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Sample records for fracture mechanics sensitivity

  1. The initial phase of fracture healing is specifically sensitive to mechanical conditions.

    PubMed

    Klein, Petra; Schell, Hanna; Streitparth, Florian; Heller, Markus; Kassi, Jean-Pierre; Kandziora, Frank; Bragulla, Hermann; Haas, Norbert P; Duda, Georg N

    2003-07-01

    Interfragmentary movements affect the quality and quantity of callus formation. The mounting plane of monolateral external fixators may give direction to those movements. Therefore, the aim of this study was to determine the influence of the fixator mounting plane on the process of fracture healing. Identically configured fixators were mounted either medially or anteromedially on the tibiae of sheep. Interfragmentary movements and ground reaction forces were evaluated in vivo during a nine week period. Histomorphological and biomechanical parameters described the bone healing processes. Changing only the mounting plane led to a modification of interfragmentary movements in the initial healing phase. The difference in interfragmentary movements between the groups was only significant during the first post-operative period. However, these initial differences in mechanical conditions influenced callus tissue formation significantly. The group with the anteromedially mounted fixator, initially showing significantly more interfragmentary movements, ended up with a significantly smaller callus diameter and a significantly higher callus stiffness as a result of advanced fracture healing. This demonstrates that the initial phase of healing is sensitive to mechanical conditions and influences the course of healing. Therefore, initial mechanical stability of an osteosynthesis should be considered an important factor in clinical fracture treatment.

  2. Pressurized thermal shock probabilistic fracture mechanics sensitivity analysis for Yankee Rowe reactor pressure vessel

    SciTech Connect

    Dickson, T.L.; Cheverton, R.D.; Bryson, J.W.; Bass, B.R.; Shum, D.K.M.; Keeney, J.A.

    1993-08-01

    The Nuclear Regulatory Commission (NRC) requested Oak Ridge National Laboratory (ORNL) to perform a pressurized-thermal-shock (PTS) probabilistic fracture mechanics (PFM) sensitivity analysis for the Yankee Rowe reactor pressure vessel, for the fluences corresponding to the end of operating cycle 22, using a specific small-break-loss- of-coolant transient as the loading condition. Regions of the vessel with distinguishing features were to be treated individually -- upper axial weld, lower axial weld, circumferential weld, upper plate spot welds, upper plate regions between the spot welds, lower plate spot welds, and the lower plate regions between the spot welds. The fracture analysis methods used in the analysis of through-clad surface flaws were those contained in the established OCA-P computer code, which was developed during the Integrated Pressurized Thermal Shock (IPTS) Program. The NRC request specified that the OCA-P code be enhanced for this study to also calculate the conditional probabilities of failure for subclad flaws and embedded flaws. The results of this sensitivity analysis provide the NRC with (1) data that could be used to assess the relative influence of a number of key input parameters in the Yankee Rowe PTS analysis and (2) data that can be used for readily determining the probability of vessel failure once a more accurate indication of vessel embrittlement becomes available. This report is designated as HSST report No. 117.

  3. Critical Chemical-Mechanical Couplings that Define Permeability Modifications in Pressure-Sensitive Rock Fractures

    SciTech Connect

    Derek Elsworth; Abraham Grader; Susan Brantley

    2007-04-25

    This work examined and quantified processes controlling changes in the transport characteristics of natural fractures, subjected to coupled thermal-mechanical-chemical (TMC) effects. Specifically, it examined the effects of mineral dissolution and precipitation mediated by mechanical effects, using laboratory through-flow experiments concurrently imaged by X-ray CT. These were conducted on natural and artificial fractures in cores using water as the permeant. Fluid and mineral mass balances are recorded and are correlated with in-sample saturation, porosity and fracture aperture maps, acquired in real-time by X-ray CT-imaging at a maximum spatial resolution of 15-50 microns per pixel. Post-test, the samples were resin-impregnated, thin-sectioned, and examined by microscopy to define the characteristics of dissolution and precipitation. The test-concurrent X-ray imaging, mass balances, and measurements of permeability, together with the post-test microscopy, were used to define dissolution/precipitation processes, and to constrain process-based models. These models define and quantify key processes of pressure solution, free-face dissolution, and shear-dilation, and the influence of temperature, stress level, and chemistry on the rate of dissolution, its distribution in space and time, and its influence on the mechanical and transport properties of the fracture.

  4. Phase Field Fracture Mechanics.

    SciTech Connect

    Robertson, Brett Anthony

    2015-11-01

    For this assignment, a newer technique of fracture mechanics using a phase field approach, will be examined and compared with experimental data for a bend test and a tension test. The software being used is Sierra Solid Mechanics, an implicit/explicit finite element code developed at Sandia National Labs in Albuquerque, New Mexico. The bend test experimental data was also obtained at Sandia Labs while the tension test data was found in a report online from Purdue University.

  5. Fracture mechanics validity limits

    NASA Technical Reports Server (NTRS)

    Lambert, Dennis M.; Ernst, Hugo A.

    1994-01-01

    Fracture behavior is characteristics of a dramatic loss of strength compared to elastic deformation behavior. Fracture parameters have been developed and exhibit a range within which each is valid for predicting growth. Each is limited by the assumptions made in its development: all are defined within a specific context. For example, the stress intensity parameters, K, and the crack driving force, G, are derived using an assumption of linear elasticity. To use K or G, the zone of plasticity must be small as compared to the physical dimensions of the object being loaded. This insures an elastic response, and in this context, K and G will work well. Rice's J-integral has been used beyond the limits imposed on K and G. J requires an assumption of nonlinear elasticity, which is not characteristic of real material behavior, but is thought to be a reasonable approximation if unloading is kept to a minimum. As well, the constraint cannot change dramatically (typically, the crack extension is limited to ten-percent of the initial remaining ligament length). Rice, et al investigated the properties required of J-type parameters, J(sub x), and showed that the time rate, dJ(sub x)/dt, must not be a function of the crack extension rate, da/dt. Ernst devised the modified-J parameter, J(sub M), that meets this criterion. J(sub M) correlates fracture data to much higher crack growth than does J. Ultimately, a limit of the validity of J(sub M) is anticipated, and this has been estimated to be at a crack extension of about 40-percent of the initial remaining ligament length. None of the various parameters can be expected to describe fracture in an environment of gross plasticity, in which case the process is better described by deformation parameters, e.g., stress and strain. In the current study, various schemes to identify the onset of the plasticity-dominated behavior, i.e., the end of fracture mechanics validity, are presented. Each validity limit parameter is developed in

  6. Linear elastic fracture mechanics primer

    NASA Technical Reports Server (NTRS)

    Wilson, Christopher D.

    1992-01-01

    This primer is intended to remove the blackbox perception of fracture mechanics computer software by structural engineers. The fundamental concepts of linear elastic fracture mechanics are presented with emphasis on the practical application of fracture mechanics to real problems. Numerous rules of thumb are provided. Recommended texts for additional reading, and a discussion of the significance of fracture mechanics in structural design are given. Griffith's criterion for crack extension, Irwin's elastic stress field near the crack tip, and the influence of small-scale plasticity are discussed. Common stress intensities factor solutions and methods for determining them are included. Fracture toughness and subcritical crack growth are discussed. The application of fracture mechanics to damage tolerance and fracture control is discussed. Several example problems and a practice set of problems are given.

  7. Electronics reliability fracture mechanics. Volume 2: Fracture mechanics

    NASA Astrophysics Data System (ADS)

    Kallis, J.; Duncan, L.; Buechler, D.; Backes, P.; Sandkulla, D.

    1992-05-01

    This is the second of two volumes. The other volume (WL-TR-92-3015) is 'Causes of Failures of Shop Replaceable Units and Hybrid Microcircuits.' The objective of the Electronics Reliability Fracture Mechanics (ERFM) program was to develop and demonstrate a life prediction technique for electronic assemblies, when subjected to environmental stresses of vibration and thermal cycling, based upon the mechanical properties of the materials and packaging configurations which make up an electronic system. The application of fracture mechanics to microscale phenomena in electronic assemblies was a pioneering research effort. The small scale made the experiments very difficult; for example, the 1-mil-diameter bond wires in microelectronic devices are 1/3 the diameter of a human hair. A number of issues had to be resolved to determine whether a fracture mechanics modelling approach is correct for the selected failures; specifically, the following two issues had to be resolved: What fraction of the lifetime is spent in crack initiation? Are macro fracture mechanics techniques, used in large structures such as bridges, applicable to the tiny structures in electronic equipment? The following structural failure mechanisms were selected for modelling: bondwire fracture from mechanical cycling; bondwire fracture from thermal (power) cycling; plated through hole (PTH) fracture from thermal cycling. The bondwire fracture test specimens were A1-1 percent Si wires, representative of wires used in the parts in the modules selected for detailed investigation in this program (see Vol. 1 of this report); 1-mil-diameter wires were tested in this program. The PTH test specimens were sections of 14-layer printed wiring boards of the type used.

  8. Mode 2 fracture mechanics

    NASA Technical Reports Server (NTRS)

    Buzzard, Robert J.; Ghosn, Louis

    1988-01-01

    Current development of high-performance rolling element bearings for aircraft engines (up to 3 million DN, where DN is the product of shaft diameter in millimeters and speed in revolutions per minute) has aroused concern about fatigue crack growth in the inner bearing race that leads to catastrophic failure of the bearing and the engine. A failure sequence was postulated by Srawley, and an analytical program was undertaken to simulate fatigue crack propagation in the inner raceway of such a bearing. A fatigue specimen was developed at NASA by which fatigue data may be obtained relative to the cracking problems. The specimen may be used to obtain either mode 2 data alone or a combination of mixed-mode (1 and 2) data as well and was calibrated in this regard. Mixed-mode fracture data for M-50 bearing steel are presented, and a method for performing reversed-loading tests is described.

  9. Fracture mechanics of cellular glass

    NASA Technical Reports Server (NTRS)

    Zwissler, J. G.; Adams, M. A.

    1981-01-01

    The fracture mechanics of cellular glasses (for the structural substrate of mirrored glass for solr concentrator reflecting panels) are discussed. Commercial and developmental cellular glasses were tested and analyzed using standard testing techniques and models developed from linear fracture mechanics. Two models describing the fracture behavior of these materials were developed. Slow crack growth behavior in cellular glass was found to be more complex than that encountered in dense glasses or ceramics. The crack velocity was found to be strongly dependent upon water vapor transport to the tip of the moving crack. The existence of a static fatigue limit was not conclusively established, however, it is speculated that slow crack growth behavior in Region 1 may be slower, by orders of magnitude, than that found in dense glasses.

  10. Fracture mechanics and corrosion fatigue.

    NASA Technical Reports Server (NTRS)

    Mcevily, A. J.; Wei, R. P.

    1972-01-01

    Review of the current state-of-the-art in fracture mechanics, particularly in relation to the study of problems in environment-enhanced fatigue crack growth. The usefulness of this approach in developing understanding of the mechanisms for environmental embrittlement and its engineering utility are discussed. After a brief review of the evolution of the fracture mechanics approach and the study of environmental effects on the fatigue behavior of materials, a study is made of the response of materials to fatigue and corrosion fatigue, the modeling of the mechanisms of the fatigue process is considered, and the application of knowledge of fatigue crack growth to the prediction of the high cycle life of unnotched specimens is illustrated.

  11. Theory of fracture mechanics based upon plasticity

    NASA Technical Reports Server (NTRS)

    Lee, J. D.

    1976-01-01

    A theory of fracture mechanics is formulated on the foundation of continuum mechanics. Fracture surface is introduced as an unknown quantity and is incorporated into boundary and initial conditions. Surface energy is included in the global form of energy conservation law and the dissipative mechanism is formulated into constitutive equations which indicate the thermodynamic irreversibility and the irreversibility of fracture process as well.

  12. (Fracture mechanics of inhomogeneous materials)

    SciTech Connect

    Bass, B.R.

    1990-10-01

    Discussions were held with Japanese researchers concerning (1) the Elastic-Plastic Fracture Mechanics in Inhomogeneous Materials and Structures (EPI) Program, and (2) ongoing large-scale pressurized- thermal-shock (PTS) experiments in Japan. In the EPI Program, major activities in the current fiscal year include round-robin analyses of measured data from inhomogeneous base metal/weld metal compact- tension (CT) specimens fabricated from welded plates of A533 grade B class 1 steel. The round-robin task involves participants from nine research organizations in Japan and is scheduled for completion by the end of 1990. Additional experiments will be performed on crack growth in inhomogeneous CT specimens and three-point bend (3PB) specimens 10 mm thick. The data will be compared with that generated previously from 19-mm-thick-specimens. A new type of inhomogeneous surface-cracked specimen will be tested this year, with ratio of crack depth to surface length (a/c) satisfying 0.2 {le} (a/c) {le} 0. 8 and using a 3PB type of applied load. Plans are under way to fabricate a new welded plate of A533 grade B class 1 steel (from a different heat than that currently being tested) in order to provide an expanded fracture-toughness data base. Other topics concerning fracture-prevention issues in reactor pressure vessels were discussed with each of the host organizations, including an overview of ongoing work in the Heavy-Section Steel Technology (HSST) Program.

  13. Mechanical Coal-Face Fracturer

    NASA Technical Reports Server (NTRS)

    Collins, E. R., Jr.

    1984-01-01

    Radial points on proposed drill bit take advantage of natural fracture planes of coal. Radial fracture points retracted during drilling and impacted by piston to fracture coal once drilling halts. Group of bits attached to array of pneumatic drivers to fracture large areas of coal face.

  14. Compendium of fracture mechanics problems

    NASA Technical Reports Server (NTRS)

    Stallworth, R.; Wilson, C.; Meyers, C.

    1990-01-01

    Fracture mechanics analysis results are presented from the following structures/components analyzed at Marshall Space Flight Center (MSFC) between 1982 and 1989: space shuttle main engine (SSME), Hubble Space Telescope (HST), external tank attach ring, B-1 stand LOX inner tank, and solid rocket booster (SRB). Results from the SSME high pressure fuel turbopump (HPFTP) second stage blade parametric analysis determine a critical flaw size for a wide variety of stress intensity values. The engine 0212 failure analysis was a time dependent fracture life assessment. Results indicated that the disk ruptured due to an overspeed condition. Results also indicated that very small flaws in the curvic coupling area could propagate and lead to failure under normal operating conditions. It was strongly recommended that a nondestructive evaluation inspection schedule be implemented. The main ring of the HST, scheduled to launch in 1990, was analyzed by safe-life and fail-safe analyses. First safe-life inspection criteria curves for the ring inner and outer skins and the fore and aft channels were derived. Afterwards the skins and channels were determined to be fail-safe by analysis. A conservative safe-life analysis was done on the 270 redesign external tank attach ring. Results from the analysis were used to determine the nondestructive evaluation technique required.

  15. Entablature: fracture types and mechanisms

    NASA Astrophysics Data System (ADS)

    Forbes, A. E. S.; Blake, S.; Tuffen, H.

    2014-05-01

    Entablature is the term used to describe zones or tiers of irregular jointing in basaltic lava flows. It is thought to form when water from rivers dammed by the lava inundates the lava flow surface, and during lava-meltwater interaction in subglacial settings. A number of different fracture types are described in entablature outcrops from the Búrfell lava and older lava flows in Þjórsárdalur, southwest Iceland. These are: striae-bearing, column-bounding fractures and pseudopillow fracture systems that themselves consist of two different fracture types—master fractures with dimpled surface textures and subsidiary fractures with curved striae. The interaction of pseudopillow fracture systems and columnar jointing in the entablature produces the chevron fracture patterns that are commonly observed in entablature. Cube-jointing is a more densely fractured version of entablature, which likely forms when more coolant enters the hot lava. The entablature tiers display closely spaced striae and dendritic crystal shapes which indicate rapid cooling. Master fracture surfaces show a thin band with an evolved composition at the fracture surface; mineral textures in this band also show evidence of quenching of this material. This is interpreted as gas-driven filter pressing of late-stage residual melt that is drawn into an area of low pressure immediately preceding or during master fracture formation by ductile extensional fracture of hot, partially crystallised lava. This melt is then quenched by an influx of water and/or steam when the master fracture fully opens. Our findings suggest that master fractures are the main conduit for coolant entering the lava flow during entablature formation.

  16. Mechanics of nanocrack: Fracture, dislocation emission, and amorphization

    NASA Astrophysics Data System (ADS)

    Huang, Shan; Zhang, Sulin; Belytschko, Ted; Terdalkar, Sachin S.; Zhu, Ting

    2009-05-01

    Understanding the nanoscale fracture mechanisms is critical for tailoring the mechanical properties of materials at small length scales. We perform an atomistic study to characterize the formation and extension of nano-sized cracks. By using atomistic reaction pathway calculations, we determine the energetics governing the brittle and ductile responses of an atomically sharp crack in silicon, involving the competing processes of cleavage bond breaking, dislocation emission, and amorphization by the formation of five- and seven-membered rings. We show that the nanoscale fracture process depends sensitively on the system size and loading method. Our results offer new perspectives on the brittle-to-ductile transition of fracture at the nanoscale.

  17. Fracture healing: mechanisms and interventions

    PubMed Central

    Einhorn, Thomas A.; Gerstenfeld, Louis C.

    2015-01-01

    Fractures are the most common large-organ, traumatic injuries to humans. The repair of bone fractures is a postnatal regenerative process that recapitulates many of the ontological events of embryonic skeletal development. Although fracture repair usually restores the damaged skeletal organ to its pre-injury cellular composition, structure and biomechanical function, about 10% of fractures will not heal normally. This article reviews the developmental progression of fracture healing at the tissue, cellular and molecular levels. Innate and adaptive immune processes are discussed as a component of the injury response, as are environmental factors, such as the extent of injury to the bone and surrounding tissue, fixation and the contribution of vascular tissues. We also present strategies for fracture treatment that have been tested in animal models and in clinical trials or case series. The biophysical and biological basis of the molecular actions of various therapeutic approaches, including recombinant human bone morphogenetic proteins and parathyroid hormone therapy, are also discussed. PMID:25266456

  18. Finite element methods in fracture mechanics

    NASA Technical Reports Server (NTRS)

    Liebowitz, H.; Moyer, E. T., Jr.

    1989-01-01

    Finite-element methodology specific to the analysis of fracture mechanics problems is reviewed. Primary emphasis is on the important algorithmic developments which have enhanced the numerical modeling of fracture processes. Methodologies to address elastostatic problems in two and three dimensions, elastodynamic problems, elastoplastic problems, special considerations for three-dimensional nonlinear problems, and the modeling of stable crack growth are reviewed. In addition, the future needs of the fracture community are discussed and open questions are identified.

  19. Fracture mechanism of a thermal barrier coating

    NASA Astrophysics Data System (ADS)

    Samoilenko, V. M.; Ravilov, R. G.; Drevnyak, V. V.; Petrova, M. A.

    2016-06-01

    The fracture mechanism of the thermal barrier coating of gas turbine blades is studied. The causes of the fracture of the ceramic layer are discussed and the possible ways to increase the fatigue life of the thermal barrier coating are considered.

  20. Mechanisms for shrinkage fracturing at Meridiani Planum

    NASA Astrophysics Data System (ADS)

    Watters, W. A.; Squyres, S. W.

    2009-12-01

    We investigate the role of water in fracturing at Meridiani Planum with the aim of shedding light on the history of densely-fractured outcroppings of light-toned rocks at low-latitudes on Mars. The fractures that occur throughout the inter-crater plains at Meridiani exhibit many characteristics of shrinkage cracks: they have significant width (i.e., not hairline), commonly connect in 90-degree and 120-degree junctions, and exhibit a "hierarchical" organization: i.e., the longest fractures are widest, and narrower fractures terminate against wider fractures at 90-degree junctions (T-shaped). Using the Pancam and Navcam stereo-pair images acquired by the Opportunity rover, we have measured the geometric scaling of fracture networks at Meridiani (e.g., fracture width vs. fracture separation) as well as the total volume change. We have also characterized the diversity of patterns in detail, as well as the modification of fractures and polygonal "tiles" by wind-blown sand abrasion. Identical observations were carried-out for an analogue site where similar fractures are ubiquitous in the playas of Death Valley, California, and where modification processes are also comparable. By also estimating the expected volume change and results from numerical models of shrinkage fracturing, we evaluate the likelihood of three candidate contraction mechanisms: loss of water bound in hydrated minerals (dehydration), loss of water from pore spaces (desiccation), and contraction from cooling (thermal fracturing). The evidence to date favors the second of these (desiccation); this result would have significant implications for the history of Meridiani since the time when sulfate-rich sediments were deposited.

  1. 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.

  2. Integration of NDE Reliability and Fracture Mechanics

    SciTech Connect

    Becker, F. L.; Doctor, S. R.; Heas!er, P. G.; Morris, C. J.; Pitman, S. G.; Selby, G. P.; Simonen, F. A.

    1981-03-01

    The Pacific Northwest Laboratory is conducting a four-phase program for measuring and evaluating the effectiveness and reliability of in-service inspection (lSI} performed on the primary system piping welds of commercial light water reactors (LWRs). Phase I of the program is complete. A survey was made of the state of practice for ultrasonic rsr of LWR primary system piping welds. Fracture mechanics calculations were made to establish required nondestrutive testing sensitivities. In general, it was found that fatigue flaws less than 25% of wall thickness would not grow to failure within an inspection interval of 10 years. However, in some cases failure could occur considerably faster. Statistical methods for predicting and measuring the effectiveness and reliability of lSI were developed and will be applied in the "Round Robin Inspections" of Phase II. Methods were also developed for the production of flaws typical of those found in service. Samples fabricated by these methods wilI be used in Phase II to test inspection effectiveness and reliability. Measurements were made of the influence of flaw characteristics {i.e., roughness, tightness, and orientation) on inspection reliability. These measurernents, as well as the predictions of a statistical model for inspection reliability, indicate that current reporting and recording sensitivities are inadequate.

  3. Fractal materials, beams, and fracture mechanics

    NASA Astrophysics Data System (ADS)

    Ostoja-Starzewski, Martin; Li, Jun

    2009-11-01

    Continuing in the vein of a recently developed generalization of continuum thermomechanics, in this paper we extend fracture mechanics and beam mechanics to materials described by fractional integrals involving D, d and R. By introducing a product measure instead of a Riesz measure, so as to ensure that the mechanical approach to continuum mechanics is consistent with the energetic approach, specific forms of continuum-type equations are derived. On this basis we study the energy aspects of fracture and, as an example, a Timoshenko beam made of a fractal material; the local form of elastodynamic equations of that beam is derived. In particular, we review the crack driving force G stemming from the Griffith fracture criterion in fractal media, considering either dead-load or fixed-grip conditions and the effects of ensemble averaging over random fractal materials.

  4. Rabotnov damageparameter and description of delayed fracture: Results, current status, application to fracture mechanics, and prospects

    NASA Astrophysics Data System (ADS)

    Stepanova, L. V.; Igonin, S. A.

    2015-03-01

    This paper presents a review of studies of delayed fracture and fracture mechanics problems in which the hypotheses and ideas of Yu. N. Rabotnov and L. M. Kachanov on the mechanisms of delayed fracture under creep conditions are extended to describe fracture processes using scalar and tensor measures of damage. The results of current research in the theory of elasticity, the mathematical theory of plasticity and creep, the mechanics of composites, and linear and nonlinear fracture mechanics, with material damage taken into account.

  5. Mechanism of cinnamaldehyde sensitization.

    PubMed

    Majeti, V A; Suskind, R R

    1977-02-01

    The skin sensitization of cinnamaldehyde is probably initiated by the reaction of cinnamaldehyde with epsilon-amino groups on protein side chains. Alpha-Substituted cinnamaldehydes, which are known not to be skin sensitizers, react very slowly or not at all with amines in comparison with cinnamaldehyde.

  6. 3-D description of fracture surfaces and stress-sensitivity analysis for naturally fractured reservoirs

    SciTech Connect

    Zhang, S.Q.; Jioa, D.; Meng, Y.F.; Fan, Y.

    1997-08-01

    Three kinds of reservoir cores (limestone, sandstone, and shale with natural fractures) were used to study the effect of morphology of fracture surfaces on stress sensitivity. The cores, obtained from the reservoirs with depths of 2170 to 2300 m, have fractures which are mated on a large scale, but unmated on a fine scale. A specially designed photoelectric scanner with a computer was used to describe the topography of the fracture surfaces. Then, theoretical analysis of the fracture closure was carried out based on the fracture topography generated. The scanning results show that the asperity has almost normal distributions for all three types of samples. For the tested samples, the fracture closure predicted by the elastic-contact theory is different from the laboratory measurements because plastic deformation of the aspirates plays an important role under the testing range of normal stresses. In this work, the traditionally used elastic-contact theory has been modified to better predict the stress sensitivity of reservoir fractures. Analysis shows that the standard deviation of the probability density function of asperity distribution has a great effect on the fracture closure rate.

  7. Damage and fracture mechanics of composite materials

    NASA Astrophysics Data System (ADS)

    Abdussalam, Saleh Ramadan

    The design of structural systems in the aerospace industry has been characterized by a continuing search for strong, yet lightweight, materials to achieve maximum payload capability for minimum weight. In recent years, this search has led to a wide use of fiber reinforced composites, such as carbon, glass and kevelar based composites. Comparison of these new materials with the traditional ones (metals) according to the basic properties, such as density, elastic modulus and also long-time and short-time strength, shows their superiority over traditional materials, when weight is a major design factor, like in the aerospace industry. Most composite materials of interest to aerospace applications have been adequately characterized under static loading conditions. Related work to study their fracture behaviour has been limited. Since most failure mechanisms involve crack growth and/or delamination, design of such components requires knowledge and understanding of their fracture properties. This thesis includes an experimental and analytical investigation of fracture characteristics of composite materials. The post-peak response of notched specimens subjected to uniaxial cyclic loading is established to evaluate the fracture energy associated with progressive matrix damage and subsequent crack growth. A total of 75 uniaxial tension specimens were tested. The experimental work consisted of first testing several un-notched specimens with different thickness (number of layers) to determine the initial and secondary elastic modulus as well as the tensile strength. The investigation studied the effect of the various fracture parameters, including thickness, fiber orientation, and crack width ratio (a/w) on the behaviour of crack propagation, peak load, and post-peak response. The specimens used in this research were prepared using the vacuum bagging technique, with a chosen number of fiber glass cloth layers and fiber orientation. The experimental results provided

  8. A review of fracture mechanics life technology

    NASA Technical Reports Server (NTRS)

    Besuner, P. M.; Harris, D. O.; Thomas, J. M.

    1986-01-01

    Lifetime prediction technology for structural components subjected to cyclic loads is examined. The central objectives of the project are: (1) to report the current state of the art, and (2) recommend future development of fracture mechanics-based analytical tools for modeling subcritical fatigue crack growth in structures. Of special interest is the ability to apply these tools to practical engineering problems and the developmental steps necessary to bring vital technologies to this stage. The authors conducted a survey of published literature and numerous discussions with experts in the field of fracture mechanics life technology. One of the key points made is that fracture mechanics analyses of crack growth often involve consideration of fatigue and fracture under extreme conditions. Therefore, inaccuracies in predicting component lifetime will be dominated by inaccuracies in environment and fatigue crack growth relations, stress intensity factor solutions, and methods used to model given loads and stresses. Suggestions made for reducing these inaccuracies include development of improved models of subcritical crack growth, research efforts aimed at better characterizing residual and assembly stresses that can be introduced during fabrication, and more widespread and uniform use of the best existing methods.

  9. A review of fracture mechanics life technology

    NASA Technical Reports Server (NTRS)

    Thomas, J. M.; Besuner, P. M.; Harris, D. O.

    1985-01-01

    Current lifetime prediction technology for structural components subjected to cyclic loads was reviewed. The central objectives of the project were to report the current state of and recommend future development of fracture mechanics-based analytical tools for modeling and forecasting subcritical fatigue crack growth in structures. Of special interest to NASA was the ability to apply these tools to practical engineering problems and the developmental steps necessary to bring vital technologies to this stage. A survey of published literature and numerous discussions with experts in the field of fracture mechanics life technology were conducted. One of the key points made is that fracture mechanics analyses of crack growth often involve consideration of fatigue and fracture under extreme conditions. Therefore, inaccuracies in predicting component lifetime will be dominated by inaccuracies in environment and fatigue crack growth relations, stress intensity factor solutions, and methods used to model given loads and stresses. Suggestions made for reducing these inaccuracies include: development of improved models of subcritical crack growth, research efforts aimed at better characterizing residual and assembly stresses that can be introduced during fabrication, and more widespread and uniform use of the best existing methods.

  10. Computational simulation methods for composite fracture mechanics

    NASA Technical Reports Server (NTRS)

    Murthy, Pappu L. N.

    1988-01-01

    Structural integrity, durability, and damage tolerance of advanced composites are assessed by studying damage initiation at various scales (micro, macro, and global) and accumulation and growth leading to global failure, quantitatively and qualitatively. In addition, various fracture toughness parameters associated with a typical damage and its growth must be determined. Computational structural analysis codes to aid the composite design engineer in performing these tasks were developed. CODSTRAN (COmposite Durability STRuctural ANalysis) is used to qualitatively and quantitatively assess the progressive damage occurring in composite structures due to mechanical and environmental loads. Next, methods are covered that are currently being developed and used at Lewis to predict interlaminar fracture toughness and related parameters of fiber composites given a prescribed damage. The general purpose finite element code MSC/NASTRAN was used to simulate the interlaminar fracture and the associated individual as well as mixed-mode strain energy release rates in fiber composites.

  11. The radiation swelling effect on fracture properties and fracture mechanisms of irradiated austenitic steels. Part I. Ductility and fracture toughness

    NASA Astrophysics Data System (ADS)

    Margolin, B.; Sorokin, A.; Shvetsova, V.; Minkin, A.; Potapova, V.; Smirnov, V.

    2016-11-01

    The radiation swelling effect on the fracture properties of irradiated austenitic steels under static loading has been studied and analyzed from the mechanical and physical viewpoints. Experimental data on the stress-strain curves, fracture strain, fracture toughness and fracture mechanisms have been represented for austenitic steel of 18Cr-10Ni-Ti grade (Russian analog of AISI 321 steel) irradiated up to neutron dose of 150 dpa with various swelling. Some phenomena in mechanical behaviour of irradiated austenitic steels have been revealed and explained as follows: a sharp decrease of fracture toughness with swelling growth; untypical large increase of fracture toughness with decrease of the test temperature; some increase of fracture toughness after preliminary cyclic loading. Role of channel deformation and channel fracture has been clarified in the properties of irradiated austenitic steel and different tendencies to channel deformation have been shown and explained for the same austenitic steel irradiated at different temperatures and neutron doses.

  12. Mechanisms of multiple chemical sensitivity.

    PubMed

    Winder, Chris

    2002-03-10

    Sensitivity to chemicals is a toxicological concept, contained in the dose-response relationship. Sensitivity also includes the concept of hypersensitivity, although controversy surrounds the nature of effects from very low exposures. The term multiple chemical sensitivity has been used to describe individuals with a debilitating, multi-organ sensitivity following chemical exposures. Many aspects of this condition extend the nature of sensitivity to low levels of exposure to chemicals, and is a designation with medical, immunological, neuropsychological and toxicological perspectives. The basis of MCS is still to be identified, although a large number of hypersensitivity, immunological, psychological, neurological and toxicological mechanisms have been suggested, including: allergy; autosuggestion; cacosomia; conditioned response; immunological; impairment of biochemical pathways involved in energy production; impairment of neurochemical pathways; illness belief system; limbic kindling; olfactory threshold sensitivity; panic disorder; psychosomatic condition; malingering; neurogenic inflammation; overload of biotransformation pathways (also linked with free radical production); psychological or psychiatric illness; airway reactivity; sensitisation of the neurological system; time dependent sensitisation, toxicant induced loss of tolerance. Most of these theories tend to break down into concepts involving: (1) disruption in immunological/allergy processes; (2) alteration in nervous system function; (3) changes in biochemical or biotransformation capacity; (4) changes in psychological/neurobehavioural function. Research into the possible mechanisms of MCS is far from complete. However, a number of promising avenues of investigation indicate that the possibility of alteration of the sensitivity of nervous system cells (neurogenic inflammation, limbic kindling, cacosomia, neurogenic switching) are a possible mechanism for MCS.

  13. Quantitative Integration of Ndt with Probabilistic Fracture Mechanics for the Assessment of Fracture Risk in Pipelines

    NASA Astrophysics Data System (ADS)

    Kurz, J. H.; Cioclov, D.; Dobmann, G.; Boller, C.

    2010-02-01

    In the context of probabilistic paradigm of fracture risk assessment in structural components a computer simulation rationale is presented which has at the base the integration of Quantitative Non-destructive Inspection and Probabilistic Fracture Mechanics. In this study the static failure under static loading is assessed in the format known as Failure Assessment Diagram (FAD). The fracture risk is evaluated in probabilistic terms. The superposed probabilistic pattern over the deterministic one is implemented via Monte-Carlo sampling. The probabilistic fracture simulation yields a more informative analysis in terms of probability of failure. The ability to simulate the influence of the quality and reliability of non-destructive inspection (NDI) is an important feature of this approach. It is achieved by integrating, algorithmically, probabilistic FAD analysis and the Probability of Detection (POD). The POD information can only be applied in a probabilistic analysis and leads to a refinement of the assessment. By this means, it can be ascertained the decrease of probability of failure when POD-characterized NDI is applied. Therefore, this procedure can be used as a tool for inspection based life time conceptions. In this paper results of sensitivity analyses are presented with the aim to outline, in terms of non-failure probabilities, the benefits of applying NDI, in various qualities, in comparison with the situation when NDI is lacking. A better substantiation is enabled of both the component reliability management and the costs-effectiveness of NDI timing.

  14. Thermal-Hydrologic-Mechanical Behavior of Single Fractures in EGS Reservoirs

    NASA Astrophysics Data System (ADS)

    Zyvoloski, G.; Kelkar, S.; Yoshioka, K.; Rapaka, S.

    2010-12-01

    Enhanced Geothermal Systems (EGS) rely on the creation a connected fracture system or the enhancement of existing (natural) fractures by hydraulic and chemical treatments. EGS studies at Fenton Hill (New Mexico, USA) and Hijiori (Japan) have revealed that only a limited number of fractures contribute to the effective heat transfer surface area. Thus, the economic viability of EGS depends strongly on the creation and spacing of single fractures in order to efficiently mine heat from given volume of rock. Though there are many similarities between EGS and natural geothermal reservoirs, a major difference between the reservoir types is the (typically) high pumping pressures and induced thermal stresses at the injection wells of an EGS reservoir. These factors can be responsible for fracture dilation/extension and thermal short circuiting and depend strongly on the surrounding state of stress in the reservoir and mechanical properties. We will present results from our study of the thermal-hydrologic-mechanical (THM) behavior of a single fracture in a realistic subsurface stress field. We will show that fracture orientation, the stress environment, fracture permeability structure, and the relationship between permeability changes in a fracture resulting from mechanical displacement are all important when designing and managing an EGS reservoir. Lastly, we present a sensitivity analysis of the important parameters that govern fracture behavior with respect to field measurements. Temperature in high permeability fracture in an EGS reservoir

  15. Analogy between fluid cavitation and fracture mechanics

    NASA Technical Reports Server (NTRS)

    Hendricks, R. C.; Mullen, R. L.; Braun, M. J.

    1983-01-01

    When the stresses imposed on a fluid are sufficiently large, rupture or cavitation can occur. Such conditions can exist in many two-phase flow applications, such as the choked flows, which can occur in seals and bearings. Nonspherical bubbles with large aspect ratios have been observed in fluids under rapid acceleration and high shear fields. These bubbles are geometrically similar to fracture surface patterns (Griffith crack model) existing in solids. Analogies between crack growth in solid and fluid cavitation are proposed and supported by analysis and observation (photographs). Healing phenomena (void condensation), well accepted in fluid mechanics, have been observed in some polymers and hypothesized in solid mechanics. By drawing on the strengths of the theories of solid mechanics and cavitation, a more complete unified theory can be developed.

  16. Geomechanics of horizontally-drilled, stress-sensitive, naturally-fractured reservoirs

    SciTech Connect

    Holcomb, D.J.; Brown, S.R.; Lorenz, J.C.; Olsson, W.A.; Teufel, L.W.; Warpinski, N.R.

    1994-09-01

    Horizontal drilling is a viable approach for accessing hydrocarbons in many types of naturally-fractured reservoirs. Cost-effective improvements in the technology to drill, complete, and produce horizontal wells in difficult geologic environments require a better understanding of the mechanical and fluid-flow behavior of these reservoirs with changes ineffective stress during their development and production history. In particular, improved understanding is needed for predicting borehole stability and reservoir response during pore pressure drawdown. To address these problems, a cooperative project between Oryx Energy Company and Sandia National Laboratories was undertaken to study the effects of rock properties, in situ stress, and changes in effective stress on the deformation and permeability of stress sensitive, naturally-fractured reservoirs. A low value for the proelastic parameter was found, implying that the reservoir should have a low sensitivity to declining pore pressure. A surprisingly diverse suite of fractures was identified from core. From the coring-induced fractures, it was plausible to conclude that the maximum principal stress was in the horizontal plane. Measurements on permeability of naturally fractured rock in a newly-developed experimental arrangement showed that slip on fractures is much more effective inchangingpcrtncability than is normal stress. The intermediate principal stress was found to have a strong effect, on the strength and ductility of the chalk, implying the need for a more sophisticated calculation of borehole stability.

  17. Sensitivity analysis of transport modeling in a fractured gneiss aquifer

    NASA Astrophysics Data System (ADS)

    Abdelaziz, Ramadan; Merkel, Broder J.

    2015-03-01

    Modeling solute transport in fractured aquifers is still challenging for scientists and engineers. Tracer tests are a powerful tool to investigate fractured aquifers with complex geometry and variable heterogeneity. This research focuses on obtaining hydraulic and transport parameters from an experimental site with several wells. At the site, a tracer test with NaCl was performed under natural gradient conditions. Observed concentrations of tracer test were used to calibrate a conservative solute transport model by inverse modeling based on UCODE2013, MODFLOW, and MT3DMS. In addition, several statistics are employed for sensitivity analysis. Sensitivity analysis results indicate that hydraulic conductivity and immobile porosity play important role in the late arrive for breakthrough curve. The results proved that the calibrated model fits well with the observed data set.

  18. Patterns and perspectives in applied fracture mechanics

    SciTech Connect

    Merkle, J.G.

    1994-12-31

    This lecture begins with a overview of applied fracture mechanics pertinent to safety of pressure vessels. It then progresses to a chronological panorama of experimental and analytical results. To be useful and dependable in safety analysis of real structures, new analysis developments must be physically realistic, which means that they must accurately describe physical cause and effect. Consequently, before mathematical modeling can begin, cause and effect must be established from experimental data. This can be difficult and time consuming, but worth the effort. Accordingly, the theme of this paper is that the search for patterns is constant and vital. This theme is illustrated by the development of small, single-specimen, fracture toughness testing techniques. It is also illustrated by the development, based on two different published large-strain, elastic-plastic, three-dimensional finite-element analyses, of a hypothesis concerning three-dimensional loss of constraint. When a generalization of Irwin`s thickness-normalized plastic-zone parameter, reaches a value close to 2{pi}, the through-thickness contraction strain at the apex of the near-tip logarithmic-spiral slip-line region becomes the dominant negative strain accommodating crack opening. Because slip lines passing from the midplane to the stress-free side surfaces do not have to curve, once these slip lines are established, stresses near the crack tip are only elevated by strain hardening and constraint becomes significantly relaxed. This hypothesis, based on published three-dimensional elastic-plastic analyses, provides a potentially valuable means for gaining additional insight into constraint effects on fracture toughness by considering the roles played by the plastic strains as well as the stresses that develop near a crack tip.

  19. Mechanics of fracture - Fundamentals and some recent developments

    NASA Technical Reports Server (NTRS)

    Liebowitz, H.; Subramonian, N.; Lee, J. D.

    1979-01-01

    An overview is presented of the fundamental aspects of and recent developments in fracture mechanics. Reference is made to linear elastic fracture mechanics including the state of stresses and displacements in the vicinity of cracks, effects of crack geometry and orientation on stress intensity factors, energy balance of Griffith, Irwin's stress intensity concept, and linear elastic fracture mechanics testing for fracture toughness. Other aspects of this paper include the non-linear behavior of materials and their influence on fracture mechanics parameters, consideration of viscoelasticity and plasticity, non-linear fracture toughness parameters as C.O.D., R-curve and J-integral, and a non-linear energy method, proposed by Liebowitz. Finite element methods applied to fracture mechanics problems are indicated. Also, consideration has been given to slow crack growth, dynamic effects on K(IC), Sih's criterion for fracture, Lee and Liebowitz's criterion relating crack growth with plastic energy, and applications of fracture mechanics to aircraft design. Suggestions are offered for future research efforts to be undertaken in fracture mechanics.

  20. Solution-adaptive finite element method in computational fracture mechanics

    NASA Technical Reports Server (NTRS)

    Min, J. B.; Bass, J. M.; Spradley, L. W.

    1993-01-01

    Some recent results obtained using solution-adaptive finite element method in linear elastic two-dimensional fracture mechanics problems are presented. The focus is on the basic issue of adaptive finite element method for validating the applications of new methodology to fracture mechanics problems by computing demonstration problems and comparing the stress intensity factors to analytical results.

  1. Compressive fracture morphology and mechanism of metallic glass

    NASA Astrophysics Data System (ADS)

    Qu, R. T.; Zhang, Z. F.

    2013-11-01

    We quantitatively investigated the fracture morphologies of Zr52.5Cu17.9Ni14.6Al10Ti5 and Pd78Cu6Si16 metallic glasses (MGs) under compression. The characteristic features of the compressive fracture morphology were captured, and the shear vein patterns were found to be not a one-to-one correspondence between two opposing fracture surfaces in an identical sample. This finding experimentally confirms that the compressive failure behaves in a fracture mode of pure shear (mode II). Quantitative measurements show that a ˜1 μm thickness layer with materials not only inside but also adjacent to the major shear band contributes to the formation of shear vein patterns. The critical shear strain to break a shear band was found to be more than 105% and higher in more ductile MGs under compression than tension. Estimation on the temperature rise at the fracture moment indicates that only ˜5% of the total elastic energy stored in the sample converts into the heat required for melting the layer to form the vein patterns. The mode II fracture toughness was also estimated based on the quantitative measurements of shear vein pattern and found larger than the mode I fracture toughness. Finally, the deformation and fracture mechanisms of MGs under tension and compression were compared and discussed. These results may improve the understanding on the fracture behaviors and mechanisms of MGs and may provide instructions on future design for ductile MGs with high resistance for fracture.

  2. Fracture Mechanics for Composites: State of the Art and Challenges

    NASA Technical Reports Server (NTRS)

    Krueger, Ronald; Krueger, Ronald

    2006-01-01

    Interlaminar fracture mechanics has proven useful for characterizing the onset of delaminations in composites and has been used with limited success primarily to investigate onset in fracture toughness specimens and laboratory size coupon type specimens. Future acceptance of the methodology by industry and certification authorities however, requires the successful demonstration of the methodology on the structural level. In this paper, the state-of-the-art in fracture toughness characterization, and interlaminar fracture mechanics analysis tools are described. To demonstrate the application on the structural level, a panel was selected which is reinforced with stringers. Full implementation of interlaminar fracture mechanics in design however remains a challenge and requires a continuing development effort of codes to calculate energy release rates and advancements in delamination onset and growth criteria under mixed mode conditions.

  3. Some recent theoretical and experimental developments in fracture mechanics

    NASA Technical Reports Server (NTRS)

    Liebowitz, H.; Eftis, J.; Hones, D. L.

    1978-01-01

    Recent theoretical and experimental developments in four distinct areas of fracture mechanics research are described. These are as follows: experimental comparisons of different nonlinear fracture toughness measures, including the nonlinear energy, R curve, COD and J integral methods; the singular elastic crack-tip stress and displacement equations and the validity of the proposition of their general adequacy as indicated, for example, by the biaxially loaded infinite sheet with a flat crack; the thermodynamic nature of surface energy induced by propagating cracks in relation to a general continuum thermodynamic description of brittle fracture; and analytical and experimental aspects of Mode II fracture, with experimental data for certain aluminum, steel and titanium alloys.

  4. 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.

  5. Fracture mechanics /Dryden Lecture/. [aerospace structural design applications

    NASA Technical Reports Server (NTRS)

    Hardrath, H. F.

    1974-01-01

    A historical outline of the engineering discipline of fracture mechanics is presented, and current analytical procedures are summarized. The current status of the discipline is assessed, and engineering applications are discussed, along with recommended directions for future study.

  6. A nonlinear high temperature fracture mechanics basis for strainrange partitioning

    NASA Technical Reports Server (NTRS)

    Kitamura, Takayuki; Halford, Gary R.

    1989-01-01

    A direct link was established between Strainrange Partitioning (SRP) and high temperature fracture mechanics by deriving the general SRP inelastic strain range versus cyclic life relationships from high temperature, nonlinear, fracture mechanics considerations. The derived SRP life relationships are in reasonable agreement based on the experience of the SRP behavior of many high temperature alloys. In addition, fracture mechanics has served as a basis for derivation of the Ductility-Normalized SRP life equations, as well as for examination of SRP relations that are applicable to thermal fatigue life prediction. Areas of additional links between nonlinear fracture mechanics and SRP were identified for future exploration. These include effects of multiaxiality as well as low strain, nominally elastic, long life creep fatigue interaction.

  7. Evaluation of fracture toughness of human dentin using elastic-plastic fracture mechanics.

    PubMed

    Yan, Jiahau; Taskonak, Burak; Platt, Jeffrey A; Mecholsky, John J

    2008-01-01

    Dentin, the mineralized tissue forming the bulk of the tooth, lies between the enamel and the pulp chamber. It is a rich source of inspiration for designing novel synthetic materials due to its unique microstructure. Most of the previous studies investigating the fracture toughness of dentin have used linear-elastic fracture mechanics (LEFM) that ignores plastic deformation and could underestimate the toughness of dentin. With the presence of collagen (approximately 30% by volume) aiding the toughening mechanisms in dentin, we hypothesize that there is a significant difference between the fracture toughness estimated using LEFM (Kc) and elastic-plastic fracture mechanics (EPFM) (KJc). Single-edge notched beam specimens with in-plane (n=10) and anti-plane (n=10) parallel fractures were prepared following ASTM standard E1820 and tested in three-point flexure. KJc of the in-plane parallel and anti-plane parallel specimens were found to be 3.1 and 3.4 MPa m 1/2 and Kc were 2.4 and 2.5 MPa m 1/2, respectively. The fracture toughness estimated based on KJc is significantly greater than that estimated based on Kc (32.5% on average; p<0.001). In addition, KJc of anti-plane parallel specimens is significantly greater than that of in-plane parallel specimens. We suggest that, in order to critically evaluate the fracture toughness of human dentin, EPFM should be employed.

  8. Investigation of translaminar fracture in fibrereinforced composite laminates---applicability of linear elastic fracture mechanics and cohesive-zone model

    NASA Astrophysics Data System (ADS)

    Hou, Fang

    With the extensive application of fiber-reinforced composite laminates in industry, research on the fracture mechanisms of this type of materials have drawn more and more attentions. A variety of fracture theories and models have been developed. Among them, the linear elastic fracture mechanics (LEFM) and cohesive-zone model (CZM) are two widely-accepted fracture models, which have already shown applicability in the fracture analysis of fiber-reinforced composite laminates. However, there remain challenges which prevent further applications of the two fracture models, such as the experimental measurement of fracture resistance. This dissertation primarily focused on the study of the applicability of LEFM and CZM for the fracture analysis of translaminar fracture in fibre-reinforced composite laminates. The research for each fracture model consisted of two sections: the analytical characterization of crack-tip fields and the experimental measurement of fracture resistance parameters. In the study of LEFM, an experimental investigation based on full-field crack-tip displacement measurements was carried out as a way to characterize the subcritical and steady-state crack advances in translaminar fracture of fiber-reinforced composite laminates. Here, the fiber-reinforced composite laminates were approximated as anisotropic solids. The experimental investigation relied on the LEFM theory with a modification with respect to the material anisotropy. Firstly, the full-field crack-tip displacement fields were measured by Digital Image Correlation (DIC). Then two methods, separately based on the stress intensity approach and the energy approach, were developed to measure the crack-tip field parameters from crack-tip displacement fields. The studied crack-tip field parameters included the stress intensity factor, energy release rate and effective crack length. Moreover, the crack-growth resistance curves (R-curves) were constructed with the measured crack-tip field parameters

  9. Deterioration in Fracture Toughness of 304LN Austenitic Stainless Steel Due to Sensitization

    NASA Astrophysics Data System (ADS)

    Ghosh, Swati; Kain, V.; Ray, A.; Roy, H.; Sivaprasad, S.; Tarafder, S.; Ray, K. K.

    2009-12-01

    The aim of this report is to examine the influence of sensitization on the mechanical properties of AISI grade 304LN stainless steel with special emphasis on its fracture toughness. A series of stainless steel samples has been sensitized by holding at 1023 K for different time periods ranging from 1 to 100 hours followed by water quenching. The degree of sensitization (DOS) for each type of the varyingly heat-treated samples has been measured by an electrochemical potentiodynamic reactivation (EPR) test. The microstructures of these samples have been characterized by optical metallography, scanning electron microscopy, transmission electron microscopy (TEM), and X-ray diffraction (XRD) analyses, together with measurements of their hardness and tensile properties. The fracture toughness of the samples has been measured by the ball indentation (BI) technique and the results are validated by conducting conventional J-integral tests. It is revealed for the first time that the fracture toughness and ductility of AISI 304LN stainless steel deteriorate significantly with increased DOS, while the tensile strength (TS) values remain almost unaltered. The results have been critically discussed in terms of the depletion of solid solution strengtheners, the nature of the grain boundary precipitations, and the strain-induced martensite formation with the increasing DOS of the 304LN stainless steel.

  10. Deformation and Fracture Mechanisms of Polymer-Silicate Nanocomposites

    NASA Astrophysics Data System (ADS)

    Harcup, Jason; Yee, Albert

    1998-03-01

    The deformation and fracture behavior of a series of nanocomposites comprising polyamide, silicate and in some cases rubber has been studied. Mechanical properties including Young modulus and fracture toughness were measured and it was found that compared to conventional composites, the nanocomposites exhibited far greater improvement in properties over the neat matrix for a given silicate fraction. It was also found that the addition of the rubber phase produced an increase in toughness. The arrested crack tip process zone was obtained using the Double Notch Four Point Bend test geometry and the process zone morphology was studied using TEM and TOM. Fracture surfaces were probed with XEDS and SEM. The use of these techniques enabled the mechanisms which occur during fracture to be studied and related to the mechanical properties and toughening of these materials.

  11. Fracture mechanics for delamination problems in composite materials

    NASA Technical Reports Server (NTRS)

    Wang, S. S.

    1983-01-01

    A fracture mechanics approach to the well-known delamination problem in composite materials is presented. Based on the theory of anisotropic laminate elasticity and interlaminar fracture mechanics concepts, the composite delamination problem is formulated and solved. The exact order of the delamination crack-tip stress singularity is determined. Asymptotic stress and displacement fields for an interlaminar crack are obtained. Fracture mechanics parameters such as mixed-mode stress intensity factors, KI, KII, KIII, and the energy release rate, G, for composite delamination problems are defined. To illustrate the fundamental nature of the delamination crack behavior, solutions for edge-delaminated graphite-epoxy composites under uniform axial extension are presented. Effects of fiber orientation, ply thickness, and delamination length on the interlaminar fracture are examined.

  12. In Vitro Fracture of Human Cortical Bone: Local Fracture Criteria and Toughening Mechanisms

    SciTech Connect

    Nalla, R; Stolken, J; Kinney, J; Ritchie, R

    2004-08-18

    A micro-mechanistic understanding of bone fracture that encompasses how cracks interact with the underlying microstructure and defines their local failure mode is lacking, despite extensive research on the response of bone to a variety of factors like aging, loading, and/or disease. Micro-mechanical models for fracture incorporating such local failure criteria have been widely developed for metallic and ceramic materials systems; however, few such deliberations have been undertaken for the fracture of bone. In fact, although the fracture event in mineralized tissues such as bone is commonly believed to be locally strain controlled, until recently there has been little experimental evidence to support this widely held belief. In the present study, a series of in vitro experiments involving a double-notch bend test geometry are performed in order to shed further light on the nature of the local cracking events that precede catastrophic fracture in bone and to define their relationship to the microstructure. Specifically, crack-microstructure interactions are examined to determine the salient toughening mechanisms in human cortical bone and to characterize how these may affect the anisotropy in fracture properties. Based on preliminary micro-mechanical models of these processes, in particular crack deflection and uncracked ligament bridging, the relative importance of these toughening mechanisms is established.

  13. Material properties and fracture mechanics in relation to ceramic machining

    SciTech Connect

    Griffith, L.V.

    1993-12-02

    Material removal rate, surface finish, and subsurface damage are largely governed by fracture mechanics and plastic deformation, when ceramics are machined using abrasive methods. A great deal of work was published on the fracture mechanics of ceramics in the late 1970s and early 1980s, although this work has never resulted in a comprehensive model of the fixed abrasive grinding process. However, a recently published model describes many of the most important features of the loose abrasive machining process, for example depth of damage, surface roughness, and material removal rate. Many of the relations in the loose abrasive machining model can be readily discerned from fracture mechanics models, in terms of material properties. By understanding the mechanisms of material removal, from a material properties perspective, we can better estimate how one material will machine in relation to another. Although the fracture mechanics models may have been developed for loose abrasive machining, the principles of crack initiation and propagation are equally valuable for fixed abrasive machining. This report provides a brief review of fracture in brittle materials, the stress distribution induced by abrasives, critical indenter loads, the extension of cracks, and the relation of the fracture process to material removal.

  14. Effects of Strain Rates on Mechanical Properties and Fracture Mechanism of DP780 Dual Phase Steel

    NASA Astrophysics Data System (ADS)

    Li, Shengci; Kang, Yonglin; Zhu, Guoming; Kuang, Shuang

    2015-06-01

    The mechanical properties of DP780 dual phase steel were measured by quasi-static and high-speed tensile tests at strain rates between 0.001 and 1000 s-1 at room temperature. The deformation and fracture mechanisms were analyzed by observation of the tensile fracture and microstructure near the fracture. Dynamic factor and feret ratio quantitative methods were applied to study the effect of strain rate on the microstructure and properties of DP780 steel. The constitutive relation was described by a modified Johnson-Cook and Zerilli-Armstrong model. The results showed that the strain rate sensitivity of yield strength is bigger than that of ultimate tensile strength; as strain rate increased, the formation of microcracks and voids at the ferrite/martensite interface can be alleviated; the strain rate effect is unevenly distributed in the plastic deformation region. Moreover, both models can effectively describe the experimental results, while the modified Zerilli-Armstrong model is more accurate because the strain-hardening rate of this model is independent of strain rate.

  15. Single-well tracer push-pull test sensitivity w. r. to fracture aperture and spacing

    NASA Astrophysics Data System (ADS)

    Ghergut, I.; Behrens, H.; Karmakar, S.; Sauter, M.

    2012-04-01

    Dealing with a parallel-fracture system of infinite lateral extension, four characteristic regimes of tracer signal sensitivity w. r. to fracture aperture and w. r. to fracture spacing s (whose reciprocal defines fracture density, or the fluid-rock interface area per volume) can be identified during the pull phase of a single-well push-pull test, also depending upon the ratio between push-phase duration Tpush and a characteristic time scale Ts (defined by s2 / D = Ts , with D denoting the tracer's effective diffusion coefficient): early-time regime: tracer signals are sensitive w. r. to fracture aperture, but insensitive w. r. to fracture spacing; sensitivity w. r. to fracture aperture first increases, then decreases with Tpush / Ts (thus there will be an optimum in terms of to Tpush / Ts , at early pull times); mid-time regime: tracer signals are sensitive w. r. to fracture spacing, but insensitive w. r. to fracture aperture; sensitivity w. r. to fracture spacing increases with Tpush / Ts ; late-time regime: with increasing pull duration, tracer signals become increasingly insensitive w. r. to fracture spacing, while regaining sensitivity w. r. to fracture aperture; 'very late'-time regime: sensitivity w. r. to fracture aperture becomes independent upon Tpush / Ts . From these different regimes, some recommendations can be derived regarding the design and dimensioning of dual-tracer single-well push-pull tests for the specific purposes of geothermal reservoir characterization, using conservative solutes and heat as tracers. Acknowledgement: This study is funded by MWK Niedersachsen (Lower-Saxony's Science and Culture Ministry) and by Baker Hughes (Celle) within task unit 'G6' of the Collaborative Research Project 'gebo' (Geothermal Energy and High-Performance Drilling).

  16. Mechanics of dynamic fracture in notched polycarbonate

    NASA Astrophysics Data System (ADS)

    Faye, Anshul; Parmeswaran, Venkitanarayanan; Basu, Sumit

    2015-04-01

    Fracture toughness of brittle amorphous polymers (e.g. polymethyl methacrylate (PMMA)) has been reported to decrease with loading rate at moderate rates and increase abruptly thereafter to close to 5 times the static value at very high loading rates. Dynamic fracture toughness that is much higher than the static values has attractive technological possibilities. However, the reasons for the sharp increase remain unclear. Motivated by these observations, the present work focuses on the dynamic fracture behavior of polycarbonate (PC), which is also an amorphous polymer but unlike PMMA, is ductile at room temperature. Towards this end, a combined experimental and numerical approach is adopted. Dynamic fracture experiments at various loading rates are conducted on single edge notched (SEN) specimens with a notch of radius 150 μm, using a Hopkinson bar setup equipped with ultra high-speed imaging (>105 fps) for real-time observation of dynamic processes during fracture. Concurrently, 3D dynamic finite element simulations are performed using a well calibrated material model for PC. Experimentally, we were able to clearly capture the intricate details of the process, for both slowly and dynamically loaded samples, of damage nucleation and growth ahead of the notch tip followed by unstable crack propagation. These observations coupled with fractography and computer simulations led us to conclude that in PC, the fracture toughness remains invariant with loading rate at Jfrac = 12 ± 3 kN / m for the entire range of loading rates (J ˙) from static to 1 ×106 kN / m - s. However, the damage initiation toughness is significantly higher in dynamic loading compared to static situations. In dynamic situations, damage nucleation is quickly followed by initiation of radial crazes from around the void periphery that initiate and quickly bridge the ligament between the initial damaged region and the notch. Thus for PC, two criteria for two major stages in the failure process emerge

  17. Colloid retention mechanisms in single, saturated, variable-aperture fractures.

    PubMed

    Rodrigues, S N; Dickson, S E; Qu, J

    2013-01-01

    The characterization of fractured aquifers is commonly limited to the methodologies developed for unconsolidated porous media aquifers, which results in many uncertainties. Recent work indicates that fractured rocks remove more particulates than they are conventionally credited for. This research was designed to quantify the number of Escherichia coli RS2-GFP retained in single, saturated, variable-aperture fractures extracted from the natural environment. Conservative solute and E. coli RS2-GFP tracer experiments were used to elucidate the relationships between dominant retention mechanisms, aperture field characteristics, and flow rate. A non-destructive method of determining a surrogate measure of a coefficient of variation (COV(S)) for each fracture was used to better understand the transport behaviour of E. coli RS2-GFP. The results from this research all point to the importance of aperture field characterization in understanding the fate and transport of contaminants in fractured aquifers. The mean aperture was a very important characteristic in determining particulate recovery, so were matrix properties, COV(s), and flow rate. It was also determined that attachment is a much more significant retention mechanism than straining under the conditions employed in this research. Finally, it was demonstrated that the dominant retention mechanism in a fracture varies depending on the specific discharge. An improved understanding of the mechanisms that influence the fate and transport of contaminants through fractures will lead to the development of better tools and methodologies for the characterization of fractured aquifers, as well as the ability to manipulate the relevant mechanisms to increase or decrease retention, depending on the application.

  18. Elastic-plastic fracture mechanics of compact bone

    NASA Astrophysics Data System (ADS)

    Yan, Jiahau

    Bone is a composite composed mainly of organics, minerals and water. Most studies on the fracture toughness of bone have been conducted at room temperature. Considering that the body temperature of animals is higher than room temperature, and that bone has a high volumetric percentage of organics (generally, 35--50%), the effect of temperature on fracture toughness of bone should be studied. Single-edged V-shaped notched (SEVN) specimens were prepared to measure the fracture toughness of bovine femur and manatee rib in water at 0, 10, 23, 37 and 50°C. The fracture toughness of bovine femur and manatee rib were found to decrease from 7.0 to 4.3 MPa·m1/2 and from 5.5 to 4.1 MPa·m1/2, respectively, over a temperature range of 50°C. The decreases were attributed to inability of the organics to sustain greater stresses at higher temperatures. We studied the effects of water and organics on fracture toughness of bone using water-free and organics-free SEVN specimens at 23°C. Water-free and organics-free specimens were obtained by placing fresh bone specimen in a furnace at different temperatures. Water and organics significantly affected the fracture toughness of bone. Fracture toughness of the water-free specimens was 44.7% (bovine femur) and 32.4% (manatee rib) less than that of fresh-bone specimens. Fracture toughness of the organics-free specimens was 92.7% (bovine femur) and 91.5% (manatee rib) less than that of fresh bone specimens. Linear Elastic Fracture Mechanics (LEFM) is widely used to study bone. However, bone often has small to moderate scale yielding during testing. We used J integral, an elastic-plastic fracture-mechanics parameter, to study the fracture process of bone. The J integral of bovine femur increased from 6.3 KJ/mm2 at 23°C to 6.7 KJ/mm2 at 37°C. Although the fracture toughness of bovine bone decreases as the temperature increases, the J integral results show a contrary trend. The energy spent in advancing the crack beyond the linear

  19. Adhesive fracture mechanics. [stress analysis for bond line interface

    NASA Technical Reports Server (NTRS)

    Bennett, S. J.; Devries, K. L.; Williams, M. L.

    1974-01-01

    In studies of fracture mechanics the adhesive fracture energy is regarded as a fundamental property of the adhesive system. It is pointed out that the value of the adhesive fracture energy depends on surface preparation, curing conditions, and absorbed monolayers. A test method reported makes use of a disk whose peripheral part is bonded to a substrate material. Pressure is injected into the unbonded central part of the disk. At a certain critical pressure value adhesive failure can be observed. A numerical stress analysis involving arbitrary geometries is conducted.

  20. Toughness of carbon nanotubes conforms to classic fracture mechanics

    PubMed Central

    Yang, Lin; Greenfeld, Israel; Wagner, H. Daniel

    2016-01-01

    Defects in crystalline structure are commonly believed to degrade the ideal strength of carbon nanotubes. However, the fracture mechanisms induced by such defects, as well as the validity of solid mechanics theories at the nanoscale, are still under debate. We show that the fracture toughness of single-walled nanotubes (SWNTs) conforms to the classic theory of fracture mechanics, even for the smallest possible vacancy defect (~2 Å). By simulating tension of SWNTs containing common types of defects, we demonstrate how stress concentration at the defect boundary leads to brittle (unstable) fracturing at a relatively low strain, degrading the ideal strength of SWNTs by up to 60%. We find that, owing to the SWNT’s truss-like structure, defects at this scale are not sharp and stress concentrations are finite and low. Moreover, stress concentration, a geometric property at the macroscale, is interrelated with the SWNT fracture toughness, a material property. The resulting SWNT fracture toughness is 2.7 MPa m0.5, typical of moderately brittle materials and applicable also to graphene. PMID:26989774

  1. RSRM nozzle actuator bracket/lug fracture mechanics qualification test

    NASA Technical Reports Server (NTRS)

    Kelley, Peggy

    1993-01-01

    This is the final report for the actuator bracket/lug fracture mechanics qualification test. The test plan (CTP-0071) outlined a two-phase test program designed to answer questions about the fracture criticality of the redesigned solid rocket motor (RSRM) nozzle actuator bracket. An analysis conducted using the NASA/FLAGRO fracture mechanics computer program indicated that the actuator bracket might be a fracture critical component. In the NASA/FLAGRO analysis, a simple lug model was used to represent the actuator bracket. It was calculated that the bracket would fracture if subjected to an actuator stall load in the presence of a 0.10 in. corner crack at the actuator attachment hole. The 0.10 in. crack size corresponds to the nondestructive inspection detectability limit for the actuator bracket. The inspection method used is the dye penetrant method. The actuator stall load (103,424 lb) is the maximum load which the actuator bracket is required to withstand during motor operation. This testing was designed to establish the accuracy of the analytical model and to directly determine whether the actuator bracket is capable of meeting fracture mechanics safe-life requirements.

  2. Toughness of carbon nanotubes conforms to classic fracture mechanics.

    PubMed

    Yang, Lin; Greenfeld, Israel; Wagner, H Daniel

    2016-02-01

    Defects in crystalline structure are commonly believed to degrade the ideal strength of carbon nanotubes. However, the fracture mechanisms induced by such defects, as well as the validity of solid mechanics theories at the nanoscale, are still under debate. We show that the fracture toughness of single-walled nanotubes (SWNTs) conforms to the classic theory of fracture mechanics, even for the smallest possible vacancy defect (~2 Å). By simulating tension of SWNTs containing common types of defects, we demonstrate how stress concentration at the defect boundary leads to brittle (unstable) fracturing at a relatively low strain, degrading the ideal strength of SWNTs by up to 60%. We find that, owing to the SWNT's truss-like structure, defects at this scale are not sharp and stress concentrations are finite and low. Moreover, stress concentration, a geometric property at the macroscale, is interrelated with the SWNT fracture toughness, a material property. The resulting SWNT fracture toughness is 2.7 MPa m(0.5), typical of moderately brittle materials and applicable also to graphene.

  3. 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. PMID:25966285

  4. 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

  5. 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.

  6. Fracture mechanics analysis of vertical root fracture from condensation of gutta-percha.

    PubMed

    Chai, Herzl; Tamse, Aviad

    2012-06-01

    A two-dimensional fracture mechanics analysis of vertical root fracture (VRF) in single-canal roots from apical condensation of gutta-percha (gp) is developed. The resulting analytic relation for apical load causing VRF agrees with major trends reported in in-vitro tests on roots subjected to either continuous or, the more clinically relevant, repeating vertical condensation of gp. The model explicitly exposes the role of root canal morphology and dentin fracture toughness on VRF. Ovoid and irregular canals are prone to fracture while the effect of mean root canal radius is modest. Canal taper and instrumentation details may affect VRF only marginally and indirectly. The model predicts dentinal cracks to occur following root canal instrumentation and obturation, which may pose long-term threats to tooth integrity. PMID:22503579

  7. On Water Flow in Hot Fractured Rock -- A Sensitivity Study on theImpact of Fracture-Matrix Heat Transfer

    SciTech Connect

    Birkholzer, Jens T.; Zhang, Yingqi

    2005-06-01

    Dual-continuum models have been widely used in modeling flowand transport in fractured porous rocks. Among many other applications,dual-continuum approaches were utilized in predictive models of thethermal-hydrological conditions near emplacement tunnels (drifts) atYucca Mountain, Nevada, the proposed site for a radioactive wasterepository in the U.S. In unsaturated formations such as those at YuccaMountain, the magnitude of mass and heat exchange between the twocontinua fracture network and matrix is largely dependent on the flowcharacteristics in the fractures, because channelized finger-type flowstrongly reduces the interface area between the matrix surfaces and theflowing liquid. This effect may have important implications, for example,during the time period that the fractured rock near the repository driftswould be heated above the boiling point of water. Depending on themagnitude of heat transfer from the matrix, water percolating down thefractures will either boil off in the hot rock region above drifts or maypenetrate all the way to the drift walls and possibly seep into the opencavities. In this paper, we describe a sensitivity analysis using avariety of approaches to treat fracture-matrix interaction in athree-dimensional dual-continuum setting. Our simulation example is alaboratory heater experiment described in the literature that providesevidence of rapid water flow in fractures, leading to drift seepagedespite above-boiling conditions in the adjacent fractured rock. Theexperimental finding can only be reproduced when the interface area forheat transfer between the matrix and fracture continua is reduced toaccount for flow channeling.

  8. Fracture mechanics life analytical methods verification testing

    NASA Technical Reports Server (NTRS)

    Favenesi, J. A.; Clemons, T. G.; Riddell, W. T.; Ingraffea, A. R.; Wawrzynek, P. A.

    1994-01-01

    The objective was to evaluate NASCRAC (trademark) version 2.0, a second generation fracture analysis code, for verification and validity. NASCRAC was evaluated using a combination of comparisons to the literature, closed-form solutions, numerical analyses, and tests. Several limitations and minor errors were detected. Additionally, a number of major flaws were discovered. These major flaws were generally due to application of a specific method or theory, not due to programming logic. Results are presented for the following program capabilities: K versus a, J versus a, crack opening area, life calculation due to fatigue crack growth, tolerable crack size, proof test logic, tearing instability, creep crack growth, crack transitioning, crack retardation due to overloads, and elastic-plastic stress redistribution. It is concluded that the code is an acceptable fracture tool for K solutions of simplified geometries, for a limited number of J and crack opening area solutions, and for fatigue crack propagation with the Paris equation and constant amplitude loads when the Paris equation is applicable.

  9. [HAND FRACTURES IN CHILDREN - CAUSES AND MECHANISMS OF INJURY].

    PubMed

    Antabak, Anko; Barišić, Branimir; Andabak, Matej; Papeš, Dino; Romić, Ivan; Fuchs, Nino; Luetić, Tomislav

    2015-01-01

    Hand is extremely exposed to various loads and traumas of everyday tasks and activities, resulting in fist fractures being fairly common injuries. The most common mechanism of injury is a direct blow. This retrospective study analyzed the data on 274 children admitted for hand fractures at Clinical Hospital Center Zagreb in the period from 2006 to 2014. The study included 76 girls (28%) and 198 boys (72%). The average patient age was 11.9 years and most were between 10 and 13 years of age. Phalangeal fractures accounted for 80%, metacarpal fractures for 17%, and carpal fractures for 3% of all injuries. Most commonly injuries occurred during recreation (4 1%), at home (37%), at school (18%) and in the street (4%). Direct blow was the major cause of injury (76%), and 24% were caused by fall. Injuries during sport activities are the most common cause of the hand fractures in pediatric population and direct blow is the main mechanism of injury. The peak incidence is at the age of 10-13 years in boys and girls, so prevention should be aimed at this age group. Preventive actions should be focused on injuries that tend to occur in parks, schools and during sport activities. PMID:26749954

  10. Relating Cohesive Zone Model to Linear Elastic Fracture Mechanics

    NASA Technical Reports Server (NTRS)

    Wang, John T.

    2010-01-01

    The conditions required for a cohesive zone model (CZM) to predict a failure load of a cracked structure similar to that obtained by a linear elastic fracture mechanics (LEFM) analysis are investigated in this paper. This study clarifies why many different phenomenological cohesive laws can produce similar fracture predictions. Analytical results for five cohesive zone models are obtained, using five different cohesive laws that have the same cohesive work rate (CWR-area under the traction-separation curve) but different maximum tractions. The effect of the maximum traction on the predicted cohesive zone length and the remote applied load at fracture is presented. Similar to the small scale yielding condition for an LEFM analysis to be valid. the cohesive zone length also needs to be much smaller than the crack length. This is a necessary condition for a CZM to obtain a fracture prediction equivalent to an LEFM result.

