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1

Robust characteristics method for modelling multiphase visco-elasto-plastic thermo-mechanical problems  

NASA Astrophysics Data System (ADS)

We have extended our previous 2D method [Gerya, T.V., Yuen, D.A., 2003. Characteristics-based marker-in-cell method with conservative finite-differences schemes for modeling geological flows with strongly variable transport properties. Phys. Earth Planet. Interiors 140, 295-320], which is a combination of conservative finite-differences with marker-in-cell techniques to include the effects of visco-elasto-plastic rheology, self-gravitation and a self-consistently derived evolving curvilinear planetary surface. This code is called I2ELVIS and can solve a new class of computationally challenging problems in geodynamics, such as shear localization with large strains, crustal intrusion emplacement of magmas, bending of realistic visco-elasto-plastic plates and core-formation by vigorous shell tectonics activities related to a global Rayleigh-Taylor instability of a metal layer formed around silicate-rich lower density (primordial) core during planetary accretion. We discuss in detail the computational strategy required the rheological constraints to be satisfied at each time step and spatial location. We show analytical benchmarks and examples drawn from comparing between numerical and analogue experiments in structural geology, subducting slab bending with a visco-elasto-plastic rheology and equilibrium spherical configurations from self-gravitation. We have also tested possibilities of future applications by addressing 3D geometries based on multigrid method and including inertial effects in the momentum equation with tracers in order to simulate meteoritic impact events and eventually earthquake instabilities.

Gerya, Taras V.; Yuen, David A.

2007-08-01

2

A possible mechanism for the initiation of the Yinggehai Basin: A visco-elasto-plastic model  

NASA Astrophysics Data System (ADS)

The Yinggehai Basin, lying along the trace of the Red River fault zone in the South China Sea, has been related to the movements of the Red River fault zone and the rotation of the Indochina block. However, the tectonic origin of the Yinggehai Basin remains unclear. This paper explores the initiation of the Yinggehai Basin using a visco-elasto-plastic model. This model concentrates on two main aspects: lateral viscosity variations (mainly controlled by temperature) in the lithosphere and internal friction angles of the pre-existing fault zone. Modeling results show that: (1) for a layered viscosity, en echelon faults would likely form when there is no pre-existing strike-slip fault; whereas, the basin would be narrow and deep, if any, when there is a pre-existing fault; (2) for moderate lateral viscosity variations, a large basin forms, even without a pre-existing fault zone; and (3) for strong lateral viscosity variations, a major rift could form over geologic time. Our results indicate that the initiation of the Yinggehai Basin requires moderate lateral viscosity variations (i.e., a pre-existing gentle upwelling of the Mohorovicic discontinuity) but no pre-existing fault. In addition, the initial extension predicted is NE-SW and is generated by the rotation of the Indochina block. This differs from the NW-SE extension that resulted from the movements of the Red River fault zone. This indicates that the left-lateral displacements of the Red River fault zone and the spreading of the South China Sea only influence the basin evolution after its initiation.

Wang, Xinguo; He, Jiankun; Ding, Lin; Gao, Risheng

2013-09-01

3

Elastic beam finite element with a transverse elasto-plastic crack  

Microsoft Academic Search

A cracked beam finite element has been formulated in this paper. The model of the element is based on elasto–plastic fracture mechanics and the finite element method. Crack tip plasticity, at the cracked cross-section, is included in the model of local flexibility. The inertia and stiffness matrices take into account the effect of flexural bending deformation due to the crack

M. Krawczuk; A. ?ak; W. Ostachowicz

2000-01-01

4

Elasto-plastic characteristics and mechanical properties of as-sprayed 8 mol% yttria-stabilized zirconia coating under nano-scales measured by nanoindentation  

NASA Astrophysics Data System (ADS)

The elasto-plastic characteristics and mechanical properties of as-received 8 mol% Y2O3-ZrO2 (8YSZ) coatings were studied by nanoindentation at ultra-low loads with a Berkovich indenter at room temperature. All experimental data including hardness H and elastic modulus E were analyzed by the Weibull statistical method due to the porous and heterogeneous nature of the tested samples. It was found that the hardness firstly exhibits interesting reverse indentation size effect, and then shows normal indentation size effect within different indentation scales. The average elastic modulus of 8YSZ was estimated as 214.8 ± 13.2 GPa. In order to reveal the elasto-plastic characteristics of 8YSZ at nano-scales, the distribution of resolved shear stresses underneath the indenter tip region was evaluated by Hertzian contact theory when the deformation behavior of 8YSZ changed from fully elastic to elasto-plastic stages. The results shed light on understanding possible foreign object damage mechanisms of thermal barrier coating systems.

Luo, J. M.; Dai, C. Y.; Shen, Y. G.; Mao, W. G.

2014-08-01

5

Electromagnetic Elasto-Plastic Dynamic Response of Conductive Plate  

NASA Astrophysics Data System (ADS)

Electromagnetic elasto-plastic dynamic response of a conductive plate in a magnetic pulse field are studied in this paper, the influence of the strain rate effect is investigated for the electromagnetic elasto-plastic deformation of the conductive plate. Basic governing equations are derived for electromagnetic field (eddy current), the elasto-plastic transient dynamic response and the heat transfer of a conductive rectangular plate, and then an appropriate numerical code is developed based on the finite element method to quantitatively simulate the magneto-elasto-plastic mechanical behaviors of the conductive rectangular plate. The Johnson-Cook model is employed to study the strain rate effect and temperature effect on the deformation of the plate. The dynamic response is explained with some characteristic curves of deformation, the eddy current, and the configurations, the temperature of the conductive plate. The numerical results indicate that the strain rate effect has to be considered for the conductive plates, especially for those with high strain rate sensitivity. Comparison of the influence of the temperature effect on the deformation of the plate with that of the strain rate effect shows that the influence of the temperature effect on the deformation of a plate is not significant.

Gao, Yuanwen

2010-05-01

6

Elasto-Plastic FEM Stress Analysis and Mechanical Characteristics of Pipe Flange Connections with Non-Asbestos Gaskets under Internal Pressure  

NASA Astrophysics Data System (ADS)

The effects of the nominal diameter of pipe flange connections with non-asbestos spiral wound gaskets(SWG) under internal pressure on the mechanical characteristics such as the contact gasket stress distribution which governs the sealing performance, the load factor and the hub stress of the connections were evaluated. The stresses in the connections with the nominal diameters from 3” to 24” under internal pressure are analyzed using the elasto-plastic(EP) FEM analysis taking account the hysteresis and non-linearity of deformation behavior of the non-asbestos SWG. As a result, it is found that the variations in the contact gasket stress distributions are substantial due to the flange rotation in the connections with the larger nominal diameter. Leakage tests were conducted to measure the axial bolt forces (the load factor) and the hub stress. The results obtained from the EP-FEM analyses are fairly consistent with the experimental results concerning the variation in the axial bolt forces (the load factor) and the hub stress. Using the obtained contact gasket stress distributions and the fundamental relationship between the amount of leakage and the contact gasket stress, the amount of the leakage of the connections is estimated. It is observed that the sealing performance of the connections with larger nominal diameter is worse than that of the connection with smaller nominal diameter because of the flange rotation. The estimated results are in a fairly good agreement with the measured results. The difference in the hub stress between the EP-FEM and ASME code is demonstrated and the differences in the load factor and the sealing performance of the connections are shown between the asbestos and non-asbestos gaskets.

Takagi, Yoshio; Omiya, Yuya; Kobayashi, Takashi; Sawa, Toshiyuki

7

Analytical and numerical study of the effect of water pressure on the mechanical response of cylindrical lined tunnels in elastic and elasto-plastic porous media  

Microsoft Academic Search

This paper revisits the classical problem of excavating a deep cylindrical tunnel in a saturated elastic or elasto-plastic porous ground that obeys Terzaghi's effective stress principle. A generalized form of the classical two-dimensional analytical solution by Lamé for the problem of excavating a cylindrical tunnel in elastic medium subject to axi-symmetric loading is presented. The solution considers the long-term (i.e.,

C. Carranza-Torres; J. Zhao

2009-01-01

8

Parameter sensitivity of anisotropic elasto-plastic shell  

Microsoft Academic Search

1.Abstract A continuum-based design sensitivity analysis (DSA) applied to the thickness design of the anisotropic elasto-plastic shell structures is developed. Since main interest lies in developing path-following algorithms for solving sensitivity problems of elasto-plasticity, such an incremental or a step-by-step formalism will be employed to implementation into the structural analysis program. Because of the response sensitivity at a given time

Sami Holopainen

9

Explicit finite element method for calculation and analysis to the elasto-plastic dynamic response of fluid-saturated porous media  

Microsoft Academic Search

In order to describe the elasto-plastic dynamic response of fluid-saturated porous media, the incremental elasto-plastic wave\\u000a propagation equations of fluid-saturated porous media are developed by the fundamental theory of continuum mechanics and appointing\\u000a to the characteristic of fluid-saturated porous media. Then, the space discretization of these equations is performed to get\\u000a their Galerkin formula. At last, the time discretization of

Liang Li; Xiuli Du; Liyun Li; Chenggang Zhao

2007-01-01

10

Micropillar compression technique applied to micron-scale mudstone elasto-plastic deformation.  

SciTech Connect

Mudstone mechanical testing is often limited by poor core recovery and sample size, preservation and preparation issues, which can lead to sampling bias, damage, and time-dependent effects. A micropillar compression technique, originally developed by Uchic et al. 2004, here is applied to elasto-plastic deformation of small volumes of mudstone, in the range of cubic microns. This study examines behavior of the Gothic shale, the basal unit of the Ismay zone of the Pennsylvanian Paradox Formation and potential shale gas play in southeastern Utah, USA. Precision manufacture of micropillars 5 microns in diameter and 10 microns in length are prepared using an ion-milling method. Characterization of samples is carried out using: dual focused ion - scanning electron beam imaging of nano-scaled pores and distribution of matrix clay and quartz, as well as pore-filling organics; laser scanning confocal (LSCM) 3D imaging of natural fractures; and gas permeability, among other techniques. Compression testing of micropillars under load control is performed using two different nanoindenter techniques. Deformation of 0.5 cm in diameter by 1 cm in length cores is carried out and visualized by a microscope loading stage and laser scanning confocal microscopy. Axisymmetric multistage compression testing and multi-stress path testing is carried out using 2.54 cm plugs. Discussion of results addresses size of representative elementary volumes applicable to continuum-scale mudstone deformation, anisotropy, and size-scale plasticity effects. Other issues include fabrication-induced damage, alignment, and influence of substrate.

Michael, Joseph Richard; Chidsey, Thomas (Utah Geological Survey, Salt Lake City, UT); Heath, Jason E.; Dewers, Thomas A.; Boyce, Brad Lee; Buchheit, Thomas Edward

2010-12-01

11

A constitutive study of thermo-elasto-plasticity of deep carbonatic clays  

NASA Astrophysics Data System (ADS)

Argillaceous masses considered for potential nuclear waste repositories may exhibit significant space variability in their carbonate content. This may affect mechanical clay properties, such as strength or maximum apparent preconsolidation stress known to strongly depend on carbonate content. This paper investigates experimentally the dependence of thermo-hydro-mechanical behaviour of clays on carbonate content. The properties investigated are thermal strains, thermally induced over-consolidation, strength changes, destructuration, and thermally developed water pressure in undrained conditions. The experimental data are analysed in terms of a thermo-elasto-plasticity theory for clays, being an extension of Cam-clay model, modified to include the variability of the carbonatic content.

Hueckel, Tomasz; Pellegrini, Rita; del Olmo, Carlos

1998-07-01

12

Micropillar Compression Technique Applied to Micron-Scale Mudstone Elasto-Plastic Deformation  

NASA Astrophysics Data System (ADS)

Mudstone mechanical testing is often limited by poor core recovery and sample size, preservation and preparation issues, which can lead to sampling bias, damage, and time-dependent effects. A micropillar compression technique, originally developed by Uchic et al. 2004, here is applied to elasto-plastic deformation of small volumes of mudstone, in the range of cubic microns. This study examines behavior of the Gothic shale, the basal unit of the Ismay zone of the Pennsylvanian Paradox Formation and potential shale gas play in southeastern Utah, USA. Precision manufacture of micropillars 5 microns in diameter and 10 microns in length are prepared using an ion-milling method. Characterization of samples is carried out using: dual focused ion - scanning electron beam imaging of nano-scaled pores and distribution of matrix clay and quartz, as well as pore-filling organics; laser scanning confocal (LSCM) 3D imaging of natural fractures; and gas permeability, among other techniques. Compression testing of micropillars under load control is performed using two different nanoindenter techniques. Deformation of 0.5 cm in diameter by 1 cm in length cores is carried out and visualized by a microscope loading stage and laser scanning confocal microscopy. Axisymmetric multistage compression testing and multi-stress path testing is carried out using 2.54 cm plugs. Discussion of results addresses size of representative elementary volumes applicable to continuum-scale mudstone deformation, anisotropy, and size-scale plasticity effects. Other issues include fabrication-induced damage, alignment, and influence of substrate. This work is funded by the US Department of Energy, Office of Basic Energy Sciences. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.

Dewers, T. A.; Boyce, B.; Buchheit, T.; Heath, J. E.; Chidsey, T.; Michael, J.

2010-12-01

13

The method of lines in three-dimensional fracture mechanics  

NASA Technical Reports Server (NTRS)

A review is presented of recent developments in the calculation of design parameters for fracture mechanics by the method of lines (MOL). Three-dimensional elastic and elasto-plastic formulations are examined and results are reported from previous and current research activities. The application of MOL to the appropriate partial differential equations of equilibrium leads to coupled sets of simultaneous ordinary differential equations. Solutions of these equations are obtained by the Peano-Baker and by the recurrence relations methods. The advantages and limitations of both solution methods from the computational standpoint are summarized.

Gyekenyesi, J.; Berke, L.

1980-01-01

14

The method of lines in three dimensional fracture mechanics  

NASA Technical Reports Server (NTRS)

A review of recent developments in the calculation of design parameters for fracture mechanics by the method of lines (MOL) is presented. Three dimensional elastic and elasto-plastic formulations are examined and results from previous and current research activities are reported. The application of MOL to the appropriate partial differential equations of equilibrium leads to coupled sets of simultaneous ordinary differential equations. Solutions of these equations are obtained by the Peano-Baker and by the recurrance relations methods. The advantages and limitations of both solution methods from the computational standpoint are summarized.

Gyekenyesi, J.; Berke, L.

1980-01-01

15

Elasto-plastic model with second order defect density tensor  

NASA Astrophysics Data System (ADS)

The paper deals with a second order finite elasto-plastic model, which involves the defect density tensor, as a measure of the extra material defects existing in the damaged microstructure. The material behaviour is described with respect to an anholonomic configuration, which is introduced through the second order plastic deformation, consisting in plastic distortion and plastic connection. The defect density tensor enters the expression of the plastic connection through its gradient and represents a measure of non-metricity. The constitutive and evolution equations are derived to be compatible with the free energy imbalance. The evolution equation for the defect density tensor is non-local and coupled with the plastic distortion.

Cleja-?igoiu, Sanda

2011-05-01

16

Visco-elasto-plastic rheology effects on free subduction dynamics  

NASA Astrophysics Data System (ADS)

Subduction dynamics on Earth is a typical three dimensional problem. Complex mantle flow can develop around and above the slabs. In addition, the 3D geometry of slabs (curvature, dip angle) evolves with time and can often be quite complicated. This last aspect strongly depends on their rheological properties and on the force balance in the bending region. Therefore understanding how bending processes, in a lithosphere with Earth-like rheology, affect the dynamics of subduction is key to compare numerical results with Earth subduction geometries. Scaling analysis based on 2D visco-elasto-plastic models has shown that one needs to take into account both the elastic and viscous strengths in order to correctly capture the bending effects on sinking velocities and dip angles. But most 3D numerical models developed so far use a visco-plastic rheology for slabs neglecting the role of elasticity in bending. We developed a new technique to model lithosphere-mantle interaction in 3D where lithosphere is a visco-elasto-plastic solid and mantle is a linear viscous fluid. At each iteration, a finite element solver is used to solve for creep in the oceanic plate and compute plate displacements. These displacements are then used as input in a boundary element software to calculate the full mantle circulation. New mantle tractions are then re-injected in the finite element software via a set of dashpots positioned around the oceanic plate. This technique has the advantage to calculate the full mantle drag only on the plate outer surface thus reducing considerably the computational time. We use this coupled approach to investigate the role of plate width and buoyancy on subduction behaviour.

Fourel, L.; Morra, G.; Goes, S.

2012-04-01

17

Thermal elasto-plastic stress analysis during laser heating of a metal plate  

NASA Astrophysics Data System (ADS)

During laser heating of a metal material, the continuity of material confines its free expansion, thermal stresses arise. On one hand the thermal expansion of the heated zone of the material increases with the increase of temperature, the thermal stress level increases correspondingly; on the other hand the mechanical properties of the material will change with the increase of temperature, especially the elastic modulus, yield strength and tensile strength drop significantly, which is the so-called thermal softening problem. Due to the effect of the two factors, as the heating time or the intensity of the laser beam increases, it is possible that the stress levels of the heated zone of the material exceed the yield strength, which leads the material to come into a plastic stage. Thus, a thermal plastic problem occurs. In this study, thermal elasto-plastic stresses during laser heating of a metal plate are computed by the finite element method (FEM) based on thermal elasto-plastic constitutive theory. The mechanical behaviors of the metal material during the laser heating are analyzed. By the analysis of the results, it is found that thermal expansion leads to the increase of stress level early during the laser irradiating, and thermal softening causes the decrease of stress levels in the plastic zone and the slow growth and even decrease of stress levels in elastic zone later. The radial stresses are all compressive stresses, and the hoop stresses are compressive stresses within about the laser spot and are tensile stresses at other place. This work may be beneficial to the laser processing of metal materials.

Chen, Yanbei; Lu, Jian; Ni, Xiaowu

2008-03-01

18

Homogenization of two-phase elasto-plastic composite materials and structures  

Microsoft Academic Search

We develop homogenization schemes and numerical algorithms for two-phase elasto-plastic composite materials and structures. A Hill-type incremental formulation enables the simulation of unloading and cyclic loadings. It also allows to handle any rate-independent model for each phase. We study the crucial issue of tangent operators: elasto-plastic (or “continuum”) versus algorithmic (or “consistent”), and anisotropic versus isotropic. We apply two methods

I. Doghri; A. Ouaar

2003-01-01

19

Elasto-plastic response of reversibly crosslinked biopolymer bundles.  

PubMed

We study the response of F-actin bundles to driving forces through a simple analytical model. We consider two filaments connected by reversibly bound crosslinks and driven by an external force. Two failure modes under load can be defined. Brittle failure is observed when crosslinks suddenly and collectively unbind, leading to catastrophic loss of bundle integrity. During ductile failure, on the other hand, bundle integrity is maintained, however at the cost of crosslink reorganization and defect formation. We present phase diagrams for the onset of failure, highlighting the importance of the crosslink stiffness for these processes. Crossing the phase boundaries, force-deflection curves display (frequency-dependent) hysteresis loops, reflecting the first-order character of the failure processes. We evidence how the introduction of defects can lead to complex elasto-plastic relaxation processes, once the force is switched off. Depending on, both the time-scale for defect motion and the crosslink stiffness, bundles can remain in a quasi-permanent plastically deformed state for a very long time. PMID:24965158

Sadhukhan, Poulomi; Schumann, Ole; Heussinger, Claus

2014-06-01

20

Finite Element Analysis of Elasto-plastic Plate Bending Problems using Transition Rectangular Plate Elements  

NASA Astrophysics Data System (ADS)

In this work, the finite element analysis of the elasto-plastic plate bending problems is carried out using transition rectangular plate elements. The shape functions of the transition plate elements are derived based on a practical rule. The transition plate elements are all quadrilateral and can be used to obtain efficient finite element models using minimum number of elements. The mesh convergence rates of the models including the transition elements are compared with the regular element models. To verify the developed elements, simple tests are demonstrated and various elasto-plastic problems are solved. Their results are compared with ANSYS results.

Kanber, Bahattin; Bozkurt, O. Yavuz

2006-08-01

21

Polycarbonate as an elasto-plastic material model for simulation of the microstructure hot imprint process.  

PubMed

The thermal imprint process of polymer micro-patterning is widely applied in areas such as manufacturing of optical parts, solar energy, bio-mechanical devices and chemical chips. Polycarbonate (PC), as an amorphous polymer, is often used in thermoforming processes because of its good replication characteristics. In order to obtain replicas of the best quality, the imprint parameters (e.g., pressure, temperature, time, etc.) must be determined. Therefore finite element model of the hot imprint process of lamellar periodical microstructure into PC has been created using COMSOL Multiphysics. The mathematical model of the hot imprint process includes three steps: heating, imprinting and demolding. The material properties of amorphous PC strongly depend on the imprint temperature and loading pressure. Polycarbonate was modelled as an elasto-plastic material, since it was analyzed below the glass transition temperature. The hot imprint model was solved using the heat transfer and the solid stress-strain application modes with thermal contact problem between the mold and polycarbonate. It was used for the evaluation of temperature and stress distributions in the polycarbonate during the hot imprint process. The quality of the replica, by means of lands filling ratio, was determined as well. PMID:23974153

Narijauskait?, Birut?; Palevi?ius, Arvydas; Gaidys, Rimvydas; Janušas, Giedrius; Sakalys, Rokas

2013-01-01

22

Polycarbonate as an Elasto-Plastic Material Model for Simulation of the Microstructure Hot Imprint Process  

PubMed Central

The thermal imprint process of polymer micro-patterning is widely applied in areas such as manufacturing of optical parts, solar energy, bio-mechanical devices and chemical chips. Polycarbonate (PC), as an amorphous polymer, is often used in thermoforming processes because of its good replication characteristics. In order to obtain replicas of the best quality, the imprint parameters (e.g., pressure, temperature, time, etc.) must be determined. Therefore finite element model of the hot imprint process of lamellar periodical microstructure into PC has been created using COMSOL Multiphysics. The mathematical model of the hot imprint process includes three steps: heating, imprinting and demolding. The material properties of amorphous PC strongly depend on the imprint temperature and loading pressure. Polycarbonate was modelled as an elasto-plastic material, since it was analyzed below the glass transition temperature. The hot imprint model was solved using the heat transfer and the solid stress-strain application modes with thermal contact problem between the mold and polycarbonate. It was used for the evaluation of temperature and stress distributions in the polycarbonate during the hot imprint process. The quality of the replica, by means of lands filling ratio, was determined as well.

Narijauskaite, Birute; Palevicius, Arvydas; Gaidys, Rimvydas; Janusas, Giedrius; Sakalys, Rokas

2013-01-01

23

Discrete optimal design of elasto-plastic trusses using compliance and stability constraints  

Microsoft Academic Search

In this paper two discrete optimization methods are presented for the minimum volume design of elasto-plastic trusses with given geometry. The design is based on given sets of discrete cross-sectional sizes. Both methods enable the use of the plastic reserve of the truss; the plastic deformations, however, are controlled by compliance constraints on plastic deformations. In the second solution method,

S. Kaliszky; J. Lógó

1998-01-01

24

A semi-smooth Newton method for elasto-plastic contact problems  

Microsoft Academic Search

In this paper we reformulate the frictional contact problem for elasto-plastic bodies as a set of unconstrained, non-smooth equations. The equations are semi-smooth so that Pang's Newton method for B-differentiable equations can be applied. An algorithm based on this method is described in detail. An example demonstrating the efficiency of the algorithm is presented.

Peter W. Christensen

2002-01-01

25

Experimental and numerical investigation of shear strain along an elasto-plastic bonded lap joint  

Microsoft Academic Search

This study investigates the use of an elasto-plastic adhesive in a bonded double lap joint to increase its ultimate capacity. The first section describes the experimental work we performed to characterize the materials and measure the shear strain along the joint. A comparison between an elastic adhesive and a highly plastic adhesive is made and the effect of the type

Sylvain Chataigner; Jean-Francois Caron; Van Anh Duong; Alberto Diaz Diaz

2011-01-01

26

Elasto-plastic analysis of interface layers for fiber reinforced metal matrix composites  

NASA Technical Reports Server (NTRS)

The mismatch in coefficients of thermal expansion (CTE) of fiber and matrix in metal matrix composites reinforced with ceramic fibers induces high thermal stresses in the matrix. Elasto-plastic analyses - with different degrees of simplification and modelization - show that an interface layer with a sufficiently high CTE can reduce the tensile hoop stress in the matrix substantially.

Doghri, I.; Leckie, F. A.

1991-01-01

27

Rate Theory of a Two-Dimensional Elasto-Plastic Continuum.  

National Technical Information Service (NTIS)

An adaption of a three dimensional rate elasto-plastic theory for two dimensional plane domains is proposed. Two basic cases are treated: (1) plane deformation in which no displacement is permitted in the direction perpendicular to the plane of deformatio...

M. Baruch D. Durban

1977-01-01

28

REVERSING CYCLIC ELASTO-PLASTIC DEMANDS ON STRUCTURES DURING STRONG MOTION EARTHQUAKE EXCITATION.  

USGS Publications Warehouse

Using the horizontal components from El Centro 1940, Taft 1952, and 4 accelerograms from the San Fernando earthquake of 2/9/71, the time history of the elasto-plastic displacement response was calculated for oscillators having periods within the range of 1 to 6 s and ductility factors within the range of 3 to 6. The Nth largest peak of the elasto-plastic response (N equals 2,4,8,16), when expressed as a percentage of maximum response (that is, N equals 1), is fairly independent of period within our period range. When considering only plastic peaks occurring, sometimes in a one-directional group of peaks, in the reverse direction from the preceding plastic peak, the amplitude of the Nth reversing plastic peak is similar to the Nth elastic peak, regardless of the ductility factor.

Perez, V.; Brady, A. G.; Safak, E.

1986-01-01

29

An elasto-plastic finite element analysis of the sheet metal stretch flanging process  

Microsoft Academic Search

The incremental updated Lagrangian elasto-plastic finite element method (FEM) was employed in this study to analyse the stretch\\u000a flanging of circular plates with a pre-determined smaller hole at the centre of the sheet metal. An extended r\\u000a min technique was employed such that each incremental step size is determined not only by the yielding of an element Gaussian\\u000a point, but

Yuung-Ming Huang

2007-01-01

30

The complex variable element-free Galerkin (CVEFG) method for elasto-plasticity problems  

Microsoft Academic Search

Based on the complex variable moving least-squares (CVMLS) approximation and element-free Galerkin (EFG) method, the complex variable element-free Galerkin (CVEFG) method for two-dimensional elasto-plasticity problems is presented in this paper. The CVMLS approximation is an approximation method for a vector function. Under the same node distribution the meshless method based on the CVMLS approximation has higher precision than the one

Miaojuan Peng; Dongming Li; Yumin Cheng

2011-01-01

31

Couple stresses and non-Riemannian plastic connection in finite elasto-plasticity  

Microsoft Academic Search

In this paper we propose a macroscopic model for elasto-plastic materials with continuously distributed dislocations. The crystal is not homogeneous and the relaxed state is described by a plastic non-Riemannian metric connection. The dynamic balance equations involve non-symmetric Cauchy stresses and couple stresses. The crystalline body behaves as an elastic material element with respect to the relaxed state. The evolution

S. Cleja-Tigoiu

2002-01-01

32

A finite-strain cam-clay model in the framework of multiplicative elasto-plasticity  

Microsoft Academic Search

The present work discusses a finite-strain plasticity model for soft clays. To motivate such a model, the infinitesimal-strain assumption is shown to be inadequate for the constitutive description of soft clays. Hence, assuming the multiplicative elasto-plastic decomposition of the deformation gradient, a finite-strain Cam-clay model is presented. In particular, with respect to the original Cam-clay formulation, this model improves the

C. Callari; F. Auricchio; E. Sacco

1998-01-01

33

The p-version of the finite element method in incremental elasto-plastic analysis  

NASA Technical Reports Server (NTRS)

Whereas the higher-order versions of the finite elements method (the p- and hp-version) are fairly well established as highly efficient methods for monitoring and controlling the discretization error in linear problems, little has been done to exploit their benefits in elasto-plastic structural analysis. Aspects of incremental elasto-plastic finite element analysis which are particularly amenable to improvements by the p-version is discussed. These theoretical considerations are supported by several numerical experiments. First, an example for which an analytical solution is available is studied. It is demonstrated that the p-version performs very well even in cycles of elasto-plastic loading and unloading, not only as compared to the traditional h-version but also in respect to the exact solution. Finally, an example of considerable practical importance - the analysis of a cold-worked lug - is presented which demonstrates how the modeling tools offered by higher-order finite element techniques can contribute to an improved approximation of practical problems.

