope, however, is much more substantial in failure analysis of overload fractures, especially for steels. By revealing specific fractographic characteristics, complemented by information about the material and the loading conditions, scanning electron microscopy provides a strong indication of the probablemore » cause of failure. A complete dimple fracture is indicative of acceptable bulk material properties; overloading, by subdimensioning or excessive external loading, has to be verified. The presence of cleavage fracture makes the material properties questionable if external conditions causing embrittlement are absent. Intergranular brittle fracture requires verification of grain-boundary weakening conditions--a sensitized structure, whether or not combined with a local stress state or a specific environment. The role of scanning electron microscopy in failure analysis is illustrated by case histories of the aforementioned fracture types.« less

Analysis of macroscopic fractures in granite in the HDR geothermal well EPS-1, Soultz-sous-Foreêts, France

NASA Astrophysics Data System (ADS)

Genter, Albert; Traineau, Hervé

1996-07-01

An exhaustive analysis of 3000 macroscopic fractures encountered in the geothermal Hot Dry Rock borehole, EPS-1, located inside the Rhine graben (Soultz-sous-Foreˆts, France), was done on a continuous core section over a depth interval from 1420 to 2230 m: 97% of the macroscopic structures were successfully reorientated with a good degree of confidence by comparison between core and acoustic borehole imagery. Detailed structural analysis of the fracture population indicates that fractures are grouped in two principal fractures sets striking N005 and N170 °, and dipping 70 °W and 70 °E, respectively. This average attitude is closely related to the past tectonic rifting activity of the graben during the Tertiary, and is consistent with data obtained from nearby boreholes and from neighbouring crystalline outcrops. Fractures are distributed in clusters of hydrothermally altered and fractured zones. They constitute a complex network of fault strands dominated by N-S trends, except within some of the most fractured depth intervals (1650 m, 2170 m), where an E-W-striking fracture set occurs. The geometry of the pre-existing fracture system strikes in a direction nearly parallel to the maximum horizontal stress. In this favorable situation, hydraulic injections will tend both to reactivate natural fractures at low pressures, and to create a geothermal reservoir.

Glacier calving, dynamics, and sea-level rise. Final report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meier, M.F.; Pfeffer, W.T.; Amadei, B.

1998-08-01

The present-day calving flux from Greenland and Antarctica is poorly known, and this accounts for a significant portion of the uncertainty in the current mass balance of these ice sheets. Similarly, the lack of knowledge about the role of calving in glacier dynamics constitutes a major uncertainty in predicting the response of glaciers and ice sheets to changes in climate and thus sea level. Another fundamental problem has to do with incomplete knowledge of glacier areas and volumes, needed for analyses of sea-level change due to changing climate. The authors proposed to develop an improved ability to predict the futuremore » contributions of glaciers to sea level by combining work from four research areas: remote sensing observations of calving activity and iceberg flux, numerical modeling of glacier dynamics, theoretical analysis of the calving process, and numerical techniques for modeling flow with large deformations and fracture. These four areas have never been combined into a single research effort on this subject; in particular, calving dynamics have never before been included explicitly in a model of glacier dynamics. A crucial issue that they proposed to address was the general question of how calving dynamics and glacier flow dynamics interact.« less

Numerical Simulation of Permeability Change in Wellbore Cement Fractures after Geomechanical Stress and Geochemical Reactions Using X-ray Computed Tomography Imaging.

PubMed

Kabilan, Senthil; Jung, Hun Bok; Kuprat, Andrew P; Beck, Anthon N; Varga, Tamas; Fernandez, Carlos A; Um, Wooyong

2016-06-21

X-ray microtomography (XMT) imaging combined with three-dimensional (3D) computational fluid dynamics (CFD) modeling technique was used to study the effect of geochemical and geomechanical processes on fracture permeability in composite Portland cement-basalt caprock core samples. The effect of fluid density and viscosity and two different pressure gradient conditions on fracture permeability was numerically studied by using fluids with varying density and viscosity and simulating two different pressure gradient conditions. After the application of geomechanical stress but before CO2-reaction, CFD revealed fluid flow increase, which resulted in increased fracture permeability. After CO2-reaction, XMT images displayed preferential precipitation of calcium carbonate within the fractures in the cement matrix and less precipitation in fractures located at the cement-basalt interface. CFD estimated changes in flow profile and differences in absolute values of flow velocity due to different pressure gradients. CFD was able to highlight the profound effect of fluid viscosity on velocity profile and fracture permeability. This study demonstrates the applicability of XMT imaging and CFD as powerful tools for characterizing the hydraulic properties of fractures in a number of applications like geologic carbon sequestration and storage, hydraulic fracturing for shale gas production, and enhanced geothermal systems.

Numerical Simulation of Permeability Change in Wellbore Cement Fractures after Geomechanical Stress and Geochemical Reactions Using X-ray Computed Tomography Imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kabilan, Senthil; Jung, Hun Bok; Kuprat, Andrew P.

X-ray microtomography (XMT) imaging combined with a three-dimensional (3D) computational fluid dynamics (CFD) modeling technique was used to study the effect of geochemical and geomechanical processes on fracture properties in composite Portland cement–basalt caprock core samples. The effect of fluid properties and flow conditions on fracture permeability was numerically studied by using fluids with varying physical properties and simulating different pressure conditions. CFD revealed that the application of geomechanical stress led to increased fluid flow, which resulted in increased fracture permeability. After CO2-reaction, XMT images displayed preferential precipitation of calcium carbonate within the fractures in the cement matrix and lessmore » precipitation in fractures located at the cement–basalt interface. CFD predicted changes in flow characteristics and differences in absolute values of flow properties due to different pressure gradients. CFD was able to highlight the profound effect of fluid properties on flow characteristics and hydraulic properties of fractures. This study demonstrates the applicability of XMT imaging and CFD as powerful tools for characterizing the hydraulic properties of fractures in a number of applications like geologic carbon sequestration and storage, hydraulic fracturing for shale gas production, and enhanced geothermal systems.« less

Fracture Analysis of Cast Steel Sling

NASA Astrophysics Data System (ADS)

Li, Xinghui

2018-02-01

The fracture reasons of ZG270-500 cast steel sling are analyzed through such means as macroscopic morphology analysis, chemical composition analysis, and microscopic metallography analysis. Results: coarse Widmanstatten structure and casting defects occurring in casting and subsequent heat treatment process reduce the strength, plasticity and toughness of the steel, which is the main reason of brittle fracture of the sling during work, and corresponding improvement suggestions are proposed herein.

Comparison of the fracture resistances of glass fiber mesh- and metal mesh-reinforced maxillary complete denture under dynamic fatigue loading

PubMed Central

2017-01-01

PURPOSE The aim of this study was to investigate the effect of reinforcing materials on the fracture resistances of glass fiber mesh- and Cr–Co metal mesh-reinforced maxillary complete dentures under fatigue loading. MATERIALS AND METHODS Glass fiber mesh- and Cr–Co mesh-reinforced maxillary complete dentures were fabricated using silicone molds and acrylic resin. A control group was prepared with no reinforcement (n = 15 per group). After fatigue loading was applied using a chewing simulator, fracture resistance was measured by a universal testing machine. The fracture patterns were analyzed and the fractured surfaces were observed by scanning electron microscopy. RESULTS After cyclic loading, none of the dentures showed cracks or fractures. During fracture resistance testing, all unreinforced dentures experienced complete fracture. The mesh-reinforced dentures primarily showed posterior framework fracture. Deformation of the all-metal framework caused the metal mesh-reinforced denture to exhibit the highest fracture resistance, followed by the glass fiber mesh-reinforced denture (P<.05) and the control group (P<.05). The glass fiber mesh-reinforced denture primarily maintained its original shape with unbroken fibers. River line pattern of the control group, dimples and interdendritic fractures of the metal mesh group, and radial fracture lines of the glass fiber group were observed on the fractured surfaces. CONCLUSION The glass fiber mesh-reinforced denture exhibits a fracture resistance higher than that of the unreinforced denture, but lower than that of the metal mesh-reinforced denture because of the deformation of the metal mesh. The glass fiber mesh-reinforced denture maintains its shape even after fracture, indicating the possibility of easier repair. PMID:28243388

Origins and nature of non-Fickian transport through fractures

NASA Astrophysics Data System (ADS)

Wang, L.; Cardenas, M. B.