  11. Fracture mechanics criteria for turbine engine hot section components

    NASA Technical Reports Server (NTRS)

    Meyers, G. J.

    1982-01-01

    The application of several fracture mechanics data correlation parameters to predicting the crack propagation life of turbine engine hot section components was evaluated. An engine survey was conducted to determine the locations where conventional fracture mechanics approaches may not be adequate to characterize cracking behavior. Both linear and nonlinear fracture mechanics analyses of a cracked annular combustor liner configuration were performed. Isothermal and variable temperature crack propagation tests were performed on Hastelloy X combustor liner material. The crack growth data was reduced using the stress intensity factor, the strain intensity factor, the J integral, crack opening displacement, and Tomkins' model. The parameter which showed the most effectiveness in correlation high temperature and variable temperature Hastelloy X crack growth data was crack opening displacement.

  12. Probabilistic fracture mechanics analysis of APT blanket tubes

    SciTech Connect

    Barsell, A. W.; Kern, K. T.

    2001-01-01

    A probabilistic fracture mechanics (PFM) model that is specific to the Accelerator Production of Tritium (APT) helium tubes was developed. The model performs Monte Carlo analyses of potential failure modes caused by cyclic stresses generated by beam trips and depressurizations 60m normal operation, coupled with material aging due to irradiation. Dominant failure probabilities are due to crack through-growth while brittle fracture and ductile tearing have lower probability. Failure mechanisms of global plastic collapse and buckling or crack initiation mechanisms of fatigue or local fracture (upon loss of ductility) have negligible probability. For the population of (7,311) tubes in the APT blanket, the worst-case, annual probability of one tube failing is 3 percent. The probability of 2 or more failures is substantially lower; therefore, unavailability impacts are driven by single failure. The average annual loss of production (unavailability) is below about 0.2 percent. Helium outflow and water inflow rates were characterized for the failures.

  13. Facilitated spinal neuropeptide signaling and upregulated inflammatory mediator expression contribute to post-fracture nociceptive sensitization

    PubMed Central

    Shi, Xiaoyou; Guo, Tian-zhi; Wei, Tzuping; Li, Wen-wu; Clark, David J; Kingery, Wade S

    2015-01-01

    Tibia fracture induces exaggerated substance P (SP) and CGRP signaling and neuropeptide-dependent nociceptive and inflammatory changes in the hindlimbs of rats similar to those seen in complex regional pain syndrome (CRPS). Inflammatory changes in the spinal cord contribute to nociceptive sensitization in a variety of animal pain models. This study tested the hypothesis that fracture induced exaggerated neuropeptide signaling up-regulates spinal inflammatory mediator expression, leading to post-fracture hindlimb nociceptive sensitization. At 4 weeks after performing tibia fracture and casting in rats, we measured hindlimb allodynia, unweighting, warmth, edema, and spinal cord neuropeptide and inflammatory mediator content. The antinociceptive effects of intrathecally injected neuropeptide and inflammatory mediator receptor antagonists were evaluated in fracture rats. Transgenic fracture mice lacking SP or the CGRP RAMP1 receptor were used to determine the effects of neuropeptide signaling on post-fracture pain behavior and spinal inflammatory mediator expression. Hindlimb allodynia, unweighting, warmth, edema, increased spinal SP and CGRP, and increased spinal inflammatory mediator expression (TNF, IL-1, IL-6, CCL2, NGF) were observed at 4 weeks after fracture in rats. Fracture induced increases in spinal inflammatory mediators were not observed in fracture mice lacking SP or the CGRP receptor and these mice had attenuated post-fracture nociceptive sensitization. Intrathecal injection of selective receptor antagonists for SP, CGRP, TNF, IL-1, IL-6, CCL2, or NGF each reduced pain behaviors in the fracture rats. Collectively, these data support the hypothesis that facilitated spinal neuropeptide signaling up-regulates the expression of spinal inflammatory mediators contributing to nociceptive sensitization in a rodent fracture model of CRPS. PMID:25932690

  14. Mechanical transport in two-dimensional networks of fractures

    SciTech Connect

    Endo, H.K.

    1984-04-01

    The objectives of this research are to evaluate directional mechanical transport parameters for anisotropic fracture systems, and to determine if fracture systems behave like equivalent porous media. The tracer experiments used to measure directional tortuosity, longitudinal geometric dispersivity, and hydraulic effective porosity are conducted with a uniform flow field and measurements are made from the fluid flowing within a test section where linear length of travel is constant. Since fluid flow and mechanical transport are coupled processes, the directional variations of specific discharge and hydraulic effective porosity are measured in regions with constant hydraulic gradients to evaluate porous medium equivalence for the two processes, respectively. If the fracture region behaves like an equivalent porous medium, the system has the following stable properties: (1) specific discharge is uniform in any direction and can be predicted from a permeability tensor; and (2) hydraulic effective porosity is directionally stable. Fracture systems with two parallel sets of continuous fractures satisfy criterion 1. However, in these systems hydraulic effective porosity is directionally dependent, and thus, criterion 2 is violated. Thus, for some fracture systems, fluid flow can be predicted using porous media assumptions, but it may not be possible to predict transport using porous media assumptions. Two discontinuous fracture systems were studied which satisfied both criteria. Hydraulic effective porosity for both systems has a value between rock effective porosity and total porosity. A length-density analysis (LDS) of Canadian fracture data shows that porous media equivalence for fluid flow and transport is likely when systems have narrow aperture distributions. 54 references, 90 figures, 7 tables.

  15. Identification of Fracture Toughness for Discrete Damage Mechanics Analysis of Glass-Epoxy Laminates

    NASA Astrophysics Data System (ADS)

    Barbero, E. J.; Cosso, F. A.; Martinez, X.

    2014-08-01

    A methodology for determination of the intralaminar fracture toughness is presented, based on fitting discrete damage mechanics (DDM) model predictions to available experimental data. DDM is constitutive model that, when incorporated into commercial finite element software via user material subroutines, is able to predict intralaminar transverse and shear damage initiation and evolution in terms of the fracture toughness of the composite. The applicability of the DDM model is studied by comparison to available experimental data for Glass-Epoxy laminates. Sensitivity of the DDM model to h- and p-refinement is studied. Also, the effect of in-situ correction of strength is highlighted.

  16. Fracture mechanics evaluation for at typical PWR primary coolant pipe

    SciTech Connect

    Tanaka, T.; Shimizu, S.; Ogata, Y.

    1997-04-01

    For the primary coolant piping of PWRs in Japan, cast duplex stainless steel which is excellent in terms of strength, corrosion resistance, and weldability has conventionally been used. The cast duplex stainless steel contains the ferrite phase in the austenite matrix and thermal aging after long term service is known to change its material characteristics. It is considered appropriate to apply the methodology of elastic plastic fracture mechanics for an evaluation of the integrity of the primary coolant piping after thermal aging. Therefore we evaluated the integrity of the primary coolant piping for an initial PWR plant in Japan by means of elastic plastic fracture mechanics. The evaluation results show that the crack will not grow into an unstable fracture and the integrity of the piping will be secured, even when such through wall crack length is assumed to equal the fatigue crack growth length for a service period of up to 60 years.

  17. Measurements of residual stress in fracture mechanics coupons

    SciTech Connect

    Prime, Michael B; Hill, Michael R; Nav Dalen, John E

    2010-01-01

    This paper describes measurements of residual stress in coupons used for fracture mechanics testing. The primary objective of the measurements is to quantify the distribution of residual stress acting to open (and/or close) the crack across the crack plane. The slitting method and the contour method are two destructive residual stress measurement methods particularly capable of addressing that objective, and these were applied to measure residual stress in a set of identically prepared compact tension (C(T)) coupons. Comparison of the results of the two measurement methods provides some useful observations. Results from fracture mechanics tests of residual stress bearing coupons and fracture analysis, based on linear superposition of applied and residual stresses, show consistent behavior of coupons having various levels of residual stress.

  18. Investigation of the fracture mechanics of boride composites

    NASA Technical Reports Server (NTRS)

    Clougherty, E. V.; Pober, R. L.; Kaufman, L.

    1972-01-01

    Significant results were obtained in fabrication studies of the role of metallic additives of Zr, Ti, Ni, Fe and Cr on the densification of ZrB2. All elemental additions lower the processing temperatures required to effect full densification of ZrB2. Each addition effects enhanced densification by a clearly distinguishable and different mechanism and the resulting fabricated materials are different. A significant improvement in strength and fracture toughness was obtained for the ZrB2/Ti composition. Mechanical characterization studies for the ZrB2/SiC/C composites and the new ZrB2/Metal materials produced data relevant to the effect of impacting load on measured impact energies, a specimen configuration for which controlled fracture could occur in a suitably hard testing apparatus, and fracture strength data. Controlled fracture--indicative of measurable fracture toughness--was obtained for the ZrB2-SiC-C composite, and a ZrB2/Ti composite fabricated from ZrB2 with an addition of 30 weight per cent Ti. The increased strength and toughness of the ZrB2/Ti composite is consistent with the presence of a significantly large amount of a fine grained acicular phase formed by reaction of Ti with ZrB2 during processing.

  19. Probabilistic fracture mechanics and optimum fracture control of the solid rocket motor case of the shuttle

    NASA Technical Reports Server (NTRS)

    Hanagud, S.; Uppaluri, B.

    1977-01-01

    Development of a procedure for the reliability analysis of the solid rocket motor case of the space shuttle is described. The analysis is based on probabilistic fracture mechanics and consideration of a probability distribution for the initial flaw sizes. The reliability analysis can be used to select design variables, such as the thickness of the SRM case, projected design life and proof factor, on the basis of minimum expected cost and specified reliability bounds. Effects of fracture control plans such as the non-destructive inspections and the material erosion between missions can also be considered in the developed methodology for selection of design variables. The reliability-based procedure can be easily modified to consider other similar structures and different fracture control plans.

  20. Fracture mechanics applied to the machining of brittle materials

    SciTech Connect

    Hiatt, G.D.; Strenkowski, J.S.

    1988-12-01

    Research has begun on incorporating fracture mechanics into a model of the orthogonal cutting of brittle materials. Residual stresses are calculated for the machined material by a combination of Eulerian and Lagrangian finite element models and then used in the calculation of stress intensity factors by the Green`s Function Method.

  1. Hydraulic fracture extending into network in shale: reviewing influence factors and their mechanism.

    PubMed

    Ren, Lan; Zhao, Jinzhou; Hu, Yongquan

    2014-01-01

    Hydraulic fracture in shale reservoir presents complex network propagation, which has essential difference with traditional plane biwing fracture at forming mechanism. Based on the research results of experiments, field fracturing practice, theory analysis, and numerical simulation, the influence factors and their mechanism of hydraulic fracture extending into network in shale have been systematically analyzed and discussed. Research results show that the fracture propagation in shale reservoir is influenced by the geological and the engineering factors, which includes rock mineral composition, rock mechanical properties, horizontal stress field, natural fractures, treating net pressure, fracturing fluid viscosity, and fracturing scale. This study has important theoretical value and practical significance to understand fracture network propagation mechanism in shale reservoir and contributes to improving the science and efficiency of shale reservoir fracturing design. PMID:25032240

  2. Hydraulic Fracture Extending into Network in Shale: Reviewing Influence Factors and Their Mechanism

    PubMed Central

    Ren, Lan; Zhao, Jinzhou; Hu, Yongquan

    2014-01-01

    Hydraulic fracture in shale reservoir presents complex network propagation, which has essential difference with traditional plane biwing fracture at forming mechanism. Based on the research results of experiments, field fracturing practice, theory analysis, and numerical simulation, the influence factors and their mechanism of hydraulic fracture extending into network in shale have been systematically analyzed and discussed. Research results show that the fracture propagation in shale reservoir is influenced by the geological and the engineering factors, which includes rock mineral composition, rock mechanical properties, horizontal stress field, natural fractures, treating net pressure, fracturing fluid viscosity, and fracturing scale. This study has important theoretical value and practical significance to understand fracture network propagation mechanism in shale reservoir and contributes to improving the science and efficiency of shale reservoir fracturing design. PMID:25032240

  3. Sensitivity and type curves of cross-borehole flowmeter tests: application to heterogeneous fractured media.

    NASA Astrophysics Data System (ADS)

    Ruelleu, S.; Bour, O.; Le Borgne, T.

    2008-12-01

    Crystalline rocks aquifers are very difficult to characterize since flow is mainly localized in few fractures or faults. In most cases, the large-scale hydraulic properties of such media strongly depend on the connectivity of few permeable fractures. To image and quantify the properties of such features, borehole flowmetry can be a very useful and efficient method that is also suitable when boreholes are screened. The methodology is based on the measurements of vertical flow both for single and cross-borehole configurations. In this study, we investigate through a numerical model the sensitivity of cross-borehole flowmeter tests to the geometry and properties of main permeable pathways. To model transient flow in heterogeneous media, we used a finite element method code where we reproduce few fractures and two boreholes. In each fracture, the diffusivity equation is solved. We considered different geometrical cases : a single fracture connecting two boreholes, two parallel fractures, and two intersecting fractures with a variable angle between the fractures. In the pumping well and in the observation borehole, we implemented borehole storage. For each geometry, we varied the hydraulic parameters and established cross-borehole flowmeters type curve as the typical variation of flow measured in an observation well in response to a pumping in an adjacent well. In most cases, our results appear very sensitive to the modelling of wellbore storage that affects the data especially in the early times, and for low fracture storativity. Nevertheless we do observe different shapes of type-curves depending on the geometrical connexion between fractures and boreholes. We also defined a new methodology more appropriate to identify the fracture connexions. However, our results show also that in some cases, one cannot distinguish the different type curves. Thus, uniqueness of the flow response is questioned. These results are compared with field examples obtained on the Ploemeur

  4. Fracture mechanics analysis of composite microcracking - Experimental results in fatigue

    NASA Technical Reports Server (NTRS)

    Nairn, J. A.; Liu, S.

    1990-01-01

    The Nairn (1989) variational mechanics analysis, which yields the energy release rate of a microcrack's formation between two existing microcracks, has proven useful in the fracture mechanics interpretation of cross-ply laminates' microcracking. Attention is presently given to the application of this energy release rate analysis to a fracture mechanics-based interpretation of microcrack formation during fatigue loading, for the case of fatigue experiments on three layups of Avimid K/IM6 laminates and four layups of Fiberite 934/T300 laminates. The single master Paris-law plot onto which the data from all layups of a given material system fall is claimed to offer a complete characterization of that system's microcrack-formation resistance during fatigue loading.

  5. Thermodynamic and fracture mechanical processes in the context of frost wedging in ice shelves

    NASA Astrophysics Data System (ADS)

    Plate, Carolin; Müller, Ralf; Humbert, Angelika; Gross, Dietmar

    2015-04-01

    Ice shelves, the link between ice shields or glaciers and the ocean are sensitive elements of the polar environment. The ongoing break up and disintegration of huge ice shelf parts or entire ice shelf demands for an explication of the underlying processes. The first analyses of crack growth and break up events in ice shelves date back to more than half a century. Nevertheless, the mechanisms that trigger and influence the collapse of whole ice shelf parts are not yet fully understood. Popular presumptions link ice shelf disintegration to surface meltwater and hydro fracturing, explaining break up events in warm polar seasons. Fracture events during colder seasons are possibly triggered by more complex mechanisms. A well-documented break up event at the Wilkins Ice Shelf bridge inspires the possibility of frost wedging as disintegration cause. The present study shows a two-dimensional thermo-dynamical model simulating the growth of an ice lid in a water-filled crevasse for measured surface temperatures. The influence of the crevasse geometry and the ice shelf temperature are shown. The resulting lid thickness is then used for the linear elastic fracture mechanical analysis. The maximum crack depth is estimated by comparing the computed stress intensity factors to critical values KIc obtained from literature. The thermodynamic as well as the fracture mechanical simulation are performed using the commercial finite element code COMSOL. The computation of KI follows in post processing routines in MATLAB exploiting the benefits of the concept of configurational forces.

  6. Critical review of the state-of-the-art of fracture mechanics with emphasis on layered rocks

    SciTech Connect

    Kuruppu, M.D.; Cheng, K.P.; Edl, J.N. Jr.

    1983-07-01

    Results are presented of a literature survey of over 70 pertinent publications and critical reviews of fracture mechanics emphasizing the fracture behavior of layered rocks. Historical perspective, fracture mechanisms, linear and nonlinear fracture mechanics, energy theories, ductile and brittle fractures, process regions, specific work of fracture, J-integrals, failure theories, static and dynamic fractures, rock fracture mechanics, fracture toughness of layered rocks (e.g., oil shale), experimental and numerical methods are reviewed and discussed. Innovative and promising methods tailored for the fracture mechanics of layered rocks are recommended.

  7. Elastic plastic fracture mechanics methodology for surface cracks

    NASA Technical Reports Server (NTRS)

    Ernst, Hugo A.; Lambert, D. M.

    1994-01-01

    The Elastic Plastic Fracture Mechanics Methodology has evolved significantly in the last several years. Nevertheless, some of these concepts need to be extended further before the whole methodology can be safely applied to structural parts. Specifically, there is a need to include the effect of constraint in the characterization of material resistance to crack growth and also to extend these methods to the case of 3D defects. As a consequence, this project was started as a 36 month research program with the general objective of developing an elastic plastic fracture mechanics methodology to assess the structural reliability of pressure vessels and other parts of interest to NASA which may contain flaws. The project is divided into three tasks that deal with (1) constraint and thickness effects, (2) three-dimensional cracks, and (3) the Leak-Before-Burst (LBB) criterion. This report period (March 1994 to August 1994) is a continuation of attempts to characterize three dimensional aspects of fracture present in 'two dimensional' or planar configuration specimens (Chapter Two), especially, the determination of, and use of, crack face separation data. Also, included, are a variety of fracture resistance testing results (J(m)R-curve format) and a discussion regarding two materials of NASA interest (6061-T651 Aluminum alloy and 1N718-STA1 nickel-base super alloy) involving a bases for like constraint in terms of ligament dimensions, and their comparison to the resulting J(m)R-curves (Chapter Two).

  8. Deformation and fracture of Macadamia nuts Part 2: Microstructure and fracture mechanics analysis of nutshell

    NASA Astrophysics Data System (ADS)

    Wang, Chun-Hui; Mai, Yiu-Wing

    A study of the microstructure and mechanical properties of Macadamia nutshells subjected to various heat treatments is given in Part 2 of this paper. It is found that the nutshell has a three-dimensional, close-packed, cell structure. The cells have a diameter to length ratio of about 1 to 3, and the orientation of the cells is reasonably isotropic with no apparent variation with either position or direction. The material behaves in a very brittle manner under tension and compression. Based on the elastic stress analysis of a nut under diametrical compression and the mechanical properties of the shell, it is shown that cracks that cause the final fracture are initiated from the inner surface beneath the loading point. A theoretical model is proposed and predictions of the fracture load for Macadamia nuts are in good agreement with experimental results.

  9. Fracture control methods for space vehicles. Volume 2: Assessment of fracture mechanics technology for space shuttle applications

    NASA Technical Reports Server (NTRS)

    Ehret, R. M.

    1974-01-01

    The concepts explored in a state of the art review of those engineering fracture mechanics considered most applicable to the space shuttle vehicle include fracture toughness, precritical flaw growth, failure mechanisms, inspection methods (including proof test logic), and crack growth predictive analysis techniques.

  10. Mechanical Stability and Reversible Fracture of Vault Particles

    PubMed Central

    Llauró, Aida; Guerra, Pablo; Irigoyen, Nerea; Rodríguez, José F.; Verdaguer, Núria; de Pablo, Pedro J.

    2014-01-01

    Vaults are the largest ribonucleoprotein particles found in eukaryotic cells, with an unclear cellular function and promising applications as vehicles for drug delivery. In this article, we examine the local stiffness of individual vaults and probe their structural stability with atomic force microscopy under physiological conditions. Our data show that the barrel, the central part of the vault, governs both the stiffness and mechanical strength of these particles. In addition, we induce single-protein fractures in the barrel shell and monitor their temporal evolution. Our high-resolution atomic force microscopy topographies show that these fractures occur along the contacts between two major vault proteins and disappear over time. This unprecedented systematic self-healing mechanism, which enables these particles to reversibly adapt to certain geometric constraints, might help vaults safely pass through the nuclear pore complex and potentiate their role as self-reparable nanocontainers. PMID:24507609

  11. Discrete fracture patterns of virus shells reveal mechanical building blocks.

    PubMed

    Ivanovska, Irena L; Miranda, Roberto; Carrascosa, Jose L; Wuite, Gijs J L; Schmidt, Christoph F

    2011-08-01

    Viral shells are self-assembled protein nanocontainers with remarkable material properties. They combine simplicity of construction with toughness and complex functionality. These properties make them interesting for bionanotechnology. To date we know little about how virus structure determines assembly pathways and shell mechanics. We have here used atomic force microscopy to study structural failure of the shells of the bacteriophage Φ29. We observed rigidity patterns following the symmetry of the capsid proteins. Under prolonged force exertion, we observed fracture along well-defined lines of the 2D crystal lattice. The mechanically most stable building block of the shells was a trimer. Our approach of "reverse engineering" the virus shells thus made it possible to identify stable structural intermediates. Such stable intermediates point to a hierarchy of interactions among equal building blocks correlated with distinct next-neighbor interactions. The results also demonstrate that concepts from macroscopic materials science, such as fracture, can be usefully employed in molecular engineering. PMID:21768340

  12. Microstructure-Sensitive Investigation of Fracture Using Acoustic Emission Coupled With Electron Microscopy

    NASA Technical Reports Server (NTRS)

    Wisner, Brian; Cabal, Mike; Vanniamparambiland, Prashanth A.; Leser, William; Hochhalter, Jacob; Kontsos, Antonios

    2015-01-01

    A novel technique using Scanning Electron Microscopy (SEM) in conjunction with Acoustic Emission (AE) monitoring is proposed to investigate microstructure-sensitive fatigue and fracture of metals. The coupling between quasi in situ microscopy with actual in situ nondestructive evaluation falls into the ICME framework and the idea of quantitative data-driven characterization of material behavior. To validate the use of AE monitoring inside the SEM chamber, Aluminum 2024-B sharp notch specimen were tested both inside and outside the microscope using a small scale mechanical testing device. Subsequently, the same type of specimen was tested inside the SEM chamber. Load data were correlated with both AE information and observations of microcracks around grain boundaries as well as secondary cracks, voids, and slip bands. The preliminary results are in excellent agreement with similar findings at the mesoscale. Extensions of the application of this novel technique are discussed.

  13. Mechanisms of Salt-Sensitive Hypertension.

    PubMed

    Luzardo, Leonella; Noboa, Oscar; Boggia, José

    2015-01-01

    Hypertension and its consequences, including heart failure, stroke, and kidney disease, are responsible for substantial morbidity and mortality worldwide. Lifestyle changes, particularly sodium reduction, contribute to blood pressure control. However, not all individuals, whether normotensive or hypertensive, have the same susceptibility to the effects of salt. While a variety of approaches have been proposed to identify salt sensitive patients, there is no consensus for a definition of salt sensitivity and the precise mechanisms that explain their association are not yet fully understood. In this review we summarize the current understanding of the various pathophysiological mechanisms potentially involved in determining the salt sensitive phenotype. Genetic, neuronal, and immune alterations are reviewed. Additionally, we provide an update on the current knowledge of a new approach proposing the interstitium of the skin may act as a sodium reservoir. The role of dietary potassium on salt sensitive hypertension is also summarized.

  14. Results of fracture mechanics tests on PNC SUS 304 plate

    SciTech Connect

    Mills, W.J.; James, L.A.; Blackburn, L.D.

    1985-08-01

    PNC provided SUS 304 plate to be irradiated in FFTF at about 400/sup 0/C to a target fluence of 5 x 10/sup 21/ n/cm/sup 2/ (E > 0.1 MeV). The actual irradiation included two basically different exposure levels to assure that information would be available for the exposure of interest. After irradiation, tensile properties, fatigue-crack growth rates and J-integral fracture toughness response were determined. These same properties were also measured for the unirradiated material so radiation damage effects could be characterized. This report presents the results of this program. It is expected that these results would be applicable for detailed fracture analysis of reactor components. Recent advances in elastic-plastic fracture mechanics enable reasonably accurate predictions of failure conditions for flawed stainless steel components. Extensive research has focused on the development of J-integral-based engineering approach for assessing the load carrying capacity of low-strength, high-toughness structural materials. Furthermore, Kanninen, et al., have demonstrated that J-integral concepts can accurately predict the fracture response for full-scale cracked structures manufactured from Type 304 stainless steel.

  15. Probing the Molecular Mechanisms of the Fracture of Semicrystalline Polyethylene

    NASA Astrophysics Data System (ADS)

    Benkoski, J. J.; Flores, P.; Kramer, E. J.

    2003-03-01

    The effects of molecular architecture on the fracture properties of semicrystalline polymers were probed at diblock copolymer-reinforced interfaces between polystyrene (PS) and polyethylene (PE). The PE used for this study was a model ethylene-butene copolymer which was chosen for its compatibility with hydrogenated poly(styrene-b-1,4-tetradeuteriobutadiene). For a series of these diblock copolymers, the areal chain density (Σ) and the molecular weight of the PE block (M_n) were varied systematically to observe their effects on the interfacial fracture energy (G_c). At low Σ, Gc stayed relatively constant, and was roughly 1 J/m^2. Above a critical value of Σ, the fracture energy climbed rapidly. This critical value decreased with increasing M_n. The detection of deuterium on the fracture surfaces indicated that pullout of the PE block was the predominant failure mechanism when Mn <= 30 kg/mol. Since the entanglement molecular weight of PE is approximately 1 kg/mol, interfacial reinforcement does not appear to depend on the formation of entanglements for this system. The critical Mn coincides instead with the point at which the root-mean-square end-to-end length of the PE block exceeds the long period of the PE crystal lamellae (L).

  16. Fracture and Stress Evolution on Europa: New Insights Into Fracture Interpretation and Ice Thickness Estimates Using Fracture Mechanics Analyses

    NASA Technical Reports Server (NTRS)

    Kattenhorn, Simon

    2004-01-01

    The work completed during the funding period has provided many important insights into fracturing behavior in Europa's ice shell. It has been determined that fracturing through time is likely to have been controlled by the effects of nonsynchronous rotation stresses and that as much as 720 deg of said rotation may have occurred during the visible geologic history. It has been determined that there are at least two distinct styles of strike-slip faulting and that their mutual evolutionary styles are likely to have been different, with one involving a significant dilational component during shear motion. It has been determined that secondary fracturing in perturbed stress fields adjacent to older structures such as faults is a prevalent process on Europa. It has been determined that cycloidal ridges are likely to experience shear stresses along the existing segment portions as they propagate, which affects propagation direction and ultimately induces tailcracking at the segment tip than then initiates a new cycle of cycloid segment growth. Finally, it has been established that mechanical methods (e.g., flexure analysis) can be used to determine the elastic thickness of the ice shell, which, although probably only several km thick, is likely to be spatially variable, being thinner under bands but thicker under ridged plains terrain.

  17. State-of-the-art report on piping fracture mechanics

    SciTech Connect

    Wilkowski, G.M.; Olson, R.J.; Scott, P.M.

    1998-01-01

    This report is an in-depth summary of the state-of-the-art in nuclear piping fracture mechanics. It represents the culmination of 20 years of work done primarily in the US, but also attempts to include important aspects from other international efforts. Although the focus of this work was for the nuclear industry, the technology is also applicable in many cases to fossil plants, petrochemical/refinery plants, and the oil and gas industry. In compiling this detailed summary report, all of the equations and details of the analysis procedure or experimental results are not necessarily included. Rather, the report describes the important aspects and limitations, tells the reader where he can go for further information, and more importantly, describes the accuracy of the models. Nevertheless, the report still contains over 150 equations and over 400 references. The main sections of this report describe: (1) the evolution of piping fracture mechanics history relative to the developments of the nuclear industry, (2) technical developments in stress analyses, material property aspects, and fracture mechanics analyses, (3) unresolved issues and technically evolving areas, and (4) a summary of conclusions of major developments to date.

  18. Calcium Sensitization Mechanisms in Gastrointestinal Smooth Muscles

    PubMed Central

    Perrino, Brian A

    2016-01-01

    An increase in intracellular Ca2+ is the primary trigger of contraction of gastrointestinal (GI) smooth muscles. However, increasing the Ca2+ sensitivity of the myofilaments by elevating myosin light chain phosphorylation also plays an essential role. Inhibiting myosin light chain phosphatase activity with protein kinase C-potentiated phosphatase inhibitor protein-17 kDa (CPI-17) and myosin phosphatase targeting subunit 1 (MYPT1) phosphorylation is considered to be the primary mechanism underlying myofilament Ca2+ sensitization. The relative importance of Ca2+ sensitization mechanisms to the diverse patterns of GI motility is likely related to the varied functional roles of GI smooth muscles. Increases in CPI-17 and MYPT1 phosphorylation in response to agonist stimulation regulate myosin light chain phosphatase activity in phasic, tonic, and sphincteric GI smooth muscles. Recent evidence suggests that MYPT1 phosphorylation may also contribute to force generation by reorganization of the actin cytoskeleton. The mechanisms responsible for maintaining constitutive CPI-17 and MYPT1 phosphorylation in GI smooth muscles are still largely unknown. The characteristics of the cell-types comprising the neuroeffector junction lead to fundamental differences between the effects of exogenous agonists and endogenous neurotransmitters on Ca2+ sensitization mechanisms. The contribution of various cell-types within the tunica muscularis to the motor responses of GI organs to neurotransmission must be considered when determining the mechanisms by which Ca2+ sensitization pathways are activated. The signaling pathways regulating Ca2+ sensitization may provide novel therapeutic strategies for controlling GI motility. This article will provide an overview of the current understanding of the biochemical basis for the regulation of Ca2+ sensitization, while also discussing the functional importance to different smooth muscles of the GI tract. PMID:26701920

  19. The fracture properties and mechanical design of human fingernails.

    PubMed

    Farren, L; Shayler, S; Ennos, A R

    2004-02-01

    Fingernails are a characteristic feature of primates, and are composed of three layers of the fibrous composite keratin. This study examined the structure and fracture properties of human fingernails to determine how they resist bending forces while preventing fractures running longitudinally into the nail bed. Nail clippings were first torn manually to examine the preferred crack direction. Next, scissor cutting tests were carried out to compare the fracture toughness of central and outer areas in both the transverse and longitudinal direction. The fracture toughness of each of the three isolated layers was also measured in this way to determine their relative contributions to the toughness. Finally, the structure was examined by carrying out scanning electron microscopy of free fracture surfaces and polarized light microscopy of nail sections. When nails were torn, cracks were always diverted transversely, parallel to the free edge of the nail. Cutting tests showed that this occurred because the energy to cut nails transversely, at approximately 3 kJ m(-2), was about half that needed (approx. 6 kJ m(-2)) to cut them longitudinally. This anisotropy was imparted by the thick intermediate layer, which comprises long, narrow cells that are oriented transversely; the energy needed to cut this layer transversely was only a quarter of that needed to cut it longitudinally. In contrast the tile-like cells in the thinner dorsal and ventral layers showed isotropic behaviour. They probably act to increase the nail's bending strength, and as they wrap around the edge of the nail, they also help prevent cracks from forming. These results cast light on the mechanical behaviour and care of fingernails.

  20. [Current concepts of the mechanisms of formation of gunshot fractures].

    PubMed

    Pigolkin, Iu I; Dubrovin, I A; Leonov, S V; Mikhaĭlenko, A V; Dubrovin, A I; Zotkin, D A

    2013-01-01

    The mechanisms of formation of gunshot fractures in flat bones inflicted by a semispherical bullet were investigated using expert and experimental materials. The process of crack formation was considered in terms of the Hertzian contact problem and the Hill-Johnson model. It was shown that the fracture develops as a result of combination of stresses and strains in the bone tissue leading to the formation of a hydrostatic nucleus prior to tissue fragmentation. Dynamic fluctuations (waves) generated in the zone of hydrostatic compression resulting from the gunshot injury propagate with the velocity of sound from the nucleus in the direction of the bullet movement. According to the Hill-Johnson model, the waves propagate in the direction of the impact within a parabolically expanding space; this accounts for the mechanism of formation of parabolic cracks and the specific shape of the defect that the bullet produces in the flat bones. The dynamic load applied by means of an indentor forms at a higher rate than the velocity of sound in the affected material. It gives reason to consider the effect of a bullet moving with the speed of 250 m/s as quasi-static loading. The results obtained in this study make a contribution to the theory of impact effect of a bullet and provide a deeper insight into the physical nature of the direct and sideway action of a gunshot projectile. Moreover, they explain the cause behind the widening of the outlet part of the perforating fracture in the flat bones.

  1. [Bone fracture and the healing mechanisms. Fragility fracture and bone quality].

    PubMed

    Mawatari, Taro; Iwamoto, Yukihide

    2009-05-01

    Fracture occurs in bone having less than normal elastic resistance without any violence. Numerous terms have been used to classify various types of fractures from low trauma events; "fragility fracture", "stress fracture", "insufficiency fracture", "fatigue fracture", "pathologic fracture", etc. The definitions of these terms and clinical characteristics of these fractures are discussed. Also state-of-the-art bone quality assessments; Finite element analysis of clinical CT scans, assessments of the Microdamage, and the Cross-links of Collagen are introduced in this review.

  2. Mechanical sensitivity reveals evolutionary dynamics of mechanical systems.

    PubMed

    Anderson, P S L; Patek, S N

    2015-04-01

    A classic question in evolutionary biology is how form-function relationships promote or limit diversification. Mechanical metrics, such as kinematic transmission (KT) in linkage systems, are useful tools for examining the evolution of form and function in a comparative context. The convergence of disparate systems on equivalent metric values (mechanical equivalence) has been highlighted as a source of potential morphological diversity under the assumption that morphology can evolve with minimal impact on function. However, this assumption does not account for mechanical sensitivity-the sensitivity of the metric to morphological changes in individual components of a structure. We examined the diversification of a four-bar linkage system in mantis shrimp (Stomatopoda), and found evidence for both mechanical equivalence and differential mechanical sensitivity. KT exhibited variable correlations with individual linkage components, highlighting the components that influence KT evolution, and the components that are free to evolve independently from KT and thereby contribute to the observed pattern of mechanical equivalence. Determining the mechanical sensitivity in a system leads to a deeper understanding of both functional convergence and morphological diversification. This study illustrates the importance of multi-level analyses in delineating the factors that limit and promote diversification in form-function systems. PMID:25716791

  3. Effects of hydrogen on mechanical properties and fracture mechanism of 8090 Al-Li alloy

    NASA Astrophysics Data System (ADS)

    Chen, Lian; Chen, Wenxiu; Liu, Zhonghao; Shao, Yuxia; Hu, Zhuangqi

    1993-06-01

    The effects of hydrogen and strain rate on the mechanical properties and fracture mechanism of 8090 Al-Li alloy under electrochemical charging conditions have been studied. Experimental results demonstrate that the tensile strength [ultimate tensile strength (UTS) and yield strength (YS)] and plasticity [reduction of area (RA) and elongation (EL)] drop linearly with the decrease of strain rate. The charged hydrogen increases the tensile strength but markedly impair the plasticity. The susceptibility of hydrogen embrittlement increases with the decreases of strain rate, and the susceptibility of the charged specimens was larger than that of the uncharged ones over the strain-rate range. Observation by scanning electron microscope (SEM) reveals that the charged hydrogen enhances intergranular delamination cracking on the fracture surface. The fracture model of charged specimens at low strain rates(dot \\varepsilon {text{< 3}}{text{.4 X 10}}^{{text{ - 4}}} /s) is grain boundary brittle fracture (GBBF), while that of other conditions is grain boundary ductile fracture (GBDF). Secondary ion mass spectroscopy (SIMS) study shows that the atomic binding energy of Al and Li in the alloy decreased after hydrogen charging, and the atomic binding energy drop of the former is more than the latter. In this article, the hydrogen transport through the mobile dislocation mechanism of hydrogen-induced fracture and the hydrogen effect on atomic binding energy were also discussed in detail.

  4. Brittle Fracture Resistance of Chinga Ataxite at Different Mechanical Loading Conditions

    NASA Astrophysics Data System (ADS)

    Grokhovsky, V. I.; Gladkovsky, S. V.

    2016-08-01

    In this study comparative results of Chinga meteorite material fracture resistance evaluation at different test temperatures and loading conditions using fracture mechanics approach as well as fractographic data analysis are presented.

  5. Mechanics and fracture of hybrid material interface bond

    NASA Astrophysics Data System (ADS)

    Wang, Jialai

    Considering current and future applications of hybrid materials and structures in civil engineering, the strength and durability of interface bond between the conventional materials and composites are critical to development of such products. Conventional methods mostly used for analysis of isotropic materials may not be well suitable or accurate enough for a system made of anisotropic materials with relatively low shear stiffness. A need exists for developing more accurate and explicit analytical solutions for hybrid material interface analysis and related novel experimental characterization techniques. In this study, a combined analytical and experimental approach to characterize hybrid material interface bond is developed. Using a shear deformable plate theory and an elastic interface model, a mechanics approach for interface analysis of hybrid material bond under general loading is first proposed. The resulting closed-form solution of interface stress distribution is used to compute strain energy release rate (SERB) and stress intensity factor (SIF) of the interface with or without adhesive bond. This approach is then extended to delamination of composite structures under generic loading conditions. Second, novel experimental approaches for characterization of hybrid material bonded interfaces are presented. To account for the crack tip deformations, a tapered beam on elastic foundation (TBEF) is developed. Based on the TBEF model, analysis and design of two novel fracture specimens, Tapered Double Cantilever Beam (TDCB) and Tapered End Notched Flexure (TENF), are proposed, and they are effectively used in fracture toughness tests of bonded interface under Mode-I and Mode-II loadings, respectively. A constant compliance rate change over certain crack length range is achieved for the TDCB and TENF specimens, and it alleviates the necessity of experimental compliance calibration tests. The fracture toughness data obtained from the experiments are useful to

  6. Probabilistic Fracture Mechanics Evaluation of Selected Passive Components – Technical Letter Report

    SciTech Connect

    Simonen, Fredric A.; Doctor, Steven R.; Gosselin, Stephen R.; Rudland, David L.; Xu, H.; Wilkowski, Gery M.; Lydell, Bengt O.

    2007-05-31

    This report addresses the potential application of probabilistic fracture mechanics computer codes to support the Proactive Materials Degradation Assessment (PMDA) program as a method to predict component failure probabilities. The present report describes probabilistic fracture mechanics calculations that were performed for selected components using the PRO-LOCA and PRAISE computer codes. The calculations address the failure mechanisms of stress corrosion cracking, intergranular stress corrosion cracking, and fatigue for components and operating conditions that are known to make particular components susceptible to cracking. It was demonstrated that the two codes can predict essentially the same failure probabilities if both codes start with the same fracture mechanics model and the same inputs to the model. Comparisons with field experience showed that both codes predict relatively high failure probabilities for components under operating conditions that have resulted in field failures. It was found that modeling assumptions and inputs tended to give higher calculated failure probabilities than those derived from data on field failures. Sensitivity calculations were performed to show that uncertainties in the probabilistic calculations were sufficiently large to explain the differences between predicted failure probabilities and field experience.

  7. Mechanical sensitivity reveals evolutionary dynamics of mechanical systems

    PubMed Central

    Anderson, P. S. L.; Patek, S. N.

    2015-01-01

    A classic question in evolutionary biology is how form–function relationships promote or limit diversification. Mechanical metrics, such as kinematic transmission (KT) in linkage systems, are useful tools for examining the evolution of form and function in a comparative context. The convergence of disparate systems on equivalent metric values (mechanical equivalence) has been highlighted as a source of potential morphological diversity under the assumption that morphology can evolve with minimal impact on function. However, this assumption does not account for mechanical sensitivity—the sensitivity of the metric to morphological changes in individual components of a structure. We examined the diversification of a four-bar linkage system in mantis shrimp (Stomatopoda), and found evidence for both mechanical equivalence and differential mechanical sensitivity. KT exhibited variable correlations with individual linkage components, highlighting the components that influence KT evolution, and the components that are free to evolve independently from KT and thereby contribute to the observed pattern of mechanical equivalence. Determining the mechanical sensitivity in a system leads to a deeper understanding of both functional convergence and morphological diversification. This study illustrates the importance of multi-level analyses in delineating the factors that limit and promote diversification in form–function systems. PMID:25716791

  8. Probabilistic/Fracture-Mechanics Model For Service Life

    NASA Technical Reports Server (NTRS)

    Watkins, T., Jr.; Annis, C. G., Jr.

    1991-01-01

    Computer program makes probabilistic estimates of lifetime of engine and components thereof. Developed to fill need for more accurate life-assessment technique that avoids errors in estimated lives and provides for statistical assessment of levels of risk created by engineering decisions in designing system. Implements mathematical model combining techniques of statistics, fatigue, fracture mechanics, nondestructive analysis, life-cycle cost analysis, and management of engine parts. Used to investigate effects of such engine-component life-controlling parameters as return-to-service intervals, stresses, capabilities for nondestructive evaluation, and qualities of materials.

  9. (Environmental and geophysical modeling, fracture mechanics, and boundary element methods)

    SciTech Connect

    Gray, L.J.

    1990-11-09

    Technical discussions at the various sites visited centered on application of boundary integral methods for environmental modeling, seismic analysis, and computational fracture mechanics in composite and smart'' materials. The traveler also attended the International Association for Boundary Element Methods Conference at Rome, Italy. While many aspects of boundary element theory and applications were discussed in the papers, the dominant topic was the analysis and application of hypersingular equations. This has been the focus of recent work by the author, and thus the conference was highly relevant to research at ORNL.

  10. Fracture mechanics analyses for skin-stiffener debonding

    NASA Technical Reports Server (NTRS)

    Raju, I. S.; Sistla, R.; Krishnamurthy, T.; Lotts, C. G.

    1993-01-01

    The debond configurations presently subjected to 3D FEM fracture mechanics analyses are respectively of the flange-skin strip and skin-stiffener configuration type. Two methods employing the virtual crack closure technique were used to evaluate the strain energy release rate, or 'G-value' distributions across the debond front. Both methods yielded nearly identical G-value distributions for the debond configurations studied; they were compared with plane strain and shell analyses results from the literature for the flange skin strip configuration, and found to be in good agreement. Mode II is dominant for the skin-stiffener debond configuration.

  11. Elastic, plastic, and fracture mechanisms in graphene materials

    NASA Astrophysics Data System (ADS)

    Daniels, Colin; Horning, Andrew; Phillips, Anthony; Massote, Daniel V. P.; Liang, Liangbo; Bullard, Zachary; Sumpter, Bobby G.; Meunier, Vincent

    2015-09-01

    In both research and industry, materials will be exposed to stresses, be it during fabrication, normal use, or mechanical failure. The response to external stress will have an important impact on properties, especially when atomic details govern the functionalities of the materials. This review aims at summarizing current research involving the responses of graphene and graphene materials to applied stress at the nanoscale, and to categorize them by stress-strain behavior. In particular, we consider the reversible functionalization of graphene and graphene materials by way of elastic deformation and strain engineering, the plastic deformation of graphene oxide and the emergence of such in normally brittle graphene, the formation of defects as a response to stress under high temperature annealing or irradiation conditions, and the properties that affect how, and mechanisms by which, pristine, defective, and polycrystalline graphene fail catastrophically during fracture. Overall we find that there is significant potential for the use of existing knowledge, especially that of strain engineering, as well as potential for additional research into the fracture mechanics of polycrystalline graphene and device functionalization by way of controllable plastic deformation of graphene.

  12. Elastic, plastic, and fracture mechanisms in graphene materials.

    PubMed

    Daniels, Colin; Horning, Andrew; Phillips, Anthony; Massote, Daniel V P; Liang, Liangbo; Bullard, Zachary; Sumpter, Bobby G; Meunier, Vincent

    2015-09-23

    In both research and industry, materials will be exposed to stresses, be it during fabrication, normal use, or mechanical failure. The response to external stress will have an important impact on properties, especially when atomic details govern the functionalities of the materials. This review aims at summarizing current research involving the responses of graphene and graphene materials to applied stress at the nanoscale, and to categorize them by stress-strain behavior. In particular, we consider the reversible functionalization of graphene and graphene materials by way of elastic deformation and strain engineering, the plastic deformation of graphene oxide and the emergence of such in normally brittle graphene, the formation of defects as a response to stress under high temperature annealing or irradiation conditions, and the properties that affect how, and mechanisms by which, pristine, defective, and polycrystalline graphene fail catastrophically during fracture. Overall we find that there is significant potential for the use of existing knowledge, especially that of strain engineering, as well as potential for additional research into the fracture mechanics of polycrystalline graphene and device functionalization by way of controllable plastic deformation of graphene.

  13. Substance P spinal signaling induces glial activation and nociceptive sensitization after fracture.

    PubMed

    Li, W-W; Guo, T-Z; Shi, X; Sun, Y; Wei, T; Clark, D J; Kingery, W S

    2015-12-01

    Tibia fracture in rodents induces substance P (SP)-dependent keratinocyte activation and inflammatory changes in the hindlimb, similar to those seen in complex regional pain syndrome (CRPS). In animal pain models spinal glial cell activation results in nociceptive sensitization. This study tested the hypothesis that limb fracture triggers afferent C-fiber SP release in the dorsal horn, resulting in chronic glial activation and central sensitization. At 4 weeks after tibia fracture and casting in rats, the cast was removed and hind paw allodynia, unweighting, warmth, and edema were measured, then the antinociceptive effects of microglia (minocycline) or astrocyte (L-2-aminoadipic acid (LAA)) inhibitors or an SP receptor antagonist (LY303870) were tested. Immunohistochemistry and PCR were used to evaluate microglial and astrocyte activation in the dorsal horn. Similar experiments were performed in intact rats after brief sciatic nerve electric stimulation at C-fiber intensity. Microglia and astrocytes were chronically activated at 4 weeks after fracture and contributed to the maintenance of hind paw allodynia and unweighting. Furthermore, LY303870 treatment initiated at 4 weeks after fracture partially reversed both spinal glial activation and nociceptive sensitization. Similarly, persistent spinal microglial activation and hind paw nociceptive sensitization were observed at 48 h after sciatic nerve C-fiber stimulation and this effect was inhibited by treatment with minocycline, LAA, or LY303870. These data support the hypothesis that C-fiber afferent SP signaling chronically supports spinal neuroglial activation after limb fracture and that glial activation contributes to the maintenance of central nociceptive sensitization in CRPS. Treatments inhibiting glial activation and spinal inflammation may be therapeutic for CRPS. PMID:26386297

  14. Radionuclide migration through fractured rock for arbitrary-length decay chain: Analytical solution and global sensitivity analysis

    NASA Astrophysics Data System (ADS)

    Shahkarami, Pirouz; Liu, Longcheng; Moreno, Luis; Neretnieks, Ivars

    2015-01-01

    This study presents an analytical approach to simulate nuclide migration through a channel in a fracture accounting for an arbitrary-length decay chain. The nuclides are retarded as they diffuse in the porous rock matrix and stagnant zones in the fracture. The Laplace transform and similarity transform techniques are applied to solve the model. The analytical solution to the nuclide concentrations at the fracture outlet is governed by nine parameters representing different mechanisms acting on nuclide transport through a fracture, including diffusion into the rock matrices, diffusion into the stagnant water zone, chain decay and hydrodynamic dispersion. Furthermore, to assess how sensitive the results are to parameter uncertainties, the Sobol method is applied in variance-based global sensitivity analyses of the model output. The Sobol indices show how uncertainty in the model output is apportioned to the uncertainty in the model input. This method takes into account both direct effects and interaction effects between input parameters. The simulation results suggest that in the case of pulse injections, ignoring the effect of a stagnant water zone can lead to significant errors in the time of first arrival and the peak value of the nuclides. Likewise, neglecting the parent and modeling its daughter as a single stable species can result in a significant overestimation of the peak value of the daughter nuclide. It is also found that as the dispersion increases, the early arrival time and the peak time of the daughter decrease while the peak value increases. More importantly, the global sensitivity analysis reveals that for time periods greater than a few thousand years, the uncertainty of the model output is more sensitive to the values of the individual parameters than to the interaction between them. Moreover, if one tries to evaluate the true values of the input parameters at the same cost and effort, the determination of priorities should follow a certain

  15. Sensitivities of biomechanical assessment methods for fracture healing of long bones.

    PubMed

    Chen, G; Wu, F Y; Zhang, J Q; Zhong, G Q; Liu, F

    2015-07-01

    There is a controversy as to whether the biomechanical methods are feasible to assess fracture healing of long bones. This paper investigated the sensitivities of two biomechanical methods, torsion and bending, for assessing fracture healing of long bones; both a simplified beam model and finite element model of an artificial femur were employed. The results demonstrated that, in the initial healing stage, the whole-bone stiffness of the fractured bone is extremely sensitive to the variation of the callus stiffness at the fracture site; when the shear (or Young's) modulus of the callus reaches 15% that of the intact bone, the whole-bone stiffness rises up to 90% that of the intact bone. After that, the whole-bone torsional (or bending) stiffness increases slowly; it becomes less sensitive to the variation of the callus stiffness. These results imply that the whole-bone stiffness is of limited reliability to assess the healing quality particular at late stages of the healing process. The simplified model in this paper provided a theoretical framework to explain why the whole-bone stiffness is insensitive to the healing process of fractured long bones in the late stage of healing. The conclusions obtained from the simplified model were verified with the finite element simulations of the artificial femur. PMID:25983068

  16. Sensitivities of biomechanical assessment methods for fracture healing of long bones.

    PubMed

    Chen, G; Wu, F Y; Zhang, J Q; Zhong, G Q; Liu, F

    2015-07-01

    There is a controversy as to whether the biomechanical methods are feasible to assess fracture healing of long bones. This paper investigated the sensitivities of two biomechanical methods, torsion and bending, for assessing fracture healing of long bones; both a simplified beam model and finite element model of an artificial femur were employed. The results demonstrated that, in the initial healing stage, the whole-bone stiffness of the fractured bone is extremely sensitive to the variation of the callus stiffness at the fracture site; when the shear (or Young's) modulus of the callus reaches 15% that of the intact bone, the whole-bone stiffness rises up to 90% that of the intact bone. After that, the whole-bone torsional (or bending) stiffness increases slowly; it becomes less sensitive to the variation of the callus stiffness. These results imply that the whole-bone stiffness is of limited reliability to assess the healing quality particular at late stages of the healing process. The simplified model in this paper provided a theoretical framework to explain why the whole-bone stiffness is insensitive to the healing process of fractured long bones in the late stage of healing. The conclusions obtained from the simplified model were verified with the finite element simulations of the artificial femur.

  17. [Current concepts of the mechanisms of formation of gunshot fractures].

    PubMed

    Pigolkin, Iu I; Dubrovin, I A; Leonov, S V; Mikhaĭlenko, A V; Dubrovin, A I; Zotkin, D A

    2013-01-01

    The mechanisms of formation of gunshot fractures in flat bones inflicted by a semispherical bullet were investigated using expert and experimental materials. The process of crack formation was considered in terms of the Hertzian contact problem and the Hill-Johnson model. It was shown that the fracture develops as a result of combination of stresses and strains in the bone tissue leading to the formation of a hydrostatic nucleus prior to tissue fragmentation. Dynamic fluctuations (waves) generated in the zone of hydrostatic compression resulting from the gunshot injury propagate with the velocity of sound from the nucleus in the direction of the bullet movement. According to the Hill-Johnson model, the waves propagate in the direction of the impact within a parabolically expanding space; this accounts for the mechanism of formation of parabolic cracks and the specific shape of the defect that the bullet produces in the flat bones. The dynamic load applied by means of an indentor forms at a higher rate than the velocity of sound in the affected material. It gives reason to consider the effect of a bullet moving with the speed of 250 m/s as quasi-static loading. The results obtained in this study make a contribution to the theory of impact effect of a bullet and provide a deeper insight into the physical nature of the direct and sideway action of a gunshot projectile. Moreover, they explain the cause behind the widening of the outlet part of the perforating fracture in the flat bones. PMID:25474911

  18. Fatigue and fracture mechanics in pressure vessels and piping. PVP-Volume 304

    SciTech Connect

    Mehta, H.S.; Wilkowski, G.; Takezono, S.; Bloom, J.; Yoon, K.; Aoki, S.; Rahman, S.; Nakamura, T.; Brust, F.; Yoshimura, S.

    1995-11-01

    Fracture mechanics and fatigue evaluations are an important part of the structural integrity analyses to assure safe operation of pressure vessels and piping components during their service life. The paper presented in this volume illustrate the application of fatigue and fracture mechanics techniques to assess the structural integrity of a wide variety of Pressure Vessels and Piping components. The papers are organized in six sections: (1) fatigue and fracture--vessels; (2) fatigue and fracture--piping; (3) fatigue and fracture--material property evaluations; (4) constraint effects in fracture mechanics; (5) probabilistic fracture mechanics analyses; and (6) user`s experience with failure assessment diagrams. Separate abstracts were prepared for most of the papers in this book.

  19. Coupled Flow and Mechanics in Porous and Fractured Media*

    NASA Astrophysics Data System (ADS)

    Martinez, M. J.; Newell, P.; Bishop, J.

    2012-12-01

    Numerical models describing subsurface flow through deformable porous materials are important for understanding and enabling energy security and climate security. Some applications of current interest come from such diverse areas as geologic sequestration of anthropogenic CO2, hydro-fracturing for stimulation of hydrocarbon reservoirs, and modeling electrochemistry-induced swelling of fluid-filled porous electrodes. Induced stress fields in any of these applications can lead to structural failure and fracture. The ultimate goal of this research is to model evolving faults and fracture networks and flow within the networks while coupling to flow and mechanics within the intact porous structure. We report here on a new computational capability for coupling of multiphase porous flow with geomechanics including assessment of over-pressure-induced structural damage. The geomechanics is coupled to the flow via the variation in the fluid pore pressures, whereas the flow problem is coupled to mechanics by the concomitant material strains which alter the pore volume (porosity field) and hence the permeability field. For linear elastic solid mechanics a monolithic coupling strategy is utilized. For nonlinear elastic/plastic and fractured media, a segregated coupling is presented. To facilitate coupling with disparate flow and mechanics time scales, the coupling strategy allows for different time steps in the flow solve compared to the mechanics solve. If time steps are synchronized, the controller allows user-specified intra-time-step iterations. The iterative coupling is dynamically controlled based on a norm measuring the degree of variation in the deformed porosity. The model is applied for evaluation of the integrity of jointed caprock systems during CO2 sequestration operations. Creation or reactivation of joints can lead to enhanced pathways for leakage. Similarly, over-pressures can induce flow along faults. Fluid flow rates in fractures are strongly dependent on the

  20. Structure-sensitive mechanism of nanographene failure

    SciTech Connect

    Sheka, E. F. Popova, N. A.; Popova, V. A.; Nikitina, E. A.; Shaymardanova, L. H.

    2011-04-15

    The quantum-mechanochemical-reaction-coordinate approach has disclosed atomically matched peculiarities that accompany the deformation-failure-rupture process occurring in nanographenes. The high stiffness of the graphene body is provided by the benzenoid unit. The anisotropy of the unit mechanical behavior in combination with different configurations of the unit packing with respect to the body C-C bond chains forms the ground for the structure-sensitive mechanism of the mechanical behavior that is drastically different for two different deformation modes. The zig-zag deformation mode is particularly manifested with the formation of one-atom chains. The approach allows tracing a deformation-stimulated change in the chemical reactivity of both the nanographene body and its individual atoms.

  1. Fracture Mechanics Modelling of an In Situ Concrete Spalling Experiment

    NASA Astrophysics Data System (ADS)

    Siren, Topias; Uotinen, Lauri; Rinne, Mikael; Shen, Baotang

    2015-07-01

    During the operation of nuclear waste disposal facilities, some sprayed concrete reinforced underground spaces will be in use for approximately 100 years. During this time of use, the local stress regime will be altered by the radioactive decay heat. The change in the stress state will impose high demands on sprayed concrete, as it may suffer stress damage or lose its adhesion to the rock surface. It is also unclear what kind of support pressure the sprayed concrete layer will apply to the rock. To investigate this, an in situ experiment is planned in the ONKALO underground rock characterization facility at Olkiluoto, Finland. A vertical experimental hole will be concreted, and the surrounding rock mass will be instrumented with heat sources, in order to simulate an increase in the surrounding stress field. The experiment is instrumented with an acoustic emission system for the observation of rock failure and temperature, as well as strain gauges to observe the thermo-mechanical interactive behaviour of the concrete and rock at several levels, in both rock and concrete. A thermo-mechanical fracture mechanics study is necessary for the prediction of the damage before the experiment, in order to plan the experiment and instrumentation, and for generating a proper prediction/outcome study due to the special nature of the in situ experiment. The prediction of acoustic emission patterns is made by Fracod 2D and the model later compared to the actual observed acoustic emissions. The fracture mechanics model will be compared to a COMSOL Multiphysics 3D model to study the geometrical effects along the hole axis.

  2. 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.

  3. Fundamental mechanisms of tensile fracture in aluminum sheet undirectionally reinforced with boron filament

    NASA Technical Reports Server (NTRS)

    Herring, H. W.

    1972-01-01

    Results are presented from an experimental study of the tensile-fracture process in aluminum sheet unidirectionally reinforced with boron filament. The tensile strength of the material is severely limited by a noncumulative fracture mechanism which involves the initiation and sustenance of a chain reaction of filament fractures at a relatively low stress level. Matrix fracture follows in a completely ductile manner. The minimum filament stress for initiation of the fracture mechanism is shown to be approximately 1.17 GN/sq m (170 ksi), and appears to be independent of filament diameter, number of filament layers, and the strength of the filament-matrix bond. All the commonly observed features of tensile fracture surfaces are explained in terms of the observed noncumulative fracture mechanism.

  4. Probabilistic Fracture Mechanics and Optimum Fracture Control Analytical Procedures for a Reusable Solid Rocket Motor Case

    NASA Technical Reports Server (NTRS)

    Hanagud, S.; Uppaluri, B.

    1977-01-01

    A methodology for the reliability analysis of a reusable solid rocket motor case is discussed. The analysis is based on probabilistic fracture mechanics and probability distribution for initial flaw sizes. The developed reliability analysis is used to select the structural design variables of the solid rocket motor case on the basis of minimum expected cost and specified reliability bounds during the projected design life of the case. Effects of failure prevention plans such as nondestructive inspection and the material erosion between missions are also considered in the developed procedure for selection of design variables. The reliability-based procedure can be modified to consider other similar structures of reusable space vehicle systems with different failure prevention plans.

  5. Fracture mechanics of bone--the effects of density, specimen thickness and crack velocity on longitudinal fracture.

    PubMed

    Behiri, J C; Bonfield, W

    1984-01-01

    The fracture mechanics parameters of critical stress intensity factor (Kc) and critical strain energy release rate (Gc) for longitudinal fracture of bovine tibia cortical bone were determined by the compact tension method. It was demonstrated that, for a given bone density, Kc and Gc depended on the loading rate, and resultant crack velocity, with a maximum in fracture toughness (Kc approximately 6.3 MNm-3/2, Gc approximately 2900 Jm-2) at a crack velocity approximately 10(-3) ms-1. For a given loading rate, or crack velocity, an increase in bone density, in the range from 1.92 to 2.02 Mgm-3, produced increases in Kc and Gc, but a variation in specimen thickness (from 0.5 to 2 mm) had no effect on the measured fracture mechanics parameters. PMID:6715385

  6. Elastic plastic fracture mechanics methodology for surface cracks

    NASA Technical Reports Server (NTRS)

    Ernst, Hugo A.; Boatwright, D. W.; Curtin, W. J.; Lambert, D. M.

    1993-01-01

    The Elastic Plastic Fracture Mechanics (EPFM) Methodology has evolved significantly in the last several years. Nevertheless, some of these concepts need to be extended further before the whole methodology can be safely applied to structural parts. Specifically, there is a need to include the effect of constraint in the characterization of material resistance to crack growth and also to extend these methods to the case of 3D defects. As a consequence, this project was started as a 36 month research program with the general objective of developing an EPFM methodology to assess the structural reliability of pressure vessels and other parts of interest to NASA containing defects. This report covers a computer modelling algorithm used to simulate the growth of a semi-elliptical surface crack; the presentation of a finite element investigation that compared the theoretical (HRR) stress field to that produced by elastic and elastic-plastic models; and experimental efforts to characterize three dimensional aspects of fracture present in 'two dimensional', or planar configuration specimens.

  7. Mass and mechanical sensitivity of otoliths

    NASA Astrophysics Data System (ADS)

    Kondrachuk, A.

    It is known that all vertebrate sense gravity and linear acceleration with specialized organsotoliths in which a dense mass is moved by acceleration so that it activates mechanosensory receptor cells. It is suggested that the change of otolith mass during the development of otolith in altered gravity conditions as well as the growth of otoliths in fishes in normal conditions [Lychakov, 1988] are determined by the feedback between the otolith dynamics and the processes that regulate otolith growth. The hypothesis origins from pendulum model of an otolith [de Vries, 1950,] in which otolith mass is one of the parameters. However, validity of this hypothesis is not apparent and was not analyzed so far. The hypothesis is tested by comparing pendulum model with a simplified spatially distributed model of the otolith [Kondrachuk, 2001]. It enables us to analyze the influence of physical parameters of otolith structure on sensitivity of an otolith as a bioaccelerometer. The analysis is manly based on experimental data from fishes. It was shown that in the case of spatially distributed fixation of the otolith plate (or otoconial layer) to macular surface the mechanical sensitivity of otolith does not depend on total otolith mass and its longitudinal sizes. It is determined by otolith thickness, the Young's modulus and viscosity of gel layer of growing otolith. It is assumed that correlated changes of these parameters caused by alteration of dynamic conditions are aimed to keep otolith sensitivity steady. Thus the results of analysis show that the growth of the total otolith mass does not connected with mechanical sensitivity of an otolith if its motion relative to the epithelial surface is plane-parallel. Meanwhile, the influence of altered gravity conditions on longitudinal sizes of growing otoliths in fishes and statolith (statoconia) mass formation in mollusks were observed. The following hypothesis regarding the relationship between the otolith growth, otolith dynamics

  8. Fracture and mechanical stratigraphy for Mississippian-Pennsylvanian age carbonates, Ozark Dome, NW Arkansas

    NASA Astrophysics Data System (ADS)

    Peppers, M.; Burberry, C. M.

    2014-12-01

    Identifying natural fracture patterns in an area gives a detailed look into the local tectonic history. Comparing those fractures to the mechanical properties of the rocks provides key insights into predicting fractures in the subsurface. The Ozark Dome is an ideal study area for fracture research due to multiple fracturing events resulting from the multi-stage deformation Ouachita Orogeny during the late Paleozoic. This study used field observations of lithology and fracture attributes over ~10 outcrops in the Mississppian-Pennsylvanian (360-298 ma) carbonate sequence of the Ozark Plateau. Outcrops were chosen having excellent lithological exposure up the sequence from the Boone to Atoka formations and with 3D representations of the fracture patterns. In all, the area investigated covered nearly 60 square miles. Fracture attributes collected included fracture intensity, length, and abutting relationships; and rock hardness data collected from a Schmidt Hammer. Data was analyzed using programs such as Stereonet and MOVE structural software that generated rose diagrams, structural cross sections, and products. Initial results indicate 4 main fracture orientations that resulted from at least 3 discrete phases of deformation during the Miss-Penn. Initial results also indicate that the present-day mechanical stratigraphy is not the same one that existed during the deformation phases. Work done at the Tiger Blvd. outcrops showed at least 2 distinct mechanical units. Fractures observed at the outcrop did not respect mechanical bed boundaries, and showed no relationship to the differences in mechanical properties observed. This study will aid in the interpretation of fractures in regards to mechanical stratigraphy, which allows for a better understanding of subsurface fracture prediction in carbonate sequences worldwide. Finally, the fracture work here will also help in elucidating the tectonic history of the field area during the Mississippian and Pennsylvanian.

  9. Fracture mechanics of hydroxyapatite single crystals under geometric confinement.

    PubMed

    Libonati, Flavia; Nair, Arun K; Vergani, Laura; Buehler, Markus J

    2013-04-01

    Geometric confinement to the nanoscale, a concept that refers to the characteristic dimensions of structural features of materials at this length scale, has been shown to control the mechanical behavior of many biological materials or their building blocks, and such effects have also been suggested to play a crucial role in enhancing the strength and toughness of bone. Here we study the effect of geometric confinement on the fracture mechanism of hydroxyapatite (HAP) crystals that form the mineralized phase in bone. We report a series of molecular simulations of HAP crystals with an edge crack on the (001) plane under tensile loading, and we systematically vary the sample height whilst keeping the sample and the crack length constant. We find that by decreasing the sample height the stress concentration at the tip of the crack disappears for samples with a height smaller than 4.15nm, below which the material shows a different failure mode characterized by a more ductile mechanism with much larger failure strains, and the strength approaching that of a flaw-less crystal. This study directly confirms an earlier suggestion of a flaw-tolerant state that appears under geometric confinement and may explain the mechanical stability of the reinforcing HAP platelets in bone. PMID:23500480

  10. Simple spline-function equations for fracture mechanics calculations

    NASA Technical Reports Server (NTRS)

    Orange, T. W.

    1979-01-01

    The paper presents simple spline-function equations for fracture mechanics calculations. A spline function is a sequence of piecewise polynomials of degree n greater than 1 whose coefficients are such that the function and its first n-1 derivatives are continuous. Second-degree spline equations are presented for the compact, three point bend, and crack-line wedge-loaded specimens. Some expressions can be used directly, so that for a cyclic crack propagation test using a compact specimen, the equation given allows the cracklength to be calculated from the slope of the load-displacement curve. For an R-curve test, equations allow the crack length and stress intensity factor to be calculated from the displacement and the displacement ratio.

  11. The fracture mechanics of fatigue crack propagation in compact bone.

    PubMed

    Wright, T M; Hayes, W C

    1976-07-01

    The purpose of this investigation was to apply the techniques of fracture mechanics to a study of fatigue crack propagation in compact bone. Small cracks parallel to the long axis of the bone were initiated in standardized specimens of bovine bone. Crack growth was achieved by cyclically loading these specimens. The rate of crack growth was determined from measurements of crack length versus cycles of loading. The stress intensity factor at the tip of the crack was calculated from knowledge of the applied load, the crack length, and the specimen geometry. A strong correlation was found between the experimentally determined crack growth rate and the applied stress intensity. The relationship takes the form of a power law similar to that for other materials. Visual observation and scanning electron microscopy revealed that crack propagation occurred by initiation of subcritical cracks ahead of the main crack.

  12. Microstructural fracture mechanics in high-cycle fatigue

    SciTech Connect

    Rios, E.R. de los; Navarro, A.

    1997-12-31

    Microstructural Fracture Mechanics principles are used to develop a model of crack growth in long life fatigue. In its simplest form microstructural modelling considers the material as a polycrystal of uniform grain size D, with a crack system divided into three zones: the crack, the plastic zone and the microstructural barrier zone. The solution of the equilibrium equation allows for the calculation of the stresses sustained by the crack wake, plastic zone, barrier zone and elastic enclave, and the crack tip plastic displacement {phi}. Crack growth rate is calculated through a Paris type relationship in terms of {phi}, i.e., da/dN = C{phi}{sup n}. Conditions for crack arrest and instability are established.

  13. A mechanism-based approach to modeling ductile fracture.

    SciTech Connect

    Bammann, Douglas J.; Hammi, Youssef; Antoun, Bonnie R.; Klein, Patrick A.; Foulk, James W., III; McFadden, Sam X.

    2004-01-01

    Ductile fracture in metals has been observed to result from the nucleation, growth, and coalescence of voids. The evolution of this damage is inherently history dependent, affected by how time-varying stresses drive the formation of defect structures in the material. At some critically damaged state, the softening response of the material leads to strain localization across a surface that, under continued loading, becomes the faces of a crack in the material. Modeling localization of strain requires introduction of a length scale to make the energy dissipated in the localized zone well-defined. In this work, a cohesive zone approach is used to describe the post-bifurcation evolution of material within the localized zone. The relations are developed within a thermodynamically consistent framework that incorporates temperature and rate-dependent evolution relationships motivated by dislocation mechanics. As such, we do not prescribe the evolution of tractions with opening displacements across the localized zone a priori. The evolution of tractions is itself an outcome of the solution of particular, initial boundary value problems. The stress and internal state of the material at the point of bifurcation provides the initial conditions for the subsequent evolution of the cohesive zone. The models we develop are motivated by in-situ scanning electron microscopy of three-point bending experiments using 6061-T6 aluminum and 304L stainless steel, The in situ observations of the initiation and evolution of fracture zones reveal the scale over which the failure mechanisms act. In addition, these observations are essential for motivating the micromechanically-based models of the decohesion process that incorporate the effects of loading mode mixity, temperature, and loading rate. The response of these new cohesive zone relations is demonstrated by modeling the three-point bending configuration used for the experiments. In addition, we survey other methods with the potential

  14. Fracture mechanics; Proceedings of the Seventeenth National Symposium, Albany, NY, August 7-9, 1984

    NASA Technical Reports Server (NTRS)

    Underwood, J. M. (Editor); Chait, R. (Editor); Smith, C. W. (Editor); Wilhem, D. P. (Editor); Andrews, W. A. (Editor); Newman, J. C. (Editor)

    1986-01-01

    The present conference gives attention to topics in the application of fracture mechanics, subcritical crack growth phenomena, fracture testing methods, ductile fracture behavior, and fracture mechanisms and their analysis. Specific papers treat the resistance curve approach to composite materials characterization, fracture toughness in ductile iron and cast steel, hold-time effects in elevated temperature fatigue crack propagation, creep crack growth under nonsteady conditions, viscoplastic fatigue in a superalloy at elevated temperatures, fracture testing with arc bend specimens, one-point bend impact test application, and a compact mode II fracture specimen. Also discussed are the computation of stable crack growth using the J-integral, the use of plastic energy dissipation to characterize crack growth, the extension of surface cracks under cyclic loading, the minimum time criterion for crack instability in structural materials, dynamic crack propagation and branching under biaxial loading, and boundary layer effects in cracked bodies.

  15. Effective Hydro-Mechanical Properties of Fluid-Saturated Fracture Networks

    NASA Astrophysics Data System (ADS)

    Pollmann, N.; Vinci, C.; Renner, J.; Steeb, H.