Holzer, Stefan M.; Yosibash, Zohar

1993-01-01

34

Orthotropic elasto-plastic behavior of AS4/APC-2 thermoplastic composite in compression  

NASA Technical Reports Server (NTRS)

Uniaxial compression tests were performed on off-axis coupon specimens of unidirectional AS4/APC-2 thermoplastic composite at various temperatures. The elasto-plastic and strength properties of AS4/APC-2 composite were characterized with respect to temperature variation by using a one-parameter orthotropic plasticity model and a one-parameter failure criterion. Experimental results show that the orthotropic plastic behavior can be characterized quite well using the plasticity model, and the matrix-dominant compressive strengths can be predicted very accurately by the one-parameter failure criterion.

Sun, C. T.; Rui, Y.

1989-01-01

35

A numerical model for the thermo-elasto-plastic behaviour of a material  

NASA Technical Reports Server (NTRS)

This paper presents a numerical model for the thermo-elasto-plastic behavior of an isotropic material. The model is based on the assumption that the yielding of the material obeys von Mises distortion energy theory and the material exhibits isotropic strain hardening. This unique model can be used both for isothermal and non-isothermal cases. The original formulation for the non-isothermal three-dimensional case has been specialized for plane stress conditions and the equations for the computation of warping and thickness change are provided. The finite element implementation of this model is also outlined.

Ray, Sujit K.; Utki, Senol

1989-01-01

36

Large strain elasto-plasticity for diffuse interface models  

NASA Astrophysics Data System (ADS)

Most solid-state phase transformations are accompanied by large deformations, stemming either from external load, transformation strains or plasticity. The consideration of such large deformations will affect the numerical treatment of such transformations. In this paper, we present a new scheme to embed large deformations in an explicit phase-field scheme and its implementation in the open-source framework OpenPhase. The suggested scheme combines the advantages of a spectral solver to calculate the mechanical boundary value problem in a small strain limit and an advection procedure to transport field variables over the calculation grid. Since the developed approach should be used for various sets of problems, e.g. simulations of thermodynamically driven phase transformations, the mechanic formulation is kept general. However, to ensure compatibility with phase-field methods using the concept of diffuse interface, the latter is treated with special care in the present work.

Borukhovich, E.; Engels, P. S.; Böhlke, T.; Shchyglo, O.; Steinbach, I.

2014-04-01

37

On the indentation failure of carbon-epoxy cross-ply laminates, and its suppression by elasto-plastic interleaves  

SciTech Connect

Elastic and elasto-plastic modelling of indentation in CFRP cross-ply laminates has been performed. Detailed knowledge of the field solutions in the volume below the indentor forms the basis for the reported micromechanical interpretation of the observed damage in test specimens. The analysis shows that matrix cracks originate at sites of maximum tensile stress perpendicular to fibers. The predicted stress fields due to indentation show that stress concentrations occur in the interface between alternating plies. It is found that microcracking in this zone is a precursor to the observed failure. This analysis is supported by in-situ scanning electron microscopy during loading by a cylindrical indentor onto the laminate supported on a rigid substrate. The microscopy reveals microdamage in the region of interfacial tensile stress concentrations. The onset of indentation failure in these layered composites suggests that plastic interleaves would delay failure. It is shown numerically that plastic deformation of the interleaves redistributes stresses and thereby weakens the tensile stress concentrations which arise during indentation. Experimentally it is shown that aluminium interleaves affect the formation of indentation failure. In a cross-ply laminate, where alternating ply groups are separated by aluminium sheets, matrix cracking and delamination failures are suppressed by the occurrence of plastic deformation. Since the aluminium is likely to be weakly bonded to the plies, it is seen that weak interlaminar fracture toughness does not necessarily cause delaminations, nor lead to a lower indentation strength. High indentation strength and delamination resistance are complex qualities which, among others, seem to be achieved in laminate geometries which have a minimum of stress concentration at interfaces between ply groups of different orientation.

Joergensen, O.; Horsewell, A. [Risoe National Lab., Roskilde (Denmark). Materials Dept.] [Risoe National Lab., Roskilde (Denmark). Materials Dept.

1997-08-01

38

On the symbolic manipulation and code generation for elasto-plastic material matrices  

NASA Technical Reports Server (NTRS)

A computerized procedure for symbolic manipulations and FORTRAN code generation of an elasto-plastic material matrix for finite element applications is presented. Special emphasis is placed on expression simplifications during intermediate derivations, optimal code generation, and interface with the main program. A systematic procedure is outlined to avoid redundant algebraic manipulations. Symbolic expressions of the derived material stiffness matrix are automatically converted to RATFOR code which is then translated into FORTRAN statements through a preprocessor. To minimize the interface problem with the main program, a template file is prepared so that the translated FORTRAN statements can be merged into the file to form a subroutine (or a submodule). Three constitutive models; namely, von Mises plasticity, Drucker-Prager model, and a concrete plasticity model, are used as illustrative examples.

Chang, T. Y.; Saleeb, A. F.; Wang, P. S.; Tan, H. Q.

1991-01-01

39

Elasto-Plastic Analysis of Tee Joints Using HOT-SMAC  

NASA Technical Reports Server (NTRS)

The Higher Order Theory - Structural/Micro Analysis Code (HOT-SMAC) software package is applied to analyze the linearly elastic and elasto-plastic response of adhesively bonded tee joints. Joints of this type are finding an increasing number of applications with the increased use of composite materials within advanced aerospace vehicles, and improved tools for the design and analysis of these joints are needed. The linearly elastic results of the code are validated vs. finite element analysis results from the literature under different loading and boundary conditions, and new results are generated to investigate the inelastic behavior of the tee joint. The comparison with the finite element results indicates that HOT-SMAC is an efficient and accurate alternative to the finite element method and has a great deal of potential as an analysis tool for a wide range of bonded joints.

Arnold, Steve M. (Technical Monitor); Bednarcyk, Brett A.; Yarrington, Phillip W.

2004-01-01

40

Buckling of Plates of Inhomogeneous Material with Elasto-Plastic Deformations (Izgib Plastin iz Neodnorodnogo Materials pri Uprugo-Plasticheskikh Deformatsiyakh).  

National Technical Information Service (NTIS)

The elasto-plastic buckling of rectangular plates made of inhomogeneous material when the modulus of elasticity, or shear modulus, and yield point change through the thickness of the plate, is examined. The elastic solutions method in combination with the...

A. I. Strelbitskaya S. I. Matoshko V. A. Kolgadin

1972-01-01

41

Non-linear elasto-plastic shock wave simulation in high-velocity compaction by discrete element method  

NASA Astrophysics Data System (ADS)

Non-linear elasto-plastic shock waves in particle systems at high-velocity compaction are simulated by the discrete element method. The contact laws applied between the spherical metal particles include non-linear elastic and plastic loading, adhesion and elastic unloading. Of particular interest is to study the transmission and reflection of non-linear shock waves through a particle system with and without voids between the particles. Interesting results are presented in the paper including the particle deformation at incident and reflected shocks and particle velocity oscillations as a result of voids. The study of non-linear elasto-plastic shock waves in particle systems has a strong practical relevance including high-velocity compaction of metal powder.

Shoaib, Muhammad; Kari, Leif

2012-09-01

42

Nonlinear Dynamics and Stability of a Two D.O.F. Elastic\\/ElastoPlastic Model System  

Microsoft Academic Search

The local and global nonlinear dynamics of a two-degree-of-freedom model system is studied. The undeflected model consists\\u000a of an inverted T formed by three rigid bars, with the tips of the two horizontal bars supported on springs. The springs exhibit an elasto-plastic\\u000a response, including the Bauschinger effect. The vertical rigid bar is subjected to a conservative (dead) or non-conservative\\u000a (follower)

S. V. Sorokin; A. V. Terentiev; B. L. Karihaloo

1999-01-01

43

On the predictability of elasto-plastic and geometrically non-linear oscillations of beams under harmonic excitation  

Microsoft Academic Search

Vibrations in one plane of beams with fixed ends, vibrating in the geometrically non-linear and elasto-plastic regimes under\\u000a the influence of harmonic external forces, are studied. A p-version finite element that considers transverse and longitudinal displacements, as well as shear deformation, is employed.\\u000a The incremental theory of plasticity with isotropic hardening is followed. Numerical methods are employed to solve the

P. Ribeiro

44

Elasto-Plastic Constitutive Behavior in Three Lithofacies of the Cambrian Mt. Simon Sandstone, Illinois Basin, USA  

NASA Astrophysics Data System (ADS)

The Mt. Simon Formation, a basal Cambrian sandstone underlying the Illinois Basin in the Central US, is a target for underground storage and waste injection which require an assessment of geomechanical behavior. The range of depositional environments, from braided streams and minor eolean features in the lower Mt Simon, to tidally-influenced near- and on-shore sands in the upper Mt. Simon, yield a heterogeneous formation with a range in porosity, permeability, and mechanical properties. We examine the experimental deformational behavior of three distinct Mt. Simon lithofacies via axisymmetric compressional testing. Initial yielding is confirmed with acoustic emissions in many of the tests and failure envelopes are determined for each lithofacies. The evolution of (assumed) isotropic elastic moduli are examined during testing by use of unload-reload cycles, which permit the separation of total measured strains into elastic and plastic (permanent) strains. The upper Mt Simon samples deform largely elastically at stresses encountered in the Illinois Basin, with very little modulus degradation. The lower Mt. Simon facies are weaker and deform plastically, with varying amounts of modulus degradation. Results are interpreted via petrographic observation of textural contrasts. This range in constitutive response is captured up to failure with a phenomenological elasto-plasticity model. Essential aspects to describe observed behavior used in the model include non-associative plasticity, stress-invariant dependent failure, an elliptical cap surface capturing shear effects on pore collapse, kinematic and isotropic hardening, nonlinear elasticity and elastic-plastic coupling, among other features. Static moduli derived from laboratory tests are compared to dynamic moduli from wellbore log response which can allow experimental results and model to be extrapolated to Mt. Simon occurrences across the basin. This work was funded in part by the Center for Frontiers of Subsurface Energy Security, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001114 and by the Department of Energy Office of Electricity. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Dewers, T.; Newell, P.; Broome, S. T.; Heath, J. E.; Bauer, S. J.

2012-12-01

45

A new uniformly valid asymptotic integration algorithm for elasto-plastic-creep and unified viscoplastic theories including continuum damage  

NASA Technical Reports Server (NTRS)

A new scheme to integrate a system of stiff differential equations for both the elasto-plastic creep and the unified viscoplastic theories is presented. The method has high stability, allows large time increments, and is implicit and iterative. It is suitable for use with continuum damage theories. The scheme was incorporated into MARC, a commercial finite element code through a user subroutine called HYPELA. Results from numerical problems under complex loading histories are presented for both small and large scale analysis. To demonstrate the scheme's accuracy and efficiency, comparisons to a self-adaptive forward Euler method are made.

Chulya, A.; Walker, K. P.

1989-01-01

46

A new uniformly valid asymptotic integration algorithm for elasto-plastic creep and unified viscoplastic theories including continuum damage  

NASA Technical Reports Server (NTRS)

A new scheme to integrate a system of stiff differential equations for both the elasto-plastic creep and the unified viscoplastic theories is presented. The method has high stability, allows large time increments, and is implicit and iterative. It is suitable for use with continuum damage theories. The scheme was incorporated into MARC, a commercial finite element code through a user subroutine called HYPELA. Results from numerical problems under complex loading histories are presented for both small and large scale analysis. To demonstrate the scheme's accuracy and efficiency, comparisons to a self-adaptive forward Euler method are made.

Chulya, Abhisak; Walker, Kevin P.

1991-01-01

47

Dynamic quantized fracture mechanics  

Microsoft Academic Search

A new quantum action-based theory, dynamic quantized fracture mechanics (DQFM), is presented that modifies continuum-based\\u000a dynamic fracture mechanics (DFM). The crack propagation is assumed as quantized in both space and time. The static limit case\\u000a corresponds to quantized fracture mechanics (QFM), that we have recently developed to predict the strength of nanostructures.\\u000a DQFM predicts the well-known forbidden strength and crack

N. M. Pugno; R. S. Ruoff

2006-01-01

48

A general elasto-plastic finite element formulation based on incremental deformation theory for planar anisotropy and its application to sheet metal forming  

Microsoft Academic Search

A new implicit approach for the incremental analysis of planar anisotropic elasto-plastic sheet forming processes was developed based on the incremental deformation theory of plasticity. The incremental deformation theory based on minimum work paths enables convenient decoupling of deformation and rotation by the polar decomposition. The mathematical description of a constitutive law for the incremental deformation theory has been previously

J. W. Yoon; D. Y. Yang; K. Chung; F. Barlat

1999-01-01

49

Full-Field Strain Measurement On Titanium Welds And Local Elasto-Plastic Identification With The Virtual Fields Method  

SciTech Connect

One of the main problems in welding is the microstructural transformation within the area affected by the thermal history. The resulting heterogeneous microstructure within the weld nugget and the heat affected zones is often associated with changes in local material properties. The present work deals with the identification of material parameters governing the elasto--plastic behaviour of the fused and heat affected zones as well as the base material for titanium hybrid welded joints (Ti6Al4V alloy). The material parameters are identified from heterogeneous strain fields with the Virtual Fields Method. This method is based on a relevant use of the principle of virtual work and it has been shown to be useful and much less time consuming than classical finite element model updating approaches applied to similar problems. The paper will present results and discuss the problem of selection of the weld zones for the identification.

Tattoli, F.; Casavola, C. [Dipartimento di Ingegneria Meccanica e Gestionale, Politecnico di Bari, Viale Japigia 182, 70126 Bari (Italy); Pierron, F.; Rotinat, R.; Pappalettere, C. [Ecole Nationale Superieure d'Arts et Metiers, Rue Saint Dominique, BP508, 51006 Chalons en Champagne (France)

2011-01-17

50

A full 3-D material stability analysis of a classical elasto-plastic medium through a linear perturbation approach  

NASA Astrophysics Data System (ADS)

In this paper, the linear perturbation theory is used to study material instability in a classical elasto-plastic model. In this framework, the well known Rice criterion of bifurcation into localized modes is found to be a limiting case corresponding to unbounded growth of perturbation. In the first part, derived expression of the critical plastic modulus is numerically plotted versus the spherical coordinates of the potential normal to the localization band in order to describe the whole space. In the second part, conditions of occurrence of the other types of instability are established, namely divergence and flutter types of instability, and modelling details influencing them checked. These conditions are also relative to the parameter of growth of perturbations which can be plotted versus the plastic modulus considered as the loading parameter. When several modes of instability are possible, an hierarchy is established.

Diouta, N. G.; Shahrour, I.

2006-05-01

51

Elasto-plastic bending of cracked plates, including the effects of crack closure. Ph.D. Thesis  

NASA Technical Reports Server (NTRS)

A capability for solving elasto-plastic plate bending problems is developed using assumptions consistent with Kirchhoff plate theory. Both bending and extensional modes of deformation are admitted with the two modes becoming coupled as yielding proceeds. Equilibrium solutions are obtained numerically by determination of the stationary point of a functional which is analogous to the potential strain energy. The stationary value of the functional for each load increment is efficiently obtained through use of the conjugate gradient. This technique is applied to the problem of a large centrally through cracked plate subject to remote circular bending. Comparison is drawn between two cases of the bending problem. The first neglects the possibility of crack face interference with bending, and the second includes a kinematic prohibition against the crack face from passing through the symmetry plane. Results are reported which isolate the effects of elastoplastic flow and crack closure.

Jones, D. P.

1972-01-01

52

Full-Field Strain Measurement On Titanium Welds And Local Elasto-Plastic Identification With The Virtual Fields Method  

NASA Astrophysics Data System (ADS)

One of the main problems in welding is the microstructural transformation within the area affected by the thermal history. The resulting heterogeneous microstructure within the weld nugget and the heat affected zones is often associated with changes in local material properties. The present work deals with the identification of material parameters governing the elasto-plastic behaviour of the fused and heat affected zones as well as the base material for titanium hybrid welded joints (Ti6Al4V alloy). The material parameters are identified from heterogeneous strain fields with the Virtual Fields Method. This method is based on a relevant use of the principle of virtual work and it has been shown to be useful and much less time consuming than classical finite element model updating approaches applied to similar problems. The paper will present results and discuss the problem of selection of the weld zones for the identification.

Tattoli, F.; Pierron, F.; Rotinat, R.; Casavola, C.; Pappalettere, C.

2011-01-01

53

A finite-element marker-in-cell simulation code for thermo-chemically coupled magma dynamics in a visco-elasto-plastic host rock  

NASA Astrophysics Data System (ADS)

Many prominent geodynamic scenarios such as subduction zones, plate collision and orogeny formation, mid-ocean ridges, continental rifting, etc. involve a significant amount of active magmatism. However, many numerical simulations used to address related questions focus on the deformation of the solid rock phase only, sometimes taking into account the magma dynamics in the form of some parameterized weakening mechanism. On the other hand, simulations specifically developed for magma dynamics problems have largely been restricted to the context of mantle dynamics and are not designed to deal with brittle tectonic deformation of the rock matrix as it occurs in the lithosphere and crust. Here, a 2-D finite-element marker-in-cell numerical method is presented capable of simulating thermally and compositionally coupled two-phase flow problems in a realistically deforming mantle, lithosphere and crust. The modeling approach is based on a set of well accepted equations for the conservation of mass, momentum, energy and composition, completed by constitutive laws for visco-elasto-plastic shear and compaction stresses and a much simplified yet thermodynamically consistent melting model depending on temperature, pressure and composition. The simulation code is written in Matlab and is capable of solving up to 500k degrees of freedom (requiring 2m marker particles) within few minutes per time step on a standard desktop computer. Long-term simulations of that size require run times of one to three weeks. The non-linear system of equations is solved using a Picard iterative scheme, where the linearized system of equations is solved directly during each iterative step. Sufficient convergence is usually obtained within less than 10 non-linear iterations. Generally, this numerical method is versatile, accessible and efficient enough for a wide range of 2-D problems.

Keller, Tobias

2014-05-01

54

Plane elasto-plastic analysis of v-notched plate under bending by boundary integral equation method. Ph.D. Thesis  

NASA Technical Reports Server (NTRS)

A method of solution is presented, which, when applied to the elasto-plastic analysis of plates having a v-notch on one edge and subjected to pure bending, will produce stress and strain fields in much greater detail than presently available. Application of the boundary integral equation method results in two coupled Fredholm-type integral equations, subject to prescribed boundary conditions. These equations are replaced by a system of simultaneous algebraic equations and solved by a successive approximation method employing Prandtl-Reuss incremental plasticity relations. The method is first applied to number of elasto-static problems and the results compared with available solutions. Good agreement is obtained in all cases. The elasto-plastic analysis provides detailed stress and strain distributions for several cases of plates with various notch angles and notch depths. A strain hardening material is assumed and both plane strain and plane stress conditions are considered.

Rzasnicki, W.

1973-01-01

55

The application of the finite element method and the boundary element method to fatigue and fracture, volumes 1 and 2  

NASA Astrophysics Data System (ADS)

This work introduces for the first time the use of the boundary element method for the analysis of cyclic plasticity, high cycle fatigue and low cycle fatigue. Incorporation of several yield criteria and hardening rules into elasto-plastic analysis was carried out such as: Von Mises and Tresca yield criteria, and isotropic, kinematic and mixed hardening rules. An efficient numerical algorithm for the evaluation of the J-integral parameter, based upon boundary and domain discretization was developed. A number of criteria for the estimation of the effect of mean stress on fatigue life, and for the evaluation of equivalent stress measures for multi-axial fatigue, were employed in fatigue analysis. A sophisticated finite element and boundary element programming package called FEBEFAT used for the evaluation of linear elastic fracture mechanics, elasto-plastic fracture mechanics, high cycle fatigue and low cycle fatigue analyses has been developed and tested on VAX mainframe computers, SUN and DIGITAL work stations and on an IBM compatible personal computer. A number of case studies with known solutions have been analyzed and employed for the validation of the developed theory and programming package. It was found that the package provides an efficient and reliable tool for fatigue and fracture analysis.

Hinks, Thomas

56

A finite element formulation for evaluation of crack blunting effects in elasto-plastic solids  

NASA Technical Reports Server (NTRS)

The sharp crack model allows the use of continuum analysis, linear elasticity, as a basic for predicting a micromechanical process, fracture, by providing a characterization of loading conditions affecting a very small volume of material. The model is described in detail.

Osias, J. R.

1975-01-01

57

Fracture Mechanics of Inelastic Polymers.  

National Technical Information Service (NTIS)

The author's Generalized Theory of Fracture Mechanics has been applied to several quite different polymeric materials which have in common a nonlinear and inelastic deformation behaviour. Thus the normal Linear Elastic Fracture Mechanics cannot be applied...

E. H. Andrews

1979-01-01

58

Fracture Mechanics of PGX Graphite.  

National Technical Information Service (NTIS)

Fracture mechanics tests were performed on grade PGX graphite. A compact tension specimen configuration which yields consistent values of the opening mode critical stress intensity factor K/sub IC/, was designed. For the calculation of the fracture toughn...

F. H. Ho R. E. Vollman A. D. Cull

1981-01-01

59

Fracture mechanics validity limits  

NASA Technical Reports Server (NTRS)

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 detail, and then data is presented and the various schemes for establishing a limit of the validity are compared. The selected limiting parameter is applied to a set of fracture data showing the improvement of correlation gained.

Lambert, Dennis M.; Ernst, Hugo A.

1994-01-01

60

The frictional sliding response of elasto-plastic materials in contact with a conical indenter  

Microsoft Academic Search

Over the past decade, many computational studies have explored the mechanics of normal indentation. Quantitative relationships have been well established between the load–displacement hysteresis response and material properties. By contrast, very few studies have investigated broad quantitative aspects of the effects of material properties, especially plastic deformation characteristics, on the frictional sliding response of metals and alloys. The response to

S. Bellemare; M. Dao; S. Suresh

2007-01-01

61

Saturated ElastoPlastic Porous Media under Consideration of Gaseous and Liquid Phase Transitions  

Microsoft Academic Search

Taking a closer look on, e.g., storage processes of greenhouse gases in deep geological aquifers or pressure changes in shear\\u000a bands, the observation can be made that pressure and temperature changes in porous materials can induce phase transition processes\\u000a of the respective pore fluids. For a numerical simulation of this behaviour, a continuum mechanical model based on a multiphasic\\u000a formulation

Wolfgang Ehlers; Tobias Graf

62

Elasto-Plastic Behavior of High RRR Niobium: Effects of Crystallographic Texture, Microstructure and Hydrogen Concentration  

SciTech Connect

Conventional assessments of the mechanical properties of polycrystalline high RRR niobium via tensile testing have revealed unusually low apparent Young's moduli and yield strength in annealed samples. These observations motivated the current investigation of a variety of possible contributors: crystallographic texture, grain size, and impurity concentration. It is shown that the crystallographic textures of a single lot of niobium are essentially unchanged by post-recrystallization anneals at temperatures up to 800 C. Ultrasonic measurements reveal that the elastic response is not degraded by annealing. Rather, the material's extremely low yield point gives the impression of a low elastic modulus during tensile testing.

G.R. Myneni; S.R. Agnew

2002-11-01

63

A Comparison of Mapping Algorithms for Hierarchical Adaptive FEM in Finite Elasto-Plasticity  

NASA Astrophysics Data System (ADS)

The aim of this contribution is a comparison of different mapping techniques usually applied in the field of hierarchical adaptive FE-codes. The calculation of mechanical field variables for the modified mesh is an important but sensitive aspect of adaptation approaches of the spatial discretization. Regarding non-linear boundary value problems procedures of mesh refinement and coarsening imply the determination of strains, stresses and internal variables at the nodes and the Gauss points of new elements based on the transfer of the required data from the former mesh. The kind of mapping of the field variables affects the convergence behaviour as well as the costs of an adaptive FEM-calculation in a non-negligible manner. In order to improve the stability as well as the efficiency of the adaptive process a comparison of different mapping algorithms is presented and evaluated. Within this context, the mapping methods taken into account are -an element-oriented extrapolation procedure using special shape functions, -a patch-oriented transfer approach and, -the allocation of nodal history-dependent state (field) variable data using a supplementary integration of the material law at the nodes of the elements.

Bucher, A.; Meyer, A.; Görke, U.-J.; Kreißig, R.

2007-03-01

64

Two-temperature hydrodynamics of laser-generated ultrashort shock waves in elasto-plastic solids  

NASA Astrophysics Data System (ADS)

Shock-wave generation by ultrashort laser pulses opens new doors for study of hidden processes in materials happened at an atomic-scale spatiotemporal scales. The poorly explored mechanism of shock generation is started from a short-living two-temperature (2T) state of solid in a thin surface layer where laser energy is deposited. Such 2T state represents a highly non-equilibrium warm dense matter having cold ions and hot electrons with temperatures of 1-2 orders of magnitude higher than the melting point. Here for the first time we present results obtained by our new hybrid hydrodynamics code combining detailed description of 2T states with a model of elasticity together with a wide-range equation of state of solid. New hydro-code has higher accuracy in the 2T stage than molecular dynamics method, because it includes electron related phenomena including thermal conduction, electron-ion collisions and energy transfer, and electron pressure. From the other hand the new code significantly improves our previous version of 2T hydrodynamics model, because now it is capable of reproducing the elastic compression waves, which may have an imprint of supersonic melting like as in MD simulations. With help of the new code we have solved a difficult problem of thermal and dynamic coupling of a molten layer with an uniaxially compressed elastic solid. This approach allows us to describe the recent femtosecond laser experiments.

Ilnitsky, Denis K.; Khokhlov, Viktor A.; Inogamov, Nail A.; Zhakhovsky, Vasily V.; Petrov, Yurii V.; Khishchenko, Konstantin V.; Migdal, Kirill P.; Anisimov, Sergey I.

2014-05-01

65

Modeling of the thermal elasto-plastic behavior for composite materials using the homogenization method  

SciTech Connect

In this dissertation, the homogenization method is used to investigate the thermo-mechanical behavior of composite materials. Assuming the characteristic microstructure in a composite material is spatially repeating, the equivalent material properties in one unit cell are calculated. These equivalent material properties represent the microscopic information. Using this approach, three research topics, in particular, stationary heat conduction, thermoelasticity and thermal elastoplasticity in composite materials are studied in order to determine the global behavior and the local response at the microscopic level. For heat conduction in composite materials, the well-known homogenization method is used to solve for the homogenized conductivity and the local heat flux field. Two boundary value problems, one, a local problem, the other, a global problem, are derived in order to obtain the characteristic temperature field in the microstructure and the equivalent thermal conductivity. Overall and local thermal response of the composite material is then determined. This rigorous method is extended to inquire into the stress mismatch in the microstructure and the effective stress field in macrostructure for the thermal stresses in composites. The global thermal expansion behavior as well as the microscopic thermal stress analysis is studied theoretically by employing the homogenization method. It is found that this method provides good results in comparison with other analytical theories. From the examples, it is interesting to note that the thermal effect causes severe stress concentrations at the interface between the constituents, due to the mismatch in their thermal expansion coefficients. The homogenization method is not limited by its assumption of periodicity in the microstructure. It can be used to deal with both geometrically and materially nonlinear problems such as thermal elastoplasticity in composite materials.

Cheng, Chaohsien.

1992-01-01

66

PLAN2D - A PROGRAM FOR ELASTO-PLASTIC ANALYSIS OF PLANAR FRAMES  

NASA Technical Reports Server (NTRS)

PLAN2D is a FORTRAN computer program for the plastic analysis of planar rigid frame structures. Given a structure and loading pattern as input, PLAN2D calculates the ultimate load that the structure can sustain before collapse. Element moments and plastic hinge rotations are calculated for the ultimate load. The location of hinges required for a collapse mechanism to form are also determined. The program proceeds in an iterative series of linear elastic analyses. After each iteration the resulting elastic moments in each member are compared to the reserve plastic moment capacity of that member. The member or members that have moments closest to their reserve capacity will determine the minimum load factor and the site where the next hinge is to be inserted. Next, hinges are inserted and the structural stiffness matrix is reformulated. This cycle is repeated until the structure becomes unstable. At this point the ultimate collapse load is calculated by accumulating the minimum load factor from each previous iteration and multiplying them by the original input loads. PLAN2D is based on the program STAN, originally written by Dr. E.L. Wilson at U.C. Berkeley. PLAN2D has several limitations: 1) Although PLAN2D will detect unloading of hinges it does not contain the capability to remove hinges; 2) PLAN2D does not allow the user to input different positive and negative moment capacities and 3) PLAN2D does not consider the interaction between axial and plastic moment capacity. Axial yielding and buckling is ignored as is the reduction in moment capacity due to axial load. PLAN2D is written in FORTRAN and is machine independent. It has been tested on an IBM PC and a DEC MicroVAX. The program was developed in 1988.