2014-12-01

Non-Fickian transport occurs across all scales within fractured and porous geological media. Fundamental understanding and appropriate characterization of non-Fickian transport through fractures is critical for understanding and prediction of the fate of solutes and other scalars. We use both analytical and numerical modeling, including direct numerical simulation and particle tracking random walk, to investigate the origin of non-Fickian transport through both homogeneous and heterogeneous fractures. For the simple homogenous fracture case, i.e., parallel plates, we theoretically derived a formula for dynamic longitudinal dispersion (D) within Poiseuille flow. Using the closed-form expression for the theoretical D, we quantified the time (T) and length (L) scales separating preasymptotic and asymptotic dispersive transport, with T and L proportional to aperture (b) of parallel plates to second and fourth orders, respectively. As for heterogeneous fractures, the fracture roughness and correlation length are closely associated with the T and L, and thus indicate the origin for non-Fickian transport. Modeling solute transport through 2D rough-walled fractures with continuous time random walk with truncated power shows that the degree of deviation from Fickian transport is proportional to fracture roughness. The estimated L for 2D rough-walled fractures is significantly longer than that derived from the formula within Poiseuille flow with equivalent b. Moreover, we artificially generated normally distributed 3D fractures with fixed correlation length but different fracture dimensions. Solute transport through 3D fractures was modeled with a particle tracking random walk algorithm. We found that transport transitions from non-Fickian to Fickian with increasing fracture dimensions, where the estimated L for the studied 3D fractures is related to the correlation length.

High-rate deformation and spall fracture of hadfield steel under action of high-current nanosecond relativistic electron beam

NASA Astrophysics Data System (ADS)

Gnyusov, S. F.; Rotshtein, V. P.; Polevin, S. D.; Kitsanov, S. A.

2010-09-01

Features of the plastic deformation and dynamic spall fracture of Hadfield steel under conditions of shock wave loading at a straining rate of ˜106 s-1 have been studied. The shock load (˜30 GPa, ˜0.2 μs) was produced by pulses of a SINUS-7 electron accelerator, which generated relativistic electron bunches with an electron energy of up to 1.35 MeV, a duration of 45 ns, and a peak power on the target of 3.4 × 1010 W/cm2. It is established that the spalling proceeds via mixed viscous-brittle intergranular fracture, unlike the cases of quasi-static tensile and impact loading, where viscous transgranular fracture is typical. It is shown that the intergranular character of the spall fracture is caused by the localization of plastic deformation at grain boundaries containing precipitated carbide inclusions.

Tritium and 36Cl as constraints on fast fracture flow and percolation flux in the unsaturated zone at Yucca Mountain

NASA Astrophysics Data System (ADS)

Guerin, Marianne

2001-10-01

An analysis of tritium and 36Cl data collected at Yucca Mountain, Nevada suggests that fracture flow may occur at high velocities through the thick unsaturated zone. The mechanisms and extent of this "fast flow" in fractures at Yucca Mountain are investigated with data analysis, mixing models and several one-dimensional modeling scenarios. The model results and data analysis provide evidence substantiating the weeps model [Gauthier, J.H., Wilson, M.L., Lauffer, F.C., 1992. Proceedings of the Third Annual International High-level Radioactive Waste Management Conference, vol. 1, Las Vegas, NV. American Nuclear Society, La Grange Park, IL, pp. 891-989] and suggest that fast flow in fractures with minimal fracture-matrix interaction may comprise a substantial proportion of the total infiltration through Yucca Mountain. Mixing calculations suggest that bomb-pulse tritium measurements, in general, represent the tail end of travel times for thermonuclear-test-era (bomb-pulse) infiltration. The data analysis shows that bomb-pulse tritium and 36Cl measurements are correlated with discrete features such as horizontal fractures and areas where lateral flow may occur. The results presented here imply that fast flow in fractures may be ubiquitous at Yucca Mountain, occurring when transient infiltration (storms) generates flow in the connected fracture network.

Tritium and 36Cl as constraints on fast fracture flow and percolation flux in the unsaturated zone at Yucca Mountain.

PubMed

Guerin, M

2001-10-01

An analysis of tritium and 36Cl data collected at Yucca Mountain, Nevada suggests that fracture flow may occur at high velocities through the thick unsaturated zone. The mechanisms and extent of this "fast flow" in fractures at Yucca Mountain are investigated with data analysis, mixing models and several one-dimensional modeling scenarios. The model results and data analysis provide evidence substantiating the weeps model [Gauthier, J.H., Wilson, M.L., Lauffer, F.C., 1992. Proceedings of the Third Annual International High-level Radioactive Waste Management Conference, vol. 1, Las Vegas, NV. American Nuclear Society, La Grange Park, IL, pp. 891-989] and suggest that fast flow in fractures with minimal fracture-matrix interaction may comprise a substantial proportion of the total infiltration through Yucca Mountain. Mixing calculations suggest that bomb-pulse tritium measurements, in general, represent the tail end of travel times for thermonuclear-test-era (bomb-pulse) infiltration. The data analysis shows that bomb-pulse tritium and 36Cl measurements are correlated with discrete features such as horizontal fractures and areas where lateral flow may occur. The results presented here imply that fast flow in fractures may be ubiquitous at Yucca Mountain, occurring when transient infiltration (storms) generates flow in the connected fracture network.

Failure analysis of eleven Gates Glidden drills that fractured intraorally during post space preparation. A retrieval analysis study.

PubMed

Al Jabbari, Youssef S; Fournelle, Raymond; Al Taweel, Sara M; Zinelis, Spiros

2017-07-19

The purpose of this study was to determine the failure mechanism of clinically failed Gates Glidden (GG) drills. Eleven retrieved GG drills (sizes #1 to #3) which fractured during root canal preparation were collected and the fracture location was recorded based on macroscopic observation. All fracture surfaces were investigated by a SEM. Then the fractured parts were embedded in acrylic resin and after metallographic preparation, the microstructure and elemental composition was evaluated by SEM and EDS. The Vickers hardness (HV) of all specimens was also determined. Macroscopic examination and SEM analysis showed that the drills failed near the hand piece end by torsional fatigue with fatigue cracks initiating at several locations around the circumference and propagating toward the center. Final fracture followed by a tensile overloading at the central region of cross section. Microstructural analysis, hardness measurements and EDS show that the drills are made of a martensitic stainless steel like AISI 440C. Based on the findings of this study, clinicians should expect fatigue fracture of GG drills that have small size during root canal preparation. Selection of a more fatigue resistant stainless steel alloy and enhancing the instrument design might reduce the incidence of quasi-cleavage fracture on GG drills.

Development of quality assurance methods for epoxy graphite prepreg

NASA Technical Reports Server (NTRS)

Chen, J. S.; Hunter, A. B.

1982-01-01

Quality assurance methods for graphite epoxy/prepregs were developed. Liquid chromatography, differential scanning calorimetry, and gel permeation chromatography were investigated. These methods were applied to a second prepreg system. The resin matrix formulation was correlated with mechanical properties. Dynamic mechanical analysis and fracture toughness methods were investigated. The chromatography and calorimetry techniques were all successfully developed as quality assurance methods for graphite epoxy prepregs. The liquid chromatography method was the most sensitive to changes in resin formulation. The were also successfully applied to the second prepreg system.

Mechanical behavior and failure analysis of prosthetic retaining screws after long-term use in vivo. Part 4: Failure analysis of 10 fractured retaining screws retrieved from three patients.

PubMed

Al Jabbari, Youssef S; Fournelle, Raymond; Ziebert, Gerald; Toth, Jeffrey; Iacopino, Anthony M

2008-04-01

The aim of this study was to perform a failure analysis on fractured prosthetic retaining screws after long-term use in vivo. Additionally, the study addresses the commonly asked question regarding whether complex repeated functional occlusal forces initiate fatigue-type cracks in prosthetic retaining screws. Ten fractured prosthetic retaining screws retrieved from three patients treated with fixed detachable hybrid prostheses were subjected to a failure analysis. In patients 1 and 2, the middle three retaining screws of the prostheses were found fractured at retrieval time after they had been in service for 20 and 19 months, respectively. In patient 3, the middle three and one of the posterior retaining screws were found to be fractured at retrieval after they had been in service for 18 months. Low power stereomicroscopy and high-power scanning electron microscopy (SEM) were performed to analyze the fractured surfaces of the retaining screws examining fatigue cracks in greater detail. Typical fatigue failure characterized by ratchet mark formation was revealed by light microscopy and SEM for all examined screws. Using low magnification light microscopy, ratchet marks were visible on the fracture surfaces of only two screws. SEM examination revealed all three classical stages of fatigue failure, and it was possible to see the ratchet marks on the fracture surfaces of all specimens, indicating a fatigue zone. The final catastrophic overload fracture appeared fibrous, indicating ductile fracture. The final overload ductile fracture surfaces showed equiaxed dimples, suggesting tensile overload in all examined screws except in two specimens that showed an elongated dimple pattern indicating shear/tearing overload forces. Fracture of prosthetic retaining screws in hybrid prostheses occurs mainly through a typical fatigue mode involving mostly the middle anterior three screws. Fatigue cracks can grow in more than one prosthetic retaining screw, leading to fracture before the patient or clinician determines that any problem exists.