    2015-12-01

    Consideration of hydro-mechanical processes is essential for the characterization of liquid-resources as well as for many engineering applications. Furthermore, the modeling of seismic waves in fractured porous media finds application not only in geophysical exploration but also reservoir management. Fractures exhibit high-aspect-ratio geometries, i.e. they constitute thin and long hydraulic conduits. Motivated by this peculiar geometry, the investigation of the hydro-mechanically coupled processes is performed by means of a hybrid-dimensional modeling approach. The effective material behavior of domains including complex fracture patterns in a porous rock is assessed by investigating the fluid pressure and the solid displacement of the skeleton saturated by compressible fluids. Classical balance equations are combined with a Poiseuille-type flow in the dimensionally reduced fracture. In the porous surrounding rock, the classical Biot-theory is applied. For simple geometries, our findings show that two main fluid-flow processes occur, leak-off from fractures to the surrounding rock and fracture flow within and between the connected fractures. The separation of critical frequencies of the two flow processes is not straightforward, in particular for systems containing a large number of fractures. Our aim is to model three dimensional hydro-mechanically coupled processes within complex fracture patterns and in particular determine the frequency-dependent attenuation characteristics. Furthermore, the effect of asperities of the fracture surfaces on the fracture stiffness and on the hydraulic conductivity will be added to the approach.

  16. Impact of Injury Mechanisms on Patterns and Management of Facial Fractures.

    PubMed

    Greathouse, S Travis; Adkinson, Joshua M; Garza, Ramon; Gilstrap, Jarom; Miller, Nathan F; Eid, Sherrine M; Murphy, Robert X

    2015-07-01

    Mechanisms causing facial fractures have evolved over time and may be predictive of the types of injuries sustained. The objective of this study is to examine the impact of mechanisms of injury on the type and management of facial fractures at our Level 1 Trauma Center. The authors performed an Institutional Review Board-approved review of our network's trauma registry from 2006 to 2010, documenting age, sex, mechanism, Injury Severity Score, Glasgow Coma Scale, facial fracture patterns (nasal, maxillary/malar, orbital, mandible), and reconstructions. Mechanism rates were compared using a Pearson χ2 test. The database identified 23,318 patients, including 1686 patients with facial fractures and a subset of 1505 patients sustaining 2094 fractures by motor vehicle collision (MVC), fall, or assault. Nasal fractures were the most common injuries sustained by all mechanisms. MVCs were most likely to cause nasal and malar/maxillary fractures (P < 0.01). Falls were the least likely and assaults the most likely to cause mandible fractures (P < 0.001), the most common injury leading to surgical intervention (P < 0.001). Although not statistically significant, fractures sustained in MVCs were the most likely overall to undergo surgical intervention. Age, number of fractures, and alcohol level were statistically significant variables associated with operative management. Age and number of fractures sustained were associated with operative intervention. Although there is a statistically significant correlation between mechanism of injury and type of facial fracture sustained, none of the mechanisms evaluated herein are statistically associated with surgical intervention. Clinical Question/Level of Evidence: Therapeutic, III.

  17. Modeling mechanical degradation in lithium ion batteries during cycling: Solid electrolyte interphase fracture

    NASA Astrophysics Data System (ADS)

    Laresgoiti, Izaro; Käbitz, Stefan; Ecker, Madeleine; Sauer, Dirk Uwe

    2015-12-01

    During cycling, mechanical stresses can occur in the composite electrode, inside the active material, but also in the solid electrolyte interphase layer. A mechanical model is proposed based on a system made of a spherical graphite particle surrounded by the solid electrolyte interphase layer. During lithium intercalation or de-intercalation, stresses in the graphite are produced, governed by the diffusion induced stress phenomena and in the solid electrolyte interphase, driven by the graphite expansion. The stresses in both materials were simulated and a sensitivity analysis was performed to clarify the influence of principal parameters on both processes. Finally, assuming that the solid electrolyte interphase is the weakest material and therefore more prone to fracture than graphite, the experimental capacity fade during cycling was modeled based on its break and repair effect rather than on the fracture of the active material. The mechanical model of the solid electrolyte interphase was implemented in a single particle lithium ion battery model in order to reproduce capacity fade during battery lifetime. The model results were compared against cycle life aging experimental data, reproducing accurately the influence of the depth of discharge as well as the average state of charge on the capacity fade.

  18. A Review on Recent Contribution of Meshfree Methods to Structure and Fracture Mechanics Applications

    PubMed Central

    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. PMID:24516359

  19. Isolated posterior malleolus fracture: a rare injury mechanism

    PubMed Central

    Serbest, Sancar; Tiftikçi, Uğur; Tosun, Haci Bayram; Kesgin, Engin; Karataş, Metin

    2015-01-01

    Sprain of the ankle is undoubtedly a common injury during athletic activity, and the sprain can be also associated with fracture of the ankle. Isolated posterior malleolus fracture is a very rare condition, which is usually missed. Here, we are presenting a 37 years old female patient, who suffered injury secondary pressing on brake pedal during collision in a traffic accident. Clinical evaluation is based on Ottawa Ankle Rules and a fracture is diagnosed; patient is started on daily activities at postoperative Week 8. This study aims to emphasize that Ottawa Ankle Rules are usually efficient for evaluating fractures of ankle, but clinicians should always make a detailed physical examination. PMID:26097627

  20. Fractures

    PubMed Central

    Hall, Michael C.

    1963-01-01

    Recent studies on the epidemiology and repair of fractures are reviewed. The type and severity of the fracture bears a relation to the age, sex and occupation of the patient. Bone tissue after fracture shows a process of inflammation and repair common to all members of the connective tissue family, but it repairs with specific tissue. Cartilage forms when the oxygen supply is outgrown. After a fracture, the vascular bed enlarges. The major blood supply to healing tissue is from medullary vessels and destruction of them will cause necrosis of the inner two-thirds of the cortex. Callus rapidly mineralizes, but full mineralization is achieved slowly; increased mineral metabolism lasts several years after fracture. PMID:13952119

  1. [Assessment of mechanical complications of intramedullary osteosynthesis in trochanteric fractures of the femur in elderly people].

    PubMed

    Hładki, Waldemar; Bednarenko, Marcin; Kotela, Ireneusz

    2011-01-01

    Operational treatment of trochanteric fractures of the femur, independently of the applied connecting implant, carries the risk of various types of complications. In this paper the incidence of mechanical complications in performed osteosynthesis of trochanteric fractures of the femur was analyzed as well as the risk factors influencing them and their extent were assessed. The results showed statistically significant influence of the type of implant, the type of fracture and the patients' age. It has been proven that the use of Gamma nail decreases the risk of mechanical complications almost twofold in comparison with the Ender's posts, disregarding the type of trochanteric fracture of the femur. PMID:21751513

  2. Mechanical and petrophysical study of fractured shale materials

    NASA Astrophysics Data System (ADS)

    Bonnelye, A.; Schubnel, A.; David, C.; Henry, P.; Guglielmi, Y.; Gout, C.; Dick, P.

    2015-12-01

    Mechanical and physical properties of shales are of major importance for upper crustal fault hydro-mechanical behavior. In particular, relationships between applied stress, textural anisotropy and transport properties. These relations can be investigated in the laboratory and here, was used shales from Tournemire (southern France). Triaxial tests were performed in order to determine the elasto-plastic yield envelope on 3 sets of samples with 3various bedding orientations (0°, 45°, and 90°). For each set, experiments were carried out at increasing confining pressures (2.5, 5, 10, 20, 40, 80MPa). They were performed under nominally drained conditions, at strain rates ranging between 5x10-7 s-1 - 1x10-5 s-1up to failure. During each experiment, P and S wave elastic velocities were continuously measured, in order to monitor the evolution of elastic anisotropy. Results show that the orientation of principal stress relative to bedding plays an important role on the brittle strength. Minimum strength is observed for samples deformed at 45° to bedding. Strength anisotropy increases both with confining pressure and strain rate. We interpret this result as the cohesive strength (and fracture toughness) being strain rate dependent. Although brittle failure and stress drops were systematically observed, deformation remained aseismic. This confirms that shales are good lithological candidates for shallow aseismic creep and slow slip events. Brittle failure was preceded by the development of P wave anisotropy, due to both crack growth and mineral re-orientation. Anisotropy variations were largest for samples deformed perpendicular to bedding, at the onset of rupture. Anisotropy reversal was observed at the highest confining pressures. For samples deformed parallel to bedding, the P wave anisotropy development is weaker. For both of these orientations, Thomsens parameters were inverted from the elastic wave data in order to quantify the evolution of elastic anisotropy. We

  3. The fracture energy and some mechanical properties of a polyurethane elastomer.

    NASA Technical Reports Server (NTRS)

    Mueller, H. K.; Knauss, W. G.

    1971-01-01

    The energy required to form a unit of new surface in the fracture of a polyurethane elastomer is determined. The rate sensitivity of the material has been reduced by swelling it in toluene. This paper primarily describes the experimental work of measuring the lower limit of the fracture energy. With this value and the creep compliance as a basis, the rate dependence of fracture energy for the unswollen material has been determined. It is thus shown that the dependence of the fracture energy on the rate of crack propagation can be explained by energy dissipation around the tip of the crack. Good agreement between the theoretically and experimentally determined relationships for the rate-sensitive fracture energy is demonstrated.

  4. 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.

  5. Fracture Mechanics Analyses for Interface Crack Problems - A Review

    NASA Technical Reports Server (NTRS)

    Krueger, Ronald; Shivakumar, Kunigal; Raju, Ivatury S.

    2013-01-01

    Recent developments in fracture mechanics analyses of the interfacial crack problem are reviewed. The intent of the review is to renew the awareness of the oscillatory singularity at the crack tip of a bimaterial interface and the problems that occur when calculating mode mixity using numerical methods such as the finite element method in conjunction with the virtual crack closure technique. Established approaches to overcome the nonconvergence issue of the individual mode strain energy release rates are reviewed. In the recent literature many attempts to overcome the nonconvergence issue have been developed. Among the many approaches found only a few methods hold the promise of providing practical solutions. These are the resin interlayer method, the method that chooses the crack tip element size greater than the oscillation zone, the crack tip element method that is based on plate theory and the crack surface displacement extrapolation method. Each of the methods is validated on a very limited set of simple interface crack problems. However, their utility for a wide range of interfacial crack problems is yet to be established.

  6. Fractures

    MedlinePlus

    ... commonly happen because of car accidents, falls, or sports injuries. Other causes are low bone density and osteoporosis, which cause weakening of the bones. Overuse can cause stress fractures, which are very small cracks in the ...

  7. Fracture mechanics; Proceedings of the 22nd National Symposium, Atlanta, GA, June 26-28, 1990. Vols. 1 & 2

    NASA Technical Reports Server (NTRS)

    Ernst, Hugo A. (Editor); Saxena, Ashok (Editor); Mcdowell, David L. (Editor); Atluri, Satya N. (Editor); Newman, James C., Jr. (Editor); Raju, Ivatury S. (Editor); Epstein, Jonathan S. (Editor)

    1992-01-01

    Current research on fracture mechanics is reviewed, focusing on ductile fracture; high-temperature and time-dependent fracture; 3D problems; interface fracture; microstructural aspects of fatigue and fracture; and fracture predictions and applications. Particular attention is given to the determination and comparison of crack resistance curves from wide plates and fracture mechanics specimens; a relationship between R-curves in contained and uncontained yield; the creep crack growth behavior of titanium alloy Ti-6242; a crack growth response in three heat resistant materials at elevated temperature; a crack-surface-contact model for determining effective-stress-intensity factors; interfacial dislocations in anisotropic bimaterials; an effect of intergranular crack branching on fracture toughness evaluation; the fracture toughness behavior of exservice chromium-molybdenum steels; the application of fracture mechanics to assess the significance of proof loading; and a load ratio method for estimating crack extension.

  8. The peel test in experimental adhesive fracture mechanics

    NASA Technical Reports Server (NTRS)

    Anderson, G. P.; Devries, K. L.; Williams, M. L.

    1974-01-01

    Several testing methods have been proposed for obtaining critical energy release rate or adhesive fracture energy in bond systems. These tests include blister, cone, lap shear, and peel tests. Peel tests have been used for many years to compare relative strengths of different adhesives, different surface preparation techniques, etc. The present work demonstrates the potential use of the peel test for obtaining adhesive fracture energy values.

  9. A numerical model of hydro-thermo-mechanical coupling in a fractured rock mass

    SciTech Connect

    Bower, K.M.

    1996-06-01

    Coupled hydro-thermo-mechanical codes with the ability to model fractured materials are used for predicting groundwater flow behavior in fractured aquifers containing thermal sources. The potential applications of such a code include the analysis of groundwater behavior within a geothermal reservoir. The capability of modeling hydro-thermo systems with a dual porosity, fracture flow model has been previously developed in the finite element code, FEHM. FEHM has been modified to include stress coupling with the dual porosity feature. FEHM has been further developed to implicitly couple the dependence of fracture hydraulic conductivity on effective stress within two dimensional, saturated aquifers containing fracture systems. The cubic law for flow between parallel plates was used to model fracture permeability. The Bartin-Bandis relationship was used to determine the fracture aperture within the cubic law. The code used a Newton Raphson iteration to implicitly solve for six unknowns at each node. Results from a model of heat flow from a reservoir to the moving fluid in a single fracture compared well with analytic results. Results of a model showing the increase in fracture flow due to a single fracture opening under fluid pressure compared well with analytic results. A hot dry rock, geothermal reservoir was modeled with realistic time steps indicating that the modified FEHM code does successfully model coupled flow problems with no convergence problems.

  10. An extension of fracture mechanics/technology to larger and smaller cracks/defects

    PubMed Central

    Abé, Hiroyuki

    2009-01-01

    Fracture mechanics/technology is a key science and technology for the design and integrity assessment of the engineering structures. However, the conventional fracture mechanics has mostly targeted a limited size of cracks/defects, say of from several hundred microns to several tens of centimeters. The author and his group has tried to extend that limited size and establish a new version of fracture technology for very large cracks used in geothermal energy extraction and for very small cracks/defects or damage often appearing in the combination of mechanical and electronic components of engineering structures. Those new versions are reviewed in this paper. PMID:19907123

  11. An extension of fracture mechanics/technology to larger and smaller cracks/defects.

    PubMed

    Abé, Hiroyuki

    2009-01-01

    Fracture mechanics/technology is a key science and technology for the design and integrity assessment of the engineering structures. However, the conventional fracture mechanics has mostly targeted a limited size of cracks/defects, say of from several hundred microns to several tens of centimeters. The author and his group has tried to extend that limited size and establish a new version of fracture technology for very large cracks used in geothermal energy extraction and for very small cracks/defects or damage often appearing in the combination of mechanical and electronic components of engineering structures. Those new versions are reviewed in this paper.

  12. Use of fracture mechanics theory in lifetime predictions for alumina and bioglass-coated alumina.

    PubMed

    Ritter, J E; Greenspan, D C; Palmer, R A; Hench, L L

    1979-03-01

    The fatigue behavior of alumina and bioglass-coated alumina was determined in air and biological test environments by the dynamic fatigue test technique in which strength is measured as a function of stressing rate. The good correlation found between the test data and fracture mechanics theory indicates that fatigue failure is controlled by the slow crack growth of preexisting flaws and that fracture mechanics theory can be used in making failure predictions for alumina and bioglass-coated alumina in biological environments. Thus, it is believed that lifetime predictions can be made for ceramic implants on the basis of short-term test data utilizing fracture mechanics principles.

  13. Mechanisms and Management of Stress Fractures in Physically Active Persons

    PubMed Central

    Romani, William A.; Gieck, Joe H.; Perrin, David H.; Saliba, Ethan N.; Kahler, David M.

    2002-01-01

    Objective: To describe the anatomy of bone and the physiology of bone remodeling as a basis for the proper management of stress fractures in physically active people. Data Sources: We searched PubMed for the years 1965 through 2000 using the key words stress fracture, bone remodeling, epidemiology, and rehabilitation. Data Synthesis: Bone undergoes a normal remodeling process in physically active persons. Increased stress leads to an acceleration of this remodeling process, a subsequent weakening of bone, and a higher susceptibility to stress fracture. When a stress fracture is suspected, appropriate management of the injury should begin immediately. Effective management includes a cyclic process of activity and rest that is based on the remodeling process of bone. Conclusions/Recommendations: Bone continuously remodels itself to withstand the stresses involved with physical activity. Stress fractures occur as the result of increased remodeling and a subsequent weakening of the outer surface ofthe bone. Once a stress fracture is suspected, a cyclic management program that incorporates the physiology of bone remodeling should be initiated. The cyclic program should allow the physically active person to remove the source of the stress to the bone, maintain fitness, promote a safe return to activity, and permit the bone to heal properly. PMID:16558676

  14. Analysis of seismic sources for different mechanisms of fracture growth for microseismic monitoring applications

    NASA Astrophysics Data System (ADS)

    Duchkov, A. A.; Stefanov, Yu. P.

    2015-10-01

    We have developed and illustrated an approach for geomechanic modeling of elastic wave generation (microsiesmic event occurrence) during incremental fracture growth. We then derived properties of effective point seismic sources (radiation patterns) approximating obtained wavefields. These results establish connection between geomechanic models of hydraulic fracturing and microseismic monitoring. Thus, the results of the moment tensor inversion of microseismic data can be related to different geomechanic scenarios of hydraulic fracture growth. In future, the results can be used for calibrating hydrofrac models. We carried out a series of numerical simulations and made some observations about wave generation during fracture growth. In particular when the growing fracture hits pre-existing crack then it generates much stronger microseismic event compared to fracture growth in homogeneous medium (radiation pattern is very close to the theoretical dipole-type source mechanism).

  15. Analysis of seismic sources for different mechanisms of fracture growth for microseismic monitoring applications

    SciTech Connect

    Duchkov, A. A.; Stefanov, Yu. P.

    2015-10-27

    We have developed and illustrated an approach for geomechanic modeling of elastic wave generation (microsiesmic event occurrence) during incremental fracture growth. We then derived properties of effective point seismic sources (radiation patterns) approximating obtained wavefields. These results establish connection between geomechanic models of hydraulic fracturing and microseismic monitoring. Thus, the results of the moment tensor inversion of microseismic data can be related to different geomechanic scenarios of hydraulic fracture growth. In future, the results can be used for calibrating hydrofrac models. We carried out a series of numerical simulations and made some observations about wave generation during fracture growth. In particular when the growing fracture hits pre-existing crack then it generates much stronger microseismic event compared to fracture growth in homogeneous medium (radiation pattern is very close to the theoretical dipole-type source mechanism)

  16. Effect of chemical environment and rock composition on fracture mechanics properties of reservoir lithologies in context of CO2 sequestration

    NASA Astrophysics Data System (ADS)

    Major, J. R.; Eichhubl, P.; Callahan, O. A.

    2015-12-01

    The coupled chemical and mechanical response of reservoir and seal rocks to injection of CO2 have major implications on the short and long term security of sequestered carbon. Many current numerical models evaluating behavior of reservoirs and seals during and after CO2 injection in the subsurface consider chemistry and mechanics separately and use only simple mechanical stability criteria while ignoring time-dependent failure parameters. CO2 injection irreversibly alters the subsurface chemical environment which can then affect geomechanical properties on a range of time scales by altering rock mineralogy and cements through dissolution, remobilization, and precipitation. It has also been documented that geomechanical parameters such as fracture toughness (KIC) and subcritical index (SCI) are sensitive to chemical environment. Double torsion fracture mechanics testing of reservoir lithologies under controlled environmental conditions relevant to CO2 sequestration show that chemical environment can measurably affect KIC and SCI. This coupled chemical-mechanical behavior is also influenced by rock composition, grains, amount and types of cement, and fabric. Fracture mechanics testing of the Aztec Sandstone, a largely silica-cemented, subarkose sandstone demonstrate it is less sensitive to chemical environment than Entrada Sandstone, a silty, clay-rich sandstone. The presence of de-ionized water lowers KIC by approximately 20% and SCI 30% in the Aztec Sandstone relative to tests performed in air, whereas the Entrada Sandstone shows reductions on the order of 70% and 90%, respectively. These results indicate that rock composition influences the chemical-mechanical response to deformation, and that the relative chemical reactivity of target reservoirs should be recognized in context of CO2 sequestration. In general, inert grains and cements such as quartz will be less sensitive to the changing subsurface environment than carbonates and clays.

  17. Mechanics and mechano-biology of fracture healing in normal and osteoporotic bone.

    PubMed

    Augat, Peter; Simon, Ulrich; Liedert, Astrid; Claes, Lutz

    2005-03-01

    Fracture repair, which aims at regaining the functional competence of a bone, is a complex and multifactorial process. For the success of fracture repair biology and mechanics are of immense importance. The biological and mechanical environments must be compatible with the processes of cell and tissue proliferation and differentiation. The biological environment is characterized by the vascular supply and by many biochemical components, the biochemical milieu. A good vascular supply is a prerequisite for the initiation of the fracture repair process. The biochemical milieu involves complex interactions among local and systemic regulatory factors such as growth factors or cytokines. The mechanical environment is determined by the local stress and strain within the fracture. However, the local stress and strain is not accessible, and the mechanical environment, therefore, is described by global mechanical factors, e.g., gap size or interfragmentary movement. The relationship between local stress and strain and the global mechanical factors can be obtained by numerical models (Finite Element Model). Moreover, there is considerable interaction between biological factors and mechanical factors, creating a biomechanical environment for the fracture healing process. The biomechanical environment is characterized by osteoblasts and osteocytes that sense the mechanical signal and express biological markers, which effect the repair process. This review will focus on the effects of biomechanical factors on fracture repair as well as the effects of age and osteoporosis.

  18. Integrity of the osteocyte bone cell network in osteoporotic fracture: Implications for mechanical load adaptation

    NASA Astrophysics Data System (ADS)

    Kuliwaba, J. S.; Truong, L.; Codrington, J. D.; Fazzalari, N. L.

    2010-06-01

    The human skeleton has the ability to modify its material composition and structure to accommodate loads through adaptive modelling and remodelling. The osteocyte cell network is now considered to be central to the regulation of skeletal homeostasis; however, very little is known of the integrity of the osteocyte cell network in osteoporotic fragility fracture. This study was designed to characterise osteocyte morphology, the extent of osteocyte cell apoptosis and expression of sclerostin protein (a negative regulator of bone formation) in trabecular bone from the intertrochanteric region of the proximal femur, for postmenopausal women with fragility hip fracture compared to age-matched women who had not sustained fragility fracture. Osteocyte morphology (osteocyte, empty lacunar, and total lacunar densities) and the degree of osteocyte apoptosis (percent caspase-3 positive osteocyte lacunae) were similar between the fracture patients and non-fracture women. The fragility hip fracture patients had a lower proportion of sclerostin-positive osteocyte lacunae in comparison to sclerostin-negative osteocyte lacunae, in contrast to similar percent sclerostin-positive/sclerostin-negative lacunae for non-fracture women. The unexpected finding of decreased sclerostin expression in trabecular bone osteocytes from fracture cases may be indicative of elevated bone turnover and under-mineralisation, characteristic of postmenopausal osteoporosis. Further, altered osteocytic expression of sclerostin may be involved in the mechano-responsiveness of bone. Optimal function of the osteocyte cell network is likely to be a critical determinant of bone strength, acting via mechanical load adaptation, and thus contributing to osteoporotic fracture risk.

  19. Fracture Mechanics Analyses of the Slip-Side Joggle Regions of Wing-Leading-Edge Panels

    NASA Technical Reports Server (NTRS)

    Raju, Ivatury S.; Knight, Norman F., Jr.; Song, Kyongchan; Phillips, Dawn R.

    2011-01-01

    The Space Shuttle wing-leading edge consists of panels that are made of reinforced carbon-carbon. Coating spallation was observed near the slip-side region of the panels that experience extreme heating. To understand this phenomenon, a root-cause investigation was conducted. As part of that investigation, fracture mechanics analyses of the slip-side joggle regions of the hot panels were conducted. This paper presents an overview of the fracture mechanics analyses.

  20. Mechanical behavior and fracture characteristics of off-axis fiber composites. 2: Theory and comparisons

    NASA Technical Reports Server (NTRS)

    Chamis, C. C.; Sinclair, J. H.

    1978-01-01

    The mechanical behavior and stresses inducing fracture modes of unidirectional high-modulus graphite-fiber/epoxy composites subjected to off-axis tensile loads were investigated theoretically. The investigation included the use of composite mechanics, combined-stress failure criteria, and finite-element stress analysis. The results are compared with experimental data and led to the formulation of criteria and convenient plotting procedures for identifying, characterizing, and quantifying these fracture modes.

  1. MECHANICAL FAILURE OF THE LONG GAMMA NAIL IN TWO PROXIMAL FEMUR FRACTURES

    PubMed Central

    Najibi, Soheil; Mark, Lemos; Fehnel, David

    2010-01-01

    Mechanical failure of the long gamma nail was encountered in two elderly patients with proximal femur fractures over a 6-month period. One of the patients had a known history of lymphoma. The other patient had a history of rheumatoid arthritis but no history of cancer or other metabolic bone disease. Both nails failed at the junction of the compression screw and the nail. The angle of failure of the nail was the same in both cases. The index of suspicion for imminent mechanical failure of the gamma nail should be higher in pathologic fractures and fractures which are malreduced during nailing. PMID:21046000

  2. Mechanical failure of the long gamma nail in two proximal femur fractures.

    PubMed

    Najibi, Soheil; Mark, Lemos; Fehnel, David

    2010-01-01

    Mechanical failure of the long gamma nail was encountered in two elderly patients with proximal femur fractures over a 6-month period. One of the patients had a known history of lymphoma. The other patient had a history of rheumatoid arthritis but no history of cancer or other metabolic bone disease. Both nails failed at the junction of the compression screw and the nail. The angle of failure of the nail was the same in both cases. The index of suspicion for imminent mechanical failure of the gamma nail should be higher in pathologic fractures and fractures which are malreduced during nailing. PMID:21046000

  3. Variations in Fracturing Mechanisms Observed by Broadband Microseismic Monitoring of Hydraulic Treatment

    NASA Astrophysics Data System (ADS)

    Tang, Y.; Niu, F.; Chen, H.; Zuo, Q.

    2015-12-01

    Hydraulic fracturing is the key stimulation technology to improve unconventional hydrocarbon recovery nowadays. Stimulation increases permeability of tight formations by causing fractures at depth. It involves pumping high-pressure fluid into reservoir rocks to force the opening of cracks, which could allow oil and gas to flow freely. The progress of a fracturing operation must be monitored carefully as fracturing could activate existing faults, leading the fluid mixed with chemicals to propagate beyond the targeted treatment zone. In order to study dynamic processes involved in hydraulic fracturing, we deployed a small-scale seismic array consisting of 22 broadband seismographs at the surface above a hydraulic fracturing area to monitor the whole fracturing progress. We made continuous recording for 20 days, and detected a total of 961 microseismic events with relatively high signal-to-noise ratio (SNR) recordings. We found that these events occurred either during the fracturing operation or after the fluid pumping. Some of the events also do not seem to be directly induced by the pumping, based on their locations and sizes. We determined the focal mechanisms of all events using the P-wave polarity data, and found that both the microseismicity and their focal mechanisms exhibit significant spatial and temporal variations. This variability can be associated with the hydraulic treatment, pre-existing faults, as well as the evolving stress field during the treatment. We computed the Coulomb stress changes of the observed seismicity to seek its contribution to the observed seismic variability.

  4. Effects of cement augmentation on the mechanical stability of multilevel spine after vertebral compression fracture

    PubMed Central

    Wang, Tian; Pelletier, Matthew H.; Walsh, William R.

    2016-01-01

    Background Studies on the effects of cement augmentation or vertebroplasty on multi-level spine after vertebral compression fractures are lacking. This paper seeks to establish a 3-vertebrae ovine model to determine the impact of compression fracture on spine biomechanics, and to discover if cement augmentation can restore mechanical stability to fractured spine. Methods Five lumbar spine segments (L1-L3) were obtained from 5-year-old female Merino sheep. Standardized wedge-compression fractures were generated in each L2 vertebra, and then augmented with polymethyl methacrylate (PMMA) cement mixed with 30% barium sulphate powder. Biomechanical pure moment testing in axial rotation (AR), flexion/extension (FE) and lateral bending (LB) was carried out in the intact, fractured and repaired states. Range of motion (ROM) and neutral zone (NZ) parameters were compared, and plain radiographs taken at every stage. Results Except for a significant increase in ROM between the intact and fractured states in AR between L1 and L2 (P<0.05), there were no other significant differences in ROM or NZ between the other groups. There was a trend towards an increase in ROM and NZ in all directions after fracture, but this did not reach significance. Normal biomechanics was only minimally restored after augmentation. Conclusions Results suggest that cement augmentation could not restore mechanical stability of fractured spine. Model-specific factors may have had a role in these findings. Caution should be exercised when applying these results to humans. PMID:27683707

  5. Influence of age on mechanical properties of healing fractures and intact bones in rats.

    PubMed

    Ekeland, A; Engesoeter, L B; Langeland, N

    1982-08-01

    Mechanical properties of fractured and intact femora have been studied in young and adult, male rats. A standardized, closed, mid-diaphyseal fracture was produced in the left femur, the right femur serving as control. The fracture was left to heal without immobilization. At various intervals, both fractured and intact femora were loaded in torsion until failure. The fractured femora regained the mechanical properties of the contralateral, intact bones after about 4 weeks in young and after about 12 weeks in adult rats. For intact bones, both the ultimate torsional moment (strength) and the torsional stiffness increased with age of the animals, whereas the ultimate torsional angle remained unchanged. For bone as a material, however, the ultimate torsional stress (strength) and the modulus of rigidity (stiffness) increased with age only in young rats, being almost constant in the adult animals. The various biomechanical parameters of the healing fractures did not reach those of the contralateral, intact bones simultaneously. The torsional moment required to twist a healing femoral fracture 20 degrees (0.35 radians), a deformation close to what an intact femur can resist, proved to be a functional and simple measure of the degree of fracture repair in rats.

  6. Effects of cement augmentation on the mechanical stability of multilevel spine after vertebral compression fracture

    PubMed Central

    Wang, Tian; Pelletier, Matthew H.; Walsh, William R.

    2016-01-01

    Background Studies on the effects of cement augmentation or vertebroplasty on multi-level spine after vertebral compression fractures are lacking. This paper seeks to establish a 3-vertebrae ovine model to determine the impact of compression fracture on spine biomechanics, and to discover if cement augmentation can restore mechanical stability to fractured spine. Methods Five lumbar spine segments (L1-L3) were obtained from 5-year-old female Merino sheep. Standardized wedge-compression fractures were generated in each L2 vertebra, and then augmented with polymethyl methacrylate (PMMA) cement mixed with 30% barium sulphate powder. Biomechanical pure moment testing in axial rotation (AR), flexion/extension (FE) and lateral bending (LB) was carried out in the intact, fractured and repaired states. Range of motion (ROM) and neutral zone (NZ) parameters were compared, and plain radiographs taken at every stage. Results Except for a significant increase in ROM between the intact and fractured states in AR between L1 and L2 (P<0.05), there were no other significant differences in ROM or NZ between the other groups. There was a trend towards an increase in ROM and NZ in all directions after fracture, but this did not reach significance. Normal biomechanics was only minimally restored after augmentation. Conclusions Results suggest that cement augmentation could not restore mechanical stability of fractured spine. Model-specific factors may have had a role in these findings. Caution should be exercised when applying these results to humans.

  7. How tough is bone? Application of elastic-plastic fracture mechanics to bone.

    PubMed

    Yan, Jiahau; Mecholsky, John J; Clifton, Kari B

    2007-02-01

    Bone, with a hierarchical structure that spans from the nano-scale to the macro-scale and a composite design composed of nano-sized mineral crystals embedded in an organic matrix, has been shown to have several toughening mechanisms that increases its toughness. These mechanisms can stop, slow, or deflect crack propagation and cause bone to have a moderate amount of apparent plastic deformation before fracture. In addition, bone contains a high volumetric percentage of organics and water that makes it behave nonlinearly before fracture. Many researchers used strength or critical stress intensity factor (fracture toughness) to characterize the mechanical property of bone. However, these parameters do not account for the energy spent in plastic deformation before bone fracture. To accurately describe the mechanical characteristics of bone, we applied elastic-plastic fracture mechanics to study bone's fracture toughness. The J integral, a parameter that estimates both the energies consumed in the elastic and plastic deformations, was used to quantify the total energy spent before bone fracture. Twenty cortical bone specimens were cut from the mid-diaphysis of bovine femurs. Ten of them were prepared to undergo transverse fracture and the other 10 were prepared to undergo longitudinal fracture. The specimens were prepared following the apparatus suggested in ASTM E1820 and tested in distilled water at 37 degrees C. The average J integral of the transverse-fractured specimens was found to be 6.6 kPa m, which is 187% greater than that of longitudinal-fractured specimens (2.3 kPa m). The energy spent in the plastic deformation of the longitudinal-fractured and transverse-fractured bovine specimens was found to be 3.6-4.1 times the energy spent in the elastic deformation. This study shows that the toughness of bone estimated using the J integral is much greater than the toughness measured using the critical stress intensity factor. We suggest that the J integral method is

  8. Spinal fractures in recreational bobsledders: an unexpected mechanism of injury

    PubMed Central

    Severson, Erik P.; Sofianos, Dmitri A.; Powell, Amy; Daubs, Michael; Patel, Rakesh; Patel, Alpesh A.

    2012-01-01

    Study design: Retrospective case series and literature review. Objective: To report and discuss spinal fractures occurring in recreational bobsledders. Summary of background data: Spinal fractures have been commonly described following traumatic injury during a number of recreational sports. Reports have focused on younger patients and typically involved high-impact sports or significant injuries. With an aging population and a wider array of recreational sports, spinal injuries may be seen after seemingly benign activities and without a high-impact injury. Methods: A retrospective review of two patients and review of the literature was performed. Results: Two patients with spinal fractures after recreational bobsledding were identified. Both patients, aged 57 and 54 years, noticed a simultaneous onset of severe back pain during a routine turn on a bobsled track. Neither was involved in a high-impact injury during the event. Both patients were treated conservatively with resolution of symptoms. An analysis of the bobsled track revealed that potential forces imparted to the rider may be greater than the yield strength of vertebral bone. Conclusions: Older athletes may be at greater risk for spinal fracture associated with routine recreational activities. Bobsledding imparts large amounts of force during routine events and may result in spinal trauma. Older patients, notably those with osteoporosis or metabolic bone disease, should be educated about the risks associated with seemingly benign recreational sports. PMID:23230417

  9. Baroreflex sensitivity: methods, mechanisms, and prognostic value.

    PubMed

    Vanoli, E; Adamson, P B

    1994-03-01

    A large bulk of data collected over the last 25 years links reflex autonomic activation during acute myocardial ischemia with risk of developing lethal arrhythmias. Specifically, evidence obtained in an experimental preparation in chronically infarcted dogs supported the concept that sympathetic hyperactivity enhances likelihood for ventricular tachyarrhythmias, vagal activation exerts protective effects. Based on this knowledge, it was first proposed by our group that analysis of autonomic control of heart rate could provide information relevant to risk stratification in post-myocardial infarction individuals. Among several possibilities, baroreflex sensitivity was evaluated by correlating blood pressure rise induced by bolus injections of phenylephrine with the consequent beat to beat R-R interval lengthening. Experimental studies involving direct recordings from single neural vagal fibers directed to the heart documented that baroreflex sensitivity closely reproduces cardiac vagal activity. In a large group of conscious dogs it was shown that a depressed baroreflex sensitivity was highly predictive of the risk for ventricular, fibrillation during acute myocardial ischemia. The clinical prognostic value of baroreflex sensitivity has already been confirmed in pilot studies conducted by different groups of investigators. Overall, the phenylephrine test has been performed in several hundred patients with no reports of side effects. An ongoing multicenter study, the ATRAMI (Autonomic Tone and Reflexes After Myocardial Infarction) is aimed to definitively assess the predictive value of baroreflex sensitivity and heart rate variability in patients with a prior myocardial infarction. While the enrollment is still ongoing, this study has already provided an important methodological information about the possibility of using non invasive technique to record blood pressure by means of FINAPRES, to evaluate baroreflex sensitivity. Comparison among 142 tests performed with

  10. Correlating laboratory observations of fracture mechanical properties to hydraulically-induced microseismicity in geothermal reservoirs.

    SciTech Connect

    Stephen L. Karner, Ph.D

    2006-02-01

    To date, microseismicity has provided an invaluable tool for delineating the fracture network produced by hydraulic stimulation of geothermal reservoirs. While the locations of microseismic events are of fundamental importance, there is a wealth of information that can be gleaned from the induced seismicity (e.g. fault plane solutions, seismic moment tensors, source characteristics). Closer scrutiny of the spatial and temporal evolution of seismic moment tensors can shed light on systematic characteristics of fractures in the geothermal reservoir. When related to observations from laboratory experiments, these systematic trends can be interpreted in terms of mechanical processes that most likely operate in the fracture network. This paper reports on mechanical properties that can be inferred from observations of microseismicity in geothermal systems. These properties lead to interpretations about fracture initiation, seismicity induced after hydraulic shut-in, spatial evolution of linked fractures, and temporal evolution of fracture strength. The correlations highlight the fact that a combination of temperature, stressing rate, time, and fluid-rock interactions can alter the mechanical and fluid transport properties of fractures in geothermal systems.

  11. Dynamic tuning of chemiresistor sensitivity using mechanical strain

    SciTech Connect

    Martin, James E; Read, Douglas H

    2014-09-30

    The sensitivity of a chemiresistor sensor can be dynamically tuned using mechanical strain. The increase in sensitivity is a smooth, continuous function of the applied strain, and the effect can be reversible. Sensitivity tuning enables the response curve of the sensor to be dynamically optimized for sensing analytes, such as volatile organic compounds, over a wide concentration range.

  12. Radiology of Fractures in Intoxicated Emergency Department Patients: Locations, Mechanisms, Presentation, and Initial Interpretation Accuracy

    PubMed Central

    Morita, Yuka; Nozaki, Taiki; Starkey, Jay; Okajima, Yuka; Ohde, Sachiko; Matsusako, Masaki; Yoshioka, Hiroshi; Saida, Yukihisa; Kurihara, Yasuyuki

    2015-01-01

    Abstract The purpose of this study was to investigate the relationship of alcohol intoxication to time-to-presentation following injury, fracture type, mechanism of injury leading to fracture, and initial diagnostic radiology interpretation performance of emergency physicians versus diagnostic radiologists in patients who present to the emergency department (ED) and are subsequently diagnosed with fracture. Medical records of 1286 patients who presented to the ED and were diagnosed with fracture who also underwent plain film or computed tomography (CT) imaging were retrospectively reviewed. The subjects were divided into intoxicated and sober groups. Patient characteristics, injury-to-presentation time, fracture location, and discrepancies between initial clinical and radiological evaluations were compared. Of 1286 subjects, 181 patients were included in the intoxicated group. Only intoxicated patients presented with head/neck fractures more than 24 hours after injury. The intoxicated group showed a higher rate of head/neck fractures (skull 23.2% vs 5.8%, face and orbit 30.4% vs 9.5%; P < 0.001) and a lower rate of extremity injuries. The rate of nondiagnosis of fractures by emergency physicians later identified by radiologists was the same in both groups (7.7% vs 7.7%, P = 0.984). While the same proportion of intoxicated patients presented more than 24 hours following injury, only intoxicated patients presented with craniofacial and cervical spinal fractures during this period. Alcohol-related injuries are more often associated with head/neck fractures but less extremity injuries. The rate of fractures missed by emergency physicians but later diagnosed by radiologists was the same in intoxicated and sober patients.

  13. E. coli RS2GFP Retention Mechanisms in Laboratory-Scale Fractured Rocks: A Statistical Model

    NASA Astrophysics Data System (ADS)

    Rodrigues, S. N.; Qu, J.; Dickson, S. E.

    2011-12-01

    With billions of gallons of groundwater being withdrawn every day in the US and Canada, it is imperative to understand the mechanisms which jeopardize this resource and the health of those who rely on it. Porous media aquifers have typically been considered to provide significant filtration of particulate matter (e.g. microorganisms), while the fractures in fractured rock aquifers and aquitards are considered to act as contaminant highways allowing a large fraction of pathogens to travel deep into an aquifer relatively quickly. Recent research results indicate that fractured rocks filter out more particulates than typically believed. The goal of the research presented here is to quantify the number of E. coli RS2GFP retained in a single, saturated, laboratory-scale fracture, and to relate the retention of E. coli RS2GFP to the aperture field characteristics and groundwater flow rate. To achieve this goal, physical experiments were conducted at the laboratory-scale to quantify the retention of E. coli RS2GFP through several single, saturated, dolomitic limestone fractures under a range of flow rates. These fractures were also cast with a transparent epoxy in order to visualize the transport mechanisms in the various different aperture fields. The E. coli RS2GFP is tagged with a green-fluorescent protein (GFP) that is used to obtain visualization data when excited by ultraviolet light. A series of experiments was conducted, each of which involved the release of a known number of E. coli RS2GFP at the upstream end of the fracture and measuring the effluent concentration profile. These experiments were conducted using both the natural rock and transparent cast of several different aperture fields, under a range of flow rates. The effects of different aperture field characteristics and flow rates on the retention of E. coli RS2GFP will be determined by conducting a statistical analysis of the retention data under different experimental conditions. The images captured

  14. Mechanisms of orbital floor fractures: a clinical, experimental, and theoretical study.

    PubMed Central

    Bullock, J D; Warwar, R E; Ballal, D R; Ballal, R D

    1999-01-01

    PURPOSE: The purpose of this study was to investigate the two accepted mechanisms of the orbital blow-out fracture (the hydraulic and the buckling theories) from a clinical, experimental, and theoretical standpoint. METHODS: Clinical cases in which blow-out fractures resulted from both a pure hydraulic mechanism and a pure buckling mechanism are presented. Twenty-one intact orbital floors were obtained from human cadavers. A metal rod was dropped, experimentally, onto each specimen until a fracture was produced, and the energy required in each instance was calculated. A biomathematical model of the human bony orbit, depicted as a thin-walled truncated conical shell, was devised. Two previously published (by the National Aeronautics Space Administration) theoretical structural engineering formulas for the fracture of thin-walled truncated conical shells were used to predict the energy required to fracture the bone of the orbital floor via the hydraulic and buckling mechanisms. RESULTS: Experimentally, the mean energy required to fracture the bone of the human cadaver orbital floor directly was 78 millijoules (mj) (range, 29-127 mj). Using the engineering formula for the hydraulic theory, the predicted theoretical energy is 71 mj (range, 38-120 mj); for the buckling theory, the predicted theoretical energy is 68 mj (range, 40-106 mj). CONCLUSION: Through this study, we have experimentally determined the amount of energy required to fracture the bone of the human orbital floor directly and have provided support for each mechanism of the orbital blow-out fracture from a clinical and theoretical basis. Images FIGURE 2 FIGURE 3 FIGURE 4 FIGURE 5A FIGURE 5B FIGURE 5E FIGURE 5F PMID:10703119

  15. Investigation of the fracture mechanics of boride composites

    NASA Technical Reports Server (NTRS)

    Kaufman, L.; Clougherty, E. V.; Nesor, H.

    1971-01-01

    Fracture energies of WC-6Co, Boride 5 (ZrB2+SiC), Boride 8(ZrB2+SiC+C) and Boride 8-M2(ZrB2+SiC+C) were measured by slow bend and impact tests of notched charpy bars. Cobalt bonded tungsten carbide exhibited impact energies of 0.76 ft-lb or 73.9 in-lb/square inch. Boride 5 and the Boride 8 exhibit impact energies one third and one quarter of that observed for WC-6Co comparing favorably with measurements for SiC and Si3N4. Slow bend-notched bar-fracture energies for WC-6Co were near 2.6 in-lb/square inch or 1/20 the impact energies. Slow bend energies for Boride 8-M2, Boride 8 and Boride 5 were 58%, 42% and 25% of the value observed for WC-6Co. Fractograph showed differences for WC-6Co where slow bend testing resulted in smooth transgranular cleavage while samples broken by impact exhibited intergranular failures. By contrast the boride fractures showed no distinction based on testing method. Fabrication studies were conducted to effect alteration of the boride composites by alloying and introduction of graphite cloth.

  16. Incidence, mechanism of injury, and treatment of fractures of the patella in children.

    PubMed

    Ray, J M; Hendrix, J

    1992-04-01

    Fractures of the patella in skeletally immature patients are rare. The charts of 185 patients treated for patella fractures at the University of Kentucky Medical Center between 1976 and 1988 were retrospectively reviewed. The 12 patients of these 185 aged 8 to 16 years were included in this study. The incidence was calculated to be 6.5% of all patella fractures. All patients studied were male with an average age of 12.7 years. Sleeve fractures were the most common type of patella fracture observed (five), followed by transverse fractures (four). Ten of the 12 cases required operative management ranging from irrigation and debridement to open reduction and internal fixation. Partial patellectomy was performed when indicated. Indications for operative management in this age group were similar to those for adults. As in adults, the mechanism of injury was predominantly motor vehicle and motorcycle crashes. Laws requiring seatbelt restraints for children should have a positive effect on the incidence of such fractures resulting from dashboard injuries. One mechanism of injury not reported previously was that of a flexed knee striking the gym wall after performing a basketball lay-up because the basket was placed flush with the wall.

  17. Insights into the fracture mechanisms and strength of amorphous and nanocomposite carbon.

    PubMed

    Fyta, M G; Remediakis, I N; Kelires, P C; Papaconstantopoulos, D A

    2006-05-12

    Tight-binding molecular dynamics simulations shed light into the fracture mechanisms and the ideal strength of tetrahedral amorphous carbon and of nanocomposite carbon containing diamond crystallites, two of the hardest materials. It is found that fracture in the nanocomposites, under tensile or shear load, occurs intergrain and so their ideal strength is similar to the pure amorphous phase. The onset of fracture takes place at weakly bonded sites in the amorphous matrix. On the other hand, the nanodiamond inclusions significantly enhance the elastic moduli, which approach those of diamond. PMID:16712372

  18. Fracture mechanics; Proceedings of the Nineteenth National Symposium, San Antonio, TX, June 30-July 2, 1986

    SciTech Connect

    Cruse, T.A.

    1988-01-01

    The papers contained in this volume provide an overview of current theoretical and experimental research in the field of fracture mechanics. Topics discussed include three-dimensional issues, computational and analytical issues, damage tolerance and fatigue, elastoplastic fracture, dynamic inelastic fracture, and crack arrest theory and applications. Papers are presented on approximate methods for analysis of dynamic crack growth and arrest, constraint-loss model for the growth of surface fatigue cracks, fatigue crack growth in aircraft main landing gear wheels, and near-threshold crack growth in nickel-base superalloys.

  19. Climate sensitivity: Analysis of feedback mechanisms

    NASA Astrophysics Data System (ADS)

    Hansen, J.; Lacis, A.; Rind, D.; Russell, G.; Stone, P.; Fung, I.; Ruedy, R.; Lerner, J.

    We study climate sensitivity and feedback processes in three independent ways: (1) by using a three dimensional (3-D) global climate model for experiments in which solar irradiance S0 is increased 2 percent or CO2 is doubled, (2) by using the CLIMAP climate boundary conditions to analyze the contributions of different physical processes to the cooling of the last ice age (18K years ago), and (3) by using estimated changes in global temperature and the abundance of atmospheric greenhouse gases to deduce an empirical climate sensitivity for the period 1850-1980. Our 3-D global climate model yields a warming of ˜4°C for either a 2 percent increase of S0 or doubled CO2. This indicates a net feedback factor of f = 3-4, because either of these forcings would cause the earth's surface temperature to warm 1.2-1.3°C to restore radiative balance with space, if other factors remained unchanged. Principal positive feedback processes in the model are changes in atmospheric water vapor, clouds and snow/ice cover. Feedback factors calculated for these processes, with atmospheric dynamical feedbacks implicitly incorporated, are respectively fwater vapor ˜ 1.6, fclouds ˜ 1.3 and fsnow/ice ˜ 1.1 with the latter mainly caused by sea ice changes. A number of potential feedbacks, such as land ice cover, vegetation cover and ocean heat transport were held fixed in these experiments. We calculate land ice, sea ice and vegetation feedbacks for the 18K climate to be fland ice ˜ 1.2-1.3, fsea ice ˜ 1.2 and fvegetation ˜ 1.05-1.1 from their effect on the radiation budget at the top of the atmosphere. This sea ice feedback at 18K is consistent with the smaller fsnow/ice ˜ 1.1 in the S0 and CO2 experiments, which applied to a warmer earth with less sea ice. We also obtain an empirical estimate of f = 2-4 for the fast feedback processes (water vapor, clouds, sea ice) operating on 10-100 year time scales by comparing the cooling due to slow or specified changes (land ice, C02

  20. The fracture mechanics of human bone: influence of disease and treatment

    PubMed Central

    Zimmermann, Elizabeth A; Busse, Björn; Ritchie, Robert O

    2015-01-01

    Aging and bone diseases are associated with increased fracture risk. It is therefore pertinent to seek an understanding of the origins of such disease-related deterioration in bone's mechanical properties. The mechanical integrity of bone derives from its hierarchical structure, which in healthy tissue is able to resist complex physiological loading patterns and tolerate damage. Indeed, the mechanisms through which bone derives its mechanical properties make fracture mechanics an ideal framework to study bone's mechanical resistance, where crack-growth resistance curves give a measure of the intrinsic resistance to the initiation of cracks and the extrinsic resistance to the growth of cracks. Recent research on healthy cortical bone has demonstrated how this hierarchical structure can develop intrinsic toughness at the collagen fibril scale mainly through sliding and sacrificial bonding mechanisms that promote plasticity. Furthermore, the bone-matrix structure develops extrinsic toughness at much larger micrometer length-scales, where the structural features are large enough to resist crack growth through crack-tip shielding mechanisms. Although healthy bone tissue can generally resist physiological loading environments, certain conditions such as aging and disease can significantly increase fracture risk. In simple terms, the reduced mechanical integrity originates from alterations to the hierarchical structure. Here, we review how human cortical bone resists fracture in healthy bone and how changes to the bone structure due to aging, osteoporosis, vitamin D deficiency and Paget's disease can affect the mechanical integrity of bone tissue. PMID:26380080

  1. Fracture Mechanisms of Layer-By-Layer Polyurethane/Poly(Acrylic Acid) Nanocomposite

    NASA Astrophysics Data System (ADS)

    Kheng, Eugene R.

    A layer-by-layer(LBL) manufactured material is examined in detail in this thesis. Improvements are made to the method of its manufacture. Efforts are made to understand its fracture mechanisms and take advantage of these fracture mechanisms in the absorption of impact energy. A novel series of experiments has been performed on LBL manufactured thin films to demonstrate their unique fracture mechanisms. Polyurethane/Poly(Acrylic Acid) (PU/PAA) and PU/PAA/(PU/Clay)5 nanocomposite films readily undergo Interlaminar mode II fracture, because of the relatively weak elctrostatic bonds between monolayers. Tensile tests performed while under observation by a scanning electron microscope demonstrate the tendency of these nanocomposite films to undergo interlaminar mode II fracture even when loads are applied in the plane of nanocomposite film. It is concluded that these mechanisms of energy dissipation are responsible for the enhanced toughness of these films when used as layers between glass blocks in the prevention of impact damage to the glass. A novel automated manufacturing facility has been designed and built to deposit large sheets of Layer-by-Layer nanocomposite film. These large sheets are incorporated into a borosillicate glass composite in order to compare the ballistic characteristics of LBL PU based nanocomposite films to a single cast layer of polyurethane. It is demonstrated that shear fracture is the mode of failure in the blocks containing the nanocomposite film. The shear fracture surface in the nanocomposite after it has undergone a ballistic impact is characterized. Additional experiments are performed to characterize the interlaminar fracture stresses and toughnesses of the nanocomposite LBL layers, to assist in the implementation of a numerical crack band model that describes the nanocomposite film. The computational model predicts the failure of the ballistic nanocomposite samples, and the predicted V50 velocity is found to be in good agreement with

  2. Development and fracture mechanics data for 6Al-6V-2 Sn titanium alloy

    NASA Technical Reports Server (NTRS)

    Fiftal, C. F.; Beck, E. J.

    1974-01-01

    Fracture mechanics properties of 6Al-6V-2Sn titanium in the annealed, solution-treated, and aged condition are presented. Tensile, fracture toughness, cyclic flaw growth, and sustained-load threshold tests were conducted. Both surface flaw and compact tension-specimen geometries were employed. Temperatures and/or environments used were -65 F (220 K) air, ambient, 300 F (422 K) air, and room-temperature air containing 10 and 100% relative humidity.

  3. Association of microstructural and mechanical properties of cancellous bone and their fracture risk assessment tool scores.

    PubMed

    Wu, Dengke; Li, Xin; Tao, Cheng; Dai, Ruchun; Ni, Jiangdong; Liao, Eryuan

    2015-01-01

    This study is to investigate the association between fracture probabilities determined by using the fracture risk assessment tool (FRAX) and the microstructure and mechanical properties of femoral bone trabecula in osteoporosis (OP) and osteoarthritis (OA) patients with hip replacements. By using FRAX, we evaluated fracture risks of the 102 patients with bone replacements. Using micro CT scanning, we obtained the analysis parameters of microstructural properties of cancellous bone. Through morphometric observations, fatigue tests and compression tests, we obtained parameters of mechanical properties of cancellous bones. Relevant Pearson analysis was performed to investigate the association between the fracture probability and the microstructure and mechanical properties of femoral bone trabecula in patients. Fifteen risk factors in FRAX were compared between OP and OA patients. FRAX hip fracture risk score and major osteoporotic in OP and OA patients were significantly different. FRAX was associated with tissue bone mineral density and volumetric bone mineral density. Our study suggests that the probabilities of major osteoporotic and hip fracture using FRAX is associated with bone mass but not with micro bone quality. PMID:26064297

  4. Localized force application reveals mechanically sensitive domains of Piezo1

    PubMed Central

    Wu, Jason; Goyal, Raman; Grandl, Jörg

    2016-01-01

    Piezos are mechanically activated ion channels that function as sensors of touch and pressure in various cell types. However, the precise mechanism and structures mediating mechanical activation and subsequent inactivation have not yet been identified. Here we use magnetic nanoparticles as localized transducers of mechanical force in combination with pressure-clamp electrophysiology to identify mechanically sensitive domains important for activation and inactivation. PMID:27694883

  5. Results of fracture mechanics analyses of the ederer cranes in the device assembly facility using reduced static fracture-toughness values

    SciTech Connect

    Dalder, E. N. C.

    1996-11-01

    The effects of a decreased static fracture-toughness value from that used in the previous fracture-mechanics analyses of the Ederer cranes in the Device Assembly Facility were examined to see what effects, if any, would be exerted on the fatigue crack growth and fracture behavior of the cranes. In particular, the behavior of the same 3 critical locations on the lower flanges of the load beams of the Ederer 5 ton and 4 ton cranes, were examined, with the reduced static fracture-toughness value.

  6. Updated Fatigue-Crack-Growth And Fracture-Mechanics Software

    NASA Technical Reports Server (NTRS)

    Forman, Royce G.; Shivakumar, Venkataraman; Newman, James C., Jr.

    1995-01-01

    NASA/FLAGRO 2.0 developed as analytical aid in predicting growth and stability of preexisting flaws and cracks in structural components of aerospace systems. Used for fracture-control analysis of space hardware. Organized into three modules to maximize efficiency in operation. Useful in: (1) crack-instability/crack-growth analysis, (2) processing raw crack-growth data from laboratory tests, and (3) boundary-element analysis to determine stresses and stress-intensity factors. Written in FORTRAN 77 and ANSI C.

  7. Fracture mechanics analyses of ceramic/veneer interface under mixed-mode loading.

    PubMed

    Wang, Gaoqi; Zhang, Song; Bian, Cuirong; Kong, Hui

    2014-11-01

    Few studies have focused on the interface fracture performance of zirconia/veneer bilayered structure, which plays an important role in dental all-ceramic restorations. The purpose of this study was to evaluate the fracture mechanics performance of zirconia/veneer interface in a wide range of mode-mixities (at phase angles ranging from 0° to 90°), and to examine the effect of mechanical properties of the materials and the interface on the fracture initiation and crack path of an interfacial crack. A modified sandwich test configuration with an oblique interfacial crack was proposed and calibrated to choose the appropriate geometry dimensions by means of finite element analysis. The specimens with different interface inclination angles were tested to failure under three-point bending configuration. Interface fracture parameters were obtained with finite element analyses. Based on the interfacial fracture mechanics, three fracture criteria for crack kinking were used to predict crack initiation and propagation. In addition, the effects of residual stresses due to coefficient of thermal expansion mismatch between zirconia and veneer on the crack behavior were evaluated. The crack initiation and propagation were well predicted by the three fracture criteria. For specimens at phase angle of 0, the cracks propagated in the interface; whereas for all the other specimens the cracks kinked into the veneer. Compressive residual stresses in the veneer can improve the toughness of the interface structure. The results suggest that, in zirconia/veneer bilayered structure the veneer is weaker than the interface, which can be used to explain the clinical phenomenon that veneer chipping rate is larger than interface delamination rate. Consequently, a veneer material with larger fracture toughness is needed to decrease the failure rate of all-ceramic restorations. And the coefficient of thermal expansion mismatch of the substrates can be larger to produce larger compressive

  8. Two-parameter fracture mechanics: Theory and applications

    SciTech Connect

    O'Dowd, N.P. . Dept. of Mechanical Engineering); Shih, C.F. . Div. of Engineering)

    1993-02-01

    A family of self-similar fields provides the two parameters required to characterize the full range of high- and low-triaxiality crack tip states. The two parameters, J and Q, have distinct roles: J sets the size scale of the process zone over which large stresses and strains develop, while Q scales the near-tip stress distribution relative to a high triaxiality reference stress state. An immediate consequence of the theory is this: it is the toughness values over a range of crack tip constraint that fully characterize the material's fracture resistance. It is shown that Q provides a common scale for interpreting cleavage fracture and ductile tearing data thus allowing both failure modes to be incorporated in a single toughness locus. The evolution of Q, as plasticity progresses from small scale yielding to fully yielded conditions, has been quantified for several crack geometries and for a wide range of material strain hardening properties. An indicator of the robustness of the J-Q fields is introduced; Q as a field parameter and as a pointwise measure of stress level is discussed.

  9. Natural hydraulic fractures and the mechanical stratigraphy of shale-dominated strata

    NASA Astrophysics Data System (ADS)

    Imber, Jonathan; Armstrong, Howard; Atar, Elizabeth; Clancy, Sarah; Daniels, Susan; Grattage, Joshua; Herringshaw, Liam; Trabucho-Alexandre, João; Warren, Cassandra; Wille, Jascha; Yahaya, Liyana

    2016-04-01

    .2-4.3 fractures per m, consistent with field observations that this formation is more highly fractured than the Cleveland Ironstone Formation. Semi-quantitative estimates of the mineralogical "brittleness index" suggest the highly fractured, clay-rich Mulgrave Shale Member of the Whitby Mudstone Formation has a low brittleness. Our results are therefore inconsistent with the widely held assumption that natural fracture density is greatest within units characterised by a high brittleness index. We propose that stratigraphic variations in fracture densities are more likely to result from the different distributions of crack driving stresses; formations containing decimetre-scale, and most likely stiff, carbonate layers (such as the Cleveland Ironstone Formation) will have differing crack driving stresses compared with silt- and mudstone dominated successions (such as the Whitby Mudstone Formation). The high fracture density observed within the Mulgrave Shale Member is also consistent with propagation of natural hydraulic fractures driven by fluid overpressure caused by maturation of organic matter concentrated within this unit. The next step is to investigate the relative importance of maturation-driven overpressure v. mechanical heterogeneity by analysing the stratigraphic variations in fracture density within the underlying, organic-matter lean Redcar Mudstone Formation.

  10. Brittleness of twig bases in the genus Salix: fracture mechanics and ecological relevance.

    PubMed

    Beismann, H; Wilhelmi, H; Baillères, H; Spatz, H C; Bogenrieder, A; Speck, T

    2000-03-01

    The twig bases within the genus Salix were investigated. Brittleness of twig bases as defined in the literature neither correlates with Young's modulus nor with growth strains, which were measured for S. alba, S. fragilis and S. x rubens. For the species S. alba, S. appendiculata, S. eleagnos, S. fragilis, S. purpurea, S. triandra, S. viminalis, and S. x rubens, fracture surfaces of broken twigs were investigated and semiquantitatively described in terms of 'relative roughness' (ratio of rough area of fracture surface over whole area of fracture surface). The relative roughness clearly corresponds with the classification into brittle and nonbrittle species given in the literature. An attempt was made to quantify brittleness with mechanical tests. The absolute values of stress and strain do not correlate with the brittleness of the twig bases as defined by the relative roughness. However, the 'index stress' (ratio of stress at yield over stress at fracture) or the 'index strain' (ratio of strain at yield over strain at fracture), correlate well with the relative roughness. The graphic analysis of index stress against index strain reveals a straight line on which the eight species are ordered according to their brittleness. Depending on growth form and habitat, brittle twig bases of willows may function ecologically as mechanical safety mechanisms and, additionally, as a propagation mechanism.

  11. Fracture mechanics in fiber reinforced composite materials, taking as examples B/A1 and CRFP

    NASA Technical Reports Server (NTRS)

    Peters, P. W. M.

    1982-01-01

    The validity of linear elastic fracture mechanics and other fracture criteria was investigated with laminates of boron fiber reinforced aluminum (R/A1) and of carbon fiber reinforced epoxide (CFRP). Cracks are assessed by fracture strength Kc or Kmax (critical or maximum value of the stress intensity factor). The Whitney and Nuismer point stress criterion and average stress criterion often show that Kmax of fiber composite materials increases with increasing crack length; however, for R/A1 and CFRP the curve showing fracture strength as a function of crack length is only applicable in a small domain. For R/A1, the reason is clearly the extension of the plastic zone (or the damage zone n the case of CFRP) which cannot be described with a stress intensity factor.

  12. The Mechanical Benefit of Medial Support Screws in Locking Plating of Proximal Humerus Fractures

    PubMed Central

    Liu, Yanjie; Pan, Yao; Zhang, Wei; Zhang, Changqing; Zeng, Bingfang; Chen, Yunfeng

    2014-01-01

    Background The purpose of this study was to evaluate the biomechanical advantages of medial support screws (MSSs) in the locking proximal humeral plate for treating proximal humerus fractures. Methods Thirty synthetic left humeri were randomly divided into 3 subgroups to establish two-part surgical neck fracture models of proximal humerus. All fractures were fixed with a locking proximal humerus plate. Group A was fixed with medial cortical support and no MSSs; Group B was fixed with 3 MSSs but without medial cortical support; Group C was fixed with neither medial cortical support nor MSSs. Axial compression, torsional stiffness, shear stiffness, and failure tests were performed. Results Constructs with medial support from cortical bone showed statistically higher axial and shear stiffness than other subgroups examined (P<0.0001). When the proximal humerus was not supported by medial cortical bone, locking plating with medial support screws exhibited higher axial and torsional stiffness than locking plating without medial support screws (P≤0.0207). Specimens with medial cortical bone failed primarily by fracture of the humeral shaft or humeral head. Specimens without medial cortical bone support failed primarily by significant plate bending at the fracture site followed by humeral head collapse or humeral head fracture. Conclusions Anatomic reduction with medial cortical support was the stiffest construct after a simulated two-part fracture. Significant biomechanical benefits of MSSs in locking plating of proximal humerus fractures were identified. The reconstruction of the medial column support for proximal humerus fractures helps to enhance mechanical stability of the humeral head and prevent implant failure. PMID:25084520

  13. Relationship between microstructure, material distribution, and mechanical properties of sheep tibia during fracture healing process.

    PubMed

    Gao, Jiazi; Gong, He; Huang, Xing; Fang, Juan; Zhu, Dong; Fan, Yubo

    2013-01-01

    The aim of this study was to investigate the relationship between microstructural parameters, material distribution, and mechanical properties of sheep tibia at the apparent and tissue levels during the fracture healing process. Eighteen sheep underwent tibial osteotomy and were sacrificed at 4, 8, and 12 weeks. Radiographs and micro-computed tomography (micro-CT) scanning were taken for microstructural assessment, material distribution evaluation, and micro-finite element analysis. A displacement of 5% compressive strain on the longitudinal direction was applied to the micro-finite element model, and apparent and tissue-level mechanical properties were calculated. Principle component analysis and linear regression were used to establish the relationship between principle components (PCs) and mechanical parameters. Visible bony callus formation was observed throughout the healing process from radiographic assessment. Apparent mechanical property increased at 8 weeks, but tissue-level mechanical property did not increase significantly until 12 weeks. Three PCs were extracted from microstructural parameters and material distribution, which accounted for 87.592% of the total variation. The regression results showed a significant relationship between PCs and mechanical parameters (R>0.8, P<0.05). Results of this study show that microstructure and material distribution based on micro-CT imaging could efficiently predict bone strength and reflect the bone remodeling process during fracture healing, which provides a basis for exploring the fracture healing mechanism and may be used as an approach for fractured bone strength assessment.

  14. Non-double-couple mechanisms of microearthquakes induced by hydraulic fracturing

    NASA Astrophysics Data System (ADS)

    Šílený, Jan; Hill, David P.; Eisner, Leo; Cornet, Francois H.

    2009-08-01

    We have inverted polarity and amplitude information of representative microearthquakes to investigate source mechanisms of seismicity induced by hydraulic fracturing in the Carthage Cotton Valley, east Texas, gas field. With vertical arrays of four and eight three-component geophones in two monitoring wells, respectively, we were able to reliably determine source mechanisms of the strongest events with the best signal-to-noise ratio. Our analysis indicates predominantly non-double-couple source mechanisms with positive volumetric component consistent with opening cracks oriented close to expected hydraulic fracture orientation. Our observations suggest the induced events are directly the result of opening cracks by fluid injection, in contrast to many previous studies where the seismicity is interpreted to be primarily shearing caused by pore pressure diffusion into the surrounding rock or associated with shear stresses created at the hydraulic fracture tip.

  15. Non-double-couple mechanisms of microearthquakes induced by hydraulic fracturing

    USGS Publications Warehouse

    Sileny, J.; Hill, D.P.; Eisner, L.; Cornet, F.H.

    2009-01-01

    We have inverted polarity and amplitude information of representative microearthquakes to investigate source mechanisms of seismicity induced by hydraulic fracturing in the Carthage Cotton Valley, east Texas, gas field. With vertical arrays of four and eight three-component geophones in two monitoring wells, respectively, we were able to reliably determine source mechanisms of the strongest events with the best signal-to-noise ratio. Our analysis indicates predominantly non-double-couple source mechanisms with positive volumetric component consistent with opening cracks oriented close to expected hydraulic fracture orientation. Our observations suggest the induced events are directly the result of opening cracks by fluid injection, in contrast to many previous studies where the seismicity is interpreted to be primarily shearing caused by pore pressure diffusion into the surrounding rock or associated with shear stresses created at the hydraulic fracture tip. Copyright 2009 by the American Geophysical Union.

  16. Chondral fracture of the lateral trochlea of the femur occurring in an adolescent: mechanism of injury.

    PubMed

    Oohashi, Yoshikazu; Oohashi, Yoshinori

    2007-11-01

    The trochlea of the femur is a very unusual site for chondral fracture. Little is known of the mechanism of injuries confined to the articular cartilage of the trochlea of the femur. A very unusual case of chondral fracture of the lateral trochlea of the femur occurring in an adolescent is reported here. The mechanism by which this injury occurred could be evaluated in this patient. The cartilage on the convex surface of the lateral trochlea was likely avulsed proximally by shear force of the patella during rapid extension of the weight-bearing knee from a flexed position. From a viewpoint of mechanism, this injury differs from the more usual osteochondral or chondral fractures of the weight bearing area of the femoral condyle, which are usually accompanied by twisting forces.

  17. Elastic-plastic fracture mechanics of strength-mismatching

    SciTech Connect

    Parks, D.M.; Ganti, S.; McClintock, F.A.

    1996-12-31

    Approximate solutions to stress-fields are provided for a strength-mismatched interface crack in small-scale yielding (SSY) for non-hardening and low hardening materials. Variations of local deformation intensities, characterized by a J-type contour integral, are proposed. The softer material experiences a higher deformation intensity level, J{sub S}, while the harder material sees a much lower deformation intensity level, J{sub H}, compared to that obtained from the applied J near the respective homogeneous crack-tips. For a low hardening material, the stress fields are obtained by scaling from an elastic/perfectly-plastic problem, based on an effective mismatch, M{sub eff}, which is a function of mismatch, M, and the hardening exponent, n. Triaxial stress build-up is discussed quantitatively in terms of M. The influence of strength-mismatch on cleavage fracture is discussed using Weibull statistics.

  18. Micro-computed tomography assessment of fracture healing: relationships among callus structure, composition, and mechanical function.

    PubMed

    Morgan, Elise F; Mason, Zachary D; Chien, Karen B; Pfeiffer, Anthony J; Barnes, George L; Einhorn, Thomas A; Gerstenfeld, Louis C

    2009-02-01

    Non-invasive characterization of fracture callus structure and composition may facilitate development of surrogate measures of the regain of mechanical function. As such, quantitative computed tomography- (CT-) based analyses of fracture calluses could enable more reliable clinical assessments of bone healing. Although previous studies have used CT to quantify and predict fracture healing, it is unclear which of the many CT-derived metrics of callus structure and composition are the most predictive of callus mechanical properties. The goal of this study was to identify the changes in fracture callus structure and composition that occur over time and that are most closely related to the regain of mechanical function. Micro-computed tomography (microCT) imaging and torsion testing were performed on murine fracture calluses (n=188) at multiple post-fracture timepoints and under different experimental conditions that alter fracture healing. Total callus volume (TV), mineralized callus volume (BV), callus mineralized volume fraction (BV/TV), bone mineral content (BMC), tissue mineral density (TMD), standard deviation of mineral density (sigma(TMD)), effective polar moment of inertia (J(eff)), torsional strength, and torsional rigidity were quantified. Multivariate statistical analyses, including multivariate analysis of variance, principal components analysis, and stepwise regression were used to identify differences in callus structure and composition among experimental groups and to determine which of the microCT outcome measures were the strongest predictors of mechanical properties. Although calluses varied greatly in the absolute and relative amounts of mineralized tissue (BV, BMC, and BV/TV), differences among timepoints were most strongly associated with changes in tissue mineral density. Torsional strength and rigidity were dependent on mineral density as well as the amount of mineralized tissue: TMD, BV, and sigma(TMD) explained 62% of the variation in

  19. An Overview of Innovative Strategies for Fracture Mechanics at NASA Langley Research Center

    NASA Technical Reports Server (NTRS)

    Ransom, Jonathan B.; Glaessgen, Edward H.; Ratcliffe, James G.