Lawrence, C.

1994-01-01

67

Second variation of energy and an associated line independent integral in fracture mechanics. I - Theory  

NASA Astrophysics Data System (ADS)

The perturbation domain technique (or interior variation technique), Murat and Simon (1974) was originally developed to assess the variation of an arbitrary stress, strain and displacement functional prescribed over a given bounded domain when a specified variable (geometrical or non) is changed. Using this technique, an analytical expression for the second derivative of energy with respect to crack length is derived. The formulation is valid for a system of interacting cracks in general 3D fracture behavior including non-planar fracture and shear lips. In a special case, the resulting expression for the second energy variation is shown to be equivalent in plane strain or stress fields to Nguyen and Stolz's line integral (1986) which has the same value for all paths surrounding crack tip in an elastic or deformation type elasto-plastic material.

Suo, Xiao Z.; Combescure, A.

68

On the plumbing system of volcanic complexes: field constraints from the Isle of Skye (UK) and FEM elasto-plastic modelling including gravity and tectonics.  

NASA Astrophysics Data System (ADS)

The plumbing system that connects a sub-volcanic magma reservoir to the surface has been the object of field characterization and mechanical modelling efforts since the pioneering work by Anderson (1936), who produced a detailed account of the spectacular Cullin Cone-sheet Complex (Isle of Skye, UK) and a geometrical and mechanical model aimed at defining the depth to the magma chamber. Since this work, the definition of the stress state in the half space comprised between the magma reservoir and the surface (modelled either as a flat surface or a surface comprising a volcanic edifice) was considered the key point in reconstructing dike propagation paths from the magma chamber. In fact, this process is generally seen as the propagation in an elastic media of purely tensional joints (mode I or opening mode propagation), which follow trajectories perpendicular to the least compressive principal stress axis. Later works generally used different continuum mechanics methodologies (analytic, BEM, FEM) to solve the problem of a pressure source (the magma chamber, either a point source or a finite volume) in an elastic (in some cases heterogeneous) half space (bounded by a flat topography or topped by a "volcano"). All these models (with a few limited exceptions) disregard the effect of the regional stress field, which is caused by tectonic boundary forces and gravitational body load, and consider only the pressure source represented by the magma chamber (review in Gudmundsson, 2006). However, this is only a (sometimes subordinate) component of the total stress field. Grosfils (2007) first introduced the gravitational load (but not tectonic stresses) in an elastic model solved with FEM in a 2D axisymmetric half-space, showing that "failure to incorporate gravitational loading correctly" affect the calculated stress pattern and many of the predictions that can be drawn from the models. In this contribution we report on modelling results that include: 2D axisymmetric or true 3D geometry; gravitational body load; anisotropic tectonic stresses; different shapes and depths of the magma chamber; different overpressure levels in the magma chamber; different shapes of the topographic surface (e.g. flat, volcano, caldera); linear-elastic or elasto-plastic Drucker-Prager rheology. The latter point, which in our opinion constitutes a fundamental improvement in the model, has proven necessary because in a purely elastic model the stress state would rise at levels that cannot be sustained by geologic materials. Particularly around and above the magma chamber, yielding is expected, influencing the stress field in the remaining modelling domain. The non-linear problem has been solved with the commercial finite element package Comsol Multiphysics, using a parametric solver. At the same time, a field structural analysis of the classical Cuillin Cone-sheet Complex has been performed. This analysis has shown that four distinct families of cone sheets of different age do exist. Among these, the sheets with the higher dip angle range (80-65°) are confirmed as purely tensional joints, but those with a lower dip angle range (60-40°) are quite often (when suitable markers are available) associated with a measurable shear component. Combining these new field observations with mechanical modelling results, we propose a new interpretation for the Cuillin Cone Sheet Complex. The plumbing system was composed by both purely tensional joints and mesoscopic faults with a shear component, produced in response to the regional stress field perturbed by the magma chamber, and later passively re-used as magma emplacement conduits. Under this assumption, the observed geometry of the Cuillin Cone-sheet Complex is consistent with a relatively shallow magma chamber with a flattened laccolite shape. The shape of the palaeotopography, now completely eroded, has also been considered, but is more weakly constrained by modelling results. References: Anderson E.M., 1936. The dynamics of the formation of cone-sheets, ring-dykes and cauldron subsidences.

Bistacchi, A.; Pisterna, R.; Romano, V.; Rust, D.; Tibaldi, A.

2009-04-01

69

Dynamic fracture mechanics  

NASA Technical Reports Server (NTRS)

Dynamic fracture and crack propagation concepts for ductile materials are reviewed. The equations for calculating dynamic stress integrity and the dynamic energy release rate in order to study dynamic crack propagation are provided. The stress intensity factor versus crack velocity relation is investigated. The uses of optical experimental techniques and finite element methods for fracture analyses are described. The fracture criteria for a rapidly propagating crack under mixed mode conditions are discussed; crack extension and fracture criteria under combined tension and shear loading are based on maximum circumferential stress or energy criteria such as strain energy density. The development and use of a Dugdale model and finite element models to represent crack and fracture dynamics are examined.

Kobayashi, A. S.; Ramulu, M.

1985-01-01

70

Fracture mechanics of PGX graphite  

Microsoft Academic Search

Fracture mechanics tests were performed on grade PGX graphite. A compact tension specimen configuration which yields consistent values of the opening mode critical stress intensity factor K\\/sub IC\\/, was designed. For the calculation of the fracture toughness and crack growth rate the concept of the effective crack length is used. It corresponds to the crack length of a machined notched

F. H. Ho; R. E. Vollman; A. D. Cull

1981-01-01

71

Fracture Mechanics and Ambient Temperature Sustained Load Fracture.  

National Technical Information Service (NTIS)

A generalized discussion of the phenomenological dependance of ambient temperature sustained load fracture on fracture mechanics parameters is presented. The practical interpretation and application of this analysis technique during structural materials s...

R. J. H. Wanhill H. P. Vanleeuwen

1978-01-01

72

Fracture mechanics of cellular glass  

NASA Technical Reports Server (NTRS)

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.

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

1981-01-01

73

Fracture mechanics and corrosion fatigue.  

NASA Technical Reports Server (NTRS)

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.

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

1972-01-01

74

Fracture mechanics of PGX graphite  

SciTech Connect

Fracture mechanics tests were performed on grade PGX graphite. A compact tension specimen configuration which yields consistent values of the opening mode critical stress intensity factor K/sub IC/, was designed. For the calculation of the fracture toughness and crack growth rate the concept of the effective crack length is used. It corresponds to the crack length of a machined notched specimen with the same compliance. Fracture toughness testing was performed in two environments, air and helium, both at room temperature. The critical stress intensity factor, K/sub IC/, is calculated based on the maximum load and the effective crack length. The fatigue crack growth test was performed in air only. A break-in period was observed for the machined notch to develop into a naturally occurring crack path. Half of the fatigue life was spent in this period.

Ho, F.H.; Vollman, R.E.; Cull, A.D.

1981-03-01

75

HFIR vessel probabilistic fracture mechanics analysis.  

National Technical Information Service (NTIS)

The life of the High Flux Isotope Reactor (HFIR) pressure vessel is limited by a radiation induced reduction in the material's fracture toughness. Hydrostatic proof testing and probabilistic fracture mechanics analyses are being used to meet the intent of...

R. D. Cheverton T. L. Dickson

1997-01-01

76

(Fracture mechanics of inhomogeneous materials)  

SciTech Connect

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.

Bass, B.R.

1990-10-01

77

Compendium of fracture mechanics problems  

NASA Technical Reports Server (NTRS)

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.

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

1990-01-01

78

Strength and elasto-plastic properties of non-industrial building materials manufactured with clay as a natural binder  

Microsoft Academic Search

The objective of this article is to study the mechanical performances of non-industrial materials made with soils containing argillaceous minerals as the sole binder (materials referred to as earthen). The renewed interest in earthen construction requires, in the current context, a scientific approach to these materials and a re-examination of certain techniques such as that of adobes. These adobes are

C. H. Kouakou; J. C. Morel

2009-01-01

79

Entablature: fracture types and mechanisms  

NASA Astrophysics Data System (ADS)

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.

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

2014-05-01

80

Fracture mechanics applied to superphenix reactor components  

Microsoft Academic Search

The main aspects of fracture mechanics applications to superphenix reactor components are presented. After recalling the hypotheses concerning the cracks to be considered, the material characteristics and loading, the areas of application of fracture mechanics are shown. These are essentially the assistance in the definition of an in-service inspection programme, the demonstration of acceptance of existing defects, and the explanation

M. Sperandio

1996-01-01

81

Fracture mechanism maps for advanced structural ceramics  

Microsoft Academic Search

The static fatigue behaviour of advanced structural ceramics can be controlled by a variety of failure mechanisms. A fracture mechanism map can define the stress-temperature regimes where the different mechanisms are dominant. The static fatigue resistance of a hot-pressed silicon nitride with magnesia sintering aid is limited by slow crack growth or creep fracture depending upon the specific stress-temperature conditions.

G. D. Quinn

1990-01-01

82

Fracture mechanics of functionally graded materials  

Microsoft Academic Search

In this paper, after a brief discussion of the elementary concepts of fracture mechanics in nonhomogeneous materials, a number of typical problem areas relating to the fracture of functionally gradient materials (FGMs) are identified. The main topics considered are the investigation of the nature of stress singularity near the tip of a crack fully embedded in a nonhomogeneous medium, the

F. Erdogan

1995-01-01

83

Mechanisms for shrinkage fracturing at Meridiani Planum  

NASA Astrophysics Data System (ADS)

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.

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

2009-12-01

84

Fracture Mechanics Applications in Rock-Mechanics Problems.  

National Technical Information Service (NTIS)

The application of fracture mechanics principles to the solution of rock-mechanics problems is discussed. Specifically, two examples relating to high-energy gas fracturing and oil-shale blasting are presented to illustrate the point. In high-energy gas fr...

E. P. Chen

1983-01-01

85

Fracture-mechanics studies of cementitious composites  

SciTech Connect

Attempts have been made to apply fracture mechanics to concrete. However, the experimentally observed fracture parameters for concrete were found to be dependent on specimen size. This thesis first addresses studies of size effect on fracture parameters. Following the size-effect studies, applications of the fracture mechanics to concrete and steel-fiber-reinforced concrete are developed. An experimental program is first designed to investigate the factors that cause the size-effect on the fracture parameters used for concrete. The fracture parameters studied are critical stress intensity factor, critical strain energy release rate, critical crack tip opening displacement and fracture energy. The pre-critical stable crack growth is found to be the major factor that causes the size effect on the conventional critical stress intensity factor. Based on the observation of experimental results, the critical stress intensity factor and critical crack-tip opening displacement are proposed as the two basic fracture parameters. A theoretical model is developed for steel-fiber-reinforced concrete. Based on the studies of plain concrete, the contribution of the matrix in steel-fiber-reinforced concrete can be characterized using the proposed model.

Jenq, Y.S.

1987-01-01

86

A Hierarchical Approach to Fracture Mechanics  

NASA Technical Reports Server (NTRS)

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.

Saether, Erik; Taasan, Shlomo

2004-01-01

87

Biomechanical analysis of fracture risk associated with tibia deformity in children with osteogenesis imperfecta: a finite element analysis.  

PubMed

Objectives: Osteogenesis imperfecta (OI) frequently leads to long-bone bowing requiring a surgical intervention in severe cases to avoid subsequent fractures. However, there are no objective criteria to decide when to perform such intervention. The objective is to develop a finite element model to predict the risk of tibial fracture associated with tibia deformity in patients with OI. Methods: A comprehensive FE model of the tibia was adapted to match bi-planar radiographs of a 7 year-old girl with OI. Ten additional models with different deformed geometries (from 2° to 24°) were created and the elasto-plastic mechanical properties were adapted to reflect OI conditions. Loads were obtained from mechanography of two-legged hopping. Two additional impact cases (lateral and torsion) were also simulated. Principal strain levels were used to define a risk criterion. Results: Fracture risks for the two-legged hopping load case remained low and constant until tibia bowing reached 15° and 16° in sagittal and coronal planes respectively. Fracture risks for lateral and torsion impact were equivalent whatever the level of tibial bowing. Conclusions: The finite element model of OI tibia provides an objective means of assessing the necessity of surgical intervention for a given level of tibia bowing in OI-affected children. PMID:24879024

Caouette, C; Rauch, F; Villemure, I; Arnoux, P-J; Gdalevitch, M; Veilleux, L-N; Heng, J L; Aubin, C-E

2014-06-01

88

Fracture Mechanics of Rubber Epoxy Composites  

NASA Astrophysics Data System (ADS)

The effect of the addition of rubber micro-particles to epoxy matrix on the mechanical properties and the fracture toughness were investigated. Rubber epoxy composites were prepared with different weight percentages namely, 0, 5, 10, 15, 20, 25, 30 wt pct of rubber. Both quasi-static and dynamic ultrasonic measurements of the elastic modulus were found to decrease by 60 pct, and the critical value of the stress intensity factors was found to increase by approximately 45 pct for the rubber epoxy composites. This was also confirmed with the finite element analysis that had the same increasing trend. The fracture surface morphology reveals rough cleavage fracture in the epoxy matrix with brittle intergranular decohesion caused by the impurity segregation that exhibits relatively high micro-roughness of the fracture surfaces.

El-Hadek, Medhat Awad

2014-05-01

89

Fracture mechanics parameters of autoclaved aerated concrete  

Microsoft Academic Search

The influence of the expanding direction of Autoclaved Aerated Concrete (AAC) on the nonlinear fracture mechanics parameters is determined on three different types of AAC. The nonlinear fictitious crack model introduced by Hillerborg et al. [1] is used. Based on the RILEM recommendation AAC 13.1 [2], wedge-splitting tests have been carried out on three different types of AAC. For each

B. Trunk; G. Schober; A. K. Helbling; F. H. Wittmann

1999-01-01

90

Adsorption Effect in Corrosion Fracture Mechanics  

Microsoft Academic Search

We analyze the well-known works devoted to the adsorption lowering of crack growth resistance in metals and alloys as a component of the general Karpenko theory on the role of adsorption in physicochemical fracture mechanics. We consider the cases of static and cyclic loading, and short- and long-term crack resistance of steels in liquid and gaseous media. Special attention is

O. M. Romaniv; H. M. Nykyforchyn

2005-01-01

91

A review of fracture mechanics life technology  

NASA Technical Reports Server (NTRS)

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.

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

1986-01-01

92

Pseudopillow fracture systems in lavas: Insights into cooling mechanisms and environments from lava flow fractures  

NASA Astrophysics Data System (ADS)

Detailed field observations of structures within the flow front of a Holocene trachyandesite lava from Snæfellsnes, Iceland, are presented. The lava provides exceptional three-dimensional exposure of complex brittle and ductile deformation textures that record processes of lava fracture and quenching driven by external water. The flow front interior is characterised by structures consisting of a large (metre-scale) curviplanar master fracture with many smaller (centimetre-scale) subsidiary fractures perpendicular to the master fracture. Such structures have previously been recognised in a range of lava compositions from basalt to dacite and called pseudopillows or pseudopillow fractures. We propose the term pseudopillow fracture systems to emphasise the consistent package of different fracture types occurring together. All documented occurrences of pseudopillow fracture systems are in lavas that have been inferred to interact with an aqueous coolant (i.e. liquid water, ice or snow). We use fracture surface textures and their orientation in relation to flow banding to identify three distinct types of master fracture and two types of subsidiary fractures. Master fracture surface textures used to identify fracture mechanisms include chisel marks (striae), cavitation dimples, river lines and rough/smooth fracture surface textures. These indicate both brittle and ductile fracture happening on different types of master fracture. Chisel marks on subsidiary fractures indicate comparative cooling rates, cooling directions and isotherm orientations at the time of fracture. We propose a model for pseudopillow fracture system formation taking into account all the various fracture types, textures and fracture propagation mechanisms and discuss their implications for interaction mechanisms between lava flows and external coolants.

Forbes, A. E. S.; Blake, S.; McGarvie, D. W.; Tuffen, H.

2012-11-01

93

Fracture Mechanics for Delamination Problems in Composite Materials  

Microsoft Academic Search

A fracture mechanics approach to the well-known delamination problem in com posite materials is presented. Based on the theory of anisotropic laminate elasticity and interlaminar fracture mechanics concepts, the composite delamination problem is for mulated 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

S. S. Wang

1983-01-01

94

Pseudopillow fracture systems: Insights into cooling mechanisms and environments from lava flow fractures  

NASA Astrophysics Data System (ADS)

We present field observations of lava flow structures within the remarkably well-exposed flow front of a flow-banded trachyandesite lava at Djúpalón on the coast of the Snæfellsnes peninsula, west Iceland. New discoveries from this lava flow reveal additional scales of complexity in pseudopillow fractures and give an enhanced understanding of these fracture systems and their association with particular environments containing water, ice or snow. The flow interior is characterised by large curviplanar master fractures with many smaller subsidiary fractures perpendicular to them. Such structures have previously been called pseudopillows or pseudopillow fractures. They have been recognised in a range of lava compositions from basalt to rhyolite. We propose the term pseudopillow fracture systems to emphasise the consistent package of different fracture types that occur together. All documented occurrences of these fracture systems are in lavas that have interacted with some type of an additional coolant (i.e. water, ice, snow). Thusfar little has been understood about the formation mechanisms of these fractures and the reason for their association with particular environments. We identify three distinct types of master fracture on the basis of their fracture surface texture (fractography) and orientation in relation to flow banding; and two different types of subsidiary fractures based on their shape. Surface features used to identify fracture mechanisms include straight and curved chisel marks (or striae), cavitation dimples, river lines and rough and smooth fracture surface textures. Using these fracture surface features we infer that master fractures can form by both brittle and ductile fracture, whereas subsidiary fractures only form by brittle fracture. Glass very commonly occurs in association with pseudopillow fracture systems in the Djúpalón lava flow, providing evidence of rapid cooling during their formation.

Forbes, A.; Blake, S.; McGarvie, D.; Tuffen, H.

2012-04-01

95

Bedrock stresses and extensional fracture development within an evolving Alpine landscape  

NASA Astrophysics Data System (ADS)

This study focuses on clarifying the effects of repeated glacial/interglacial cycles on the geomorphic evolution of a major Alpine valley within the southern Swiss Alps (in the region of Zermatt). We find that high erosion rates associated with the development of the Alpine landscape are likely to have induced an elastic response in exhuming bedrock that led to the generation of near-surface stresses in excess of both regional tectonic and topographic stress. Analysis using 1-D and 2-D elasto-plastic numerical models allows us to assess the development and distribution of stresses within a range of tectonic and topographic conditions, and yields results consistent with both Alpine in situ stress measurements and a global comparison of near-surface stresses with local bedrock strengths. Our 2-D model differs markedly from previous studies of topographic stress, which generally ignore the effects of endogenic and exogenic processes, and limitations resulting from long-term brittle rock behaviour. The model allows us to assess particular fracture mechanisms that lead to the development of micro- and macroscopic fractures in association with Alpine glaciation (including, but not limited to, sheeting joints in cratonic shield regions and exfoliation fractures in formerly glaciated areas). Predicted macroscopic fracture distributions within our assumed pre-glacial landscape correspond to the location of the present-day inner U-shaped valley trough in our study region. When combined with supporting sedimentary evidence from the periphery of the Alps, we propose a mechanism in which sub-glacial fracturing of intact bedrock during early glacial cycles significantly enhanced glacial erosion within this critically-stressed region, leading to the rapid erosion of the spectacular U-shaped Alpine valley.

Leith, Kerry; Moore, Jeffrey; Amann, Florian; Loew, Simon

2013-04-01

96

Mechanical Behavior of Carbide-free Medium Carbon Bainitic Steels  

NASA Astrophysics Data System (ADS)

The effect of bainitic transformation time on the microstructure and mechanical properties was investigated in a steel containing 0.4 pct C-2.8 pct Mn-1.8 pct Si. The microstructure was characterized using optical and transmission electron microscopy; it consisted of bainitic ferrite, martensite, and retained austenite. The volume fraction of bainite increased from 0.4 for the shortest bainitic transformation time (30 minutes) to 0.9 at the longest time (120 minutes). The above microstructures exhibited an extended elasto-plastic transition leading to very high initial work-hardening rates. The work-hardening behavior was investigated in detail using strain-path reversals to measure the back stresses. These measurements point to a substantial kinematic hardening due to the mechanical contrast between the microstructural constituents. The onset of necking coincided with the saturation of kinematic hardening. Examination of the fracture surfaces indicated that the prior austenite grain boundaries play an important role in the fracture process.

Zhang, Xiaoxu; Xu, Guang; Wang, Xiang; Embury, David; Bouaziz, Olivier; Purdy, Gary R.; Zurob, Hatem S.

2013-11-01

97

Analogy between fluid cavitation and fracture mechanics  

NASA Technical Reports Server (NTRS)

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.

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

1983-01-01

98

Pelvic crescent fractures: variations in injury mechanism and radiographic pattern.  

PubMed

Pelvic crescent fracture, also known as sacroiliac fracture-dislocation, is traditionally considered as a lateral compression injury and a vertically stable injury. Thirty consecutive cases were analyzed and it was found that 63% of cases were caused by lateral compression (LC), 27% by anteroposterior compression (APC), and 10% by vertical shear (VS). APC and VS injuries cause significant displacement of the anterior iliac fragment, but 21% of LC injury cases showed minimal displacement and were treated successfully with nonoperative treatment. Different injury mechanisms also produce different types of pelvic instability. More important, different injury mechanisms produce distinct radiographic fracture patterns regarding the obliquity of the fracture line and fracture surface. These differences in the fracture pattern will influence the decision of internal fixation options. Therefore, treatment of pelvic crescent fractures should be based on individual analysis of injury mechanism and radiographic fracture pattern. PMID:24875337

Gehlert, Rick J; Xing, Zhiqing; DeCoster, Thomas A

2014-01-01

99

Fracture of Sn-Ag-Cu Solder Joints on Cu Substrates. II: Fracture Mechanism Map  

NASA Astrophysics Data System (ADS)

A methodology to construct fracture mechanism maps for Sn-3.8%Ag-0.7%Cu (SAC387) solder joints attached to Cu substrates has been developed. The map, which delineates the operative mechanisms of fracture along with corresponding joint fracture toughness values, is plotted in a space described by two microstructure-dependent parameters, with the abscissa describing the interfacial intermetallic compound (IMC) and the ordinate representing the strain-rate-dependent solder yield strength. The plot space encompasses the three major mechanisms by which joints fail, namely (i) cohesive fracture of solder, (ii) cleavage fracture of interfacial intermetallic compounds (IMC), and (iii) fracture of the solder-IMC interface. Line contours of constant fracture toughness values, as well as constant fraction of each of the above mechanisms, are indicated on the plots. The plots are generated by experimentally quantifying the dependence of the operative fracture mechanism(s) on the two microstructure-dependent parameters (IMC geometry and solder yield strength) as functions of strain rate, reflow parameters, and post-reflow aging. Separate maps are presented for nominally mode I and equi-mixed mode loading conditions (loading angle ? = 0° and 45°, respectively). The maps allow rapid assessment of the operative fracture mechanism(s) along with estimation of the expected joint fracture toughness value for a given loading condition (strain rate and loading angle) and joint microstructure without conducting actual tests, and may serve as a tool for both prediction and microstructure design.

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

2012-02-01

100

References and conference proceedings towards the understanding of fracture mechanics  

NASA Technical Reports Server (NTRS)

A list of books, reports, periodicals, and conference proceedings, as well as individual papers, centered on specific aspects of fracture phenomenon has been compiled by the ASTM Committee E-24 on Fracture Testing. A list of basic references includes the articles on the development of fracture toughness, evaluation of stress intensity factors, fatigue crack growth, fracture testing, fracture of brittle materials, and fractography. Special attention is given to the references on application of fracture mechanics to new designs and on reevaluation of failed designs, many of them concerned with naval and aircraft structures.

Toor, P. M.; Hudson, C. M.

1986-01-01

101

Some Actual Problems of Fracture Mechanics of Materials and Structures  

Microsoft Academic Search

\\u000a Some theoretical and experimental results on fracture mechanics of materials and durability of structural elements are presented.\\u000a Conceptual bases (statements) of fracture mechanics and strength of cracked materials as well as urgent problems of prospective\\u000a investigations in this field of science about materials and their strength are formulated. The actual problems of fracture\\u000a mechanics and strength of materials in service

Volodymyr Panasyuk; Ihor Dmytrakh

102

Computational methods for creep fracture analysis by damage mechanics  

Microsoft Academic Search

Some mechanical problems of the computational method of creep fracture analysis based on continuum damage mechanics are discussed. After brief review of the local approach to creep crack growth analysis by means of finite element analysis and continuum damage mechanics, intrinsic feature of the fracture analysis in the framework of continuum theory and the causes of mesh-dependence of the numerical

S. Murakami; Y. Liu; M. Mizuno

2000-01-01

103

Mechanism of diffusion-controlled brittle fracture  

SciTech Connect

Two generation of UHV testing systems were developed, one for testing pre-cracked specimens at constant displacement and the other at constant load, and they were supplemented by a computer-controlled potential-drop system for measurement of crack-growth rates. The latter system was also developed during this project. Experiments were carried out on the alloy Cu-8%Sn which was used as a model system for the phenomenon of diffusion-controlled fracture by intergranular decohesion resulting from the ingress of an embrittling element from a free surface as the result of an applied stress. The cracking phenomenon found earlier in alloy steels, and shown to be due to surface-adsorbed sulfur, was reproduced in the Cu-Sn alloy. This provided verification of the earlier proposed mechanism for the cracking phenomenon in the alloy steels, known as stress-relief cracking, and it also provided support for the hypothesis that the phenomenon was of a generic nature. In conjunction with the experimental work, the development of a quantitative theory of this class of brittle fracture, which we have termed dynamic embrittlement,'' was begun.

McMahon, C.J.

1991-10-01

104

Atomic Crack Simulation in Fracture Mechanics.  

National Technical Information Service (NTIS)

Using computer simulation, the authors have attempted to relate the macroscopic fracture properties of bcc iron to phenomena on the atomic scale. Although bonds can be made to rupture in the computer model (brittle fracture), the predicted cleavage plane ...

P. C. Gehlen G. T. Hahn M. F. Kanninen

1974-01-01

105

A mesh-free approach to numerical rock mechanics simulations  

NASA Astrophysics Data System (ADS)

Numerical simulation of the nucleation, growth, and coalescence of fracture networks is a fundamental aspect of lithospheric geodynamics and engineering applications such as enhanced geothermal systems, hydraulic fracturing and CO2 sequestration. Modeling the underlying mechanics is challenging because of several numerical difficulties. In particular, fracture path evolution predicted by mesh-based models can be heavily affected by numerical resolution of the chosen discretization scheme. Additionally, large deformations can lead to numerical errors associated with highly deformed elements. We are developing algorithms that simulate fracture nucleation and growth using mesh-free methods that overcome the difficulties arising from the mesh-sensitivity of conventional mesh-based methods. We implemented a mesh-free local Petrov-Galerkin method (MLPG), which is based on the local weak form of the problem under consideration. This method requires no mesh for interpolation or integration, and thus may be well-suited to handle strain localization occurring during fracture development. Interpolation is performed using moving least squares approximation (MLS) shape functions, and since nodal integration is performed locally, this approach can be parallelized efficiently. We present a mesh-free 2D elasto-plastic model for geomaterials that includes frictional hardening and cohesion softening using the Mohr-Coulomb failure criterion to simulate fracture network evolution and dynamic fracture propagation. Model performance is further enhanced through parallelization by utilising a hybrid CPU/GPU cluster using the PETSc library. We outline the implementation of the developed code, and evaluate its performance from a series of benchmark simulations.