Modelling Laccoliths: Fluid-Driven Fracturing in the Lab

NASA Astrophysics Data System (ADS)

Ball, T. V.; Neufeld, J. A.

2017-12-01

Current modelling of the formation of laccoliths neglects the necessity to fracture rock layers for propagation to occur [1]. In magmatic intrusions at depth the idea of fracture toughness is used to characterise fracturing, however an analogue for near surface intrusions has yet to be explored [2]. We propose an analytical model for laccolith emplacement that accounts for the energy required to fracture at the tip of an intrusion. For realistic physical parameters we find that a lag region exists between the fluid magma front and the crack tip where large negative pressures in the tip cause volatiles to exsolve from the magma. Crucially, the dynamics of this tip region controls the spreading due to the competition between viscous forces and fracture energy. We conduct a series of complementary experiments to investigate fluid-driven fracturing of adhered layers and confirm the existence of two regimes: viscosity dominant spreading, controlled by the pressure in the lag region, and fracture energy dominant spreading, controlled by the energy required to fracture layers. Our experiments provide the first observations, and evolution, of a vapour tip. These experiments and our simplified model provide insight into the key physical processes in near surface magmatic intrusions with applications to fluid-driven fracturing more generally. Michaut J. Geophys. Res. 116(B5), B05205. Bunger & Cruden J. Geophys. Res. 116(B2), B02203.

Measuring the hydraulic fracture-induced deformation of reservoirs and adjacent rocks employing a deeply buried inclinometer array: GRI/DOE multi-site project

DOE Office of Scientific and Technical Information (OSTI.GOV)

Branagan, P.T.; Warpinski, N.R.; Engler, B.

A vertical inclinometer array consisting of six biaxial tiltmeters was cemented behind pipe at depths between 4,273 and 4,628 ft. This wide-aperture array provided real-time tilt profiles corresponding to a series of seven hydraulic fractures being conducted in a nearby offset well in a fluvial sandstone reservoir. Array profiles for three KCl water fracs indicated that height growth was confined to the gross thickness of the reservoir despite extensive fracture length extension. Long-term monitoring of the array suggests that a substantial residual frac: width remained long after fracture closure occurred. For two 400-bbl linear gel minifracs, some height growth wasmore » observed but it was not extensive. Tilt amplitudes related to expanded frac widths were found to increase as would be expected with these thicker frac fluids. When cross-linker and proppant were included in the last fracture, tilt-derived heights were seen to grow rapidly extending into the bounding layers as the more complex fluids entered the fracture system. This inclinometer array was one of several independent, yet complimentary, fracture diagnostics tools that included crosswell multilevel microseismic arrays, FRACPRO{reg_sign} and a remote fracture intersection well. Their purpose was to provide integrated field-scale data regarding hydraulic fracture dynamics and geometry that would be used to construct accurate fracture mapping and diagnostic techniques.« less

Pulverized granite at the brittle-ductile transition: An example from the Kellyland fault zone, eastern Maine, U.S.A.

NASA Astrophysics Data System (ADS)

Sullivan, Walter A.; Peterman, Emily M.

2017-08-01

Granite from a 50-200-m-wide damage zone adjacent to the brittle-ductile Kellyland Fault Zone contains healed fracture networks that exhibit almost all of the characteristics of dynamically pulverized rocks. Fracture networks exhibit only weak preferred orientations, are mutually cross-cutting, separate jigsaw-like interlocking fragments, and are associated with recrystallized areas likely derived from pervasively comminuted material. Fracture networks in samples with primary igneous grain shapes further indicate pulverization. Minimum fracture densities in microcline are ∼100 mm/mm2. Larger fractures in microcline and quartz are sometimes marked by neoblasts, but most fractures are optically continuous with host grains and only visible in cathodoluminescence images. Fractures in plagioclase are crystallographically controlled and typically biotite filled. Petrologic observations and cross-cutting relationships between brittle structures and mylonitic rocks show that fracturing occurred at temperatures of 400 °C or more and pressures of 200 MPa. These constraints extend the known range of pulverization to much higher temperature and pressure conditions than previously thought possible. The mutually cross-cutting healed fractures also provide the first record of repeated damage in pulverized rocks. Furthermore, pulverization must have had a significant but transient effect on wall-rock porosity, and biotite-filled fracture networks in plagioclase form weak zones that could accommodate future strain localization.

Transport with Bimolecular Reactions: Applications to In-Situ Chemical Oxidation of DNAPLs by Permanganate in Fractured Rock

NASA Astrophysics Data System (ADS)

Arshadi, Masoud

Chemical oxidation of dense nonaqueous-phase liquids (DNAPLs) by permanganate has emerged as an effective remediation strategy in fractured rock. Our objectives in this research were to carry out a sequence of experimental, computational and theoretical tasks aimed at improving current understanding of permanganate oxidation in fractured rock systems, and also develop modeling tools that can be used for preliminary design of oxidation schemes at field sites. Our research focused on both free-phase entrapped DNAPL in variable-aperture fractures and dissolved DNAPL in the rock matrix. In the first section of our research, we present high-resolution experimental investigations in transparent analog variable-aperture fractures to improve understanding of chemical oxidation of residual entrapped trichloroethylene (TCE) in fractures. Four experiments were performed with different permanganate concentrations, flow rates, and initial TCE phase geometry. The initial aperture field and evolving entrapped-phase geometry were measured quantitatively. We present results on the time-evolution of fracture-scale TCE consumption and DNAPL removal rates for all the experiments. In the next part of this work, we developed theoretical understanding of the reaction front dynamics in the case of chemical oxidation of aqueous-phase DNAPL within fracture-matrix system, backed up by numerical simulations. We also consider the influence of NOD consumption and contaminant sorption to solid aquifer materials in our models. Based on the results from this task we are able to propose simple strategies for remediation design (e.g. the time needed to degrade DNAPL inside the fracture-matrix system and the permanganate injection pattern) for a given set of conditions. Our numerical simulations of diffusion with bimolecular reaction in the rock matrix demonstrated a transition in the spatially integrated reaction rate - increasing with time initially, and transitioning to a decrease with time. We developed a general non-dimensionalization of the problem and a perturbation analysis to show that there is always an early time regime where the spatially integrated reaction rate scales as √t rather than 1/√t. The duration of this early time regime (where the total reaction rate is kinetically rather than diffusion controlled) is shown to depend on the kinetic rate parameters, diffusion coefficients and initial concentrations of the two species.

Patient factors associated with increased acute care costs of hip fractures: a detailed analysis of 402 patients.

PubMed

Aigner, R; Meier Fedeler, T; Eschbach, D; Hack, J; Bliemel, C; Ruchholtz, S; Bücking, B

2016-12-01

The aim of the present study was to identify patient factors associated with higher costs in hip fracture patients. The mean costs of a prospectively observed sample of 402 patients were 8853 €. The ASA score, Charlson comorbidity index, and fracture location were associated with increased costs. Fractures of the proximal end of the femur (hip fractures) are of increasing incidence due to demographic changes. Relevant co-morbidities often present in these patients cause high complication rates and prolonged hospital stays, thus leading to high costs of acute care. The aim of this study was to perform a precise cost analysis of the actual hospital costs of hip fractures and to identify patient factors associated with increased costs. The basis of this analysis was a prospectively observed single-center trial, which included 402 patients with fractures of the proximal end of the femur. All potential cost factors were recorded as accurately as possible for each of the 402 patients individually, and statistical analysis was performed to identify associations between pre-existing patient factors and acute care costs. The mean total acute care costs per patient were 8853 ± 5676 € with ward costs (5828 ± 4294 €) and costs for surgical treatment (1972 ± 956 €) representing the major cost factors. The ASA score, Charlson comorbidity index, and fracture location were identified as influencing the costs of acute care for hip fracture treatment. Hip fractures are associated with high acute care costs. This study underlines the necessity of sophisticated risk-adjusted payment models based on specific patient factors. Economic aspects should be an integral part of future hip fracture research due to limited health care resources.