    2010-01-01

    Engineering fracture mechanics has played a vital role in the development and certification of virtually every aerospace vehicle that has been developed since the mid-20th century. NASA Langley Research Center s Durability, Damage Tolerance and Reliability Branch has contributed to the development and implementation of many fracture mechanics methods aimed at predicting and characterizing damage in both metallic and composite materials. This paper presents a selection of computational, analytical and experimental strategies that have been developed by the branch for assessing damage growth under monotonic and cyclic loading and for characterizing the damage tolerance of aerospace structures

  20. Atomistic mechanisms of moisture-induced fracture at copper-silica interfaces

    NASA Astrophysics Data System (ADS)

    Vijayashankar, Dandapani; Zhu, Hong; Garg, Saurabh; Teki, Ranganath; Ramprasad, R.; Lane, Michael W.; Ramanath, Ganpati

    2011-09-01

    Tailoring the chemo-mechanical properties of metal-dielectric interfaces is crucial for many applications including nanodevice wiring, packaging, composites, and catalysis. Here, we combine moisture-induced fracture tests, electron spectroscopy, and density functional theory calculations to reveal fracture toughness partitioning and atomistic delamination mechanisms at copper-silica interfaces. Copper plasticity is supported above a threshold work of adhesion and delamination occurs by moisture-induced Cu-O bond scission in Cu-O-Si bridges. These results provide insights into the effects of the nature of metal-oxygen bonding on moisture-induced delamination of metal-dielectric interfaces.

  1. Permeability Evolution of Fractured Anhydrite Caused by Chemical and Mechanical Alteration

    NASA Astrophysics Data System (ADS)

    Detwiler, R. L.; Elkhoury, J. E.; Ameli, P.

    2011-12-01

    Geologic carbon sequestration requires competent structural seals (caprock) to prevent leakage over decadal time scales. Injection of large volumes of CO2 perturbs the target formation from chemical and mechanical equilibrium leading to the possible creation or enhancement of leakage pathways. We investigate the potential for leakage pathways (fractures) to grow over time under reservoir conditions in a series of anhydrite (Ca2SO4) cores. To simulate a potential leakage event in the laboratory, we fractured and jacketed the cores, and placed them in a flow-through reactor vessel. A high-pressure syringe pump applied confining stresses ranging from 7 to 17 MPa and another syringe pump pushed water through the sample at a constant flow rate with pressure control at the outlet. Effluent was sampled periodically and analyzed for Ca2+ and SO42- using an ion chromatograph. Before and after each experiment, we characterized the surfaces of the fractures using a high-resolution optical profilometer and a scanning electron microscope. Careful alignment of the surfaces during optical profiling allowed reproduction of the fracture aperture before and after each experiment. We present results from several experiments each carried out under different conditions in similar fractured anhydrite cores. One involved a well-mated pre-existing fracture and results showed that the permeability of the fractured core was similar to the intact rock matrix (O(10-18 m2); chemical alteration of the core was largely limited to the inflow face of the core and the fracture surfaces remained largely unaltered. To enhance permeability during subsequent experiments, we imposed a small (380 μm) shear displacement between the fracture surfaces resulting in a four-order-of-magnitude increase in initial permeability. The first of these was run at a constant flow rate of 0.6 ml/min for a period of 7 days. The measured pressure gradient within the core increased slowly for a period of 4 days followed

  2. Design sensitivity analysis of mechanical systems in frequency domain

    NASA Astrophysics Data System (ADS)

    Nalecz, A. G.; Wicher, J.

    1988-02-01

    A procedure for determining the sensitivity functions of mechanical systems in the frequency domain by use of a vector-matrix approach is presented. Two examples, one for a ground vehicle passive front suspension, and the second for a vehicle active suspension, illustrate the practical applications of parametric sensitivity analysis for redesign and modification of mechanical systems. The sensitivity functions depend on the frequency of the system's oscillations. They can be easily related to the system's frequency characteristics which describe the dynamic properties of the system.

  3. Fatigue damage-fracture mechanics interaction in cortical bone.

    PubMed

    Yeni, Y N; Fyhrie, D P

    2002-03-01

    Fatigue loading causes accumulation of damage that may lead to the initiation of a macrocrack and result in a catastrophic failure of bone. The objective of this study was to examine the influence of fatigue damage on crack growth parameters in bovine cortical bone. Nineteen rectangular beam specimens (4 x 4 x 48 mm) were machined from bovine tibiae. The long axis of the beams was aligned with the long axis of bones. Using a four-point bending fatigue setup, ten specimens were fatigue-damaged to different levels as indicated by stiffness loss. A through-thickness notch was machined at the center of each damaged and undamaged beam. The notched specimens were then monotonically loaded beyond failure using a three-point bending protocol. Critical stress intensity factor, K(I), and work to critical load, W(Q), were significantly lower in the damaged group than in the undamaged group (p < 0.03). When the undamaged specimens were assigned a percent stiffness loss of zero and pooled with the damaged group, significant negative correlations of percent stiffness loss with K(I) (R = 0.58, p < 0.01), W(Q) (R = 0.54, p < 0.02), maximum load, P(max) (R = 0.59, p < 0.008), deflection at maximum load, Delta(max) (R = 0.48, p < 0.04), structural stiffness, S(max) (R = 0.53, p < 0.02), W(max) (R = 0.55, p < 0.02), and load at 1.4 mm deflection (a value beyond failure but without complete fracture), P(1.4) (R = 0.47, p < 0.05), were found. Post hoc analysis revealed that the average load-deflection curve from the damaged group was transformable into that from the undamaged group through a special shift on the load-deflection plane. Fatigue damage reduces bone stiffness and resistance to crack initiation, maximum load-carrying capacity, and deflection before and after failure in cortical bone. The data suggest there is a single rule that governs the overall effect of fatigue damage on the fracture behavior of cortical bone. PMID:11882466

  4. Evaluation of fracture strength of metal/epoxy joint by interface mechanics

    SciTech Connect

    Nakai, Yoshikazu

    1995-11-01

    Tension tests of metal/epoxy joints with or without interface cracks were conducted and fracture criteria of the joints were discussed based on interface mechanics. The variation of the fracture strength of each specimen was large, and the strength showed Gaussian distribution. The fracture strength of smooth specimens was lower for wider specimens, but the cumulative probability of fracture of smooth specimens was not controlled by the stress singularity parameter. In interface cracked specimens, the cracks were propagated either along the interface or in epoxy resin, depending on crack length. When cracks propagated along the interface, the cumulative probability of the fracture of the specimen was controlled by the real part of the complex stress intensity factor along the interface, K{sub 1}. When cracks kinked to epoxy resin, the angle was almost identical to that of the maximum tangential stress, {sigma}{sub {theta}max}. In this case, the cumulative probability of fracture was controlled by the value of K{sub {theta}max}.

  5. American Society of Biomechanics Journal of Biomechanics Award 2013: cortical bone tissue mechanical quality and biological mechanisms possibly underlying atypical fractures.

    PubMed

    Geissler, Joseph R; Bajaj, Devendra; Fritton, J Christopher

    2015-04-13

    The biomechanics literature contains many well-understood mechanisms behind typical fracture types that have important roles in treatment planning. The recent association of "atypical" fractures with long-term use of drugs designed to prevent osteoporosis has renewed interest in the effects of agents on bone tissue-level quality. While this class of fracture was recognized prior to the introduction of the anti-resorptive bisphosphonate drugs and recently likened to stress fractures, the mechanism(s) that lead to atypical fractures have not been definitively identified. Thus, a causal relationship between these drugs and atypical fracture has not been established. Physicians, bioengineers and others interested in the biomechanics of bone are working to improve fracture-prevention diagnostics, and the design of treatments to avoid this serious side-effect in the future. This review examines the mechanisms behind the bone tissue damage that may produce the atypical fracture pattern observed increasingly with long-term bisphosphonate use. Our recent findings and those of others reviewed support that the mechanisms behind normal, healthy excavation and tunnel filling by bone remodeling units within cortical tissue strengthen mechanical integrity. The ability of cortical bone to resist the damage induced during cyclic loading may be altered by the reduced remodeling and increased tissue age resulting from long-term bisphosphonate treatment. Development of assessments for such potential fractures would restore confidence in pharmaceutical treatments that have the potential to spare millions in our aging population from the morbidity and death that often follow bone fracture.

  6. Mechanisms and impact of damage resulting from hydraulic fracturing. Topical report, May 1995-July 1996

    SciTech Connect

    Penny, G.S.; Conway, M.W.; Almond, S.W.; Himes, R.; Nick, K.E.

    1996-08-01

    This topical report documents the mechanisms of formation damage following hydraulic fracturing and their impact upon gas well productivity. The categories of damage reviewed include absolute or matrix permeability damage, relative permeability alterations, the damage of natural fracture permeability mechanisms and proppant conductivity impairment. Case studies are reviewed in which attempts are made to mitigate each of the damage types. Industry surveys have been conducted to determine the perceptions of the industry on the topic of formation damage following hydraulic fracturing and to identify key formations in which formation damage is a problem. From this information, technical hurdles and new technology needs are identified and estimates are made of the benefits of developing and applying minimum formation damage technology.

  7. Effect of root canal preparation, type of endodontic post and mechanical cycling on root fracture strength

    PubMed Central

    RIPPE, Marília Pivetta; SANTINI, Manuela Favarin; BIER, Carlos Alexandre Souza; BALDISSARA, Paolo; VALANDRO, Luiz Felipe

    2014-01-01

    Objective To evaluate the impact of the type of root canal preparation, intraradicular post and mechanical cycling on the fracture strength of roots. Material and Methods eighty human single rooted teeth were divided into 8 groups according to the instruments used for root canal preparation (manual or rotary instruments), the type of intraradicular post (fiber posts- FRC and cast post and core- CPC) and the use of mechanical cycling (MC) as follows: Manual and FRC; Manual, FRC and MC; Manual and CPC; Manual, CPC and MC; Rotary and FRC; Rotary, FRC and MC; Rotary and CPC; Rotary, CPC and MC. The filling was performed by lateral compactation. All root canals were prepared for a post with a 10 mm length, using the custom #2 bur of the glass fiber post system. For mechanical cycling, the protocol was applied as follows: an angle of incidence of 45°, 37°C, 88 N, 4 Hz, 2 million pulses. All groups were submitted to fracture strength test in a 45° device with 1 mm/ min cross-head speed until failure occurred. Results The 3-way ANOVA showed that the root canal preparation strategy (p<0.03) and post type (p<0.0001) affected the fracture strength results, while mechanical cycling (p=0.29) did not. Conclusion The root canal preparation strategy only influenced the root fracture strength when restoring with a fiber post and mechanical cycling, so it does not seem to be an important factor in this scenario. PMID:25025556

  8. Constraints on bed scale fracture chronology with a FEM mechanical model of folding: The case of Split Mountain (Utah, USA)

    NASA Astrophysics Data System (ADS)

    Sassi, W.; Guiton, M. L. E.; Leroy, Y. M.; Daniel, J.-M.; Callot, J.-P.

    2012-11-01

    A technique is presented for improving the structural analysis of natural fractures development in large scale fold structures. A 3D restoration of a fold provides the external displacement loading conditions to solve, by the finite element method, the forward mechanical problem of an idealized rock material with a stress-strain relationship based on the activation of pervasive fracture sets. In this elasto-plasticity constitutive law, any activated fracture set contributes to the total plastic strain by either an opening or a sliding mode of rock failure. Inherited versus syn-folding fracture sets development can be studied using this mechanical model. The workflow of this methodology was applied to the Weber sandstone formation deformed by forced folding at Split Mountain Anticline, Utah for which the different fracture sets were created and developed successively during the Sevier and the syn-folding Laramide orogenic phases. The field observations at the top stratigraphic surface of the Weber sandstone lead to classify the fracture sets into a pre-fold WNW-ESE fracture set, and a NE-SW fracture set post-dating the former. The development and relative chronology of the fracture sets are discussed based on the geomechanical modeling results. Starting with a 3D restoration of the Split Mountain Anticline, three fold-fracture development models were generated, alternately assuming that the WNW-ESE fracture set is either present or absent prior to folding process. Depending on the initial fracture configuration, the calculated fracture patterns are markedly different, showing that assuming a WNW-ESE joint set to predate the fold best correlates with field observations. This study is a first step addressing the complex problem of identification of fold-related fracturing events using an elementary concept of rock mechanics. When tight to complementary field observations, including petrography, diagenesis and burial history, the approach can be used to better

  9. Data Resolution and Scale-dependent Fracture Clustering: Implications for Deformation Mechanisms

    NASA Astrophysics Data System (ADS)

    Roy, A.; Aydin, A.; Mukerji, T.; Cilona, A.

    2015-12-01

    zones that have relatively uniform spacing while higher resolution data capture both thin and short splay joints and shear joints that form fracture clusters. Therefore, it may be concluded that data resolution is critical for identifying deformation mechanisms and their products.

  10. Advances in Fatigue and Fracture Mechanics Analyses for Aircraft Structures

    NASA Technical Reports Server (NTRS)

    Newman, J. C., Jr.

    1999-01-01

    This paper reviews some of the advances that have been made in stress analyses of cracked aircraft components, in the understanding of the fatigue and fatigue-crack growth process, and in the prediction of residual strength of complex aircraft structures with widespread fatigue damage. Finite-element analyses of cracked structures are now used to determine accurate stress-intensity factors for cracks at structural details. Observations of small-crack behavior at open and rivet-loaded holes and the development of small-crack theory has lead to the prediction of stress-life behavior for components with stress concentrations under aircraft spectrum loading. Fatigue-crack growth under simulated aircraft spectra can now be predicted with the crack-closure concept. Residual strength of cracked panels with severe out-of-plane deformations (buckling) in the presence of stiffeners and multiple-site damage can be predicted with advanced elastic-plastic finite-element analyses and the critical crack-tip-opening angle (CTOA) fracture criterion. These advances are helping to assure continued safety of aircraft structures.

  11. Effects of chemical alteration on fracture mechanical properties in hydrothermal systems

    NASA Astrophysics Data System (ADS)

    Callahan, O. A.; Eichhubl, P.; Olson, J. E.

    2015-12-01

    Fault and fracture networks often control the distribution of fluids and heat in hydrothermal and epithermal systems, and in related geothermal and mineral resources. Additional chemical influences on conduit evolution are well documented, with dissolution and precipitation of mineral species potentially changing the permeability of fault-facture networks. Less well understood are the impacts of chemical alteration on the mechanical properties governing fracture growth and fracture network geometry. We use double-torsion (DT) load relaxation tests under ambient air conditions to measure the mode-I fracture toughness (KIC) and subcritical fracture growth index (SCI) of variably altered rock samples obtained from outcrop in Dixie Valley, NV. Samples from southern Dixie Valley include 1) weakly altered granite, characterized by minor sericite in plagioclase, albitization and vacuolization of feldspars, and incomplete replacement of biotite with chlorite, and 2) granite from an area of locally intense propylitic alteration with chlorite-calcite-hematite-epidote assemblages. We also evaluated samples of completely silicified gabbro obtained from the Dixie Comstock epithermal gold deposit. In the weakly altered granite KIC and SCI are 1.3 ±0.2 MPam1/2 (n=8) and 59 ±25 (n=29), respectively. In the propylitic assemblage KIC is reduced to 0.6 ±0.1 MPam1/2 (n=11), and the SCI increased to 75 ±36 (n = 33). In both cases, the altered materials have lower fracture toughness and higher SCI than is reported for common geomechanical standards such as Westerly Granite (KIC ~1.7 MPam1/2; SCI ~48). Preliminary analysis of the silicified gabbro shows a significant increase in fracture toughness, 3.6 ±0.4 MPam1/2 (n=2), and SCI, 102 ±45 (n=19), compared to published values for gabbro (2.9 MPam1/2 and SCI = 32). These results suggest that mineralogical and textural changes associated with different alteration assemblages may result in spatially variable rates of fracture

  12. Analysis of frequency characteristics and sensitivity of compliant mechanisms

    NASA Astrophysics Data System (ADS)

    Liu, Shanzeng; Dai, Jiansheng; Li, Aimin; Sun, Zhaopeng; Feng, Shizhe; Cao, Guohua

    2016-07-01

    Based on a modified pseudo-rigid-body model, the frequency characteristics and sensitivity of the large-deformation compliant mechanism are studied. Firstly, the pseudo-rigid-body model under the static and kinetic conditions is modified to enable the modified pseudo-rigid-body model to be more suitable for the dynamic analysis of the compliant mechanism. Subsequently, based on the modified pseudo-rigid-body model, the dynamic equations of the ordinary compliant four-bar mechanism are established using the analytical mechanics. Finally, in combination with the finite element analysis software ANSYS, the frequency characteristics and sensitivity of the compliant mechanism are analyzed by taking the compliant parallel-guiding mechanism and the compliant bistable mechanism as examples. From the simulation results, the dynamic characteristics of compliant mechanism are relatively sensitive to the structure size, section parameter, and characteristic parameter of material on mechanisms. The results could provide great theoretical significance and application values for the structural optimization of compliant mechanisms, the improvement of their dynamic properties and the expansion of their application range.

  13. Discrete fracture modeling of hydro-mechanical damage processes in geological systems

    NASA Astrophysics Data System (ADS)

    Kim, K.; Rutqvist, J.; Houseworth, J. E.; Birkholzer, J. T.

    2014-12-01

    This study presents a modeling approach for investigating coupled thermal-hydrological-mechanical (THM) behavior, including fracture development, within geomaterials and structures. In the model, the coupling procedure consists of an effective linkage between two codes: TOUGH2, a simulator of subsurface multiphase flow and mass transport based on the finite volume approach; and an implementation of the rigid-body-spring network (RBSN) method, a discrete (lattice) modeling approach to represent geomechanical behavior. One main advantage of linking these two codes is that they share the same geometrical mesh structure based on the Voronoi discretization, so that a straightforward representation of discrete fracture networks (DFN) is available for fluid flow processes. The capabilities of the TOUGH-RBSN model are demonstrated through simulations of hydraulic fracturing, where fluid pressure-induced fracturing and damage-assisted flow are well represented. The TOUGH-RBSN modeling methodology has been extended to enable treatment of geomaterials exhibiting anisotropic characteristics. In the RBSN approach, elastic spring coefficients and strength parameters are systematically formulated based on the principal bedding direction, which facilitate a straightforward representation of anisotropy. Uniaxial compression tests are simulated for a transversely isotropic material to validate the new modeling scheme. The model is also used to simulate excavation fracture damage for the HG-A microtunnel in the Opalinus Clay rock, located at the Mont Terri underground research laboratory (URL) near Saint-Ursanne, Switzerland. The Opalinus Clay has transversely isotropic material properties caused by natural features such as bedding, foliation, and flow structures. Preferential fracturing and tunnel breakouts were observed following excavation, which are believed to be strongly influenced by the mechanical anisotropy of the rock material. The simulation results are qualitatively

  14. The mechanism and dynamics of rock fracture upon mechanical impact and electric discharge

    NASA Astrophysics Data System (ADS)

    Vettegren, V. I.; Kuksenko, V. S.; Shcherbakov, I. P.

    2016-09-01

    The mechanism and dynamics of the deformation and fracture of quartz, granite, and marble samples under the striker blow on their surface and electric discharge inside them are studied by the fractoluminescence (FL), electromagnetic (EME), and acoustic emission (AE) methods with 10-ns resolution. The impact excites a forced deformation wave with a velocity within 0.8 to 2 km/s depending on the mineral. The atomic bonds rupture and microcracks are formed at the nodes of the wave, which leads to the emergence of the FL flashes and disruption of the time dependences of EME. Based on the intensity of the flashes, the dimensions of microcracks are estimated to vary from 2 to 70 µm depending on the mineral. In turn, the emergence of microcracks initiates additional deformation waves.The discharge inside the studied samples excites a pressure shock wave which transforms into the tension wave after reflection from the surface. According to the analysis of FL spectra, this leads to the breakdown of the rocks into positively charged ions and electrons. The shock wave velocity in granites is measured at 4.8 km/s, which is close to the velocity of the longitudinal acoustic vibrations ~5 km/s. The microcracks in the rock have not enough time to form with this loading velocity. It is supposed that the shock wave stretches the deformed interatomic bonds at the dislocation nuclei in the crystal lattices of the minerals up to their breakdown into positively charged ions.

  15. Fracture pain-Traveling unknown pathways.

    PubMed

    Alves, Cecília J; Neto, Estrela; Sousa, Daniela M; Leitão, Luís; Vasconcelos, Daniel M; Ribeiro-Silva, Manuel; Alencastre, Inês S; Lamghari, Meriem

    2016-04-01

    An increase of fracture incidence is expected for the next decades, mostly due to the undeniable increase of osteoporotic fractures, associated with the rapid population ageing. The rise in sports-related fractures affecting the young and active population also contributes to this increased fracture incidence, and further amplifies the economical burden of fractures. Fracture often results in severe pain, which is a primary symptom to be treated, not only to guarantee individual's wellbeing, but also because an efficient management of fracture pain is mandatory to ensure proper bone healing. Here, we review the available data on bone innervation and its response to fracture, and discuss putative mechanisms of fracture pain signaling. In addition, the common therapeutic approaches to treat fracture pain are discussed. Although there is still much to learn, research in fracture pain has allowed an initial insight into the mechanisms involved. During the inflammatory response to fracture, several mediators are released and will putatively activate and sensitize primary sensory neurons, in parallel, intense nerve sprouting that occurs in the fracture callus area is also suggested to be involved in pain signaling. The establishment of hyperalgesia and allodynia after fracture indicates the development of peripheral and central sensitization, still, the underlying mechanisms are largely unknown. A major concern during the treatment of fracture pain needs to be the preservation of proper bone healing. However, the most common therapeutic agents, NSAIDS and opiates, can cause significant side effects that include fracture repair impairment. The understanding of the mechanisms of fracture pain signaling will allow the development of mechanisms-based therapies to effectively and safely manage fracture pain.

  16. Fracture pain-Traveling unknown pathways.

    PubMed

    Alves, Cecília J; Neto, Estrela; Sousa, Daniela M; Leitão, Luís; Vasconcelos, Daniel M; Ribeiro-Silva, Manuel; Alencastre, Inês S; Lamghari, Meriem

    2016-04-01

    An increase of fracture incidence is expected for the next decades, mostly due to the undeniable increase of osteoporotic fractures, associated with the rapid population ageing. The rise in sports-related fractures affecting the young and active population also contributes to this increased fracture incidence, and further amplifies the economical burden of fractures. Fracture often results in severe pain, which is a primary symptom to be treated, not only to guarantee individual's wellbeing, but also because an efficient management of fracture pain is mandatory to ensure proper bone healing. Here, we review the available data on bone innervation and its response to fracture, and discuss putative mechanisms of fracture pain signaling. In addition, the common therapeutic approaches to treat fracture pain are discussed. Although there is still much to learn, research in fracture pain has allowed an initial insight into the mechanisms involved. During the inflammatory response to fracture, several mediators are released and will putatively activate and sensitize primary sensory neurons, in parallel, intense nerve sprouting that occurs in the fracture callus area is also suggested to be involved in pain signaling. The establishment of hyperalgesia and allodynia after fracture indicates the development of peripheral and central sensitization, still, the underlying mechanisms are largely unknown. A major concern during the treatment of fracture pain needs to be the preservation of proper bone healing. However, the most common therapeutic agents, NSAIDS and opiates, can cause significant side effects that include fracture repair impairment. The understanding of the mechanisms of fracture pain signaling will allow the development of mechanisms-based therapies to effectively and safely manage fracture pain. PMID:26851411

  17. Adaptive finite element methods for two-dimensional problems in computational fracture mechanics

    NASA Technical Reports Server (NTRS)

    Min, J. B.; Bass, J. M.; Spradley, L. W.

    1994-01-01

    Some recent results obtained using solution-adaptive finite element methods in two-dimensional problems in linear elastic fracture mechanics are presented. The focus is on the basic issue of adaptive finite element methods for validating the new methodology by computing demonstration problems and comparing the stress intensity factors to analytical results.

  18. Structural Reliability of Ceramics at High Temperature: Mechanisms of Fracture and Fatigue Crack Growth

    SciTech Connect

    Reinhold H. Dauskardt

    2005-08-01

    Final report of our DOE funded research program. Aim of the research program was to provide a fundamental basis from which the mechanical reliability of layered structures may be understood, and to provide guidelines for the development of technologically relevant layered material structures with optimum resistance to fracture and subcritical debonding. Progress in the program to achieve these goals is described.

  19. Fracture mechanics research at NASA related to the aging commercial transport fleet

    NASA Technical Reports Server (NTRS)

    Newman, James C., Jr.; Harris, Charles E.

    1992-01-01

    NASA is conducting the Airframe Structural Integrity Program in support of the aging commercial transport fleet. This interdisciplinary program is being worked in cooperation with the U.S. airframe manufacturers, airline operators, and the FAA. Advanced analysis methods are under development and an extensive testing program is under way to study fatigue crack growth and fracture in complex built-up shell structures. Innovative nondestructive examination technologies are also being developed to provide large area inspection capability to detect corrosion, disbonds, and cracks. Recent fracture mechanics results applicable to predicting the growth of cracks under monotonic and cyclic loading at rivets in fuselage lap-splice joints are reviewed.

  20. Code System for Fracture Mechanics Analysis of Circumferential Surface Cracks in Pipes.

    1999-07-28

    Version 00 The NRCPIPES software is designed to perform elastic and elastic-plastic fracture mechanics analysis for a circumferential surface cracked pipe, i.e., to establish the fracture-failure condition in terms of sustainable load (or stress) or displacement. The NRCPIPES software also includes several evaluation procedures and acceptance criteria for circumferential surface flaws based on the ASME Boiler and Pressure Vessel Code, Section XI criteria, the British R6 Revision 3 Option 1 criteria, and the original Net-Section-Collapsemore » (limit-load) analysis.« less

  1. Kinetics and fracture resistance of lithiated silicon nanostructure pairs controlled by their mechanical interaction

    NASA Astrophysics Data System (ADS)

    Lee, Seok Woo; Lee, Hyun-Wook; Ryu, Ill; Nix, William D.; Gao, Huajian; Cui, Yi

    2015-06-01

    Following an explosion of studies of silicon as a negative electrode for Li-ion batteries, the anomalous volumetric changes and fracture of lithiated single Si particles have attracted significant attention in various fields, including mechanics. However, in real batteries, lithiation occurs simultaneously in clusters of Si in a confined medium. Hence, understanding how the individual Si structures interact during lithiation in a closed space is necessary. Here, we demonstrate physical and mechanical interactions of swelling Si structures during lithiation using well-defined Si nanopillar pairs. Ex situ SEM and in situ TEM studies reveal that compressive stresses change the reaction kinetics so that preferential lithiation occurs at free surfaces when the pillars are mechanically clamped. Such mechanical interactions enhance the fracture resistance of lithiated Si by lessening the tensile stress concentrations in Si structures. This study will contribute to improved design of Si structures at the electrode level for high-performance Li-ion batteries.

  2. Kinetics and fracture resistance of lithiated silicon nanostructure pairs controlled by their mechanical interaction

    SciTech Connect

    Lee, Seok Woo; Lee, Hyun -Wook; Ryu, Ill; Nix, William D.; Gao, Huajian; Cui, Yi

    2015-06-26

    Following an explosion of studies of silicon as a negative electrode for Li-ion batteries, the anomalous volumetric changes and fracture of lithiated single Si particles have attracted significant attention in various fields, including mechanics. However, in real batteries, lithiation occurs simultaneously in clusters of Si in a confined medium. Hence, understanding how the individual Si structures interact during lithiation in a closed space is necessary. Here, we demonstrate physical and mechanical interactions of swelling Si structures during lithiation using well-defined Si nanopillar pairs. Ex situ SEM and in situ TEM studies reveal that compressive stresses change the reaction kinetics so that preferential lithiation occurs at free surfaces when the pillars are mechanically clamped. Such mechanical interactions enhance the fracture resistance of lithiated Si by lessening the tensile stress concentrations in Si structures. Lastly, this study will contribute to improved design of Si structures at the electrode level for high-performance Li-ion batteries.

  3. Tissue-Level Mechanical Properties of Bone Contributing to Fracture Risk.

    PubMed

    Nyman, Jeffry S; Granke, Mathilde; Singleton, Robert C; Pharr, George M

    2016-08-01

    Tissue-level mechanical properties characterize mechanical behavior independently of microscopic porosity. Specifically, quasi-static nanoindentation provides measurements of modulus (stiffness) and hardness (resistance to yielding) of tissue at the length scale of the lamella, while dynamic nanoindentation assesses time-dependent behavior in the form of storage modulus (stiffness), loss modulus (dampening), and loss factor (ratio of the two). While these properties are useful in establishing how a gene, signaling pathway, or disease of interest affects bone tissue, they generally do not vary with aging after skeletal maturation or with osteoporosis. Heterogeneity in tissue-level mechanical properties or in compositional properties may contribute to fracture risk, but a consensus on whether the contribution is negative or positive has not emerged. In vivo indentation of bone tissue is now possible, and the mechanical resistance to microindentation has the potential for improving fracture risk assessment, though determinants are currently unknown.

  4. Rock mechanics issues and research needs in the disposal of wastes in hydraulic fractures

    SciTech Connect

    Doe, T.W.; McClain, W.C.

    1984-07-01

    The proposed rock mechanics studies outlined in this document are designed to answer the basic questions concerning hydraulic fracturing for waste disposal. These questions are: (1) how can containment be assured for Oak Ridge or other sites; and (2) what is the capacity of a site. The suggested rock mechanics program consists of four major tasks: (1) numerical modeling, (2) laboratory testing, (3) field testing, and (4) monitoring. These tasks are described.

  5. Effect of CO2-induced reactions on the mechanical behaviour of fractured wellbore cement

    NASA Astrophysics Data System (ADS)

    Wolterbeek, Timotheus; Hangx, Suzanne; Spiers, Christopher

    2016-04-01

    Geomechanical damage, such as fracturing of wellbore cement, can severely impact well integrity in CO2 storage fields. Chemical reactions between the cement and CO2-bearing fluids may subsequently alter the cement's mechanical properties, either enhancing or inhibiting damage accumulation during ongoing changes in wellbore temperature and stress-state. To evaluate the potential for such effects, we performed triaxial compression tests on Class G Portland cement, conducted at down-hole temperature (80 ° C) and effective confining pressures ranging from 1 to 25 MPa. After deformation, samples displaying failure on localised shear fractures were reacted with CO2-H2O, and then subjected to a second triaxial test to assess changes in mechanical properties. Using results from the first phase of deformation, baseline yield and failure criteria were constructed for virgin cement. These delineate stress conditions where unreacted cement is most prone to dilatational (permeability-enhancing) failure. Once shear-fractures formed, later reaction with CO2 did not produce further geomechanical weakening. Instead, after six weeks of reaction, we observed up to 83% recovery of peak-strength and increased frictional strength (15-40%) in the post-failure regime, due to calcium carbonate precipitation in the fractures. As such, our results suggest more or less complete mechanical healing on timescales of the order of months.

  6. Fracture properties of polycrystalline silicon - a material for micro-electro-mechanical systems

    SciTech Connect

    Johnson, G.C.; Jones, P.T.

    1995-12-31

    A great deal of research has been performed during the past few years to apply the microfabrication technology used for making integrated circuits to the manufacture of microscopic pressure sensors, accelerometers, and other micro-electro-mechanical systems (MEMS). One result of this work has been the choice of polycrystalline silicon (polysilicon) as a primary structural material employed in MEMS devices, particularly when the polysilicon has been doped with such elements as phosphorus for improved electrical and mechanical properties. As MEMS devices become more relied upon for real world applications, it will be necessary to establish design rules to ensure adequate product lifetimes. However, very little work has been done to deter- mine the failure mechanisms of polysilicon. The work presented here offers an experimental evaluation of the ultimate strength and fracture toughness of polysilicon with regard to the effects of exposure to hydrofluoric acid, a commonly used etchant in MEMS fabrication. A series of micromechanical structures have been designed to measure the strain at fracture and fracture toughness of a thin film. These test structures are patterned onto a thin film of polysilicon covering a silicon wafer using standard microfabrication techniques. Since the structures have dimensions on the order of microns, hundreds of multiple test structures are patterned on a single wafer providing a large amount of statistical data. Results using these structures indicate that prolonged exposure to HF can result in a decrease in the fracture strength of polysilicon.

  7. The effect of hydrogen on strain hardening and fracture mechanism of high-nitrogen austenitic steel

    NASA Astrophysics Data System (ADS)

    Maier, G. G.; Astafurova, E. G.; Melnikov, E. V.; Moskvina, V. A.; Vojtsik, V. F.; Galchenko, N. K.; Zakharov, G. N.

    2016-07-01

    High-nitrogen austenitic steels are perspective materials for an electron-beam welding and for producing of wear-resistant coatings, which can be used for application in aggressive atmospheres. The tensile behavior and fracture mechanism of high-nitrogen austenitic steel Fe-20Cr-22Mn-1.5V-0.2C-0.6N (in wt.%) after electrochemical hydrogen charging for 2, 10 and 40 hours have been investigated. Hydrogenation of steel provides a loss of yield strength, uniform elongation and tensile strength. The degradation of tensile properties becomes stronger with increase in charging duration - it occurs more intensive in specimens hydrogenated for 40 hours as compared to ones charged for 2-10 hours. Fracture analysis reveals a hydrogen-induced formation of brittle surface layers up to 6 μm thick after 40 hours of saturation. Hydrogenation changes fracture mode of steel from mixed intergranular-transgranular to mainly transgranular one.

  8. Continuum mechanics analysis of fracture progression in the vitrified cryoprotective agent DP6.

    PubMed

    Steif, Paul S; Palastro, Matthew C; Rabin, Yoed

    2008-04-01

    As part of an ongoing effort to study the continuum mechanics effects associated with cryopreservation, the current report focuses on the prediction of fracture formation in cryoprotective agents. Fractures had been previously observed in 1 ml samples of the cryoprotective agent cocktail DP6, contained in a standard 15 ml glass vial, and subjected to various cooling rates. These experimental observations were obtained by means of a cryomacroscope, which has been recently presented by the current research team. High and low cooling rates were found to produce very distinct patterns of cracking. The current study seeks to explain the observed patterns on the basis of stresses predicted from finite element analysis, which relies on a simple viscoelastic constitutive model and on estimates of the critical stress for cracking. The current study demonstrates that the stress, which results in instantaneous fracture at low cooling rates, is consistent with the stress to initiate fracture at high cooling rate. This consistency supports the credibility of the proposed constitutive model and analysis, and the unified criterion for fracturing, that is, a critical stress threshold.

  9. The fifth metatarsal base: anatomic evaluation regarding fracture mechanism and treatment algorithms.

    PubMed

    DeVries, J George; Taefi, Erfan; Bussewitz, Bradly W; Hyer, Christopher F; Lee, Thomas H

    2015-01-01

    Fractures occurring within the 1.5-cm proximal portion of the fifth metatarsal are commonly considered avulsion fractures. The exact mechanisms of such fractures are controversial. The present study focused on determining the likely mechanism of fracture according to the exact anatomy to allow for more successful treatment. The research sample included 10 frozen cadaveric specimens. The lateral band of the plantar fascia, peroneus brevis, and articular surface were identified and separated from their attachments, thereby splitting the fifth metatarsal base into zones A, B, and C. In zone A, the attachment of the plantar fascia was 6.6 ± 2.2 mm from the inferior aspect, 9.5 ± 2.9 mm from the proximal aspect, and 11.5 ± 0.9 mm from the lateral aspect. In zone B, the attachment of the peroneus brevis was 12.0 ± 2.2 mm from the inferior aspect, 10.2 ± 2.2 mm from the proximal aspect, and 11.5 ± 0.9 mm from the lateral aspect. Zone C was measured from the border of zone B and encompassed the articulation of the fifth metatarsal to the cuboid. We propose that fractures occurring in the most proximal end of the fifth metatarsal, zone A, are caused by a lateral band of plantar fascia and might be able to be treated conservatively by immobilization with weightbearing. We also propose that fractures occurring in zones B and C result from traumatic tension on peroneus brevis and might need to be treated with strict immobilization and non-weightbearing or open reduction internal fixation.

  10. Can Deterministic Mechanical Size Effects Contribute to Fracture and Microdamage Accumulation in Trabecular Bone?

    PubMed Central

    Siegmund, Thomas; Allen, Matthew R.; Burr, David B.

    2010-01-01

    Failure of bone under monotonic and cyclic loading is related to the bone mineral density, the quality of the bone matrix and the evolution of microcracks. The theory of linear elastic fracture mechanics has commonly been applied to describe fracture in bone. Evidence is presented that bone failure can be described through a non-linear theory of fracture. Thereby, deterministic size effects are introduced. Concepts of a non-linear theory are applied to discern how the interaction among bone matrix constituents (collagen and mineral), microcrack characteristics, and trabecular architecture can create distinctively differences in the fracture resistance at the bone tissue level. The nonlinear model is applied to interpret pre-clinical data concerning the effects of anti-osteoporotic agents on bone properties. The results show that bisphosphonate (BP) treatments that suppress bone remodeling will change trabecular bone in ways such that the size of the failure process zone relative to the trabecular thickness is reduced. Selective estrogen receptor modulators (SERMs) that suppress bone remodeling will change trabecular bone in ways such that the size of the failure process zone relative to the trabecular thickness is increased. The consequences of these changes are reflected in bone mechanical response and predictions are consistent with experimental observations in the animal model which show that BP treatment is associated with more brittle fracture and microcracks without altering the average length of the cracks, whereas SERM treatments lead to a more ductile fracture and mainly increase crack length with a smaller increase in microcrack density. The model suggests that BPs may be more effective in cases in which bone mass is very low, whereas SERMS may be more effective when milder osteoporotic symptoms are present. PMID:20398678

  11. Analysis of propagation mechanisms of stimulation-induced fractures in rocks

    NASA Astrophysics Data System (ADS)

    Krause, Michael; Renner, Joerg

    2016-04-01

    Effectivity of geothermal energy production depends crucially on the heat exchange between the penetrated hot rock and the circulating water. Hydraulic stimulation of rocks at depth intends to create a network of fractures that constitutes a large area for exchange. Two endmembers of stimulation products are typically considered, tensile hydro-fractures that propagate in direction of the largest principal stress and pre-existing faults that are sheared when fluid pressure reduces the effective normal stress acting on them. The understanding of the propagation mechanisms of fractures under in-situ conditions is still incomplete despite intensive research over the last decades. Wing-cracking has been suggested as a mechanism of fracture extension from pre-existent faults with finite length that are induced to shear. The initiation and extension of the wings is believed to be in tensile mode. Open questions concern the variability of the nominal material property controlling tensile fracture initiation and extension, the mode I facture toughness KIC, with in-situ conditions, e.g., its mean-stress dependence. We investigated the fracture-propagation mechanism in different rocks (sandstones and granites) under varying conditions mimicking those representative for geothermal systems. To determine KIC-values we performed 3-point bending experiments. We varied the confining pressure, the piston velocity, and the position of the chevron notch relative to the loading configuration. Additional triaxial experiments at a range of confining pressures were performed to study wing crack propagation from artificial flaws whose geometrical characteristics, i.e., length, width, and orientation relative to the axial load are varied. We monitored acoustic emissions to constrain the spacio-temporal evolution of the fracturing. We found a significant effect of the length of the artificial flaw and the confining pressure on wing-crack initiation but did not observe a systematic dependence

  12. Phenomenological and mechanics aspects of nondestructive evaluation and characterization by sound and ultrasound of material and fracture properties

    NASA Technical Reports Server (NTRS)

    Fu, L. S. W.

    1982-01-01

    Developments in fracture mechanics and elastic wave theory enhance the understanding of many physical phenomena in a mathematical context. Available literature in the material, and fracture characterization by NDT, and the related mathematical methods in mechanics that provide fundamental underlying principles for its interpretation and evaluation are reviewed. Information on the energy release mechanism of defects and the interaction of microstructures within the material is basic in the formulation of the mechanics problems that supply guidance for nondestructive evaluation (NDE).

  13. Nonlinear fracture mechanics-based analysis of thin wall cylinders

    NASA Technical Reports Server (NTRS)

    Brust, Frederick W.; Leis, Brian N.; Forte, Thomas P.

    1994-01-01

    This paper presents a simple analysis technique to predict the crack initiation, growth, and rupture of large-radius, R, to thickness, t, ratio (thin wall) cylinders. The method is formulated to deal both with stable tearing as well as fatigue mechanisms in applications to both surface and through-wall axial cracks, including interacting surface cracks. The method can also account for time-dependent effects. Validation of the model is provided by comparisons of predictions to more than forty full scale experiments of thin wall cylinders pressurized to failure.

  14. Fracture Mechanics Analyses of Subsurface Defects in Reinforced Carbon-Carbon Joggles Subjected to Thermo-Mechanical Loads

    NASA Technical Reports Server (NTRS)

    Knight, Norman F., Jr.; Raju, Ivatury S.; Song, Kyongchan

    2011-01-01

    Coating spallation events have been observed along the slip-side joggle region of the Space Shuttle Orbiter wing-leading-edge panels. One potential contributor to the spallation event is a pressure build up within subsurface voids or defects due to volatiles or water vapor entrapped during fabrication, refurbishment, or normal operational use. The influence of entrapped pressure on the thermo-mechanical fracture-mechanics response of reinforced carbon-carbon with subsurface defects is studied. Plane-strain simulations with embedded subsurface defects are performed to characterize the fracture mechanics response for a given defect length when subjected to combined elevated-temperature and subsurface-defect pressure loadings to simulate the unvented defect condition. Various subsurface defect locations of a fixed-length substrate defect are examined for elevated temperature conditions. Fracture mechanics results suggest that entrapped pressure combined with local elevated temperatures have the potential to cause subsurface defect growth and possibly contribute to further material separation or even spallation. For this anomaly to occur, several unusual circumstances would be required making such an outcome unlikely but plausible.

  15. The Merging of Fatigue and Fracture Mechanics Concepts: A Historical Perspective

    NASA Technical Reports Server (NTRS)

    Newman, James C., Jr.

    1997-01-01

    The seventh Jerry L. Swedlow Memorial Lecture presents a review of some of the technical developments, that have occurred during the past 40 years, which have led to the merger of fatigue and fracture mechanics concepts. This review is made from the viewpoint of 'crack propagation.' As methods to observe the 'fatigue' process have improved, the formation of fatigue micro-cracks have been observed earlier in life and the measured crack sizes have become smaller. These observations suggest that fatigue damage can now be characterized by 'crack size.' In parallel, the crack-growth analysis methods, using stress-intensity factors, have also improved. But the effects of material inhomogeneities, crack-fracture mechanisms, and nonlinear behavior must now be included in these analyses. The discovery of crack-closure mechanisms, such as plasticity, roughness, and oxide/corrosion/fretting product debris, and the use of the effective stress-intensity factor range, has provided an engineering tool to predict small- and large-crack-growth rate behavior under service loading, conditions. These mechanisms have also provided a rationale for developing, new, damage-tolerant materials. This review suggests that small-crack growth behavior should be viewed as typical behavior, whereas large-crack threshold behavior should be viewed as the anomaly. Small-crack theory has unified 'fatigue' and 'fracture mechanics' concepts; and has bridged the cap between safe-life and durability/damage-tolerance design concepts.

  16. Understanding Irreversible Degradation of Nb3Sn Wires with Fundamental Fracture Mechanics

    SciTech Connect

    Zhai, Yuhu; Calzolaio, Ciro; Senatore, Carmine

    2014-08-01

    Irreversible performance degradation of advanced Nb3Sn superconducting wires subjected to transverse or axial mechanical loading is a critical issue for the design of large-scale fusion and accelerator magnets such as ITER and LHC. Recent SULTAN tests indicate that most cable-in-conduit conductors for ITER coils made of Nb3Sn wires processed by various fabrication techniques show similar performance degradation under cyclic loading. The irreversible degradation due to filament fracture and local strain accumulation in Nb3Sn wires cannot be described by the existing strand scaling law. Fracture mechanic modeling combined with X-ray diffraction imaging of filament micro-crack formation inside the wires under mechanical loading may reveal exciting insights to the wire degradation mechanisms. We apply fundamental fracture mechanics with a singularity approach to study influence of wire filament microstructure of initial void size and distribution to local stress concentration and potential crack propagation. We report impact of the scale and density of the void structure on stress concentration in the composite wire materials for crack initiation. These initial defects result in an irreversible degradation of the critical current beyond certain applied stress. We also discuss options to minimize stress concentration in the design of the material microstructure for enhanced wire performance for future applications.

  17. Mechanical Models of Bed-Perpendicular Fractures in Layered Rocks Subjected to Extensional Strain

    NASA Astrophysics Data System (ADS)

    Sanz, P.; Pollard, D. D.; Borja, R. I.

    2010-12-01

    Natural fractures (joints) enhance permeability and therefore are important for the economical production of low-permeability hydrocarbon reservoirs and aquifers. In this work we investigate the formation of bed-perpendicular joints during extension in a stiff brittle layer surrounded by thick softer layers. The quasi-static finite element models consist of three elasto-plastic layers with frictional bedding interfaces and the middle layer contains layer-perpendicular fractures that can accommodate opening at the bedding surface accompanied by interface sliding. The upper and lower boundaries are subject to normal tractions appropriate for the depth of burial. Lateral boundaries are displaced horizontally to represent the extensional tectonic regime. We use an interface model that captures the most important mechanical features during sliding of bedding interfaces and opening of joints: unilateral contact, elastic and plastic relative deformation, tensile strength, cohesion, frictional sliding, and non-associative plastic flow. The constitutive law extends the Coulomb slip criterion to the tensile regime to capture opening of fractures in a quasi-brittle manner. The finite element implementation employs a penalty scheme to impose the contact constraints along the interfaces. The numerical simulations show the effects of mechanical properties of layers and interfaces in the development and spacing of bed-perpendicular joints. We evaluate the concepts of fracture saturation and sequential infilling, and the relationship between joint spacing and layer thickness in the context of the new modeling capabilities.

  18. Fracture toughening mechanism of cortical bone: an experimental and numerical approach.

    PubMed

    An, Bingbing; Liu, Yang; Arola, Dwayne; Zhang, Dongsheng

    2011-10-01

    In this investigation, the crack propagation mechanisms contributing to the toughness of cortical bone were studied using a combination of experimental and numerical approaches. Compact tension (CT) specimens were prepared from bovine cortical bones to achieve crack propagation in the longitudinal and transverse directions. Stable crack extension experiments were conducted to distinguish the crack growth resistance curves, and virtual multidimensional internal bond (VMIB) modeling was adopted to simulate the fracture responses. Results from experiments indicated that cortical bone exhibited rising resistance curves (R-curves) for crack extension parallel and perpendicular to the bone axis; the transverse fracture toughness was significantly larger, indicating that the fracture properties of cortical bone are substantially anisotropic. Microscopic observations showed that the toughening mechanisms in the longitudinal and transverse directions were different. When the crack grew in the transverse direction, the crack deflected significantly, and crack bifurcations were found at the crack wake, while, in the longitudinal direction, the crack was straight and uncracked ligaments were observed. Numerical simulations also revealed that the fracture resistance in the transverse direction was greater than that in the longitudinal direction.

  19. Exploring particulate retention mechanisms through visualization of E. coli transport through a single, saturated fracture

    NASA Astrophysics Data System (ADS)

    Burke, M. G.; Dickson, S. E.; Schutten, M.

    2011-12-01

    Groundwater is an extremely valuable resource; a large body of work has been conducted towards remediating, tracking and reducing its contamination. Even so, there are large gaps within the current understanding of groundwater flow and contaminant transport, particularly within fractured media. Fractured media has the ability transport contaminants over longer distances in less time relative to porous media. Furthermore, colloids display unique transport characteristics in comparison to dissolved constituents, including the fact that they typically exhibit earlier initial arrival times. Of particular concern to human health are pathogenic microorganisms, which often originate from fecal contamination. Escherichia coli is a common indicator for fecal contamination; some strains are pathogenic, causing acute illness and sometimes death, in humans. A comprehensive understanding of the transport and retention of E. coli in fractured media will improve our ability to accurately assess whether a site is at risk of becoming contaminated by pathogenic microorganisms. Therefore, the goal of this work is to expand our mechanistic understanding particulate retention, specifically E. coli, in fractures, and the influence of flow rate on these mechanisms. In order to achieve this goal, clear epoxy casts were fabricated of two dolomitic limestone fractures retrieved from a quarry in Guelph, Ontario. Each aperture field was characterized through hydraulic and tracer tests, and measured directly using the light transmission technique. E. coli RS2-GFP, which is a non-pathogenic strain of E. coli that has been tagged with a green fluorescent protein, was injected into the cast under three separate specific discharges ranging from 5 - 30 m/d. These experiments were conducted on an ultraviolet light source, and a high resolution charged-couple device (CCD) camera was employed to take photos at regular intervals in order to capture the dominant flow paths and the areas of retention

  20. Sensitivity Analysis and Assessment of Prior Model Probabilities in MLBMA with Application to Unsaturated Fractured Tuff

    SciTech Connect

    Ye, Ming; Neuman, Shlomo P.; Meyer, Philip D.; Pohlmann, Karl

    2005-12-24

    Previous application of Maximum Likelihood Bayesian Model Averaging (MLBMA, Neuman [2002, 2003]) to alternative variogram models of log air permeability data in fractured tuff has demonstrated its effectiveness in quantifying conceptual model uncertainty and enhancing predictive capability [Ye et al., 2004]. A question remained how best to ascribe prior probabilities to competing models. In this paper we examine the extent to which lead statistics of posterior log permeability predictions are sensitive to prior probabilities of seven corresponding variogram models. We then explore the feasibility of quantifying prior model probabilities by (a) maximizing Shannon's entropy H [Shannon, 1948] subject to constraints reflecting a single analyst's (or a group of analysts?) prior perception about how plausible each alternative model (or a group of models) is relative to others, and (b) selecting a posteriori the most likely among such maxima corresponding to alternative prior perceptions of various analysts or groups of analysts. Another way to select among alternative prior model probability sets, which however is not guaranteed to yield optimum predictive performance (though it did so in our example) and would therefore not be our preferred option, is a min-max approach according to which one selects a priori the set corresponding to the smallest value of maximum entropy. Whereas maximizing H subject to the prior perception of a single analyst (or group) maximizes the potential for further information gain through conditioning, selecting the smallest among such maxima gives preference to the most informed prior perception among those of several analysts (or groups). We use the same variogram models and log permeability data as Ye et al. [2004] to demonstrate that our proposed approach yields the least amount of posterior entropy (residual uncertainty after conditioning) and enhances predictive model performance as compared to (a) the non-informative neutral case in

  1. Fracture mechanics applied to the analysis of the degradation of anti-corrosion glass/resin pipes as a function of the fiber/matrix interface quality

    SciTech Connect

    Krawczak, P.; Pabiot, J.

    1995-10-01

    The aim of this paper is to propose a characterization method of the damage of glass/epoxy pipes, based on mode 1 fracture mechanics, making it possible to separate the cracks initiation and cracks propagation mechanisms that exist in practice. In a first part, it is shown that this technique is highly sensitive (in factors 4 to 5) to the fiber/matrix interface quality, the latter being either modified by the use of different sizings or degraded by hydrothermal aging. In a second part, the application of this method to pipes under pressure shows that mode I fracture mechanics tests performed on unidirectionally fiber reinforced flat test pieces monoaxially loaded allow the explanation of the short term as well as long term behavior and damage of complex composite structures under biaxial loading, and this on the basis of the participation of the fiber/matrix interface to the observed phenomena.

  2. Controlled mechanical fracture for fabricating microchannels with various size gradients.

    PubMed

    Kim, Hong-Nam; Lee, Sung-Hoon; Suh, Kahp-Yang

    2011-02-21

    We present a simple method to generate cracks with controllable size (depth and width) and space gradients using deep surface oxidation and anisotropic mechanical stretching. To generate a thick oxidation layer (<∼7 µm), a polydimethylsiloxane (PDMS) slab of uniform or varying thickness was exposed to UV/ozone for less than 30 min in the UV-C wavelength including wavelengths of 185 and 254 nm. Subsequently, the PDMS slab was wrapped on a cylindrical support (radius: 11 mm) to apply a uniform bending strain (<21%), resulting in equally separated, anisotropic cracks over a large area. By modulating initial oxidation depth and applied bending stress, cracks of varying sizes and spaces were formed on a single PDMS slab. Furthermore, multiple, sequential cracks were generated by increasing the strain in a step-wise fashion and multi-directional cracks by applying the strain with an orientation angle. Finally, size and space-varying cracks were formed between two adjacent large channels in an interconnected format by selective masking and irreversible bonding.

  3. A mechanical model for predicting the probability of osteoporotic hip fractures based in DXA measurements and finite element simulation

    PubMed Central

    2012-01-01

    Background Osteoporotic hip fractures represent major cause of disability, loss of quality of life and even mortality among the elderly population. Decisions on drug therapy are based on the assessment of risk factors for fracture, from BMD measurements. The combination of biomechanical models with clinical studies could better estimate bone strength and supporting the specialists in their decision. Methods A model to assess the probability of fracture, based on the Damage and Fracture Mechanics has been developed, evaluating the mechanical magnitudes involved in the fracture process from clinical BMD measurements. The model is intended for simulating the degenerative process in the skeleton, with the consequent lost of bone mass and hence the decrease of its mechanical resistance which enables the fracture due to different traumatisms. Clinical studies were chosen, both in non-treatment conditions and receiving drug therapy, and fitted to specific patients according their actual BMD measures. The predictive model is applied in a FE simulation of the proximal femur. The fracture zone would be determined according loading scenario (sideway fall, impact, accidental loads, etc.), using the mechanical properties of bone obtained from the evolutionary model corresponding to the considered time. Results BMD evolution in untreated patients and in those under different treatments was analyzed. Evolutionary curves of fracture probability were obtained from the evolution of mechanical damage. The evolutionary curve of the untreated group of patients presented a marked increase of the fracture probability, while the curves of patients under drug treatment showed variable decreased risks, depending on the therapy type. Conclusion The FE model allowed to obtain detailed maps of damage and fracture probability, identifying high-risk local zones at femoral neck and intertrochanteric and subtrochanteric areas, which are the typical locations of osteoporotic hip fractures. The

  4. Fracture Mechanics Analyses of Reinforced Carbon-Carbon Wing-Leading-Edge Panels

    NASA Technical Reports Server (NTRS)

    Raju, Ivatury S.; Phillips, Dawn R.; Knight, Norman F., Jr.; Song, Kyongchan

    2010-01-01

    Fracture mechanics analyses of subsurface defects within the joggle regions of the Space Shuttle wing-leading-edge RCC panels are performed. A 2D plane strain idealized joggle finite element model is developed to study the fracture behavior of the panels for three distinct loading conditions - lift-off and ascent, on-orbit, and entry. For lift-off and ascent, an estimated bounding aerodynamic pressure load is used for the analyses, while for on-orbit and entry, thermo-mechanical analyses are performed using the extreme cold and hot temperatures experienced by the panels. In addition, a best estimate for the material stress-free temperature is used in the thermo-mechanical analyses. In the finite element models, the substrate and coating are modeled separately as two distinct materials. Subsurface defects are introduced at the coating-substrate interface and within the substrate. The objective of the fracture mechanics analyses is to evaluate the defect driving forces, which are characterized by the strain energy release rates, and determine if defects can become unstable for each of the loading conditions.

  5. A study of fracture mechanisms in ATD roller bearing

    NASA Technical Reports Server (NTRS)

    Zee, Ralph H.

    1990-01-01

    The purpose was to investigate how microstructures, especially anisotropy, affects internal stresses and the overall mechanical response of bearings. Samples with the stress axis along the aligned carbide direction possessed high modulus values compared to those with their axis perpendicular to the carbide stringers. The difference in the modulus was found to be more than a factor of two. A series of experiments was conducted on rolled samples to further investigate this effect; the two sets of results were consistent with each other. The degree of anisotropy of the microstructure in terms of the carbide and matrix orientations was determined using x-ray diffraction. The stress state determination was conducted using neutron diffraction. It was found that there was little variation in the distribution of the internal stresses amongst different samples, indicating that small changes in the processing and geometrical conditions did not result in significant variations in the internal stress. A nominal tensile hoop stress of 39 ksi was obtained for the inner raceway. Furthermore, during the course of the investigation, it was apparent that there was a need to determine the stress state induced by the shrink fitting process. Therefore, a series of experiments was conducted using strain gages to identify the stress distribution in a shrink fitting process in three different types of geometries. Correlations were obtained to estimate the highest stress values in the outer and inner groove geometry. A finite element program based on the ANSYS system was developed to compute the stress distribution in the inner raceway geometry. This analysis indicates that the highest tensile stress in the system occurs at the ID of the ring with a stress value of over 5 times that of the applied radial stress. Results from all these facets were correlated with one another. It appears that the material does not fail as a result of any one single factor, but results from a combination of

  6. The mechanics of delamination in fiber-reinforced composite materials. II - The delamination behavior and fracture mechanics parameters

    NASA Technical Reports Server (NTRS)

    Wang, S. S.; Choi, I.

    1983-01-01

    Based on theories of laminate anisotropic elasticity and interlaminar fracture, the complete solution structure associated with a composite delamination is determined. Fracture mechanics parameters characterizing the interlaminar crack behavior are defined from asymptotic stress solutions for delaminations with different crack-tip deformation configurations. A numerical method employing singular finite elements is developed to study delaminations in fiber composites with any arbitrary combinations of lamination, material, geometric, and crack variables. The special finite elements include the exact delamination stress singularity in its formulation. The method is shown to be computationally accurate and efficient, and operationally simple. To illustrate the basic nature of composite delamination, solutions are shown for edge-delaminated (0/-0/-0/0) and (+ or - 0/+ or - 0/90/90 deg) graphite-epoxy systems under uniform axial extension. Three-dimensional crack-tip stress intensity factors, associated energy release rates, and delamination crack-closure are determined for each individual case. The basic mechanics and mechanisms of composite delamination are studied, and fundamental characteristics unique to recently proposed tests for interlaminar fracture toughness of fiber composite laminates are examined. Previously announced in STAR as N84-13222

  7. The mechanics of delamination in fiber-reinforced composite materials. Part 2: Delamination behavior and fracture mechanics parameters

    NASA Technical Reports Server (NTRS)

    Wang, S. S.; Choi, I.

    1983-01-01

    Based on theories of laminate anisotropic elasticity and interlaminar fracture, the complete solution structure associated with a composite delamination is determined. Fracture mechanics parameters characterizing the interlaminar crack behavior are defined from asymptotic stress solutions for delaminations with different crack-tip deformation configurations. A numerical method employing singular finite elements is developed to study delaminations in fiber composites with any arbitrary combinations of lamination, material, geometric, and crack variables. The special finite elements include the exact delamination stress singularity in its formulation. The method is shown to be computationally accurate and efficient, and operationally simple. To illustrate the basic nature of composite delamination, solutions are shown for edge-delaminated (0/-0/-0/0) and (+ or - 0/+ or - 0/90/90 deg) graphite-epoxy systems under uniform axial extenstion. Three-dimensional crack-tip stress intensity factors, associated energy release rates, and delamination crack-closure are determined for each individual case. The basic mechanics and mechanisms of composite delamination are studied, and fundamental characteristics unique to recently proposed tests for interlaminar fracture toughness of fiber composite laminates are examined.

  8. EGS in sedimentary basins: sensitivity of early-flowback tracer signals to induced-fracture parameters

    NASA Astrophysics Data System (ADS)

    Karmakar, Shyamal; Ghergut, Julia; Sauter, Martin

    2015-04-01

    Artificial-fracture design, and fracture characterization during or following stimulation treatment is a central aspect of many EGS ('enhanced' or 'engineered' geothermal system) projects. During the creation or stimulation of an EGS, the injection of fluids, followed by flowback and production stages offers the opportunity for conducting various tracer tests in a single-well (SW) configuration, and given the typical operational and time limitations associated with such tests, along with the need to assess treatment success in real time, investigators mostly favour using short-time tracer-test data, rather than awaiting long-term 'tailings' of tracer signals. Late-time tracer signals from SW injection-flowback and production tests have mainly been used for the purpose of multiple-fracture inflow profiling in multi-layer reservoirs [1]. However, the potential of using SW short-term tracer signals for fracture characterization [2, 3] remained little explored as yet. Dealing with short-term flowback signals, we face a certain degree of parameter interplay, leading to ambiguity in fracture parameter inversion from the measured signal of a single tracer. This ambiguity can, to a certain extent, be overcome by - combining different sources of information (lithostratigraphy, and hydraulic monitoring) in order to constrain the variation range of hydrogeologic parameters (matrix and fracture permeability and porosity, fracture size), - using different types of tracers, such as conservative tracer pairs with contrasting diffusivity, or tracers pairs with contrasting sorptivity onto target surfaces. Fracture height is likely to be constrained by lithostratigraphy, while fracture length is supposed to be determinable from hydraulic monitoring (pressure recordings); the flowback rate can be assumed as a known (measurable) quantity during individual-fracture flowback. This leaves us with one or two unknown parameters to be determined from tracer signals: - the transport

  9. A qualitative engineering analysis of occlusion effects on mandibular fracture repair mechanics.

    PubMed

    Katona, Thomas R

    2011-01-01

    Objectives. The purpose of this analytical study was to examine and critique the engineering foundations of commonly accepted biomechanical principles of mandible fracture repair. Materials and Methods. Basic principles of static equilibrium were applied to intact and plated mandibles, but instead of the traditional lever forces, the mandibles were subjected to more realistic occlusal forces. Results. These loading conditions produced stress distributions within the intact mandible that were very different and more complex than the customary lever-based gradient. The analyses also demonstrated the entirely different mechanical environments within intact and plated mandibles. Conclusions. Because the loading and geometry of the lever-idealized mandible is incomplete, the associated widely accepted bone stress distribution (tension on top and compression on the bottom) should not be assumed. Furthermore, the stress gradients within the bone of an intact mandible should not be extrapolated to the mechanical environment within the plated regions of a fractured mandible.

  10. The effect of adhesive layer elasticity on the fracture mechanics of a blister test specimen

    NASA Technical Reports Server (NTRS)

    Updike, D. P.

    1975-01-01

    An analytical model of a blister type specimen for evaluating adhesive bond strength was developed. Plate theory with shear deformation was used to model the deformation of the plate, and elastic deformation of the adhesive layer is taken into account. It is shown that the inclusion of the elastic deformation of the adhesive layer can have a significant influence in the energy balance calculations of fracture mechanics.

  11. Fracture mechanics analysis of a high-pressure hydrogen facility compressor

    NASA Technical Reports Server (NTRS)

    Vroman, G. A.

    1974-01-01

    The investigation and analysis of a high-pressure hydrogen facility compressor is chronicled, and a life prediction based on fracture mechanics is presented. Crack growth rates in SA 105 Gr II steel are developed for the condition of sustained loading, using a hypothesis of hydrogen embrittlement associated with plastic zone reverse yielding. The resultant formula is compared with test data obtained from laboratory specimens.

  12. Numerical Modeling of Fracture Propagation in Naturally Fractured Formations

    NASA Astrophysics Data System (ADS)

    Wang, W.; Prodanovic, M.; Olson, J. E.; Schultz, R.

    2015-12-01

    Hydraulic fracturing consists of injecting fluid at high pressure and high flowrate to the wellbore for the purpose of enhancing production by generating a complex fracture network. Both tensile failure and shear failure occur during the hydraulic fracturing treatment. The shear event can be caused by slip on existing weak planes such as faults or natural fractures. From core observation, partially cemented and fully cemented opening mode natural fractures, often with considerable thickness are widely present. Hydraulic fractures can propagate either within the natural fracture (tensile failure) or along the interface between the natural fracture and the rock matrix (tensile/shear failure), depending on the relative strength of cement and rock matrix materials, the bonding strength of interface, as well as the presence of any heterogeneities. In this study, we evaluate the fracture propagation both experimentally and numerically. We embed one or multiple inclusions of different mechanical properties within synthetic hydrostone samples in order to mimic cemented natural fractures and rock. A semi-circular bending test is performed for each set of properties. A finite element model built with ABAQUS is used to mimic the semi-circular bending test and study the fracture propagation path, as well as the matrix-inclusion bonding interface status. Mechanical properties required for the numerical model are measured experimentally. The results indicate that the match between experiment and modeling fracture path are extremely sensitive to the chosen interface (bonding) model and related parameters. The semi-circular bending test is dry and easily conducted, providing a good platform for validating numerical approaches. A validated numerical model will enable us to add pressurized fluid within the crack and simulate hydraulic fracture-natural fracture interaction in the reservoir conditions, ultimately providing insights into the extent of the fracture network.

  13. Incorporation of Interfacial Intermetallic Morphology in Fracture Mechanism Map for Sn-Ag-Cu Solder Joints

    NASA Astrophysics Data System (ADS)

    Huang, Z.; Kumar, P.; Dutta, I.; Sidhu, R.; Renavikar, M.; Mahajan, R.

    2014-01-01

    A fracture mechanism map (FMM) is a powerful tool which correlates the fracture behavior of a material to its microstructural characteristics in an explicit and convenient way. In the FMM for solder joints, an effective thickness of the interfacial intermetallic compound (IMC) layer ( t eff) and the solder yield strength ( σ ys,eff) are used as abscissa and ordinate axes, respectively, as these two predominantly affect the fracture behavior of solder joints. Earlier, a definition of t eff, based on the uniform thickness of IMC ( t u) and the average height of the IMC scallops ( t s), was proposed and shown to aptly explain the fracture behavior of solder joints on Cu. This paper presents a more general definition of t eff that is more widely applicable to a range of metallizations, including Cu and electroless nickel immersion gold (ENIG). Using this new definition of t eff, mode I FMM for SAC387/Cu joints has been updated and its validity was confirmed. A preliminary FMM for SAC387/Cu joints with ENIG metallization is also presented.

  14. Distal radius fractures-Design of locking mechanism in plate system and recent surgical procedures.

    PubMed

    Inagaki, Katsunori; Kawasaki, Keikichi

    2016-05-01

    Recently, many studies have emphasized the importance of the comprehension of detailed functional anatomy of the distal forearm and wrist joint, and their biomechanics. A significant contribution which yields good functional outcomes of surgical treatment was the development of the locking plate technology; this technology has facilitated the improvement of the surgical technique for the fixation of fractures. This article reviews the locking mechanism and design of the fixation screws and plate, and the details of the surgical technique including the double-tired subchondral support procedure as it is applied to common fractures. Arthroscopic-assisted surgical procedures can be used to reduce the intra-articular fracture fragments after realignment of the distal radius with the locking plate. This technique is also useful at the time of fixation to assess soft tissue injury. The combination of arthroscopic-assisted reduction and locking plate fixation is now indicated for AO type C2 and C3 intra-articular comminuted fractures. PMID:27006135

  15. Fracture toughness testing and toughening mechanisms of some commercial cobalt-free hardfacing alloys

    SciTech Connect

    Cockeram, B.V.

    1998-04-27

    Hardfacing alloys are weld deposited to provide a wear resistant surface for structural base materials. Commercial low cobalt hardfacing alloys are being evaluated to reduce plant activation levels. Since hardfacing alloys typically must be resistant to cracking to assure adequate in service performance, fracture toughness is a critical material property. Fracture toughness (K{sub IC}) measurements of Fe base, Ni-base, and Co-base hardfacing were performed in accordance with ASTM E399-90 procedure in an effort to identify a tough cobalt-free alternative. Reduced scatter in K{sub IC} data was observed for the Fe base hardfacing, and the 95% lower bound K{sub IC} values were generally higher than the Ni-base Hardfacing alloys. Preliminary crack growth data obtained during precracking indicate that the Ni-base hardfacing possess better fatigue crack growth resistance. However, none of the Fe-base or Ni-base hardfacing have K{sub IC} values that are comparable to the reference Co-base hard facing. The test specimens were machined from thick (0.5 inches) weld deposits, and the microstructures of the test specimens are compared with the more prototypic, thinner deposits. Microstructural and fractographic examinations are used to characterize the fracture mechanisms and delineate the operative toughening mechanisms. Crack deflection and crack bridging toughening mechanisms are shown to be relevant for most of the commercial hardfacing.

  16. Damage and fracture mechanisms in cross-woven C/SiC composite subjected to tensile loading

    SciTech Connect

    Wang, M.; Laird, C.

    1994-12-31

    In order to investigate the structure sensitivity of composite behavior, tensile tests were conducted on CVI processed cross-woven C/SiC composites. Tensile damage mechanisms were observed using SEM on loaded and then unloaded samples. The damage modes identified include bundle matrix cracking, fiber/matrix debonding, fiber breaking delamination and bundle splitting. Because of the inhomogeneous SiC distribution in the fiber bundles, matrix cracking was observed to develop three dimensionally, including the following processes: lateral growth in matrix dominated regions such as bundle coatings, and crack arrest due to the decrease in matrix volume fraction, followed by formation of new matrix cracks inside the bundle, producing a damage zone characterized by a high density of small inter-fiber cracks. Final failure of the composite resulted from fiber breaks at different locations across the fiber bundles, producing in a rugged fracture surface.

  17. Hydro-mechanical coupled simulation of hydraulic fracturing using the eXtended Finite Element Method (XFEM)

    NASA Astrophysics Data System (ADS)

    Youn, Dong Joon

    This thesis presents the development and validation of an advanced hydro-mechanical coupled finite element program analyzing hydraulic fracture propagation within unconventional hydrocarbon formations under various conditions. The realistic modeling of hydraulic fracturing is necessarily required to improve the understanding and efficiency of the stimulation technique. Such modeling remains highly challenging, however, due to factors including the complexity of fracture propagation mechanisms, the coupled behavior of fracture displacement and fluid pressure, the interactions between pre-existing natural and initiated hydraulic fractures and the formation heterogeneity of the target reservoir. In this research, an eXtended Finite Element Method (XFEM) scheme is developed allowing for representation of single or multiple fracture propagations without any need for re-meshing. Also, the coupled flows through the fracture are considered in the program to account for their influence on stresses and deformations along the hydraulic fracture. In this research, a sequential coupling scheme is applied to estimate fracture aperture and fluid pressure with the XFEM. Later, the coupled XFEM program is used to estimate wellbore bottomhole pressure during fracture propagation, and the pressure variations are analyzed to determine the geometry and performance of the hydraulic fracturing as pressure leak-off test. Finally, material heterogeneity is included into the XFEM program to check the effect of random formation property distributions to the hydraulic fracture geometry. Random field theory is used to create the random realization of the material heterogeneity with the consideration of mean, standard deviation, and property correlation length. These analyses lead to probabilistic information on the response of unconventional reservoirs and offer a more scientific approach regarding risk management for the unconventional reservoir stimulation. The new stochastic approach

  18. American Society of Biomechanics Journal of Biomechanics Award 2013: Cortical bone tissue mechanical quality and biological mechanisms possibly underlying atypical fractures

    PubMed Central

    Geissler, Joseph R.; Bajaj, Devendra; Fritton, J. Christopher

    2015-01-01

    The biomechanics literature contains many well-understood mechanisms behind typical fracture types that have important roles in treatment planning. The recent association of “atypical” fractures with long-term use of drugs designed to prevent osteoporosis has renewed interest in the effects of agents on bone tissue-level quality. While this class of fracture was recognized prior to the introduction of the anti-resorptive bisphosphonate drugs and recently likened to stress fractures, the mechanism(s) that lead to atypical fractures have not been definitively identified. Thus, a causal relationship between these drugs and atypical fracture has not been established. Physicians, bioengineers and others interested in the biomechanics of bone are working to improve fracture-prevention diagnostics, and the design of treatments to avoid this serious side-effect in the future. This review examines the mechanisms behind the bone tissue damage that may produce the atypical fracture pattern observed increasingly with long-term bisphosphonate use. Our recent findings and those of others reviewed support that the mechanisms behind normal, healthy excavation and tunnel filling by bone remodeling units within cortical tissue strengthen mechanical integrity. The ability of cortical bone to resist the damage induced during cyclic loading may be altered by the reduced remodeling and increased tissue age resulting from long-term bisphosphonate treatment. Development of assessments for such potential fractures would restore confidence in pharmaceutical treatments that have the potential to spare millions in our aging population from the morbidity and death that often follow bone fracture. PMID:25683519

  19. Application of dynamic fracture mechanics to the investigation of catastrophic failure in aircraft structures

    NASA Astrophysics Data System (ADS)

    Chow, Benjamin Bin

    A dynamic fracture mechanics approach to the estimation of the residual strength of aircraft structures is presented. The dependence of the dynamic crack initiation toughness of aluminum 2024-T3 on loading rate is first studied experimentally. Based on the experimental results and on established dynamic fracture mechanic concepts, a fracture mechanics based failure model is established and is used to estimate the residual strength of aircraft structures. A methodology to determine residual strength of dynamically loaded structures based on global structural analysis coupled with local finite element analysis is introduced. Local finite element calculations were performed for different loading rates to simulate the conditions encountered in an explosively loaded aircraft fuselage. The results from the analyses were then used in conjunction with the experimental results for the dynamic fracture toughness of a 2024-T3 aluminum alloy as a function of loading rate, KdIC vs. K˙d(t), to determine the time to failure, tf, for a given loading rate. A failure envelope, sf vs. ṡ , based on the failure model and finite element analysis, is presented for the different cases and the implications for the residual strength of aircraft structures is discussed. Mixed mode dynamic crack initiation in aluminum 2024-T3 alloy is investigated by combining experiments with numerical simulations. The optical technique of coherent gradient sensing (CGS) and a strain gage method are employed to study the evolution of the mixed mode stress intensity factors. The dynamic mixed mode failure envelope is obtained using the crack initiation data from the experiments at a nominal loading rate of 7 x 105 MPam/s . Numerical simulations of the experiments are conducted to both help in designing the experiments and to validate the results of the experiments. The numerical simulations show good correlation with the experimental results.