Jansen, Gunnar; Galvan, Boris; Miller, Stephen

2014-05-01

106

Discrete probability distributions for probabilistic fracture mechanics  

SciTech Connect

Recently, discrete probability distributions (DPDs) have been suggested for use in risk analysis calculations to simplify the numerical computations which must be performed to determine failure probabilities. Specifically, DPDs have been developed to investigate probabilistic functions, that is, functions whose exact form is uncertain. The analysis of defect growth in materials by probabilistic fracture mechanics (PFM) models provides an example in which probabilistic functions play an important role. This paper compares and contrasts Monte Carlo simulation and DPDs as tools for calculating material failure due to fatigue crack growth. For the problem studied, the DPD method takes approximately one third the computation time of the Monte Carlo approach for comparable accuracy. It is concluded that the DPD method has considerable promise in low-failure-probability calculations of importance in risk assessment. In contrast to Monte Carlo, the computation time for the DPD approach is relatively insensitive to the magnitude of the probability being estimated.

Kurth, R.E.; Cox, D.C.

1985-09-01

107

A Damage Evolution Approach in Fracture Mechanics of Pipelines  

Microsoft Academic Search

\\u000a The paper concentrates on perspectives of the damage evolution approach in fracture mechanics of oil and gas pipelines. This\\u000a approach is based on the generalised concept of damage. It is postulated that deformation and fracture processes in solids\\u000a are determined by some general functional law related to the accumulation of damage. Fracture mechanics parameters are accepted\\u000a as the controlling parameters

Yu. G. Matvienko

108

Fractal mechanics of deformable media and fracture topology of solids  

NASA Astrophysics Data System (ADS)

Numerous geophysical and laboratory fractographic studies provide evidence of the non-Euclidean geometry of the irreversible deformation and fracture of solids. Here, various approaches to the construction of fracture models are compared with a view to establishing the fundamental characteristics of the fractal mechanics of deformable media that are independent of the model concepts underlying a particular approach. The discussion covers stochastic models of the fracture of elastic bodies, percolation fracture models, kinetic models of fracture, and plasticity theories without a yield surface.

Balankin, A. S.

109

Fractals and fractal scaling in fracture mechanics  

Microsoft Academic Search

A review of modern fractal models of fracture in brittle and quasibrittle materials is given. The difference between mathematical\\u000a and physical fractal approaches is emphasized. The scaling for both a fractal solitary crack and a fractal pattern of microcracks\\u000a surrounding the main fracture is considered. Some concepts appropriate for fractal description of fracture are discussed.\\u000a It is shown that if

Feodor M. Borodich

1999-01-01

110

Mixed-mode Mechanism of Hydraulic Fracture Segmentation  

NASA Astrophysics Data System (ADS)

Mixed-mode I+III loading is one of the primary causes of fracture front segmentation. Although such segmented fractures have been observed both in nature and laboratory, we are not aware of direct laboratory experiments on the mode III mechanism of segmentation of hydraulically induced fractures. In this work, we developed a laboratory technique and a theoretical model for studying not only the effect of mode III loading on the onset of hydraulic fracture segmentation, but also the effect of segmentation on the subsequent growth of hydraulic fractures. In quasi-brittle materials, even a small mode III component may cause fracture segmentation due to a tensile stress field induced near the fracture front [Rice, 1968]. Previously, this has been confirmed in experiments with non-hydraulic fractures [Knauss, 1970; Cooke and Pollard, 1996]. In one occasion, quasi-hydraulic fractures propagated in fast, uncontrollable manner [Sommer, 1969]. This is why, we focused on controlled hydraulic fractures with a rather small KIII/KI ratio (1-10 %). For mixed mode I+III experiments, we used transparent, cylindrical PMMA samples with circular internal fractures perpendicular to the sample axis. Fracture orientation was controlled by thermoelastic stresses induced in each sample by preheating it before creating a fracture. In order to apply mode III loading to the initial fracture, a constant torque was applied to the specimen while fluid was injected into the fracture at a constant rate to pressurize it and to induce mode I loading. The velocity of fracture propagation was constrained by controlling the rate of fluid injection. In spite of a small magnitude of the mode III component, we observed segmented fracture fronts in all tested samples. The segments had similar dimensions and shape elongated around the perimeter of the initial fracture. When the fractures were further pressurized by injecting additional fluid into the sample, second-order segments developed along the fronts of the first-order segments. The obtained results indicate that, similar to the case of non-hydraulic fractures, a KIII/KI ratio as small as 1 % is sufficient for fracture front segmentation, even in materials as homogeneous and fracture resistant as PMMA. In reality, a small component of mode III is always expected, for example, due to slight deviations of a fracture shape from planar or interaction with boundaries or other fractures. As a result, front segmentation (at an appropriate scale) is likely to accompany the growth of most (if not all) real, sufficiently large fractures (hydraulic or not) in quasi-brittle materials, which is consistent with many observations of hydraulic fractures and magmatic dikes. However, the described above shape of segments in stable, controllable hydraulic fractures, which appeared in our experiments, was dramatically different from narrow lance-like segments, elongated in the direction of growth, of uncontrollable, unstable, non-hydraulic fractures that were propagated in a similar setting [Sommer, 1969; Hull, 1995]. We also developed a simple theoretical model, which is based on the beam asymptotic approximation. It appears that mechanical interaction between the segments and the parent fracture can be taken into account by considering an effective single fracture of equal total size. The model has one fitting parameter and shows good agreement with the experimental observations.

Hurt, R. S.; Germanovich, L.; Wu, R.

2006-12-01

111

Increased fracture toughness of ceramics by energy-dissipative mechanisms  

Microsoft Academic Search

A theoretical model for the fracture toughness of ceramics is developed which takes into account such energy-dissipative mechanisms as stress-induced microcracking or phase transformation. To establish the general fracture criterion, a Griffith-type energy balance is employed. This energy balance comprises the elastic energy, the fracture surface work consumed in the process zone at the crack tip, the energy dissipated in

W. Kreher; W. Pompe

1981-01-01

112

On nonlinear effects in fracture mechanics.  

NASA Technical Reports Server (NTRS)

Linear elastic treatment of fracture is considered applicable for net section stress up to about 0.8 the uniaxial tensile yield stress. Crack front plastic yield is still small enough to be viewed and treated as a small perturbation to the local crack front elastic stress field. Assuming these same circumstances and adopting the same point of view, an approach is presented for incorporating the nonlinear effects of small scale crack front plastic yield and slow crack extension in determination of the energy release rate and fracture toughness. Deviation from linearity of the load-displacement record in a fracture toughness test offers a quantifiable measure of these effects and is used to calculate the energy release rate. Fracture toughness values for one-eight inch thick 7075-T6 center cracked aluminum sheet are compared with uncorrected values and with values obtained by the Irwin method of plasticity correction.

Liebowitz, H.; Eftis, J.

1971-01-01

113

Mechanisms of Hydrogen Related Fracture of Metals.  

National Technical Information Service (NTIS)

The number of studies of hydrogen related fracture in recent years in quite impressive both in the variety of systems studied and in the amount of materials characterization which has been obtained. Despite this effort there is still incomplete understand...

H. K. Birnbaum

1989-01-01

114

Finite deformation of elasto-plastic solids  

NASA Technical Reports Server (NTRS)

A theoretical basis is established for analysis of finite deformation of metals. The observation that finite deformation of such elastoplastic materials may be viewed as a process rather than an event leads to derivation of a complete initial and boundary value problem distinguished by its quasilinear nature. This feature of the formulation motivates adoption of an incremental approach to numerical problem solving. Numerical solution capability is established for problems of plane stress and plane strain. The validity of the theory and numerical analysis is demonstrated by consideration of a number of problems of homogeneous finite deformation for which analytic solutions are available. Subsequently the analysis is employed for the investigation of necking in flat metal tensile bars. The results of this investigation provide the first full numerical solutions for tensile necking in plane stress and plane strain. In addition a basis is provided for assessment of the validity of stress-strain relations inferred from tensile test data.

Osias, J. R.

1973-01-01

115

On Mechanisms of Hydraulic Fracturing in Cohesionless Materials  

NASA Astrophysics Data System (ADS)

Based on the developed experimental techniques, hydraulic fracturing in particulate materials has been directly observed in the laboratory. We have conducted an experimental series by varying such controlling parameters as the properties of particulate materials and fracturing fluids, boundary conditions, initial stress states, and injection volumes and rates. As a result, we suggested some (hopefully, fundamental) mechanisms of hydraulic fracturing in particulate materials and determined some (hopefully, relevant) scaling relationships (e.g., the interplay between elastic and plastic processes). While the ongoing work is likely to change at least some conclusions, it is important that the results reported in this paper appear to form the framework for modeling and, perhaps, even for (qualitative) interpretation of some field data. The main conclusion of our work is that hydraulic fracturing in particulate materials is not only possible, but even probable if the fluid leakoff is minimized (e.g., high flow rate, high viscosity, or low permeability). The observed fracture geometry and the measured pressure injection curves suggest that hydraulic fracturing occurs in soft sediments in the following sequence: (i) cavity expansion before the injection pressure reaches its peak; (ii) fracture front initiation from the expanding cavity near the pressure peak; and (iii) propagation of the developed fracture after the peak. Another important conclusion of our work is that all parts of the particulate material (including the tip zone of hydraulic fracture) are likely to be in compression. The compressive stress state is an important characteristic of hydraulic fracturing in particulate materials with low, or no, cohesion (such as were used in our experiments). For the fracture initiation at the peak pressure (i.e., following the initial cavity expansion), there exists a threshold value of cohesion that results in compressive stresses everywhere in the particulate material. For less cohesion, the cohesive materials can be considered to be effectively cohesionless. Three main types of fracture fronts were observed in our laboratory experiments: round, beveled and fingered. Accordingly, three physical mechanisms of fracture propagation corresponding to the three observed front types were suggested. These are ``pile driving'' or cavity expansion, shear banding, and induced cohesion, which appear to be consistent with round, beveled, and fingered fracture fronts, respectively. It is important to emphasize the importance of leakoff effect on hydraulic fractures in particulate materials. In our experiments, fractures appear rather different compared to those in the no-leakoff case. The fluid leakoff region manifests itself as a (bubbly) layer around the fracture, which thins towards the fracture tip, which is similar to brittle fractures. Furthermore, even the tip details of these fractures remarkably resemble cracks in brittle materials. Therefore, currently available experimental observations suggest that even small leakoff may change the fracture pattern rather dramatically. For example, while at the stage of fracture initiation, the cavity expansion mechanism may still be important, the mechanism of induced cohesion may prevail at the developed stage of fracture growth.

Hurt, R. S.; Wu, R.; Germanovich, L.; Chang, H.; Dyke, P. V.

2005-12-01

116

APPLICATION OF FRACTURE MECHANICS TO THE TEXTURE OF FOOD  

Microsoft Academic Search

The fracture mechanics of food is a rational and useful branch of materials science which can yield information of more general interest. The critical stress intensity factor, KIC, is a valid replacement for the organoleptic (sensory) assessment of \\

Julian FV Vincent

2003-01-01

117

A nonlinear high temperature fracture mechanics basis for strainrange partitioning  

NASA Technical Reports Server (NTRS)

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.

Kitamura, Takayuki; Halford, Gary R.

1989-01-01

118

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

NASA Technical Reports Server (NTRS)

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.

Hardrath, H. F.

1974-01-01

119

Fatigue and fracture mechanics: Twenty-ninth volume  

SciTech Connect

The twenty ninth National Symposium on Fatigue and Fracture Mechanics met at Stanford University in Stanford, California on June 24--25, 1997. Information was exchanged on recent developments on modeling and analyzing fatigue and fracture processes; on applications to real structures and new materials; and on directions for future research. Papers were presented on fracture mechanics with mathematical modeling and new materials, fatigue with crack growth models and improved fatigue test methods, and structural applications covering a variety of materials and their performance. Fifty papers have been processed separately for inclusion on the data base.

Panontin, T.L. (ed.) (National Aeronautics and Space Administration, Moffett Field, CA (United States). Ames Research Center); Sheppard, S.D. (ed.) (Stanford Univ., CA (United States))

1999-01-01

120

Comparison of Fracture Initiation and Propagation in Untreated and Thermally Damaged Westerly granites Using a Geophysical Imaging Cell  

NASA Astrophysics Data System (ADS)

By performing controlled thermal cracking experiments, we compare quantitatively the influence of microcracks on strength, deformation, elastic wave velocities (compressional and shear waves) and acoustic emission activity of a pre-heated (850C) specimen with that of an unheated (room temperature, RT) specimen of Westerly granite. Comparison shows a distinctive difference as they undergo a similar stress path during the experiment. The RT specimen shows a failure strength of 420 MPa and axial strain of 0.013, characterized by an elasto-plastic stress-strain curve exhibiting class-2 unstable post-failure behaviour. The 850C specimen fails at 360 MPa with an axial strain of 0.022, characterized by a plasto-elasto-plastic stress-strain curve showing class-1 stable post-failure fracture propagation behaviour. VP measured in the axial direction for the 850C specimen increases steadily from ~4.6 to 5.7 km/s up to the failure point and then decrease to 5.4 km/s at post-failure. VP measured in both horizontal directions increases from 4.6 km/s to a maximum of 5.25 km/s, then decreases to 4.9 km/s during the 33 minutes period prior to failure and settles at 4.3 km/s after the full development of fracture planes. Propagation of axial fractures parallel to sigma1 cause the reduction of VP measured normal to the axial planes which is concomitant to the change in the pre-failure nature of the stress-strain curve shown by the 850C specimen when it experiences increased plasticity at the beginning of dilation. Fracture clustering, coalescence and propagation happened at three distinct stages, as demonstrated from analysis of the AE hit count, AE source location and stress-time curve for a period of 3 to 4 minutes during the pre to post-failure regime of the 850C specimen. AE sensors show a peak number of AE hits/s roughly 25 seconds prior to each stress drop. Induced AE source location analysis demonstrates the evolution of fracture propagation corresponding to each stress drop. Source mechanisms were computed for events that occurred in a 15 minute window covering both the pre and post failure regimes of the 850C specimen. Prior to failure the observed events are close to a +Dipole type event appearing outside the significantly deviatoric region on the source type plot and showing a 20-30% volumetric component. At each of the subsequent three stress drops the source mechanisms migrate into the significantly deviatoric region on the source type plot and cluster around a Double Couple shear type event. Between the second and third stress drops a cluster of compressive events resembling -Dipole and +Crack type events appear. Evolution of the stress-strain curve for the RT specimen shows only one stress drop during the pre-failure to post-failure regime, which is accompanied by only one peak for AE hits/s prior to sudden brittle failure. Evolution of AE for RT specimen shows fracture initiation taking place at the middle of the specimen, propagating rapidly towards the outer edges of the specimen along an inclined fault plane. This study aims at comparing the evolution of strength, deformation, seismic wave velocities and AE response for two different media representing intact and highly damaged rocks under a similar stress regime.

Nasseri, M. B.; Goodfellow, S.; Young, R.

2011-12-01

121

Work of fracture of a composite resin: fracture-toughening mechanisms.  

PubMed

The aim of this work was to investigate those mechanical parameters able to describe the fracture behavior of dental composite resins. A commercially available fine-particle micro-hybrid resin composite was used. Classical parameters as Young's modulus, strength distribution, and critical stress intensity factor were considered. Strength values were determined using the diametrical compression of discs test and for the critical stress intensity factor both unstable and controlled fracture tests were used. Controlled fracture tests allowed determining the work of fracture. Microstructure was studied by optical and field emission scanning electron microscopy. The obtained properties have been Young's modulus, 17.7 +/- 0.6 GPa; Weibull modulus, m = 14 (upper and lower limits for 90% confidence: 17 and 10); characteristic strength 51 MPa (upper and lower limits for 90% confidence: 53 and 49 MPa); critical stress intensity factor in mode I, K(IC) = 1.3 +/- 0.1 and work of fracture, gamma(wof) = 8-9 J/m(2). Pores and bubbles formed during the packing of the composite were identified as critical defects in the tested specimens. Crack deflection and branching have been identified as toughening mechanisms. Classical mechanical parameters (Young's modulus, hardness...) are not able to efficiently predict the major clinical failure mode of composite resins by fatigue. Work of fracture analysis, which is dependant on microstructural parameters such as particle size and shape, have to be included when testing mechanical properties of dental composite resins in future research studies. PMID:18465813

Baudin, Carmen; Osorio, Raquel; Toledano, Manuel; de Aza, Salvador

2009-06-01

122

Solid particle erosion mechanisms of protective coatings for aerospace applications  

NASA Astrophysics Data System (ADS)

The main objective of this PhD project is to investigate the material loss mechanisms during Solid Particle Erosion (SPE) of hard protective coatings, including nanocomposite and nanostructured systems. In addition, because of the complex nature of SPE mechanisms, rigorous testing methodologies need to be employed and the effects of all testing parameters need to be fully understood. In this PhD project, the importance of testing methodology is addressed throughout in order to effectively study the SPE mechanisms of brittle materials and coatings. In the initial stage of this thesis, we studied the effect of the addition of silicon (Si) on the microstructure, mechanical properties and, more specifically, on the SPE resistance of thick CrN-based coatings. It was found that the addition of Si significantly improved the erosion resistance and that SPE correlated with the microhardness values, i.e. the coating with the highest microhardness also had the lowest erosion rate (ER). In fact, the ERs showed a much higher dependence on the surface hardness than what has been proposed for brittle erosion mechanisms. In the first article, we study the effects of the particle properties on the SPE behavior of six brittle bulk materials using glass and alumina powders. First, we apply a robust methodology to accurately characterize the elasto-plastic and fracture properties of the studied materials. We then correlate the measured ER to materials' parameters with the help of a morphological study and an analysis of the quasi-static elasto-plastic erosion models. Finally, in order to understand the effects of impact on the particles themselves and to support the energy dissipation-based model proposed here, we study the particle size distributions of the powders before and after erosion testing. It is shown that tests using both powders lead to a material loss mechanism related to lateral fracture, that the higher than predicted velocity exponents point towards a velocity-dependent damage accumulation mechanism correlated to target yield pressure, and that damage accumulation effects are more pronounced for the softer glass powder because of kinetic energy dissipation through different means. In the second article, we study the erosion mechanisms for several hard coatings deposited by pulsed DC magnetron sputtering. We first validate a new methodology for the accurate measurement of volume loss, and we show the importance of optimizing the testing parameters in order to obtain results free from experimental artefacts. We then correlate the measured ERs to the material parameters measured by depth-sensing indentation. In order to understand the material loss mechanisms, we study three of the coating systems in greater detail with the help of fracture characterization and a morphological study of the eroded surfaces. Finally, we study the particle size distributions of the powders before and after erosion testing in an effort to understand the role of particle fracture. We demonstrate that the measured ERs of the coatings are strongly dependent on the target hardness and do not correlate with coating toughness. In fact, the material removal mechanism is found to occur through repeated ductile indentation and cutting of the surface by the impacting particles and that particle breakup is not sufficiently large to influence the results significantly. Studying SPE mechanisms of hard protective coating systems in detail has proven to be quite challenging in the past, given that conventional SPE testing is notoriously inaccurate due to its aggressive nature and its many methodological uncertainties. In the third article, we present a novel in situ real-time erosion testing methodology using a quartz crystal microbalance, developed in order to study the SPE process of hard protective coating systems. Using conventional mass loss SPE testing, we validate and discuss the advantages and challenges related to such a method. In addition, this time-resolved technique enables us to discuss some transient events present during SPE testing of hard coatin

Bousser, Etienne

123

Adhesive fracture mechanics. [stress analysis for bond line interface  

NASA Technical Reports Server (NTRS)

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.

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

1974-01-01

124

Mechanical testing - In situ fracture device for Auger electron spectroscopy  

NASA Technical Reports Server (NTRS)

An in situ fracture device for Auger spectroscopy is 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 are presented. Results indicate that impurity segregation at interfaces other than grain boundary may play a significant role in the mechanism of ductile fracture.

Moorhead, R. D.

1976-01-01

125

Trabecular Bone Mechanical Properties in Patients with Fragility Fractures  

Microsoft Academic Search

Fragility fractures are generally associated with substantial loss in trabecular bone mass and alterations in structural anisotropy.\\u000a Despite the high correlations between measures of trabecular mass and mechanical properties, significant overlap in density\\u000a measures exists between individuals with osteoporosis and those who do not fracture. The purpose of this paper is to provide\\u000a an analysis of trabecular properties associated with

Jaclynn M. Kreider; Steven A. Goldstein

2009-01-01

126

RSRM nozzle actuator bracket/lug fracture mechanics qualification test  

NASA Technical Reports Server (NTRS)

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.

Kelley, Peggy

1993-01-01

127

Primer: Fracture mechanics in the nuclear power industry  

SciTech Connect

This Primer is intended to familiarize utility engineers with the fracture mechanics technology and to provide the basis for a working knowledge of the subject. It is directed towards all the engineering disciplines that are involved either directly or indirectly with the structural reliability of electrical power generation equipment and systems. These engineering disciplines include such areas as: design and stress analysis, metallurgy and materials, nondestructive inspection and quality control, structural analysis and reliability engineering, chemical engineering and water chemistry control, and architectural engineering. This Primer does not provide a comprehensive, in-depth treatment of all the detailed aspects involved in fracture mechanics. It does, however, provide sufficient information and a common vocabulary that should enable engineers to: read and converse intelligently about the subject, understand and utilize ASME Codes and Regulatory Guides involving fracture mechanics, absorb technical information presented and discussed at various technical meetings, and begin to apply this technology towards actual engineering problems encountered in the course of their work. Example problems are provided to further enhance an understanding of fracture mechanics. Also, Appendix A describes fracture mechanics computer codes available through EPRI to analyze rotors, reactor pressure vessels and piping.

Wessel, E.T. (Wessel (E.T.), Murrysville, PA (USA)); Server, W.L. (Tenera Corp., Berkeley, CA (USA)); Kennedy, E.L. (Failure Analysis Associates, Inc., Palo Alto, CA (USA))

1990-01-01

128

Calculations to Benchmark Probabilistic Fracture Mechanics Computer Codes  

Microsoft Academic Search

This paper describes calculations to estimate component failure frequencies for components using the PRO-LOCA and PRAISE probabilistic fracture mechanics (PFM) computer codes. These calculations focused on the failure mechanism of intergranular stress corrosion cracking for operating conditions that were known to have failed field components. The objective was to benchmark the newly developed PRO-LOCA code against the older PRAISE code

Fredric A. Simonen; Stephen R. Gosselin; Gery M. Wilkowski; David L. Rudland; H. Xu

2007-01-01

129

Fracture mechanics life analytical methods verification testing  

NASA Technical Reports Server (NTRS)

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.

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

1994-01-01

130

The Fracture Mechanics of the Pin and Collar Test for High Temperature Anaerobic Adhesives  

Microsoft Academic Search

A mechanical test method for the studies of high-temperature anaerobic adhesives has been established, based on fracture mechanics, by modifying the standard test method of collar and pin test. Linear Elastic Fracture Mechanics approach was applied to the establishment of the relationship between adhesive fracture surface energy “R”, fracture load and crack length. Hence, from the joints containing a given

B. W. Cherry; Y. Q. Ye

1992-01-01

131

Modeling fracture of random media via stochastic molecular mechanics  

NASA Astrophysics Data System (ADS)

Inspired by recent experimental results suggesting that the heterogeneous distribution of the elastic modulus in bone tissue leads to increased toughness, we determine the toughness modulus of a flawed discrete particle system with stochastic elastic properties. We consider an elastic solid in plane strain conditions in uniaxial tension with a Young's modulus distribution modeled as a 2-d Gaussian process with covariance modeled as an exponential kernel. We solve the problem from a continuum perspective, both employing spectral methods with stochastic finite elements and Monte Carlo methods with conventional finite elements. We also analyze an equivalent discrete particle system, modeled as a spring bead network of FCC-lattices. Our results validate the persistence of the Cauchy Born rule in a stochastic system. We then analyze a flawed discrete particle system to assess the effect of heterogeneity on fracture properties. By studying the fracture mechanics of this system with a range of variance and correlation length parameters in the exponential kernel we gain fundamental insights in to the essential length scales of heterogeneity critical to enhanced fracture properties. This validated stochastic molecular mechanics framework further supports the inverse computation of local elastic properties, not accessible with continuum mechanics, to tailor global mechanical properties such as the fracture toughness. Specifically, Markov Chain Monte Carlo can be used to infer the elastic and geometric parameters. Our work sets the foundation for stochastic modeling in a micromechanical environment and unveils mechanisms by which mechanical behavior can be tailored due to increasingly heterogeneous mechanical properties.

Dimas, Leon; Giesa, Tristan; Buehler, Markus

2013-03-01

132

Fracture mechanics criteria for turbine engine hot section components  

NASA Technical Reports Server (NTRS)

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.

Meyers, G. J.

1982-01-01

133

Open bicondylar Hoffa fracture associated with extensor mechanism injury.  

PubMed

Two cases of open bicondylar Hoffa fracture of the knee associated with extensor mechanism injury are described in two active young patients with multiple fractures. The level of the fracture was determined by the proximal insertion of the posterior cruciate ligament and anterior cruciate ligament in the medial and lateral condyle. The level of the extensor mechanism injury was determined by the degree of flexion of the knee at the moment of impact. No ligament or meniscal tears were found. Open reduction and internal fixation with four lag screws and bone-to-tendon repair of the patellar and quadriceps tendon gave excellent results after more than 2 years of follow-up. The mechanism of injury and the therapeutic implications are discussed, and the literature is reviewed. PMID:15105758

Calmet, J; Mellado, J M; García Forcada, I L; Giné, J

2004-01-01

134

Relating Cohesive Zone Model to Linear Elastic Fracture Mechanics  

NASA Technical Reports Server (NTRS)

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.

Wang, John T.

2010-01-01

135

Mechanical transport in two-dimensional networks of fractures  

SciTech Connect

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.

Endo, H.K.

1984-04-01

136

Measurements of residual stress in fracture mechanics coupons  

SciTech Connect

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.

Prime, Michael B [Los Alamos National Laboratory; Hill, Michael R [U.C. DAVIS; Nav Dalen, John E [HILL ENGINEERING

2010-01-01

137

Investigation of the fracture mechanics of boride composites  

NASA Technical Reports Server (NTRS)

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.

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

1972-01-01

138

Fracture Mechanics of Functionally Graded Materials.  

National Technical Information Service (NTIS)

Functionally graded materials are generally two-phase composites with continuously varying volume fractions. Used as coatings and interfacial zones, they help to reduce mechanically and thermally induced stresses caused by the material property mismatch a...

F. Erdogan

1996-01-01

139

Fracture Mechanics Investigations on HTR (High Temperature Reactor)-Materials.  

National Technical Information Service (NTIS)

A Prototype of Nuclear Process-heat (PNP) plant as well as the gascooled high temperature reactor (HTR) needs materials which can withstand temperatures up to 1223 deg K (950 deg C). An elaboration of fracture mechanics concepts which hold for the complet...

K. Krompholz E. Bodmann G. Gnirss H. Huthmann

1983-01-01

140

Mechanical deformation and fracture mode of polycrystalline graphene: Atomistic simulations  

NASA Astrophysics Data System (ADS)

Mechanics of polycrystalline graphene are studied through molecular dynamics simulations. Local buckling forms the ridge or funnel centering on pentagon, and fluctuating stress occurs under small tensile strain due to out-of-plane distortion. In addition, brittle breaking is initialized from heptagons and ends with fracture of pentagons.

Hao, Feng; Fang, Daining

2012-05-01

141

Unique mechanism of chance fracture in a young adult male.  

PubMed

Since the first description of the Chance fracture in 1948, there have been few case reports of unique mechanisms causing this classical flexion-extension injury to the spine in motor vehicle accidents, sports injury, and falls. To our knowledge, this injury has not been reported from a fall with the mechanistic forces acting laterally on the spine and with spinal support in place. We present a 21-year-old male who slid down a flight of stairs onto his side wearing a heavy mountaineering style backpack, subsequently sustaining a Chance fracture of his first lumbar vertebrae. PMID:23599852

Birch, Aaron; Walsh, Ryan; Devita, Diane

2013-03-01

142

The fracture properties and toughening mechanisms of bone and dentin  

NASA Astrophysics Data System (ADS)

The mechanical properties of bone and dentin and in particular their fracture properties, are the subject of intense research. The relevance of these properties is increasing as our population ages and fracture incidence impacts the lives of a greater portion of the population. A robust framework is needed to understand the fracture properties of bone and dentin to guide researchers as they attempt to characterize the effects of aging, disease, and pharmaceutical treatments on the properties of these mineralized tissues. In the present work, this framework is provided and applied to human bone, human dentin, and animal bone. In situ electron microscopy was also used to identify the salient toughening mechanisms in bone and dentin. It was found that bone and dentin are extrinsically toughened materials and consequently their fracture properties are best characterized utilizing a crack-growth resistance approach. A description of the different mechanical measurements commonly employed when using small animal models (rats and mice) to evaluate the influence of drug therapies on bone fragility is provided. A study where these properties were measured for a large population of wild-type rats and mice was also conducted. Given my findings, it was determined that for the most complete understanding of small animal bone it was necessary to measure strength and toughness. Strength measurements probe the flaw distribution and toughness measurements to evaluate the resistance to facture in the presence of a single dominant worst-case flaw.