Thermomechanical coupling and dynamic strain ageing in ductile fracture

NASA Astrophysics Data System (ADS)

Delafosse, David

1995-01-01

This work is concerned with plastic deformation at the tip of a ductile tearing crack during propagation. Two kinds of effects are investigated: the thermomechanical coupling at the tip of a mobile ductile crack, and the influence of Dynamic Strain Aging (DSA) on ductile fracture. Three alloys are studied: a nickel based superalloy (N18), a soft carbon steel, and an Al-Li light alloy (2091). The experimental study of the thermo mechanical coupling effects by means of infrared thermography stresses the importance of plastic dissipation in the energy balance of ductile fracture. Numerical simulations involving plastic deformation as the only dissipation mechanism account for the main part of the measured heating. The effects of DSA on ductile tearing are investigated in the 2091 Al-Li alloy. Based on the strain rate/temperature dependence predicted by the standard model of DSA, an experimental procedure is set up for this purpose. Three main effects are evidenced. A maximum in tearing resistance is shown to be associated with the minimum of strain rate sensitivity. Through a simple model, this peak in tearing resistance is attributed to an increase in plastic dissipation as the strain rate sensitivity is decreased. Heterogenous plastic deformation is observed in the crack tip plastic zone. Comparison with uniaxial testing allows us to identify the observed strain heterogeneities as Portevin-Le Chatelier instabilities in the crack tip plastic zone. We perform a simplified numerical analysis of the effect of strain localization on crack tip screening. Finally, small crack propagation instabilities appear at temperatures slightly above that of the tearing resistance peak. These are interpreted as resulting from a positive feed-back between the local heating at the tip of a moving crack and the decrease in tearing resistance with increasing temperature.

Correction to the Dynamic Tensile Strength of Ice and Ice-Silicate Mixtures (Lange & Ahrens 1983)

NASA Astrophysics Data System (ADS)

Stewart, S. T.; Ahrens, T. J.

1999-03-01

We present a correction to the Weibull parameters for ice and ice-silicate mixtures (Lange & Ahrens 1983). These parameters relate the dynamic tensile strength to the strain rate. These data are useful for continuum fracture models of ice.

Quantifying Seasonal Dynamic Water Storage in a Fractured Bedrock Vadose Zone With Borehole Nuclear Magnetic Resonance

NASA Astrophysics Data System (ADS)

Schmidt, L.; Minton, B.; Soto-Kerans, N.; Rempe, D.; Heidari, Z.

2017-12-01

In many uplands landscapes, water is transiently stored in the weathered and fractured bedrock that underlies soils. The timing and spatial pattern of this "rock moisture" has strong implications for ecological and biogeochemical processes that influence global cycling of water and solutes. However, available technologies for direct monitoring of rock moisture are limited. Here, we quantify temporal and spatial changes in rock moisture at the field scale across thick (up to 20 m) fractured vadose zone profiles using a novel narrow diameter borehole nuclear magnetic resonance system (BNMR). Successive BNMR surveys were performed using the Vista Clara Inc. Dart system in a network of boreholes within two steep, intensively hydrologically monitored hillslopes associated with the Eel River Critical Zone Observatory (ERCZO) in Northern California. BNMR data showed agreement with estimates of the temporal and spatial pattern of rock moisture depletion over the dry season via downhole neutron and gamma density surveys, as well as permanently installed continuous time domain reflectometry. Observable shifts in the BNMR-derived T2 distribution over time provide a direct measure of changes in the amount of water held within different pore sizes (large vs. small) in fractured rock. Analysis of both BNMR and laboratory-scale NMR (using a 2MHz benchtop NMR spectrometer) measurements of ERCZO core samples at variable saturation suggest that rock moisture changes associated with summer depletion occur within both large (fracture) and small (matrix) pore sizes. Collectively, our multi-method field- and laboratory- scale measurements highlight the potential for BNMR to improve quantification of rock moisture storage for better understanding of the biogeochemical and ecohydrological implications of rock moisture circulation in the Critical Zone.

Dynamic fracture behavior of single and contacting Poly(methyl methacrylate) particles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Parab, Niranjan D.; Guo, Zherui; Hudspeth, Matthew C.

Fracture behaviors of single, two, and multiple contacting spherical Poly (methyl methacrylate) (PMMA) particles were recorded using high speed synchrotron X-ray phase contrast imaging. A miniaturized Kolsky bar setup was used to apply dynamic compressive loading on the PMMA particles. In both single and two particle experiments, cracking initiated near the center of the particles and propagated towards the contacts. The crack bifurcated near the contact points for single particle experiments, thus forming conical fragments. The crack bifurcation and subsequent conical fragment formation was observed only at the particle-particle contact for two particle experiments. The particles were observed to fracturemore » in hemispherical fragments normal to the contact plane in the multiparticle experiments. The observed failure mechanisms strongly suggest that the maximum tensile stress near the center of the particle is the critical parameter governing fracture of the particles. Moreover, the compressive stress under the contact areas led to the bifurcation and subsequent conical fragment formation.« less

Dynamic fracture behavior of single and contacting Poly(methyl methacrylate) particles

DOE PAGES

Parab, Niranjan D.; Guo, Zherui; Hudspeth, Matthew C.; ...

2017-09-19

Fracture behaviors of single, two, and multiple contacting spherical Poly (methyl methacrylate) (PMMA) particles were recorded using high speed synchrotron X-ray phase contrast imaging. A miniaturized Kolsky bar setup was used to apply dynamic compressive loading on the PMMA particles. In both single and two particle experiments, cracking initiated near the center of the particles and propagated towards the contacts. The crack bifurcated near the contact points for single particle experiments, thus forming conical fragments. The crack bifurcation and subsequent conical fragment formation was observed only at the particle-particle contact for two particle experiments. The particles were observed to fracturemore » in hemispherical fragments normal to the contact plane in the multiparticle experiments. The observed failure mechanisms strongly suggest that the maximum tensile stress near the center of the particle is the critical parameter governing fracture of the particles. Moreover, the compressive stress under the contact areas led to the bifurcation and subsequent conical fragment formation.« less

The International Costs and Utilities Related to Osteoporotic Fractures Study (ICUROS)--quality of life during the first 4 months after fracture.

PubMed

Borgström, F; Lekander, I; Ivergård, M; Ström, O; Svedbom, A; Alekna, V; Bianchi, M L; Clark, P; Curiel, M D; Dimai, H P; Jürisson, M; Kallikorm, R; Lesnyak, O; McCloskey, E; Nassonov, E; Sanders, K M; Silverman, S; Tamulaitiene, M; Thomas, T; Tosteson, A N A; Jönsson, B; Kanis, J A

2013-03-01

The quality of life during the first 4 months after fracture was estimated in 2,808 fractured patients from 11 countries. Analysis showed that there were significant differences in the quality of life (QoL) loss between countries. Other factors such as QoL prior fracture and hospitalisation also had a significant impact on the QoL loss. The International Costs and Utilities Related to Osteoporotic Fractures Study (ICUROS) was initiated in 2007 with the objective of estimating costs and quality of life related to fractures in several countries worldwide. The ICUROS is ongoing and enrols patients in 11 countries (Australia, Austria, Estonia, France, Italy, Lithuania, Mexico, Russia, Spain, UK and the USA). The objective of this paper is to outline the study design of ICUROS and present results regarding the QoL (measured using the EQ-5D) during the first 4 months after fracture based on the patients that have been thus far enrolled ICUROS. ICUROS uses a prospective study design where data (costs and quality of life) are collected in four phases over 18 months after fracture. All countries use the same core case report forms. Quality of life was collected using the EQ-5D instrument and a time trade-off questionnaire. The total sample for the analysis was 2,808 patients (1,273 hip, 987 distal forearm and 548 vertebral fracture). For all fracture types and countries, the QoL was reduced significantly after fracture compared to pre-fracture QoL. A regression analysis showed that there were significant differences in the QoL loss between countries. Also, a higher level of QoL prior to the fracture significantly increased the QoL loss and patients who were hospitalised for their fracture also had a significantly higher loss compared to those who were not. The findings in this study indicate that there appear to be important variations in the QoL decrements related to fracture between countries.

Analysis of 213 currently used rehabilitation protocols in foot and ankle fractures.