  20. Study of fracture mechanisms of short fiber reinforced AS composite by acoustic emission technique

    SciTech Connect

    Kida, Sotoaki; Suzuki, Megumu

    1995-11-01

    The fracture mechanisms of short fiber reinforced AS composites are studied by acoustic emission technique for examining the effects of fiber contents. The loads P{sub b} and P{sub c} which the damage mechanisms change are obtained at the inflection points of the total AE energy curve the energy gradient method. The damages are generated by fiber breaking at the load point of P{sub b} and P{sub c} in B material, and by the fiber breaking and the debonding between resin and fiber at the load points of P{sub b} and P{sub c} in C material.

  1. Martensitic stainless steel AISI 420—mechanical properties, creep and fracture toughness

    NASA Astrophysics Data System (ADS)

    Brnic, J.; Turkalj, G.; Canadija, M.; Lanc, D.; Krscanski, S.

    2011-11-01

    In this paper some experimental results and analyses regarding the behavior of AISI 420 martensitic stainless steel under different environmental conditions are presented. That way, mechanical properties like ultimate tensile strength and 0.2 percent offset yield strength at lowered and elevated temperatures as well as short-time creep behavior for selected stress levels at selected elevated temperatures of mentioned material are shown. The temperature effect on mentioned mechanical properties is also presented. Fracture toughness was calculated on the basis of Charpy impact energy. Experimentally obtained results can be of importance for structure designers.

  2. Mechanical stress, fracture risk and beak evolution in Darwin's ground finches (Geospiza)

    PubMed Central

    Soons, Joris; Herrel, Anthony; Genbrugge, Annelies; Aerts, Peter; Podos, Jeffrey; Adriaens, Dominique; de Witte, Yoni; Jacobs, Patric; Dirckx, Joris

    2010-01-01

    Darwin's finches have radiated from a common ancestor into 14 descendent species, each specializing on distinct food resources and evolving divergent beak forms. Beak morphology in the ground finches (Geospiza) has been shown to evolve via natural selection in response to variation in food type, food availability and interspecific competition for food. From a mechanical perspective, however, beak size and shape are only indirectly related to birds' abilities to crack seeds, and beak form is hypothesized to evolve mainly under selection for fracture avoidance. Here, we test the fracture-avoidance hypothesis using finite-element modelling. We find that across species, mechanical loading is similar and approaches reported values of bone strength, thus suggesting pervasive selection on fracture avoidance. Additionally, deep and wide beaks are better suited for dissipating stress than are more elongate beaks when scaled to common sizes and loadings. Our results illustrate that deep and wide beaks in ground finches enable reduction of areas with high stress and peak stress magnitudes, allowing birds to crack hard seeds while limiting the risk of beak failure. These results may explain strong selection on beak depth and width in natural populations of Darwin's finches. PMID:20194171

  3. Characterization of the Microstructure, Fracture, and Mechanical Properties of Aluminum Alloys 7085-O and 7175-T7452 Hollow Cylinder Extrusions

    NASA Astrophysics Data System (ADS)

    Benoit, Samuel G.; Chalivendra, Vijaya B.; Rice, Matthew A.; Doleski, Robert F.

    2016-09-01

    Microstructural, tensile, and fracture characterizations of cylindrically forged forms of aluminum alloys AA7085-O and AA7175-T7452 were performed. Mechanical and fracture properties were investigated along radial, circumferential, and longitudinal directions to determine directional dependency. American Society for Testing and Materials (ASTM) test methods (ASTM E8-04 and ASTM E1820) were employed for both the tensile and fracture characterizations, respectively. The tensile and fracture properties were related to microstructure in each direction. The strength, elongation at break, and ultimate tensile strength of AA7085-O were higher than those of AA7175-T7452. AA7175-T7452 alloy failed in a brittle manner during fracture studies. AA7085-O outperformed AA7175-T7452 on fracture energy in all of the orientations studied. Smaller grain sizes on the planes normal to circumferential and longitudinal directions showed improvement in both elongation at break and fracture energy values compared to those of radial direction. Scanning electron microscopy images demonstrated cleavage fracture in AA7175-T7452 and transgranular fracture in AA7085-O.

  4. Investigation of the fracture mechanism in Ti-5Al-2.5Sn at cryogenic temperatures

    NASA Technical Reports Server (NTRS)

    Vanstone, R. H.; Low, J. R., Jr.; Shannon, J. L., Jr.

    1977-01-01

    The influence of microstructure on the fracture mechanism and plane-strain fracture toughness of Ti-5Al-2.5Sn was studied through the use of fractography and metallographic sectioning techniques. One-inch thick plates of extra low interstitial (ELI) and normal interstitial Ti-5Al-2.5Sn were mill annealed at 815 C followed by either air or furnace cooling. These variations in composition and cooling rate resulted in differences in the volume fraction and internal structure of the iron-stabilized phase, and in the crystallographic texture and ordering of the alpha matrix. The tensile properties of these plates were determined at 20 K, 77 K, and 295 K. The air-cooled ELI plate was the toughest material evaluated.

  5. A fracture mechanics study of the turbine wheel in the Space Shuttle auxiliary power unit

    NASA Technical Reports Server (NTRS)

    Forman, R. G.

    1985-01-01

    The experimental and analytical efforts performed for fracture control of the Space Shuttle auxiliary power unit (APU) wheel are described and a summary of fracture mechanics concepts relevant to safe-life analysis of fatigue loaded parts is given. An environmental crack growth test program is conducted by NASA on candidate wheel materials exposed to decomposed hydrazine which is found to be no more severe in causing crack growth than an environment of high-temperature air. Details of the crack growth testing and the safe-life analysis are presented. The results show that special nondestructive examination is needed for the APU wheel to meet the required mission life for either the maximum design or expected speed-range operations.

  6. A novel Lagrangian approach for the stable numerical simulation of fault and fracture mechanics

    NASA Astrophysics Data System (ADS)

    Franceschini, Andrea; Ferronato, Massimiliano; Janna, Carlo; Teatini, Pietro

    2016-06-01

    The simulation of the mechanics of geological faults and fractures is of paramount importance in several applications, such as ensuring the safety of the underground storage of wastes and hydrocarbons or predicting the possible seismicity triggered by the production and injection of subsurface fluids. However, the stable numerical modeling of ground ruptures is still an open issue. The present work introduces a novel formulation based on the use of the Lagrange multipliers to prescribe the constraints on the contact surfaces. The variational formulation is modified in order to take into account the frictional work along the activated fault portion according to the principle of maximum plastic dissipation. The numerical model, developed in the framework of the Finite Element method, provides stable solutions with a fast convergence of the non-linear problem. The stabilizing properties of the proposed model are emphasized with the aid of a realistic numerical example dealing with the generation of ground fractures due to groundwater withdrawal in arid regions.

  7. ADDITIONAL STRESS AND FRACTURE MECHANICS ANALYSES OF PRESSURIZED WATER REACTOR PRESSURE VESSEL NOZZLES

    SciTech Connect

    Walter, Matthew; Yin, Shengjun; Stevens, Gary; Sommerville, Daniel; Palm, Nathan; Heinecke, Carol

    2012-01-01

    In past years, the authors have undertaken various studies of nozzles in both boiling water reactors (BWRs) and pressurized water reactors (PWRs) located in the reactor pressure vessel (RPV) adjacent to the core beltline region. Those studies described stress and fracture mechanics analyses performed to assess various RPV nozzle geometries, which were selected based on their proximity to the core beltline region, i.e., those nozzle configurations that are located close enough to the core region such that they may receive sufficient fluence prior to end-of-life (EOL) to require evaluation of embrittlement as part of the RPV analyses associated with pressure-temperature (P-T) limits. In this paper, additional stress and fracture analyses are summarized that were performed for additional PWR nozzles with the following objectives: To expand the population of PWR nozzle configurations evaluated, which was limited in the previous work to just two nozzles (one inlet and one outlet nozzle). To model and understand differences in stress results obtained for an internal pressure load case using a two-dimensional (2-D) axi-symmetric finite element model (FEM) vs. a three-dimensional (3-D) FEM for these PWR nozzles. In particular, the ovalization (stress concentration) effect of two intersecting cylinders, which is typical of RPV nozzle configurations, was investigated. To investigate the applicability of previously recommended linear elastic fracture mechanics (LEFM) hand solutions for calculating the Mode I stress intensity factor for a postulated nozzle corner crack for pressure loading for these PWR nozzles. These analyses were performed to further expand earlier work completed to support potential revision and refinement of Title 10 to the U.S. Code of Federal Regulations (CFR), Part 50, Appendix G, Fracture Toughness Requirements, and are intended to supplement similar evaluation of nozzles presented at the 2008, 2009, and 2011 Pressure Vessels and Piping (PVP

  8. Dyke propagation and tensile fracturing at high temperature and pressure, insights from experimental rock mechanics.

    NASA Astrophysics Data System (ADS)

    Bakker, Richard; Benson, Philip; Vinciguerra, Sergio

    2014-05-01

    It is well known that magma ascends trough the crust by the process of dyking. To enable dyke emplacement, basement rocks typically fail in a mode 1 fracture, which acts as conduits for magma transport. An overpressure of the ascending magma will further open/widen the fracture and permit the fracture to propagate. In order to further understand the emplacement and arrest of dykes in the subsurface, analogue and numerical studies have been conducted. However, a number of assumptions regarding rock mechanical behaviour frequently has to be made as such data are very hard to directly measure at the pressure/temperature conditions of interest: high temperatures at relatively shallow depths. Such data are key to simulating the magma intrusion dynamics through the lithologies that underlie the volcanic edifice. Here we present a new laboratory setup, which allows us to investigate the tensile fracturing properties under both temperature and confining pressure, and the emplacement of molten material within the newly formed fracture. We have modified a traditional tri-axial test assembly setup to be able to use a Paterson type High Pressure, High Temperature deformation apparatus. Sample setup consists of cylindrical rock samples with a 22 mm diameter and a 8 mm bore at their centre, filled with a material chosen as such that it's in a liquid state at the experimental temperature and solid at room temperature to enable post-experiment analysis. The top and lower parts of the rock sample are fitted with plugs, sealing in the melt. The assembly is then placed between ceramic pistons to ensure there are no thermal gradients across the sample. The assembly is jacketed to ensure the confining medium (Ar) cannot enter the assembly. A piston is driven into the sample such that the inner conduit materials pressure is slowly increased. At some point a sufficient pressure difference between the inner and outer surfaces causes the sample to deform and fail in the tensile regime

  9. NESC-VII: Fracture Mechanics Analyses of WPS Experiments on Large-scale Cruciform Specimen

    SciTech Connect

    Yin, Shengjun; Williams, Paul T; Bass, Bennett Richard

    2011-01-01

    This paper describes numerical analyses performed to simulate warm pre-stress (WPS) experiments conducted with large-scale cruciform specimens within the Network for Evaluation of Structural Components (NESC-VII) project. NESC-VII is a European cooperative action in support of WPS application in reactor pressure vessel (RPV) integrity assessment. The project aims in evaluation of the influence of WPS when assessing the structural integrity of RPVs. Advanced fracture mechanics models will be developed and performed to validate experiments concerning the effect of different WPS scenarios on RPV components. The Oak Ridge National Laboratory (ORNL), USA contributes to the Work Package-2 (Analyses of WPS experiments) within the NESCVII network. A series of WPS type experiments on large-scale cruciform specimens have been conducted at CEA Saclay, France, within the framework of NESC VII project. This paper first describes NESC-VII feasibility test analyses conducted at ORNL. Very good agreement was achieved between AREVA NP SAS and ORNL. Further analyses were conducted to evaluate the NESC-VII WPS tests conducted under Load-Cool-Transient- Fracture (LCTF) and Load-Cool-Fracture (LCF) conditions. This objective of this work is to provide a definitive quantification of WPS effects when assessing the structural integrity of reactor pressure vessels. This information will be utilized to further validate, refine, and improve the WPS models that are being used in probabilistic fracture mechanics computer codes now in use by the NRC staff in their effort to develop risk-informed updates to Title 10 of the U.S. Code of Federal Regulations (CFR), Part 50, Appendix G.

  10. Nonlinear mechanical resonators for ultra-sensitive mass detection

    SciTech Connect

    Datskos, Panos G; Lavrik, Nickolay V

    2014-01-01

    The fundamental sensitivity limit of an appropriately scaled down mechanical resonator can approach one atomic mass unit when only thermal noise is present in the system. However, operation of such nanoscale mechanical resonators is very challenging due to minuteness of their oscillation amplitudes and presence of multiple noise sources in real experimental environments. In order to surmount these challenges, we use microscale cantilever resonators driven to large amplitudes, far beyond their nonlinear instability onset. Our experiments show that such a nonlinear cantilever resonator, described analytically as a Duffing oscillator, has mass sensing performance comparable to that of much smaller resonators operating in a linear regime. We demonstrate femtogram level mass sensing that relies on a bifurcation point tracking that does not require any complex readout means. Our approaches enable straightforward detection of mass changes that are near the fundamental limit imposed by thermo-mechanical fluctuations.

  11. Fracture mechanics of human cortical bone: The relationship of geometry, microstructure and composition with the fracture of the tibia, femoral shaft and the femoral neck

    NASA Astrophysics Data System (ADS)

    Yeni, Yener Nail

    Bone fracture is a major health problem in old population with its complications leading to mortality and morbidity. Therapies mostly involve preventing bone mass loss. Individuals with high bone mass, however, may still suffer fractures suggesting that additional components such as bone microstructure and composition may be responsible for increased fracture risk in the elderly. The relationship of bone constituents with bone fragility, however, is not well-understood. A better understanding of these relationships will help improving therapies by controlling the relevant biological processes. Bone is a composite material with many constituents such as osteons embedded with vascular channels, collagen fibers, mineral crystals, etc. The nature of interfacing between these constituents makes bone a more complex material. Bone also has a structure that adapts itself, both internally and externally, to better fit its needs. This suggested that, unlike man-made materials, a relationship between material properties and structural properties may exist. Because bone has some similarities with engineering composite materials and also experiences microcracks, a fracture mechanics approach would be more appropriate for investigating its fragility. Choosing mode I and mode II fracture toughness (Gsb{Ic} and Gnsb{IIc}, respectively) as indicators of bone fragility, their relationship with bone microstructure (porosity, osteon morphology, mineral crystal imperfection and microdamage), composition (density, mineral, organic, water and collagen content) and macrostructure (thickness, diameter and moment of inertia of the shaft and angle between the femoral neck and femoral shaft from different views) was investigated. Use of x-ray radiogrammetry for detecting the latter was tested. Differences among the femoral shaft, femoral neck and the tibia were investigated for an age range of 22-94 years. In general, fracture toughness increased with increasing bone quantity. However, the

  12. A nonlinear fracture mechanics approach to the growth of small cracks

    NASA Technical Reports Server (NTRS)

    Newman, J. C., Jr.

    1983-01-01

    An analytical model of crack closure is used to study the crack growth and closure behavior of small cracks in plates and at notches. The calculated crack opening stresses for small and large cracks, together with elastic and elastic plastic fracture mechanics analyses, are used to correlate crack growth rate data. At equivalent elastic stress intensity factor levels, calculations predict that small cracks in plates and at notches should grow faster than large cracks because the applied stress needed to open a small crack is less than that needed to open a large crack. These predictions agree with observed trends in test data. The calculations from the model also imply that many of the stress intensity factor thresholds that are developed in tests with large cracks and with load reduction schemes do not apply to the growth of small cracks. The current calculations are based upon continuum mechanics principles and, thus, some crack size and grain structure exist where the underlying fracture mechanics assumptions become invalid because of material inhomogeneity (grains, inclusions, etc.). Admittedly, much more effort is needed to develop the mechanics of a noncontinuum. Nevertheless, these results indicate the importance of crack closure in predicting the growth of small cracks from large crack data.

  13. Characterization of an injectable, degradable polymer for mechanical stabilization of mandibular fractures.

    PubMed

    Henslee, Allan M; Yoon, Diana M; Lu, Benjamin Y; Yu, Joseph; Arango, Andrew A; Marruffo, Liann P; Seng, Luke; Anver, Tamir D; Ather, Hunaiza; Nair, Manitha B; Piper, Sean O; Demian, Nagi; Wong, Mark E K; Kasper, F Kurtis; Mikos, Antonios G

    2015-04-01

    This study investigated the use of injectable poly(propylene fumarate) (PPF) formulations for mandibular fracture stabilization applications. A full factorial design with main effects analysis was employed to evaluate the effects of the PPF:N-vinyl pyrrolidone (NVP, crosslinking agent) ratio and dimethyl toluidine (DMT, accelerator) concentration on key physicochemical properties including setting time, maximum temperature, mechanical properties, sol fraction, and swelling ratio. Additionally, the effects of formulation crosslinking time on the mechanical and swelling properties were investigated. The results showed that increasing the PPF:NVP ratio from 3:1 to 4:1 or decreasing the DMT concentration from 0.05 to 0.01 v/w % significantly decreased all mechanical properties as well as significantly increased the sol fraction and swelling ratio. Also, increasing the crosslinking time at 37°C from 1 to 7 days significantly increased all mechanical properties and decreased both the sol fraction and swelling ratio. This study further showed that the flexural stiffness of ex vivo stabilized rabbit mandibles increased from 1.7 ± 0.3 N/mm with a traditional mini-plate fixator to 14.5 ± 4.1 N/mm for the 4:1 (0.05 v/w % DMT) PPF formulation at day 1. Overall, the formulations tested in this study were found to have properties suitable for potential further consideration in mandibular fracture fixation applications.

  14. Kinetics and fracture resistance of lithiated silicon nanostructure pairs controlled by their mechanical interaction

    DOE PAGES

    Lee, Seok Woo; Lee, Hyun -Wook; Ryu, Ill; Nix, William D.; Gao, Huajian; Cui, Yi

    2015-06-26

    Following an explosion of studies of silicon as a negative electrode for Li-ion batteries, the anomalous volumetric changes and fracture of lithiated single Si particles have attracted significant attention in various fields, including mechanics. However, in real batteries, lithiation occurs simultaneously in clusters of Si in a confined medium. Hence, understanding how the individual Si structures interact during lithiation in a closed space is necessary. Here, we demonstrate physical and mechanical interactions of swelling Si structures during lithiation using well-defined Si nanopillar pairs. Ex situ SEM and in situ TEM studies reveal that compressive stresses change the reaction kinetics somore » that preferential lithiation occurs at free surfaces when the pillars are mechanically clamped. Such mechanical interactions enhance the fracture resistance of lithiated Si by lessening the tensile stress concentrations in Si structures. Lastly, this study will contribute to improved design of Si structures at the electrode level for high-performance Li-ion batteries.« less

  15. Characterization of an injectable, degradable polymer for mechanical stabilization of mandibular fractures.

    PubMed

    Henslee, Allan M; Yoon, Diana M; Lu, Benjamin Y; Yu, Joseph; Arango, Andrew A; Marruffo, Liann P; Seng, Luke; Anver, Tamir D; Ather, Hunaiza; Nair, Manitha B; Piper, Sean O; Demian, Nagi; Wong, Mark E K; Kasper, F Kurtis; Mikos, Antonios G

    2015-04-01

    This study investigated the use of injectable poly(propylene fumarate) (PPF) formulations for mandibular fracture stabilization applications. A full factorial design with main effects analysis was employed to evaluate the effects of the PPF:N-vinyl pyrrolidone (NVP, crosslinking agent) ratio and dimethyl toluidine (DMT, accelerator) concentration on key physicochemical properties including setting time, maximum temperature, mechanical properties, sol fraction, and swelling ratio. Additionally, the effects of formulation crosslinking time on the mechanical and swelling properties were investigated. The results showed that increasing the PPF:NVP ratio from 3:1 to 4:1 or decreasing the DMT concentration from 0.05 to 0.01 v/w % significantly decreased all mechanical properties as well as significantly increased the sol fraction and swelling ratio. Also, increasing the crosslinking time at 37°C from 1 to 7 days significantly increased all mechanical properties and decreased both the sol fraction and swelling ratio. This study further showed that the flexural stiffness of ex vivo stabilized rabbit mandibles increased from 1.7 ± 0.3 N/mm with a traditional mini-plate fixator to 14.5 ± 4.1 N/mm for the 4:1 (0.05 v/w % DMT) PPF formulation at day 1. Overall, the formulations tested in this study were found to have properties suitable for potential further consideration in mandibular fracture fixation applications. PMID:24934595

  16. Kinetics and fracture resistance of lithiated silicon nanostructure pairs controlled by their mechanical interaction

    SciTech Connect

    Lee, Seok Woo; Lee, Hyun-Wook; Ryu, Ill; Nix, William D.; Gao, Huajian; Cui, Yi; /Stanford U., Materials Sci. Dept. /SLAC

    2015-06-01

    Following an explosion of studies of silicon as a negative electrode for Li-ion batteries, the anomalous volumetric changes and fracture of lithiated single Si particles have attracted significant attention in various fields, including mechanics. However, in real batteries, lithiation occurs simultaneously in clusters of Si in a confined medium. Hence, understanding how the individual Si structures interact during lithiation in a closed space is necessary. Herein, we demonstrate physical/mechanical interactions of swelling Si structures during lithiation using well-defined Si nanopillar pairs. Ex situ SEM and in situ TEM studies reveal that compressive stresses change the reaction kinetics so that preferential lithiation occurs at free surfaces when the pillars are mechanically clamped. Such mechanical interactions enhance the fracture resistance of This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, under Contract No. DE-AC02-76SF00515. SLAC-PUB-16300 2 lithiated Si by lessening the tensile stress concentrations in Si structures. This study will contribute to improved design of Si structures at the electrode level for high performance Li-ion batteries.

  17. Control of a mechanical aeration process via topological sensitivity analysis

    NASA Astrophysics Data System (ADS)

    Abdelwahed, M.; Hassine, M.; Masmoudi, M.

    2009-06-01

    The topological sensitivity analysis method gives the variation of a criterion with respect to the creation of a small hole in the domain. In this paper, we use this method to control the mechanical aeration process in eutrophic lakes. A simplified model based on incompressible Navier-Stokes equations is used, only considering the liquid phase, which is the dominant one. The injected air is taken into account through local boundary conditions for the velocity, on the injector holes. A 3D numerical simulation of the aeration effects is proposed using a mixed finite element method. In order to generate the best motion in the fluid for aeration purposes, the optimization of the injector location is considered. The main idea is to carry out topological sensitivity analysis with respect to the insertion of an injector. Finally, a topological optimization algorithm is proposed and some numerical results, showing the efficiency of our approach, are presented.

  18. Fracture mechanisms in dual phase steels based on the acicular ferrite + martensite/austenite microstructure

    NASA Astrophysics Data System (ADS)

    Poruks, Peter

    The fracture mechanisms of low carbon microalloyed plate steels based on the acicular ferrite + marten site/austenite microstructure (AF + M/A) are investigated. The final microstructure consists of a dispersed phase of submicron equi-axed martensite particles with a bainitic ferrite matrix. A series of plates with M/A volume fractions of 0.076--0.179 are studied. Brittle fracture is investigated by Instrumented Charpy impact testing of samples at -196°C and subsequent metallography. The M/A particles are identified as the crack nucleation sites and the cleavage fracture stress calculated to be 2400 MPa in a complete AF microstrucuture. This value is significantly larger than in steels that contain significant proportions of conventional bainite. Standard Charpy and Instrumented Charpy impact testing is conducted through a temperature range from -80 to + 22°C to study ductile fracture behaviour. The total absorbed energy is separated into energies of crack nucleation and of crack propagation. It is found that the energy of crack nucleation is weakly dependent on the volume fraction of M/A and completely independent of temperature over the range studied. The crack propagation energy varies significantly with both variables, decreasing with increased volume fraction of M/A and with decreasing temperature. The peak load in the instrumented Charpy data is used to calculate the dynamic fracture toughness, KId, which is found to be 105--120 MPa-m1/2. The void nucleation and void growth stages of ductile fracture are studied by metallographic examination of tensile bars. The sites of void nucleation are identified as inclusions and M/A particles. Voids nucleate at the M/A particles by decohesion of the particle-matrix interface. A constant void nucleation strain of epsilon = 0.90 +/- 0.05 is measured for all of the samples independent of the volume fraction of M/A. A stress-based criterion is used to predict void nucleation and the interface strength is determined to be

  19. Comprehensive mechanisms for combustion chemistry: Experiment, modeling, and sensitivity analysis

    SciTech Connect

    Dryer, F.L.; Yetter, R.A.

    1993-12-01

    This research program is an integrated experimental/numerical effort to study pyrolysis and oxidation reactions and mechanisms for small-molecule hydrocarbon structures under conditions representative of combustion environments. The experimental aspects of the work are conducted in large diameter flow reactors, at pressures from one to twenty atmospheres, temperatures from 550 K to 1200 K, and with observed reaction times from 10{sup {minus}2} to 5 seconds. Gas sampling of stable reactant, intermediate, and product species concentrations provides not only substantial definition of the phenomenology of reaction mechanisms, but a significantly constrained set of kinetic information with negligible diffusive coupling. Analytical techniques used for detecting hydrocarbons and carbon oxides include gas chromatography (GC), and gas infrared (NDIR) and FTIR methods are utilized for continuous on-line sample detection of light absorption measurements of OH have also been performed in an atmospheric pressure flow reactor (APFR), and a variable pressure flow (VPFR) reactor is presently being instrumented to perform optical measurements of radicals and highly reactive molecular intermediates. The numerical aspects of the work utilize zero and one-dimensional pre-mixed, detailed kinetic studies, including path, elemental gradient sensitivity, and feature sensitivity analyses. The program emphasizes the use of hierarchical mechanistic construction to understand and develop detailed kinetic mechanisms. Numerical studies are utilized for guiding experimental parameter selections, for interpreting observations, for extending the predictive range of mechanism constructs, and to study the effects of diffusive transport coupling on reaction behavior in flames. Modeling using well defined and validated mechanisms for the CO/H{sub 2}/oxidant systems.

  20. Mechanisms predisposing penile fracture and long-term outcomes on erectile and voiding functions.

    PubMed

    Reis, Leonardo O; Cartapatti, Marcelo; Marmiroli, Rafael; de Oliveira Júnior, Eduardo Jeronimo; Saade, Ricardo Destro; Fregonesi, Adriano

    2014-01-01

    Purpose. To determine the mechanisms predisposing penile fracture as well as the rate of long-term penile deformity and erectile and voiding functions. Methods. All fractures were repaired on an emergency basis via subcoronal incision and absorbable suture with simultaneous repair of eventual urethral lesion. Patients' status before fracture and voiding and erectile functions at long term were assessed by periodic follow-up and phone call. Detailed history included cause, symptoms, and single-question self-report of erectile and voiding functions. Results. Among the 44 suspicious cases, 42 (95.4%) were confirmed, mean age was 34.5 years (range: 18-60), mean follow-up 59.3 months (range 9-155). Half presented the classical triad of audible crack, detumescence, and pain. Heterosexual intercourse was the most common cause (28 patients, 66.7%), followed by penile manipulation (6 patients, 14.3%), and homosexual intercourse (4 patients, 9.5%). "Woman on top" was the most common heterosexual position (n = 14, 50%), followed by "doggy style" (n = 8, 28.6%). Four patients (9.5%) maintained the cause unclear. Six (14.3%) patients had urethral injury and two (4.8%) had erectile dysfunction, treated by penile prosthesis and PDE-5i. No patient showed urethral fistula, voiding deterioration, penile nodule/curve or pain. Conclusions. "Woman on top" was the potentially riskiest sexual position (50%). Immediate surgical treatment warrants long-term very low morbidity. PMID:24822062

  1. Friction Stir-Welded Titanium Alloy Ti-6Al-4V: Microstructure, Mechanical and Fracture Properties

    NASA Astrophysics Data System (ADS)

    Sanders, D. G.; Edwards, P.; Cantrell, A. M.; Gangwar, K.; Ramulu, M.

    2015-05-01

    Friction stir welding (FSW) has been refined to create butt welds from two sheets of Ti-6Al-4V alloy to have an ultra-fine grain size. Weld specimen testing was completed for three different FSW process conditions: As welded, stress relieved, stress relieved and machined, and for the un-welded base material. The investigation includes macrostructure, microstructure, microhardness, tensile property testing, notched bar impact testing, and fracture toughness evaluations. All experiments were conducted in accordance with industry standard testing specifications. The microstructure in the weld nugget was found to consist of refined and distorted grains of alpha in a matrix of transformed beta containing acicular alpha. The enhanced fracture toughness of the welds is a result of increased hardness, which is attributed to an increase in alpha phase, increase in transformed beta in acicular alpha, and grain refinement during the weld process. The noted general trend in mechanical properties from as welded, to stress relieved, to stress relieved and machined conditions exhibited a decrease in ultimate tensile strength, and yield strength with a small increase in ductility and a significant increase in fracture toughness.

  2. Fracture Mechanisms of Zirconium Diboride Ultra-High Temperature Ceramics under Pulse Loading

    NASA Astrophysics Data System (ADS)

    Skripnyak, Vladimir V.; Bragov, Anatolii M.; Skripnyak, Vladimir A.; Lomunov, Andrei K.; Skripnyak, Evgeniya G.; Vaganova, Irina K.

    2015-06-01

    Mechanisms of failure in ultra-high temperature ceramics (UHTC) based on zirconium diboride under pulse loading were studied experimentally by the method of SHPB and theoretically using the multiscale simulation method. The obtained experimental and numerical data are evidence of the quasi-brittle fracture character of nanostructured zirconium diboride ceramics under compression and tension at high strain rates and the room temperatures. Damage of nanostructured porous zirconium diboride -based UHTC can be formed under stress pulse amplitude below the Hugoniot elastic limit. Fracture of nanostructured ultra-high temperature ceramics under pulse and shock-wave loadings is provided by fast processes of intercrystalline brittle fracture and relatively slow processes of quasi-brittle failure via growth and coalescence of microcracks. A decrease of the shear strength can be caused by nano-voids clusters in vicinity of triple junctions between ceramic matrix grains and ultrafine-grained ceramics. This research was supported by grants from ``The Tomsk State University Academic D.I. Mendeleev Fund Program'' and also N. I. Lobachevski State University of Nizhny Novgorod (Grant of post graduate mobility).

  3. Gating-by-Tilt of Mechanically Sensitive Membrane Channels

    NASA Astrophysics Data System (ADS)

    Turner, Matthew S.; Sens, Pierre

    2004-09-01

    We propose an alternative mechanism for the gating of biological membrane channels in response to membrane tension that involves a change in the slope of the membrane near the channel. Under biological membrane tensions we show that the energy difference between the closed (tilted) and open (untilted) states can far exceed kBT and is comparable to what is available under simple dilational gating. Recent experiments demonstrate that membrane leaflet asymmetries (spontaneous curvature) can strongly affect the gating of some channels. Such a phenomenon would be easier to explain under gating-by-tilt, given its novel intrinsic sensitivity to such asymmetry.

  4. An automated system for measuring multi-dimensional, time dependent mechanical properties of a human tibial fracture.

    PubMed

    Ogrodnik, Peter J; Moorcroft, C Ian; Thomas, Peter B M

    2007-12-01

    An automated loading and measurement device has been developed for assessment of the mechanical properties of a healing human tibial fracture. The characteristics of the device are presented with assessments of errors. This paper constitutes a small part of a long term research project determining a clinically quantifiable end point for fracture healing in humans, hence a sample of results is presented to demonstrate the potential application of the device. A more detailed analysis of the results will be the basis of further publications. The initial results confirm that the non-linear behaviour of callus cannot be ignored in fracture assessment methodologies. They further reinforce the requirement to measure load-rate when measuring fracture stiffness. Polar plots of stiffness demonstrate that when measuring fracture stiffness not only should load-rate be considered, but also the orientation of measurement. The results from this work support the view that fracture stiffness should be measured in at least two planes. A new material property for the assessment of fracture healing, the gamma ratio gamma, is examined and preliminary results are shown. The paper also demonstrates how creep properties of a healing tibia can be assessed and proposes that this property may form the basis for future fracture assessment investigations. PMID:17875395

  5. Measuring multi-dimensional, time-dependent mechanical properties of a human tibial fracture using an automated system.

    PubMed

    Ogrodnik, P J; Moorcroft, C I; Thomas, P B

    2007-08-01

    This paper presents an element of a long-term research project determining a clinically quantifiable end point for fracture healing in humans. An automated loading and measurement device is presented. It has been developed as a research tool for the assessment of the mechanical properties of a healing human tibial fracture. The device has been specifically designed for use with patients treated with external fixation. The characteristics of the device have been presented together with an assessment of errors. A typical sample of results has been presented to demonstrate the significance of the device; subsequent papers will examine the whole data set in greater depth. The results presented here confirm the non-linear behaviour of callus and reinforce the requirement to measure the load rate when measuring the fracture stiffness. A new material property for the assessment of fracture healing, namely gamma, is examined and preliminary results are shown. Polar plots of stiffness demonstrate that, when measuring fracture stiffness, not only should the load rate be considered, but also the orientation of measurement. The results from this work support the view that the fracture stiffness should be measured in at least two planes. Currently a fracture can be considered healed when the fracture stiffness exceeds 15 N m/deg; this paper questions whether this value is now valid and suggests that it should be re-examined. PMID:17937203

  6. Fracture mechanics. [review of fatigue crack propagation and technology of constructing safe structures

    NASA Technical Reports Server (NTRS)

    Hardrath, H. F.

    1974-01-01

    Fracture mechanics is a rapidly emerging discipline for assessing the residual strength of structures containing flaws due to fatigue, corrosion or accidental damage and for anticipating the rate of which such flaws will propagate if not repaired. The discipline is also applicable in the design of structures with improved resistance to such flaws. The present state of the design art is reviewed using this technology to choose materials, to configure safe and efficient structures, to specify inspection procedures, to predict lives of flawed structures and to develop reliability of current and future airframes.

  7. Materials characterization and fracture mechanics of a space grade dielectric silicone insulation

    NASA Technical Reports Server (NTRS)

    Abdel-Latif, A. I.; Tweedie, A. T.

    1982-01-01

    The present investigation is concerned with the DC 93-500 high voltage silicone insulation material employed to pot the gun and the collector end of a traveling wave tube (TWT) used on the Landsat D Satellite. The fracture mechanics behavior of the silicone resin was evaluated by measuring the slow crack velocity as a function of the opening mode of the stress intensity factor at +25 and -10 C, taking into account various uniaxial discrete strain values. It was found that the silicone resins slow crack growth is faster than that for a high voltage insulation polyurethane material at the same stress intensity factor value and room temperature.

  8. Results of fracture mechanics analyses of the ederer cranes in the device assembly

    SciTech Connect

    Dalder, E.

    1996-08-01

    Fracture mechanics analyses were conducted on three critical locations on the lower flange of the load-beam of the Ederer 5 ton and 4 ton cranes in the D.A.F. Facility. Based on these results, it appears that: 1. Propagation of a 5 mm long flaw, previously undetected by non-destructive examination (NDE), to a length sufficient to cause structural failure of either flange, should not occur in at least 100 times the postulated operating scenarios for each crane; 2. Should each crane undergo annual inspection, any surface flaw with a length greater that 20 mm should be removed and repaired by qualified and approved repair procedures.

  9. Recent fracture mechanics results from NASA research related to the aging commercial transport fleet

    NASA Technical Reports Server (NTRS)

    Harris, Charles E.

    1991-01-01

    NASA is conducting the Airframe Structural Integrity Program in support of the aging commercial transport fleet. This interdisciplinary program is being worked in cooperation with the U.S. airframe manufacturers, airline operators, and the FAA. Advanced analysis methods are under development to predict the fatigue crack growth in complex built-up shell structures. Innovative nondestructive examination technologies are also under development to provide large area inspection capability to detect corrosion, disbonds, and fatigue cracks. Recent fracture mechanics results applicable to predicting the growth of cracks initiating at the rivets of fuselage splice joints are reviewed.

  10. Modeling and additive manufacturing of bio-inspired composites with tunable fracture mechanical properties.

    PubMed

    Dimas, Leon S; Buehler, Markus J

    2014-07-01

    Flaws, imperfections and cracks are ubiquitous in material systems and are commonly the catalysts of catastrophic material failure. As stresses and strains tend to concentrate around cracks and imperfections, structures tend to fail far before large regions of material have ever been subjected to significant loading. Therefore, a major challenge in material design is to engineer systems that perform on par with pristine structures despite the presence of imperfections. In this work we integrate knowledge of biological systems with computational modeling and state of the art additive manufacturing to synthesize advanced composites with tunable fracture mechanical properties. Supported by extensive mesoscale computer simulations, we demonstrate the design and manufacturing of composites that exhibit deformation mechanisms characteristic of pristine systems, featuring flaw-tolerant properties. We analyze the results by directly comparing strain fields for the synthesized composites, obtained through digital image correlation (DIC), and the computationally tested composites. Moreover, we plot Ashby diagrams for the range of simulated and experimental composites. Our findings show good agreement between simulation and experiment, confirming that the proposed mechanisms have a significant potential for vastly improving the fracture response of composite materials. We elucidate the role of stiffness ratio variations of composite constituents as an important feature in determining the composite properties. Moreover, our work validates the predictive ability of our models, presenting them as useful tools for guiding further material design. This work enables the tailored design and manufacturing of composites assembled from inferior building blocks, that obtain optimal combinations of stiffness and toughness. PMID:24700202

  11. Modeling and additive manufacturing of bio-inspired composites with tunable fracture mechanical properties.

    PubMed

    Dimas, Leon S; Buehler, Markus J

    2014-07-01

    Flaws, imperfections and cracks are ubiquitous in material systems and are commonly the catalysts of catastrophic material failure. As stresses and strains tend to concentrate around cracks and imperfections, structures tend to fail far before large regions of material have ever been subjected to significant loading. Therefore, a major challenge in material design is to engineer systems that perform on par with pristine structures despite the presence of imperfections. In this work we integrate knowledge of biological systems with computational modeling and state of the art additive manufacturing to synthesize advanced composites with tunable fracture mechanical properties. Supported by extensive mesoscale computer simulations, we demonstrate the design and manufacturing of composites that exhibit deformation mechanisms characteristic of pristine systems, featuring flaw-tolerant properties. We analyze the results by directly comparing strain fields for the synthesized composites, obtained through digital image correlation (DIC), and the computationally tested composites. Moreover, we plot Ashby diagrams for the range of simulated and experimental composites. Our findings show good agreement between simulation and experiment, confirming that the proposed mechanisms have a significant potential for vastly improving the fracture response of composite materials. We elucidate the role of stiffness ratio variations of composite constituents as an important feature in determining the composite properties. Moreover, our work validates the predictive ability of our models, presenting them as useful tools for guiding further material design. This work enables the tailored design and manufacturing of composites assembled from inferior building blocks, that obtain optimal combinations of stiffness and toughness.

  12. Behavioural and physiological mechanisms of polarized light sensitivity in birds.

    PubMed

    Muheim, Rachel

    2011-03-12

    Polarized light (PL) sensitivity is relatively well studied in a large number of invertebrates and some fish species, but in most other vertebrate classes, including birds, the behavioural and physiological mechanism of PL sensitivity remains one of the big mysteries in sensory biology. Many organisms use the skylight polarization pattern as part of a sun compass for orientation, navigation and in spatial orientation tasks. In birds, the available evidence for an involvement of the skylight polarization pattern in sun-compass orientation is very weak. Instead, cue-conflict and cue-calibration experiments have shown that the skylight polarization pattern near the horizon at sunrise and sunset provides birds with a seasonally and latitudinally independent compass calibration reference. Despite convincing evidence that birds use PL cues for orientation, direct experimental evidence for PL sensitivity is still lacking. Avian double cones have been proposed as putative PL receptors, but detailed anatomical and physiological evidence will be needed to conclusively describe the avian PL receptor. Intriguing parallels between the functional and physiological properties of PL reception and light-dependent magnetoreception could point to a common receptor system.

  13. Behavioural and physiological mechanisms of polarized light sensitivity in birds

    PubMed Central

    Muheim, Rachel

    2011-01-01

    Polarized light (PL) sensitivity is relatively well studied in a large number of invertebrates and some fish species, but in most other vertebrate classes, including birds, the behavioural and physiological mechanism of PL sensitivity remains one of the big mysteries in sensory biology. Many organisms use the skylight polarization pattern as part of a sun compass for orientation, navigation and in spatial orientation tasks. In birds, the available evidence for an involvement of the skylight polarization pattern in sun-compass orientation is very weak. Instead, cue-conflict and cue-calibration experiments have shown that the skylight polarization pattern near the horizon at sunrise and sunset provides birds with a seasonally and latitudinally independent compass calibration reference. Despite convincing evidence that birds use PL cues for orientation, direct experimental evidence for PL sensitivity is still lacking. Avian double cones have been proposed as putative PL receptors, but detailed anatomical and physiological evidence will be needed to conclusively describe the avian PL receptor. Intriguing parallels between the functional and physiological properties of PL reception and light-dependent magnetoreception could point to a common receptor system. PMID:21282180

  14. Source Mechanisms of Low Frequency Seismicity in a Hydraulic Fracturing Context

    NASA Astrophysics Data System (ADS)

    Zecevic, M.; Daniel, G.; Hubans, F.; Gouedard, P.

    2014-12-01

    In recent years, long-period long-duration (LPLD) events have been observed during hydraulic fracturing of hydrocarbon reservoirs (Das & Zoback, 2013). LPLDs are low-amplitude signals lasting from tens of seconds to minutes. Their source mechanisms are not fully understood. However, as they are remarkably similar in character to tectonic tremors it has been suggested that they may also have comparable source models. Current models suggest that a tectonic tremor consists of numerous slow-slip earthquakes superposed on each other to form continuous waveforms (Shelley et al., 2007). These slow-slip earthquakes are thought to be a result of shear slip on faults close to failure with low confining pressure, most likely due to the presence of fluid with pore pressures close to lithostatic pressures (Peng & Gomberg, 2010). This study aims to further understand the source mechanism of LPLDs. A hydraulic fracturing dataset containing thousands of located microseismic earthquakes (MEQs) and numerous LPLDs is presented. The MEQs are located around the injection stages whereas the LPLDs are clustered in a limited region within the reservoir. This clustering suggests that LPLDs can only be generated where the conditions in the reservoir are favorable. These results correspond with the possibility that LPLDs are manifestations of slow-slip, with the source locations confined by variations in the mechanical properties of the reservoir. To test this hypothesis a further understanding of the mechanisms of LPLDs and the stress field in which they occur is needed. However, calculating focal mechanisms for LPLDs is difficult due to their emergent onset and lack of clear phases. Consequently, LPLDs must be put into context with the observed MEQs. We will present the spatial distribution of the focal mechanisms of the MEQs and analyze our findings with respect to the occurrence of the LPLD events.

  15. Low frequency, high sensitive tunable mechanical monolithic horizontal sensors

    NASA Astrophysics Data System (ADS)

    Acernese, Fausto; De Rosa, Rosario; Giordano, Gerardo; Romano, Rocco; Vilasi, Silvia; Barone, Fabrizio

    2011-04-01

    This paper describes an optimized version of the mechanical version of the monolithic tunable folded pendulum, developed at the University of Salerno, configurable both as seismometer and, in a force-feedback configuration, as accelerometer. Typical application of the sensors are in the field of geophysics, including the study of seismic and newtonian noise for characterization of suitable sites for underground interferometer for gravitational waves detection. The sensor, shaped with precision machining and electric-discharge-machining, like the previous version, is a very compact instrument, very sensitive in the low-frequency seismic noise band, with a very good immunity to environmental noises. Important characteristics are the tunability of the resonance frequency and the integrated laser optical readout, consisting of an optical lever and an interferometer. The theoretical sensitivity curves, largely improved due to a new design of the pendulum arms and of the electronics, are in a very good agreement with the measurements. The very large measurement band (10-6 +/- 10Hz) is couple to a very good sensitivity (10-12 m/√Hz in the band 0.1 +/- 10Hz), as seismometer. Prototypes of monolithic seismometers are already operational in selected sites around the world both to acquire seismic data for scientific analysis of seismic noise and to collect all the useful information to understand their performances in the very low frequency band (f < 1mHz). The results of the monolithic sensor as accelerometer (force feed-back configuration) are also presented and discussed. Particular relevance has their sensitivity that is better than 10-11 m/s2/√Hz in the band 0.1 +/- 10Hz. Finally, hypotheses are made on further developments and improvements of monolithic sensors.

  16. Mechanisms of defect complex formation and environmental-assisted fracture behavior of iron aluminides

    SciTech Connect

    Cooper, B.R.; Muratov, L.S.; Kang, B.S.J.; Li, K.Z.

    1997-12-01

    Iron aluminide has excellent corrosion resistance in high-temperature oxidizing-sulfidizing environments; however, there are problems at room and medium temperature with hydrogen embrittlement as related to exposure to moisture. In this research, a coordinated computational modeling/experimental study of mechanisms related to environmental-assisted fracture behavior of selected iron aluminides is being undertaken. The modeling and the experimental work will connect at the level of coordinated understanding of the mechanisms for hydrogen penetration and for loss of strength and susceptibility to fracture. The focus of the modeling component at this point is on the challenging question of accurately predicting the iron vacancy formation energy in Fe{sub 3}A{ell} and the subsequent tendency, if present, for vacancy clustering. The authors have successfully performed, on an ab initio basis, the first calculation of the vacancy formation energy in Fe{sub 3}A{ell}. These calculations include lattice relaxation effects which are quite large. This has significant implications for vacancy clustering effects with consequences to be explored for hydrogen diffusion. The experimental work at this stage has focused on the relationship of the choice and concentration of additives to the improvement of resistance to hydrogen embrittlement and hence to the fracture behavior. For this reason, comparative crack growth tests of FA-186, FA-187, and FA-189 iron aluminides (all with basic composition of Fe-28A{ell}-5Cr, at % with micro-alloying additives of Zr, C or B) under, air, oxygen, or water environment have been performed. These tests showed that the alloys are susceptible to room temperature hydrogen embrittlement in both B2 and DO{sub 3} conditions. Test results indicated that FA-187, and FA-189 are intrinsically more brittle than FA-186.

  17. Long-term cumulative survival and mechanical complications of single-tooth Ankylos Implants: focus on the abutment neck fractures

    PubMed Central

    2015-01-01

    PURPOSE To evaluate the cumulative survival rate (CSR) and mechanical complications of single-tooth Ankylos® implants. MATERIALS AND METHODS This was a retrospective clinical study that analyzed 450 single Ankylos® implants installed in 275 patients between December 2005 and December 2012. The main outcomes were survival results CSR and implant failure) and mechanical complications (screw loosening, fracture, and cumulative fracture rate [CFR]). The main outcomes were analyzed according to age, sex, implant length or diameter, bone graft, arch, and position. RESULTS The 8-year CSR was 96.9%. Thirteen (2.9%) implants failed because of early osseointegration failure in 3, marginal bone loss in 6, and abutment fracture in 4. Screw loosening occurred in 10 implants (2.2%), and 10 abutment fractures occurred. All abutment fractures were located in the neck, and concurrent screw fractures were observed. The CSR and rate of screw loosening did not differ significantly according to factors. The CFR was higher in middle-aged patients (5.3% vs 0.0% in younger and older patients); for teeth in a molar position (5.8% vs 0.0% for premolar or 1.1% for anterior position); and for larger-diameter implants (4.5% for 4.5 mm and 6.7% for 5.5 mm diameter vs 0.5% for 3.5 mm diameter) (all P<.05). CONCLUSION The Ankylos® implant is suitable for single-tooth restoration in Koreans. However, relatively frequent abutment fractures (2.2%) were observed and some fractures resulted in implant failures. Middle-aged patients, the molar position, and a large implant diameter were associated with a high incidence of abutment fracture. PMID:26813443

  18. Fracture mechanics models developed for piping reliability assessment in light water reactors: piping reliability project

    SciTech Connect

    Harris, D.O.; Lim, E.Y.; Dedhia, D.D.; Woo, H.H.; Chou, C.K.

    1982-06-01

    The efforts concentrated on modifications of the stratified Monte Carlo code called PRAISE (Piping Reliability Analysis Including Seismic Events) to make it more widely applicable to probabilistic fracture mechanics analysis of nuclear reactor piping. Pipe failures are considered to occur as the result of crack-like defects introduced during fabrication, that escape detection during inspections. The code modifications allow the following factors in addition to those considered in earlier work to be treated: other materials, failure criteria and subcritical crack growth characteristic; welding residual and vibratory stresses; and longitudinal welds (the original version considered only circumferential welds). The fracture mechanics background for the code modifications is included, and details of the modifications themselves provided. Additionally, an updated version of the PRAISE user's manual is included. The revised code, known as PRAISE-B was then applied to a variety of piping problems, including various size lines subject to stress corrosion cracking and vibratory stresses. Analyses including residual stresses and longitudinal welds were also performed.

  19. Mechanisms of fracture of the free surface of shock-compressed metals

    SciTech Connect

    Mokhova, V. V. Mikhailov, A. L.; Til’kunov, A. V.; Orlov, N. I.; Kanunova, L. I.; Bragunets, V. A.; Tkachenko, M. I.; Simakov, V. G.; Sokolov, S. S.; Podurets, A. M.

    2015-12-15

    The mechanisms of the ejection of aluminum and copper microparticles from the free surfaces of these metals have been studied under conditions of the escape of a moderate-intensity shock wave from a sample. The free surfaces of samples contained 0.7–0.9 mm deep artificial wells and protrusions simulating (on a greater scale of 10: 1) the natural surface roughness retained upon mechanical processing. The pressure in a shock-wave pulse at the base of a protrusion was controlled within P = 5–20 GPa (i.e., below the melting region), and the variable duration of pressure pulses was 0.02, 0.2, and 1 μs. Analysis of the free surfaces of postloaded samples showed that, for certain loading and roughness parameters, the ejection of metal from vertices of protruding ridges or pyramids (as a result of the longitudinal fracture) was about ten times greater than the amount of metal ejected in the form of cumulative jets from wells. The amount of ejected metal and the size distribution of metal microparticles were quantitatively characterized using “soft collecting targets” and by measuring mass losses of samples upon fracture.

  20. Fracture mechanics based design for radioactive material transport packagings -- Historical review

    SciTech Connect

    Smith, J.A.; Salzbrenner, D.; Sorenson, K.; McConnell, P.

    1998-04-01

    The use of a fracture mechanics based design for the radioactive material transport (RAM) packagings has been the subject of extensive research for more than a decade. Sandia National Laboratories (SNL) has played an important role in the research and development of the application of this technology. Ductile iron has been internationally accepted as an exemplary material for the demonstration of a fracture mechanics based method of RAM packaging design and therefore is the subject of a large portion of the research discussed in this report. SNL`s extensive research and development program, funded primarily by the U. S. Department of Energy`s Office of Transportation, Energy Management and Analytical Services (EM-76) and in an auxiliary capacity, the office of Civilian Radioactive Waste Management, is summarized in this document along with a summary of the research conducted at other institutions throughout the world. In addition to the research and development work, code and standards development and regulatory positions are also discussed.

  1. A predictive mechanical model for evaluating vertebral fracture probability in lumbar spine under different osteoporotic drug therapies.

    PubMed

    López, E; Ibarz, E; Herrera, A; Puértolas, S; Gabarre, S; Más, Y; Mateo, J; Gil-Albarova, J; Gracia, L

    2016-07-01

    Osteoporotic vertebral fractures represent a major cause of disability, loss of quality of life and even mortality among the elderly population. Decisions on drug therapy are based on the assessment of risk factors for fracture from bone mineral density (BMD) measurements. A previously developed model, based on the Damage and Fracture Mechanics, was applied for the evaluation of the mechanical magnitudes involved in the fracture process from clinical BMD measurements. BMD evolution in untreated patients and in patients with seven different treatments was analyzed from clinical studies in order to compare the variation in the risk of fracture. The predictive model was applied in a finite element simulation of the whole lumbar spine, obtaining detailed maps of damage and fracture probability, identifying high-risk local zones at vertebral body. For every vertebra, strontium ranelate exhibits the highest decrease, whereas minimum decrease is achieved with oral ibandronate. All the treatments manifest similar trends for every vertebra. Conversely, for the natural BMD evolution, as bone stiffness decreases, the mechanical damage and fracture probability show a significant increase (as it occurs in the natural history of BMD). Vertebral walls and external areas of vertebral end plates are the zones at greatest risk, in coincidence with the typical locations of osteoporotic fractures, characterized by a vertebral crushing due to the collapse of vertebral walls. This methodology could be applied for an individual patient, in order to obtain the trends corresponding to different treatments, in identifying at-risk individuals in early stages of osteoporosis and might be helpful for treatment decisions. PMID:27265047

  2. Simulating Thermal-Hydrologic-Mechanical-Chemical Evolution Surrounding Fluid Injection in a Fractured Porous Geothermal Reservoir

    NASA Astrophysics Data System (ADS)

    Taron, J.; Min, K.; Elsworth, D.

    2006-12-01

    Computational analysis is conducted on the coupled thermal-hydrologic-mechanical-chemical (THMC) behavior of a stimulated EGS geothermal reservoir. Numerical analyses utilize a newly developed simulator capable of examining THMC processes in fractured porous geologic media. The simulator links the thermal-hydrologic- chemical (THC) computational code TOUGHREACT with the mechanical (M) capability of FLAC3D, where the response of pore fluid pressure to mechanical disturbance is treated as an undrained system and mineral precipitation/dissolution generates porosity and permeability change within each dual-permeability continuum. Non-linear permeability response to thermal-hydrologic-mechanical (THM) mechanisms is accommodated via embryonic mechanical and transport constitutive laws, and is considered to act in union with permeability changes associated with the removal or addition of minerals within the system. This construct is applied to the geometry of an injector-withdrawal doublet within the Coso Geothermal field, where in situ stress conditions, thermal state, and mineralogical composition at 3000m depth are extracted from recorded field data. Initial results for feasible parametric settings show that permeability reduction in the vicinity of a cool (80°C) injection well may be significant, within an order of magnitude, and accompanied by large (MPa) changes in the stress field throughout the reservoir for imposed boundary conditions of constant stress.

  3. Hydraulic fracture propagation modeling and data-based fracture identification

    NASA Astrophysics Data System (ADS)

    Zhou, Jing

    Successful shale gas and tight oil production is enabled by the engineering innovation of horizontal drilling and hydraulic fracturing. Hydraulically induced fractures will most likely deviate from the bi-wing planar pattern and generate complex fracture networks due to mechanical interactions and reservoir heterogeneity, both of which render the conventional fracture simulators insufficient to characterize the fractured reservoir. Moreover, in reservoirs with ultra-low permeability, the natural fractures are widely distributed, which will result in hydraulic fractures branching and merging at the interface and consequently lead to the creation of more complex fracture networks. Thus, developing a reliable hydraulic fracturing simulator, including both mechanical interaction and fluid flow, is critical in maximizing hydrocarbon recovery and optimizing fracture/well design and completion strategy in multistage horizontal wells. A novel fully coupled reservoir flow and geomechanics model based on the dual-lattice system is developed to simulate multiple nonplanar fractures' propagation in both homogeneous and heterogeneous reservoirs with or without pre-existing natural fractures. Initiation, growth, and coalescence of the microcracks will lead to the generation of macroscopic fractures, which is explicitly mimicked by failure and removal of bonds between particles from the discrete element network. This physics-based modeling approach leads to realistic fracture patterns without using the empirical rock failure and fracture propagation criteria required in conventional continuum methods. Based on this model, a sensitivity study is performed to investigate the effects of perforation spacing, in-situ stress anisotropy, rock properties (Young's modulus, Poisson's ratio, and compressive strength), fluid properties, and natural fracture properties on hydraulic fracture propagation. In addition, since reservoirs are buried thousands of feet below the surface, the

  4. Mechanical characterization of temperature-sensitive objects using picosecond ultrasonics

    NASA Astrophysics Data System (ADS)

    Dehoux, T.; Audoin, B.; Zouani, O.; Durrieu, M. C.

    2011-01-01

    Biological objects are exquisitely sensitive to temperature variations and their mechanical characterization is often a challenge when using the picosecond ultrasonics technique. To reduce the laser-induced temperature rise, we place single biological cells on a thin metal transducer and we focus the laser beam that generates the acoustic waves at frequencies <= 150 GHz on the rear side of the transducer. The acoustic waves propagate through the transducer and are partially transmitted to the cell to create the so-called Brillouin oscillations. The frequency of these oscillations provides a direct measurement of the sound velocity. The simultaneous measurement of the acoustic reflection coefficient at the transducer/cell interface allows the determination of both the density and the compressibility of the cell.

  5. Synaptic mechanisms of adaptation and sensitization in the retina

    PubMed Central

    Nikolaev, Anton; Leung, Kin-Mei; Odermatt, Benjamin; Lagnado, Leon

    2014-01-01

    Sensory systems continually adjust the way stimuli are processed. What are the circuit mechanisms underlying this plasticity? We investigated how synapses in the retina of zebrafish adjust to changes in the temporal contrast of a visual stimulus by imaging activity in vivo. Following an increase in contrast, bipolar cell synapses with strong initial responses depressed, whereas synapses with weak initial responses facilitated. Depression and facilitation predominated in different strata of the inner retina, where bipolar cell output was anticorrelated with the activity of amacrine cell synapses providing inhibitory feedback. Pharmacological block of GABAergic feedback converted facilitating bipolar cell synapses into depressing ones. These results indicate that depression intrinsic to bipolar cell synapses causes adaptation of the ganglion cell response to contrast, whereas depression in amacrine cell synapses causes sensitization. Distinct microcircuits segregating to different layers of the retina can cause simultaneous increases or decreases in the gain of neural responses. PMID:23685718

  6. Rapid Dye Regeneration Mechanism of Dye-Sensitized Solar Cells.

    PubMed

    Jeon, Jiwon; Park, Young Choon; Han, Sang Soo; Goddard, William A; Lee, Yoon Sup; Kim, Hyungjun

    2014-12-18

    During the light-harvesting process of dye-sensitized solar cells (DSSCs), the hole localized on the dye after the charge separation yields an oxidized dye, D(+). The fast regeneration of D(+) using the redox pair (typically the I(-)/I3(-) couple) is critical for the efficient DSSCs. However, the kinetic processes of dye regeneration remain uncertain, still promoting vigorous debates. Here, we use molecular dynamics simulations to determine that the inner-sphere electron-transfer pathway provides a rapid dye regeneration route of ∼4 ps, where penetration of I(-) next to D(+) enables an immediate electron transfer, forming a kinetic barrier. This explains the recently reported ultrafast dye regeneration rate of a few picoseconds determined experimentally. We expect that our MD based comprehensive understanding of the dye regeneration mechanism will provide a helpful guideline in designing TiO2-dye-electrolyte interfacial systems for better performing DSSCs. PMID:26273975

  7. A 37-year-old mechanic with multiple chemical sensitivities.

    PubMed Central

    Kipen, H M; Fiedler, N

    2000-01-01

    A 37-year-old heating, ventilation, and air-conditioning mechanic developed respiratory, musculoskeletal, and central nervous system symptoms associated with a variety of odorous environmental chemicals. Organic disease was not evident, but the patient was distressed by these symptoms and was at risk for becoming disabled by them. His symptoms fit broadly into the condition recognized as multiple chemical sensitivity. Multiple chemical sensitivity is a diagnostic term for a group of symptoms without demonstrated organic basis. The symptoms are characteristic of dysfunction in multiple organ systems, they increase and decrease according to exposure to low levels of chemical agents in the patient's environment, and they sometimes occur after a distinct environmental change or insult such as an industrial accident or remodeling. Although traditional medical organizations have not agreed on a definition for this syndrome, it is being increasingly recognized and makes up an increasing percentage of the caseload at occupational and environmental medicine clinics. Although there is often dispute about whether the symptoms have a functional or organic basis, an informed approach to evaluation, diagnosis, and management and a careful assessment of impairment, disability, and work relatedness are necessary. Careful exclusion of organic causes is critical, and this should be followed by a judicious approach to coping with symptoms. PMID:10753098

  8. Role of aortic arch vascular mechanics in cardiovagal baroreflex sensitivity.

    PubMed

    Klassen, Stephen A; Chirico, Daniele; Dempster, Kylie S; Shoemaker, J Kevin; O'Leary, Deborah D

    2016-07-01

    Cardiovagal baroreflex sensitivity (cvBRS) measures the efficiency of the cardiovagal baroreflex to modulate heart rate in response to increases or decreases in systolic blood pressure (SBP). Given that baroreceptors are located in the walls of the carotid sinuses (CS) and aortic arch (AA), the arterial mechanics of these sites are important contributors to cvBRS. However, the relative contribution of CS and AA mechanics to cvBRS remains unclear. This study employed sex differences as a model to test the hypothesis that differences in cvBRS between groups would be explained by the vascular mechanics of the AA but not the CS. Thirty-six young, healthy, normotensive individuals (18 females; 24 ± 2 yr) were recruited. cvBRS was measured using transfer function analysis of the low-frequency region (0.04-0.15 Hz). Ultrasonography was performed at the CS and AA to obtain arterial diameters for the measurement of distensibility. Local pulse pressure (PP) was taken at the CS using a hand-held tonometer, whereas AA PP was estimated using a transfer function of brachial PP. Both cvBRS (25 ± 11 vs. 19 ± 7 ms/mmHg, P = 0.04) and AA distensibility (16.5 ± 6.0 vs. 10.5 ± 3.8 mmHg(-1) × 10(-3), P = 0.02) were greater in females than males. Sex differences in cvBRS were eliminated after controlling for AA distensibility (P = 0.19). There were no sex differences in CS distensibility (5.32 ± 2.3 vs. 4.63 ± 1.3 mmHg(-1) × 10(-3), P = 0.32). The present data demonstrate that AA mechanics are an important contributor to differences in cvBRS.

  9. Experimental Investigation of Fracture Aperture Evolution Under Coupled Thermo-Hydro-Mechanical-Chemical Processes Encountered in Enhanced Geyhermal Systems

    NASA Astrophysics Data System (ADS)

    Ghazanfari, E.

    2015-12-01

    The success and sustainability of an Enhance Gethermal System (EGS) reservoir depends strongly on the permeability of its fracture network. Several processes affect the permeability of the system, including thermo, hydro, mechanical and chemical processes. These processes interact with one another temporally and contribute to the evolution of permeability within an EGS reservoir during normal operation. This study attempts to experimentally investigate the fracture aperture evolution under coupled processes in EGS reservoir. Granite specimens extracted from the Barre Granite quarry (Barre, Vermont) were used in the experiments. The artificially fractured core rock specimens were scanned using X-Ray Micro- CT and steady-state flow-through experiments were performed on the fractured specimens using high pressure/temperature servo-hydraulic operated system (Autolab 1500). The rock specimens were subjected to 30 MPa of confining pressure and 5 MPa of static internal pore pressure and Temperature of 120 °C. After 24 hours of equilibration, the flow of deionized water was initiated through the artificial fracture at a rate of 0.000351 ml/min for 40 days, during which effluent samples were collected for ICP-MS analysis and fracture permeability was monitored using upstream and downstream pore pressures. Upon termination of the experiments, the core rocks were scanned again to investigate the changes in fracture aperture and dissolution/precipitation of minerals at different sections of the core rock. The experimental results demonstrated that fracture surface asperities initially prop the fracture open, but upon introduction to deionized water, the asperities dissolve and the fracture aperture closes, resulting in decreased permeability. In most experiments, fracture aperture decreased steadily with the presumed dissolution of fracture surface asperities up to 30 days and then a decrease of upstream pore pressure was observed, which might be explained by etching

  10. A coupled thermo-poro-mechanical finite element analysis of fractured porous rocks using a cohesive interface element

    NASA Astrophysics Data System (ADS)

    Wang, W.; Regueiro, R. A.

    2014-12-01

    The coupling between multiphase flow, heat transfer, and poromechanics in fractured geomaterials has aroused great interest in the areas of geomechanics, geoenvironmental engineering, and petroleum engineering. Relevant applications include nuclear waste repositories, geological sequestration of CO2, geothermal systems, and exploitation of shale gas reservoirs. The paper presents a fully coupled thermo-poro-mechanical (TPM) cohesive interface element (CIE) model, which can represent fluid and heat flow along and across the fracture, and shear/normal deformation of the fracture surfaces. The proposed model is then applied to analyze two popular geological engineering problems using the finite element method (FEM) with a small strain formulation. The first application is the fracturing process in organic-rich shale due to heating. In the finite element analysis, multiple horizontal microcracks parallel to the bedding plane are assumed to preexist in the porous source rock, and are represented by coupled TPM cohesive interface elements. The porous bulk rock is assumed to be homogeneous, isotropic (for the time being, with transverse isotropy a natural extension), and linearly elastic. The excess pore fluid pressure, which mainly causes the development of the fractures, is actually induced by the rapid decomposition of organic matter during heating according to the literature. However, the involved complex chemical reaction process is beyond the scope of the paper, and is therefore substituted by a fluid injection process within the cracks under room temperature (25C) and high temperature (400C) in the paper. We investigate the fracture propagation due to pore fluid pressure increase and the development of fracture-induced permeability. The second application is a nuclear waste repository in a partially saturated fractured rock. Multiphase transport of moisture and heat, thermally-induced stress, as well as the change of fracture apertures are investigated due to short

  11. Evaluation of hydrogen pressure vessels using slow strain rate testing and fracture mechanics analysis

    SciTech Connect

    Murray, S.H.; Desai, V.H.

    1998-12-31

    A total of 108 seamless, forged pressure vessels, fabricated from ASTM A372 type IV (UNS K14508) and type V low alloy steel, are currently in 4,200 psi (29 MPa) gaseous hydrogen (GH{sub 2}) service at the Kennedy Space Center`s (KSC) Space Shuttle Launch Complex 39 (LC-39). The vessels were originally used in 6,000 psi (41 MPa) GH{sub 2} service during the Apollo program. NASA recently received a letter of warning from the manufacturer of the vessels stating that the subject vessels should be now be removed from GH{sub 2} service due to the fact that the ultimate tensile strength (UTS) of many of the vessels exceeds the maximum limit of 126 ksi (869 MPa) now imposed on A372 steel intended for GH{sub 2} service, and therefore are susceptible to hydrogen environment embrittlement. Due to the expense associated with vessel replacement, it was decided to determine by testing and analysis whether or not the vessels needed to be removed from GH{sub 2} service. Slow strain rate testing was performed under hydrogen charging conditions to determine the value of the threshold fracture toughness for sustained loading crack growth in GH{sub 2}, (K{sub H}) for the vessel material, this value was then used in a fracture mechanics safe-life analysis (a 20-year service life was modeled) that indicated the vessels are safe for continued use.

  12. Analysis of mechanical strength to fixing the femoral neck fracture in synthetic bone type Asnis

    PubMed Central

    Freitas, Anderson; Lula, Welder Fernandes; de Oliveira, Jonathan Sampaio; Maciel, Rafael Almeida; Souto, Diogo Ranier de Macedo; Godinho, Patrick Fernandes

    2014-01-01

    OBJECTIVE: To analyze the results of biomechanical assays of fixation of Pauwels type III femoral neck fracture in synthetic bone, using 7.5mm cannulated screws in inverted triangle formation, in relation to the control group. METHODS: Ten synthetic bones were used, from a domestic brand, divided into two groups: test and control. In the test group, a 70° tilt osteotomy of the femoral neck was fixated using three cannulated screws in inverted triangle formation. The resistance of this fixation and its rotational deviation were analyzed at 5mm displacement (phase 1) and 10mm displacement (phase 2). The control group was tested in its integrity until the fracture of the femoral neck occurred. The Mann-Whitney test was used for group analysis and comparison. RESULTS: The values in the test group in phase 1, in samples 1-5, showed a mean of 579N and SD =77N. Rotational deviations showed a mean of 3.33°, SD = 2.63°. In phase 2, the mean was 696N and SD =106N. The values of the maximum load in the control group had a mean of 1329N and SD=177N. CONCLUSION: The analysis of mechanical strength between the groups determined a statistically significant lower value in the test group. Level of Evidence III, Control Case. PMID:25246851

  13. Neural Mechanisms of Rapid Sensitivity to Syntactic Anomaly

    PubMed Central

    Kim, Albert E.; Gilley, Phillip M.

    2013-01-01

    Recent psycholinguistic models hypothesize that anticipatory processing can speed the response to linguistic input during language comprehension by pre-activating representations necessary for word recognition. We investigated the neurocognitive mechanisms of anticipatory processing by recording event-related potentials (ERPs) to syntactically anomalous (The thief was caught by for police) and well-formed (e.g., The thief was caught by the police) sentences. One group of participants saw anomalies elicited by the same word in every instance (e.g., for; low-variability stimuli), providing high affordances for predictions about the word-form appearing in the critical position. A second group saw anomalies elicited by seven different prepositions (at, of, on, for, from, over, with; high-variability stimuli) across the study, creating a more difficult prediction task. Syntactic category anomalies enhanced the occipital-temporal N170 component of the ERP, indicating rapid sensitivity – within 200 ms of word-onset – to syntactic anomaly. For low-variability but not the high-variability stimuli, syntactic anomaly also enhanced the earlier occipital-temporal P1 component, around 130 ms after word-onset, indicating that affordances for prediction engendered earlier sensitivity to syntactic anomaly. Independent components analysis revealed three sources within the ERP signal whose functional dynamics were consistent with predictive processing and early responses to syntactic anomaly. Distributed neural source modeling (sLORETA) of these early active sources produced a candidate network for early responses to words during reading in the right posterior occipital, left occipital-temporal, and medial parietal cortex. PMID:23515395

  14. Fundamental Mechanisms of Tensile Fracture in Aluminum Sheet Unidirectionally Reinforced with Boron Filament. Ph.D. Thesis - Virginia Polytechnic Inst.