Koester, Kurt John

143

A field theory of distortion incompatibility for coupled fracture and plasticity  

NASA Astrophysics Data System (ADS)

The displacement discontinuity arising between the crack surfaces is assigned to smooth areal/tensorial densities of crystal defects referred to as disconnections, through the incompatibility of the continuous distortion tensor. In a dual way, the disconnections are defined as line defects terminating surfaces where the displacement encounters a discontinuity. A conservation argument for their strength (the crack opening displacement) provides a natural framework for their dynamics in the form of a transport law for the disconnection densities. Similar methodology is applied to the discontinuity of the plastic displacement arising from the presence of dislocations in the body, which results in the concurrent involvement of the dislocation density tensor in the analysis. The present model can therefore be viewed as an extension of the mechanics of dislocation fields to the case where continuity of the body is disrupted by cracks. From the continuity of the elastic distortion tensor, it is expected that the stress field remains bounded everywhere in the body, including at the crack tip. Thermodynamic arguments provide the driving forces for disconnection and dislocation motion, and guidance for the formulation of constitutive relationships insuring non-negative dissipation. The conventional Peach-Koehler force on dislocations is retrieved in the analysis, and a Peach-Koehler-type force on disconnections is defined. A threshold in the disconnection driving force vs. disconnection velocity constitutive relationship provides for a Griffith-type fracture criterion. Application of the theory to the slit-crack (Griffith-Inglis crack) in elastic and elasto-plastic solids through finite element modeling shows that it allows recovering earlier results on the stress field around cracks, and that crack propagation can be consistently described by the transport scheme. Shielding/anti-shielding of cracks by dislocations is considered to illustrate the static/dynamic interactions between dislocations and disconnections resulting from the theory. Sample size effects on crack growth are evidenced in solids encountering plastic yielding.

Fressengeas, Claude; Taupin, Vincent

2014-08-01

144

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

PubMed Central

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.

Ren, Lan; Zhao, Jinzhou; Hu, Yongquan

2014-01-01

145

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

PubMed

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

Ren, Lan; Zhao, Jinzhou; Hu, Yongquan

2014-01-01

146

Mapping the Isotropic Component of Focal Mechanisms in Hydraulic Fractures  

NASA Astrophysics Data System (ADS)

We present the results of a hydraulic fracture monitoring study where the events induced by the treatment are recorded with a three-dimensional sensor distribution. The fact that the microseismicity is recorded over multiple azimuths allows not only for better convergence of the location algorithm, but also acheives sufficient coverage of the focal sphere to reliably invert for the full moment tensor. Unlike in tectonic settings, many of these focal mechanisms have very strong non-double-couple components, due to the intrusion of proppants into the surrounding rock, and are thus characterized by mechanisms consistant with tensile cracks opening or closing. Mapping these mechanisms in time and space offers insight into both the processes responsible for the fracturing, but also how effectively the treatment propped open the rock and identifying which areas may have opened and subsequently closed.

Baig, A. M.; Urbancic, T. I.

2009-12-01

147

Elastic plastic fracture mechanics methodology for surface cracks  

NASA Technical Reports Server (NTRS)

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).

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

1994-01-01

148

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

NASA Technical Reports Server (NTRS)

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.

Ehret, R. M.

1974-01-01

149

Extrinsic fracture mechanisms in two laminated metal composites  

SciTech Connect

The crack growth behavior and fracture toughness of two laminated metal composites (6090/SiC/25p laminated with 5182 and ultrahigh-carbon steel laminated with brass) have been studied in both ``crack arrester`` and ``crack divider`` orientations. The mechanisms of crack growth were analyzed and extrinsic toughening mechanisms were found to contribute significantly to the toughness. The influence of laminate architecture (layer thickness and component volume function), component material properties and residual stress on these mechanisms and the resulting crack growth resistance are discussed.

Lesuer, D.; Syn, C.; Riddle, R.; Sherby, O.

1994-11-29

150

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

NASA Astrophysics Data System (ADS)

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.

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

2010-02-01

151

Discrete fracture patterns of virus shells reveal mechanical building blocks  

NASA Astrophysics Data System (ADS)

Viral shells are self-assembled protein nanocontainers with remarkable material properties. They combine simplicity of construction with toughness and complex functionality. To date we know little about how virus structure determines assembly pathways and shell mechanics. We have used atomic force microscopy to study structural failure of the shells of the bacteriophage ?29. We observed rigidity patterns following the symmetry of the capsid proteins and under prolonged force exertion, we see fractures along well-defined lines of the 2D crystal lattice. We found 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.

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

2012-02-01

152

Combining damage and fracture mechanics to model calving  

NASA Astrophysics Data System (ADS)

Calving of icebergs is a major negative component of polar ice-sheet mass balance. We present a new calving modeling framework relying on both continuum damage mechanics and linear elastic fracture mechanics. This combination accounts for both the slow sub-critical surface crevassing and fast propagation of crevasses when calving occurs. First, damage of the ice occurs over long timescales and enhances the viscous flow of ice. Then brittle fracture propagation happens downward, over very short timescales, in ice considered as an elastic medium. The model is validated on Helheim Glacier, South-West Greenland, one of the most monitored fast-flowing outlet glacier. This allows to identify sets of model parameters giving a consistent response of the model and producing a dynamic equilibrium in agreement with observed stable position of the Helheim ice front between 1930 and today.

Krug, J.; Weiss, J.; Gagliardini, O.; Durand, G.

2014-03-01

153

Fracture Mechanics Determinations of Allowable Crack Size in Railroad Rails  

Microsoft Academic Search

An evaluation of fatigue behavior of rail steel is necessary to ensure rail transportation safety. Fatigue in these steels\\u000a was studied with fracture mechanics techniques. The goal of these studies was to find out the appropriate way of preventing\\u000a a crack from reaching its critical size in the rail. Tests were conducted on rail head, and transverse head cracks were

R. Ravaee; A. Hassani

2007-01-01

154

Dynamic Fracture Toughness and Failure Mechanisms of ZnO Whiskers Secondary Reinforced Composites  

NASA Astrophysics Data System (ADS)

Quasi-static and dynamic fracture properties and damage mechanism of glass fiber polymer composites embedded with different mass percentages of ZnO whiskers are investigated by using an Instron Testing machine and a Split-Hopkinson pressure bar. According to the experimental results and linear fracture mechanics, the quasi-static fracture toughness KIc and the dynamic fracture toughness KId under various impact velocities of specimens are obtained. Fracture mechanism is investigated by fractography analysis with a scanning electron microscope. The experimental results show that the mass percentage of ZnOw has little influence on the quasi-static fracture toughness, but a little influence on the dynamic fracture toughness and time of initial fracture point of specimens by the reason of various fracture mechanisms.

Rong, Ji-Li; Wang, Xi; Cao, Mao-Sheng; Xu, Tian-Fu

2010-08-01

155

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

SciTech Connect

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.

Wilkowski, G.M.; Olson, R.J.; Scott, P.M. [Battelle, Columbus, OH (United States)

1998-01-01

156

Results of fracture mechanics tests on PNC SUS 304 plate  

SciTech Connect

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.

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

1985-08-01

157

Computational methods for viscoplastic dynamic fracture mechanics analysis  

SciTech Connect

The role of nonlinear rate-dependent effects in the interpretation of crack run-arrest events in ductile materials is being investigated by the Heavy-Section Steel Technology (HSST) program through development and applications of viscoplastic-dynamic finite element analysis techniques. This paper describes a portion of these studies wherein various viscoplastic constitutive models and several proposed nonlinear fracture criteria are being installed in general purpose (ADINA) and special purpose (VISCRK) finite element computer program. The constitutive models implemented in these computer programs include the Bodner-Parton and the Perzyna viscoplastic formulations; the proposed fracture criteria include three parameters that are based on energy principles. The predictive capabilities of the nonlinear techniques are evaluated through applications to a series of HSST wide-plate crack-arrest tests. To assess the impact of including viscoplastic effects in the computational models, values of fracture parameters calculated in elastodynamic and viscoplastic-dynamic analyses are compared for a large wide-plate test. Finally, plans are reviewed for additional computational and experimental studies to assess the utility of viscoplastic analysis techniques in constructing a dynamic inelastic fracture mechanics model for ductile steels. 34 refs., 14 figs.

Bass, B.R.; Pugh, C.E.; Kenney-Walker, J.; Dexter, R.J.; O'Donoghue, P. E.; Schwartz, C. W.

1988-01-01

158

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

NASA Technical Reports Server (NTRS)

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.

Kattenhorn, Simon

2004-01-01

159

Mechanics of Delamination in Fiber-Reinforced Composite Materials. Part 2: Delamination Behavior and Fracture Mechanics Parameters.  

National Technical Information Service (NTIS)

Based on theories of laminate anisotropic elasticity and interlaminar fracture, the complete solution structue associated with a composite delamination is determined. Fracture mechanics parameters characterizing the interlaminar crack behavior are defined...

S. S. Wang I. Choi

1983-01-01

160

Measurement of residual stresses using fracture mechanics weight functions  

SciTech Connect

A residual stress measurement method has been developed to quantify through-the-thickness residual stresses. Accurate measurement of residual stresses is crucial for many engineering structures. Fabrication processes such as welding and machining generate residual stresses that are difficult to predict. Residual stresses affect the integrity of structures through promoting failures due to brittle fracture, fatigue, stress corrosion cracking, and wear. In this work, the weight function theory of fracture mechanics is used to measure residual stresses. The weight function theory is an important development in computational fracture mechanics. Stress intensity factors for arbitrary stress distribution on the crack faces can be accurately and efficiently computed for predicting crack growth. This paper demonstrates that the weight functions are equally useful in measuring residual stresses. In this method, an artificial crack is created by a thin cut in a structure containing residual stresses. The cut relieves the residual stresses normal to the crack-face and allows the relieved residual stresses to deform the structure. Strain gages placed adjacent to the cut measure the relieved strains corresponding to incrementally increasing depths of the cut. The weight functions of the cracked body relate the measured strains to the residual stresses normal to the cut within the structure. The procedure details, such as numerical integration of the singular functions in applying the weight function method, will be discussed.

Fan, Y.

2000-10-01

161

Biomechanical mechanisms of orbital wall fractures - a transient finite element analysis.  

PubMed

As the biomechanical mechanisms of orbital wall fractures are still under research, three different fracture mechanisms were tested in a finite element based investigation. In contrast to earlier studies, a finer skeletal model and a transient dynamic simulation were used to test pure hydraulic, pure buckling and a mixed force transmission. Results showed that each set-up led to different orbital fracture patterns, which correlate well with clinical findings. Therefore the conclusion is that different mechanisms may act together explaining the variety of clinical fracture situations. Biomechanical testing has proven to be appropriate in answering questions regarding fracture mechanisms. PMID:22417768

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

2013-12-01

162

Probabilistic/Fracture-Mechanics Model For Service Life  

NASA Technical Reports Server (NTRS)

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.

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

1991-01-01

163

Analysis of Fracture Mechanics Tests on Opalinus Clay  

NASA Astrophysics Data System (ADS)

Many studies have recently been conducted to evaluate various mechanical characteristics of the Opalinus Clay (OPA) formation in view of its potential use as the hosting rock for the Swiss nuclear waste repositories. Its sedimentary bedding makes OPA a transversely isotropic rock and its directional mechanical properties need to be measured. This paper reports on an experimental and computational approach that was adopted to define the parallel-to-bedding fracture mechanics (FM) parameters of OPA in Mode-I. OPA cores from Mont Terri Underground Research Laboratory (URL) were submitted to laboratory tests on notched semi-circular specimens under three-point bending (SCB). In these tests, crack propagation is forced along the notch direction. However, the 45° bedding inclination of the specimen axis frequently deviated the crack from the expected direction. An analysis of the SCB tests was performed by means of non-linear FM techniques and the pertinent Mode-I parameters along the bedding were estimated.

Valente, S.; Fidelibus, C.; Loew, S.; Cravero, M.; Iabichino, G.; Barpi, F.

2012-09-01

164

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

National Technical Information Service (NTIS)

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 rotati...

S. Kattenhorn

2004-01-01

165

Improving detection of pediatric elbow fractures by understanding their mechanics.  

PubMed

Fractures around the elbow are among the most common fractures in children, but they can also be some of the most elusive to detect. Although elbow fractures result from a variety of stresses applied to the three bones constituting the elbow joint, hyperextension-rotation injuries with valgus or varus stress are the most common cause of elbow fractures. Less common are direct impact injuries to the posterior aspect of the elbow. Because all three bones and their articulations are morphologically different, the various traumatic forces applied result in distinctly different types of fractures in each of the bones. For example, hyperextension with vertical stress produces supracondylar fractures of the distal humerus, longitudinal linear ulnar fractures, and buckle fractures; hyperextension with valgus stress causes impaction fractions of the radial head and neck, transverse olecranon fractures, and medial epicondylar fractures, whereas varus stress produces Monteggia fractures, lateral condylar avulsion fractures, transverse olecranon fractures, and longitudinal linear ulnar fractures. Understanding these forces and their effects is important because it facilitates detection of the wide variety of fractures in their more subtle forms. PMID:8946546

John, S D; Wherry, K; Swischuk, L E; Phillips, W A

1996-11-01

166

Coupled Flow and Mechanics in Porous and Fractured Media*  

NASA Astrophysics Data System (ADS)

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 effective hydraulic aperture, which is a non-linear function of effective normal stress. The dynamically evolving aperture field updates the effective, anisotropic permeability tensor, thus resulting in a highly coupled multiphysics problem. Two models of geomechanical damage are discussed: critical shear-slip criteria and a sub-grid joint model. Leakage rates through the caprock resulting from the joint model are compared to those assuming intact material, allowing a correlation between potential for leakage and injection rates/pressures, for various in-situ stratigraphies. *This material is based upon work supported as part of the Center for Frontiers of Subsurface Energy Security, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001114. Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energys National Nuclear Security Administration under Contract DE-AC04-94AL85000.

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

2012-12-01

167

Fracture-mechanisms in pure iron, two austenitic steels, and one ferritic steel  

Microsoft Academic Search

The mechanisms of fracture of round tensile specimens of pure iron, two austenitic stainless steels (types 304 and 316) and\\u000a one ferritic steel (2¼ Cr-1 Mo) have been studied. These new observations have been combined with published information to\\u000a construct two types of fracture mechanism diagram which show the regions of dominance of each mechanism, and summarize the\\u000a fracture observations

R. J. Fields; T. Weerasooriya; M. F. Ashby

1980-01-01

168

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

NASA Technical Reports Server (NTRS)

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.

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

2004-01-01

169

Fracture mechanics of ceramics. Vol. 8. Microstructure, methods, design, and fatigue  

SciTech Connect

This paper presents information on the following topics: fracture mechanics and microstructures; non-lubricated sliding wear of Al/sub 2/O/sub 3/, PSZ and SiC; mixed-mode fracture of ceramics; some fracture properties of alumina-containing electrical porcelains; transformation toughening in the Al/sub 2/O/sub 3/-Cr/sub 2/O/sub 3//ZrO/sub 2/-HfO/sub 2/ system; strength toughness relationships for transformation toughened ceramics; tensile strength and notch sensitivity of Mg-PSZ; fracture mechanisms in lead zirconate titanate ceramics; loading-unloading techniques for determining fracture parameters of brittle materials utilizing four-point bend, chevron-notched specimens; application of the potential drop technique to the fracture mechanics of ceramics; ceramics-to-metal bonding from a fracture mechanics perspective; observed changes in fracture strength following laser irradiation and ion beam mixing of Ni overlayers on sintered alpha-SiC; crack growth in single-crystal silicon; a fracture mechanics and non-destructive evaluation investigation of the subcritical-fracture process in rock; slow crack growth in sintered silicon nitride; uniaxial tensile fatigue testing of sintered silicon carbide under cyclic temperature change; and effect of surface corrosion on glass fracture.

Bradt, R.C.; Evans, A.G.; Hasselman, D.P.H.; Lange, F.F.

1986-01-01

170

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

NASA Technical Reports Server (NTRS)

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.

Herring, H. W.

1972-01-01

171

Mechanical analysis of femoral neck fracture fixation in synthetic bone  

PubMed Central

OBJECTIVE: To analyze statistically results obtained between biomechanical assays on fixation of femoral neck fracture type Pauwels III, on synthetic bone, using 7.5 mm non parallel cannulated screws and control group. METHODS: Ten synthetic bones from a national brand were used. Test group: fixation of 70(o) tilt femoral neck osteotomy was performed using three 7.5 mm non parallel cannulated screws. We analyzed the resistance of this fixation with 5 mm of displacement, and rotational deviation (phase 1) and with 10 mm offset (phase 2). Control group: the models were tested in their integrity until the femoral neck fracture occurred. RESULTS: the values of the test group in phase 1, in sample 1-5 had a mean of 517N and SD = 96N. Rotational deviations showed a mean of 3.79° e SD = 2. 03°. In phase 2, mean was 649N and SD = 94N. The values of the maximum load in the control group were: 1544N, 1110N, 1359N, 1194N, 1437N; respectively. Statistical analysis between the groups showed a statistically significant lower value in the test group. CONCLUSION: the analysis of mechanical resistance between the groups has determined statistically significant value for the test group. Level of Evidence III, Case-control Study.

Freitas, Anderson; Azevedo, Bruna Alves Soares; de Souza, Roberto Rodrigues; da Costa, Helio Ismael; Maciel, Rafael Almeida; Souto, Diogo Ranier de Macedo

2014-01-01

172

Fracture Mechanics Analysis of LH2 Feed Line Flow Liners  

NASA Technical Reports Server (NTRS)

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.

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

2006-01-01

173

Elastic plastic fracture mechanics methodology for surface cracks  

NASA Technical Reports Server (NTRS)

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.

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

1993-01-01

174

Fracture mechanics concepts in reliability analysis of monolithic ceramics  

NASA Technical Reports Server (NTRS)

Basic design concepts for high-performance, monolithic ceramic structural components are addressed. The design of brittle ceramics differs from that of ductile metals because of the inability of ceramic materials to redistribute high local stresses caused by inherent flaws. Random flaw size and orientation requires that a probabilistic analysis be performed in order to determine component reliability. The current trend in probabilistic analysis is to combine linear elastic fracture mechanics concepts with the two parameter Weibull distribution function to predict component reliability under multiaxial stress states. Nondestructive evaluation supports this analytical effort by supplying data during verification testing. It can also help to determine statistical parameters which describe the material strength variation, in particular the material threshold strength (the third Weibull parameter), which in the past was often taken as zero for simplicity.

Manderscheid, Jane M.; Gyekenyesi, John P.

1987-01-01

175

Structural, mechanical properties and fracture mechanism of RuB(1.1).  

PubMed

Polycrystalline RuB(1.1) has been prepared by using an arc-melting method and its structure and mechanical properties including elastic modulus, hardness and fracture behavior have been characterized. Also, the electronic structure and bond characteristics for this compound have been investigated by first-principles calculations. The lattice parameters of RuB(1.1) have been precisely determined by a Rietveld refinement. First-principles calculations show that this compound has a high bulk modulus and a big Poisson's ratio compared to RuB2. The measured hardness of ~10.6 GPa for RuB(1.1) is three times lower than the theoretical value. This low hardness can be attributed to bond characteristics such as the bonding state and orientation, and fracture mechanism, in which the features of the Ru-B bonds plays an important role in the hardness. We found that there is an isosceles triangle bonding state including the B-B and Ru-B bonds, and the two-dimensionally inclined Ru-B bonds along the a-b plane weaken the hardness and C33. The scanning electron microscopy images show that this RuB(1.1) compound exhibits a twinning fracture, and this fracture model is also confirmed by first-principle calculations. PMID:24496462

Pan, Yong; Guan, Weiming; Zheng, Weitao

2014-04-01

176

A rare case of open bicondylar Hoffa fracture with extensor mechanism disruption.  

PubMed

The incidence of open bicondylar Hoffa fractures is extremely rare. We report one such case of a 42-year-old woman who presented to the emergency department with an open injury over the knee. Imaging revealed bicondylar Hoffa fracture. The patient was taken up for debridement and internal fixation. Intraoperative findings included an entrapped patella between the fracture fragments and extensor mechanism disruption. Hoffas fracture was fixed with lag screws and patellar tendon repaired on to the inferior patella. The patient was started on early postoperative range of motion exercises. The fracture united at 12 weeks with 120° knee flexion at 2 year follow-up. PMID:23645653

Kini, Sunil Gurpur; Sharma, Mrinal; Raman, Rajeev

2013-01-01

177

Mechanical properties of bioactive glass (13-93) scaffolds fabricated by robotic deposition for structural bone repair  

PubMed Central

There is a need to develop synthetic scaffolds for repairing large defects in load-bearing bones. Bioactive glasses have attractive properties as a scaffold material for bone repair, but data on their mechanical properties are limited. The objective of the present study was to comprehensively evaluate the mechanical properties of strong porous scaffolds of silicate 13-93 bioactive glass fabricated by robocasting. As-fabricated scaffolds with a grid-like microstructure (porosity = 47%; filament diameter = 330 ?m; pore width = 300) were tested in compressive and flexural loading to determine their strength, elastic modulus, Weibull modulus, fatigue resistance, and fracture toughness. Scaffolds were also tested in compression after they were immersed in simulated body fluid (SBF) in vitro or implanted in a rat subcutaneous model in vivo. As fabricated, the scaffolds had a strength = 86 ± 9 MPa, elastic modulus = 13 ± 2 GPa, and a Weibull modulus = 12 when tested in compression. In flexural loading, the strength, elastic modulus, and Weibull modulus were 11 ± 3 MPa, 13 ± 2 GPa, and 6, respectively. In compression, the as-fabricated scaffolds had a mean fatigue life of ~106 cycles when tested in air at room temperature or in phosphate-buffered saline at 37 °C under cyclic stresses of 1–10 MPa or 2–20 MPa. The compressive strength of the scaffolds decreased markedly during the first 2 weeks of immersion in SBF or implantation in vivo, but more slowly thereafter. The brittle mechanical response of the scaffolds in vitro changed to an elasto-plastic response after implantation for longer than 2–4 weeks in vivo. In addition to providing critically needed data for designing bioactive glass scaffolds, the results are promising for the application of these strong porous scaffolds in loaded bone repair.

Liu, Xin; Rahaman, Mohamed N.; Hilmas, Gregory E.; Bal, B. Sonny

2013-01-01

178

Fracture mechanism of NCG reinforced MMC fabricated by the squeeze casting method  

Microsoft Academic Search

When carbon fiber is coated by metal in order to increase the wettability of carbon fiber and metal matrix, the coating layer is affected by the processing conditions. The fracture mechanism of the composite depends on how the coating layers are affected with the processing conditions. In order to investigate the fracture mechanism of composites with the processing conditions, we

Y. M. Ryu; E. P. Yoon; M. H. Rhee

2000-01-01

179

Experimental and theoretical fracture mechanics applied to fracture of the crust of Venus  

Microsoft Academic Search

Mapping of closely spaced, parallel extensional fractures in the Guinevere and Sedna Planitia regions of Venus reveals a concentric pattern of fractures around the edge of the large topographic rise of Western Eistla Regio. We have constructed 13 transects through these closely spaced parallel fractures (CSPF) and find a mean spacing of between 0.8 and 1.2 km. A two-dimensional, nonlayered,

Matthew R. Balme; Peter R. Sammonds; Claudio Vita-Finzi; Jonathon P. Couchman

2004-01-01

180

Effect of high-frequency excitation on a class of mechanical systems with dynamic friction  

NASA Astrophysics Data System (ADS)

The effect of high-frequency excitation on a class of systems with friction is considered. Friction is represented by the LuGre and the elasto-plastic model of friction. Analytical expressions are obtained for the effective friction characteristics under two types of fast excitation. Numerical simulation using MATLAB validates the analytical results. The stability of a velocity tracking system with friction is discussed in light of the effective friction characteristics. Numerical simulation of a MATLAB™ SIMULINK model is carried out to unfold the basic physical mechanism underneath the mathematical expressions.

Chatterjee, S.; Singha, T. K.; Karmakar, S. K.

2004-01-01

181

Thermal mechanical modeling of cooling history and fracture development in inflationary basalt lava flows  

NASA Astrophysics Data System (ADS)

Thermal-mechanical analyses of isotherms in low-volume basalt flows having a range of aspect ratios agree with inferred isotherm patterns deduced from cooling fracture patterns in field examples on the eastern Snake River Plain, Idaho, and highlight the caveats of analytical models of sheet flow cooling when considering low-volume flows. Our field observations show that low-volume lava flows have low aspect ratios (width divided by thickness), typically < 5. Four fracture types typically develop: column-bounding, column-normal, entablature (all of which are cooling fractures), and inflation fractures. Cooling fractures provide a proxy for isotherms during cooling and produce patterns that are strongly influenced by flow aspect ratio. Inflation fractures are induced by lava pressure-driven inflationary events and introduce a thermal perturbation to the flow interior that is clearly evidenced by fracture patterns around them. Inflation fracture growth occurs incrementally due to blunting of the lower tip within viscoelastic basalt, allowing the inflation fracture to pivot open. The final stage of growth involves propagation beyond the blunted tip towards the stress concentration at the tapered tip of a lava core, resulting in penetration of the core that causes quenching of the lava and the formation of a densely fractured entablature. We present numerical models that include the effects of inflation fractures on lava cooling and which support field-based inferences that inflation fractures depress the isotherms in the vicinity of the fracture, cause a subdivision of the lava core, control the location of the final portion of the lava flow to solidify, and cause significant changes in the local cooling fracture orientations. In addition to perturbing isotherms, inflation fractures cause a lava flow to completely solidify in a shorter amount of time than an identically shaped flow that does not contain an inflation fracture.

Kattenhorn, Simon A.; Schaefer, Conrad J.

2008-03-01

182

Fracture mechanics analysis for various fiber/matrix interface loadings  

NASA Technical Reports Server (NTRS)

Fiber/matrix (F/M) cracking was analyzed to provide better understanding and guidance in developing F/M interface fracture toughness tests. Two configurations, corresponding to F/M cracking at a broken fiber and at the free edge, were investigated. The effects of mechanical loading, thermal cooldown, and friction were investigated. Each configuration was analyzed for two loadings: longitudinal and normal to the fiber. A nonlinear finite element analysis was performed to model friction and slip at the F/M interface. A new procedure for fitting a square-root singularity to calculated stresses was developed to determine stress intensity factors (K sub I and K sub II) for a bimaterial interface crack. For the case of F/M cracking at a broken fiber with longitudinal loading, crack tip conditions were strongly influenced by interface friction. As a result, an F/M interface toughness test based on this case was not recommended because nonlinear data analysis methods would be required. For the free edge crack configuration, both mechanical and thermal loading caused crack opening, thereby avoiding frictional effects. A F/M interface toughness test based on this configuration would provide data for K(sub I)/K(sub II) ratios of about 0.7 and 1.6 for fiber and radial normal loading, respectively. However, thermal effects must be accounted for in the data analysis.

Naik, R. A.; Crews, J. H., Jr.

1991-01-01

183

Fracture mechanics analysis for various fiber/matrix interface loadings  

NASA Technical Reports Server (NTRS)

Fiber/matrix (F/M) cracking was analyzed to provide better understanding and guidance in developing F/M interface fracture toughness tests. Two configurations, corresponding to F/M cracking at a broken fiber and at the free edge, were investigated. The effects of mechanical loading, thermal cooldown, and friction were investigated. Each configuration was analyzed for two loadings: longitudinal and normal to the fiber. A nonlinear finite element analysis was performed to model friction and slip at the F/M interface. A new procedure for fitting a square-root singularity to calculated stresses was developed to determine stress intensity factors (K sub I and K sub II) for a bimaterial interface crack. For the case of F/M cracking at a broken fiber with longitudinal loading, crack tip conditions were strongly influenced by interface friction. As a result, an F/M interface toughness test based on this case was not recommended because nonlinear data analysis methods would be required. For the free edge crack configuration, both mechanical and thermal loading caused crack opening, thereby avoiding frictional effects. An F/M interface toughness test based on this configuration would provide data for K(sub I)/K(sub II) ratios of about 0.7 and 1.6 for fiber and radial normal loading, respectively. However, thermal effects must be accounted for in the data analysis.