PubMed

Pfeifer, Christian G; Grechenig, Stephan; Frankewycz, Borys; Ernstberger, Antonio; Nerlich, Michael; Krutsch, Werner

2015-10-01

Fractures of the ankle, hind- and midfoot are amongst the five most common fractures. Besides initial operative or non-operative treatment, rehabilitation of the patients plays a crucial role for fracture union and long term functional outcome. Limited evidence is available with regard to what a rehabilitation regimen should include and what guidelines should be in place for the initial clinical course of these patients. This study therefore investigated the current rehabilitation concepts after fractures of the ankle, hind- and midfoot. Written rehabilitation protocols provided by orthopedic and trauma surgery institutions in terms of recommendations for weight bearing, range of motion (ROM), physiotherapy and choice of orthosis were screened and analysed. All protocols for lateral ankle fractures type AO 44A1, AO 44B1 and AO 44C1, for calcaneal fractures and fractures of the metatarsal as well as other not specific were included. Descriptive analysis was carried out and statistical analysis applied where appropriate. 209 rehabilitation protocols for ankle fractures type AO 44B1 and AO 44C1, 98 for AO 44A1, 193 for metatarsal fractures, 142 for calcaneal fractures, 107 for 5(th) metatarsal base fractures and 70 for 5(th) metatarsal Jones fractures were evaluated. The mean time recommended for orthosis treatment was 6.04 (SD 0.04) weeks. While the majority of protocols showed a trend towards increased weight bearing and increased ROM over time, the best consensus was noted for weight bearing recommendations. Our study shows that there exists a huge variability in rehabilitation of fractures of the ankle-, hind- and midfoot. This may be contributed to a lack of consensus (e.g. missing publication of guidelines), individualized patient care (e.g. in fragility fractures) or lack of specialization. This study might serve as basis for prospective randomized controlled trials in order to optimize rehabilitation for these common fractures. Copyright © 2015 Elsevier Ltd. All rights reserved.

Discontinuities in effective permeability due to fracture percolation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hyman, Jeffrey De'Haven; Karra, Satish; Carey, James William

Motivated by a triaxial coreflood experiment with a sample of Utica shale where an abrupt jump in permeability was observed, possibly due to the creation of a percolating fracture network through the sample, we perform numerical simulations based on the experiment to characterize how the effective permeability of otherwise low-permeability porous media depends on fracture formation, connectivity, and the contrast between the fracture and matrix permeabilities. While a change in effective permeability due to fracture formation is expected, the dependence of its magnitude upon the contrast between the matrix permeability and fracture permeability and the fracture network structure is poorlymore » characterized. We use two different high-fidelity fracture network models to characterize how effective permeability changes as percolation occurs. The first is a dynamic two-dimensional fracture propagation model designed to mimic the laboratory settings of the experiment. The second is a static three-dimensional discrete fracture network (DFN) model, whose fracture and network statistics are based on the fractured sample of Utica shale. Once the network connects the inflow and outflow boundaries, the effective permeability increases non-linearly with network density. In most networks considered, a jump in the effective permeability was observed when the embedded fracture network percolated. We characterize how the magnitude of the jump, should it occur, depends on the contrast between the fracture and matrix permeabilities. For small contrasts between the matrix and fracture permeabilities the change is insignificant. However, for larger contrasts, there is a substantial jump whose magnitude depends non-linearly on the difference between matrix and fracture permeabilities. A power-law relationship between the size of the jump and the difference between the matrix and fracture permeabilities is observed. In conclusion, the presented results underscore the importance of fracture network topology on the upscaled properties of the porous medium in which it is embedded.« less

Discontinuities in effective permeability due to fracture percolation

DOE PAGES

Hyman, Jeffrey De'Haven; Karra, Satish; Carey, James William; ...

2018-01-31

Motivated by a triaxial coreflood experiment with a sample of Utica shale where an abrupt jump in permeability was observed, possibly due to the creation of a percolating fracture network through the sample, we perform numerical simulations based on the experiment to characterize how the effective permeability of otherwise low-permeability porous media depends on fracture formation, connectivity, and the contrast between the fracture and matrix permeabilities. While a change in effective permeability due to fracture formation is expected, the dependence of its magnitude upon the contrast between the matrix permeability and fracture permeability and the fracture network structure is poorlymore » characterized. We use two different high-fidelity fracture network models to characterize how effective permeability changes as percolation occurs. The first is a dynamic two-dimensional fracture propagation model designed to mimic the laboratory settings of the experiment. The second is a static three-dimensional discrete fracture network (DFN) model, whose fracture and network statistics are based on the fractured sample of Utica shale. Once the network connects the inflow and outflow boundaries, the effective permeability increases non-linearly with network density. In most networks considered, a jump in the effective permeability was observed when the embedded fracture network percolated. We characterize how the magnitude of the jump, should it occur, depends on the contrast between the fracture and matrix permeabilities. For small contrasts between the matrix and fracture permeabilities the change is insignificant. However, for larger contrasts, there is a substantial jump whose magnitude depends non-linearly on the difference between matrix and fracture permeabilities. A power-law relationship between the size of the jump and the difference between the matrix and fracture permeabilities is observed. In conclusion, the presented results underscore the importance of fracture network topology on the upscaled properties of the porous medium in which it is embedded.« less

Numerical analysis of fracture propagation during hydraulic fracturing operations in shale gas systems

EPA Pesticide Factsheets

Researchers used the TOUGH+ geomechanics computational software and simulation system to examine the likelihood of hydraulic fracture propagation (the spread of fractures) traveling long distances to connect with drinking water aquifers.

Use of satellite pictures for determining major shield fractures relevant for ore prospecting, northern Finland

NASA Technical Reports Server (NTRS)

Tuominen, H. V.; Aarnisalo, J. (Principal Investigator)

1976-01-01

The author has identified the following significant results. A combined analysis of LANDSAT 1 imagery, aeromagnetic and other maps, and aerial photos has revealed a dense network of bedrock fractures in northern Finland. They form several fracturing zones, which obviously represent surficial manifestations of major fractures. The fractures follow, in general, the eight main trends of crustal shear characteristics of the Baltic Shield, but show distinct deviations from them in detail. The major fracture zones divide the bedrock into a mosaic of polygonal blocks, which in many cases coincide with the main rock units of the area and are characterized by different patterns of internal fracturing. Known mineralizations show a tendency to concentrate along the fracture zones. Optical filtering of original LANDSAT images might provide a rapid tool for the analysis of major structural trends in extensive areas such as shields or entire continents.

Scanning electron microscopy fractography analysis of fractured hollow implants.

PubMed

Sbordone, Ludovico; Traini, Tonino; Caputi, Sergio; Scarano, Antonio; Bortolaia, Claudia; Piattelli, Adriano

2010-01-01

Fracture of the implant is one of the possible complications affecting dental implants; it is a rare event but of great clinical relevance. The aim of the present study was to perform a scanning electron microscopy (SEM) fractography evaluation of 7 International Team for oral Implantology (ITI) hollow implants removed because of fracture. The most common clinical risk factors, such as malocclusion, bruxism, and cantilevers on the prosthesis, were absent. Seven fractured ITI hollow implants were retrieved from 5 patients and were analyzed with the use of SEM. SEM analysis showed typical signs of a cleavage-type fracture. Fractures could be due to an association of multiple factors such as fatigue, inner defects, material electrochemical problems, and tensocorrosion.

Computational simulation of progressive fracture in fiber composites

NASA Technical Reports Server (NTRS)

Chamis, C. C.

1986-01-01

Computational methods for simulating and predicting progressive fracture in fiber composite structures are presented. These methods are integrated into a computer code of modular form. The modules include composite mechanics, finite element analysis, and fracture criteria. The code is used to computationally simulate progressive fracture in composite laminates with and without defects. The simulation tracks the fracture progression in terms of modes initiating fracture, damage growth, and imminent global (catastrophic) laminate fracture.