    NASA Technical Reports Server (NTRS)

    Herring, H. W.

    1971-01-01

    Results are presented from an experimental research effort to gain a more complete understanding of the physics of tensile fracture in unidirectionally reinforced B-Al composite sheet. By varying the degree of filament degradation resulting from fabrication, composite specimens were produced which failed in tension by the cumulative mode, the noncumulative mode, or by any desired combination of the two modes. Radiographic and acoustic emission techniques were combined to identify and physically describe a previously unrecognized fundamental fracture mechanism which was responsible for the noncumulative mode. The tensile strength of the composite was found to be severely limited by the noncumulative mechanism which involved the initiation and sustenance of a chain reaction of filament fractures at a relatively low stress level followed by ductile fracture of the matrix. The minimum average filament stress required for initiation of the fracture mechanism was shown to be approximately 170 ksi, and appeared to be independent of filament diameter, number of filament layers, and the identity of the matrix alloy.

  15. Mechanics of tungsten blistering II: Analytical treatment and fracture mechanical assessment

    NASA Astrophysics Data System (ADS)

    Li, Muyuan; You, Jeong-Ha

    2015-10-01

    Since a decade the blistering of pure tungsten under hydrogen implantation has been one of the major research topics in relation to the plasma-wall interaction of tungsten-armored first wall. Overall blistering may reduce the erosion lifetime of the wall. Mature blisters grown by high internal pressure are likely to burst leading to exfoliation of the surface. Therefore, the control and suppression of blistering is an important concern for sustainable operation of the tungsten-armored plasma-facing components. In this context, a quantitative assessment of the mechanical conditions for blister bulging and growth is an important concern. In this article a theoretical framework is presented to describe the bulging deformation of tungsten blisters and to estimate the mechanical driving force of blister growth. The validity of the analytical formulations based on the theory of elastic plates is evaluated with the help of finite element analysis. Plastic strains and J-integral values at the blister boundary edge are assessed by means of numerical simulation. Extensive parametric studies were performed for a range of blister geometry (cap aspect ratio), gas pressure, yield stress and hardening rate. The characteristic features of the blistering mechanics are discussed and the cracking energy is quantitatively estimated for the various combinations of parameters.

  16. Fracture mechanics of matrix cracking and delamination in glass/epoxy laminates

    NASA Technical Reports Server (NTRS)

    Caslini, M.; Zanotti, C.; Obrien, T. K.

    1986-01-01

    This study focused on characterizing matrix cracking and delamination behavior in multidirectional laminates. Static tension and tension-tension fatigue tests were conducted on two different layups. Damage onset, accumulation, and residual properties were measured. Matrix cracking was shown to have a considerable influence on residual stiffness of glass epoxy laminates, and could be predicted reasonably well for cracks in 90 deg piles using a simple shear lag analysis. A fracture mechanics analysis for the strain energy release rate associated with 90 deg ply-matrix crack formation was developed and was shown to correlate the onset of 90 deg ply cracks in different laminates. The linear degradation of laminate modulus with delamination area, previously observed for graphite epoxy laminates, was predicted for glass epoxy laminates using a simple rule of mixtures analysis. The strain energy release rate associated with edge delamination formation under static and cyclic loading was difficult to analyze because of the presence of several contemporary damage phenomena.

  17. Addendum to the User Manual for NASGRO Elastic-Plastic Fracture Mechanics Software Module

    NASA Technical Reports Server (NTRS)

    Gregg, M. Wayne (Technical Monitor); Chell, Graham; Gardner, Brian

    2003-01-01

    The elastic-plastic fracture mechanics modules in NASGRO have been enhanced by the addition of of the following: new J-integral solutions based on the reference stress method and finite element solutions; the extension of the critical crack and critical load modules for cracks with two degrees of freedom that tear and failure by ductile instability; the addition of a proof test analysis module that includes safe life analysis, calculates proof loads, and determines the flaw screening 1 capability for a given proof load; the addition of a tear-fatigue module for ductile materials that simultaneously tear and extend by fatigue; and a multiple cycle proof test module for estimating service reliability following a proof test.

  18. DEFORMATION AND FRACTURE OF POORLY CONSOLIDATED MEDIA - Borehole Failure Mechanisms in High-Porosity Sandstone

    SciTech Connect

    Bezalel c. Haimson

    2005-06-10

    We investigated failure mechanisms around boreholes and the formation of borehole breakouts in high-porosity sandstone, with particular interest to grain-scale micromechanics of failure leading to the hitherto unrecognized fracture-like borehole breakouts and apparent compaction band formation in poorly consolidated granular materials. We also looked at a variety of drilling-related factors that contribute to the type, size and shape of borehole breakouts. The objective was to assess their effect on the ability to establish correlations between breakout geometry and in situ stress magnitudes, as well as on borehole stability prediction, and hydrocarbon/water extraction in general. We identified two classes of medium to high porosity (12-30%) sandstones, arkosic, consisting of 50-70% quartz and 15 to 50% feldspar, and quartz-rich sandstones, in which quartz grain contents varied from 90 to 100%. In arkose sandstones critical far-field stress magnitudes induced compressive failure around boreholes in the form of V-shaped (dog-eared) breakouts, the result of dilatant intra-and trans-granular microcracking subparallel to both the maximum horizontal far-field stress and to the borehole wall. On the other hand, boreholes in quartz-rich sandstones failed by developing fracture-like breakouts. These are long and very narrow (several grain diameters) tabular failure zones perpendicular to the maximum stress. Evidence provided mainly by SEM observations suggests a failure process initiated by localized grain-bond loosening along the least horizontal far-field stress springline, the packing of these grains into a lower porosity compaction band resembling those discovered in Navajo and Aztec sandstones, and the emptying of the loosened grains by the circulating drilling fluid starting from the borehole wall. Although the immediate several grain layers at the breakout tip often contain some cracked or even crushed grains, the failure mechanism enabled by the formation of the

  19. A fracture mechanics analysis of impact damage in a thick composite laminate

    NASA Technical Reports Server (NTRS)

    Poe, C. C., Jr.

    1985-01-01

    Graphite/epoxy filament-wound cases (FWC) for the solid rocket motors of the space shuttle are being made by NASA. The FWC cases are wound with AS4W graphite fiber impregnated with an epoxy resin and are about 1.4 inches or more thick. Graphite-epoxy composite laminates, unlike metals, can be damaged easily by low velocity impacts of objects like dropped tools. The residual tension strength of the FWC laminate, after impact, is being studied at Langley Research Center. The conditions that give minimum visual evidence of damage are being emphasized. A fracture mechanics analysis was developed to predict the residual strength, after impact, using radiographs to measure the size of the damage and an equivalent surface crack to represent the damage.

  20. The role of fracture mechanics in the design of fuel tanks in space vehicles

    NASA Technical Reports Server (NTRS)

    Denton, S. J.; Liu, C. K.

    1976-01-01

    With special reference to design of fuel tanks in space vehicles, the principles of fracture mechanics are reviewed. An approximate but extremely simple relationship is derived among the operating stress level, the length of crack, and the number of cycles of failure. Any one of the variables can be computed approximately from the knowledge of the other two, if the loading schedule (mission of the tank) is not greatly altered. Two sample examples illustrating the procedures of determining the allowable safe operating stress corresponding to a set of assumed loading schedule are included. The selection of sample examples is limited by the relatively meager available data on the candidate material for various stress ratios in the cycling.

  1. 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.

  2. Stress and Fracture Mechanics Analyses of Boiling Water Reactor and Pressurized Water Reactor Pressure Vessel Nozzles

    SciTech Connect

    Yin, Shengjun; Bass, Bennett Richard; Stevens, Gary; Kirk, Mark

    2011-01-01

    This paper describes stress analysis and fracture mechanics work performed to assess boiling water reactor (BWR) and pressurized water reactor (PWR) nozzles located in the reactor pressure vessel (RPV) adjacent to the core beltline region. Various RPV nozzle geometries were investigated: 1. BWR recirculation outlet nozzle; 2. BWR core spray nozzle3 3. PWR inlet nozzle; ; 4. PWR outlet nozzle; and 5. BWR partial penetration instrument nozzle. The above nozzle designs were selected based on their proximity to the core beltline region, i.e., those nozzle configurations that are located close enough to the core region such that they may receive sufficient fluence prior to end-of-license (EOL) to require evaluation as part of establishing the allowed limits on heatup, cooldown, and hydrotest (leak test) conditions. These nozzles analyzed represent one each of the nozzle types potentially requiring evaluation. The purpose of the analyses performed on these nozzle designs was as follows: To model and understand differences in pressure and thermal stress results using a two-dimensional (2-D) axi-symmetric finite element model (FEM) versus a three-dimensional (3-D) FEM for all nozzle types. In particular, the ovalization (stress concentration) effect of two intersecting cylinders, which is typical of RPV nozzle configurations, was investigated; To verify the accuracy of a selected linear elastic fracture mechanics (LEFM) hand solution for stress intensity factor for a postulated nozzle corner crack for both thermal and pressure loading for all nozzle types; To assess the significance of attached piping loads on the stresses in the nozzle corner region; and To assess the significance of applying pressure on the crack face with respect to the stress intensity factor for a postulated nozzle corner crack.

  3. A mechanism for value-sensitive decision-making.

    PubMed

    Pais, Darren; Hogan, Patrick M; Schlegel, Thomas; Franks, Nigel R; Leonard, Naomi E; Marshall, James A R

    2013-01-01

    We present a dynamical systems analysis of a decision-making mechanism inspired by collective choice in house-hunting honeybee swarms, revealing the crucial role of cross-inhibitory 'stop-signalling' in improving the decision-making capabilities. We show that strength of cross-inhibition is a decision-parameter influencing how decisions depend both on the difference in value and on the mean value of the alternatives; this is in contrast to many previous mechanistic models of decision-making, which are typically sensitive to decision accuracy rather than the value of the option chosen. The strength of cross-inhibition determines when deadlock over similarly valued alternatives is maintained or broken, as a function of the mean value; thus, changes in cross-inhibition strength allow adaptive time-dependent decision-making strategies. Cross-inhibition also tunes the minimum difference between alternatives required for reliable discrimination, in a manner similar to Weber's law of just-noticeable difference. Finally, cross-inhibition tunes the speed-accuracy trade-off realised when differences in the values of the alternatives are sufficiently large to matter. We propose that the model, and the significant role of the values of the alternatives, may describe other decision-making systems, including intracellular regulatory circuits, and simple neural circuits, and may provide guidance in the design of decision-making algorithms for artificial systems, particularly those functioning without centralised control.

  4. On the mechanical interaction between a fluid-filled fracture and the earth's surface

    USGS Publications Warehouse

    Pollard, D.D.; Holzhausen, G.

    1979-01-01

    The mechanical interaction between a fluid-filled fracture (e.g., hydraulic fracture joint, or igneous dike) and the earth's surface is analyzed using a two-dimensional elastic solution for a slit of arbitrary inclination buried beneath a horizontal free surface and subjected to an arbitrary pressure distribution. The solution is obtained by iteratively superimposing two fundamental sets of analytical solutions. For uniform internal pressure the slit behaves essentially as if it were in an infinite region if the depth-to-center is three times greater than the half-length. For shallower slits interaction with the free surface is pronounced: stresses and displacements near the slit differ by more than 10% from values for the deeply buried slit. The following changes are noted as the depth-to-center decreases: 1. (1) the mode I stress intensity factor increases for both ends of the slit, but more rapidly at the upper end; 2. (2) the mode II stress-intensity factor is significantly different from zero (except for vertical slits) suggesting propagation out of the original plane of the slit; 3. (3) displacements of the slit wall are asymmetric such that the slit gaps open more widely near the upper end. Similar changes are noted if fluid density creates a linear pressure gradient that is smaller than the lithostatic gradient. Under such conditions natural fractures should propagate preferentially upward toward the earth's surface requiring less pressure as they grow in length. If deformation near the surface is of interest, the model should account explicitly for the free surface. Stresses and displacements at the free surface are not approximated very well by values calculated along a line in an infinite region, even when the slit is far from the line. As depth-to-center of a shallow pressurized slit decreases, the following changes are noted: 1. (1) displacements of the free surface increase to the same order of magnitude as the displacements of the slit walls, 2. (2

  5. Comment on"Sensitivity of the active fracture model parameter to fracture network orientation and injection scenarios" by Basagaoglu et al. (2009)

    SciTech Connect

    Liu, H.H.

    2010-04-01

    Basagaoglu et al. (2009) present a study on detailed unsaturated flow behavior in two-dimensional fracture networks using numerical experiments (simulations) based on the lattice-Boltzmann method. Their results are valuable for improving our understanding of unsaturated flow processes and evaluating the active fracture model (AFM) that was developed for capturing large-scale preferential flow in fractured rocks (Liu et al., 1998; 2003). As indicated in Basagaoglu et al. (2009), a previous study was conducted to evaluate the AFM with numerical experiments (Seol et al., 2003). However, the methodology used in that study and the corresponding conclusions are highly questioned for the following two reasons. First, the evaluation relies on a condition that simulated water flow processes in a fracture network are adequately represented with a continuum approach, because they draw their conclusions by comparing simulation results with those obtained from a dual-continuum model based on the AFM. No effort was made by Seol et al. (2003) to justify the validity of the continuum approach for their specific fracture network that includes a small number of fractures only. (The analyses of Basagaoglu et al. (2009) do not need the similar condition.) Second, Seol et al. (2003) use numerical dispersion to represent the matrix diffusion process. This treatment is not valid simply because numerical dispersion results from numerical errors and is not a physical process.

  6. Mechanisms of hyoid bone fracture after modelling: evaluation of anthropological criteria defining two relevant models.

    PubMed

    Pollard, J; Piercecchi-Marti, M D; Thollon, L; Bartoli, C; Adalian, Pascal; Bécart-Robert, A; Tournel, G; Hédouin, V; Panuel, M; Gosset, D; Leonetti, G

    2011-10-10

    according to the gender and corpulence of an individual because these parameters are correlated. These findings are crucial in establishing a protocol for modelling the mechanism of fracture of the hyoid bone in strangulation. Two models of the hyoid bone appear to be needed to meet the practical requirements that are the purpose of these biomechanical studies.

  7. Mechanism-Based QSAR Modeling of Skin Sensitization.

    PubMed

    Dearden, J C; Hewitt, M; Roberts, D W; Enoch, S J; Rowe, P H; Przybylak, K R; Vaughan-Williams, G D; Smith, M L; Pillai, G G; Katritzky, A R

    2015-10-19

    Many chemicals can induce skin sensitization, and there is a pressing need for non-animal methods to give a quantitative indication of potency. Using two large published data sets of skin sensitizers, we have allocated each sensitizing chemical to one of 10 mechanistic categories and then developed good QSAR models for the seven categories that have a sufficient number of chemicals to allow modeling. Both internal and external validation checks showed that each model had good predictivity.

  8. THERMO-HYDRO-MECHANICAL MODELING OF WORKING FLUID INJECTION AND THERMAL ENERGY EXTRACTION IN EGS FRACTURES AND ROCK MATRIX

    SciTech Connect

    Robert Podgorney; Chuan Lu; Hai Huang

    2012-01-01

    Development of enhanced geothermal systems (EGS) will require creation of a reservoir of sufficient volume to enable commercial-scale heat transfer from the reservoir rocks to the working fluid. A key assumption associated with reservoir creation/stimulation is that sufficient rock volumes can be hydraulically fractured via both tensile and shear failure, and more importantly by reactivation of naturally existing fractures (by shearing), to create the reservoir. The advancement of EGS greatly depends on our understanding of the dynamics of the intimately coupled rock-fracture-fluid-heat system and our ability to reliably predict how reservoirs behave under stimulation and production. Reliable performance predictions of EGS reservoirs require accurate and robust modeling for strongly coupled thermal-hydrological-mechanical (THM) processes. Conventionally, these types of problems have been solved using operator-splitting methods, usually by coupling a subsurface flow and heat transport simulators with a solid mechanics simulator via input files. An alternative approach is to solve the system of nonlinear partial differential equations that govern multiphase fluid flow, heat transport, and rock mechanics simultaneously, using a fully coupled, fully implicit solution procedure, in which all solution variables (pressure, enthalpy, and rock displacement fields) are solved simultaneously. This paper describes numerical simulations used to investigate the poro- and thermal- elastic effects of working fluid injection and thermal energy extraction on the properties of the fractures and rock matrix of a hypothetical EGS reservoir, using a novel simulation software FALCON (Podgorney et al., 2011), a finite element based simulator solving fully coupled multiphase fluid flow, heat transport, rock deformation, and fracturing using a global implicit approach. Investigations are also conducted on how these poro- and thermal-elastic effects are related to fracture permeability

  9. Fracture of ECAP-deformed iron and the role of extrinsic toughening mechanisms

    PubMed Central

    Hohenwarter, A.; Pippan, R.

    2013-01-01

    The fracture behaviour of pure iron deformed by equal-channel angular pressing via route A was examined. The fracture toughness was determined for different specimen orientations and measured in terms of the critical plane strain fracture toughness, KIC, the critical J integral, JIC, and the crack opening displacement for crack initiation, CODi. The results demonstrate that the crack plane orientation has a pronounced effect on the fracture toughness. Different crack plane orientations lead to either crack deflection or delamination, resulting in increased fracture resistance in comparison to one remarkably weak specimen orientation. The relation between the microstructure typical for the applied deformation route and the enormous differences in the fracture toughness depending on the crack plane orientation will be analyzed in this paper. PMID:23645995

  10. Modeling of the fracture behavior of spot welds using advanced micro-mechanical damage models

    NASA Astrophysics Data System (ADS)

    Sommer, Silke

    2010-06-01

    This paper presents the modeling of deformation and fracture behavior of resistance spot welded joints in DP600 steel sheets. Spot welding is still the most commonly used joining technique in automotive engineering. In overloading situations like crash joints are often the weakest link in a structure. For those reasons, crash simulations need reliable and applicable tools to predict the load bearing capacity of spot welded components. Two series of component tests with different spot weld diameters have shown that the diameter of the weld nugget is the main influencing factor affecting fracture mode (interfacial or pull-out fracture), load bearing capacity and energy absorption. In order to find a correlation between nugget diameter, load bearing capacity and fracture mode, the spot welds are simulated with detailed finite element models containing base metal, heat affected zone and weld metal in lap-shear loading conditions. The change in fracture mode from interfacial to pull-out or peel-out fracture with growing nugget diameter under lap-shear loading was successfully modeled using the Gologanu-Leblond model in combination with the fracture criteria of Thomason and Embury. A small nugget diameter is identified to be the main cause for interfacial fracture. In good agreement with experimental observations, the calculated pull-out fracture initiates in the base metal at the boundary to the heat affected zone.

  11. Fracture Mechanics Method for Word Embedding Generation of Neural Probabilistic Linguistic Model

    PubMed Central

    Bi, Size; Liang, Xiao

    2016-01-01

    Word embedding, a lexical vector representation generated via the neural linguistic model (NLM), is empirically demonstrated to be appropriate for improvement of the performance of traditional language model. However, the supreme dimensionality that is inherent in NLM contributes to the problems of hyperparameters and long-time training in modeling. Here, we propose a force-directed method to improve such problems for simplifying the generation of word embedding. In this framework, each word is assumed as a point in the real world; thus it can approximately simulate the physical movement following certain mechanics. To simulate the variation of meaning in phrases, we use the fracture mechanics to do the formation and breakdown of meaning combined by a 2-gram word group. With the experiments on the natural linguistic tasks of part-of-speech tagging, named entity recognition and semantic role labeling, the result demonstrated that the 2-dimensional word embedding can rival the word embeddings generated by classic NLMs, in terms of accuracy, recall, and text visualization. PMID:27698659

  12. Fracture Mechanics Method for Word Embedding Generation of Neural Probabilistic Linguistic Model

    PubMed Central

    Bi, Size; Liang, Xiao

    2016-01-01

    Word embedding, a lexical vector representation generated via the neural linguistic model (NLM), is empirically demonstrated to be appropriate for improvement of the performance of traditional language model. However, the supreme dimensionality that is inherent in NLM contributes to the problems of hyperparameters and long-time training in modeling. Here, we propose a force-directed method to improve such problems for simplifying the generation of word embedding. In this framework, each word is assumed as a point in the real world; thus it can approximately simulate the physical movement following certain mechanics. To simulate the variation of meaning in phrases, we use the fracture mechanics to do the formation and breakdown of meaning combined by a 2-gram word group. With the experiments on the natural linguistic tasks of part-of-speech tagging, named entity recognition and semantic role labeling, the result demonstrated that the 2-dimensional word embedding can rival the word embeddings generated by classic NLMs, in terms of accuracy, recall, and text visualization.

  13. Fracture mechanics by three-dimensional crack-tip synchrotron X-ray microscopy

    PubMed Central

    Withers, P. J.

    2015-01-01

    To better understand the relationship between the nucleation and growth of defects and the local stresses and phase changes that cause them, we need both imaging and stress mapping. Here, we explore how this can be achieved by bringing together synchrotron X-ray diffraction and tomographic imaging. Conventionally, these are undertaken on separate synchrotron beamlines; however, instruments capable of both imaging and diffraction are beginning to emerge, such as ID15 at the European Synchrotron Radiation Facility and JEEP at the Diamond Light Source. This review explores the concept of three-dimensional crack-tip X-ray microscopy, bringing them together to probe the crack-tip behaviour under realistic environmental and loading conditions and to extract quantitative fracture mechanics information about the local crack-tip environment. X-ray diffraction provides information about the crack-tip stress field, phase transformations, plastic zone and crack-face tractions and forces. Time-lapse CT, besides providing information about the three-dimensional nature of the crack and its local growth rate, can also provide information as to the activation of extrinsic toughening mechanisms such as crack deflection, crack-tip zone shielding, crack bridging and crack closure. It is shown how crack-tip microscopy allows a quantitative measure of the crack-tip driving force via the stress intensity factor or the crack-tip opening displacement. Finally, further opportunities for synchrotron X-ray microscopy are explored. PMID:25624521

  14. Environment enhanced fatigue crack propagation in metals: Inputs to fracture mechanics life prediction models

    NASA Technical Reports Server (NTRS)

    Gangloff, Richard P.; Kim, Sang-Shik

    1993-01-01

    This report is a critical review of both environment-enhanced fatigue crack propagation data and the predictive capabilities of crack growth rate models. This information provides the necessary foundation for incorporating environmental effects in NASA FLAGRO and will better enable predictions of aerospace component fatigue lives. The review presents extensive literature data on 'stress corrosion cracking and corrosion fatigue.' The linear elastic fracture mechanics approach, based on stress intensity range (Delta(K)) similitude with microscopic crack propagation threshold and growth rates, provides a basis for these data. Results are presented showing enhanced growth rates for gases (viz., H2 and H2O) and electrolytes (e.g. NaCl and H2O) in aerospace alloys including: C-Mn and heat treated alloy steels, aluminum alloys, nickel-based superalloys, and titanium alloys. Environment causes purely time-dependent accelerated fatigue crack growth above the monotonic load cracking threshold (KIEAC) and promotes cycle-time dependent cracking below (KIEAC). These phenomenon are discussed in terms of hydrogen embrittlement, dissolution, and film rupture crack tip damage mechanisms.

  15. Formation of conical fractures in sedimentary basins: Experiments involving pore fluids and implications for sandstone intrusion mechanisms

    NASA Astrophysics Data System (ADS)

    Mourgues, R.; Bureau, D.; Bodet, L.; Gay, A.; Gressier, J. B.

    2012-01-01

    a flat cone. We make use of a P.I.V. (Particle Imaging Velocimetry) technique to analyse plastic deformation, showing that these inclined fractures are opened in mixed modes. Close to the surface, they change into steep shear bands where fluids can infiltrate. The final morphology of the fracture network is very similar to the common tripartite architecture of various injection complexes, indicating that different mechanisms may be involved in the formation of dykes. Feeder dykes under the sill zones may open as tensile fractures, while overlying dykes may be guided by the deformation induced by the growth of sills. These deformation conditions may also favour the formation of fluid escape structures and pockmarks.

  16. In vitro mechanical assessment of 2.0-mm system three-dimensional miniplates in anterior mandibular fractures.

    PubMed

    de Oliveira, K P; de Moraes, P H; da Silva, J S P; de Queiroz, W F; Germano, A R

    2014-05-01

    This study constituted a comparative assessment of the mechanical resistance of square and rectangular 2.0-mm system three-dimensional miniplates as compared to the standard configuration using two straight miniplates. 90 polyurethane replica mandibles were used for the mechanical trials. Groups 1, 2, and 3 simulated complete symphyseal fractures characterized by linear separation of the central incisors; groups 4, 5, and 6 simulated parasymphyseal fractures with an oblique configuration. Groups 1 and 4 represented the standard method with two straight miniplates set parallel to one another. Square miniplates were used in groups 2 and 5, and rectangular miniplates in groups 3 and 6. A universal testing machine set to a velocity of 10mm/min and delivering a vertical linear load to the first left molar was used to test each group. Maximum load values and load values with pre-established dislocation of 5mm were obtained and submitted to statistical analysis using a calculated reliability interval of 95%. The mechanical performances of the devices were similar, except in the case of rectangular plates used in the parasymphyseal fractures. The innovative fixation methods used showed significantly better results in the case of symphyseal fractures.

  17. Damage mechanisms and fracture toughness of GlidCop ® CuAl25 IG0 copper alloy

    NASA Astrophysics Data System (ADS)

    Tähtinen, S.; Laukkanen, A.; Singh, B. N.

    2000-12-01

    Crack nucleation and growth behaviour are important parameters in deciding about the applicability of the dispersion strengthened copper alloy CuAl25 in components such as the first wall and divertor in ITER. The effective strain to fracture of notched tensile specimens decreased with increasing stress state triaxiality and with increasing temperature at constant constraint level following the Rice and Tracey model for void growth. In three point bend tests, the strain for stable crack initiation decreased significantly with increasing temperature. The CuAl25 alloy failed by a ductile microvoid mechanism where extensive void nucleation occurred at very low strains at grain boundaries with increasing stress state triaxiality. At elevated temperatures the fracture surface morphology changed from microvoid to intergranular fracture in three-point bend tests.

  18. Rib stress fractures among rowers: definition, epidemiology, mechanisms, risk factors and effectiveness of injury prevention strategies.

    PubMed

    McDonnell, Lisa K; Hume, Patria A; Nolte, Volker

    2011-11-01

    Rib stress fractures (RSFs) can have serious effects on rowing training and performance and accordingly represent an important topic for sports medicine practitioners. Therefore, the aim of this review is to outline the definition, epidemiology, mechanisms, intrinsic and extrinsic risk factors, injury management and injury prevention strategies for RSF in rowers. To this end, nine relevant books, 140 journal articles, the proceedings of five conferences and two unpublished presentations were reviewed after searches of electronic databases using the keywords 'rowing', 'rib', 'stress fracture', 'injury', 'mechanics' and 'kinetics'. The review showed that RSF is an incomplete fracture occurring from an imbalance between the rate of bone resorption and the rate of bone formation. RSF occurs in 8.1-16.4% of elite rowers, 2% of university rowers and 1% of junior elite rowers. Approximately 86% of rowing RSF cases with known locations occur in ribs four to eight, mostly along the anterolateral/lateral rib cage. Elite rowers are more likely to experience RSF than nonelite rowers. Injury occurrence is equal among sweep rowers and scullers, but the regional location of the injury differs. The mechanism of injury is multifactorial with numerous intrinsic and extrinsic risk factors contributing. Posterior-directed resultant forces arising from the forward directed force vector through the arms to the oar handle in combination with the force vector induced by the scapula retractors during mid-drive, or repetitive stress from the external obliques and rectus abdominis in the 'finish' position, may be responsible for RSF. Joint hypomobility, vertebral malalignment or low bone mineral density may be associated with RSF. Case studies have shown increased risk associated with amenorrhoea, low bone density or poor technique, in combination with increases in training volume. Training volume alone may have less effect on injury than other factors. Large differences in seat and handle

  19. Multiple bilateral lower limb fractures in a 2-year-old child: previously unreported injury with a unique mechanism.

    PubMed

    Repswal, Basant; Jain, Anuj; Gupta, Sunil; Aggarwal, Aditya; Kohli, Tushar; Pathrot, Devendra

    2014-01-01

    Fall from height is a common cause of unintentional injuries in children and accounts for 6% of all trauma-related childhood deaths, usually from head injury. We report a case of a 2-year-old child with multiple fractures of the bilateral lower limbs due to this reason. A child fell from a height of around 15 feet after toppling from a balcony. He developed multiple fractures involving the right femoral shaft, right distal femoral epiphysis (Salter Harris type 2), right distal metaphysis of the tibia and fibula, and undisplaced Salter Harris type 2 epiphyseal injury of the left distal tibia. There were no head, abdominal or spinal injuries. The patient was taken into emergency operation theatre after initial management which consisted of intravenous fluids, blood transfusion, and splintage of both lower limbs. Fracture of the femoral shaft was treated by closed reduction and fixation using two titanium elastic nails. Distal femoral physeal injury required open reduction and fixation with K wires. Distal tibia fractures were closely reduced and managed nonoperatively in both the lower limbs. All the fractures united in four weeks. At the last follow-up, the child had no disability and was able to perform daily activities comfortably. We also proposed the unique mechanism of injury in this report. PMID:25293902

  20. Architecture, fracture system, mechanical properties and permeability structure of a fault zone in Lower Triassic sandstone, Upper Rhine Graben

    NASA Astrophysics Data System (ADS)

    Bauer, Johanna F.; Meier, Silke; Philipp, Sonja L.

    2015-04-01

    Close to the western Upper Rhine Graben Main Fault, Alsace, a NNE-SSW-striking fault zone, crosscutting porous, thick bedded Lower Triassic Bunter sandstone was investigated in detail, including its architecture, discontinuity system, mechanical rock properties and implications on its permeability structure and fault zone type. Field observations indicate a three-part fault zone structure including core-, transition- and damage zone. The at least 14 m thick fault core is composed of various slip surfaces and deformation bands, which encompass fractured host rock lenses. When connected, host rock lenses may transport fluids through the core zone. Adjacent transition zones are highly fractured in R1-orientation, show folded beds and contain P1-oriented deformation bands. R1 and P1-fractures are synthetic shear fractures and project with an acute angle (10-20°) toward the fault plane. Only in the damage zone, fault-parallel striking fractures occur. Here, increasing fracture apertures and connectivity may increase the permeability toward the fault core. Mechanical rock properties from 12 rock samples (Young's modulus, uniaxial compressive strength, tensile strength) measured in all the parts of the fault zone, show highest values within the transition zone. In-situ measurements of rebound-hardnesses with a Schmidt-Hammer and analytical approaches, however, indicate that effective Young's moduli are two to sixteen times lower than the Young's moduli of intact rock. Values clearly decrease toward the fault core, even in the transition zone and are in average lower than effective Young's moduli in the damage zone. Although many fault zones in sandstone are sealing structures these field study show, that fault zones in porous sandstone may allow fluid flow.

  1. Proceedings of the 1985 pressure vessels and piping conference. Volume PVP-98-8. Fracture, fatigue and advanced mechanics

    SciTech Connect

    Short, W.E.; Zamrik, S.Y.

    1985-01-01

    State-of-the-art engineering practices in pressure vessel and piping technology are the result of continual efforts in the evaluation of problems which have been experienced and the development of appropriate design and analysis methods for those applications. The resulting advances in technology benefit industry with properly engineered, safe, cost-effective pressure vessels and piping systems. To this end, advanced study continues in specialized areas of mechanical engineering such as fracture mechanics, experimental stress analysis, high pressure applications and related material considerations, as well as advanced techniques for evaluation of commonly encountered design problems. This volume is comprised of current technical papers on various aspects of fracture, fatigue and advanced mechanics as related to the design and analysis of pressure vessels and piping.

  2. 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

  3. FRACTURE PROPAGATION PROPENSITY OF CERAMIC LINERS DURING IMPINGEMENT-SUBLUXATION

    PubMed Central

    Elkins, Jacob M.; Pedersen, Douglas R.; Callaghan, John J.; Brown, Thomas D.

    2011-01-01

    Although improvements in materials engineering have greatly reduced fracture rates in ceramic femoral heads, concerns still exist for liners. Ceramics are vulnerable fracture due to impact, and from stress concentrations (point and line loading) such as those associated with impingement-subluxation. Thus, ceramic cup fracture propensity is presumably very sensitive to surgical cup positioning. A novel fracture mechanics finite element formulation was developed to identify cup orientations most susceptible to liner fracture propagation, for several impingement-prone patient maneuvers. Other factors being equal, increased cup inclination and increased anteversion were found to elevate fracture risk. Squatting, stooping and leaning shoe-tie maneuvers were associated with highest fracture risk. These results suggest that fracture risk can be reduced by surgeons’ decreasing cup abduction and by patients’ avoiding of specific activities. PMID:21855277

  4. Nose fracture

    MedlinePlus

    Fracture of the nose; Broken nose; Nasal fracture; Nasal bone fracture; Nasal septal fracture ... A fractured nose is the most common fracture of the face. It ... with other fractures of the face. Sometimes a blunt injury can ...

  5. Tissue level microstructure and mechanical properties of the femoral head in the proximal femur of fracture patients

    NASA Astrophysics Data System (ADS)

    Lü, Linwei; Meng, Guangwei; Gong, He; Zhu, Dong; Gao, Jiazi; Fan, Yubo

    2015-04-01

    This study aims to investigate the regional variations of trabecular morphological parameters and mechanical parameters of the femoral head, as well as to determine the relationship between trabecular morphological and mechanical parameters. Seven femoral heads from patients with fractured proximal femur were scanned using a micro-CT system. Each femoral head was divided into 12 sub-regions according to the trabecular orientation. One trabecular cubic model was reconstructed from each sub-region. A total of 81 trabecular models were reconstructed, except three destroyed sub-regions from two femoral heads during the surgery. Trabecular morphological parameters, i.e. trabecular separation (Tb.Sp), trabecular thickness (Tb.Th), specific bone surface (BS/BV), bone volume fraction (BV/TV), structural model index (SMI), and degree of anisotropy (DA) were measured. Micro-finite element analyses were performed for each cube to obtain the apparent Young's modulus and tissue level von Mises stress distribution under 1 % compressive strain along three orthogonal directions, respectively. Results revealed significant regional variations in the morphological parameters (). Young's moduli along the trabecular orientation were significantly higher than those along the other two directions. In general, trabecular mechanical properties in the medial region were lower than those in the lateral region. Trabecular mechanical parameters along the trabecular orientation were significantly correlated with BS/BV, BV/TV, Tb.Th, and DA. In this study, regional variations of microstructural features and mechanical properties in the femoral head of patients with proximal femur fracture were thoroughly investigated at the tissue level. The results of this study will help to elucidate the mechanism of femoral head fracture for reducing fracture risk and developing treatment strategies for the elderly.

  6. Mechanical Fracturing of Core-Shell Undercooled Metal Particles for Heat-Free Soldering.

    PubMed

    Çınar, Simge; Tevis, Ian D; Chen, Jiahao; Thuo, Martin

    2016-01-01

    Phase-change materials, such as meta-stable undercooled (supercooled) liquids, have been widely recognized as a suitable route for complex fabrication and engineering. Despite comprehensive studies on the undercooling phenomenon, little progress has been made in the use of undercooled metals, primarily due to low yields and poor stability. This paper reports the use of an extension of droplet emulsion technique (SLICE) to produce undercooled core-shell particles of structure; metal/oxide shell-acetate ('/' = physisorbed, '-' = chemisorbed), from molten Field's metal (Bi-In-Sn) and Bi-Sn alloys. These particles exhibit stability against solidification at ambient conditions. Besides synthesis, we report the use of these undercooled metal, liquid core-shell, particles for heat free joining and manufacturing at ambient conditions. Our approach incorporates gentle etching and/or fracturing of outer oxide-acetate layers through mechanical stressing or shearing, thus initiating a cascade entailing fluid flow with concomitant deformation, combination/alloying, shaping, and solidification. This simple and low cost technique for soldering and fabrication enables formation of complex shapes and joining at the meso- and micro-scale at ambient conditions without heat or electricity. PMID:26902483

  7. Computational and numerical aspects of using the integral equation method for adhesive layer fracture mechanics analysis

    SciTech Connect

    Giurgiutiu, V.; Ionita, A.; Dillard, D.A.; Graffeo, J.K.

    1996-12-31

    Fracture mechanics analysis of adhesively bonded joints has attracted considerable attention in recent years. A possible approach to the analysis of adhesive layer cracks is to study a brittle adhesive between 2 elastic half-planes representing the substrates. A 2-material 3-region elasticity problem is set up and has to be solved. A modeling technique based on the work of Fleck, Hutchinson, and Suo is used. Two complex potential problems using Muskelishvili`s formulation are set up for the 3-region, 2-material model: (a) a distribution of edge dislocations is employed to simulate the crack and its near field; and (b) a crack-free problem is used to simulate the effect of the external loading applied in the far field. Superposition of the two problems is followed by matching tractions and displacements at the bimaterial boundaries. The Cauchy principal value integral is used to treat the singularities. Imposing the traction-free boundary conditions over the entire crack length yielded a linear system of two integral equations. The parameters of the problem are Dundurs` elastic mismatch coefficients, {alpha} and {beta}, and the ratio c/H representing the geometric position of the crack in the adhesive layer.

  8. Mechanical Fracturing of Core-Shell Undercooled Metal Particles for Heat-Free Soldering

    NASA Astrophysics Data System (ADS)

    Çınar, Simge; Tevis, Ian D.; Chen, Jiahao; Thuo, Martin

    2016-02-01

    Phase-change materials, such as meta-stable undercooled (supercooled) liquids, have been widely recognized as a suitable route for complex fabrication and engineering. Despite comprehensive studies on the undercooling phenomenon, little progress has been made in the use of undercooled metals, primarily due to low yields and poor stability. This paper reports the use of an extension of droplet emulsion technique (SLICE) to produce undercooled core-shell particles of structure; metal/oxide shell-acetate (‘/’ = physisorbed, ‘-’ = chemisorbed), from molten Field’s metal (Bi-In-Sn) and Bi-Sn alloys. These particles exhibit stability against solidification at ambient conditions. Besides synthesis, we report the use of these undercooled metal, liquid core-shell, particles for heat free joining and manufacturing at ambient conditions. Our approach incorporates gentle etching and/or fracturing of outer oxide-acetate layers through mechanical stressing or shearing, thus initiating a cascade entailing fluid flow with concomitant deformation, combination/alloying, shaping, and solidification. This simple and low cost technique for soldering and fabrication enables formation of complex shapes and joining at the meso- and micro-scale at ambient conditions without heat or electricity.

  9. A review of path-independent integrals in elastic-plastic fracture mechanics, task 4

    NASA Technical Reports Server (NTRS)

    Kim, K. S.

    1985-01-01

    The path independent (P-I) integrals in elastic plastic fracture mechanics which have been proposed in recent years to overcome the limitations imposed on the J integral are reviewed. The P-I integrals considered herein are the J integral by Rice, the thermoelastic P-I integrals by Wilson and Yu and by Gurtin, the J* integral by Blackburn, the J sub theta integral by Ainsworth et al., the J integral by Kishimoto et al., and the delta T sub p and delta T* sub p integrals by Atluri et al. The theoretical foundation of these P-I integrals is examined with emphasis on whether or not path independence is maintained in the presence of nonproportional loading and unloading in the plastic regime, thermal gradients, and material inhomogeneities. The similarities, differences, salient features, and limitations of these P-I integrals are discussed. Comments are also made with regard to the physical meaning, the possibility of experimental measurement, and computational aspects.

  10. Scaling of strength and lifetime probability distributions of quasibrittle structures based on atomistic fracture mechanics.

    PubMed

    Bazant, Zdenek P; Le, Jia-Liang; Bazant, Martin Z

    2009-07-14

    The failure probability of engineering structures such as aircraft, bridges, dams, nuclear structures, and ships, as well as microelectronic components and medical implants, must be kept extremely low, typically <10(-6). The safety factors needed to ensure it have so far been assessed empirically. For perfectly ductile and perfectly brittle structures, the empirical approach is sufficient because the cumulative distribution function (cdf) of random material strength is known and fixed. However, such an approach is insufficient for structures consisting of quasibrittle materials, which are brittle materials with inhomogeneities that are not negligible compared with the structure size. The reason is that the strength cdf of quasibrittle structure varies from Gaussian to Weibullian as the structure size increases. In this article, a recently proposed theory for the strength cdf of quasibrittle structure is refined by deriving it from fracture mechanics of nanocracks propagating by small, activation-energy-controlled, random jumps through the atomic lattice. This refinement also provides a plausible physical justification of the power law for subcritical creep crack growth, hitherto considered empirical. The theory is further extended to predict the cdf of structural lifetime at constant load, which is shown to be size- and geometry-dependent. The size effects on structure strength and lifetime are shown to be related and the latter to be much stronger. The theory fits previously unexplained deviations of experimental strength and lifetime histograms from the Weibull distribution. Finally, a boundary layer method for numerical calculation of the cdf of structural strength and lifetime is outlined.

  11. Fracture Mechanics Analyses of the Slip-Side Joggle Regions of Wing-Leading Edge Panels

    NASA Technical Reports Server (NTRS)

    Raju, Ivatury S.; Knight, Norman F., Jr.; Song, Kyongchan; Phillips, Dawn R.

    2010-01-01

    The Space Shuttle Orbiter wing comprises of 22 leading edge panels on each side of the wing. These panels are part of the thermal protection system that protects the Orbiter wings from extreme heating that take place on the reentry in to the earth atmosphere. On some panels that experience extreme heating, liberation of silicon carbon (SiC) coating was observed on the slip side regions of the panels. Global structural and local fracture mechanics analyses were performed on these panels as a part of the root cause investigation of this coating liberation anomaly. The wing-leading-edge reinforced carbon-carbon (RCC) panels, Panel 9, T-seal 10, and Panel 10, are shown in Figure 1 and the progression of the stress analysis models is presented in Figure 2. The global structural analyses showed minimal interaction between adjacent panels and the T-seal that bridges the gap between the panels. A bounding uniform temperature is applied to a representative panel and the resulting stress distribution is examined. For this loading condition, the interlaminar normal stresses showed negligible variation in the chord direction and increased values in the vicinity of the slip-side joggle shoulder. As such, a representative span wise slice on the panel can be taken and the cross section can be analyzed using plane strain analysis.

  12. Development of fracture mechanics data for two hydrazine APU turbine wheel materials

    NASA Technical Reports Server (NTRS)

    Curbishley, G.

    1975-01-01

    The effects of high temperature, high pressure ammonia were measured on the fracture mechanics and fatigue properties of Astroloy and Rene' 41 turbine wheel materials. Also, the influence of protective coatings on these properties was investigated. Specimens of forged bar stock were subjected to LCF and HCF tests at 950 K (1250 F) and 3.4 MN/sq m (500 psig) pressure, in ammonia containing about 1.5 percent H2O. Aluminized samples (Chromizing Company's Al-870) and gold plated test bars were compared with uncoated specimens. Comparison tests were also run in air at 950 K (1250 F), but at ambient pressures. K sub IE and K sub TH were determined on surface flawed specimens in both the air and ammonia in both uncoated and gold plated conditions. Gold plated specimens exhibited better properties than uncoated samples, and aluminized test bars generally had lower properties. The fatigue properties of specimens tested in ammonia were higher than those tested in air, yet the K sub TH values of ammonia tested samples were lower than those tested in air. However, insufficient specimens were tested to develop significant design data.

  13. COMPARISON OF THE TRADITIONAL STRENGTH OF MATERIALS APPROACH TO DESIGN WITH THE FRACTURE MECHANICS APPROACH

    SciTech Connect

    Z. Ceylan

    2002-04-30

    The objective of this activity is to show that the use of the traditional strength of materials approach to the drip shield and the waste package (WP) designs is bounding and appropriate when compared to the fracture mechanics approach. The scope of this activity is limited to determining the failure assessment diagrams for the two materials at issue: Ti-7 and Alloy 22. This calculation is intended for use in support of the license application design of the drip shield and the WP. This activity is associated with the drip shield and the WP designs. The activity evaluation for work package number P32 12234F2, included in ''Technical Work Plan for: Waste Package Design Description for LA'' (Ref. 1, p. A-6), has determined that the development of this document is subject to ''Quality Assurance Requirements and Description'' requirements. The control of the electronic management of data is accomplished in accordance with the methods specified in Reference 1, Section 10. AP-3.124, ''Design Calculations and Analysis'' (Ref. 2), is used to develop and document the calculation.

  14. Low Magnitude Mechanical Signals Reduce Risk-Factors for Fracture during 90-Day Bed Rest

    NASA Technical Reports Server (NTRS)

    Muir, J. W.; Xia, Y.; Holquin, N.; Judex, S.; Qin, Y.; Evans, H.; Lang, T.; Rubin, C.

    2007-01-01

    Long duration spaceflight leads to multiple deleterious changes to the musculoskeletal system, where loss of bone density, an order of magnitude more severe than that which follows the menopause, combined with increased instability, conspire to elevate the risk of bone fracture due to falls on return to gravitational fields. Here, a ground-based analog for spaceflight is used to evaluate the efficacy of a low-magnitude mechanical intervention, VIBE (Vibrational Inhibition of Bone Erosion), as a potential countermeasure to preserve musculoskeletal integrity in the face of disuse. Twenty-six subjects consented to ninety days of six-degree head-down tilt bed-rest. 18 completed the 90d protocol, 8 of which received daily 10-minute exposure to 30 Hz, 0.3g VIBE, applied in the supine position using a vest elastically coupled to the vibrating platform. The shoulder harness induced a load of 60% of the subjects body weight. At baseline and 90d, Qualitative Ultrasound Scans (QUS) of the calcaneus and CT-scans of the hip and spine were performed to measure changes in bone density. Postural control (PC) was assessed through center of pressure (COP) recordings while subjects stood on a force platform for 4 minutes of quiet stance with eyes closed, and again with eyes opened. As compared to control bedrest subjects,

  15. Mechanical Fracturing of Core-Shell Undercooled Metal Particles for Heat-Free Soldering

    PubMed Central

    Çınar, Simge; Tevis, Ian D.; Chen, Jiahao; Thuo, Martin

    2016-01-01

    Phase-change materials, such as meta-stable undercooled (supercooled) liquids, have been widely recognized as a suitable route for complex fabrication and engineering. Despite comprehensive studies on the undercooling phenomenon, little progress has been made in the use of undercooled metals, primarily due to low yields and poor stability. This paper reports the use of an extension of droplet emulsion technique (SLICE) to produce undercooled core-shell particles of structure; metal/oxide shell-acetate (‘/’ = physisorbed, ‘-’ = chemisorbed), from molten Field’s metal (Bi-In-Sn) and Bi-Sn alloys. These particles exhibit stability against solidification at ambient conditions. Besides synthesis, we report the use of these undercooled metal, liquid core-shell, particles for heat free joining and manufacturing at ambient conditions. Our approach incorporates gentle etching and/or fracturing of outer oxide-acetate layers through mechanical stressing or shearing, thus initiating a cascade entailing fluid flow with concomitant deformation, combination/alloying, shaping, and solidification. This simple and low cost technique for soldering and fabrication enables formation of complex shapes and joining at the meso- and micro-scale at ambient conditions without heat or electricity. PMID:26902483

  16. Structural Mechanics Predictions Relating to Clinical Coronary Stent Fracture in a 5 Year Period in FDA MAUDE Database.

    PubMed

    Everett, Kay D; Conway, Claire; Desany, Gerard J; Baker, Brian L; Choi, Gilwoo; Taylor, Charles A; Edelman, Elazer R

    2016-02-01

    Endovascular stents are the mainstay of interventional cardiovascular medicine. Technological advances have reduced biological and clinical complications but not mechanical failure. Stent strut fracture is increasingly recognized as of paramount clinical importance. Though consensus reigns that fractures can result from material fatigue, how fracture is induced and the mechanisms underlying its clinical sequelae remain ill-defined. In this study, strut fractures were identified in the prospectively maintained Food and Drug Administration's (FDA) Manufacturer and User Facility Device Experience Database (MAUDE), covering years 2006-2011, and differentiated based on specific coronary artery implantation site and device configuration. These data, and knowledge of the extent of dynamic arterial deformations obtained from patient CT images and published data, were used to define boundary conditions for 3D finite element models incorporating multimodal, multi-cycle deformation. The structural response for a range of stent designs and configurations was predicted by computational models and included estimation of maximum principal, minimum principal and equivalent plastic strains. Fatigue assessment was performed with Goodman diagrams and safe/unsafe regions defined for different stent designs. Von Mises stress and maximum principal strain increased with multimodal, fully reversed deformation. Spatial maps of unsafe locations corresponded to the identified locations of fracture in different coronary arteries in the clinical database. These findings, for the first time, provide insight into a potential link between patient adverse events and computational modeling of stent deformation. Understanding of the mechanical forces imposed under different implantation conditions may assist in rational design and optimal placement of these devices. PMID:26467552

  17. Engineering geological characteristics and the hydraulic fracture propagation mechanism of the sand-shale interbedded formation in the Xu5 reservoir

    NASA Astrophysics Data System (ADS)

    Lu, Cong; Li, Mei; Guo, Jian-Chun; Tang, Xu-Hai; Zhu, Hai-Yan; Yong-Hui, Wang; Liang, Hao

    2015-06-01

    In the Xu5 formation the sandstone reservoir and the shale reservoir are interbedded with each other. The average thickness of each formation is about 8 m, which increases the difficulty of the hydraulic fracturing treatment. The shale thickness ratio (the ratio of shale thickness to formation thickness) is 55-62.5%. The reservoir is characterized by ultra-low porosity and permeability. The brittleness index of sandstone is 0.5-0.8, and the brittleness index of shale is 0.3-0.8. Natural fractures are poorly developed and are mainly horizontal and at a low angle. The formation strength is medium and the reservoir is of the hybrid strike-slip fault and reverse fault stress regime. The difference between the minimum principal stress and the vertical stress is small, and the maximum horizontal principal stress is 20 MPa higher than the minimum horizontal principal stress and vertical stress. A mechanical model of a hydraulic fracture encountering natural fractures is built according to geological characteristics. Fracture mechanics theory is then used to establish a hydraulic fracturing model coupling the seepage-stress-damage model to simulate the initiation and propagation of a fracture. The hydraulic fracture geometry is mainly I-shaped and T-shaped, horizontal propagation dominates the extension, and vertical propagation is limited. There is a two to three meter stress diversion area around a single hydraulic fracture. The stress diversion between a hydraulic fracture and a natural fracture is advantageous in forming a complex fracture. The research results can provide theoretical guidance for tight reservoir fracturing design.

  18. Future target for geothermal development -- Fractal Fracture Mechanics and its application to conceptual HDR reservoir design

    SciTech Connect

    Takahashi, Hideaki; Watanable, Kimio; Hashida, Toshiyuki

    1995-01-26

    A simple model is proposed for water/rock interaction in rock fractures through which geothermal water flows. Water/rock interaction experiments were carried out at high temperature and pressure (200-350 C, 18 MPa) in order to obtain basic solubility and reaction rate data. Based on the experimental data, changes of idealized fracture apertures with time are calculated numerically. The results of the calculations show that the precipitation from water can lead to plugging of the fractures under certain conditions. Finally, the results are compared with the experimental data.

  19. Insights into Reference Point Indentation Involving Human Cortical Bone: Sensitivity to Tissue Anisotropy and Mechanical Behavior

    PubMed Central

    Granke, Mathilde; Coulmier, Aurélie; Uppuganti, Sasidhar; Gaddy, Jennifer A; Does, Mark D; Nyman, Jeffry S

    2014-01-01

    Reference point indentation (RPI) is a microindentation technique involving 20 cycles of loading in “force-control” that can directly assess a patient’s bone tissue properties. Even though preliminary clinical studies indicate a capability for fracture discrimination, little is known about what mechanical behavior the various RPI properties characterize and how these properties relate to traditional mechanical properties of bone. To address this, the present study investigated the sensitivity of RPI properties to anatomical location and tissue organization as well as examined to what extent RPI measurements explain the intrinsic mechanical properties of human cortical bone. Multiple indents with a target force of 10 N were done in 2 orthogonal directions (longitudinal and transverse) per quadrant (anterior, medial, posterior, and lateral) of the femoral mid-shaft acquired from 26 donors (25–101 years old). Additional RPI measurements were acquired for 3 orthogonal directions (medial only). Independent of age, most RPI properties did not vary among these locations, but they did exhibit transverse isotropy such that resistance to indentation is greater in the longitudinal (axial) direction than in the transverse direction (radial or circumferential). Next, beam specimens (~ 2 mm × 5 mm × 40 mm) were extracted from the medial cortex of femoral mid-shafts, acquired from 34 donors (21–99 years old). After monotonically loading the specimens in three-point bending to failure, RPI properties were acquired from an adjacent region outside the span. Indent direction was orthogonal to the bending axis. A significant inverse relationship was found between resistance to indentation and the apparent-level mechanical properties. Indentation distance increase (IDI) and a linear combination of IDI and the loading slope, averaged over cycles 3 through 20, provided the best explanation of the variance in ultimate stress (r2=0.25, p=0.003) and toughness (r2=0.35, p=0

  20. Application of fracture mechanics and half-cycle theory to the prediction of fatigue life of aerospace structural components

    NASA Technical Reports Server (NTRS)

    Ko, William L.

    1989-01-01

    The service life of aircraft structural components undergoing random stress cycling was analyzed by the application of fracture mechanics. The initial crack sizes at the critical stress points for the fatigue crack growth analysis were established through proof load tests. The fatigue crack growth rates for random stress cycles were calculated using the half-cycle method. A new equation was developed for calculating the number of remaining flights for the structural components. The number of remaining flights predicted by the new equation is much lower than that predicted by the conventional equation. This report describes the application of fracture mechanics and the half-cycle method to calculate the number of remaining flights for aircraft structural components.

  1. Aspects of fracture mechanics in cryogenic model design. Part 2: NTF materials

    NASA Technical Reports Server (NTRS)

    Newman, J. C., Jr.; Lisagor, W. B.

    1983-01-01

    Results of fatigue crack growth and fracture toughness tests conducted on three candidate materials are presented. Fatigue crack growth and fracture toughness tests were conducted on NITRONIC 40 at room temperature and -275 F. Fracture toughness tests were also conducted on Vascomax 200 and 250 maraging steel from room temperature to -320 F. NITRONIC 40 was used to make the Pathfinder 1 model. The fatigue crack growth rate tests were conducted at room temperature and -275 F on three-point notch bend specimens. The fracture toughness tests on the as received and stress relieved materials at -275 F were conducted on the center crack tension specimens. Toughness tests were also conducted on Vascomax CVM-200 and CVM-250 maraging steel from room temperature to -320 F using round and rectangular compact specimens.

  2. Fracture mechanics data for 2024-T861 and 2124-T851 aluminum

    NASA Technical Reports Server (NTRS)

    Pionke, L. J.; Linback, R. K.

    1974-01-01

    The fracture toughness and fatigue flaw growth characteristics of 2024-T861 and 2124-T851 aluminum were evaluated under plane stress conditions. Center cracked tension specimens were employed to evaluate these properties under a number of different test conditions which included variations in specimen thickness, specimen orientation, test environment, and initial flaw size. The effect of buckling was also investigated for all tests of thin gage specimens, and the effect of frequency and stress ratio was evaluated for the cyclic tests. Fracture toughness test results were analyzed and presented in terms of fracture resistance curves; fatigue flaw growth data was analyzed using empirical rate models. The results of the study indicate that both fracture toughness and resistance to fatigue crack growth improve with increasing temperature and decreasing thickness. The presence of buckling during testing of thin gage panels was found to degrade the resistance to fatigue flaw growth only at elevated temperatures.

  3. Mechanical behavior of polycrystalline ceramics: Brittle fracture of SiC-Si3N4 materials

    NASA Technical Reports Server (NTRS)

    Ceipold, M. H.; Kapadia, C. M.; Kelkar, A. H.

    1972-01-01

    Research on the fracture behavior of silicon nitride and silicon carbide is reported along with the role of anion impurities in the fabrication and behavior of magnesium oxide. The results of a survey of crack propagation in SiC and Si3N4 are presented. Studies in the following areas are reported: development of a fracture toughness testing technique, constant moment beam, microcrack examination, and etching techniques.

  4. Development of a balanced experimental-computational approach to understanding the mechanics of proximal femur fractures.

    PubMed

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

    2014-06-01

    The majority of people who sustain hip fractures after a fall to the side would not have been identified using current screening techniques such as areal bone mineral density. Identifying them, however, is essential so that appropriate pharmacological or lifestyle interventions can be implemented. A protocol, demonstrated on a single specimen, is introduced, comprising the following components; in vitro biofidelic drop tower testing of a proximal femur; high-speed image analysis through digital image correlation; detailed accounting of the energy present during the drop tower test; organ level finite element simulations of the drop tower test; micro level finite element simulations of critical volumes of interest in the trabecular bone. Fracture in the femoral specimen initiated in the superior part of the neck. Measured fracture load was 3760N, compared to 4871N predicted based on the finite element analysis. Digital image correlation showed compressive surface strains as high as 7.1% prior to fracture. Voxel level results were consistent with high-speed video data and helped identify hidden local structural weaknesses. We found using a drop tower test protocol that a femoral neck fracture can be created with a fall velocity and energy representative of a sideways fall from standing. Additionally, we found that the nested explicit finite element method used allowed us to identify local structural weaknesses associated with femur fracture initiation. PMID:24629624

  5. Development of a balanced experimental-computational approach to understanding the mechanics of proximal femur fractures.

    PubMed

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

    2014-06-01

    The majority of people who sustain hip fractures after a fall to the side would not have been identified using current screening techniques such as areal bone mineral density. Identifying them, however, is essential so that appropriate pharmacological or lifestyle interventions can be implemented. A protocol, demonstrated on a single specimen, is introduced, comprising the following components; in vitro biofidelic drop tower testing of a proximal femur; high-speed image analysis through digital image correlation; detailed accounting of the energy present during the drop tower test; organ level finite element simulations of the drop tower test; micro level finite element simulations of critical volumes of interest in the trabecular bone. Fracture in the femoral specimen initiated in the superior part of the neck. Measured fracture load was 3760N, compared to 4871N predicted based on the finite element analysis. Digital image correlation showed compressive surface strains as high as 7.1% prior to fracture. Voxel level results were consistent with high-speed video data and helped identify hidden local structural weaknesses. We found using a drop tower test protocol that a femoral neck fracture can be created with a fall velocity and energy representative of a sideways fall from standing. Additionally, we found that the nested explicit finite element method used allowed us to identify local structural weaknesses associated with femur fracture initiation.

  6. Sensitivity of mechanically transmitted pathogens to different disinfectants

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The intensive hands-on activities of greenhouse tomato propagation and production favor the spread of mechanically transmitted pathogens, particularly Clavibacter michiganensis subsp. michiganensis (Cmm), viruses, viroids, and Botrytis cinerea. These pathogens can spread during crop handling, graft...

  7. Mechanism of sensitivity of a three-collector magnetotransistor

    NASA Astrophysics Data System (ADS)

    Amelichev, V. V.; Cheremisinov, A. A.; Polomoshnov, S. A.; Tikhonov, R. D.

    2013-01-01

    The sensitivity of bipolar magnetotransistor with the base in the well - 3CBМТBW has been studied. A low velocity of surface recombination and an extraction of the injected electrons by a base-well р-n junction determined operating mode with a deviation of two flows of charge carriers has been established. The voltage magnetosensitivity (~11 V/T) has been determined.

  8. Mechanisms of differential strain sensitivity in gastric carcinogenesis.

    PubMed

    Weisburger, J H; Jones, R C; Barnes, W S; Pegg, A E

    1988-12-01

    The genetically-controlled, distinct sensitivity of different rat strains to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-induced cancer of the glandular stomach and duodenum was investigated. MNNG is activated through thiols, and the thiol content of the glandular stomach, duodenum, and liver of the BN rat tended to be slightly, but not significantly higher than that of the Wistar, Sprague-Dawley, Lewis, and Buffalo rats. The levels of the DNA repair system, O6-alkylguanine transferase (AGT), in sensitive Wistar strain rats had values similar to those in resistant Buffalo strain rats. Administration of 80 mg/liter of MNNG in the drinking water for six weeks up to the time of tissue collection yielded the same AGT levels. Of all the parameters examined to account for genetically-mediated sensitivity to gastrointestinal cancer induction, namely, N-denitrosation, thiol activation, AGT-related DNA repair, and cell duplication rates, the latter yielded the best association, although these factors acting together may be involved.

  9. Application of Fracture Mechanics to Specify the Proof Load Factor for Clamp Band Systems of Launch Vehicles

    NASA Astrophysics Data System (ADS)

    Singaravelu, J.; Sundaresan, S.; Nageswara Rao, B.

    2013-04-01

    This article presents a methodology for evaluation of the proof load factor (PLF) for clamp band system (CBS) made of M250 Maraging steel following fracture mechanics principles.CBS is most widely used as a structural element and as a separation system. Using Taguchi's design of experiments and the response surface method (RSM) the compact tension specimens were tested to establish an empirical relation for the failure load ( P max) in terms of the ultimate strength, width, thickness, and initial crack length. The test results of P max closely matched with the developed RSM empirical relation. Crack growth rates of the maraging steel in different environments were examined. Fracture strength (σf) of center surface cracks and through-crack tension specimens are evaluated utilizing the fracture toughness ( K IC). Stress induced in merman band at flight loading conditions is evaluated to estimate the higher load factor and PLF. Statistical safety factor and reliability assessments were made for the specified flaw sizes useful in the development of fracture control plan for CBS of launch vehicles.

  10. Effects of heat treatment and testing temperature on fracture mechanics behavior of low-Si CA-15 stainless steel

    NASA Astrophysics Data System (ADS)

    Hsu, Cheng-Hsun; Lee, Shen-Chih; Teng, Hwei-Yuan

    2004-02-01

    This research studied the effects of heat treatment and testing temperature on fracture mechanics behavior of Si-modified CA-15 martensitic stainless steel (MSS), which is similar to AISI 403 grade stainless steel, which has been widely used in wall and blanket structures and in the pipe of nuclear power plant reactors, turbine blades, and nozzles. The results indicated that fracture toughness of low-Si CA-15 MSS is better than that of AISI 403. The specimens of the low-Si CA-15 MSS after austenitization at 1010 °C and then tempering at 300 °C have higher plane-strain fracture toughness (K IC ) values for both 25 °C and -150 °C testing temperatures. However, the specimens tested at 150 °C cannot satisfy the plane-strain fracture toughness criteria. The fatigue crack growth rate is the slowest after austenitization at 1010 °C for 2 hours and tempering at 400 °C. Observing the crack propagation paths using a metallographic test, it was found that the cracking paths preferred orientation and branched along ferrite phase, owing to martensite-phase strengthening and grain-boundary-carbide retarding after 300 °C to 400 °C tempering. Also, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction analysis were performed to correlate the properties attained to the microstructural observation.

  11. Fracture Mechanical Measurements with Commercial Stainless Steels at 4 K and with Cp-Titanium at 173 K

    NASA Astrophysics Data System (ADS)

    Nyilas, A.; Mitterbacher, H.

    2010-04-01

    Using the JETT (J-Evaluation on Tensile Test) technique, measurements have been performed with commercial stainless steels in forged and cast condition for the reason of an assessment for low temperature service down to 4 K. These steels frequently used for industrial applications are designated by German Werkstoff (WNr) 1.4308 and 1.4408 cast stainless steels and a forged material with the number 1.4307. The fracture toughness tests at 4 K with forged material 1.4307 comprised apart from the base metal also the weld zone and additionally the 5% and 8% pre-strained conditions of the base metal. Fracture toughness reduced slightly for cold worked condition gradually as well as for the weld joint. The Reliability of the JETT measurements has been also checked using the ASTM E 1820—99a standard. In addition, to these measurements, commercial pure ASTM grade 2 titanium (WNr 3.7035) has been also examined using the same JETT method for the reason of industrial application and the requirement of minimum fracture toughness of 100 MPa√m was fulfilled at 173 K. Furthermore, test results performed at 7 K of pure titanium plate material (ASTM grade 1) with respect to fracture mechanical JETT method are presented.

  12. Proximal fifth metatarsal fractures.

    PubMed

    Ramponi, Denise R

    2013-01-01

    The most common fracture of the foot is a fracture of the proximal fifth metatarsal. In general, there are 3 types of fractures involving the proximal fifth metatarsal area, including a proximal diaphyseal stress fracture, a Jones fracture, and an avulsion fracture of the tuberosity. Some fractures of the fifth metatarsal heal without difficulty, whereas some have the potential for nonunion or delayed healing. Each fracture has some variation in the anatomical location on the fifth metatarsal, the mechanism of injury, the radiographic findings, and the treatment plan. Avulsion fractures of the tuberosity often heal without difficulty, yet fractures distal to the area of insertion of the peroneus brevis tendon are prone to nonunion and delayed healing (). Differential diagnosis of a fifth metatarsal midfoot injury includes ankle sprains, midfoot sprains, plantar facial ruptures, peroneus tendon ruptures, and other foot fractures.

  13. Mechanics of tidally driven fractures in Europa's ice shell and implications for seismic and radar profiling

    NASA Astrophysics Data System (ADS)

    Lee, S.; Pappalardo, R. T.; Makris, N. C.

    2005-12-01

    Among Europa's surface features, cycloidal cracks are probably the most important for proving the existence of a subsurface liquid ocean. This is because (1) there is strong evidence that they are caused by tidally induced stress [1], and (2) this stress likely only approaches the ice failure strength if an ocean is present. There are a number of outstanding issues, however, in quantitatively explaining cycloidal cracks. First, current estimates of the pure diurnal tidal stress necessary to cause cycloidal cracks even in the presence of an ocean [1,2] is well below the typical stress known to cause tensile failure in natural terrestrial ice [3]. Second, models of ridge formation suggest that cycloidal cracks penetrate through the entire brittle-ice layer [1,4], but current models limit the depth of tidally induced surface cracks to be less than 100 m even in the presence of an ocean [1,5]. Third, the 3-km/h crack propagation speed determined by [1] is three orders of magnitude lower than the roughly 2-km/s speed at which cracks are known to propagate in ice. Our goal is to quantitatively address these issues in a unified manner. To do this, a fracture mechanics model is developed for the initiation and propagation of a crack through an ice layer of finite thickness in the presence of gravitational overburden and porosity. It is shown that Europa's ice shell may be highly porous and salt-rich. This implies that the strength of Europa's outer ice shell may be sufficiently low to make the crack initiation strengths arrived at by current kinematic models [1,2] highly plausible, even though they are much lower than those typically measured for terrestrial ice. A model is developed for the stress intensity factor at a crack tip in an ice shell with finite thickness, gravitational overburden, and depth-dependent porosity. This leads to the conclusion that cycloids are generated as a sequence of discrete and near instantaneous fracture events, each of which penetrates

  14. Mechanical sensitivity of Piezo1 ion channels can be tuned by cellular membrane tension.

    PubMed

    Lewis, Amanda H; Grandl, Jörg

    2015-12-08

    Piezo1 ion channels mediate the conversion of mechanical forces into electrical signals and are critical for responsiveness to touch in metazoans. The apparent mechanical sensitivity of Piezo1 varies substantially across cellular environments, stimulating methods and protocols, raising the fundamental questions of what precise physical stimulus activates the channel and how its stimulus sensitivity is regulated. Here, we measured Piezo1 currents evoked by membrane stretch in three patch configurations, while simultaneously visualizing and measuring membrane geometry. Building on this approach, we developed protocols to minimize resting membrane curvature and tension prior to probing Piezo1 activity. We find that Piezo1 responds to lateral membrane tension with exquisite sensitivity as compared to other mechanically activated channels and that resting tension can drive channel inactivation, thereby tuning overall mechanical sensitivity of Piezo1. Our results explain how Piezo1 can function efficiently and with adaptable sensitivity as a sensor of mechanical stimulation in diverse cellular contexts.

  15. The Relationships between Weight Functions, Geometric Functions,and Compliance Functions in Linear Elastic Fracture Mechanics

    SciTech Connect

    Yuan, Rong

    2007-01-01

    Linear elastic fracture mechanics is widely used in industry because it established simple and explicit relationships between the permissible loading conditions and the critical crack size that is allowed in a structure. Stress intensity factors are the above-mentioned functional expressions that relate load with crack size through geometric functions or weight functions. Compliance functions are to determine the crack/flaw size in a structure when optical inspection is inconvenient. As a result, geometric functions, weight functions and compliance functions have been intensively studied to determine the stress intensity factor expressions for different geometries. However, the relations between these functions have received less attention. This work is therefore to investigate the intrinsic relationships between these functions. Theoretical derivation was carried out and the results were verified on single-edge cracked plate under tension and bending. It is found out that the geometric function is essentially the non-dimensional weight function at the loading point. The compliance function is composed of two parts: a varying part due to crack extension and a constant part from the intact structure if no crack exists. The derivative of the compliance function at any location is the product of the geometric function and the weight function at the evaluation point. Inversely, the compliance function can be acquired by the integration of the product of the geometric function and the weight function with respect to the crack size. The integral constant is just the unchanging compliance from the intact structure. Consequently, a special application of the relations is to obtain the compliance functions along a crack once the geometric function and weight functions are known. Any of the three special functions can be derived once the other two functions are known. These relations may greatly simplify the numerical process in obtaining either geometric functions, weight

  16. Petrophysical and Mechanical Properties of Fractured Aquifers in the Northern Newark Basin: Implications for Carbon Sequestration

    NASA Astrophysics Data System (ADS)

    Zakharova, N. V.; Goldberg, D.; Collins, D.; Olsen, P. E.