Naik, R. A.; Crews, J. H., Jr.

1991-01-01

184

Fracture mechanics analysis for various fiber/matrix interface loadings  

NASA Technical Reports Server (NTRS)

Fiber/matrix (F/M) cracking was analyzed to provide better understanding and guidance in developing F/M interface fracture toughness tests. Two configurations, corresponding to F/M cracking at a broken fiber and at the free edge, were investigated. The effects of mechanical loading, thermal cooldown, and friction were investigated. Each configuration was analyzed for two loadings: longitudinal and normal to the fiber. A nonlinear finite element analysis was performed to model friction and slip at the F/M interface. A new procedure for fitting a square-root singularity to calculated stresses was developed to determine stress intensity factors (K sub I and K sub II) for a bimaterial interface crack. For the case of F/M cracking at a broken fiber with longitudinal loading, crack tip conditions were strongly influenced by interface friction. As a result, an F/M interface toughness test based on this case was not recommended because nonlinear data analysis methods would be required. For the free edge crack configuration, both mechanical and thermal loading caused crack opening, theory avoiding fractional effects. A F/M interface toughness test based on this configuration would provide data for K(sub I/K(sub II) ratios of about 0.7 and 1.6 for fiber and radial normal loading, respectively. However, thermal effects must be accounted for in the data analysis.

Naik, Rajiv A.; Crews, John H., Jr.

1992-01-01

185

Fracture mechanisms of thin amorphous carbon films in nanoindentation  

Microsoft Academic Search

The nanoindentation fracture of amorphous carbon films on silicon substrate was studied. Load-displacement curves were obtained during indentation in conjunction with the scanning electron microscope (SEM) observations of fractured surfaces at different loads. The fracture process was found to progress in three stages: (1) first ring-like through-thickness cracks form around the indenter by high stresses in the contact area; (2)

Xiaodong Li; Dongfeng Diao; Bharat Bhushan

1997-01-01

186

Application of fracture mechanics in electrical/mechanical failures of dielectrics  

NASA Astrophysics Data System (ADS)

Theoretical and experimental study of the mechanical/electrical fracture behavior of dielectric materials, piezoelectric ceramics PZT 8, PZT 4, and polymeric material poly vinyl chloride (PVC), was made in this work. The charge-free zone (CFZ) model proposed by Zhang et al. for the failure of conductive cracks in dielectrics, which was well verified by the experimental results of depoled piezoelectric ceramics PZT 4, was extended to predict the failure behavior of conductive cracks in piezoelectric ceramics. Piezoelectric ceramics were treated as mechanically brittle and electrically ductile materials in the charge-free zone model. The failure criterion, developed from the CFZ model, for conductive cracks in piezoelectric ceramics under mechanical and/or electrical loading has an elliptic shape in terms of the normalized electric intensity factor and the normalized stress intensity factor. To verify the theoretical prediction from the CFZ model for piezoelectric ceramics, experiment was conducted to study the failure behavior of electrically conductive cracks (deep notches) in poled lead zirconate titanate PZT-8 ceramics. When the critical stress intensity factor was normalized by the critical stress intensity factor under purely mechanical loading and the critical electric intensity factor was normalized by the critical electric intensity factor under purely electric loading, the experimental results revealed that the failure behavior of the conductive cracks in the ceramics was described by an elliptic function of the normalized electric intensity factor versus the normalized stress intensity factor under combined mechanical and electric loading. The experimental results verified well the theoretical predictions from the CFZ model. The relationship between strain (deformation) and electric field (voltage) is linear when electric fled (voltage) is low. The relationship becomes nonlinear at high electric field (voltage). In order to adopt the linear constitutive equations which have simple forms, and to cover the actual applying procedure at the same time, a novel concept of secant piezoelectric constant was introduced to refine the CFZ model. In addition, the concepts of fracture mechanics, which were successfully applied in the study of poled PZT 4, PZT 8 and depoled PZT 4, were introduced to study the electrical failure behavior of polymeric material poly vinyl chloride (PVC). Two kinds of samples, compact tensile (CT) samples and the double notched samples, were used to obtain the electrical fracture toughnesses. The electrical fracture toughnesses obtained from CT samples were higher than those obtained from the double notched samples. This showed that for polymers, electrical fracture toughnesses were not only related to the tested materials, but also related to the conditions of how the notch tips were electrically biased.

Liu, Guoning

187

Chemically- and mechanically-mediated influences on the transport and mechanical characteristics of rock fractures  

SciTech Connect

A model is presented to represent changes in the mechanical and transport characteristics of fractured rock that result from coupled mechanical and chemical effects. The specific influence is the elevation of dissolution rates on contacting asperities, which results in a stress- and temperature-dependent permanent closure. A model representing this pressure-dissolution-like behavior is adapted to define the threshold and resulting response in terms of fundamental thermodynamic properties of a contacting fracture. These relations are incorporated in a stress-stiffening model of fracture closure to define the stress- and temperature-dependency of aperture loss and behavior during stress and temperature cycling. These models compare well with laboratory and field experiments, representing both decoupled isobaric and isothermal responses. The model was applied to explore the impact of these responses on heated structures in rock. The result showed a reduction in ultimate induced stresses over the case where chemical effects were not incorporated, with permanent reduction in final stresses after cooling to ambient conditions. Similarly, permeabilities may be lower than they were in the case where chemical effects were not considered, with a net reduction apparent even after cooling to ambient temperature. These heretofore-neglected effects may have a correspondingly significant impact on the performance of heated structures in rock, such as repositories for the containment of radioactive wastes.

Min, K.-B.; Rutqvist, J.; Elsworth, D.

2009-02-01

188

Fluid flow, structural, and fracture mechanics modeling associated with hydraulic stimulation operations  

SciTech Connect

A summary review of hydraulic fracture modeling is given. The equations governing pertinent fluid flow, structural, and fracture mechanics responses are presented along with salient assumptions. The finite element modeling approach is used to discretize the field equations and compute the fracture dimensions, fluid pressure profile, leak-off, and stress intensity factors. In addition, the effects of frac fluid properties, layered strata, in situ stresses, and bi-material interface characteristics are discussed and numerical examples are presented. 50 refs.

Advani, S.H.; Lee, J.K.; Hamid, M.S.; Gurdogan, O.; Khattab, H.

1982-01-01

189

Fracture criterion for conductive cracks in soda-lime glass under combined mechanical and electrical loading  

Microsoft Academic Search

Fracture tests of electrically conductive cracks on pre-notched four-point bending soda-lime glass samples were conducted\\u000a under combined mechanical and electrical loading. The experimental results show that the critical stress intensity factor\\u000a at fracture is reduced if an electric field is applied, thereby indicating that the electric field makes contributions to\\u000a the fracture of conductive cracks. Base on the charge-free zone

Dong-Jun Yan; Hai-You Huang; Chi-Wai Cheung; Tong-Yi Zhang

2010-01-01

190

Mechanical factors associated with posterior rib fractures: laboratory and case studies  

Microsoft Academic Search

Objective. The objective of this study was to explore the mechanical factors associated with posterior rib fractures. Materials and methods. Radiographs were reviewed in ten cadavers where rib fractures were produced by opening a median sternotomy with a sternal\\u000a retractor. A second study used CT to evaluate for rib fractures following digital sternal depression and anteroposterior bimanual\\u000a thoracic compression in

Paul K. Kleinman; Alan E. Schlesinger

1997-01-01

191

Probalistic Finite Elements (PFEM) structural dynamics and fracture mechanics  

NASA Technical Reports Server (NTRS)

The purpose of this work is to develop computationally efficient methodologies for assessing the effects of randomness in loads, material properties, and other aspects of a problem by a finite element analysis. The resulting group of methods is called probabilistic finite elements (PFEM). The overall objective of this work is to develop methodologies whereby the lifetime of a component can be predicted, accounting for the variability in the material and geometry of the component, the loads, and other aspects of the environment; and the range of response expected in a particular scenario can be presented to the analyst in addition to the response itself. Emphasis has been placed on methods which are not statistical in character; that is, they do not involve Monte Carlo simulations. The reason for this choice of direction is that Monte Carlo simulations of complex nonlinear response require a tremendous amount of computation. The focus of efforts so far has been on nonlinear structural dynamics. However, in the continuation of this project, emphasis will be shifted to probabilistic fracture mechanics so that the effect of randomness in crack geometry and material properties can be studied interactively with the effect of random load and environment.

Liu, Wing-Kam; Belytschko, Ted; Mani, A.; Besterfield, G.

1989-01-01

192

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

NASA Technical Reports Server (NTRS)

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.

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

193

NUMERICAL SIMULATION OF FRACTURE MECHANICS IN A BRONZE VALVE THAT LEADS THE WATER FLOW  

Microsoft Academic Search

To understand better the generation and propagation of fracture in solid pieces when they are submitted to constant or cyclical loads, one of the greater and simpler alternative is to simulate numerically the mechanic fractures in the crack generated in the solid, because, now modern softwares exist to accomplish this study type. Well then, many phenomena can be understood and

F. Bertelli; M. M. Pariona

194

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

PubMed Central

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.

Abe, Hiroyuki

2009-01-01

195

Probabilistic Fracture Mechanics: A Validation of Predictive Capability.  

National Technical Information Service (NTIS)

A two-phase task was undertaken to the Probabilistic Fracture Analysis Code (PROFRANC) developed under this project. Phase one consisted in predicting deterministically the outcome of a subset of a larger number of experiments in which variability in geom...

A. R. Ingraffea M. Grigoriu

1990-01-01

196

Acoustic Emission and Fracture Mechanics Testing of Metals and Composites.  

National Technical Information Service (NTIS)

Acoustic emission testing has found many uses in recent years and new applications are constantly being uncovered. One of the most fruitful areas for application lies in the characterization of microscopic processes of yielding and fracture, and macroscop...

A. S. Tetelman

1972-01-01

197

Some basic fracture mechanics concepts in functionally graded materials  

Microsoft Academic Search

In this paper, the crack-tip fields in a general nonhomogeneous material are summarized. The fracture toughness and R-curve of functionally graded materials (FGMs) are studied based on the crack-bridging concept and a rule of mixtures. It is shown that the fracture toughness is significantly increased when a crack grows from the ceramic-rich region into the metal-rich region in an alumina-nickel

Z.-H. Jin; R. C. Batra

1996-01-01

198

Mechanisms and Management of Stress Fractures in Physically Active Persons  

PubMed Central

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.

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

2002-01-01

199

Fracture Mechanics and Surface Chemistry Studies of Fatigue Crack Growth in an Aluminum Alloy.  

National Technical Information Service (NTIS)

Fracture mechanics and surface chemistry studies were carried out to develop further understanding of the influence of water vapor on fatigue crack growth in aluminum alloys. The room temperature fatigue crack growth response was determined for 2219-T851 ...

R. P. Wei P. S. Pao R. G. Hart T. W. Weir G. W. Simmons

1979-01-01

200

Analyses of Some Benchmark Cases in Fracture Mechanics Using Boundary Element Method.  

National Technical Information Service (NTIS)

The boundary element method and especially the analysis of fracture mechanics problems by using the dual boundary element program Cracker (Portela and Aliabadi 1992) is introduced. This code is especially suitable for studying crack growth in two-dimensio...

J. Tuhkuri

1994-01-01

201

Applications and Limits of Application of Fracture Mechanics Methods in Assessing the Safety of Components.  

National Technical Information Service (NTIS)

On the basis of fracture mechanics calculations and experimental investigations, it is shown how cracks of different shape and location behave under given static and cyclic loads. In particular, component safety with regard to spontaneous failure and crac...

R. Stahlberg

1977-01-01

202

Mode I cracking versus dilatancy banding: Experimental constraints on the mechanisms of extension fracturing  

NASA Astrophysics Data System (ADS)

Fractures or discontinuities perpendicular to the least stress ?3 were generated in a synthetic rock analogue (granular, frictional, cohesive, and dilatant) material in axisymmetric extension tests. These fractures are of two types defined by the mean stress ?. When ? is very small, the fractures form through the mode I cracking at tensile ?3 equal to the material tensile strength. The fracture walls have smooth surfaces. At higher ?, these surfaces become rougher, with the topography features forming faint or delicate plumose patterns. The amplitude of the plumose topography increases with ?. The axial stress ?3 at fracturing reduces in magnitude and changes in sign with the ? increase. Thus ?3 orthogonal discontinuities can form at compressive ?3. SEM observations show that these discontinuities are deformation localization bands where the material is characterized by the heterogeneous decohesion and volume and porosity increase due to dilatancy. The band thickness is several grain sizes. At formation, the bands are not opened, so they are not mode I fractures. They become fractures with plumose fractography after the separation of the sample parts along the band. The formation mechanism of these discontinuities or fractures is not completely clear, but it is suggested that it represents a running constitutive instability in the form of dilatancy banding (with further ? increase the bands become inclined to ?1, i.e., shear). The similarity between the experimentally generated plumose surface fractures and natural joints is discussed, and it is suggested that they can be formed as propagating constitutive instabilities.

Chemenda, A. I.; Nguyen, S.-H.; Petit, J.-P.; Ambre, J.

2011-04-01

203

Some Fundamental Fracture Mechanisms Applicable to Advanced Filament Reinforced Composites  

Microsoft Academic Search

The object of this study is to establish experimentally the critical fracture modes of an epoxy matrix in the vicinity of a break in a high modulus, high strength filament simulating the effect of tensile loading on unidirectional composites. Three distinct failure modes were observed to occur and the nature of these three modes is explained through an analysis of

J. Mullin; J. M. Berry; A. Gatti

1968-01-01

204

Measurement of residual stresses using fracture mechanics weight functions  

Microsoft Academic Search

A residual stress measurement method has been developed to quantify through-the-thickness residual stresses. Accurate measurement of residual stresses is crucial for many engineering structures. Fabrication processes such as welding and machining generate residual stresses that are difficult to predict. Residual stresses affect the integrity of structures through promoting failures due to brittle fracture, fatigue, stress corrosion cracking, and wear. In

Fan

2000-01-01

205

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

SciTech Connect

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.

Stephen L. Karner, Ph.D

2006-02-01

206

Elasto-plasticity in wrinkled polymerized lipid membranes.  

PubMed

Biomembranes shown to behave like elastic sheets, can also suffer plastic deformations. Neutron scattering experiments on partially polymerised wrinkled membranes revealed that when a critical degree of polymerisation is crossed, the wrinkled membranes do not resume their spherical shapes. Instead they remain wrinkled and rigid while their non-polymerised counterparts resume their spherical floppy shapes. The yield stress of these membranes, measured for the first time via the fractal dimension, is intimately related to the degree of polymerisation probably through a 2D disorder that quenches the lateral diffusion of the lipid molecules. This work might shed light on the physical reason behind the irreversible deformation of echinocytes, acanthocytes and malaria infected red blood cells. PMID:24424373

Chaieb, Sahraoui

2014-01-01

207

Potential impact of enhanced fracture-toughness data on fracture mechanics assessment of PWR vessel integrity for pressurized thermal shock  

SciTech Connect

The Heavy Section Steel Technology (HSST) Program is involved with the generation of enhanced fracture-initiation toughness and fracture-arrest toughness data of prototypic nuclear reactor vessel steels. These two sets of data are enhanced because they have distinguishing characteristics that could potentially impact PWR pressure vessel integrity assessments for the pressurized-thermal shock (PTS) loading condition which is a major plant-life extension issue to be confronted in the 1990's. A series of large-scale fracture-mechanics experiments have produced crack-arrest (K{sub Ia}) data with the distinguishing characteristic that the values are considerably above 220 MPA {center dot} {radical}m. The implicit limit of the ASME Code and the limit used in the Integrated Pressurized Thermal Shock (IPTS) studies. Currently, the HSST Program is planning experiments to verify and quantify for A533B steel the distinguishing characteristic of elevated the distinguishing characteristic of elevated initiation-fracture toughness for shallow flaws which has been observed for other steels. The results of the analyses indicated that application of the enhanced K{sub Ia} data does reduce the conditional probability of failure P(F{vert bar}E); however, it does not appear to have the potential to significantly impact the results of PTS analyses. The application of enhanced fracture-initiation-toughness data for shallow flaws also reduces P(F{vert bar}E), and does appear to have a potential for significantly affecting the results of PTS analyses. 19 refs., 11 figs., 1 tab.

Dickson, T.L.; Theiss, T.J.

1991-01-01

208

Fast water infiltration: a mechanism for fracture formation during land subsidence  

NASA Astrophysics Data System (ADS)

A mechanism for fracture generation and for triggering land subsidence is presented. Infiltration through a pre-existing fracture zone into a two-layered system, as well as the deformation of unconsolidated sediments on the land surface, was numerically investigated. The numerical simulation of infiltration is based on a two-phase flow-model concept for porous media, and for the deformation, it is based on a Mohr-Coulomb model concept. Different studies with variations of the fracture parameter and infiltration conditions have been carried out. The infiltration results show that fast infiltration in a partially saturated aquifer leads to land subsidence, extension of pre-existing fractured zones and the generation of new cracks. If the water column is only on the fracture, the clay layer acts like a barrier and inhibits the infiltration through the fracture. If the water column covers the entire surface, the barrier effect is overcome; the infiltration intensity depends on the height of the water column, the fracture permeability and the fracture width. The deformation results show that a strong rainfall event of 2 h leads to deformations that are about 30 % of the vertical and 70 % of the horizontal annual land-subsidence rates.

Martinez, Isaac; Hinkelmann, Reinhard; Savidis, Stavros

2013-06-01

209

Computational methods for viscoplastic dynamic fracture mechanics analysis  

Microsoft Academic Search

The role of nonlinear rate-dependent effects in the interpretation of crack run-arrest events in ductile materials is being investigated by the Heavy-Section Steel Technology (HSST) program through development and applications of viscoplastic-dynamic finite element analysis techniques. This paper describes a portion of these studies wherein various viscoplastic constitutive models and several proposed nonlinear fracture criteria are being installed in general

B. R. Bass; C. E. Pugh; J. Kenney-Walker; R. J. Dexter; P. E. ODonoghue; C. W. Schwartz

1988-01-01

210

The WST method, a fracture mechanics test method for FRC  

Microsoft Academic Search

The applicability of the wedge-splitting test method (WST), for determining fracture properties of fibre-reinforced concrete,\\u000a is discussed. Experimental results, using the WST method, are compared with results from uniaxial tension tests (UTT) and\\u000a three-point bending tests (3PBT) for five different FRC compositions. Furthermore, for the WST method, two different specimen\\u000a sizes have been investigated. Results from this investigation demonstrate the

I. Löfgren; H. Stang; J. F. Olesen

2008-01-01

211

Nondestructive evaluation of mechanical and fracture characteristics of ferritic steels using automated ball identation testing  

SciTech Connect

Mechanical properties of various ferritic steels commonly used for pressure boundary applications in light water reactors are characterized using a novel portable stress-strain microprobe (SSM) system. The SSM system utilizes an automated ball indentation (ABI) technique to measure yield strength, stress-strain curve, strength coefficient, and strain-hardening-exponent (uniform ductility). The technique is essentially nondestructive, albeit small indentations are left following the tests. These, however, leave surface compressive stresses that could actually retard crack initiation characteristics. The ABI-derived mechanical properties agreed with those obtained using conventional destructive tensile tests. To minimize specimen-to-specimen scatter, the grip/shoulder sections were used for ABI testing. In addition, the fracture properties are characterized in terms of a new fracture parameter, indentation energy to fracture (IEF), derived from the temperature variation of the true stress compared with true strain using the critical-stress-to-fracture concept.

Murty, K.L.; Mathew, M.D.; Miraglia, P.Q. [North Carolina State Univ., Raleigh, NC (United States)] [and others

1997-12-01

212

Fracture characteristics of Al4 pct Mg mechanically alloyed with SiC  

Microsoft Academic Search

Subcritical crack growth and rapid fracture of the mechanically alloyed aluminum alloy IN-9052* reinforced with SiC particles\\u000a have been investigated. Fatigue crack growth rates for the composite exceed those of the unreinforced alloy, except that the\\u000a threshold stress intensity for growth is higher for the composite. Fracture toughness of the composite is about 9 MPa?m compared\\u000a to a (reported) value

D. L. Davidson

1987-01-01

213

Investigation of the fracture mechanism in Ti5Al2.5Sn at cryogenic temperatures  

Microsoft Academic Search

Fractography and metallographic sectioning were used to investigate the influence of microstructure on the fracture mechanism and fracture toughness of normal interstitial and extra low interstitial (EL) plates of Ti-5Al-2.5Sn at cryogenic temperatures. Plates of each grade were mill annealed at 815 C followed by either air or furnace cooling. The lower iron content of the ELI alloys resulted in

R. H. Vanstone

1977-01-01

214

Investigation of the fracture mechanism of Ti5AI2.5Sn at cryogenic temperatures  

Microsoft Academic Search

Fractography and metallographic sectioning were used to investigate the influence of microstructure on the fracture mechanism\\u000a and fracture toughness (KIc) of normal interstitial and extra low interstitial (ELI) Ti-5Al-2.5Sn at 20 K (-423F) and 77 K (-320F). Plates of each\\u000a grade were mill annealed at 815C (1500F) followed by either air or furnace cooling. These variations in composition and\\u000a cooling

R. H. Van Stone; J. R. Low; J. L. Shannon

1978-01-01

215

Investigation of the fracture mechanism of Ti5AI2.5Sn at cryogenic temperatures  

Microsoft Academic Search

Fractography and metallographic sectioning were used to investigate the influence of microstructure on the fracture mechanism and fracture toughness (KIc) of normal interstitial and extra low interstitial (ELI) Ti-5Al-2.5Sn at 20 K (-423°F) and 77 K (-320°F). Plates of each grade were mill annealed at 815°C (1500°F) followed by either air or furnace cooling. These variations in composition and cooling

R. H. van Stone; J. R. Low; J. L. Shannon

1978-01-01

216

The influence of compositional and microstructural variations on the mechanism of static fracture in aluminum alloys  

Microsoft Academic Search

The object of the paper is to examine the effects of alloy purity and state of aging on the fracture mechanism and resultant\\u000a toughness of pure Al-Cu alloys, and commercial duralumin. In pure alloys, the transition from a shear to an intergranular\\u000a mode of fracture with overaging is associated with changes in the nature and size of the matrix precipitate,

G. G. Garrett; J. F. Knott

1978-01-01

217

Modeling naturally fractured reservoirs: From experimental rock mechanics to flow simulation  

NASA Astrophysics Data System (ADS)

Fractures have a big impact on reservoir production but are inherently difficult to quantify. This study gives a robust and practical workflow to obtain a mechanically consistent naturally fractured reservoir model without direct sampling of the fracture network. The three tiers of the workflow are: (1) subcritical testing, (2) geomechanical modeling, and (3) flow modeling. Subcritical fracture index, a rock property, has been shown to influence fracture attributes such as length, spacing and connectivity. Subcritical tests show that the average subcritical index for sandstones in ambient air is around 62, whereas the average value for microstructurally comparable carbonates samples is 120. Thin-section analysis shows that an increase in cement content increases the subcritical index. Furthermore, sandstone samples containing more than 15% carbonate cement, sandstone samples containing more than 40% clay, and pure carbonate samples exhibit a large drop in subcritical index when the environment is changed from ambient air or oil to fresh water or brine. Geomechanical modeling has shown that the mechanical bed thickness has a large influence on fracture pattern characteristics and has the potential to overshadow fracture pattern changes due to strain level, strain anisotropy and subcritical index. Furthermore, an increase in strain anisotropy reduces the number of dominant through-going fracture sets and decreases the fracture spacing between the through-going fractures. This spacing variation not only influences the preferential drainage direction, it can also enhance the drainage efficiency, because more rock is exposed to the through-going fractures which are more likely to be intersected by a borehole. The level of detail provided by the geomechanical model greatly exceeds the level of detail normally used in reservoir simulation. Therefore, upscaling of the geomechanically generated fracture patterns is necessary for practical flow modeling. This study shows that different upscaling methods can lead to large variations in permeability prediction. A Local Grid Refinement around the well should be maintained, because it will almost always ensure accurate production prediction. This method is preferred over the dual permeability approach, which can be calibrated to match production data in some cases, but often requires using an unrealistic representation of the fracture pattern.

Rijken, Margaretha Catharina Maria

218

Mechanical behavior and fracture characteristics of off-axis fiber composites. 1: Experimental investigation. [at the Lewis Research Center  

NASA Technical Reports Server (NTRS)

The mechanical behavior, fracture surfaces, and fracture modes of unidirectional high-modulus graphite-fiber/epoxy composites subjected to off-axis tensile loads were investigated experimentally. The investigation included the generation of stress-strain-to-fracture data and scanning electron microscope studies of the fractured surfaces. The results led to the identification of fracture modes and distinct fracture surface characteristics for off-axis tensile loading. The results also led to the formulation of critical for identifying and characterizing these fracture modes and their associated fracture surfaces. The results presented and discussed herein were used in the theoretical investigation and comparisons described in Part 2. These results should also provide a good foundation for identifying, characterizing, and quantifying fracture modes in both off-axis and angle-plied laminates.

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

1977-01-01

219

Modelling the physical properties of cracked rocks using fracture mechanics and statistical physics  

Microsoft Academic Search

Cracks play a major role in most rocks submitted to crustal conditions. Mechanically, cracks make the rock much more compliant. They also make it much easier for fluid to flow through any rock body. Relying on Fracture Mechanics and Statistical Physics, we introduce a few key concepts which allow to understand and quantify how cracks do modify both the elastic

P. Benson; A. Schubnel; S. Vinciguerra; J. Hazzard; R. Young; P. Meredith

2004-01-01

220

Fracture mechanisms in rigid core-shell particle modified high performance epoxies  

Microsoft Academic Search

The fracture mechanisms of a high performance epoxy system modified with two types of preformed rigid core-shell particles (RCSP) were investigated. The use of the preformed RCSP anables the control of the dispersion of the toughener phase in the epoxy, which, in turn, allows the mechanical properties of the modified epoxy to be optimized. The toughening effect via the RCSP

H.-J. Sue; E. I. Garcia Meitin; D. M. Pickelman; C. J. Bott

1996-01-01

221

Fracture mechanics analysis of coating\\/substrate systems Part I: Analysis of tensile and bending experiments  

Microsoft Academic Search

A flnite fracture mechanics model is used to predict the development of multiple cracks in the coating layer of coating\\/substrate systems. The stresses in a cracked coating are evaluated by a variational mechanics approach. These stresses are then used to calculate the total energy released due to the formation of a complete crack in the coating layer. The analysis can

Sung-Ryong Kim; John A. Nairn

222

Modeling of Colloid Transport Mechanisms Facilitating Migration of Radionuclides in Fractured Media  

SciTech Connect

Performance assessments of high-level radioactive waste disposal have emphasized the role of colloids in the migration of radionuclides in the geosphere. The transport of colloids often brings them in contact with fracture surfaces or porous rock matrix. Colloids that attach to these surfaces are treated as being immobile and are called filtered colloids. The filtered colloids could be released into the fracture again; that is, the attachment of colloids may be reversible. Also, the colloids in the fracture could diffuse into the porous matrix rock. A methodology is proposed to evaluate a predictive model to assess transport within the fractured rock as well as various phenomenological coefficients employed in the different mechanisms, such as filtration, remobilization, and matrix diffusion of colloids. The governing equations of colloids considering mechanisms of the colloidal transport in the fractured media, including filtration, remobilization, and matrix diffusion, have been modeled and solved analytically in previous studies. In the present study, transport equations of colloids and radionuclides that consider the combination of the aforementioned transport mechanisms have also been solved numerically and investigated. The total concentration of mobile radionuclides in the fracture becomes lower because the concentration of mobile colloids in the fracture decreases when the filtration coefficient for colloids increases. Additionally, the concentration of mobile radionuclides was increased at any given time step due to the higher sorption partition coefficient of radionuclides associated with colloids. The results also show that the concentration of radionuclides in the fracture zone decreases when the remobilization coefficient of colloids or the percentages of the matrix diffusion flux of colloids increase.