Dynamic seismic signatures of saturated porous rocks containing two orthogonal sets of fractures: theory versus numerical simulations

NASA Astrophysics Data System (ADS)

Guo, Junxin; Rubino, J. Germán; Glubokovskikh, Stanislav; Gurevich, Boris

2018-05-01

The dispersion and attenuation of seismic waves are potentially important attributes for the non-invasive detection and characterization of fracture networks. A primary mechanism for these phenomena is wave-induced fluid flow (WIFF), which can take place between fractures and their embedding background (FB-WIFF), as well as within connected fractures (FF-WIFF). In this work, we propose a theoretical approach to quantify seismic dispersion and attenuation related to these two manifestations of WIFF in saturated porous rocks permeated by two orthogonal sets of fractures. The methodology is based on existing theoretical models for rocks with aligned fractures, and we consider three types of fracture geometries, namely, periodic planar fractures, randomly spaced planar fractures and penny-shaped cracks. Synthetic 2-D rock samples with different degrees of fracture intersections are then explored by considering both the proposed theoretical approach and a numerical upscaling procedure that provides the effective seismic properties of generic heterogeneous porous media. The results show that the theoretical predictions are in overall good agreement with the numerical simulations, in terms of both the stiffness coefficients and the anisotropic properties. For the seismic dispersion and attenuation caused by FB-WIFF, the theoretical model for penny-shaped cracks matches the numerical simulations best, whereas for representing the effects due to FF-WIFF the periodic planar fractures model turns out to be the most suitable one. The proposed theoretical approach is easy to apply and is applicable not only to 2-D but also to 3-D fracture systems. Hence, it has the potential to constitute a useful framework for the seismic characterization of fractured reservoirs, especially in the presence of intersecting fractures.

Fracture in Westerly granite under AE feedback and constant strain rate loading: Nucleation, quasi-static propagation, and the transition to unstable fracture propagation

USGS Publications Warehouse

Thompson, B.D.; Young, R.P.; Lockner, D.A.

2006-01-01

New observations of fracture nucleation are presented from three triaxial compression experiments on intact samples of Westerly granite, using Acoustic Emission (AE) monitoring. By conducting the tests under different loading conditions, the fracture process is demonstrated for quasi-static fracture (under AE Feedback load), a slowly developing unstable fracture (loaded at a 'slow' constant strain rate of 2.5 ?? 10-6/s) and an unstable fracture that develops near instantaneously (loaded at a 'fast' constant strain rate of 5 ?? 10-5/s). By recording a continuous ultrasonic waveform during the critical period of fracture, the entire AE catalogue can be captured and the exact time of fracture defined. Under constant strain loading, three stages are observed: (1) An initial nucleation or stable growth phase at a rate of ??? 1.3 mm/s, (2) a sudden increase to a constant or slowly accelerating propagation speed of ??? 18 mm/s, and (3) unstable, accelerating propagation. In the ??? 100 ms before rupture, the high level of AE activity (as seen on the continuous record) prevented the location of discrete AE events. A lower bound estimate of the average propagation velocity (using the time-to-rupture and the existing fracture length) suggests values of a few m/s. However from a low gain acoustic record, we infer that in the final few ms, the fracture propagation speed increased to 175 m/s. These results demonstrate similarities between fracture nucleation in intact rock and the nucleation of dynamic instabilities in stick slip experiments. It is suggested that the ability to constrain the size of an evolving fracture provides a crucial tool in further understanding the controls on fracture nucleation. ?? Birkha??user Verlag, Basel, 2006.

Fracture control procedures for aircraft structural integrity

NASA Technical Reports Server (NTRS)

Wood, H. A.

1972-01-01

The application of applied fracture mechanics in the design, analysis, and qualification of aircraft structural systems are reviewed. Recent service experiences are cited. Current trends in high-strength materials application are reviewed with particular emphasis on the manner in which fracture toughness and structural efficiency may affect the material selection process. General fracture control procedures are reviewed in depth with specific reference to the impact of inspectability, structural arrangement, and material on proposed analysis requirements for safe crack growth. The relative impact on allowable design stress is indicated by example. Design criteria, material, and analysis requirements for implementation of fracture control procedures are reviewed together with limitations in current available data techniques. A summary of items which require further study and attention is presented.

Immediate versus delayed intramedullary nailing for open fractures of the tibial shaft: a multivariate analysis of factors affecting deep infection and fracture healing.

PubMed

Yokoyama, Kazuhiko; Itoman, Moritoshi; Uchino, Masataka; Fukushima, Kensuke; Nitta, Hiroshi; Kojima, Yoshiaki

2008-10-01

The purpose of this study was to evaluate contributing factors affecting deep infection and fracture healing of open tibia fractures treated with locked intramedullary nailing (IMN) by multivariate analysis. We examined 99 open tibial fractures (98 patients) treated with immediate or delayed locked IMN in static fashion from 1991 to 2002. Multivariate analyses following univariate analyses were derived to determine predictors of deep infection, nonunion, and healing time to union. The following predictive variables of deep infection were selected for analysis: age, sex, Gustilo type, fracture grade by AO type, fracture location, timing or method of IMN, reamed or unreamed nailing, debridement time (< or =6 h or >6 h), method of soft-tissue management, skin closure time (< or =1 week or >1 week), existence of polytrauma (ISS< 18 or ISS> or =18), existence of floating knee injury, and existence of superficial/pin site infection. The predictive variables of nonunion selected for analysis was the same as those for deep infection, with the addition of deep infection for exchange of pin site infection. The predictive variables of union time selected for analysis was the same as those for nonunion, excluding of location, debridement time, and existence of floating knee and superficial infection. Six (6.1%; type II Gustilo n=1, type IIIB Gustilo n=5) of the 99 open tibial fractures developed deep infections. Multivariate analysis revealed that timing or method of IMN, debridement time, method of soft-tissue management, and existence of superficial or pin site infection significantly correlated with the occurrence of deep infection (P< 0.0001). In the immediate nailing group alone, the deep infection rate in type IIIB + IIIC was significantly higher than those in type I + II and IIIA (P = 0.016). Nonunion occurred in 17 fractures (20.3%, 17/84). Multivariate analysis revealed that Gustilo type, skin closure time, and existence of deep infection significantly correlated with occurrence of nonunion (P < 0.05). Gustilo type and existence of deep infection were significantly correlated with healing time to union on multivariate analysis (r(2) = 0.263, P = 0.0001). Multivariate analyses for open tibial fractures treated with IMN showed that IMN after EF (especially in existence of pin site infection) was at high risk of deep infection, and that debridement within 6 h and appropriate soft-tissue managements were also important factor in preventing deep infections. These analyses postulated that both the Gustilo type and the existence of deep infection is related with fracture healing in open fractures treated with IMN. In addition, immediate IMN for type IIIB and IIIC is potentially risky, and canal reaming did not increase the risk of complication for open tibial fractures treated with IMN.

The emerging trend of non-operative treatment in paediatric type I open forearm fractures.

PubMed

Zhang, H; Fanelli, M; Adams, C; Graham, J; Seeley, M

2017-08-01

Open fractures are considered an orthopaedic emergency and are generally an indication for operative debridement. Recent studies have questioned this approach for the management of Gustilo-Anderson Type I open fractures in the paediatric population. This meta-analysis studies the non-operative management of Type I open paediatric forearm fractures. An Ovid MEDLINE and PubMed database literature search was performed for studies that involved a quantified number of Gustilo-Anderson Type I open forearm fractures in the paediatric population, which were treated without operative intervention. A fixed-effect meta-analysis, weighting each study based on the number of patients, and a pooled estimate of infection risk (with 95% confidence interval (CI)) was performed. The search results yielded five studies that were eligible for inclusion. No included patients had operative debridement and all were treated with antibiotics. The number of patients in each study ranged from 3 to 45, with a total of 127 paediatric patients in the meta-analysis. The infection rate was 0% for all patients included. The meta-analysis estimated a pooled infection risk of 0% (95% CI 0 to 2.9). The five included studies had a total of 127 patients with no cases of infection after non-operative management of Type I open paediatric forearm fractures. The infection rate of Type I fractures among operatively managed patients is 1.9%. The trend in literature towards non-operative treatment of paediatric Type I open fractures holds true in this meta-analysis.

Stress-Induced Fracturing of Reservoir Rocks: Acoustic Monitoring and μCT Image Analysis

NASA Astrophysics Data System (ADS)

Pradhan, Srutarshi; Stroisz, Anna M.; Fjær, Erling; Stenebråten, Jørn F.; Lund, Hans K.; Sønstebø, Eyvind F.