    2012-12-01

    One of the key factors in predicting the performance of low-permeability fractured reservoirs is a detailed understanding of the in-situ state of stress and the distribution and orientation of natural fractures and faults. In this study we analyze borehole geophysical data from a deep characterization well in the northern Newark Basin, a candidate CO2-storage site, and provide petrophysical and geomechanical characterization of fractured sedimentary and igneous formations. Previous studies in the northern Newark basin demonstrated no unique relationship between hydraulic conductivity and degree of fracturing, fracture apertures or orientation. Therefore, in the absence of hydraulic testing data predicting fracture behavior under CO2 injection condition presents a significant challenge for baseline formation characterization. Moreover, fluid injection in deep wells can cause reactivation of existing faults or new fracture initiation due to significant increase in the pore pressure. We analyze electrical resistivity images and full-wave sonic data to constrain the state of the current in-situ stress in the northern Newark basin, and to evaluate how the interaction between in-situ stress and the distribution and orientation of natural fractures influences their hydraulic properties. We then combine it with the full suite of wireline logs to describe petrophysical, hydraulic, and geomechanical properties of the fractured aquifers at the locality. The Sandia Technologies, LLC Tandem Lot #1 geologic characterization well (Rockland County, NY) is about 6,800 ft deep and transects Triassic terrestrial sediments and the Palisades diabase sill that are both characterized by abundant natural fractures. A suite of standard wireline logs, high-resolution electrical resistivity images and full-wave sonic data were collected in the borehole but no hydraulic data or in-situ stress estimates are available. Borehole breakouts are clearly observed in the resistivity images in

  17. Elastic stress transmission and transformation (ESTT) by confined liquid: A new mechanics for fracture in elastic lithosphere of the earth

    NASA Astrophysics Data System (ADS)

    Xu, Xing-Wang; Peters, Stephen G.; Liang, Guang-He; Zhang, Bao-Lin

    2016-03-01

    We report on a new mechanical principle, which suggests that a confined liquid in the elastic lithosphere has the potential to transmit a maximum applied compressive stress. This stress can be transmitted to the internal contacts between rock and liquid and would then be transformed into a normal compressive stress with tangential tensile stress components. During this process, both effective compressive normal stress and tensile tangential stresses arise along the liquid-rock contact. The minimum effective tensile tangential stress causes the surrounding rock to rupture. Liquid-driven fracture initiates at the point along the rock-liquid boundary where the maximum compressive stress is applied and propagates along a plane that is perpendicular to the minimum effective tensile tangential stress and also is perpendicular to the minimum principal stress. Liquid-driven fractures and dikes propagate along the axes of cylindrical zones that are perpendicular to the minimum compressive principal stress in rocks in non-tectonic regions. The minimum depth for liquid-driven fracture, which is induced by a spherical confined liquid and an isolated magma chamber in the elastic lithosphere, ranges from 2 to 6 km, whereas dikes with hemi-cylinder-shaped ends propagate upwards closer to the surface under gravity. Transmission of pumping pressure, i.e. the pressure differences on the underside of a dike that is connected with a chamber, from the source magma chamber to intermediate and shallow chambers increases liquid pressure and also the effective tensile tangential stress and therefore leads to new fractures and dike formation and to upwards transport of magmas that have stagnated in the intermediate chamber. Tectonic stress alters local stress fields in the surrounding country rocks and therefore synchronously varies the local effective tensile tangential stress and the nature and geometry of the liquid-driven fractures.

  18. Effect of nicotine and tobacco administration method on the mechanical properties of healing bone following closed fracture.

    PubMed

    Hastrup, Sidsel Gaarn; Chen, Xinqian; Bechtold, Joan E; Kyle, Richard F; Rahbek, Ole; Keyler, Daniel E; Skoett, Martin; Soeballe, Kjeld

    2010-09-01

    We previously showed different effects of tobacco and nicotine on fracture healing, but due to pump reservoir limits, maximum exposure period was 4 weeks. To allow flexibility in pre- and post-fracture exposure periods, the objective of this study was to compare a new oral administration route for nicotine to the established pump method. Four groups were studied: (1) pump saline, (2) pump saline + oral tobacco, (3) pump saline/nicotine + oral tobacco, and (4) pump saline + oral nicotine/tobacco. Sprague-Dawley rats (n = 84) received a transverse femoral fracture stabilized with an intramedullary pin 1 week after initiating dosing. After 3 weeks, no difference was found in torsional strength or stiffness between oral nicotine/tobacco or pump nicotine + tobacco, while energy absorption with oral nicotine/tobacco was greater than pump nicotine + tobacco (p < 0.05). Compared to saline control, strength for oral nicotine/tobacco was higher than control (p < 0.05), and stiffnesses for pump nicotine + tobacco and oral nicotine/tobacco were higher than control (p < 0.05). No differences in energy were found for either nicotine-tobacco group compared to saline control. Mean serum cotinine (stable nicotine metabolite) was different between pump and oral nicotine at 1 and 4 weeks, but all groups were in the range of 1-2 pack/day smokers. In summary, relevant serum cotinine levels can be reached in rats with oral nicotine, and, in the presence of tobacco, nicotine can influence mechanical aspects of fracture healing, dependent on administration method. Caution should be exercised when comparing results of fracture healing studies using different methods of nicotine administration.

  19. The Mechanisms of Dispersion Strengthening and Fracture in Al-based XD (TM) Alloys

    NASA Technical Reports Server (NTRS)

    Aiken, R. M., Jr.

    1990-01-01

    The influence of reinforcement size, volume fraction, and matrix deformation behavior on room and elevated temperature strength, and the fracture toughness of metal matrix composites of both pure aluminum and Al(4 percent)Cu(1.5 percent)Mg with 0 to 15 vol percent TiB2 were examined. Higher TiB2 volume fractions increased the tensile yield strength both at room and elevated temperatures, and reduced the elongation to fracture. Tensile tests also indicate that small particles provided a greater increase in strength for a given volume fraction than larger particles, whereas elongation to fracture appeared to be insensitive to reinforcement size. The fracture toughness of the Al(4 percent)Cu(1.5 percent)Mg alloys decreased rapidly with TiB2 additions of 0 to 5 vol percent and more slowly with TiB2 additions of 5 to 15 vol percent. Fracture toughness appears to be independent of TiB2 particle size. The isothermal-aging response of the precipitation strengthened Al(4 percent)Cu(1.5 percent)Mg alloys was not altered by the presence of TiB2.

  20. Sensitivity of a cavityless opto-mechanical system

    NASA Astrophysics Data System (ADS)

    Fermani, Rachele; Mancini, Stefano; Tombesi, Paolo

    2004-05-01

    Optomechanical systems play a crucial role in a variety of precision measurement like gravitational wave detection and atomic force microscope. They are based on the interaction between a movable mirror, a meter experiencing tiny forces, and a radiation field, a probe reading out the mirror's position. In these applications one needs a very high resolution measurement and a good control of the various noise sources, classical and quantum, because one has to detect the effect of a very weak force. As optomechanical system, it is usually considered a Fabry-Perot cavity with a movable mirror coupled to the external force and to the radiation probe. Instead, in our work, we consider a single perfectly reflecting mirror shined by an intense and quasi-monochromatic optical beam. The physical process is very similar to a stimulate Brillouin scattering, even though in this case the Stokes and anti-Stokes component are back scattered by the acoustic wave at reflection, and the optomechanical coupling is provided by the radiation pressure. An effective interaction Hamiltonian for that system has been derived; we further consider the action of a classical coherent force on the probe and its readout through radiation field. Since the Hamiltonian was written in a frame rotating at the frequency of the mirror, we obtain a new Hamiltonian whit new related Heisenberg equations, by assuming the force constant. The mirror is considered initially in a thermal state, and the meter modes in pure entangled state (two mode squeezed state). Then, supposing to perform the heterodyne detection on the reflected sidebands modes, the relevant quantities for the sensitivity of the system are determined to get the signal to noise ratio, from which the minimum detectable force is also obtained. The latter is compared with the standard quantum limit (SQL), showing the possibility to go beyond it by using nonclassical entangled state, (likewise to what happens in the model involving an optical

  1. Mechanisms of Plastic and Fracture Instabilities for Alloy Development of Fusion Materials. Final Project Report for period July 15, 1998 - July 14, 2003

    SciTech Connect

    Ghoniem, N. M.

    2003-07-14

    The main objective of this research was to develop new computational tools for the simulation and analysis of plasticity and fracture mechanisms of fusion materials, and to assist in planning and assessment of corresponding radiation experiments.

  2. Mechanisms and characteristics of airway sensitization to indoor allergens.

    PubMed

    Liccardi, G; Cazzola, M; Russo, M; Gilder, J A; D'Amato, M; D'Amato, G

    2001-02-01

    The increasing prevalence of allergic respiratory diseases, and particularly of bronchial asthma, has been linked to changes induced by human activities in outdoor and indoor environments. People living in industrialized countries spend most of their time indoors: in private homes, offices and means of transport. Indoor environments are not a refuge from outdoor air pollution. Modern systems for energy saving such as insulated windows and doors reduce the indoor natural ventilation and consequently increase the rate of indoor humidity. These conditions may determine an increase in the level of indoor pollutants (tobacco smoke, gases produced by cooling processes etc.) and of allergens derived from mites, domestic animals and cockroaches. Upholstered furniture, wall-to-wall carpets, central heating systems and/or humidifiers may also contribute to the growth of mite populations. The increasing levels of exposure to pollutants and allergens in indoor environments represents a risk factor for the development of airway sensitization, especially if these materials are inhaled early in life. The major cat allergen Fel d 1 is considered an ubiquitous allergen, since it has been found in many indoor environments where a cat has never been kept. The clothing of cat owners seems to help spread Fel d 1 in cat-free environments. Sensitization to cockroach allergens is very common in patients living in urban areas where unhygenic conditions may favour the growth of cockroach populations. Monitoring of the levels of allergens and strategies of allergen and pollutant avoidance in indoor environments are the main ways to reduce the prevalence of respiratory allergies induced by these materials.

  3. A thermo-hydro-mechanical coupled model in local thermal non-equilibrium for fractured HDR reservoir with double porosity

    NASA Astrophysics Data System (ADS)

    Gelet, R.; Loret, B.; Khalili, N.

    2012-07-01

    The constitutive thermo-hydro-mechanical equations of fractured media are embodied in the theory of mixtures applied to three-phase poroelastic media. The solid skeleton contains two distinct cavities filled with the same fluid. Each of the three phases is endowed with its own temperature. The constitutive relations governing the thermomechanical behavior, generalized diffusion and transfer are structured by, and satisfy, the dissipation inequality. The cavities exchange both mass and energy. Mass exchanges are driven by the jump in scaled chemical potential, and energy exchanges by the jump in coldness. The finite element approximation uses the displacement vector, the two fluid pressures and the three temperatures as primary variables. It is used to analyze a generic hot dry rock geothermal reservoir. Three parameters of the model are calibrated from the thermal outputs of Fenton Hill and Rosemanowes HDR reservoirs. The calibrated model is next applied to simulate circulation tests at the Fenton Hill HDR reservoir. The finer thermo-hydro-mechanical response provided by the dual porosity model with respect to a single porosity model is highlighted in a parameter analysis. Emphasis is put on the influence of the fracture spacing, on the effective stress response and on the permeation of the fluid into the porous blocks. The dual porosity model yields a thermally induced effective stress that is less tensile compared with the single porosity response. This effect becomes significant for large fracture spacings. In agreement with field data, fluid loss is observed to be high initially and to decrease with time.

  4. Competition of fracture mechanisms in monolithic dental ceramics: flat model systems.

    PubMed

    Zhang, Yu; Kim, Jae-Won; Bhowmick, Sanjit; Thompson, Van P; Rekow, E Dianne

    2009-02-01

    Monolithic (single layer) glass-ceramic restorations often fail from chipping and fracture. Using blunt indentation of a model flat porcelain-like brittle layer bonded onto a dentin-like polymer support system, a variety of fatigue fracture modes has been identified and analyzed: outer cone, inner cone, and median cracks developing in the near-contact region at the occlusal surface; radial cracks developing at the internal cementation surface along the loading axis. Our findings indicate that monolithic glass-ceramic layers are vulnerable to both occlusal surface damage and cementation internal surface fracture. Clinical issues in the longevity of ceramic restorations are discussed in relation to biting force, physical properties of ceramic crowns and luting cement, and thicknesses of ceramic and cement layers.

  5. Competition of Fracture Mechanisms in Monolithic Dental Ceramics: Flat Model Systems

    PubMed Central

    Zhang, Yu; Kim, Jae-Won; Bhowmick, Sanjit; Thompson, Van P.; Rekow, E. Dianne

    2015-01-01

    Monolithic (single layer) glass-ceramic restorations often fail from chipping and fracture. Using blunt indentation of a model flat porcelain-like brittle layer bonded onto a dentin-like polymer support system, a variety of fatigue fracture modes has been identified and analyzed: outer cone, inner cone, and median cracks developing in the near-contact region at the occlusal surface; radial cracks developing at the internal cementation surface along the loading axis. Our findings indicate that monolithic glass-ceramic layers are vulnerable to both occlusal surface damage and cementation internal surface fracture. Clinical issues in the longevity of ceramic restorations are discussed in relation to biting force, physical properties of ceramic crowns and luting cement, and thicknesses of ceramic and cement layers. PMID:18478533

  6. Mechanical Properties and Fracture Surfaces of Thixoformed HP9/4/30 Steel

    SciTech Connect

    Omar, M. Z.; Jaharah, A. G.; Atkinson, H. V.; Kapranos, P.

    2007-04-07

    Most work in semi-solid metal processing has been focused on relatively low-melting temperature materials such as aluminium, magnesium, tin, lead and their composites. Because of the high melting temperatures and related measurement difficulties, there is relatively small amount of experimental data available on the thixoforming of high temperature materials such as steels. This paper discusses the relationships between tensile tests data and the fracture surfaces of HP9/4/30 steel samples, in as-received and as-thixoformed conditions. Some of the as-thixoformed samples were subjected to commercial heat treatments before the tests were carried out. The as-received samples showed a typical ductile fracture of 'cup' and 'cone' surface appearance. The thixoformed samples, although showing some significant increase in tensile strength values, failed in a brittle manner, with the fracture surfaces showing a 'cobbled' surface appearance. The application of the commercial heat treatment to the thixoformed samples has significantly improved their ductility.

  7. Mechanisms affecting the transport and retention of bacteria, bacteriophage and microspheres in laboratory-scale saturated fractures

    NASA Astrophysics Data System (ADS)

    Seggewiss, G.; Dickson, S. E.

    2013-12-01

    Groundwater is becoming an increasingly important water source due to the ever-increasing demands from agricultural, residential and industrial consumers. In search of more secure sources, wells are routinely finished over large vertical depths in bedrock aquifers, creating new hydraulic pathways and thus increasing the risk of cross contamination. Moreover, hydraulic pathways are also being altered and created by increasing water withdrawal rates from these wells. Currently, it is not well understood how biological contaminants are transported through, and retained in, fractured media thereby making risk assessment and land use decisions difficult. Colloid transport within fractured rock is a complex process with several mechanisms affecting transport and retention, including: advection, hydrodynamic dispersion, diffusion, size exclusion, adsorption, and decay. Several researchers have investigated the transport of bacteria, bacteriophage, and microspheres (both carboxylated and plain) to evaluate the effects of surface properties and size on transport and retention. These studies have suggested that transport is highly dependent on the physico-chemical properties of the particle, the fracture, and the carrying fluid. However, these studies contain little detail regarding the specific mechanisms responsible for transport beyond speculating about their existence. Further, little work has been done to compare the transport of these particulate materials through the same fracture, allowing for direct observations based on particulate size and surface properties. This research examines the similarities and differences in transport and retention between four different particles through two different laboratory-scale, saturated fractures. This work is designed to explore the effects of particle size, surface properties, ionic strength of the carrying solution, and aperture field characteristics on transport and retention in single, saturated fractures. The particulates

  8. Mechanical characterization of a CO2 fractured reservoir by means of microseismicity induced by high pressure injection tests

    NASA Astrophysics Data System (ADS)

    De Simone, Silvia; Soler, Joaquim; Carrera, Jesus; Slooten, Luit Jan; Ortiz, Gema

    2014-05-01

    Reservoir characterization is an essential issue in geological storage of CO2 in Technological Development Plant (TDP). In particular, hydromechanical characterization of the caprock-reservoir system is crucial, in order to define the maximum suitable injection pressure and the in-situ mechanical properties. Thus, it is possible to conjecture the hydromechanical behavior of the system during CO2 injection. Microseismicity induced by fluid injection may be used as instruments to find out fractured reservoir properties. Indeed, the hydromechanical response is controlled by permeability (k), Young modulus (E) and Poisson ratio (ν). In caprock-reservoir systems, reservoir stiffness controls the stress transfer towards the caprock, where failure may occur. Therefore, the location of the microseismic hypocenters could give information on the reservoir stiffness. In this work we propose a simulation and calibration method of the microseismicity induced by high pressure fluid injection in a fractured reservoir. Coupled hydromechanical models are peformed. The methology is applied to a particular case study.

  9. Effects of the precipitation of stabilizers on the mechanism of grain fracturing in a zirconia metering nozzle

    NASA Astrophysics Data System (ADS)

    Zhao, Liang; Xue, Qun-hu; Ding, Dong-hai

    2016-09-01

    The mechanism of grain fracturing in a zirconia metering nozzle used in the continuous casting process was studied. The phase composition, microstructure, and chemical composition of the residual samples were studied using an X-ray fluorescence analyzer, scanning electron microscope, and electron probe. Results revealed that the composition, structure, and mineral phase of the original layer, transition layer, and affected layer of the metering nozzle differed because of stabilizer precipitation and steel slag permeation. The stabilizer MgO formed low-melting phases with steel slag and impure SiO2 on the boundaries (pores) of zirconia grains; consequently, grain fracturing occurred and accelerated damage to the metering nozzle was observed.

  10. Double torsion fracture mechanics testing of shales under chemically reactive conditions

    NASA Astrophysics Data System (ADS)

    Chen, X.; Callahan, O. A.; Holder, J. T.; Olson, J. E.; Eichhubl, P.

    2015-12-01

    Fracture properties of shales is vital for applications such as shale and tight gas development, and seal performance of carbon storage reservoirs. We analyze the fracture behavior from samples of Marcellus, Woodford, and Mancos shales using double-torsion (DT) load relaxation fracture tests. The DT test allows the determination of mode-I fracture toughness (KIC), subcritical crack growth index (SCI), and the stress-intensity factor vs crack velocity (K-V) curves. Samples are tested at ambient air and aqueous conditions with variable ionic concentrations of NaCl and CaCl2, and temperatures up to 70 to determine the effects of chemical/environmental conditions on fracture. Under ambient air condition, KIC determined from DT tests is 1.51±0.32, 0.85±0.25, 1.08±0.17 MPam1/2 for Marcellus, Woodford, and Mancos shales, respectively. Tests under water showed considerable change of KIC compared to ambient condition, with 10.6% increase for Marcellus, 36.5% decrease for Woodford, and 6.7% decrease for Mancos shales. SCI under ambient air condition is between 56 and 80 for the shales tested. The presence of water results in a significant reduction of the SCI from 70% to 85% compared to air condition. Tests under chemically reactive solutions are currently being performed with temperature control. K-V curves under ambient air conditions are linear with stable SCI throughout the load-relaxation period. However, tests conducted under water result in an initial cracking period with SCI values comparable to ambient air tests, which then gradually transition into stable but significantly lower SCI values of 10-20. The non-linear K-V curves reveal that crack propagation in shales is initially limited by the transport of chemical agents due to their low permeability. Only after the initial cracking do interactions at the crack tip lead to cracking controlled by faster stress corrosion reactions. The decrease of SCI in water indicates higher crack propagation velocity due to

  11. A partitioned model order reduction approach to rationalise computational expenses in nonlinear fracture mechanics

    PubMed Central

    Kerfriden, P.; Goury, O.; Rabczuk, T.; Bordas, S.P.A.

    2013-01-01

    We propose in this paper a reduced order modelling technique based on domain partitioning for parametric problems of fracture. We show that coupling domain decomposition and projection-based model order reduction permits to focus the numerical effort where it is most needed: around the zones where damage propagates. No a priori knowledge of the damage pattern is required, the extraction of the corresponding spatial regions being based solely on algebra. The efficiency of the proposed approach is demonstrated numerically with an example relevant to engineering fracture. PMID:23750055

  12. Fracture mechanics and statistical modeling of ternary blends of polylactide/ethylene-acrylate copolymer /wood-flour composites

    NASA Astrophysics Data System (ADS)

    Afrifah, Kojo Agyapong

    This study examined the mechanisms of toughening the brittle bio-based poly(lactic acid) (PLA) with a biodegradable rubbery impact modifier to develop biodegradable and cost effective PLA/wood-flour composites with improved impact strength, toughness, high ductility, and flexibility. Semicrystalline and amorphous PLA grades were impact modified by melt blending with an ethylene-acrylate copolymer (EAC) impact modifier. EAC content was varied to study the effectiveness and efficiency of the impact modifier in toughening the semicrystalline and amorphous grades of the PLA. Impact strength was used to assess the effectiveness and efficiency of the EAC in toughening the blends, whereas the toughening mechanisms were determined with the phase morphologies and the miscibilities of the blends. Subsequent tensile property analyses were performed on the most efficiently toughened PLA grade. Composites were made from PLA, wood flour of various particle sizes, and EAC. Using two-level factorial design the interaction between wood flour content, wood flour particle size, and EAC content and its effect on the mechanical properties of the PLA/wood-flour composites was statistically studied. Numerical optimization was also performed to statistically model and optimize material compositions to attain mechanical properties for the PLA/wood-flour composites equivalent to at least those of unfilled PLA. The J-integral method of fracture mechanics was applied to assess the crack initiation (Jin) and complete fracture (J f) energies of the composites to account for imperfections in the composites and generate data useful for engineering designs. Morphologies of the fractured surfaces of the composites were analyzed to elucidate the failure and toughening mechanisms of the composites. The EAC impact modifier effectively improved the impact strength of the PLA/EAC blends, regardless of the PLA type. However, the EAC was more efficient in the semicrystalline grades of PLA compared to the

  13. Enhanced Sensitivity of Micro Mechanical Chemical Sensors Through Structural Variation

    SciTech Connect

    Harris, J.C.

    2001-04-16

    Chemical detection devices are very effective; however, their bulkiness makes them undesirable for portable applications. The next generation of chemical detectors is microscopic mechanical devices capable of measuring trace amounts of chemical vapor within the environment. The chemicals do not react directly with the detector, instead intermolecular forces cause chemicals to adhere to the surface. This surface adhesion of the chemical creates surface stress on the detectors leading to measurable movement. Modifications to the structural design of these microstructures have resulted in signal enhancement to over seven hundred percent.

  14. Development of a new code to solve hydro-mechanical coupling, shear failure and tensile failure due to hydraulic fracturing operations.

    NASA Astrophysics Data System (ADS)

    María Gómez Castro, Berta; De Simone, Silvia; Carrera, Jesús

    2016-04-01

    Nowadays, there are still some unsolved relevant questions which must be faced if we want to proceed to the hydraulic fracturing in a safe way. How much will the fracture propagate? This is one of the most important questions that have to be solved in order to avoid the formation of pathways leading to aquifer targets and atmospheric release. Will the fracture failure provoke a microseismic event? Probably this is the biggest fear that people have in fracking. The aim of this work (developed as a part of the EU - FracRisk project) is to understand the hydro-mechanical coupling that controls the shear of existing fractures and their propagation during a hydraulic fracturing operation, in order to identify the key parameters that dominate these processes and answer the mentioned questions. This investigation focuses on the development of a new C++ code which simulates hydro-mechanical coupling, shear movement and propagation of a fracture. The framework employed, called Kratos, uses the Finite Element Method and the fractures are represented with an interface element which is zero thickness. This means that both sides of the element lie together in the initial configuration (it seems a 1D element in a 2D domain, and a 2D element in a 3D domain) and separate as the adjacent matrix elements deform. Since we are working in hard, fragile rocks, we can assume an elastic matrix and impose irreversible displacements in fractures when rock failure occurs. The formulation used to simulate shear and tensile failures is based on the analytical solution proposed by Okada, 1992 and it is part of an iterative process. In conclusion, the objective of this work is to employ the new code developed to analyze the main uncertainties related with the hydro-mechanical behavior of fractures derived from the hydraulic fracturing operations.

  15. Fracturing of earthquake rupture mechanics on the fault with self-similarity and fault surface heterogeneity

    NASA Astrophysics Data System (ADS)

    Lee, Y.; Ma, K.; Yen, Y.

    2013-12-01

    The work of finite fault slip models have been done in several earthquake events. We compiled the finite fault slip models of 19 earthquakes in Taiwan within the magnitude range from Mw=4.56 to 7.69 which include different fault types. We analyzed the distribution of slip on the fault surface to get the scaling relation of slip values, and found the scaling relation can be shown as Rs=10^(a+n(Rd)) (where Rd is (d/dm) as the ratio of slip, d, to the average of the effective slip, dm, Rs is A/Ae as the ratio of the fault area, A, where slip d>R_d×d_m to the effective area, Ae. The effective area and slip were determined according to the normalization of the autocorrelation of slip in length and width. The fault slip was displayed a self-similar scaling, the scaling exponent values (n) are within n=0~-1.1 which can be relative with fractal dimension of fault slip system. The scaling exponents (n) also can be seen as a measure for the roughness degree of the slip distribution on the fault surface. For lower values of n, the gradient of the slip distribution increases, and the slip models become more heterogeneous. Based on the definition of asperity as Sa(d/dm>1.5), we also got a scaling relation between asperity and magnitude as Sa(d/dm>1.5)=1.27Mw-6.49. As found in several large earthquakes, we also observed that Sa is about 20% of Ae, where Sa is the area with the slip larger than 1.5 times of the mean slip. Very intriguing feature on the relationship of the average area ratio of the examined earthquakes (M~4.5-7.6) for Rs as function of Rd follows a fractal dimension of about 0.5, as logRs= 0.428Rd-0.078. This fractal dimension might bring some hints in understanding of earthquake rupture mechanics on fault fracturing. The correlation between the average area ratio of the examined earthquakes (M~4.5-7.6) for Rs to Rd. Rs is the ratio of the fault area where slip d>R_d×d_m to the effective area, and Rd is the ratio of slip to the average of the effective slip.

  16. The mechanics and physics of fracturing: application to thermal aspects of crack propagation and to fracking.

    PubMed

    Cherepanov, Genady P

    2015-03-28

    By way of introduction, the general invariant integral (GI) based on the energy conservation law is presented, with mention of cosmic, gravitational, mass, elastic, thermal and electromagnetic energy of matter application to demonstrate the approach, including Coulomb's Law generalized for moving electric charges, Newton's Law generalized for coupled gravitational/cosmic field, the new Archimedes' Law accounting for gravitational and surface energy, and others. Then using this approach the temperature track behind a moving crack is found, and the coupling of elastic and thermal energies is set up in fracturing. For porous materials saturated with a fluid or gas, the notion of binary continuum is used to introduce the corresponding GIs. As applied to the horizontal drilling and fracturing of boreholes, the field of pressure and flow rate as well as the fluid output from both a horizontal borehole and a fracture are derived in the fluid extraction regime. The theory of fracking in shale gas reservoirs is suggested for three basic regimes of the drill mud permeation, with calculating the shape and volume of the local region of the multiply fractured rock in terms of the pressures of rock, drill mud and shale gas. PMID:25713454

  17. Mechanical behavior of polycrystalline ceramics: Brittle fracture of Si C - Si3N4 materials

    NASA Technical Reports Server (NTRS)

    Leipold, M. H.; Kapadia, C. M.; Kelkar, A. H.

    1973-01-01

    The results are described of the final stage of the research involving the role of anions in the behavior of magnesium oxide, as well as the continued efforts of the fracture behavior of silicon nitride materials. These efforts, particularly the first, are further sub-divided in subsections describing individual types of behavior of materials.

  18. Mechanical test in-situ fracture device for Auger electron spectroscopy

    NASA Technical Reports Server (NTRS)

    Moorhead, R. D.

    1975-01-01

    An in-situ fracture device for Auger spectroscopy was described. The device is designed to handle small tensile specimens or small double cantilever beam specimens and is fully instrumented with load and displacement transducers so that quantitative stress-strain measurements can be made directly. Some initial test results for specimens made from 4130 and 1020 steel were presented.

  19. The mechanics and physics of fracturing: application to thermal aspects of crack propagation and to fracking.

    PubMed

    Cherepanov, Genady P

    2015-03-28

    By way of introduction, the general invariant integral (GI) based on the energy conservation law is presented, with mention of cosmic, gravitational, mass, elastic, thermal and electromagnetic energy of matter application to demonstrate the approach, including Coulomb's Law generalized for moving electric charges, Newton's Law generalized for coupled gravitational/cosmic field, the new Archimedes' Law accounting for gravitational and surface energy, and others. Then using this approach the temperature track behind a moving crack is found, and the coupling of elastic and thermal energies is set up in fracturing. For porous materials saturated with a fluid or gas, the notion of binary continuum is used to introduce the corresponding GIs. As applied to the horizontal drilling and fracturing of boreholes, the field of pressure and flow rate as well as the fluid output from both a horizontal borehole and a fracture are derived in the fluid extraction regime. The theory of fracking in shale gas reservoirs is suggested for three basic regimes of the drill mud permeation, with calculating the shape and volume of the local region of the multiply fractured rock in terms of the pressures of rock, drill mud and shale gas.

  20. Effect of orientation on the in vitro fracture toughness ofdentin: The role of toughening mechanisms

    SciTech Connect

    Nalla, R.K.; Kinney, J.H.; Ritchie, R.O.

    2003-01-28

    A micro-mechanistic understanding of bone fracture thatencompasses how cracks interact with the underlying microstructure anddefines their local failure mode is lacking, despite extensive research nthe response of bone to a variety of factors like aging, loading, and/ordisease.

  1. Mechanical Comparison of Headless Screw Fixation and Locking Plate Fixation for Talar Neck Fractures.

    PubMed

    Karakasli, Ahmet; Hapa, Onur; Erduran, Mehmet; Dincer, Cemal; Cecen, Berivan; Havitcioglu, Hasan

    2015-01-01

    For talar neck fractures, open reduction and internal fixation have been thought to facilitate revascularization and prevent osteonecrosis. Newer screw systems allow for placement of cannulated headless screws, which provide compression by virtue of a variable pitch thread. The present study compared the biomechanical fixation strength of cannulated headless variable-pitch screw fixation and locking plate fixation. A reproducible talar neck fracture was created in 14 fresh cadaver talar necks. Talar head fixation was then performed using 2 cannulated headless variable-pitch 4-mm/5-mm diameter (4/5) screws (Acutrak; Acumed, Hillsboro, OR) and locking plate fixation. Headless variable-pitch screw fixation had lower failure displacement than did locking plate fixation. No statistically significant differences were found in failure stiffness, yield stiffness (p = .655), yield load (p = .142), or ultimate load between the 2 fixation techniques. Cannulated headless variable-pitch screw fixation resulted in better failure displacement than locking plate fixation in a cadaveric talus model and could be considered a viable option for talus fracture fixation. Headless, fully threaded, variable-pitch screw fixation has inherent advantages compared with locking plate fixation, because it might cause less damage to the articular surface and can compress the fracture for improved reduction. Additionally, plate fixation can increase the risk of avascular necrosis owing to the wider incision and dissection of soft tissues.

  2. Mechanism of voltage-sensitive fluorescence in a microbial rhodopsin

    PubMed Central

    Maclaurin, Dougal; Venkatachalam, Veena; Lee, Hohjai; Cohen, Adam E.

    2013-01-01

    Microbial rhodopsins were recently introduced as genetically encoded fluorescent indicators of membrane voltage. An understanding of the mechanism underlying this function would aid in the design of improved voltage indicators. We asked, what states can the protein adopt, and which states are fluorescent? How does membrane voltage affect the photostationary distribution of states? Here, we present a detailed spectroscopic characterization of Archaerhodopsin 3 (Arch). We performed fluorescence spectroscopy on Arch and its photogenerated intermediates in Escherichia coli and in single HEK293 cells under voltage-clamp conditions. These experiments probed the effects of time-dependent illumination and membrane voltage on absorption, fluorescence, membrane current, and membrane capacitance. The fluorescence of Arch arises through a sequential three-photon process. Membrane voltage modulates protonation of the Schiff base in a 13-cis photocycle intermediate (M ⇌ N equilibrium), not in the ground state as previously hypothesized. We present experimental protocols for optimized voltage imaging with Arch, and we discuss strategies for engineering improved rhodopsin-based voltage indicators. PMID:23530193

  3. 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.

  4. Multiwell fracturing experiments. [Nitrogen foam fracture treatment

    SciTech Connect

    Warpinski, N.

    1985-01-01

    The objective of the Multiwell fracturing experiments is to test and develop the technology for the efficient stimulation of tight, lenticular gas sands. This requires basic understanding of: (1) fracture behavior and geometry in this complex lithologic environment, and (2) subsequent production into the created fracture. The intricate interplay of the hydraulic fracture with the lens geometry, the internal reservoir characteristics (fractures, reservoir breaks, etc.), the in situ stresses, and the mechanical defects (fracture, bedding, etc.) need to be defined in order to develop a successful stimulation program. The stimulation phase of the Multiwell Experiment is concerned with: (1) determining important rock/reservoir properties that influence or control fracture geometry and behavior, (2) designing fracture treatments to achieve a desired size and objectives, and (3) conducting post-treatment analyses to evaluate the effectiveness of the treatment. Background statement, project description, results and evaluation of future plans are presented. 5 refs., 2 figs., 2 tabs.

  5. Displaced patella fractures.

    PubMed

    Della Rocca, Gregory J

    2013-10-01

    Displaced patella fractures often result in disruption of the extensor mechanism of the knee. An intact extensor mechanism is a requirement for unassisted gait. Therefore, operative treatment of the displaced patella fracture is generally recommended. The evaluation of the patella fracture patient includes examination of extensor mechanism integrity. Operative management of patella fractures normally includes open reduction with internal fixation, although partial patellectomy is occasionally performed, with advancement of quadriceps tendon or patellar ligament to the fracture bed. Open reduction with internal fixation has historically been performed utilizing anterior tension band wiring, although comminution of the fracture occasionally makes this fixation construct inadequate. Supplementation or replacement of the tension band wire construct with interfragmentary screws, cerclage wire or suture, and/or plate-and-screw constructs may add to the stability of the fixation construct. Arthrosis of the patellofemoral joint is very common after healing of patella fractures, and substantial functional deficits may persist long after fracture healing has occurred.

  6. Micromechanics, Fracture Mechanics and Gas Permeability of Composite Laminates for Cryogenic Storage Systems

    NASA Technical Reports Server (NTRS)

    Choi, Sukjoo; Sankar, Bhavani; Ebaugh, Newton C.

    2005-01-01

    A micromechanics method is developed to investigate microcrack propagation in a liquid hydrogen composite tank at cryogenic temperature. The unit cell is modeled using square and hexagonal shapes depends on fiber and matrix layout from microscopic images of composite laminates. Periodic boundary conditions are applied to the unit cell. The temperature dependent properties are taken into account in the analysis. The laminate properties estimated by the micromechanics method are compared with empirical solutions using constituent properties. The micro stresses in the fiber and matrix phases based on boundary conditions in laminate level are calculated to predict the formation of microcracks in the matrix. The method is applied to an actual liquid hydrogen storage system. The analysis predicts micro stresses in the matrix phase are large enough to cause microcracks in the composite. Stress singularity of a transverse crack normal to a ply-interface is investigated to predict the fracture behavior at cryogenic conditions using analytical and finite element analysis. When a transverse crack touches a ply-interface of a composite layer with same fiber orientation, the stress singularity is equal to 1/2. When the transverse crack propagates to a stiffer layer normal to the ply-direction, the singularity becomes less than 1/2 and vice versa. Finite element analysis is performed to predict the fracture toughness of a laminated beam subjected to fracture loads measured by four-point bending tests at room and cryogenic temperatures. As results, the fracture load at cryogenic temperature is significantly lower than that at room temperature. However, when thermal stresses are taken into consideration, for both cases of room and cryogenic temperatures, the difference of the fracture toughness becomes insignificant. The result indicates fracture toughness is a characteristic property, which is independent to temperature changes. The experimental analysis is performed to

  7. Elastic-Plastic Fracture Mechanics Analysis of Critical Flaw Size in ARES I-X Flange-to-Skin Welds

    NASA Technical Reports Server (NTRS)

    Chell, G. Graham; Hudak, Stephen J., Jr.

    2008-01-01

    NASA's Ares 1 Upper Stage Simulator (USS) is being fabricated from welded A516 steel. In order to insure the structural integrity of these welds it is of interest to calculate the critical initial flaw size (CIFS) to establish rational inspection requirements. The CIFS is in turn dependent on the critical final flaw size (CFS), as well as fatigue flaw growth resulting from transportation, handling and service-induced loading. These calculations were made using linear elastic fracture mechanics (LEFM), which are thought to be conservative because they are based on a lower bound, so called elastic, fracture toughness determined from tests that displayed significant plasticity. Nevertheless, there was still concern that the yield magnitude stresses generated in the flange-to-skin weld by the combination of axial stresses due to axial forces, fit-up stresses, and weld residual stresses, could give rise to significant flaw-tip plasticity, which might render the LEFM results to be non-conservative. The objective of the present study was to employ Elastic Plastic Fracture Mechanics (EPFM) to determine CFS values, and then compare these values to CFS values evaluated using LEFM. CFS values were calculated for twelve cases involving surface and embedded flaws, EPFM analyses with and without plastic shakedown of the stresses, LEFM analyses, and various welding residual stress distributions. For the cases examined, the computed CFS values based on elastic analyses were the smallest in all instances where the failures were predicted to be controlled by the fracture toughness. However, in certain cases, the CFS values predicted by the elastic-plastic analyses were smaller than those predicted by the elastic analyses; in these cases the failure criteria were determined by a breakdown in stress intensity factor validity limits for deep flaws (a greater than 0.90t), rather than by the fracture toughness. Plastic relaxation of stresses accompanying shakedown always increases the

  8. A Thermo-Hydro-Mechanical modeling of fracture opening and closing due heat extraction from geothermal reservoir

    NASA Astrophysics Data System (ADS)

    Nand Pandey, Sachchida; Chaudhuri, Abhijit; Kelkar, Sharad

    2015-04-01

    Increasing the carbon dioxide concentration in atmosphere become challenging task for the scientific community. To achieve the sustainable growth with minimum pollution in atmosphere requires the development of low carbon technology or switch towards renewable energy. Geothermal energy is one of the promising source of clean energy. Geothermal energy is also considered a sustainable, reliable and least-expensive. This study presents a numerical modeling of subsurface heat extraction from the reservoir. The combine flow, heat transfer and geo-mechanical problem are modeled using FEHM code, which was validated against existing field data, numerical code and commercial software. In FEHM the flow and heat transfer in reservoir are solved by control volume method while for mechanical deformation finite element technique is used. The 3-D computational domain (230m × 200m × 1000m) has single horizontal fault/fracture, which is located at 800 m depth from the ground surface. The fracture connects the injection and production wells. The distance between the wells is 100 m. A geothermal gradient 0.08 °C/m is considered. The temperatures at top and bottom boundaries are held fixed as 20 and 100 °C respectively. The zero heat and mass flux boundary conditions are imposed to all vertical side boundaries of the domain. The simulation results for 100 days suggests that the computational domain is sufficiently large as the temperature along the vertical boundaries are not affected by cold-water injection. To model the thermo-poro-elastic deformation, zero all three components of displacement are specified as zero at the bottom. The zero stress condition along all other boundaries allows the boundaries to move freely. The temperature and pressure dependent fluid properties such as density and viscosity with single phase flow in saturated medium is considered. We performed a series of thermo-hydro-mechanical (THM) simulations to show aperture alteration due to cold

  9. Modeling Shear-Enhanced Permeability as the Mechanism for Fluid Flow in Fractured Reservoirs - A Promising Improvement to Predicting Reservoir Production

    NASA Astrophysics Data System (ADS)

    Barton, C.; Moos, D.

    2011-12-01

    An accurate geomechanical reservoir model including constraints on stress magnitudes and orientations, mechanical rock properties, and the orientations and characteristics of natural fractures is essential to understanding reservoir response to stimulation and production in low permeability reservoirs such as crystalline basement geothermal or oil and gas reservoirs. In these low permeability reservoirs, stimulation response is controlled largely by the properties of natural and induced fracture networks which are in turn controlled by the in situ stresses, the fracture distribution and the hydraulic behavior of the fractures. These hydraulic properties of the fractures, their width, stiffness and strength are often difficult to quantify, leading to large uncertainties in predicted response to stimulation of fractured reservoirs. A well-constrained and calibrated fracture model makes it possible not only to predict reservoir response to stimulation, including the shape and orientation of the stimulated region, but also to predict the required stimulation pressure. Such a model also makes it possible to predict the change in flow properties during production due to depletion, resulting in better predictions of production rate and ultimate recovery. As part of the evaluation process of a compartmentalized fractured basement reservoir, wellbore image and other data were used to develop a 3D geomechanical model of stress and natural fractures through the reservoir volume. Although the results clearly defined the optimal directions in which to drill wells to exploit pre-existing natural fractures, large uncertainties in the models resulted in significant uncertainties in predictions of stimulation response. Because the pre-existing natural fractures were insufficiently permeable and operational constraints precluded the use of hydraulic fracturing to stimulate the reservoir, an innovative approach was taken to determine the extent to which injection at pressures below

  10. The effect of coating/substrate interface curvature on fracture of Si-Al-N coatings subjected to mechanical loading

    NASA Astrophysics Data System (ADS)

    Shugurov, Artur

    2015-10-01

    The effect of curvature of the film/substrate interface on the fracture mechanisms of Si-Al-N coatings on Cu substrates subjected to uniaxial tension and alternating bending is studied. Local interface curvature due to substrate surface roughening caused by its plastic deformation in the course of the uniaxial tension is shown to have a profound effect on their delamination and buckling. Interface curvature induced by specimen bending promotes kinking of through-the-coating cracks at the interface that is followed by delamination and spalling of the coatings.

  11. Numerical simulation of a class of models that combine several mechanisms of dissipation: Fracture, plasticity, viscous dissipation

    NASA Astrophysics Data System (ADS)

    Bonnetier, Eric; Jakabčin, Lukáš; Labbé, Stéphane; Replumaz, Anne

    2014-08-01

    We study a class of time evolution models that contain dissipation mechanisms exhibited by geophysical materials during deformation: plasticity, viscous dissipation and fracture. We formally prove that they satisfy a Clausius-Duhem type inequality. We describe a semi-discrete time evolution associated with these models, and report numerical 1D and 2D traction experiments, that illustrate that several dissipation regimes can indeed take place during the deformation. Finally, we report 2D numerical simulation of an experiment by Peltzer and Tapponnier, who studied the indentation of a layer of plasticine as an analogue model for geological materials.

  12. Observation of mechanical fracture and corresponding domain structure changes of polycrystalline PbTiO{sub 3} nanotubes.

    SciTech Connect

    Choi, H.; Hong, S.; Kim, Y.; Kim, M.; Sung, T.-H.; Shin, H.; No, K.

    2011-02-01

    PbTiO{sub 3} (PTO) nanotubes (NTs) were synthesized at various temperatures by gas phase reaction between PbO gas and anatase TiO{sub 2} NTs and characterized by piezoresponse force microscopy (PFM). PTO ferroelectric phase was synthesized at as low as 400 C as evidenced by PFM domain images and piezoresponse hysteresis loop measurement. Furthermore, the PTO NTs fabricated at above 500 C underwent mechanical fracture through development of nanocracks due to grain growth, leading to ferroelectric domains with larger size and lower aspect ratio.

  13. Influence of internal fixator flexibility on murine fracture healing as characterized by mechanical testing and microCT imaging.

    PubMed

    Steck, Roland; Ueno, Masaki; Gregory, Laura; Rijken, Noortje; Wullschleger, Martin E; Itoman, Moritoshi; Schuetz, Michael A

    2011-08-01

    Mechanically well-defined stabilization systems have only recently become available, providing standardized conditions for studying the role of the mechanical environment on mouse bone fracture healing. The aim of this study was to characterize the time course of strength recovery and callus development of mouse femoral osteotomies stabilized with either low or high flexibility (in bending and torsion) internal fixation plates. Animals were euthanized and femora excised at 14, 21, and 28 days post-osteotomy for microCT analysis and torsional strength testing. While a larger mineralized callus was observed in osteotomies under more flexible conditions at all time points, the earlier bridging of the mineralized callus under less flexible conditions by 1 week resulted in an earlier recovery of torsional strength in mice stabilized with low flexibility fixation. Ultimate torque values for these bones were significantly higher at 14 and 21 days post-osteotomy compared to bones with the more flexible stabilization. Our study confirms the high reproducibility of the results that are achieved with this new implant system, therefore making it ideal for studying the influence of the mechanical environment on murine fracture healing under highly standardized conditions.

  14. Fractures of modern high nitrogen stainless steel cemented stems: cause, mechanism, and avoidance in 14 cases.

    PubMed

    Yates, Piers J; Quraishi, Nasir A; Kop, Allan; Howie, Donald W; Marx, Clare; Swarts, Eric

    2008-02-01

    We present 14 cases of fracture of modern, high-nitrogen, stainless steel stems. Our clinical and radiological data suggest that heavy patients with small stems and poor proximal support are at risk for fracturing their implants. "Champagne-glass" canals can lead to the use of smaller stems often placed in varus, which can lead to cantilever bending and fatigue failure in the distal half of the stem. Metallurgical assessment of the retrieved high-nitrogen, stainless steel stems reveals microstructural inconsistencies that may contribute to their failure. Based on our findings, careful consideration and attention to technique is required when using stainless steel stems in patients with high body mass index or high weight. Technique is particularly important in femurs with champagne-glass canals. PMID:18280411

  15. Analysis of Subcritical Crack Growth in Dental Ceramics Using Fracture Mechanics and Fractography

    PubMed Central

    Taskonak, Burak; Griggs, Jason A.; Mecholsky, John J.; Yan, Jia-Hau

    2008-01-01

    Objectives The aim of this study was to test the hypothesis that the flexural strengths and critical flaw sizes of dental ceramic specimens will be affected by the testing environment and stressing rate even though their fracture toughness values will remain the same. Methods Ceramic specimens were prepared from an aluminous porcelain (Vitadur Alpha; VITA Zahnfabrik, Bad Säckingen, Germany) and an alumina-zirconia-glass composite (In-Ceram® Zirconia; VITA Zahnfabrik). Three hundred uniaxial flexure specimens (150 of each material) were fabricated to dimensions of 25 mm × 4 mm × 1.2 mm according to the ISO 6872 standard. Each group of 30 specimens was fractured in water using one of four different target stressing rates ranging on a logarithmic scale from 0.1 to 100 MPa/s for Vitadur Alpha and from 0.01 to 10 MPa/s for In-Ceram® Zirconia. The fifth group was tested in inert environment (oil) with a target stressing rate of 100 MPa/s for Vitadur Alpha and 1000 MPa/s for In-Ceram® Zirconia. The effects of stressing rate and environment on flexural strength, critical flaw size, and fracture toughness were analyzed statistically by Kruskal-Wallis one-way ANOVA on ranks followed by post-hoc comparisons using Dunn’s test (α=0.05). In addition, 20 Vitadur Alpha specimens were fabricated with controlled flaws to simplify fractography. Half of these specimens were fracture tested in water and half in oil at a target stressing rate of 100 MPa/s, and the results were compared using Mann-Whitney rank sum tests (α=0.05). A logarithmic regression model was used to determine the fatigue parameters for each material. Results For each ceramic composition, specimens tested in oil had significantly higher strength (P≤0.05) and smaller critical flaw size (significant for Vitadur Alpha, P≤0.05) than those tested in water but did not have significantly different fracture toughness (P>0.05). Specimens tested at faster stressing rates had significantly higher strength (P≤0

  16. Diabetes reduces mesenchymal stem cells in fracture healing through a TNFα-mediated mechanism

    PubMed Central

    Tian, Chen; Alblowi, Jazia; Kayal, Rayyan A.; Einhorn, Thomas A.; Gerstenfeld, Louis C.; Pignolo, Robert J.; Graves, Dana T.

    2015-01-01

    Aims/hypothesis Diabetes interferes with bone formation and impairs fracture healing, an important complication in humans and animal models. The aim of this study was to examine the impact of diabetes on mesenchymal stem cells (MSCs) during fracture repair. Methods Fracture of the long bones was induced in a streptozotocin-induced type 1 diabetic mouse model with or without insulin or a specific TNFα inhibitor, pegsunercept. MSCs were detected with cluster designation-271 (also known as p75 neurotrophin receptor) or stem cell antigen-1 (Sca-1) antibodies in areas of new endochondral bone formation in the calluses. MSC apoptosis was measured by TUNEL assay and proliferation was measured by Ki67 antibody. In vitro apoptosis and proliferation were examined in C3H10T1/2 and human-bone-marrow-derived MSCs following transfection with FOXO1 small interfering (si)RNA. Results Diabetes significantly increased TNFα levels and reduced MSC numbers in new bone area. MSC numbers were restored to normal levels with insulin or pegsunercept treatment. Inhibition of TNFα significantly reduced MSC loss by increasing MSC proliferation and decreasing MSC apoptosis in diabetic animals, but had no effect on MSCs in normoglycaemic animals. In vitro experiments established that TNFα alone was sufficient to induce apoptosis and inhibit proliferation of MSCs. Furthermore, silencing forkhead box protein O1 (FOXO1) prevented TNFα-induced MSC apoptosis and reduced proliferation by regulating apoptotic and cell cycle genes. Conclusions/interpretation Diabetes-enhanced TNFα significantly reduced MSC numbers in new bone areas during fracture healing. Mechanistically, diabetes-enhanced TNFα reduced MSC proliferation and increased MSC apoptosis. Reducing the activity of TNFα in vivo may help to preserve endogenous MSCs and maximise regenerative potential in diabetic patients. PMID:25563724

  17. Proppant backproduction during hydraulic fracturing -- A new failure mechanism for resin-coated proppants

    SciTech Connect

    Vreeburg, R.J.; Roodhart, L.P.; Davies, D.R.; Penny, G.S. )

    1994-10-01

    Backproduction of proppant from hydraulically fractured wells, particularly those completed in the northern European Rotliegend formation, is a major operational problem, necessitating costly and manpower-intensive surface-handling procedures. Further, the development of unmanned platform operations offshore, required in today's economic climate, is impossible as long as this problem remains unsolved. The most cost-effective potential solution to this problem is provided by curable resin-coated proppant (RCP), which consolidates in the fracture. Early field trials with RCP's, however, were not completely effective in stopping the backproduction of proppant. Typically, some 10% of the total volume of RCP placed in the fracture was backproduced. The authors performed a laboratory study to help clarify the effect of curing temperature, water production rate, proppant size, and stress cycling on the integrity of RCP packs. The experiments confirmed the field experience that stress cycling has a dramatic effect on proppant backproduction of commercial RCP packs. The number of applied stress cycles (i.e., the number of times the well is shut in) and the initial RCP pack strength appear to be the dominant factors that govern proppant backproduction. Dedicated experiments are therefore required to evaluate the use of RCP's to eliminate proppant backproduction for a particular field application.

  18. Analogous cellular contribution and healing mechanisms following digit amputation and phalangeal fracture in mice

    PubMed Central

    Dawson, Lindsay A.; Simkin, Jennifer; Sauque, Michelle; Pela, Maegan; Palkowski, Teresa

    2016-01-01

    Abstract Regeneration of amputated structures is severely limited in humans and mice, with complete regeneration restricted to the distal portion of the terminal phalanx (P3). Here, we investigate the dynamic tissue repair response of the second phalangeal element (P2) post amputation in the adult mouse, and show that the repair response of the amputated bone is similar to the proximal P2 bone fragment in fracture healing. The regeneration‐incompetent P2 amputation response is characterized by periosteal endochondral ossification resulting in the deposition of new trabecular bone, corresponding to a significant increase in bone volume; however, this response is not associated with bone lengthening. We show that cells of the periosteum respond to amputation and fracture by contributing both chondrocytes and osteoblasts to the endochondral ossification response. Based on our studies, we suggest that the amputation response represents an attempt at regeneration that ultimately fails due to the lack of a distal organizing influence that is present in fracture healing. PMID:27499878

  19. Connecting biology and mechanics in fracture healing: an integrated mathematical modeling framework for the study of nonunions.

    PubMed

    Geris, L; Sloten, J Vander; Van Oosterwyck, H

    2010-12-01

    Both mechanical and biological factors play an important role in normal as well as impaired fracture healing. This study aims to provide a mathematical framework in which both regulatory mechanisms are included. Mechanics and biology are coupled by making certain parameters of a previously established bioregulatory model dependent on local mechanical stimuli. To illustrate the potential added value of such a framework, this coupled model was applied to investigate whether local mechanical stimuli influencing only the angiogenic process can explain normal healing as well as overload-induced nonunion development. Simulation results showed that mechanics acting directly on angiogenesis alone was not able to predict the formation of overload-induced nonunions. However, the direct action of mechanics on both angiogenesis and osteogenesis was able to predict overload-induced nonunion formation, confirming the hypotheses of several experimental studies investigating the interconnection between angiogenesis and osteogenesis. This study shows that mathematical models can assist in testing hypothesis on the nature of the interaction between biology and mechanics.

  20. Corrosion fatigue of iron-chromium-nickel alloys: Fracture mechanics, microstructure and chemistry

    SciTech Connect

    Wei, R.P.

    1992-01-29

    This progress report briefly summarizes the research performed under the referenced grant for the period from 1 December 1990 to 31 December 1991, and contains a cumulative listing of technical presentations and publications dating back to 1 June 1988. Under this grant, a multi-disciplinary research program is undertaken to address certain fundamental issues relating to corrosion fatigue crack growth in structurally important alloys in aqueous environments. The principal goal of the research is to develop and expand the scientific understanding of the processes that control corrosion fatigue crack growth, particularly for ferrous alloys in terms of the controlling mechanical and chemical/electrochemical processes and their interactions with the microstructure. Focus is placed upon the austenitic iron-chromium-nickel (FeCrNi) alloys because of the need to resolve certain mechanistic issues and because of extensive utilization of these alloys in the power generation and chemical industries. Emphasis is given to the growth of short (small) cracks at low growth rates because crack growth in this regime is expected to be more sensitive to changes in external chemical/electrochemical variables.

  1. [The central mechanisms underlying the phenomenon of acupoint sensitization evoked by visceral nociceptive afferent].

    PubMed

    Li, Liang; Rong, Peijing; Luo, Man; Zhao, Jingjun; Ben, Hui; Zhu, Bing

    2015-11-01

    The physiological mechanism underlying the acupoint sensitization was evaluated systemically by using the method of electric physiology at spinal cord, medulla, and thalamus levels; the dynamic change of acupoint from the relative "silence" to the relative "activation" function was explained through the study on the dynamic process of acupoint sensitization; the biological process of the therapeutic effect of acupoint stimulation was illuminated through the research of the central mechanism underlining the dose effect relationship between the sensitive acupoint and the related brain area, thus scientific evidence for the functional link between the acupoint and internal organs as well as the nature of the acupoint were provided. PMID:26939345

  2. Cleavage fracture and irradiation embrittlement of fusion reactor alloys: mechanisms, multiscale models, toughness measurements and implications to structural integrity assessment

    NASA Astrophysics Data System (ADS)

    Odette, G. R.; Yamamoto, T.; Rathbun, H. J.; He, M. Y.; Hribernik, M. L.; Rensman, J. W.

    2003-12-01

    We describe the highly efficient master curves-shifts (MC-Δ T) method to measure and apply cleavage fracture toughness, KJc ( T), data and show that it is applicable to 9Cr martensitic steels. A reference temperature, T0, indexes the invariant MC shape on an absolute temperature scale. Then, T0 shifts (Δ T) are used to account for various effects of size and geometry, loading rate and irradiation embrittlement (Δ Ti). The paper outlines a multiscale model, relating atomic to structural scale fracture processes, that underpins the MC-Δ T method. At the atomic scale, we propose that the intrinsic microarrest toughness, Kμ( T), of the body-centered cubic ferrite lattice dictates an invariant shape of the macroscopic KJc ( T) curve. KJc ( T) can be modeled in terms of the true stress-strain ( σ- ɛ) constitutive law, σ ( T, ɛ), combined with a temperature-dependent critical local stress, σ*( T) and stressed volume, V*. The local fracture properties, σ*( T)- V*, are governed by coarse-scale brittle trigger particles and Kμ( T). Irradiation (and high strain rate) induced increases in the yield stress, Δ σy, lead to Δ Ti, with typical Δ Ti/Δ σy≈0.6±0.15 °C/MPa. However, Δ Ti associated with decreases in σ* and V* can result from a number of potential non-hardening embrittlement (NHE) mechanisms, including a large amount of He on grain boundaries. Estimates based on available data suggest that this occurs at >500-700 appm bulk He. Hardening and NHE are synergistic, and can lead to very large Δ Ti. NHE is signaled by large (>1 °C/MPa), or even negative, values of Δ Ti/Δ σy (for Δ σy<0), and is often coupled with increasing amounts of intergranular fracture. The measured and effective fracture toughness pertinent to structures almost always depends on the size and geometry of the cracked body, and is typically significantly greater than KJc . Size and geometry effects arise from both weakest link statistics, related to the volume under high

  3. Viscoelastic Fracturing As a Migration and Expulsion Mechanism for Hydrocarbons in Shales: Analog Experiments

    NASA Astrophysics Data System (ADS)

    Van Damme, H.

    2014-12-01

    We report the results of simple laboratory experiments aimed at mimicking the generation, migration, and expulsion process of oil or gas from soft clayey sediments, triggered by thermal decomposition of organic matter. In previously published work, we showed that the injection of fluids into a soft sediment layer confined within a quasi-2D Hele-Shaw cell led to the transition from a viscous fingering invasion regime to a viscoelastic fracturing regime. The transition is controlled by the ratio of the characteristic times for the invasion process and for the structural relaxation in the sediment, respectively (Deborah number). Here we show that expulsion is a discontinuous quasi-periodic process, driven by the elastic energy stored in the embedding layers. We report also about two sets of experiments aimed at understanding the conditions in which fluid generation from multiple sources can generate a highly connected network of fractures for expulsion. In a first set of experiments, a Hele-Shaw cell with multiple injection points and multiple outlets was used. It is shown that, due to attractive elastic interactions between cracks, a network spontaneously forms as soon as invasion proceeds in the viscoelastic regime. On the contrary, no network of migration paths is forming in the viscous fingering regime, due to the effective repulsion of the fluid channels. In the second set of analog experiments, we used a thermostated mini-Hele-Shaw cell, the gap of which was filled with a strong clay mud in which microcrystals of reactive organic matter (azoisobutyronitrile, AIBN) are dispersed, or with a mud prepared with clay particles on which the organic matter was pre-impregnated. AIBN decomposes around 70°C, releasing nitrogen gas. It was again observed that, depending on the viscoelastic properties of the clay matrix, gas evolution occurs either by formation and coalescence of bubbles, or by formation of a percolating network of fractures. The length of the fracture

  4. Assessment of strength-limiting flaws in ceramic heat exchanger components INEL support: Fracture mechanics and nondestructive evaluation technology. Final report, June 1, 1986--May 31, 1993

    SciTech Connect

    Lloyd, W.R.; Reuter, W.G.

    1993-06-01

    An examination of a siliconized SiC material, CS101K, has been performed to determine if linear fracture mechanics concepts can be used to characterize and predict the behavior of this material. Phase II of this project showed that a value that appeared to represent the true fracture toughness could be measured using small specimens with a machined notch, if the notch root radius was less than 75 {mu}m. Methods to produce sharply cracked specimens were then investigated to verify this hypothesis. A new technique, called the {open_quotes}beam support{close_quotes} precracking method, was subsequently developed and used to make sharply cracked SE(B) specimens. Tests of these specimens showed a slightly rising R-curve-type of behavior, with elevated values of plane strain fracture toughness. Interference of the crack surfaces in the precrack wake was hypothesized as the most likely cause of these phenomena. Subsequent testing with various precrack lengths provided preliminary verification of the hypothesis. Test results show that, for fracture mechanics-based design and assessment, adequate values of fracture toughness can be obtained from EDM-notched specimens, instead of the more costly precracked specimens. These results imply that, for the Si-SiC material tested, caution is warranted when using any of the methods of assessing fracture toughness that use a sharp precrack. It is also reasoned that these results may generally be more applicable to the coarser-grained structural ceramics that exhibit a rougher fracture surface. Based on results of testing EDM-notched bend specimens in 1250{degrees}C air, no degradation of material properties were observed for exposures, under applied stress, up to 900 h. Instead, some increase in fracture toughness was measured for these conditions. These same tests indicated that the threshold stress intensity factor for stress corrosion cracking (static fatigue) in the hot air environment was the same as the fracture toughness.

  5. Intrinsic mechanical behavior of femoral cortical bone in young, osteoporotic and bisphosphonate-treated individuals in low- and high energy fracture conditions

    DOE PAGES

    Zimmermann, Elizabeth A.; Schaible, Eric; Gludovatz, Bernd; Schmidt, Felix N.; Riedel, Christoph; Krause, Matthias; Vettorazzi, Eik; Acevedo, Claire; Hahn, Michael; Püschel, Klaus; et al

    2016-02-16

    Bisphosphonates are a common treatment to reduce osteoporotic fractures. This treatment induces osseous structural and compositional changes accompanied by positive effects on osteoblasts and osteocytes. Here, we test the hypothesis that restored osseous cell behavior, which resembles characteristics of younger, healthy cortical bone, leads to improved bone quality. Microarchitecture and mechanical properties of young, treatment-naïve osteoporosis, and bisphosphonate-treated cases were investigated in femoral cortices. Tissue strength was measured using three-point bending. Collagen fibril-level deformation was assessed in non-traumatic and traumatic fracture states using synchrotron small-angle x-ray scattering (SAXS) at low and high strain rates. The lower modulus, strength and fibrilmore » deformation measured at low strain rates reflects susceptibility for osteoporotic low-energy fragility fractures. Independent of age, disease and treatment status, SAXS revealed reduced fibril plasticity at high strain rates, characteristic of traumatic fracture. We find the significantly reduced mechanical integrity in osteoporosis may originate from porosity and alterations to the intra/extrafibrillar structure, while the fibril deformation under treatment indicates improved nano-scale characteristics. In conclusion, losses in strength and fibril deformation at low strain rates correlate with the occurrence of fragility fractures in osteoporosis, while improvements in structural and mechanical properties following bisphosphonate treatment may foster resistance to fracture during physiological strain rates.« less

  6. Intrinsic mechanical behavior of femoral cortical bone in young, osteoporotic and bisphosphonate-treated individuals in low- and high energy fracture conditions.

    PubMed

    Zimmermann, Elizabeth A; Schaible, Eric; Gludovatz, Bernd; Schmidt, Felix N; Riedel, Christoph; Krause, Matthias; Vettorazzi, Eik; Acevedo, Claire; Hahn, Michael; Püschel, Klaus; Tang, Simon; Amling, Michael; Ritchie, Robert O; Busse, Björn

    2016-02-16

    Bisphosphonates are a common treatment to reduce osteoporotic fractures. This treatment induces osseous structural and compositional changes accompanied by positive effects on osteoblasts and osteocytes. Here, we test the hypothesis that restored osseous cell behavior, which resembles characteristics of younger, healthy cortical bone, leads to improved bone quality. Microarchitecture and mechanical properties of young, treatment-naïve osteoporosis, and bisphosphonate-treated cases were investigated in femoral cortices. Tissue strength was measured using three-point bending. Collagen fibril-level deformation was assessed in non-traumatic and traumatic fracture states using synchrotron small-angle x-ray scattering (SAXS) at low and high strain rates. The lower modulus, strength and fibril deformation measured at low strain rates reflects susceptibility for osteoporotic low-energy fragility fractures. Independent of age, disease and treatment status, SAXS revealed reduced fibril plasticity at high strain rates, characteristic of traumatic fracture. The significantly reduced mechanical integrity in osteoporosis may originate from porosity and alterations to the intra/extrafibrillar structure, while the fibril deformation under treatment indicates improved nano-scale characteristics. In conclusion, losses in strength and fibril deformation at low strain rates correlate with the occurrence of fragility fractures in osteoporosis, while improvements in structural and mechanical properties following bisphosphonate treatment may foster resistance to fracture during physiological strain rates.

  7. Intrinsic mechanical behavior of femoral cortical bone in young, osteoporotic and bisphosphonate-treated individuals in low- and high energy fracture conditions

    PubMed Central

    Zimmermann, Elizabeth A.; Schaible, Eric; Gludovatz, Bernd; Schmidt, Felix N.; Riedel, Christoph; Krause, Matthias; Vettorazzi, Eik; Acevedo, Claire; Hahn, Michael; Püschel, Klaus; Tang, Simon; Amling, Michael; Ritchie, Robert O.; Busse, Björn

    2016-01-01

    Bisphosphonates are a common treatment to reduce osteoporotic fractures. This treatment induces osseous structural and compositional changes accompanied by positive effects on osteoblasts and osteocytes. Here, we test the hypothesis that restored osseous cell behavior, which resembles characteristics of younger, healthy cortical bone, leads to improved bone quality. Microarchitecture and mechanical properties of young, treatment-naïve osteoporosis, and bisphosphonate-treated cases were investigated in femoral cortices. Tissue strength was measured using three-point bending. Collagen fibril-level deformation was assessed in non-traumatic and traumatic fracture states using synchrotron small-angle x-ray scattering (SAXS) at low and high strain rates. The lower modulus, strength and fibril deformation measured at low strain rates reflects susceptibility for osteoporotic low-energy fragility fractures. Independent of age, disease and treatment status, SAXS revealed reduced fibril plasticity at high strain rates, characteristic of traumatic fracture. The significantly reduced mechanical integrity in osteoporosis may originate from porosity and alterations to the intra/extrafibrillar structure, while the fibril deformation under treatment indicates improved nano-scale characteristics. In conclusion, losses in strength and fibril deformation at low strain rates correlate with the occurrence of fragility fractures in osteoporosis, while improvements in structural and mechanical properties following bisphosphonate treatment may foster resistance to fracture during physiological strain rates. PMID:26879146

  8. Intrinsic mechanical behavior of femoral cortical bone in young, osteoporotic and bisphosphonate-treated individuals in low- and high energy fracture conditions

    NASA Astrophysics Data System (ADS)

    Zimmermann, Elizabeth A.; Schaible, Eric; Gludovatz, Bernd; Schmidt, Felix N.; Riedel, Christoph; Krause, Matthias; Vettorazzi, Eik; Acevedo, Claire; Hahn, Michael; Püschel, Klaus; Tang, Simon; Amling, Michael; Ritchie, Robert O.; Busse, Björn

    2016-02-01

    Bisphosphonates are a common treatment to reduce osteoporotic fractures. This treatment induces osseous structural and compositional changes accompanied by positive effects on osteoblasts and osteocytes. Here, we test the hypothesis that restored osseous cell behavior, which resembles characteristics of younger, healthy cortical bone, leads to improved bone quality. Microarchitecture and mechanical properties of young, treatment-naïve osteoporosis, and bisphosphonate-treated cases were investigated in femoral cortices. Tissue strength was measured using three-point bending. Collagen fibril-level deformation was assessed in non-traumatic and traumatic fracture states using synchrotron small-angle x-ray scattering (SAXS) at low and high strain rates. The lower modulus, strength and fibril deformation measured at low strain rates reflects susceptibility for osteoporotic low-energy fragility fractures. Independent of age, disease and treatment status, SAXS revealed reduced fibril plasticity at high strain rates, characteristic of traumatic fracture. The significantly reduced mechanical integrity in osteoporosis may originate from porosity and alterations to the intra/extrafibrillar structure, while the fibril deformation under treatment indicates improved nano-scale characteristics. In conclusion, losses in strength and fibril deformation at low strain rates correlate with the occurrence of fragility fractures in osteoporosis, while improvements in structural and mechanical properties following bisphosphonate treatment may foster resistance to fracture during physiological strain rates.

  9. From rock fracture to plate tectonics. Evidence of non extensive statistical mechanics in Earth physics, A review

    NASA Astrophysics Data System (ADS)

    Vallianatos, F.

    2012-04-01

    The non-extensive statistical mechanics pioneered by the Tsallis group offers a consistent theoretical framework, based on a generalization of entropy, to analyze the behavior of systems with fractal or multi-fractal distribution of their elements. Such systems where long-range interactions or intermittency are important, lead to power law behavior. The question of whether earth systems are described by non-extensive statistical physics, even at the phenomenological level (i.e., without specifying any underlying model), represents a challenge. This is the problem we review here. Our aim is not to present a precise model, but rather to emphasize in simple arguments of physical plausibility. Examples supporting the non-additive behavior of earth system, from rocks fracture (e.g., acoustic emissions) to geodynamic (e.g., plate tectonics, global seismicity) scale are presented. Acknowledgments. This work was partly supported by the THALES Program of the Ministry of Education of Greece and the European Union in the framework of the project entitled "Integrated understanding of Seismicity, using innovative Methodologies of Fracture mechanics along with Earthquake and non extensive statistical physics - Application to the geodynamic system of the Hellenic Arc. SEISMO FEAR HELLARC".

  10. Atomistic study on mixed-mode fracture mechanisms of ferrite iron interacting with coherent copper and nickel nanoclusters

    NASA Astrophysics Data System (ADS)

    Al-Motasem, Ahmed Tamer; Mai, Nghia Trong; Choi, Seung Tae; Posselt, Matthias

    2016-04-01

    The effect of copper and/or nickel nanoclusters, generally formed by neutron irradiation, on fracture mechanisms of ferrite iron was investigated by using molecular statics simulation. The equilibrium configuration of nanoclusters was obtained by using a combination of an on-lattice annealing based on Metropolis Monte Carlo method and an off-lattice relaxation by molecular dynamics simulation. Residual stress distributions near the nanoclusters were also calculated, since compressive or tensile residual stresses may retard or accelerate, respectively, the propagation of a crack running into a nanocluster. One of the nanoclusters was located in front of a straight crack in ferrite iron with a body-centered cubic crystal structure. Two crystallographic directions, of which the crack plane and crack front direction are (010)[001] and (111) [ 1 bar 10 ] , were considered, representing cleavage and non-cleavage orientations in ferrite iron, respectively. Displacements corresponding to pure opening-mode and mixed-mode loadings were imposed on the boundary region and the energy minimization was performed. It was observed that the fracture mechanisms of ferrite iron under the pure opening-mode loading are strongly influenced by the presence of nanoclusters, while under the mixed-mode loading the nanoclusters have no significant effect on the crack propagation behavior of ferrite iron.

  11. A micro resonant charge sensor with enhanced sensitivity based on differential sensing scheme and leverage mechanisms

    NASA Astrophysics Data System (ADS)

    Chen, Dongyang; Zhao, Jiuxuan; Xu, Zhonggui; Xie, Jin

    2016-10-01

    This letter reports a micro-electro-mechanical systems (MEMS) resonant charge sensor with enhanced sensitivity based on differential sensing scheme and leverage mechanisms. The sensor comprises two symmetrically-distributed double-ended tuning fork (DETF) resonators, each of which connects with dual micro-leverage mechanisms. The micro-leverages amplify electrostatic force in opposite directions and cause differential frequency shift of the two resonators. Both the resonators show a similar trend in behaviors of electrical and mechanical nonlinearity. Effect of environment disturbance is suppressed by the differential sensing scheme. The measured sensitivity of the two resonators are 3.31×10-4 Hz/fC2 and 1.85×10-4 Hz/fC2 respectively, and an overall sensitivity for the resonant charge sensor is 5.16×10-4 Hz/fC2.