Li Shihhai [National Tsing Hua University, Taiwan (China); Yang, H.-T. [National Tsing Hua University, Taiwan (China); Jen, C.-P. [National Cheng Kung University, Taiwan (China)

2004-12-15

223

[The fatigue fracture of the calcaneous. The experimental proof of its mechanical genesis (author's transl)].  

PubMed

The calcaneus is generally stressed by bending. Spongious bone has a trajectorial structure, and is adapted to the stress to an optimal degree. In fatigue fractures, the dense zone runs perpendicularly to the compressive bundles of the spongious bone. Presuming a mechanical genesis, the sclerotic band is expected to run rectangularly to the tensile bundles. This mechanical condition can be performed in a photoelastic experiment. The proof of the presence of a similar mechanical situation during movement of the foot may be derived from electromyygraphic examinations (Mac Conaill 1969, Basmajian 1974). The appearance of these fractures shows that the time is too short to allow the bone to adapt functionally. It may be concluded from this, that the cause of the fracture is a sudden, sharp increase in exercise. PMID:888523

Gierse, H

1977-06-01

224

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

USGS Publications Warehouse

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.

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

2009-01-01

225

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

NASA Astrophysics Data System (ADS)

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.

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

2009-08-01

226

Fracture Mechanism in Fatigue of Nickel-Based Superalloy Inconel 718 at Elevated Temperatures  

NASA Astrophysics Data System (ADS)

In order to investigate the fracture mechanism in fatigue of nickel-based superalloy at elevated temperature, rotating bending fatigue tests were carried out for Inconel 718 at 500°C and 600°C up to 108 cycles. At both temperatures, fatigue fracture initiated from the subsurface of specimens in the long life region, though the origin of fracture was on the surface of specimens in the short life region. As a result, S-N curves showed a two-step shape. Although surface cracking was observed even in the long life region at elevated temperatures, similar results as observed at room temperature, surface cracks ceased propagating after extending to approximately 20-30?m at elevated temperatures. Meanwhile, intergranular cracking was observed at the origins of subsurface fracture, which was found to be nucleated in the early stage of fatigue.

Kawagoishi, Norio; Chen, Qiang; Yan, Nu; Goto, Masahiro; Wang, Qingyuan; Ohzono, Yoshihisa

227

Micro-Computed Tomography Assessment of Fracture Healing: Relationships among Callus Structure, Composition, and Mechanical Function  

PubMed Central

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 (?CT) 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 (?TMD), effective polar moment of inertia (Jeff), 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 ?CT 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 ?TMD explained 62% of the variation in torsional strength (p<0.001); and TMD, BMC, BV/TV, and ?TMD explained 70% of the variation in torsional rigidity (p<0.001). These results indicate that fracture callus mechanical properties can be predicted by several ?CT-derived measures of callus structure and composition. These findings form the basis for developing non-invasive assessments of fracture healing and for identifying biological and biomechanical mechanisms that lead to impaired or enhanced healing.

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

2009-01-01

228

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

NASA Astrophysics Data System (ADS)

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.

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

2011-09-01

229

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

NASA Technical Reports Server (NTRS)

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

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

2010-01-01

230

Permeability Evolution of Fractured Anhydrite Caused by Chemical and Mechanical Alteration  

NASA Astrophysics Data System (ADS)

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 ?m) 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 by a rapid increase in differential pressure corresponding to a two-order-of-magnitude decrease in permeability. During the experiment, the diameter of the core decreased by ~300 ?m at the inlet and a skin of gypsum (Ca2SO42H2O) was created along the length of the fracture. Dissolution of anhydrite and transition to gypsum of additional anhydrite weakened the fracture surfaces leading to closure of the fracture with a corresponding reduction in aperture and permeability. Additional experiments explore the influence of flow at a lower flow rate, which, in the absence of a large confining stress, has been shown to lead to the development of dissolution channels or wormholes.

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

2011-12-01

231

Accurate in vitro identification of fracture onset in bones: failure mechanism of the proximal human femur.  

PubMed

Bone fractures have extensively been investigated, especially for the proximal femur. While failure load can easily be recorded, and the fracture surface is readily accessible, identification of the point of fracture initiation is difficult. Accurate location of fracture initiation is extremely important to understand the multi-scale determinants of bone fracture. In this study, a recently developed technique based on electro-conductive lines was applied to the proximal femoral metaphysis to elucidate the fracture mechanism. Eight cadaveric femurs were prepared with 15-20 electro-conductive lines (crack-grid) covering the proximal region. The crack-grid was connected to a dedicated data-logger that monitored electrical continuity of each line at 700 kHz. High-speed videos (12,000 frames/s, 0.1-0.2 mm pixel size) of the destructive tests were acquired. Most crack-grid-lines failed in a time-span of 0.08-0.50 ms, which was comparable to that identified in the high-speed videos, and consistent with previous video recordings. However, on all specimens 1-3 crack-grid-lines failed significantly earlier (2-200 ms) than the majority of the crack-grid-lines. The first crack-grid-line to fail was always the closest one to the point of fracture initiation identified in the high-speed videos (superior-lateral neck region). Then the crack propagated simultaneously, at comparable velocity on the anterior and posterior sides of the neck. Such a failure pattern has never been observed before, as spatial resolution of the high-speed videos prevented from observing the initial opening of a crack. This mechanism (fracture onset, time-lag, followed by catastrophic failure) can be explained with a transfer of load to the internal trabecular structure caused by the initial fracture of the thin cortical shell. This study proves the suitability of the crack-grid method to investigate bone fractures associated to tensile stress. The crack-grid method enables significantly faster sampling than high-speed cameras. The present findings elucidate some aspects of the failure mechanism of the proximal human femoral metaphysis. PMID:23218142

Juszczyk, Mateusz Maria; Cristofolini, Luca; Salvà, Marco; Zani, Lorenzo; Schileo, Enrico; Viceconti, Marco

2013-01-01

232

Case histories involving fatigue and fracture mechanics; Proceedings of the Symposium, Charleston, SC, Mar. 21, 22, 1985  

NASA Technical Reports Server (NTRS)

Papers are presented on cracking at nozzle corners in the nuclear pressure vessel industry, applied fracture mechanics for assessing defect significance in a crude oil pipeline, failure analysis of a large wind-tunnel compressor blade, analysis of a compressor-wheel failure, and preventing fracture by inspection and analysis. Consideration is also given to the fatigue crack growth predictions of welded aircraft structures containing flaws in the residual stress field, the fatigue and fracture mechanics analysis of a compression loaded aircraft structure, fracture of an aircraft horizontal stabilizer, fatigue life analysis of fuel tank skins under combined loads, and aircraft structural maintenance recommendations based on fracture mechanics analysis. Additional papers discuss an analysis of two metal-forming die failures, an analysis of a failed saw arbor, and the role of fracture mechanics in assessing the effect on fatigue life of design changes in welded fabrications.

Hudson, C. Michael (editor); Rich, Thomas P. (editor)

1986-01-01

233

Development of hyperplasticity models for soil mechanics  

NASA Astrophysics Data System (ADS)

Hyperplasticity theory was developed by Collins and Houlsby (Proc. Roy. Soc. Lon. A 1997; 453:1975-2001) and Houlsby and Puzrin (Int. J. Plasticity 2000; 16(9):1017-1047). Further research has extended the method to continuous hyperplasticity, in which smooth transitions between elastic and plastic behaviour can be modelled. This paper illustrates a development of a new constitutive model for soils using hyperplasticity theory. The research begins with a simple one-dimensional elasticity model. This is extended in stages to an elasto-plastic model with a continuous internal function. The research aims to develop a soil model, which addresses some of the shortcomings of the modified cam-clay model, specifically the fact that it cannot model small strain stiffness, or the effects of immediate stress history. All expressions used are consistent with critical state soil mechanics terminology. Finally, a numerical implementation of the model using a rate-dependent algorithm is described.

Likitlersuang, S.; Houlsby, G. T.

2006-03-01

234

Mechanical property and fracture behavior of squeeze-cast Mg matrix composites  

SciTech Connect

The present study aims to investigate the microstructure and fracture properties of AZ91 Mg matrix composites fabricated by the squeeze-casting technique, with variations in the reinforcement material and applied pressure. Microstructural and fractographic observations, along with in situ fracture tests, were conducted on three different Mg matrix composites to identify the microfracture process. Two of them are reinforced with two different short fibers and the other is a whisker-reinforced composite. From the in situ fracture observation of Kaowool-reinforced composites, the effect of the applied pressure on mechanical properties is explained using a competing mechanism: the detrimental effects of fiber breakage act to impair the beneficial effects of the grain refinement and improved densification as the applied pressure increases. On the other hand, for the composites reinforced with Saffil short fibers, microcracks were initiated mainly at the fiber/matrix interfaces at considerably higher stress intensity factor levels, while the degradation of fibers was not observed even in the case of the highest applied pressure. This finding indicates that the higher applied pressure yields better mechanical properties, attributable to the Saffil short fibers having relatively high resistance to cracking. Although an improved microstructure was obtained by accommodating the appropriate applied pressure in the short fiber-reinforced composites, their mechanical properties were far below those of conventional Al matrix composites. In this regard, the Alborex aluminum borate whisker is suggested as a replacement for the short fibers used in the present investigation, to achieve better mechanical properties and fracture toughness.

Sohn, K.S. [Korea Research Inst. of Chemical Technology, Daejon (Korea, Republic of). Advanced Materials Div.; Euh, K.; Lee, S. [Pohang Univ. of Science and Technology (Korea, Republic of). Center for Advanced Aerospace Materials; Park, I. [Pusan National Univ. (Korea, Republic of). Dept. o Metallurgical Engineering

1998-10-01

235

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

PubMed Central

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.

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

2014-01-01

236

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

PubMed

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

Rippe, Marília Pivetta; Santini, Manuela Favarin; Bier, Carlos Alexandre Souza; Baldissara, Paolo; Valandro, Luiz Felipe

2014-06-01

237

Disadvantages of interfragmentary shear on fracture healing-mechanical insights through numerical simulation.  

PubMed

The outcome of secondary fracture healing processes is strongly influenced by interfragmentary motion. Shear movement is assumed to be more disadvantageous than axial movement, however, experimental results are contradictory. Numerical fracture healing models allow simulation of the fracture healing process with variation of single input parameters and under comparable, normalized mechanical conditions. Thus, a comparison of the influence of different loading directions on the healing process is possible. In this study we simulated fracture healing under several axial compressive, and translational and torsional shear movement scenarios, and compared their respective healing times. Therefore, we used a calibrated numerical model for fracture healing in sheep. Numerous variations of movement amplitudes and musculoskeletal loads were simulated for the three loading directions. Our results show that isolated axial compression was more beneficial for the fracture healing success than both isolated shearing conditions for load and displacement magnitudes which were identical as well as physiological different, and even for strain-based normalized comparable conditions. Additionally, torsional shear movements had less impeding effects than translational shear movements. Therefore, our findings suggest that osteosynthesis implants can be optimized, in particular, to limit translational interfragmentary shear under musculoskeletal loading. © 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:865-872, 2014. PMID:24648331

Steiner, Malte; Claes, Lutz; Ignatius, Anita; Simon, Ulrich; Wehner, Tim

2014-07-01

238

Fracture and failure: Analyses, mechanisms and applications; Proceedings of the Symposium, Los Angeles, CA, March 17-20, 1980  

NASA Technical Reports Server (NTRS)

Papers are presented on the application of fracture mechanics to spacecraft design, fracture control applications on the Space Shuttle reaction control thrusters, and an assessment of fatigue crack growth rate relationships for metallic airframe materials. Also considered are fracture mechanisms and microstructural relationships in Ni-base alloy systems, the use of surface deformation markings to determine crack propagation directions, case histories of metallurgical failures in the electronics industry, and a failure analysis of silica phenolic nozzle liners.

Tung, P. P. (editor); Agrawal, S. P.; Kumar, A.; Katcher, M.

1981-01-01

239

Similarity Solutions of Creep — Damage Coupled Problems in Fracture Mechanics  

Microsoft Academic Search

The asymptotic solution to Mode III and Mode I crack problems in a creeping solid in the framework of Continuum Damage Mechanics\\u000a is presented. The kinetic law of damage evolution is the Kachanov — Rabotnov equation [1]. The damage parameter is incorporated into the power-law creep constitutive equations. Thus the coupled system of damage\\u000a mechanics — creep theory equations is

L. V. Stepanova; M. E. Fedina

240

Fracture Mechanics on PVDF Polymeric Material : Specimen Geometry Effects  

Microsoft Academic Search

Polyvinylidene fluoride (PVDF) is a semi-crystalline polymer that has been widely studied for structural applications, because\\u000a it exhibits good mechanical properties and chemical resistance. Mechanical properties investigations of the PVDF under study\\u000a have been already published elsewhere [1] where the macroscopic tensile and creep behaviour over several strain rate decades, and over a large range of temperatures\\u000a have been investigated.

L. Laiarinandrasana; G. Hochstetter

241

Mechanical properties of carbonated apatite bone mineral substitute: strength, fracture and fatigue behaviour  

Microsoft Academic Search

The synthesis and properties of carbonated apatite materials have received considerable attention due to their importance for medical and dental applications. Such apatites closely resemble the mineral phase of bone, exhibiting superior osteoconductive and osteogenic properties. When formed at physiological temperature they present significant potential for bone repair and fracture fixation. The present study investigates the mechanical properties of a

E. F MORGAN; D. N YETKINLER; B. R CONSTANTZ; R. H DAUSKARDT

1997-01-01

242

Fracture Strength and Mechanism of Dental Ceramic Crown with Zirconia Thickness  

Microsoft Academic Search

As the development of zirconia crown using CAD\\/CAM technology, the usage of full zirconia crown is gradually increased. Compare to the layering technique which is fabricated with zirconia coping and veneering porcelain, full zirconia crown shows higher strength and easier laboratory procedure. To prevent mechanical fracture of the full zirconia crown, the thickness of zirconia crown and proper sintering process

G. W. Jang; H. S. Kim; H. C. Choe; M. K. Son

2011-01-01

243

The use of fracture mechanics in failure analysis in the offshore diamond mining industry  

Microsoft Academic Search

This paper considers two major failures of offshore diamond mining equipment, which should not have occurred had both fracture mechanics aspects and materials behaviour been more fully understood. The two case studies include (a) failure of a wire rope swivel, and (b) failure of a load cell (used for monitoring rope load). In case (a) the swivel shank had failed

R. B. Tait; C. Emslie

2005-01-01

244

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

NASA Technical Reports Server (NTRS)

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.

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

1994-01-01

245

Application of Parallel Processing to Probabilistic Fracture Mechanics Analysis of Gas Turbine Disks  

Microsoft Academic Search

A parallel processing methodology is developed and applied to improve the efficiency of probabilistic fracture mechanics analyses of gas turbine disks subject to metallurgical defects. A parallel processing spatial decomposition approach using a network of workstations and personal computers is described whereby each computer analyzes a region of the disk. The individual analyses are then combined to obtain the probability

Harry R. Millwater; Brian D. Shook; Sridhar Guduru; George Constantinides

246

Probabilistic fracture mechanics assessment of flaws in turbine disks including quality assurance procedures  

Microsoft Academic Search

A stochastic model for the failure of turbine disks including quality assurance procedures is established. The underlying reliability analysis is based on a fracture mechanics description using both a direct Monte Carlo simulation and a first-order reliability method. The failure probability and its sensitivity to input parameters are obtained together with confidence bounds with respect to uncertain input quantities. Assessment

G. Walz; H. Riesch-Oppermann

2006-01-01

247

Applicability of fracture mechanics to lifetime prediction of B and W ceramic heat exchanger tubes  

Microsoft Academic Search

Fracture mechanics concepts are used to predict a minimum service lifetime for silicon carbide heat exchanger tubes to be tested in a prototype industrial heat recuperator installation. Available data and the assumptions used are identified, the analytical procedures are described, and the results and implications are discussed. The primary conclusion is that no evidence exists to indicate that the service

1986-01-01

248

A fracture mechanics approach to thermal fatigue life prediction of solder joints  

Microsoft Academic Search

A life prediction approach for solder joints under thermal fatigue, based on fracture mechanics and assuming that the thermal fatigue crack propagation in solder joints is primarily controlled by the C* and the J Integrals, is presented. The approach is applied to model experiments in which surface mounted electronic components were mounted on substrates with eutectic Pb\\/Sn solder joints and

Yi-Hsin Pao

1992-01-01

249

Application of fracture mechanics concepts to hierarchical biomechanics of bone and bone-like materials  

Microsoft Academic Search

Fracture mechanics concepts are applied to gain some understanding of the hierarchical nanocomposite structures of hard biological tissues such as bone, tooth and shells. At the most elementary level of structural hierarchy, bone and bone-like materials exhibit a generic structure on the nanometer length scale consisting of hard mineral platelets arranged in a parallel staggered pattern in a soft protein

HUAJIAN GAO

250

Mode I interlaminar fracture behavior and mechanical properties of CFRPs with nanoclay-filled epoxy matrix  

Microsoft Academic Search

The mechanical properties and fracture behavior of nanocomposites and carbon fiber composites (CFRPs) containing organoclay in the epoxy matrix have been investigated. Morphological studies using TEM and XRD revealed that the clay particles within the epoxy resin were intercalated or orderly exfoliated. The organoclay brought about a significant improvement in flexural modulus, especially in the first few wt% of loading,

Naveed A. Siddiqui; Ricky S. C. Woo; Jang-Kyo Kim; Christopher C. K. Leung; Arshad Munir

2007-01-01

251

Development of Probabilistic Fracture Mechanics Analysis Code for Pipes with Stress Corrosion Cracks  

Microsoft Academic Search

Risk-Informed integrity management methodologies have been developed for Japanese nuclear power plants. One of the issues of concern is the reliability assessment of piping with flaws due to stress corrosion cracking (SCC). Therefore, the probabilistic fracture mechanics analysis code has been developed, which can perform the reliability assessment for austenitic stainless steel piping with flaws due to SCC. This paper

Hideo Machida; Manabu Arakawa; Norimichi Yamashita; Shinobu Yoshimura

2009-01-01

252

Failure probability assessment of wall-thinned nuclear pipes using probabilistic fracture mechanics  

Microsoft Academic Search

The integrity of nuclear piping system has to be maintained during operation. In order to maintain the integrity, reliable assessment procedures including fracture mechanics analysis, etc., are required. Up to now, this has been performed using conventional deterministic approaches even though there are many uncertainties to hinder a rational evaluation. In this respect, probabilistic approaches are considered as an appropriate

Sang-Min Lee; Yoon-Suk Chang; Jae-Boong Choi; Young-Jin Kim

2006-01-01

253

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

Microsoft Academic Search

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

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

1982-01-01

254

Probabilistic fracture mechanics analysis of nuclear piping considering variation of seismic loading  

Microsoft Academic Search

In conventional probabilistic fracture mechanics (PFM) analyses, seismic loading is considered as a large deterministic value, although there exists the variation of the seismic load as well as response of building and components. On the other hand, such stochastic behaviours have already been taken into account in the field of seismic probabilistic safety assessment. This paper proposes a new PFM

Hideo Machida; Shinobu Yoshimura

2002-01-01

255

Combining discrete-time Markov processes and probabilistic fracture mechanics in RI-ISI risk estimates  

Microsoft Academic Search

Based on the research conducted in the Finnish SAFIR project, which is a national nuclear energy research program, discrete-time Markov processes and probabilistic fracture mechanics (PFM) methods are further developed and applied in this paper. The purpose of this work is to increase the accuracy of risk estimates used in RI-ISI, and to quantitatively evaluate the effects of different inspection

Otso Cronvall; Ilkka Männistö

2009-01-01

256

Simultaneous uncertainty quantification of fracture mechanics based life prediction model parameters  

Microsoft Academic Search

A Bayesian technique is developed for simultaneous estimation of the equivalent initial flaw size (EIFS) and crack growth rate distributions in fracture mechanics based life prediction models from inspection data. The inference method separately quantifies the different sources of variability to obtain a data set independent EIFS distribution without the requirement for prior knowledge of the uncertainties in other parameters.

Richard Cross; Andrew Makeev; Erian Armanios

2007-01-01

257

Risk–benefit analyses of SG tube maintenance based on probabilistic fracture mechanics  

Microsoft Academic Search

As an application of probabilistic fracture mechanics (PFM), a risk–benefit analysis was performed for the purpose of optimizing maintenance activities of steam generator (SG) tubes used in pressurized water reactors (PWRs). The probabilities of the SG tube leakage and rupture are defined as risks in this study. A model was made modifying pc-PRAISE (Piping Reliability Analysis Including Seismic Events) to

Y Isobe; M Sagisaka; S Yoshimura; G Yagawa

2001-01-01

258

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

SciTech Connect

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.

Reinhold H. Dauskardt

2005-08-01

259

A statistical fracture mechanics analysis of time-dependent strength behaviour of partially stabilized zirconia  

Microsoft Academic Search

The time-dependent strength behaviour of a partially stabilized zirconia ceramic (Mg-PSZ) when subjected to constant static and cyclic stresses as well as constant stress rates is analysed in terms of a statistical fracture mechanics model given earlier by the authors. Given the lifetimes for either constant static stresses or constant stress rates it is possible to estimate the lifetimes for

Kai Duan; Yiu-Wing Mai; Brian Cotterell

1988-01-01

260

FRACTURE MECHANICAL APPROACH AND MODELS FOR FAILURE ANALYSIS OF THERMAL BARRIER COATINGS  

Microsoft Academic Search

Two simplistic models using fracture mechanics considerations are used to advance understanding of the failure conditions in TBC system. One model assumes isostrain behavior prior to the onset of crack initiation and is based on elastic energy balance approach. The other model is used for crack propagation behavior. The analysis for crack initiation suggests that the crack tip driving force,

Amar N. Kumar; Amiya Nayak; Alok R. Patnaik; Xijia Wu; Prakash C. Patnaik

261

A general solution procedure for fracture mechanics weight function evalution based on the boundary element method  

Microsoft Academic Search

This paper reports on the development of an efficient and accurate means for the direct computation of crack surface weight functions for two dimensional fracture mechanics analysis. Weight functions are mathematical representations which can be used to efficiently calculate stress intensity factors for a variety of crack loading and boundary conditions. The method is inherently capable of handling mixed-mode problems.

T. A. Cruse; S. T. Raveendra

1988-01-01

262

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

NASA Astrophysics Data System (ADS)

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.

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

1992-07-01

263

Computing a-posteriori bounds for stress intensity factors in elastic fracture mechanics  

Microsoft Academic Search

This paper mainly focuses on computing the lower and upper bounds on stress intensity factors in elastic fracture mechanics\\u000a with an efficient finite element output bound procedure on quantities of interest in engineering. The bounds procedure is\\u000a obtained by minimizing the quadratic energy functional of output with constraints of equilibrium conditions of mechanics and\\u000a continuity conditions of finite element space.

K. H. Lee; Z. C. Xuan

2004-01-01

264

Fracture Mechanics Approach to Stress Corrosion Cracking of Pipeline Steels: When Hydrogen Is the Circumstance  

Microsoft Academic Search

\\u000a Stress corrosion cracking is a problem of major concern in pipeline steels. This paper deals with the fracture mechanics approach\\u000a to the phenomenon. Paraphrasing the famous sentence by Ortega y Gasset “yo soy yo y mi circunstancia”, one could say that\\u000a the material is itself and its circumstance, the latter being the physico-chemical and mechanical environment. The paper analyzes\\u000a situations

J. Toribio

265

Study of fracture mechanisms of a Ni-Base superalloy at different temperatures  

Microsoft Academic Search

Purpose: The Ni-base superalloy GTD-111 gains its appropriate microstructure and high temperature strength through precipitation hardening mechanism. Because of their service condition, tensile properties of the alloy have strong influence on stability and life of the blades. Design\\/methodology\\/approach: Tensile fracture mechanisms of the cast and heat treated superalloy were studied over a wide range of temperatures from 25 to 950°C

S. A. Sajjadi; S. M. Zebarjad

266

A study on probabilistic fracture mechanics for nuclear pressure vessels and piping  

Microsoft Academic Search

This paper describes some recent research activities on probabilistic fracture mechanics (PFM) for nuclear pressure vessels and piping (PV&P) performed by the RC111 research committee of the Japan Society of Mechanical Engineers (JSME) under a subcontract of the Japan Atomic Energy Research Institute (JAERI). To establish standard procedures for evaluating failure probabilities of nuclear PV&P, we have set up the

Genki Yagawa; Shinobu Yoshimura

1997-01-01

267

Fracture surface analysis to understand the failure mechanisms of collagen degraded bone  

Microsoft Academic Search

Fracture surface analysis is a powerful technique to investigate bone failure mechanisms. Previously, emu tibiae were endocortically\\u000a treated with 1 M potassium hydroxide (KOH) solution for 14 days. This treatment caused in situ collagen degradation rather\\u000a than removal, with no differences in geometrical parameters, but with significant changes in mechanical properties. KOH-treated\\u000a tibiae showed significant decreases in failure stress and increased failure

Lisa Wise-Milestone; Sidney Omelon; Zhirui Wang; Marc Grynpas

2011-01-01

268

Deformation and Fracture Mechanisms of Bone and Nacre  

NASA Astrophysics Data System (ADS)

Bone and nacre are the most-known biological hard tissues to materials researchers. Although highly mineralized, both bone and nacre are amazingly tough and exhibit remarkable inelasticity, properties that are still beyond the reach of many modern ceramic materials. Very interestingly, the two hard tissues seem to have adopted totally different structural strategies for achieving mechanical robustness. Starting from a true nanocomposite of the mineralized collagen fibril and following up to seven levels of hierarchical organization, bone is built on a structure with extreme complexity. In contrast, nacre possesses a structure of surprising simplicity. Polygonal mineral tablets of micrometer size are carefully cemented together into a macroscopic wonder. A comparative analysis of the structure-property relations in bone and nacre helps us to unveil the underlying mechanisms of this puzzling phenomenon. In this review, we critically compare the various levels of structures and their mechanical contributions between bone and nacre, with a focus on inelasticity and the toughening process. We demonstrate that, although nacre and bone differ from each other in many aspects, they have adopted very similar deformation and toughening mechanisms.

Wang, Rizhi; Gupta, Himadri S.

2011-08-01

269

Simulation of crack propagation in fiber-reinforced concrete by fracture mechanics  

SciTech Connect

Mode I crack propagation in fiber-reinforced concrete (FRC) is simulated by a fracture mechanics approach. A superposition method is applied to calculate the crack tip stress intensity factor. The model relies on the fracture toughness of hardened cement paste (K{sub IC}) and the crack bridging law, so-called stress-crack width ({sigma}-{delta}) relationship of the material, as the fundamental material parameters for model input. As two examples, experimental data from steel FRC beams under three-point bending load are analyzed with the present fracture mechanics model. A good agreement has been found between model predictions and experimental results in terms of flexural stress-crack mouth opening displacement (CMOD) diagrams. These analyses and comparisons confirm that the structural performance of concrete and FRC elements, such as beams in bending, can be predicted by the simple fracture mechanics model as long as the related material properties, K{sub IC} and ({sigma}-{delta}) relationship, are known.

Zhang Jun; Li, Victor C

2004-02-01

270

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

SciTech Connect

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.

Derek Elsworth; Abraham Grader; Susan Brantley

2007-04-25

271

Nontraumatic Fracture of the Femoral Condylar Prosthesis in a Total Knee Arthroplasty Leading to Mechanical Failure  

PubMed Central

This paper reports a case of fatigue fracture of the femoral component in a cruciate-retaining cemented total knee arthroplasty (TKA). A 64-year-old man had undergone a primary TKA for osteoarthritis 10 years previously at another institution using the PFC-Sigma prosthesis. The patient recovered fully and was back to his regular activities. He presented with a history of sudden onset pain and locking of the left knee since the preceding three months. There was no history of trauma, and the patient was mobilizing with difficulty using crutches. Radiographs revealed fracture of the posterior condyle of the femoral prosthesis. Revision surgery was performed as an elective procedure revealing the broken prosthesis. The TC3RP-PFC revision prosthesis was used with a medial parapatellar approach. The patient recovered fully without any squeal. Mechanical failure of the knee arthroplasty prosthesis is rare, and nontraumatic fracture of the femoral metallic component has not been reported before.

Swamy, Girish N.; Quah, Conal; Bagouri, Elmunzar; Badhe, Nitin P.