2015-11-01

Stress-induced fracturing in reservoir rocks is an important issue for the petroleum industry. While productivity can be enhanced by a controlled fracturing operation, it can trigger borehole instability problems by reactivating existing fractures/faults in a reservoir. However, safe fracturing can improve the quality of operations during CO2 storage, geothermal installation and gas production at and from the reservoir rocks. Therefore, understanding the fracturing behavior of different types of reservoir rocks is a basic need for planning field operations toward these activities. In our study, stress-induced fracturing of rock samples has been monitored by acoustic emission (AE) and post-experiment computer tomography (CT) scans. We have used hollow cylinder cores of sandstones and chalks, which are representatives of reservoir rocks. The fracture-triggering stress has been measured for different rocks and compared with theoretical estimates. The population of AE events shows the location of main fracture arms which is in a good agreement with post-test CT image analysis, and the fracture patterns inside the samples are visualized through 3D image reconstructions. The amplitudes and energies of acoustic events clearly indicate initiation and propagation of the main fractures. Time evolution of the radial strain measured in the fracturing tests will later be compared to model predictions of fracture size.

Calcium plus vitamin D supplementation and risk of fractures: an updated meta analysis from the National Osteoporosis Foundation

USDA-ARS?s Scientific Manuscript database

Introduction: Calcium plus vitamin D supplementation has been widely recommended to prevent osteoporosis and subsequent fractures; however, considerable controversy exists regarding the association of such supplementation and fracture risk. The aim was to conduct a meta-analysis of randomized contr...

Experimental evidence for dynamic friction on rock fractures from frequency-dependent nonlinear hysteresis and harmonic generation

NASA Astrophysics Data System (ADS)

Saltiel, Seth; Bonner, Brian P.; Mittal, Tushar; Delbridge, Brent; Ajo-Franklin, Jonathan B.

2017-07-01

Frictional properties affect the propagation of high-amplitude seismic waves across rock fractures and faults. Laboratory evidence suggests that these properties can be measured in active seismic surveys, potentially offering a route to characterizing friction in situ. We present experimental results from a subresonance torsional modulus and attenuation apparatus that utilizes micron-scale sinusoidal oscillations to probe the nonlinear stress-strain relation at a range of strain amplitudes and rates. Nonlinear effects are further quantified using harmonic distortion; however, time series data best illuminate underlying physical processes. The low-frequency stress-strain hysteretic loops show stiffening at the sinusoid's static ends, but stiffening is reduced above a threshold frequency. This shape is determined by harmonic generation in the strain; the stress signal has no harmonics, confirming that the fractured sample is the source of the nonlinearity. These qualitative observations suggest the presence of rate-dependent friction and are consistent between fractures in three different rock types. We propose that static friction at the low strain rate part of the cycle, when given sufficient "healing" time at low oscillation frequencies, causes this stiffening cusp shape in the hysteresis loop. While rate-and-state friction is commonly used to represent dynamic friction, it cannot capture static friction or negative slip velocities. So we implement another dynamic friction model, based on the work of Dahl, which describes this process and produces similar results. Since the two models have a similar form, parameterizations of field data could constraint fault model inputs, such as specific location velocity strengthening or weakening properties.

Substantial vertebral body osteophytes protect against severe vertebral fractures in compression

PubMed Central

Aubin, Carl-Éric; Chaumoître, Kathia; Mac-Thiong, Jean-Marc; Ménard, Anne-Laure; Petit, Yvan; Garo, Anaïs; Arnoux, Pierre-Jean

2017-01-01

Recent findings suggest that vertebral osteophytes increase the resistance of the spine to compression. However, the role of vertebral osteophytes on the biomechanical response of the spine under fast dynamic compression, up to failure, is unclear. Seventeen human spine specimens composed of three vertebrae (from T5-T7 to T11-L1) and their surrounding soft tissues were harvested from nine cadavers, aged 77 to 92 years. Specimens were imaged using quantitative computer tomography (QCT) for medical observation, classification of the intervertebral disc degeneration (Thomson grade) and measurement of the vertebral trabecular density (VTD), height and cross-sectional area. Specimens were divided into two groups (with (n = 9) or without (n = 8) substantial vertebral body osteophytes) and compressed axially at a dynamic displacement rate of 1 m/s, up to failure. Normalized force-displacement curves, videos and QCT images allowed characterizing failure parameters (force, displacement and energy at failure) and fracture patterns. Results were analyzed using chi-squared tests for sampling distributions and linear regression for correlations between VTD and failure parameters. Specimens with substantial vertebral body osteophytes present higher stiffness (2.7 times on average) and force at failure (1.8 times on average) than other segments. The presence of osteophytes significantly influences the location, pattern and type of fracture. VTD was a good predictor of the dynamic force and energy at failure for specimens without substantial osteophytes. This study also showed that vertebral body osteophytes provide a protective mechanism to the underlying vertebra against severe compression fractures. PMID:29065144

Dynamic compressive properties obtained from a split Hopkinson pressure bar test of Boryeong shale

NASA Astrophysics Data System (ADS)

Kang, Minju; Cho, Jung-Woo; Kim, Yang Gon; Park, Jaeyeong; Jeong, Myeong-Sik; Lee, Sunghak

2016-09-01

Dynamic compressive properties of a Boryeong shale were evaluated by using a split Hopkinson pressure bar, and were compared with those of a Hwangdeung granite which is a typical hard rock. The results indicated that the dynamic compressive loading reduced the resistance to fracture. The dynamic compressive strength was lower in the shale than in the granite, and was raised with increasing strain rate by microcracking effect as well as strain rate strengthening effect. Since the number of microcracked fragments increased with increasing strain rate in the shale having laminated weakness planes, the shale showed the better fragmentation performance than the granite at high strain rates. The effect of transversely isotropic plane on compressive strength decreased with increasing strain rate, which was desirable for increasing the fragmentation performance. Thus, the shale can be more reliably applied to industrial areas requiring good fragmentation performance as the striking speed of drilling or hydraulic fracturing machines increased. The present dynamic compressive test effectively evaluated the fragmentation performance as well as compressive strength and strain energy density by controlling the air pressure, and provided an important idea on which rock was more readily fragmented under dynamically processing conditions such as high-speed drilling and blasting.

Dynamics of Model Hydraulic Fracturing Liquid Studied by Two-Dimensional Infrared Spectroscopy

NASA Astrophysics Data System (ADS)

Daley, Kim; Kubarych, Kevin J.

2014-06-01

The technique of two-dimensional infrared (2DIR) spectroscopy is used to expose the chemical dynamics of various concentrations of polymers and their monomers in heterogeneous mixtures. An environmentally relevant heterogeneous mixture, which inspires this study, is hydraulic fracturing liquid (HFL). Hydraulic fracking is a technique used to extract natural gas from shale deposits. HFL consists of mostly water, proppant (sand), an emulsifier (guar), and other chemicals specific to the drilling site. Utilizing a metal carbonyl as a probe, we observe the spectral dynamics of the polymer, guar, and its monomer, mannose, and compare the results to see how hydration dynamics change with varying concentration. Another polymer, Ficoll, and its monomer, sucrose, are also compared to see how polymer size affects hydration dynamics. The two results are as follows: (1) Guar experiences collective hydration at high concentrations, where as mannose experiences independent hydration; (2) no collective hydration is observed for Ficoll in the same concentration range as guar, possibly due to polymer shape and size. HFL experiences extremely high pressure during natural gas removal, so future studies will focus on how increased pressure affects the hydration dynamics of polymers and monomers.

A review on fracture prevention of stent in femoropopliteal artery

NASA Astrophysics Data System (ADS)

Atan, Bainun Akmal Mohd; Ismail, Al Emran; Taib, Ishkrizat; Lazim, Zulfaqih

2017-01-01

Heavily calcific lesions, total occlusions, tortuous blood vessels, variable lengths of arteries, various dynamic loads and deformations in the femoropopliteal (FP) arterial segment make stenosis treatments are complicated. The dynamic forces in FP artery including bending, torsion and radial compression may lead to stent fracture (SF) and eventually to in-stent restenosis (ISR). Stent design specifically geometrical configurations are a major factor need to be improved to optimize stent expansion and flexibility both bending and torsion during stent deployment into the diseased FP artery. Previous studies discovered the influence of various stent geometrical designs resulted different structural behaviour. Optimizing stent design can improve stent performances: flexibility and radial strength to prevent SF in FP arterial segment

[Using dynamic magnetotherapy and transdermal electroneurostimulation in the combined treatment of patients with mandibular fractures and concomitant periodontal inflammatory diseases].

PubMed

Lepilin, A V; Erokina, N L; Rogatina, T V; Khlusov, I Iu

2009-01-01

The objective of this study was to compare results of dynamic magnetotherapy (DMT), transdermal electroneurostimulation (TDENS), and traditional ultrahigh frequency (UHF) therapy in 473 patients with mandibular fractures and concomitant inflammatory diseases of paradontium. The parameters measured in the study included hygienic and paradontal indices, microcirculation patterns (using laser Doppler flowmetry), and the degree of mandibular fragment consolidation. It was shown that combined treatment with DMT and TDENS using an AMO-ATOS-E apparatus permits to eliminate clinical symptoms of paradontal inflammatory diseases twice as fast as traditional ultrahigh frequency therapy and ensures a two-fold reduction in the frequency of complications.