  12. Hydromechanical coupling in fractured rock masses: mechanisms and processes of selected case studies

    NASA Astrophysics Data System (ADS)

    Zangerl, Christian

    2015-04-01

    Hydromechanical (HM) coupling in fractured rock play an important role when events including dam failures, landslides, surface subsidences due to water withdrawal or drainage, injection-induced earthquakes and others are analysed. Generally, hydromechanical coupling occurs when a rock mass contain interconnected pores and fractures which are filled with water and pore/fracture pressures evolves. In the on hand changes in the fluid pressure can lead to stress changes, deformations and failures of the rock mass. In the other hand rock mass stress changes and deformations can alter the hydraulic properties and fluid pressures of the rock mass. Herein well documented case studies focussing on surface subsidence due to water withdrawal, reversible deformations of large-scale valley flanks and failure as well as deformation processes of deep-seated rock slides in fractured rock masses are presented. Due to pore pressure variations HM coupling can lead to predominantly reversible rock mass deformations. Such processes can be considered by the theory of poroelasticity. Surface subsidence reaching magnitudes of few centimetres and are caused by water drainage into deep tunnels are phenomenas which can be assigned to processes of poroelasticity. Recently, particular focus was given on large tunnelling projects to monitor and predict surface subsidence in fractured rock mass in oder to avoid damage of surface structures such as dams of large reservoirs. It was found that surface subsidence due to tunnel drainage can adversely effect infrastructure when pore pressure drawdown is sufficiently large and spatially extended and differential displacements which can be amplified due to topographical effects e.g. valley closure are occurring. Reversible surface deformations were also ascertained on large mountain slopes and summits with the help of precise deformation measurements i.e. permanent GPS or episodic levelling/tacheometric methods. These reversible deformations are often

  13. Development of spiral notch torsion test: A new Fracture mechanics approach to determination of KISCC

    SciTech Connect

    Wang, Jy-An John; Singh, R. K.; Bayles, Robert; Knight, S. P.; Hinton, B. R.W.; Muddle, B. C.

    2007-11-01

    SNTT utilizes an extremely innovative concept of testing round-rod specimens having a V-grooved spiral notch line with a 45 a-pitch angle. The paper discusses the validity of SNTT in determining the fracture toughness, KIC, as established at ORNL. The paper also presents preliminary results of a collaborative research program of Monash University, NRL, ORNL and DSTO, for development and use of the novel technique of Spiral Notch Torsion Test (SNTT) for determination of threshold stress intensity for stress corrosion cracking, i.e., KISCC. SNTT experiments have been carried out in chloride and air environments, using fatigue pre-cracked SNTT specimens of Al-alloy, 7075.

  14. Corrosion fatigue of iron-chromium-nickel alloys: Fracture mechanics, microstructure and chemistry

    SciTech Connect

    Wei, R.P.

    1993-01-25

    Phase transformation and cracking during RT aging of charged, high-purity Fe18Cr12Ni alloy and commerical 304 ss were examined; results show that [epsilon]* (hcp) hydride formed on Fe18Cr12Ni upon charging, and it decomposed rapidly to form first [epsilon] and then [alpha]' martensite. Morphology of fracture surfaces of Fe18Cr12Ni produced by corrosion fatigue in NaCl solutions and in hydrogen was found to be identical. Effort was made to examine the approaches and methodologies used in service life predictions and reliability analyses.

  15. Corrosion fatigue of iron-chromium-nickel alloys: Fracture mechanics and chemistry

    SciTech Connect

    Wei, R.P.

    1990-11-29

    Peak bare-surface current densities based on the scratched electrode test are seriously in error and repasivation rates grossly overestimated. Influences of potential and pH on reactions of bare surfaces are better understood. Correlation between charge transfer and corrosion fatigue crack growth response was established for Fe18Cr12Ni alloy in deaerated 0.6N NaCl at RT. Strong correlation was established between morphology of corrosion fatigue fracture surfaces and cracking in hydrogen charged samples. Attempts at growing bicrystals by strain annealing were not successful.

  16. Melt fracturing and healing: A mechanism for degassing and origin of silicic obsidian

    USGS Publications Warehouse

    Cabrera, A.; Weinberg, R.F.; Wright, H.M.N.; Zlotnik, S.; Cas, Ray A.F.

    2011-01-01

    We present water content transects across a healed fault in pyroclastic obsidian from Lami pumice cone, Lipari, Italy, using synchrotron Fourier transform infrared spectroscopy. Results indicate that rhyolite melt degassed through the fault surface. Transects define a trough of low water content coincident with the fault trace, surrounded on either side by high-water-content plateaus. Plateaus indicate that obsidian on either side of the fault equilibrated at different pressure-temperature (P-T) conditions before being juxtaposed. The curves into the troughs indicate disequilibrium and water loss through diffusion. If we assume constant T, melt equilibrated at pressures differing by 0.74 MPa before juxtaposition, and the fault acted as a low-P permeable path for H2O that diffused from the glass within time scales of 10 and 30 min. Assuming constant P instead, melt on either side could have equilibrated at temperatures differing by as much as 100 ??C, before being brought together. Water content on the fault trace is particularly sensitive to post-healing diffusion. Its preserved value indicates either higher temperature or lower pressure than the surroundings, indicative of shear heating and dynamic decompression. Our results reveal that water contents of obsidian on either side of the faults equilibrated under different P-T conditions and were out of equilibrium with each other when they were juxtaposed due to faulting immediately before the system was quenched. Degassing due to faulting could be linked to cyclical seismic activity and general degassing during silicic volcanic activity, and could be an efficient mechanism of producing low-water-content obsidian. ?? 2011 Geological Society of America.

  17. Enhanced fatigue endurance of metallic glasses through a staircase-like fracture mechanism.

    PubMed

    Gludovatz, Bernd; Demetriou, Marios D; Floyd, Michael; Hohenwarter, Anton; Johnson, William L; Ritchie, Robert O

    2013-11-12

    Bulk-metallic glasses (BMGs) are now candidate materials for structural applications due to their exceptional strength and toughness. However, their fatigue resistance can be poor and inconsistent, severely limiting their potential as reliable structural materials. As fatigue limits are invariably governed by the local arrest of microscopically small cracks at microstructural features, the lack of microstructure in monolithic glasses, often coupled with other factors, such as the ease of crack formation in shear bands or a high susceptibility to corrosion, can lead to low fatigue limits (some ~1/20 of their tensile strengths) and highly variable fatigue lives. BMG-matrix composites can provide a solution here as their duplex microstructures can arrest shear bands at a second phase to prevent cracks from exceeding critical size; under these conditions, fatigue limits become comparable with those of crystalline alloys. Here, we report on a Pd-based glass that similarly has high fatigue resistance but without a second phase. This monolithic glass displays high intrinsic toughness from extensive shear-band proliferation with cavitation and cracking effectively obstructed. We find that this property can further promote fatigue resistance through extrinsic crack-tip shielding, a mechanism well known in crystalline metals but not previously reported in BMGs, whereby cyclically loaded cracks propagate in a highly "zig-zag" manner, creating a rough "staircase-like" profile. The resulting crack-surface contact (roughness-induced crack closure) elevates fatigue properties to those comparable to crystalline alloys, and the accompanying plasticity helps to reduce flaw sensitivity in the glass, thereby promoting structural reliability. PMID:24167284

  18. Salt-sensitive hypertension: mechanisms and effects of dietary and other lifestyle factors.

    PubMed

    Pilic, Leta; Pedlar, Charles R; Mavrommatis, Yiannis

    2016-10-01

    Salt sensitivity, which is an increase in blood pressure in response to high dietary salt intake, is an independent risk factor for cardiovascular disease and mortality. It is associated with physiological, environmental, demographic, and genetic factors. This review focuses on the physiological mechanisms of salt sensitivity in populations at particular risk, along with the associated dietary factors. The interplay of mechanisms such as the renin-angiotensin aldosterone system, endothelial dysfunction, ion transport, and estrogen decrease in women contributes to development of salt sensitivity. Because of their effects on these mechanisms, higher dietary intakes of potassium, calcium, vitamin D, antioxidant vitamins, and proteins rich in L-arginine, as well as adherence to dietary patterns similar to the DASH (Dietary Approaches to Stop Hypertension) diet, can be beneficial to salt-sensitive populations. In contrast, diets similar to the typical Western diet, which is rich in saturated fats, sucrose, and fructose, together with excessive alcohol consumption, may exacerbate salt-sensitive changes in blood pressure. Identifying potential mechanisms of salt sensitivity in susceptible populations and linking them to protective or harmful dietary and lifestyle factors can lead to more specific guidelines for the prevention of hypertension and cardiovascular disease. PMID:27566757

  19. Fracture Toughness, Mechanical Property, And Chemical Characterization Of A Critical Modification To The NASA SLS Solid Booster Internal Material System

    NASA Technical Reports Server (NTRS)

    Pancoast, Justin; Garrett, William; Moe, Gulia

    2015-01-01

    A modified propellant-liner-insulation (PLI) bondline in the Space Launch System (SLS) solid rocket booster required characterization for flight certification. The chemical changes to the PLI bondline and the required additional processing have been correlated to mechanical responses of the materials across the bondline. Mechanical properties testing and analyses included fracture toughness, tensile, and shear tests. Chemical properties testing and analyses included Fourier transform infrared (FTIR) spectroscopy, cross-link density, high-performance liquid chromatography (HPLC), gas chromatography (GC), gel permeation chromatography (GPC), and wave dispersion X-ray fluorescence (WDXRF). The testing identified the presence of the expected new materials and found the functional bondline performance of the new PLI system was not significantly changed from the old system.

  20. [Isolated fractures of the scaphoid: classification, treatment and outcome].

    PubMed

    Drexler, Michael; Haim, Amir; Pritsch, Tamir; Rosenblatt, Yishai

    2011-01-01

    Scaphoid fracture is the most common fracture in carpal bone of the wrist and represents 11% of all upper extremity fractures. In most cases, the mechanism of injury is a fall with an outstretched hand. Scaphoid fracture detection can be made by clinical examination and standard radiography. Computed tomography (CT), bone scan and MRI improve the sensitivity of the diagnosis. Non-displaced fractures of the scaphoid are treated with cast immobilization in most cases. Operative treatment should be considered in displaced fractures or non-displaced fractures in young active patients by using internal fixation with cannulated screw for definitive anatomic and stable fixation. The main goals of operative treatment are attempts to reduce immobilization time and enable earlier return to work and activity. Displaced fractures of scaphoid, should be treated operatively, as they carry a greater risk for nonunion and malunion, which are associated with the development of radiocarpal arthritis, stiffness and wrist instability. Computed tomography is more useful as an assessment tool in pre-operative planning to determine the fracture location and fragment displacement. Early detection and appropriate treatment of scaphoid fractures is the key to favorable outcome in the treatment of scaphoid fractures.

  1. Mechanical sensitivity of Piezo1 ion channels can be tuned by cellular membrane tension

    PubMed Central

    Lewis, Amanda H; Grandl, Jörg

    2015-01-01

    Piezo1 ion channels mediate the conversion of mechanical forces into electrical signals and are critical for responsiveness to touch in metazoans. The apparent mechanical sensitivity of Piezo1 varies substantially across cellular environments, stimulating methods and protocols, raising the fundamental questions of what precise physical stimulus activates the channel and how its stimulus sensitivity is regulated. Here, we measured Piezo1 currents evoked by membrane stretch in three patch configurations, while simultaneously visualizing and measuring membrane geometry. Building on this approach, we developed protocols to minimize resting membrane curvature and tension prior to probing Piezo1 activity. We find that Piezo1 responds to lateral membrane tension with exquisite sensitivity as compared to other mechanically activated channels and that resting tension can drive channel inactivation, thereby tuning overall mechanical sensitivity of Piezo1. Our results explain how Piezo1 can function efficiently and with adaptable sensitivity as a sensor of mechanical stimulation in diverse cellular contexts. DOI: http://dx.doi.org/10.7554/eLife.12088.001 PMID:26646186

  2. A fracture mechanics analysis of adhesive failure in a single lap shear joint.

    NASA Technical Reports Server (NTRS)

    Devries, K. L.; Williams, M. L.; Chang, M. D.

    1972-01-01

    Discussion of adhesive fracture of single lap shear joints in terms of a maximum stress criterion and an energy balance. The Goland and Reissner (1944) analysis is used to determine the stress distribution in the adhesive assembly, and the results obtained are introduced into an energy balance to determine the initiation of adhesive fracture. In the stress analysis the loads at the edges of the joint are first determined. This is a problem in which the deformation of the joint sheets must be taken into account and is solved by using the finite-deflection theory of cylindrically bent plates. Then the stress in the joint due to applied loads is determined. This problem is formulated as one in plane strain consisting of two rectangular sheets of equal thickness and unit width. With the aid of this stress analysis and the stresses obtained from the conditions of equilibrium the contributions to the energy change with crack length are calculated. The analysis performed is then compared with a maximum stress criterion for a lap joint.

  3. Fracture mechanics life analytical methods verification testing. Final report, 1 September 1991-12 September 1994

    SciTech Connect

    Favenesi, J.A.; Clemons, T.G.; Riddell, W.T.; Ingraffea, A.R.; Wawrzynek, P.A.

    1994-09-01

    The objective was to evaluate NASCRAC (trademark) version 2.0, a second generation fracture analysis code, for verification and validity. NASCRAC was evaluated using a combination of comparisons to the literature, closed-form solutions, numerical analyses, and tests. Several limitations and minor errors were detected. Additionally, a number of major flaws were discovered. These major flaws were generally due to application of a specific method or theory, not due to programming logic. Results are presented for the following program capabilities: K versus a, J versus a, crack opening area, life calculation due to fatigue crack growth, tolerable crack size, proof test logic, tearing instability, creep crack growth, crack transitioning, crack retardation due to overloads, and elastic-plastic stress redistribution. It is concluded that the code is an acceptable fracture tool for K solutions of simplified geometries, for a limited number of J and crack opening area solutions, and for fatigue crack propagation with the Paris equation and constant amplitude loads when the Paris equation is applicable.

  4. Galeazzi fracture.

    PubMed

    Atesok, Kivanc I; Jupiter, Jesse B; Weiss, Arnold-Peter C

    2011-10-01

    Galeazzi fracture is a fracture of the radial diaphysis with disruption at the distal radioulnar joint (DRUJ). Typically, the mechanism of injury is forceful axial loading and torsion of the forearm. Diagnosis is established on radiographic evaluation. Underdiagnosis is common because disruption of the ligamentous restraints of the DRUJ may be overlooked. Nonsurgical management with anatomic reduction and immobilization in a long-arm cast has been successful in children. In adults, nonsurgical treatment typically fails because of deforming forces acting on the distal radius and DRUJ. Open reduction and internal fixation is the preferred surgical option. Anatomic reduction and rigid fixation should be followed by intraoperative assessment of the DRUJ. Further intraoperative interventions are based on the reducibility and postreduction stability of the DRUJ. Misdiagnosis or inadequate management of Galeazzi fracture may result in disabling complications, such as DRUJ instability, malunion, limited forearm range of motion, chronic wrist pain, and osteoarthritis.

  5. Proceedings of the Joint IAEA/CSNI Specialists` Meeting on Fracture Mechanics Verification by Large-Scale Testing held at Pollard Auditorium, Oak Ridge, Tennessee

    SciTech Connect

    Pugh, C.E.; Bass, B.R.; Keeney, J.A.

    1993-10-01

    This report contains 40 papers that were presented at the Joint IAEA/CSNI Specialists` Meeting Fracture Mechanics Verification by Large-Scale Testing held at the Pollard Auditorium, Oak Ridge, Tennessee, during the week of October 26--29, 1992. The papers are printed in the order of their presentation in each session and describe recent large-scale fracture (brittle and/or ductile) experiments, analyses of these experiments, and comparisons between predictions and experimental results. The goal of the meeting was to allow international experts to examine the fracture behavior of various materials and structures under conditions relevant to nuclear reactor components and operating environments. The emphasis was on the ability of various fracture models and analysis methods to predict the wide range of experimental data now available. The individual papers have been cataloged separately.

  6. Interaction of mechanical and electrical oscillations and sensitivity in a model of sensory hair cell

    NASA Astrophysics Data System (ADS)

    Amro, Rami M.; Neiman, Alexander B.

    2013-03-01

    Sensory hair cells are the first stage in conveying the mechanical stimuli into the electrical signals in auditory and vestibular organs of vertebrates. Experiments showed that hair cells rely on active processes in hair bundles to achieve high selective sensitivity, e.g. due to myosin molecular motors inside stereocilia. In lower vertebrates these active processes result in spontaneous oscillations of hair bundles which can be accompanied by oscillations of the cells' membrane potentials. We use modeling to study how the dynamics of both the membrane potential and the hair bundle interact to produce coherent self-sustained oscillations and how this interaction contributes to the cell's sensitivity to external mechanical perturbations. The model incorporates a mechanical stochastic hair bundle system coupled to a Hodgkin-Huxley type system for the membrane potential. We show that oscillatory regimes result in enhanced sensitivity and selectivity to harmonic stimuli.

  7. Mechanisms of psychological distress following war in the former Yugoslavia: the role of interpersonal sensitivity.

    PubMed

    Nickerson, Angela; Priebe, Stefan; Bryant, Richard A; Morina, Nexhmedin

    2014-01-01

    While high prevalence rates of psychological symptoms have been documented in civilian survivors of war, little is known about the mechanisms by which trauma exposure might lead to poor psychological outcomes in these populations. One potential mechanism that may underpin the association between war-related traumatic experiences and psychopathology is interpersonal sensitivity. In the current study, we applied structural equation modeling to investigate the impact of interpersonal sensitivity on posttraumatic stress disorder (PTSD) symptoms, depression symptoms, and anger responses following exposure to war trauma. 3313 survivors of the war in the former Yugoslavia were identified and selected using a multistage, probabilistic sampling frame and random walk technique. Participants were interviewed regarding trauma exposure, interpersonal sensitivity, and PTSD symptoms, depression symptoms, and anger responses. Structural equation modeling analyses revealed that the relationship between trauma and PTSD symptoms and depression symptoms was partly statistically mediated by interpersonal sensitivity. Further, findings indicated that the relationship between trauma and anger responses was fully statistically mediated by interpersonal sensitivity. These results suggest that interpersonal sensitivity may function as a key mechanism that contributes to psychopathology following trauma.

  8. Mechanisms of Psychological Distress following War in the Former Yugoslavia: The Role of Interpersonal Sensitivity

    PubMed Central

    Nickerson, Angela; Priebe, Stefan; Bryant, Richard A.; Morina, Nexhmedin

    2014-01-01

    While high prevalence rates of psychological symptoms have been documented in civilian survivors of war, little is known about the mechanisms by which trauma exposure might lead to poor psychological outcomes in these populations. One potential mechanism that may underpin the association between war-related traumatic experiences and psychopathology is interpersonal sensitivity. In the current study, we applied structural equation modeling to investigate the impact of interpersonal sensitivity on posttraumatic stress disorder (PTSD) symptoms, depression symptoms, and anger responses following exposure to war trauma. 3313 survivors of the war in the former Yugoslavia were identified and selected using a multistage, probabilistic sampling frame and random walk technique. Participants were interviewed regarding trauma exposure, interpersonal sensitivity, and PTSD symptoms, depression symptoms, and anger responses. Structural equation modeling analyses revealed that the relationship between trauma and PTSD symptoms and depression symptoms was partly statistically mediated by interpersonal sensitivity. Further, findings indicated that the relationship between trauma and anger responses was fully statistically mediated by interpersonal sensitivity. These results suggest that interpersonal sensitivity may function as a key mechanism that contributes to psychopathology following trauma. PMID:24658334

  9. Prediction of the time course of callus stiffness as a function of mechanical parameters in experimental rat fracture healing studies--a numerical study.

    PubMed

    Wehner, Tim; Steiner, Malte; Ignatius, Anita; Claes, Lutz

    2014-01-01

    Numerous experimental fracture healing studies are performed on rats, in which different experimental, mechanical parameters are applied, thereby prohibiting direct comparison between each other. Numerical fracture healing simulation models are able to predict courses of fracture healing and offer support for pre-planning animal experiments and for post-hoc comparison between outcomes of different in vivo studies. The aims of this study are to adapt a pre-existing fracture healing simulation algorithm for sheep and humans to the rat, to corroborate it using the data of numerous different rat experiments, and to provide healing predictions for future rat experiments. First, material properties of different tissue types involved were adjusted by comparing experimentally measured callus stiffness to respective simulated values obtained in three finite element (FE) models. This yielded values for Young's moduli of cortical bone, woven bone, cartilage, and connective tissue of 15,750 MPa, 1,000 MPa, 5 MPa, and 1 MPa, respectively. Next, thresholds in the underlying mechanoregulatory tissue differentiation rules were calibrated by modifying model parameters so that predicted fracture callus stiffness matched experimental data from a study that used rigid and flexible fixators. This resulted in strain thresholds at higher magnitudes than in models for sheep and humans. The resulting numerical model was then used to simulate numerous fracture healing scenarios from literature, showing a considerable mismatch in only 6 of 21 cases. Based on this corroborated model, a fit curve function was derived which predicts the increase of callus stiffness dependent on bodyweight, fixation stiffness, and fracture gap size. By mathematically predicting the time course of the healing process prior to the animal studies, the data presented in this work provides support for planning new fracture healing experiments in rats. Furthermore, it allows one to transfer and compare new in vivo

  10. Fracture mechanics and surface chemistry investigations of environment-assisted crack growth

    NASA Technical Reports Server (NTRS)

    Wei, R. P.; Klier, K.; Simmons, G. W.; Chou, Y. T.

    1984-01-01

    It is pointed out that environment-assisted subcritical crack growth in high-strength steels and other high-strength alloys (particularly in hydrogen and in hydrogenous environments) is an important technological problem of long standing. This problem is directly related to issues of structural integrity, durability, and reliability. The terms 'hydrogen embrittlement' and 'stress corrosion cracking' have been employed to describe the considered phenomenon. This paper provides a summary of contributions made during the past ten years toward the understanding of environmentally assisted crack growth. The processes involved in crack growth are examined, and details regarding crack growth and chemical reactions are discussed, taking into account crack growth in steels exposed to water/water vapor, the effect of hydrogen, reactions involving hydrogen sulfide, and aspects of fracture surface morphology and composition. Attention is also given to the modeling of crack growth response, crack growth in gas mixtures, and the interaction of solute atoms with the crack-tip stress field.

  11. Finite element method for simulating coupled thermo-hydro-mechanical processes in discretely fractured porous media and application to enhanced geothermal reservoir analysis

    NASA Astrophysics Data System (ADS)

    Watanabe, N.; Wong, L.; Bloecher, G.; Cacace, M.; Kolditz, O.

    2012-12-01

    We present our recent development of the finite element method (FEM) for simulating coupled thermo-hydro-mechanical (THM) processes in discretely fractured porous media and an application to geothermal reservoir modeling for the research test site Gross Schoenebeck in Germany operated by the GFZ German Research Centre for Geosciences. Numerical analysis of multi-physics problems in fractured rocks is important for various geotechnical applications. In particular for enhanced geothermal reservoirs where induced fractures and possibly natural fault systems dominate the system behavior, explicit modeling of those characteristic fractures (i.e. discrete fracture models) is essential to get more detailed understanding of in-situ processes and reliable estimations of heat extraction from those deep reservoirs. However, as fractures are mechanical discontinuities, it is difficult to solve the problems using continuity based numerical methods such as the FEM. Currently, equivalent porous medium or multiple continuum model approaches are often only the way to model fractured rocks with the FEM. The authors have recently developed lower-dimensional interface elements (LIEs) for modeling mechanics-involved coupled processes with pre-existing fractures (Watanabe et al. 2012 IJNME). The method does not require any double nodes unlike conventional interface elements. Moreover, for coupled problems, the approach allows for the use of a single mesh for both mechanical and other related processes such as flow and transport. All the code developments have been carried out within the scientific open source project OpenGeoSys (www.opengeosys.net) (Kolditz et al. 2012 EES). Using both traditional and new simulation techniques, a geothermal reservoir model for the research test site Gross Schoenebeck has been developed. Unstructured meshing of the complex faulted reservoir including both rock matrix and fracture elements has been conducted using recently developed automatic

  12. Trans-Endplate Pedicle Pillar System in Unstable Spinal Burst Fractures: Design, Technique, and Mechanical Evaluation

    PubMed Central

    Zhao, Chunfeng; Hongo, Michio; Ilharreborde, Brice; Zhao, Kristin D.; Currier, Bradford L.; An, Kai-Nan

    2015-01-01

    Background Short-segment pedicle screw instrumentation (SSPI) is used for unstable burst fractures to correct deformity and stabilize the spine for fusion. However, pedicle screw loosening, pullout, or breakage often occurs due to the large moment applied during spine motion, leading to poor outcomes. The purpose of this study was to test the ability of a newly designed device, the Trans-Endplate Pedicle Pillar System (TEPPS), to enhance SSPI rigidity and decrease the screw bending moment with a simple posterior approach. Methods Six human cadaveric spines (T11-L3) were harvested. A burst fracture was created at L1, and the SSPI (Moss Miami System) was used for SSPI fixation. Strain gauge sensors were mounted on upper pedicle screws to measure screw load bearing. Segmental motion (T12-L2) was measured under pure moment of 7.5 Nm. The spine was tested sequentially under 4 conditions: intact; first SSPI alone (SSPI-1); SSPI+TEPPS; and second SSPI alone (SSPI-2). Results SSPI+TEPPS increased fixation rigidity by 41% in flexion/extension, 28% in lateral bending, and 37% in axial rotation compared with SSPI-1 (P<0.001), and it performed even better compared to SSPI-2 (P<0.001 for all). Importantly, the bending moment on the pedicle screws for SSPI+TEPPS was significantly decreased 63% during spine flexion and 47% in lateral bending (p<0.001). Conclusion TEPPS provided strong anterior support, enhanced SSPI fixation rigidity, and dramatically decreased the load on the pedicle screws. Its biomechanical benefits could potentially improve fusion rates and decrease SSPI instrumentation failure. PMID:26502352

  13. Mechanism of degradation of electrolyte solutions for dye-sensitized solar cells under ultraviolet light irradiation

    NASA Astrophysics Data System (ADS)

    Nakajima, Shohei; Katoh, Ryuzi

    2015-01-01

    We studied the mechanism of the degradation of I-/I3--containing electrolyte solutions for dye-sensitized solar cells under UV light irradiation. The yellow electrolyte solutions underwent achromatization during irradiation, indicating the reduction of I3-. We propose a mechanism involving the production of holes in TiO2, reaction of the holes with solvent molecules, and subsequent reduction of I3- by electrons remaining in the TiO2. Although the quantum yield of the photodegradation reaction is estimated to be low (3 × 10-3), this reaction can nevertheless be expected to affect the long-term stability of dye-sensitized solar cell devices.

  14. Energetic composite and system with enhanced mechanical sensitivity to initiation of self-sustained reaction

    DOEpatents

    Gash, Alexander E.; Barbee, Jr., Troy W.

    2012-05-29

    An energetic composition and system using amassed energetic multilayer pieces which are formed from the division, such as for example by cutting, scoring, breaking, crushing, shearing, etc., of a mechanically activatable monolithic energetic multilayer(s) (e.g. macro-scale sheets of multilayer films), for enhancing the sensitivity of the energetic composite and system to mechanical initiation of self-sustained reaction. In particular, mechanical initiation of the energetic composition may be achieved with significantly lower mechanical energy inputs than that typically required for initiating the monolithic energetic multilayers from which it is derived.

  15. Testing a mechanical model of fracture formation by compaction-related burial in Gale crater, Mars: Implications for the origin of Aeolis Mons

    NASA Astrophysics Data System (ADS)

    Watkins, Jessica; Grotzinger, John P.

    2016-10-01

    Gale crater's 5-km-high central mound, Aeolis Mons (Mt. Sharp), has two leading hypotheses for its formation: buildup of windblown sediments, and exhumation of deeply buried strata. The deep burial hypothesis implies deformation by gravitational body forces and we evaluate that idea here. Ubiquitous fracture-related features have been regionally mapped from orbit and observed by the Curiosity rover in sedimentary strata including the Murray formation (dominantly mudstone) and the unconformably overlying Stimson formation (sandstone). Large fractures which exhibit complex banding structures with distinct chemical trends (e.g. halos) are primarily found in the Stimson fm, but do extend into the Murray fm in one location. Smaller, sulfate-filled fractures are most prevalent in the Murray but are also associated with haloed fractures in the Stimson. We test a compaction-related burial origin for these features based on a mechanical model for mode I fracture formation in order to constrain the regional stress history. According to the Mohr-Coulomb failure criterion, extension fracturing requires that the minimum principal stress (σ3) exceed the elastic tensile strength in the plane perpendicular to the opening. Given that tectonic driving processes are inoperative within Gale, non-tectonic mechanisms including overburden (maximum compressive stress; σ1 = ρgD) and pore fluid pressure (pf α D) must account for this tensile stress. Significant compaction as a result of increased depth of burial is required for pf to exceed σ3 and cause fracturing. When applied to Gale, we find that the estimated horizontal stress (σ3), as influenced by crater geometry, requires a substantial burial depth to produce sufficient pf to cause hydrofracture. Rheology contrasts likely caused fractures to develop and propagate more easily in the Stimson sandstone, which can support a smaller σ3, than in the Murray mudstone. In these permeable rocks, the sudden local decrease of pf at

  16. The effect of friction stir processing on the microstructure, mechanical properties and fracture behavior of investment cast titanium aluminum vanadium

    NASA Astrophysics Data System (ADS)

    Pilchak, Adam L.

    . Thus, the mechanical properties were investigated using micropillar compression and microtensile specimens. The effect of friction stir processing on crack initiation resistance was assessed using high cycle fatigue tests conducted in four-point bend which put only the stir zone in maximum tension. The results indicated that at constant stress amplitude, there was greater than an order of magnitude increase in fatigue life after friction stir processing. In addition, the fatigue strength of the investment cast material was improved between 20 pct. and 60 pct. by friction stir processing. These improvements have been verified with a statistically significant number of tests. Finally, the wide range of microstructures created by friction stir processing provided an opportunity to study the effect of underlying microstructure on the fracture behavior of alpha + beta titanium alloys. For this purpose, high resolution fractography coupled with quantitative tilt fractography and electron backscatter diffraction was used to provide a direct link between microstructure, crystallography and fracture topography. These techniques have been used extensively to study the early stages of post-initiation crack growth in Ti-6Al-4V, especially at low stress intensity ranges (DeltaK) in the as-cast material. A limited number of experiments were also performed on Ti-6Al-4V specimens in other microstructural conditions to assess the generality of the detailed results obtained for the fully lamellar material. The results show that fracture topography depends strongly on DeltaK and microstructural length scale. In addition, many of the features observed on the fracture surface were directly related to the underlying crystallographic orientation.

  17. Flight monitor for jet engine disk cracks and the use of critical length criterion of fracture mechanics

    NASA Technical Reports Server (NTRS)

    Barranger, J. P.

    1973-01-01

    A disk crack detector is discussed which is intended to operate under flight conditions. It monitors the disk rim for surface cracks emanating from the blade root interface. An eddy current type sensor, with a remotely located capacitance/conductance bridge and signal analyzer, can reliably detect a simulated crack 3 mm long. The sensor was tested on a spinning turbine disk at 540 C. Tests indicate that the system is useful at disk rim velocities to 460 m/sec. By using fracture mechanics, it is shown for Inconel 718 th at a crack operating under a rim stress of 34 x ten to the 7th power N/sqm has a critical length of 18 mm.

  18. Fractures in anisotropic media

    NASA Astrophysics Data System (ADS)

    Shao, Siyi

    Rocks may be composed of layers and contain fracture sets that cause the hydraulic, mechanical and seismic properties of a rock to be anisotropic. Coexisting fractures and layers in rock give rise to competing mechanisms of anisotropy. For example: (1) at low fracture stiffness, apparent shear-wave anisotropy induced by matrix layering can be masked or enhanced by the presence of a fracture, depending on the fracture orientation with respect to layering, and (2) compressional-wave guided modes generated by parallel fractures can also mask the presence of matrix layerings for particular fracture orientations and fracture specific stiffness. This report focuses on two anisotropic sources that are widely encountered in rock engineering: fractures (mechanical discontinuity) and matrix layering (impedance discontinuity), by investigating: (1) matrix property characterization, i.e., to determine elastic constants in anisotropic solids, (2) interface wave behavior in single-fractured anisotropic media, (3) compressional wave guided modes in parallel-fractured anisotropic media (single fracture orientation) and (4) the elastic response of orthogonal fracture networks. Elastic constants of a medium are required to understand and quantify wave propagation in anisotropic media but are affected by fractures and matrix properties. Experimental observations and analytical analysis demonstrate that behaviors of both fracture interface waves and compressional-wave guided modes for fractures in anisotropic media, are affected by fracture specific stiffness (controlled by external stresses), signal frequency and relative orientation between layerings in the matrix and fractures. A fractured layered medium exhibits: (1) fracture-dominated anisotropy when the fractures are weakly coupled; (2) isotropic behavior when fractures delay waves that are usually fast in a layered medium; and (3) matrix-dominated anisotropy when the fractures are closed and no longer delay the signal. The

  19. Stress fractures in athletes.

    PubMed

    Fredericson, Michael; Jennings, Fabio; Beaulieu, Christopher; Matheson, Gordon O

    2006-10-01

    A stress fracture is a partial or complete bone fracture that results from repeated application of stress lower than the stress required to fracture the bone in a single loading. Otherwise healthy athletes, especially runners, sustain stress injuries or fractures. Prevention or early intervention is the preferable treatment. However, it is difficult to predict injury because runners vary with regard to biomechanical predisposition, training methods, and other factors such as diet, muscle strength, and flexibility. Stress fractures account for 0.7% to 20% of all sports medicine clinic injuries. Track-and-field athletes have the highest incidence of stress fractures compared with other athletes. Stress fractures of the tibia, metatarsals, and fibula are the most frequently reported sites. The sites of stress fractures vary from sport to sport (eg, among track athletes, stress fractures of the navicular, tibia, and metatarsal are common; in distance runners, it is the tibia and fibula; in dancers, the metatarsals). In the military, the calcaneus and metatarsals were the most commonly cited injuries, especially in new recruits, owing to the sudden increase in running and marching without adequate preparation. However, newer studies from the military show the incidence and distribution of stress fractures to be similar to those found in sports clinics. Fractures of the upper extremities are relatively rare, although most studies have focused only on lower-extremity injuries. The ulna is the upper-extremity bone injured most frequently. Imaging plays a key role in the diagnosis and management of stress injuries. Plain radiography is useful when positive, but generally has low sensitivity. Radionuclide bone scanning is highly sensitive, but lacks specificity and the ability to directly visualize fracture lines. In this article, we focus on magnetic resonance imaging, which provides highly sensitive and specific evaluation for bone marrow edema, periosteal reaction as well

  20. Skeletal mechanism generation for surrogate fuels using directed relation graph with error propagation and sensitivity analysis

    SciTech Connect

    Niemeyer, Kyle E.; Sung, Chih-Jen; Raju, Mandhapati P.

    2010-09-15

    A novel implementation for the skeletal reduction of large detailed reaction mechanisms using the directed relation graph with error propagation and sensitivity analysis (DRGEPSA) is developed and presented with examples for three hydrocarbon components, n-heptane, iso-octane, and n-decane, relevant to surrogate fuel development. DRGEPSA integrates two previously developed methods, directed relation graph-aided sensitivity analysis (DRGASA) and directed relation graph with error propagation (DRGEP), by first applying DRGEP to efficiently remove many unimportant species prior to sensitivity analysis to further remove unimportant species, producing an optimally small skeletal mechanism for a given error limit. It is illustrated that the combination of the DRGEP and DRGASA methods allows the DRGEPSA approach to overcome the weaknesses of each, specifically that DRGEP cannot identify all unimportant species and that DRGASA shields unimportant species from removal. Skeletal mechanisms for n-heptane and iso-octane generated using the DRGEP, DRGASA, and DRGEPSA methods are presented and compared to illustrate the improvement of DRGEPSA. From a detailed reaction mechanism for n-alkanes covering n-octane to n-hexadecane with 2115 species and 8157 reactions, two skeletal mechanisms for n-decane generated using DRGEPSA, one covering a comprehensive range of temperature, pressure, and equivalence ratio conditions for autoignition and the other limited to high temperatures, are presented and validated. The comprehensive skeletal mechanism consists of 202 species and 846 reactions and the high-temperature skeletal mechanism consists of 51 species and 256 reactions. Both mechanisms are further demonstrated to well reproduce the results of the detailed mechanism in perfectly-stirred reactor and laminar flame simulations over a wide range of conditions. The comprehensive and high-temperature n-decane skeletal mechanisms are included as supplementary material with this article

  1. ClC-3 chloride channel functions as a mechanically sensitive channel in osteoblasts.

    PubMed

    Wang, Huan; Wang, Rong; Wang, Zhe; Liu, Qian; Mao, Yong; Duan, Xiaohong

    2015-12-01

    Mechanical stimulation usually causes the volume changes of osteoblasts. Whether these volume changes could be sensed by the ClC-3 chloride channel, a volume-sensitive ion channel, and further promote the osteodifferentiation in osteoblasts has not been determined. In this study, we applied persistent static compression on MC3T3-E1 cells to detect the expression changes of ClC-3, osteogenic markers, as well as some molecules related with signaling transduction pathway. We tested the key role of ClC-3 in transferring the mechanical signal to osteoinduction by ClC-3 overexpressing and siRNA technique. We found that ClC-3 level was up-regulated by mechanical stimulation in MC3T3-E1 cells. Mechanical force also up-regulated the mRNA level of osteogenic markers such as alkaline phosphatase (Alp), bone sialoprotein (Bsp), and osteocalcin (Oc), which could be blocked or strengthened by Clcn3 siRNA or overexpressing, and Alp expression was more sensitive to the changes of ClC-3 level. We also found that runt-related transcription factor 2 (Runx2), transforming growth factor beta 1 (TGF-β1), and Wnt pathway might be involved in ClC-3 mediated mechanical transduction in osteoblasts. The data from the current study suggest that the ClC-3 chloride channel acts as a mechanically sensitive channel to regulate osteodifferentiation in osteoblasts.

  2. Theoretical and user`s manual for pc-PRAISE: A probabilistic fracture mechanics computer code for piping reliability analysis

    SciTech Connect

    Harris, D.O.; Dedhia, D.D.; Lu, S.C.

    1992-07-01

    The purpose of this document is to collect under one cover and update the documentation related to the PRAISE Computer Code. pc-PRAISE is the most recent version of the code, which is a probabilistic fracture mechanics code that has recently been modified to run on an IBM personal computer to evaluate the reliability of welds in nuclear power plant piping systems. pc-PRAISE was adapted from the PRAISE Computer Code, which was originally developed in 1980--81 by Lawrence Livermore National Laboratory (LLNL) under funding from the US Nuclear Regulatory Commission for assessment of the influence of seismic events on the failure probability of piping in pressurized water reactors. PRAISE is an acronym for Piping Reliability Analysis Including Seismic Events, and has been significantly expanded in recent years to allow consideration of both crack initiation and growth in a variety of piping materials in pressurized and boiling water reactors. PRAISE has a deterministic basis in fracture mechanics. Some of the inputs, such as initial crack size and inspection detection probability, are considered to be random variables, and failure probability versus time for a given weldment is evaluated by Monte Carlo simulation. Complex realistic stress histories can be treated by the code, and sets of random material properties for representative piping materials are built into the code. This document provides a comprehensive summary of the deterministic basis of the code, along with description of statistical distributions of random variables. Code inputs are described and an extensive set of sample problems is provided along with descriptions of representative outputs.

  3. Theoretical and user's manual for pc-PRAISE: A probabilistic fracture mechanics computer code for piping reliability analysis

    SciTech Connect

    Harris, D.O.; Dedhia, D.D. ); Lu, S.C. )

    1992-07-01

    The purpose of this document is to collect under one cover and update the documentation related to the PRAISE Computer Code. pc-PRAISE is the most recent version of the code, which is a probabilistic fracture mechanics code that has recently been modified to run on an IBM personal computer to evaluate the reliability of welds in nuclear power plant piping systems. pc-PRAISE was adapted from the PRAISE Computer Code, which was originally developed in 1980--81 by Lawrence Livermore National Laboratory (LLNL) under funding from the US Nuclear Regulatory Commission for assessment of the influence of seismic events on the failure probability of piping in pressurized water reactors. PRAISE is an acronym for Piping Reliability Analysis Including Seismic Events, and has been significantly expanded in recent years to allow consideration of both crack initiation and growth in a variety of piping materials in pressurized and boiling water reactors. PRAISE has a deterministic basis in fracture mechanics. Some of the inputs, such as initial crack size and inspection detection probability, are considered to be random variables, and failure probability versus time for a given weldment is evaluated by Monte Carlo simulation. Complex realistic stress histories can be treated by the code, and sets of random material properties for representative piping materials are built into the code. This document provides a comprehensive summary of the deterministic basis of the code, along with description of statistical distributions of random variables. Code inputs are described and an extensive set of sample problems is provided along with descriptions of representative outputs.

  4. Mechanical assessment of local bone quality to predict failure of locked plating in a proximal humerus fracture model.

    PubMed

    Röderer, Götz; Brianza, Stefano; Schiuma, Damiano; Schwyn, Ronald; Scola, Alexander; Gueorguiev, Boyko; Gebhard, Florian; Tami, Andrea

    2013-09-01

    The importance of osteoporosis in proximal humerus fractures is well recognized. However, the local distribution of bone quality in the humeral head may also have a significant effect because it remains unclear in what quality of bone screws of standard implants purchase. The goal of this study was to investigate whether the failure of proximal humerus locked plating can be predicted by the DensiProbe (ARI, Davos, Switzerland). A 2-part fracture with metaphyseal impaction was simulated in 12 fresh-frozen human cadaveric humeri. Using the DensiProbe, local bone quality was determined in the humeral head in the course of 6 proximal screws of a standard locking plate (Philos; Synthes GmbH, Solothurn, Switzerland). Cyclic mechanical testing with increasing axial loading until failure was performed. Bone mineral density (BMD) significantly correlated with cycles until failure. Head migration significantly increased between 1000 and 2000 loading cycles and significantly correlated with BMD after 3000 cycles. DensiProbe peak torque in all screw positions and their respective mean torque correlated significantly with the BMD values. In 3 positions, the peak torque significantly correlated with cycles to failure; here BMD significantly influenced mechanical stability. The validity of the DensiProbe was proven by the correlation between its peak torque measurements and BMD. The correlation between the peak torque and cycles to failure revealed the potential of the DensiProbe to predict the failure of locked plating in vitro. This method provides information about local bone quality, potentially making it suitable for intraoperative use by allowing the surgeon to take measures to improve stability.

  5. Theoretical insight into the sensitive mechanism of multilayer-shaped cocrystal explosives: compression and slide.

    PubMed

    Gao, Hong-fei; Zhang, Shu-hai; Ren, Fu-de; Gou, Rui-jun; Han, Gang; Wu, Jing-bo; Ding, Xiong; Zhao, Wen-hu

    2016-05-01

    Multilayer-shaped compression and slide models were employed to investigate the complex sensitive mechanisms of cocrystal explosives in response to external mechanical stimuli. Here, density functional theory (DFT) calculations implementing the generalized gradient approximation (GGA) of Perdew-Burke-Ernzerhof (PBE) with the Tkatchenko-Scheffler (TS) dispersion correction were applied to a series of cocrystal explosives: diacetone diperoxide (DADP)/1,3,5-trichloro-2,4,6-trinitrobenzene (TCTNB), DADP/1,3,5-tribromo-2,4,6-trinitrobenzene (TBTNB) and DADP/1,3,5-triiodo-2,4,6-trinitrobenzene (TITNB). The results show that the GGA-PBE-TS method is suitable for calculating these cocrystal systems. Compression and slide models illustrate well the sensitive mechanism of layer-shaped cocrystals of DADP/TCTNB and DADP/TITNB, in accordance with the results from electrostatic potentials and free space per molecule in cocrystal lattice analyses. DADP/TCTNB and DADP/TBTNB prefer sliding along a diagonal direction on the a-c face and generating strong intermolecular repulsions, compared to DADP/TITNB, which slides parallel to the b-c face. The impact sensitivity of DADP/TBTNB is predicted to be the same as that of DADP/TCTNB, and the impact sensitivity of DADP/TBTNB may be slightly more insensitive than that of DADP and much more sensitive than that of TBTNB. PMID:27094730

  6. Training and Research on Probabilistic Hydro-Thermo-Mechanical Modeling of Carbon Dioxide Geological Sequestration in Fractured Porous Rocks

    SciTech Connect

    Gutierrez, Marte

    2013-05-31

    Colorado School of Mines conducted research and training in the development and validation of an advanced CO{sub 2} GS (Geological Sequestration) probabilistic simulation and risk assessment model. CO{sub 2} GS simulation and risk assessment is used to develop advanced numerical simulation models of the subsurface to forecast CO2 behavior and transport; optimize site operational practices; ensure site safety; and refine site monitoring, verification, and accounting efforts. As simulation models are refined with new data, the uncertainty surrounding the identified risks decrease, thereby providing more accurate risk assessment. The models considered the full coupling of multiple physical processes (geomechanical and fluid flow) and describe the effects of stochastic hydro-mechanical (H-M) parameters on the modeling of CO{sub 2} flow and transport in fractured porous rocks. Graduate students were involved in the development and validation of the model that can be used to predict the fate, movement, and storage of CO{sub 2} in subsurface formations, and to evaluate the risk of potential leakage to the atmosphere and underground aquifers. The main major contributions from the project include the development of: 1) an improved procedure to rigorously couple the simulations of hydro-thermomechanical (H-M) processes involved in CO{sub 2} GS; 2) models for the hydro-mechanical behavior of fractured porous rocks with random fracture patterns; and 3) probabilistic methods to account for the effects of stochastic fluid flow and geomechanical properties on flow, transport, storage and leakage associated with CO{sub 2} GS. The research project provided the means to educate and train graduate students in the science and technology of CO{sub 2} GS, with a focus on geologic storage. Specifically, the training included the investigation of an advanced CO{sub 2} GS simulation and risk assessment model that can be used to predict the fate, movement, and storage of CO{sub 2} in

  7. Fracture Mechanics of Thin, Cracked Plates Under Tension, Bending and Out-of-Plane Shear Loading

    NASA Technical Reports Server (NTRS)

    Zehnder, Alan T.; Hui, C. Y.; Potdar, Yogesh; Zucchini, Alberto

    1999-01-01

    Cracks in the skin of aircraft fuselages or other shell structures can be subjected to very complex stress states, resulting in mixed-mode fracture conditions. For example, a crack running along a stringer in a pressurized fuselage will be subject to the usual in-plane tension stresses (Mode-I) along with out-of-plane tearing stresses (Mode-III like). Crack growth and initiation in this case is correlated not only with the tensile or Mode-I stress intensity factor, K(sub I), but depends on a combination of parameters and on the history of crack growth. The stresses at the tip of a crack in a plate or shell are typically described in terms of either the small deflection Kirchhoff plate theory. However, real applications involve large deflections. We show, using the von-Karman theory, that the crack tip stress field derived on the basis of the small deflection theory is still valid for large deflections. We then give examples demonstrating the exact calculation of energy release rates and stress intensity factors for cracked plates loaded to large deflections. The crack tip fields calculated using the plate theories are an approximation to the actual three dimensional fields. Using three dimensional finite element analyses we have explored the relationship between the three dimensional elasticity theory and two dimensional plate theory results. The results show that for out-of-plane shear loading the three dimensional and Kirchhoff theory results coincide at distance greater than h/2 from the crack tip, where h/2 is the plate thickness. Inside this region, the distribution of stresses through the thickness can be very different from the plate theory predictions. We have also explored how the energy release rate varies as a function of crack length to plate thickness using the different theories. This is important in the implementation of fracture prediction methods using finite element analysis. Our experiments show that under certain conditions, during fatigue crack

  8. The local effect of octreotide on mechanical pain sensitivity is more sensitive in DA rats than DA.1U rats.

    PubMed

    Yao, Fan-Rong; Wang, Hui-Sheng; Guo, Yuan; Zhao, Yan

    2016-02-01

    A recent study by the authors indicated that major histocompatibility complex (MHC) genes are associated with the differences in basal pain sensitivity and in formalin model between Dark-Agouti (DA) and novel congenic DA.1U rats, which have the same genetic background as DA rats except for the u alleles of MHC. The objective of the present study is to investigate whether there is a difference in the pristane-induced arthritis (PIA) model and local analgesic effect of octreotide (OCT) between DA and DA.1U rats. The hindpaw mechanical withdrawal threshold (MWT) and heat withdrawal latency (HWL) were observed. The C unit firings of the tibial nerve evoked by non-noxious and noxious toe movements were recorded by electrophysiological methods in normal and PIA models in DA and DA.1U rats before and after local OCT administration. The expression of somatostatin receptor 2A (SSTR2A) was observed by immunohistochemistry. The results demonstrate that DA rats have a higher mechanical sensitivity than DA.1U rats after PIA. Local OCT administration significantly elevated MWT in DA rats under normal and PIA sate, but not in DA.1U rats. The electrophysiological experiments showed OCT significantly attenuated the firings of C units evoked by non-noxious and noxious stimulation in DA rats more than those in DA.1U rats both in normal and PIA states. In addition, the expression of SSTR2A in the dorsal horn of the spinal cord was significantly higher in DA than in DA.1U rats. All of the findings suggest a higher local analgesic effect of OCT in DA rats than DA.1U rats, which might be associated with the MHC genes.

  9. A high-sensitivity biaxial resonant accelerometer with two-stage microleverage mechanisms

    NASA Astrophysics Data System (ADS)

    Ding, Hong; Zhao, Jiuxuan; Ju, Bing-Feng; Xie, Jin

    2016-01-01

    This paper presents a design and experimental evaluation of a micro-electro-mechanical system biaxial resonant accelerometer with two-stage microleverage mechanisms. The device incorporates two pairs of double-ended tuning fork resonators coupled to a single proof mass. The two-stage microleverage mechanisms possess a higher amplification factor than single-stage microleverage mechanisms, so that the proposed accelerometer has a high level of sensitivity. In addition, a low level of cross-axis sensitivity is realized because of the decoupling beams. The accelerometer is theoretically analyzed and then simulated in the system level by the finite element method. The device is fabricated in a silicon-on-insulator wafer. The experimental results demonstrate that the average differential sensitivity of the resonant accelerometer is 275 Hz g-1 at a resonant frequency of 290 kHz under a polarization voltage of 5 V. The measured cross-axis sensitivity is lower than 3.4%.

  10. Correlating chemical sensitivity and basal gene expression reveals mechanism of action | Office of Cancer Genomics

    Cancer.gov

    Changes in cellular gene expression in response to small-molecule or genetic perturbations have yielded signatures that can connect unknown mechanisms of action (MoA) to ones previously established. We hypothesized that differential basal gene expression could be correlated with patterns of small-molecule sensitivity across many cell lines to illuminate the actions of compounds whose MoA are unknown.

  11. Perceiving Group Behavior: Sensitive Ensemble Coding Mechanisms for Biological Motion of Human Crowds

    ERIC Educational Resources Information Center

    Sweeny, Timothy D.; Haroz, Steve; Whitney, David

    2013-01-01

    Many species, including humans, display group behavior. Thus, perceiving crowds may be important for social interaction and survival. Here, we provide the first evidence that humans use ensemble-coding mechanisms to perceive the behavior of a crowd of people with surprisingly high sensitivity. Observers estimated the headings of briefly presented…

  12. Inhibition of GSK-3β rescues the impairments in bone formation and mechanical properties associated with fracture healing in osteoblast selective connexin 43 deficient mice.

    PubMed

    Loiselle, Alayna E; Lloyd, Shane A J; Paul, Emmanuel M; Lewis, Gregory S; Donahue, Henry J

    2013-01-01

    Connexin 43 (Cx43) is the most abundant gap junction protein in bone and is required for osteoblastic differentiation and bone homeostasis. During fracture healing, Cx43 is abundantly expressed in osteoblasts and osteocytes, while Cx43 deficiency impairs bone formation and healing. In the present study we selectively deleted Cx43 in the osteoblastic lineage from immature osteoblasts through osteocytes and tested the hypothesis that Cx43 deficiency results in delayed osteoblastic differentiation and impaired restoration of biomechanical properties due to attenuated β-catenin expression relative to wild type littermates. Here we show that Cx43 deficiency results in alterations in the mineralization and remodeling phases of healing. In Cx43 deficient fractures the mineralization phase is marked by delayed expression of osteogenic genes. Additionally, the decrease in the RankL/Opg ratio, osteoclast number and osteoclast size suggest decreased osteoclast bone resorption and remodeling. These changes in healing result in functional deficits as shown by a decrease in ultimate torque at failure. Consistent with these impairments in healing, β-catenin expression is attenuated in Cx43 deficient fractures at 14 and 21 days, while Sclerostin (Sost) expression, a negative regulator of bone formation is increased in Cx43cKO fractures at 21 days, as is GSK-3β, a key component of the β-catenin proteasomal degradation complex. Furthermore, we show that alterations in healing in Cx43 deficient fractures can be rescued by inhibiting GSK-3β activity using Lithium Chloride (LiCl). Treatment of Cx43 deficient mice with LiCl restores both normal bone formation and mechanical properties relative to LiCl treated WT fractures. This study suggests that Cx43 is a potential therapeutic target to enhance fracture healing and identifies a previously unknown role for Cx43 in regulating β-catenin expression and thus bone formation during fracture repair.

  13. Fracture mechanics of propagating 3-D fatigue cracks with parametric dislocations

    NASA Astrophysics Data System (ADS)

    Takahashi, Akiyuki; Ghoniem, Nasr M.

    2013-07-01

    Propagation of 3-D fatigue cracks is analyzed using a discrete dislocation representation of the crack opening displacement. Three dimensional cracks are represented with Volterra dislocation loops in equilibrium with the applied external load. The stress intensity factor (SIF) is calculated using the Peach-Koehler (PK) force acting on the crack tip dislocation loop. Loading mode decomposition of the SIF is achieved by selection of Burgers vector components to correspond to each fracture mode in the PK force calculations. The interaction between 3-D cracks and free surfaces is taken into account through application of the superposition principle. A boundary integral solution of an elasticity problem in a finite domain is superposed onto the elastic field solution of the discrete dislocation method in an infinite medium. The numerical accuracy of the SIF is ascertained by comparison with known analytical solution of a 3-D crack problem in pure mode I, and for mixed-mode loading. Finally, fatigue crack growth simulations are performed with the Paris law, showing that 3-D cracks do not propagate in a self-similar shape, but they re-configure as a result of their interaction with external boundaries. A specific numerical example of fatigue crack growth is presented to demonstrate the utility of the developed method for studies of 3-D crack growth during fatigue.

  14. Advances in Fatigue and Fracture Mechanics Analyses for Metallic Aircraft Structures

    NASA Technical Reports Server (NTRS)

    Newman, J. C., Jr.

    2000-01-01

    This paper reviews some of the advances that have been made in stress analyses of cracked aircraft components, in the understanding of the fatigue and fatigue-crack growth process, and in the prediction of residual strength of complex aircraft structures with widespread fatigue damage. Finite-element analyses of cracked metallic structures are now used to determine accurate stress-intensity factors for cracks at structural details. Observations of small-crack behavior at open and rivet-loaded holes and the development of small-crack theory has lead to the prediction of stress-life behavior for components with stress concentrations under aircraft spectrum loading. Fatigue-crack growth under simulated aircraft spectra can now be predicted with the crack-closure concept. Residual strength of cracked panels with severe out-of-plane deformations (buckling) in the presence of stiffeners and multiple-site damage can be predicted with advanced elastic-plastic finite-element analyses and the critical crack-tip-opening angle (CTOA) fracture criterion. These advances are helping to assure continued safety of aircraft structures.

  15. Fracture and Medium Modeling, by Analizing Hidraulic Fracturing Induced Microseismicity

    NASA Astrophysics Data System (ADS)

    Gomez Alba, S.; Vargas Jiménez, C. A.

    2014-12-01

    Hydraulic fracturing is an essential technology for most unconventional hydrocarbon resources and many conventional ones as well. The primary limitation on the improvement and optimization of the fracturing process is the minimal access to observe the behavior of the fracture in the subsurface. Without direct observational evidence, hypothetical mechanisms must be assumed and then tested for their validity with indirect information such as wellbore measurements, indirect production and pressure behavior. One of the most important sources of information today is the relation made between micro seismic source mechanisms and fracture behavior. Hydraulic fractures induce some level of micro seismicity when the stress conditions in the Earth are altered by changes in stress during the operations. The result is the sudden movement between rock elements and the radiation of both compressional and shear energy in a seismic range that can be detected and recorded with sensitive receivers. The objective of this work is to provide reasonable information when applying inversion methods in order to estimate the vertical and horizontal spatial heterogeneities in medium and energy radiation distribution of microseisms while fracking operations. The method consist in record microseisms at a previous lineal array of stations (triaxial accelerometers) which are located close to the source coordinates and cover the area of study. The analysis clarify some ideas about what information can be gained from the micro seismic source data and according to the obtained results, what kind of comparisons and associations might be done to evaluate the fracking performance operation. Non uniformities in medium such as faults would be revealed by interpreted scattering coefficients. Fracture properties like distance, velocity and orientation would be also determined by analyzing energy radiation.

  16. Antipsychotic-induced sensitization and tolerance: Behavioral characteristics, developmental impacts, and neurobiological mechanisms

    PubMed Central

    Li, Ming

    2016-01-01

    Antipsychotic sensitization and tolerance refer to the increased and decreased drug effects due to past drug use, respectively. Both effects reflect the long-term impacts of antipsychotic treatment on the brain and result from the brain’s adaptive response to the foreign property of the drug. In this review, clinical evidence of the behavioral aspect of antipsychotic sensitization and tolerance is selectively reviewed, followed by an overview of preclinical literature that examines these behavioral characteristics and the related pharmacological and nonpharmacological factors. Next, recent work on the developmental impacts of adolescent antipsychotic sensitization and tolerance is presented and recent research that delineates the neurobiological mechanisms of antipsychotic sensitization and tolerance is summarized. A theoretical framework based on “drug learning and memory” principles is proposed to account for the phenomena of antipsychotic sensitization and tolerance. It is maintained that antipsychotic sensitization and tolerance follow basic principles of learning or acquisition (“induction”) and memory (“expression”). The induction and expression of both effects reflect the consequences of associative and nonassociative processing and are strongly influenced by various pharmacological, environmental, and behavioral factors. Drug-induced neuroplasticity, such as functional changes of striatal dopamine D2 and prefrontal serotonin (5-HT)2A receptors and their mediated signaling pathways, in principle, is responsible for antipsychotic sensitization and tolerance. Understanding the behavioral characteristics and neurobiological underpinnings of antipsychotic sensitization and tolerance has greatly enhanced our understanding of mechanisms of antipsychotic action, and may have important implications for future drug discovery and clinical practice. PMID:27371498

  17. A fracture mechanics approach for estimating fatigue crack initiation in carbon and low-alloy steels in LWR coolant environments

    SciTech Connect

    Park, H. B.; Chopra, O. K.

    2000-04-10

    A fracture mechanics approach for elastic-plastic materials has been used to evaluate the effects of light water reactor (LWR) coolant environments on the fatigue lives of carbon and low-alloy steels. The fatigue life of such steel, defined as the number of cycles required to form an engineering-size crack, i.e., 3-mm deep, is considered to be composed of the growth of (a) microstructurally small cracks and (b) mechanically small cracks. The growth of the latter was characterized in terms of {Delta}J and crack growth rate (da/dN) data in air and LWR environments; in water, the growth rates from long crack tests had to be decreased to match the rates from fatigue S-N data. The growth of microstructurally small cracks was expressed by a modified Hobson relationship in air and by a slip dissolution/oxidation model in water. The crack length for transition from a microstructurally small crack to a mechanically small crack was based on studies on small crack growth. The estimated fatigue S-N curves show good agreement with the experimental data for these steels in air and water environments. At low strain amplitudes, the predicted lives in water can be significantly lower than the experimental values.

  18. Osteoporotic vertebral fractures redux.

    PubMed

    Lentle, B C; Gordon, P; Ward, L

    2008-02-01

    Osteoporosis remains an important cause of morbidity and mortality especially in the elderly. This fact is largely due to fractures of the proximal femur and spine. As recently recognized, vertebral fractures are as much a threat to health and longevity as fractures of the proximal femur. In recent decades, the development of tools to evaluate fracture risk as well as medications to treat osteoporosis has altered the management of people who are at fracture risk. At the same time identification and management procedures concerning spinal fracturing are not very clear. Besides there is not even clear consensus about what exactly constitutes a vertebral fracture, particularly those of minor degree. While height loss is a simple and valuable tool to detect vertebral fractures, it is neither sensitive nor specific enough to replace radiographs. Some 65% of fractures cause no symptoms. Often vertebral fractures are misdiagnosed, especially if they have occurred silently and if the opportunity for diagnosis arises fortuitously. It is to the patient's benefit that radiologists report and physicians identify vertebral fractures evident on a chest or other radiograph, no matter how incidental to the immediate clinical indication for the examination. Technological evolution now allows dual-energy x-ray absorptiometry machines to be used to take spine images while doing a densitometry. The images are adequate, even if not of high radiographic quality, and, more important, the patient undergoes a smaller radiation dose than with conventional spinal radiographs. Such technology may promote fracture recognition. The recognition of vertebral fractures, as well as the prevention and treatment of further fractures, will likely do much to reduce both the burden of osteoporosis-related morbidity and mortality, as well as fracture-related costs to healthcare systems.

  19. Results of fracture mechanics analyses of the Adorer cranes in the device assembly facility using actual, rather than conservative, stress-components

    SciTech Connect

    Dalder, E.N.C.

    1996-12-26

    Fracture mechanics analyses were done on 3 critical locations on the lower flange of the load beam of the Ederer 5 ton and 4 ton cranes in the D.A.F. Facility. This was done to determine appropriate flaw sizes for NDE detection during periodic inspection, and appropriate inspection intervals.

  20. Development of a Titanium Plate for Mandibular Angle Fractures with a Bone Defect in the Lower Border: Finite Element Analysis and Mechanical Test

    PubMed Central

    Goulart, Douglas Rangel; Kemmoku, Daniel Takanori; Noritomi, Pedro Yoshito

    2015-01-01

    ABSTRACT Objectives The aim of the present study was to develop a plate to treat mandibular angle fractures using the finite element method and mechanical testing. Material and Methods A three-dimensional model of a fractured mandible was generated using Rhinoceros 4.0 software. The models were exported to ANSYS®, in which a static application of displacement (3 mm) was performed in the first molar region. Three groups were assessed according to the method of internal fixation (2 mm system): two non-locking plates; two locking plates and a new design locking plate. The computational model was transferred to an in vitro experiment with polyurethane mandibles. Each group contained five samples and was subjected to a linear loading test in a universal testing machine. Results A balanced distribution of stress was associated with the new plate design. This plate modified the mechanical behavior of the fractured region, with less displacement between the fractured segments. In the mechanical test, the group with two locking plates exhibited greater resistance to the 3 mm displacement, with a statistically significant difference when compared with the new plate group (ANOVA, P = 0.016). Conclusions The new plate exhibited a more balanced distribution of stress. However, the group with two locking plates exhibited greater mechanical resistance. PMID:26539287

  1. Epicutaneous Allergic Sensitization by Cooperation between Allergen Protease Activity and Mechanical Skin Barrier Damage in Mice.

    PubMed

    Shimura, Sakiko; Takai, Toshiro; Iida, Hideo; Maruyama, Natsuko; Ochi, Hirono; Kamijo, Seiji; Nishioka, Izumi; Hara, Mutsuko; Matsuda, Akira; Saito, Hirohisa; Nakae, Susumu; Ogawa, Hideoki; Okumura, Ko; Ikeda, Shigaku

    2016-07-01

    Allergen sources such as mites, insects, fungi, and pollen contain proteases. Airway exposure to proteases induces allergic airway inflammation and IgE/IgG1 responses via IL-33-dependent mechanisms in mice. We examined the epicutaneous sensitization of mice to a model protease allergen, papain; the effects of tape stripping, which induces epidermal barrier dysfunction; and the atopic march upon a subsequent airway challenge. Papain painting on ear skin and tape stripping cooperatively promoted dermatitis, the skin gene expression of proinflammatory cytokines and growth factors, up-regulation of serum total IgE, and papain-specific IgE/IgG1 induction. Epicutaneous sensitization induced T helper (Th) 2 cells and Th17 differentiation in draining lymph nodes. Ovalbumin and protease inhibitor-treated papain induced no or weak responses, whereas the co-administration of ovalbumin and papain promoted ovalbumin-specific IgE/IgG1 induction. Wild-type and IL-33-deficient mice showed similar responses in the epicutaneous sensitization phase. The subsequent airway papain challenge induced airway eosinophilia and maintained high papain-specific IgE levels in an IL-33-dependent manner. These results suggest that allergen source-derived protease activity and mechanical barrier damage such as that caused by scratching cooperatively promote epicutaneous sensitization and skin inflammation and that IL-33 is dispensable for epicutaneous sensitization but is crucial in the atopic march upon a subsequent airway low-dose encounter with protease allergens. PMID:26987428

  2. A multiregional, multimodel examination of the sensitivities, mechanisms, and consequences of the ozone climate penalty

    NASA Astrophysics Data System (ADS)

    Porter, W. C.; Heald, C. L.

    2015-12-01

    Tropospheric ozone (O3) pollution levels have widely observed correlations to daytime surface temperatures, especially in highly polluted regions. This nonlinear correlation occurs through a variety of temperature-dependent mechanisms related to O3 precursor emissions, lifetimes, and reaction rates, making the reproduction of temperature sensitivities - and the associated human health risks connected to increased pollution - a problematic task. Here we examine the observed summertime O3 climate penalty across several regions worldwide using quantile regression, allowing for an examination of temperature sensitivities across the O3 response distribution. Through this methodology, we show significant differences between the sensitivities of high vs. low O3 percentiles, suggesting that climate penalties based on means and ordinary least squares regressions may in fact underestimate the magnitude of expected changes to extreme O3 events. We then examine these relationships as reproduced by the global chemical transport model GEOS-Chem, perturbing individual mechanisms within the model to both highlight possible explanations for model/observation discrepancies, and also better understand the regionality and magnitude of individual mechanism contribution to the observed penalty. Finally, we explore the future consequences of the climate penalty as forecast by commonly used global climate models, proposing corrections based on the quantile and regional differences from observed sensitivities.

  3. U.S. National Committee for Rock Mechanics; and Conceptual model of fluid infiltration in fractured media. Project summary, July 28, 1997--July 27, 1998

    SciTech Connect

    1998-09-01

    The title describes the two tasks summarized in this report. The remainder of the report contains information on meetings held or to be held on the subjects. The US National Committee for Rock Mechanics (USNC/RM) provides for US participation in international activities in rock mechanics, principally through adherence to the International Society for Rock Mechanics (ISRM). It also keeps the US rock mechanics community informed about new programs directed toward major areas of national concern in which rock mechanics problems represent critical or limiting factors, such as energy resources, excavation, underground storage and waste disposal, and reactor siting. The committee also guides or produces advisory studies and reports on problem areas in rock mechanics. A new panel under the auspices of the US National Committee for Rock Mechanics has been appointed to conduct a study on Conceptual Models of Fluid Infiltration in Fractured Media. The study has health and environmental applications related to the underground flow of pollutants through fractured rock in and around mines and waste repositories. Support of the study has been received from the US Nuclear Regulatory Commission and the Department of Energy`s Yucca Mountain Project Office. The new study builds on the success of a recent USNC/RM report entitled Rock Fractures and Fluid Flow: Contemporary Understanding and Applications (National Academy Press, 1996, 551 pp.). A summary of the new study is provided.

  4. Structural integrity assessment of carbon and low-alloy steel pressure vessels using a simplified fracture mechanics procedure

    SciTech Connect

    Rana, M.D. . Research and Development Dept.)

    1994-08-01

    This paper describes a simplified fracture analysis procedure which was developed by Pellini to quantify fracture critical-crack sizes and crack-arrest temperatures of carbon and low-alloy steel pressure vessels. Fracture analysis diagrams have been developed using the simplified analysis procedure for various grades of carbon and low-alloy steels used in the construction of ASME, Section VIII, Division 1 pressure vessels. Structural integrity assessments have been conducted from the analysis diagrams.

  5. Flexion-type Salter II fracture of the proximal tibia. Proposed mechanism of injury and two case studies.

    PubMed

    Blanks, R H; Lester, D K; Shaw, B A

    1994-04-01

    An uncommon fracture of the proximal tibial epiphysis is described in two cases. A flexion-type Salter II fracture of the proximal tibia resulting from a partially closed physis can be reduced easily and appears to have no long-lasting effects. Radiographic review of the adolescent knees showed that physeal closure of the proximal tibial epiphysis proceeds from posterior to anterior, thereby making this particular fracture more likely during this phase of development.

  6. Attractive mechanical properties of a lightweight highly sensitive bi layer thermistor: polycarbonate/organic molecular conductor

    NASA Astrophysics Data System (ADS)

    Laukhina, E.; Lebedev, V.; Rovira, C.; Laukhin, V.; Veciana, J.

    2016-03-01

    The paper covers some of the basic mechanical characteristics of a recently developed bi layer thermistor: polycarbonate/(001) oriented layer of organic molecular conductor α’-(BEDT-TTF)2IxBr3-x, were BEDT-TTF=bis(ethylenedithio)tetrathiafulvalen. The nano and macro mechanical properties have been studied in order to use this flexible, low cost thermistor in sensing applications by proper way. The nano-mechanical properties of the temperature sensitive semiconducting layer of α’-(BEDT-TTF)2IxBr3-x were tested using nanoindentation method. The value of Young's modulus in direction being perpendicular to the layer plan was found as 9.0 ±1.4 GPa. The macro mechanical properties of the thermistor were studied using a 5848 MicroTester. The tensile tests showed that basic mechanical characteristics of the thermistor are close to those of polycarbonate films. This indicates a good mechanical strength of the developed sensor. Therefore, the thermistor can be used in technologies that need to be instrumented with highly robustness lightweight low cost temperature sensors. The paper also reports synthetic details on fabricating temperature sensing e-textile. As the temperature control is becoming more and more important in biomedical technologies like healthcare monitoring, this work strongly contributes on the ongoing research on engineering sensitive conducting materials for biomedical applications.

  7. Atraumatic sternum fracture

    PubMed Central

    Abrahamsen, Sebastian Ørskov; Madsen, Christina Friis

    2014-01-01

    The spine, pelvic bones and long bones of the lower extremities are common sites for insufficiency fractures. Cases of sternum insufficiency fractures have rarely been reported among elderly patients. Insufficiency fractures tend to occur in bones with decreased mechanical strength especially among elderly patients, in postmenopausal women and patients with underlying diseases. We describe a case of spontaneous sternum insufficiency fracture in a healthy man, with no known risk factors to fracture, or previous history of fractures. Sternum insufficiency fracture is