Early and late fracture following extensive limb lengthening in patients with achondroplasia and hypochondroplasia.

PubMed

Kitoh, H; Mishima, K; Matsushita, M; Nishida, Y; Ishiguro, N

2014-09-01

Two types of fracture, early and late, have been reported following limb lengthening in patients with achondroplasia (ACH) and hypochondroplasia (HCH). We reviewed 25 patients with these conditions who underwent 72 segmental limb lengthening procedures involving the femur and/or tibia, between 2003 and 2011. Gender, age at surgery, lengthened segment, body mass index, the shape of the callus, the amount and percentage of lengthening and the healing index were evaluated to determine predictive factors for the occurrence of early (within three weeks after removal of the fixation pins) and late fracture (> three weeks after removal of the pins). The Mann‑Whitney U test and Pearson's chi-squared test for univariate analysis and stepwise regression model for multivariate analysis were used to identify the predictive factor for each fracture. Only one patient (two tibiae) was excluded from the analysis due to excessively slow formation of the regenerate, which required supplementary measures. A total of 24 patients with 70 limbs were included in the study. There were 11 early fractures in eight patients. The shape of the callus (lateral or central callus) was the only statistical variable related to the occurrence of early fracture in univariate and multivariate analyses. Late fracture was observed in six limbs and the mean time between removal of the fixation pins and fracture was 18.3 weeks (3.3 to 38.4). Lengthening of the tibia, larger healing index, and lateral or central callus were related to the occurrence of a late fracture in univariate analysis. A multivariate analysis demonstrated that the shape of the callus was the strongest predictor for late fracture (odds ratio: 19.3, 95% confidence interval: 2.91 to 128). Lateral or central callus had a significantly larger risk of fracture than fusiform, cylindrical, or concave callus. Radiological monitoring of the shape of the callus during distraction is important to prevent early and late fracture of lengthened limbs in patients with ACH or HCH. In patients with thin callus formation, some measures to stimulate bone formation should be considered as early as possible. ©2014 The British Editorial Society of Bone & Joint Surgery.

Structural and Geophysical Characterization of Oklahoma Basement

NASA Astrophysics Data System (ADS)

Morgan, C.; Johnston, C. S.; Carpenter, B. M.; Reches, Z.

2017-12-01

Oklahoma has experienced a large increase in seismicity since 2009 that has been attributed to wastewater injection. Most earthquakes, including four M5+ earthquakes, nucleated at depths > 4 km, well within the pre-Cambrian crystalline basement, even though wastewater injection occurred almost exclusively in the sedimentary sequence above. To better understand the structural characteristics of the rhyolite and granite that makeup the midcontinent basement, we analyzed a 150 m long core recovered from a basement borehole (Shads 4) in Rogers County, NE Oklahoma. The analysis of the fracture network in the rhyolite core included measurements of fracture inclination, aperture, and density, the examination fracture surface features and fill minerology, as well as x-ray diffraction analysis of secondary mineralization. We also analyzed the highly fractured and faulted segments of the core with a portable gamma-ray detector, magnetometer, and rebound hammer. The preliminary analysis of the fractures within the rhyolite core showed: (1) Fracture density increasing with depth by a factor of 10, from 4 fractures/10m in the upper core segment to 40 fracture/10m at 150 m deeper. (2) The fractures are primarily sub-vertical, inclined 10-20° from the axis of the vertical core. (3) The secondary mineralization is dominated by calcite and epidote. (4) Fracture aperture ranges from 0.35 to 2.35mm based on the thickness of secondary filling. (5) About 8% of the examined fractures display slickenside striations. (6) Increases of elasticity (by rebound hammer) and gamma-ray emissions are systematically correlated with a decrease in magnetic susceptibility in core segments of high fracture density and/or faulting; this observation suggests diagenetic fracture re-mineralization.

Fractography: determining the sites of fracture initiation.

PubMed

Mecholsky, J J

1995-03-01

Fractography is the analysis of fracture surfaces. Here, it refers to quantitative fracture surface analysis (FSA) in the context of applying the principles of fracture mechanics to the topography observed on the fracture surface of brittle materials. The application of FSA is based on the principle that encoded on the fracture surface of brittle materials is the entire history of the fracture process. It is our task to develop the skills and knowledge to decode this information. There are several motivating factors for applying our knowledge of FSA. The first and foremost is that there is specific, quantitative information to be obtained from the fracture surface. This information includes the identification of the size and location of the fracture initiating crack or defect, the stress state at failure, the existence, or not, of local or global residual stress, the existence, or not, of stress corrosion and a knowledge of local processing anomalies which affect the fracture process. The second motivating factor is that the information is free. Once a material is tested to failure, the encoded information becomes available. If we decide to observe the features produced during fracture then we are rewarded with much information. If we decide to ignore the fracture surface, then we are left to guess and/or reason as to the cause of the failure without the benefit of all of the possible information available. This paper addresses the application of quantitative fracture surface analysis to basic research, material and product development, and "trouble-shooting" of in-service failures. First, the basic principles involved will be presented. Next, the methodology necessary to apply the principles will be presented. Finally, a summary of the presentation will be made showing the applicability to design and reliability.

Effect of Measured Welding Residual Stresses on Crack Growth

NASA Technical Reports Server (NTRS)

Hampton, Roy W.; Nelson, Drew; Doty, Laura W. (Technical Monitor)

1998-01-01

Welding residual stresses in thin plate A516-70 steel and 2219-T87 aluminum butt weldments were measured by the strain-gage hole drilling and X-ray diffraction methods. The residual stress data were used to construct 3D strain fields which were modeled as thermally induced strains. These 3D strain fields were then analyzed with the WARP31) FEM fracture analysis code in order to predict their effect on fatigue and on fracture. For analyses of fatigue crack advance and subsequent verification testing, fatigue crack growth increments were simulated by successive saw-cuts and incremental loading to generate, as a function of crack length, effects on crack growth of the interaction between residual stresses and load induced stresses. The specimen experimental response was characterized and compared to the WARM linear elastic and elastic-plastic fracture mechanics analysis predictions. To perform the fracture analysis, the plate material's crack tearing resistance was determined by tests of thin plate M(T) specimens. Fracture analyses of these specimen were performed using WARP31D to determine the critical Crack Tip Opening Angle [CTOA] of each material. These critical CTOA values were used to predict crack tearing and fracture in the weldments. To verify the fracture predictions, weldment M(T) specimen were tested in monotonic loading to fracture while characterizing the fracture process.

Screw Loosening and Pelvic Canal Narrowing After Lateral Plating of Feline Ilial Fractures With Locking and Nonlocking Plates.

PubMed

Schmierer, Philipp A; Kircher, Patrick R; Hartnack, Sonja; Knell, Sebastian C

2015-10-01

To compare the frequency of complications, including screw loosening and pelvic canal narrowing, associated with dynamic compression plating, locking plating, and double locking plating of ilial fractures in cats. Historical cohort study. The radiographs and medical records of cats with pelvic fractures that were presented between 2004 and 2013 were reviewed. The cases were categorized based on the plate type and number as dynamic compression plate (DCP), single locking plate (LPS) and double locking plates (dLPS). The frequency of screw loosening was compared across categories using a Fisher's exact test. The change in pelvic alignment, described by the change in sacral index (postoperative sacral index-followup sacral index), was compared across plate categories using ANOVA. The frequency of screw loosening for DCP (5/10) was significantly higher than LPS (1/13) and dLPS (0/11) (P = .05, P = .012, respectively). There was no significant difference in the SI change across plate categories. The mean change in sacral index for DCP was -0.11 (95%CI -0.25 to 0.03), for LPS was 0.0007 (95%CI -0.07 to 0.08), and for dLPS was -0.01 (95%CI -0.04 to 0.02). None of the cats showed constipation postoperatively. Screw loosening occurred less often but the change in pelvic canal alignment was not significantly different in ilial fractures repaired with LPS or dLPS compared to ilial fractures repaired with DCP. Locking plating of ilial fractures in cats may offer advantages compared to nonlocking plating. © Copyright 2015 by The American College of Veterinary Surgeons.