2014-01-01

272

Recent finite element studies in plasticity and fracture mechanics  

NASA Technical Reports Server (NTRS)

The paper reviews recent work on fundamentals of elastic-plastic finite-element analysis and its applications to the mechanics of crack opening and growth in ductile solids. The presentation begins with a precise formulation of incremental equilibrium equations and their finite-element forms in a manner valid for deformations of arbitrary magnitude. Special features of computational procedures are outlined for accuracy in view of the near-incompressibility of elastic-plastic response. Applications to crack mechanics include the analysis of large plastic deformations at a progressively opening crack tip, the determination of J integral values and of limitations to J characterizations of the intensity of the crack tip field, and the determination of crack tip fields in stable crack growth.

Rice, J. R.; Mcmeeking, R. M.; Parks, D. M.; Sorensen, E. P.

1979-01-01

273

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

PubMed Central

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 m? samples of the cryoprotective agent cocktail DP6, contained in a standard 15 m? 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.

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

2008-01-01

274

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

PubMed Central

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.

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

2010-01-01

275

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

NASA Technical Reports Server (NTRS)

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.

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

2011-01-01

276

Metal cutting simulation of 4340 steel using an accurate mechanical description of meterial strength and fracture  

SciTech Connect

Strength and fracture constitutive relationships containing strain rate dependence and thermal softening are important for accurate simulation of metal cutting. The mechanical behavior of a hardened 4340 steel was characterized using the von Mises yield function, the Mechanical Threshold Stress model and the Johnson- Cook fracture model. This constitutive description was implemented into the explicit Lagrangian FEM continuum-mechanics code EPIC, and orthogonal plane-strain metal cutting calculations were performed. Heat conduction and friction at the toolwork-piece interface were included in the simulations. These transient calculations were advanced in time until steady state machining behavior (force) was realized. Experimental cutting force data (cutting and thrust forces) were measured for a planning operation and compared to the calculations. 13 refs., 6 figs.

Maudlin, P.J.; Stout, M.G.

1996-09-01

277

Nonlinear fracture mechanics-based analysis of thin wall cylinders  

NASA Technical Reports Server (NTRS)

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.

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

1994-01-01

278

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

NASA Technical Reports Server (NTRS)

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.

Newman, James C., Jr.

1997-01-01

279

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

NASA Astrophysics Data System (ADS)

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 within the epoxy fracture. Samples were drawn downstream to obtain the E. coli breakthrough curve and determine the percent retained within the fracture. This paper will present the dominant retention mechanisms of E. coli at various effective flow rates as determined from an analysis of the images showing trapped E. coli, together with the aperture field information from the direct measurement. This information will help to improve the robustness and of contaminant transport models in fractures, and will therefore improve the ability to assess the risk posed by using bedrock aquifers as drinking water sources.

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

2011-12-01

280

Mechanical boundary conditions of fracture healing: borderline indications in the treatment of unreamed tibial nailing.  

PubMed

Unreamed nailing favors biology at the expense of the achievable mechanical stability. It is therefore of interest to define the limits of the clinical indications for this method. The extended usage of unreamed tibial nailing resulted in reports of an increased rate of complications, especially for the distal portion of the tibia. The goals of this work were to gain a thorough understanding of the load-sharing mechanism between unreamed nail and bone in a fractured tibia, to identify the mechanical reasons for the unfavorable clinical results, and to identify borderline indications due to biomechanical factors. In a three-dimensional finite element model of a human tibia, horizontal defects were stabilized by means of unreamed nailing for five different fracture locations, including proximal and distal borderline indications for this treatment method. The loading of the bone, the loading of the implant and the inter-fragmentary strains were computed. The findings of this study show that with all muscle and joint contact forces included, nailing leads to considerable unloading of the interlocked bone segments. Unreamed nailing of the distal defect results in an extremely low axial and high shear strain between the fragments. The results suggest that mechanical conditions are advantageous to unreamed nailing of proximal and mid-diaphyseal defects. Apart from biological reasons, clinical problems reported for distal fractures may be due to the less favorable mechanical conditions in unreamed nailing. From a biomechanical perspective, the treatment of distal tibial shaft fractures by means of unreamed nailing without additional fragment contact or without stabilizing the fibula should be carefully reconsidered. PMID:11311705

Duda, G N; Mandruzzato, F; Heller, M; Goldhahn, J; Moser, R; Hehli, M; Claes, L; Haas, N P

2001-05-01

281

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

NASA Technical Reports Server (NTRS)

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.

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

2010-01-01

282

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

SciTech Connect

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.

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

2007-05-31

283

On the mechanical modeling of nucleation and propagation of fractures in folding rock strata  

NASA Astrophysics Data System (ADS)

Mechanical models that follow the evolution of stresses and deformation provide insight into the origin of folding and the sequence of fracturing in geologic strata. Modeling of fracturing and deformation banding in folding strata is not a trivial task since the intense strain along a very narrow zone in a body experiencing very large deformation is a complex kinematics that is difficult to resolve even with the most advanced numerical techniques such as the finite element and boundary element methods. In this paper we present comparative studies and critical assessments of various numerical techniques for modeling the processes of nucleation and growth of fractures and deformation bands in folding strata using the finite element method. The presentation is divided into two parts: the first part focuses on frictional sliding along a preexisting defect, while the second part focuses on nucleation and growth of a new fracture. For a preexisting discontinuity we utilize finite deformation contact mechanics to capture frictional sliding along a well-defined surface of discontinuity. Finite element sides are aligned along the prescribed surface of discontinuity, and node-to-segment contact elements impose the kinematical friction law on this surface. Contact mechanics cannot be used for capturing fracture growth, however, since neither the orientation nor extent of a future surface of discontinuity is known at the outset, which means that element sides cannot be a priori aligned with an advancing fracture. To address this difficulty we utilize two computational techniques that capture an advancing discontinuity. The first is based on an embedded strong discontinuity where a finite element is allowed to rupture completely to simulate a propagating crack that cuts through and across it. The second utilizes a so-called extended finite element method (XFEM), which allows the element to rupture partially through the introduction of additional nodes surrounding the elements intersected by the crack. By presenting the advantages and disadvantages of these numerical techniques we provide an opportunity to select the most appropriate technique for resolving the multi-scale problem of meter-scale fracturing within kilometer-scale folds.

Foster, C. D.; Borja, R. I.; Pollard, D. D.

2006-12-01

284

A study of fracture mechanisms in ATD roller bearing  

NASA Technical Reports Server (NTRS)

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 the various factors investigated.

Zee, Ralph H.

1990-01-01

285

Effects of mechanical fracturing and experimental trampling on Hawaiian corals.  

PubMed

In situ trampling occurred under experimental conditions to quantify the differences in the responses to anthropogenic trampling in four dominant species of Hawaiian corals, Porites compressa, Porites lobata, Montipora capitata, and Pocillopora meandrina. Trampling was simulated daily for a period of nine days at which time further breakage was minimal. Forty treatment colonies produced 559 fragments. Trampling was followed by an 11-month recovery period. Coral colony and fragment mortality was low. All four species were highly tolerant of inflicted damage, suggesting that some species of corals can withstand limited pulse events that allow time for recovery. Growth rates following trampling were significantly lower in the treatment groups for three of the four species. This study demonstrated that very few trampling events can produce significant changes in growth even after a long recovery period. Survivorship of fragments is clearly size- and species-dependent in M. capitata and P. compressa. Smaller fragments (<5 cm) had higher mortality than larger fragments (>5 cm). High breakage rates for M. capitata and P. compressa are consistent with the near shore, low-energy regions they inhabit-the same environment frequented by skin divers and waders. Mechanical tests were conducted to determine tensile and compressive strengths. Pocillopora meandrina exhibited the strongest skeletal strength, followed in decreasing order by Porites lobata, Porites compressa, and Montipora capitata. The skeletal strength obtained from the experiments correlate with the wave energy present in the environments in the regions they inhabit, suggesting that structural strength of corals is an adaptive response to hydraulic stress. PMID:12592453

Rodgers, Ku'ulei; Cox, Evelyn; Newtson, Craig

2003-03-01

286

Mechanics of Impact and Crack Propagation. Phase 1. Development of an Analytical Fracture Model of Projectile Penetration. .  

National Technical Information Service (NTIS)

The report is concerned with the application of fracture mechanics theory to the problem of projectile penetration and the situation where an excessive amount of energy is available to damage the target material in the form of fracture followed by crack p...

G. C. Sih G. T. Embley

1971-01-01

287

A BEM analysis of fracture mechanics in 2D anisotropic piezoelectric solids  

Microsoft Academic Search

This paper presents a single-domain boundary element method (BEM) analysis of fracture mechanics in 2D anisotropic piezoelectric solids. In this analysis, the extended displacement (elastic displacement and electrical potential) and extended traction (elastic traction and electrical displacement) integral equations are collocated on the outside boundary (no-crack boundary) of the problem and on one side of the crack surface, respectively. The

Ernian Pan

1999-01-01

288

Applications of FEM and BEM in two-dimensional fracture mechanics problems  

NASA Technical Reports Server (NTRS)

A comparison of the finite element method (FEM) and boundary element method (BEM) for the solution of two-dimensional plane strain problems in fracture mechanics is presented in this paper. Stress intensity factors (SIF's) were calculated using both methods for elastic plates with either a single-edge crack or an inclined-edge crack. In particular, two currently available programs, ANSYS for finite element analysis and BEASY for boundary element analysis, were used.

Min, J. B.; Steeve, B. E.; Swanson, G. R.

1992-01-01

289

Effect of dynamic strain aging on mechanical and fracture properties of A516Gr70 steel  

Microsoft Academic Search

The effects of dynamic strain aging (DSA) on mechanical and fracture characteristics were investigated in a ferritic steel type A516Gr70 commonly used for reactor support steels and pressure vessels. Tensile and 3-point bend tests were performed on miniature tensile and subsize Charpy specimens at various temperatures from ambient to about 700K with specific purpose of delineating the friction and source

C. S Seok; K. L Murty

1999-01-01

290

Problems of fracture mechanics of solid bodies with V-shaped notches  

Microsoft Academic Search

We present a survey of the research into the problems of fracture mechanics of solid bodies with V-shaped notches. The methods\\u000a used for the solution of plane problems of the theory of elasticity in the domains with corner points on the boundary contours\\u000a are analyzed. Special attention is given to the unified approach to the solution of the problems of

M. P. Savruk; A. Kazberuk

2009-01-01

291

Failure modes and fracture mechanisms in flexure of Kevlar-epoxy composites  

Microsoft Academic Search

The results of testing in three-point bending of aramid fibre-reinforced epoxy composites are described. This loading mode\\u000a has been chosen in order to increase the variety of failure modes and of fracture mechanisms. The main failure modes observed\\u000a are tensile and delamination, with a transition at a fibre volume fraction of about 46%. This mode transition is detectable\\u000a by monitoring

M. Davidovitz; A. Mittelman; I. Roman; G. Marom

1984-01-01

292

Fracture Mechanics Analysis of Notch Fatigue of A Single Crystal Superalloy—CMSX-4  

Microsoft Academic Search

The above fracture mechanics solutions are applied to the analysis of the fatigue behavior of CMSX-4 notched specimens. The single crystal superalloy exhibits an order-of-magnitude difference in its fatigue life when tested under the same cyclic loading condition. The scatter has been attributed to the geometry and location of inter-dendrite pores, which were primarily crack initiation sites. Assuming that the

X. J. Wu; Z. Zhang; P. A. S. Reed

293

Analyses of fibre push-out test based on the fracture mechanics approach  

Microsoft Academic Search

Theoretical analyses based on the concept of fracture mechanics have been developed to evaluate the interfacial properties of ceramic matrix composites in single fibre push-out tests. Two different fibre push-out models, i.e. single fibre-matrix model and three-cylinder model, were presented for different specimen geometries. The interfacial debonding and fibre push-out stresses were analyzed similar to the fibre pull-out test (Zhou

Li-Min Zhou; Yiu-Wing Mai; Lin Ye

1995-01-01

294

Application of the element-free Galerkin meshless method to 3-D fracture mechanics problems  

Microsoft Academic Search

The present paper deals with the development of a simple meshless method, known as element-free Galerkin method (EFG), and its numerical implementation and application for the solution of 3-D elastic fracture mechanics problems.Meshless methods are rather new computational techniques that do not require the use of any connectivity concept, such as those used in the finite element method (FEM); since

Roberto Brighenti

2005-01-01

295

Application of Fracture Mechanics Concepts to Hierarchical Biomechanics of Bone and Bone-like Materials  

Microsoft Academic Search

Fracture mechanics concepts are applied to gain some understanding of the hierarchical nanocomposite structures of hard biological\\u000a tissues such as bone, tooth and shells. At the most elementary level of structural hierarchy, bone and bone-like materials\\u000a exhibit a generic structure on the nanometer length scale consisting of hard mineral platelets arranged in a parallel staggered\\u000a pattern in a soft protein

Huajian Gao

2006-01-01

296

Fracture mechanics analysis of a high-pressure hydrogen facility compressor  

NASA Technical Reports Server (NTRS)

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.

Vroman, G. A.

1974-01-01

297

Thermal–mechanical modeling of cooling history and fracture development in inflationary basalt lava flows  

Microsoft Academic Search

Thermal–mechanical analyses of isotherms in low-volume basalt flows having a range of aspect ratios agree with inferred isotherm patterns deduced from cooling fracture patterns in field examples on the eastern Snake River Plain, Idaho, and highlight the caveats of analytical models of sheet flow cooling when considering low-volume flows. Our field observations show that low-volume lava flows have low aspect

Simon A. Kattenhorn; Conrad J. Schaefer

2008-01-01

298

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

SciTech Connect

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.

Cockeram, B.V.

1998-04-27

299

Resistance Against the Intrinsic Rate of Fracture Mechanics Parameters for Polymeric Materials Under Moderate Impact Loading  

NASA Astrophysics Data System (ADS)

This study contributes towards understanding crack toughness as resistance against the intrinsic rate of fracture mechanics parameters. Up to now only few investigations have been done under moderate impact loading conditions. Based on experimental investigations using the crack resistance (R) concept, it has been shown that the stop block method combined with the multiple-specimen technique is a unique method for polymers under impact loading conditions in comparison with different R-curve methods. Other methods for the determination of R curve such as the low-blow technique are normally not applicable for polymers due to their time-dependent mechanical properties. The crack-tip opening displacement (CTOD) rate is a measurement of the rate sensibility of stable fracture process depending on the type of deformation, which can provide deep insights into the micromechanics and activation mechanisms during the fracture processes. In the polymeric materials mostly investigated, one can understand the stable crack propagation with three-stage processes; crack-tip blunting/crack initiation, non-stationary stable crack growth and steady-state stable crack growth (an equilibrium state). In this stable crack propagation, the values of normalized CTOD rate converge rapidly to a ‘matrix’-specific threshold. The stop block method in the multiple-specimen technique assures the criteria of the time-independent strain field around the crack tip and constant crack speed therewith and the J-integral is a valid toughness parameter.

Lach, R.; Seidler, S.; Grellmann, W.

2005-09-01

300

The microstructural, mechanical, and fracture properties of austenitic stainless steel alloyed with gallium  

NASA Astrophysics Data System (ADS)

The mechanical and fracture properties of austenitic stainless steels (SSs) alloyed with gallium require assessment in order to determine the likelihood of premature storage-container failure following Ga uptake. AISI 304 L SS was cast with 1, 3, 6, 9, and 12 wt pct Ga. Increased Ga concentration promoted duplex microstructure formation with the ferritic phase having a nearly identical composition to the austenitic phase. Room-temperature tests indicated that small additions of Ga (less than 3 wt pct) were beneficial to the mechanical behavior of 304 L SS but that 12 wt pct Ga resulted in a 95 pct loss in ductility. Small additions of Ga are beneficial to the cracking resistance of stainless steel. Elastic-plastic fracture mechanics analysis indicated that 3 wt pct Ga alloys showed the greatest resistance to crack initiation and propagation as measured by fatigue crack growth rate, fracture toughness, and tearing modulus. The 12 wt pct Ga alloys were least resistant to crack initiation and propagation and these alloys primarily failed by transgranular cleavage. It is hypothesized that Ga metal embrittlement is partially responsible for increased embrittlement.

Kolman, D. G.; Bingert, J. F.; Field, R. D.

2004-11-01

301

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

PubMed

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. PMID:12798066

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

2003-07-01

302

Integration of Nondestructive Examination (NDE) Reliability and Fracture Mechanics: Semi-Annual Report April 1984 - September 1984.  

National Technical Information Service (NTIS)

The progress report summarizes work performed by Pacific Northwest Laboratory on the NDE and fracture mechanics of nuclear reactor primary circuit components during the six months from April 1984 through September 1984.

S. R. Doctor D. J. Bates L. A. Charlot H. D. Collins M. S. Good

1986-01-01

303

Mechanisms for fracture and fatigue-crack propagation in a bulk metallic glass  

NASA Astrophysics Data System (ADS)

The fracture and fatigue properties of a newly developed bulk metallic glass alloy, Zr41.2Ti13.8Cu12.5 Ni10Be22.5 (at. pct), have been examined. Experimental measurements using conventional fatigue precracked compact-tension C(T) specimens (˜7-mm thick) indicated that the fully amorphous alloy has a plane-strain fracture toughness comparable to polycrystalline aluminum alloys. However, significant variability was observed and possible sources are identified. The fracture surfaces exhibited a vein morphology typical of metallic glasses, and, in some cases, evidence for local melting was observed. Attempts were made to rationalize the fracture toughness in terms of a previously developed micromechanical model based on the Taylor instability, as well as on the observation of extensive crack branching and deflection. Upon partial or complete crystallization, however, the alloy was severely embrittled, with toughnesses dropping to ˜1 MPa sqrt m . Commensurate with this drop in toughness was a marginal increase in hardness and a reduction in ductility (as measured via depthsensing indentation experiments). Under cyclic loading, crack-propagation behavior in the amorphous structure was similar to that observed in polycrystalline steel and aluminum alloys. Moreover, the crack-advance mechanism was associated with alternating blunting and resharpening of the crack tip. This was evidenced by striations on fatigue fracture surfaces. Conversely, the (unnotched) stress/life (S/N) properties were markedly different. Crack initiation and subsequent growth occurred quite readily, due to the lack of microstructural barriers that would normally provide local crack-arrest points. This resulted in a low fatigue limit of ˜4 pct of ultimate tensile strength.

Gilbert, C. J.; Schroeder, V.; Ritchie, R. O.

1999-07-01

304

Non-Singular Dislocation Elastic Fields and Linear Elastic Fracture Mechanics  

NASA Astrophysics Data System (ADS)

One of the hallmarks of the traditional linear elastic fracture mechanics (LEFM) is the presence of an (integrable) inverse square root singularity of strains and stresses in the vicinity of the crack tip. It is the presence of this singularity that necessitates the introduction of the concepts of stress intensity factor (and its critical value, the fracture toughness) and the energy release rate (and material toughness). This gives rise to the Griffith theory of strength that includes, apart from applied stresses, the considerations of defect size and geometry. A highly successful framework for the solution of crack problems, particularly in the two-dimensional case, due to Muskhelishvili (1953), Bilby and Eshelby (1968) and others, relies on the mathematical concept of dislocation. Special analytical and numerical methods of dealing with the characteristic 1/r (Cauchy) singularity occupy a prominent place within this theory. Recently, in a different context of dislocation dynamics simulations, Cai et al. (2006) proposed a novel means of removing the singularity associated with the dislocation core, by introducing a blunting radius parameter a into the expressions for elastic fields. Here, using the example of two-dimensional elasticity, we demonstrate how the adoption of the similar mathematically expedient tool leads naturally to a non-singular formulation of fracture mechanics problems. This opens an efficient means of treating a variety of crack problems.

Korsunsky, Alexander M.

2010-03-01

305

Transformation of creep stresses in ice shelves for fracture mechanical analyses  

NASA Astrophysics Data System (ADS)

Recent disintegrations of ice shelves and calving at ice fronts require a better understanding of fracture mechanical processes involved in these events. Previous studies on cracks in ice shelves with different stress states, density profiles and material parameters highlighted the dependence of the crack criticality on the choice of boundary conditions and the applied material law. To this end, we present different approaches how to transfer the flow induced viscous stresses into the fracture mechanical analysis for the study of vertical and horizontal crack scenarios. The numerical simulations are performed using Finite Elements and the concept of configurational forces for the evaluation of stress intensity factors. This approach is rather flexible and can account for inhomogeneous material properties, volume forces and crack face loadings, e.g. due to additional water pressure. The methods are applied to 2-dimensional geometries under various loading conditions and material parameters. The methods are validated using data from the literature and the results are compared to fracture events that have been documented using remote sensing data analysis.

Plate, C.; Müller, R.; Humbert, A.; Wilkens, N.; Gross, D.

2012-04-01

306

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

SciTech Connect

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) Conferences. This work is also relevant to the ongoing efforts of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (B&PV) Code, Section XI, Working Group on Operating Plant Criteria (WGOPC) efforts to incorporate nozzle fracture mechanics solutions into a revision to ASME B&PV Code, Section XI, Nonmandatory Appendix G.

Walter, Matthew [Structural Integrity Associates, Inc.; Yin, Shengjun [ORNL; Stevens, Gary [U.S. Nuclear Regulatory Commission; Sommerville, Daniel [Structural Integrity Associates, Inc.; Palm, Nathan [Westinghouse Electric Company, Cranberry Township, PA; Heinecke, Carol [Westinghouse Electric Company, Cranberry Township, PA

2012-01-01

307

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

NASA Technical Reports Server (NTRS)

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.

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

1977-01-01

308

CSNI/NRC workshop on ductile piping fracture mechanics: Proceedings. [Includes combined bending and tension stress  

SciTech Connect

This report contains the papers presented at a workshop meeting that was conducted to compare the various different elastic-plastic fracture mechanics analysis methods that can be applied to assess the margin of safety in cracked nuclear plant pipes. A specific problem -- a circumferentially cracked Type 304 stainless steel pipe in combined axial tension and bending -- was addressed. The applied bending moments at crack growth initiation and at fracture instability were sought. Seven estimation type solutions were performed along with a benchmark elastic-plastic finite element solution. It was learned that precise specification of the material stress-strain curve must be made to obtain meaningful results. But, when applied under controlled conditions, the different estimation method solutions do provide reasonably consistent results. These results appear to be conservative in comparison with an elastic-plastic finite element solution that was performed to provide a comparison with these results. Individual papers have been entered into EDB and ERA.

Kanninen, M.F. (comp.)

1988-05-01

309

Study on Shear Fatigue Fracture and Delamination Mechanism of Thermal Barrier Coatings After Thermal Loading  

NASA Astrophysics Data System (ADS)

In this study, it is investigated experimentally and analytically that fracture process and fatigue behavior of Thermal Barrier Coatings (TBCs) used in a high temperature component in a land based gas turbine. The effects of the thermal load on TBCs are investigated by measuring residual stress of top coat, finite element method and torsion test. It is found that delamination of top coat under thermal load occurs at a peak of undulation in top coat and bond coat interface. Around the peak, a tearing stress is generated. Fracture and fatigue tests under torsion are carried out by using cylindrical butted specimens. It is found that the mechanical property of bond coat changes after thermal aging and the shear fatigue behavior of TBCs is affected by bond coat strength.

Kaneko, Kenji; Takatou, Satoshi; Enomoto, Kazuki

310

Molecular Mechanisms Controlling Bone Formation during Fracture Healing and Distraction Osteogenesis  

PubMed Central

Fracture healing and distraction osteogenesis have important applications in orthopedic, maxillofacial, and periodontal treatment. In this review, the cellular and molecular mechanisms that regulate fracture repair are contrasted with bone regeneration that occurs during distraction osteogenesis. While both processes have many common features, unique differences are observed in the temporal appearance and expression of specific molecular factors that regulate each. The relative importance of inflammatory cytokines in normal and diabetic healing, the transforming growth factor beta superfamily of bone morphogenetic mediators, and the process of angiogenesis are discussed as they relate to bone repair. A complete summary of biological activities and functions of various bioactive factors may be found at COPE (Cytokines & Cells Online Pathfinder Encyclopedia), http://www.copewithcytokines.de/cope.cgi.

AI-Aql, Z.S.; Alagl, A.S.; Graves, D.T.; Gerstenfeld, L.C.; Einhorn, T.A.

2011-01-01

311

Quantifying mechanical properties in a murine fracture healing system using inverse modeling: preliminary work  

NASA Astrophysics Data System (ADS)

Understanding bone remodeling and mechanical property characteristics is important for assessing treatments to accelerate healing or in developing diagnostics to evaluate successful return to function. The murine system whereby mid-diaphaseal tibia fractures are imparted on the subject and fracture healing is assessed at different time points and under different therapeutic conditions is a particularly useful model to study. In this work, a novel inverse geometric nonlinear elasticity modeling framework is proposed that can reconstruct multiple mechanical properties from uniaxial testing data. To test this framework, the Lame' constants were reconstructed within the context of a murine cohort (n=6) where there were no differences in treatment post tibia fracture except that half of the mice were allowed to heal 4 days longer (10 day, and 14 day healing time point, respectively). The properties reconstructed were a shear modulus of G=511.2 +/- 295.6 kPa, and 833.3+/- 352.3 kPa for the 10 day, and 14 day time points respectively. The second Lame' constant reconstructed at ?=1002.9 +/-42.9 kPa, and 14893.7 +/- 863.3 kPa for the 10 day, and 14 day time points respectively. An unpaired Student t-test was used to test for statistically significant differences among the groups. While the shear modulus did not meet our criteria for significance, the second Lame' constant did at a value p<0.0001. Traditional metrics that are commonly used within the bone fracture healing research community were not found to be statistically significant.

Miga, Michael I.; Weis, Jared A.; Granero-Molto, Froilan; Spagnoli, Anna

2010-03-01

312

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

SciTech Connect

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.

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

2011-01-01

313

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

NASA Astrophysics Data System (ADS)

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. Tensile fractures can occur when the hoop stress exerted on the outer shell exceeds its tensile strength. The molten conduit material is then likely to flow into the newly formed fracture, depending on its viscosity and the fracture dimensions, allowing comparisons to be made between the temperature and intrusions dynamics of the simulated dyke process. As a starting point, we are now testing an analogue material to replace the magma to avoid complex multi-phase rheology (bubbles, crystals) and the need for high experimental temperatures, relying of maintaining similar temperature/viscosity ratios between magma/country rock in the laboratory and the field. We chose PMMA (commonly known as plexiglass) for this task as it displays a large range in viscosities (log(visc)range = 10 -1) with temperatures between 100 and 300 °C, making it an excellent analogue material. In the future experiments at higher temperatures will be conducted with NIST-glasses and field collected glasses. 2D and 3D imaging of post-deformation samples show no preferential location of the fractures. Fractures are formed both around and trough crystals. Some evidence suggests the formation of microcracks and linking up as predicted by Griffith's theory. Correcting for apparatus distortion and friction of o-rings and the filler material we can calculate the conduit stress and arrive at a tensile strength values for different basement rock types in the order of 1-15 MPa.

Bakker, Richard; Benson, Philip; Vinciguerra, Sergio

2014-05-01

314

CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES: Dynamic Response and Fracture Mechanism of a Novel Structural Radar Absorbing Material  

NASA Astrophysics Data System (ADS)

A novel structural radar absorbing material (SRAM), which gives the normal resin-base composites new function, is prepared. The dynamic compressive tests of SRAM are carried out in both in-plane and normal directions of composites by means of the split Hopkinson pressure bar (SHPB). In the compressive test along in-plane direction, failure occurs at the interface between a fibre and the matrix. A fracture mode and mechanism was proposed to explain these results. The addition of absorbing particles results in the deterioration of the compressive properties. However, there is no obvious decrease on compressive strength of SRAM with the radar absorbing properties.

Cao, Mao-Sheng; Zhou, Wei; Qu, Gui-Min; Rong, Ji-Li

2008-08-01

315

Potential impact of enhanced fracture-toughness data on fracture mechanics assessment of PWR vessel integrity for pressurized thermal shock  

Microsoft Academic Search

The Heavy Section Steel Technology (HSST) Program is involved with the generation of enhanced fracture-initiation toughness and fracture-arrest toughness data of prototypic nuclear reactor vessel steels. These two sets of data are enhanced because they have distinguishing characteristics that could potentially impact PWR pressure vessel integrity assessments for the pressurized-thermal shock (PTS) loading condition which is a major plant-life extension

T. L. Dickson; T. J. Theiss

1991-01-01

316

Determinants of the mechanical behavior of human lumbar vertebrae after simulated mild fracture.  

PubMed

The ability of a vertebra to carry load after an initial deformation and the determinants of this postfracture load-bearing capacity are critical but poorly understood. This study aimed to determine the mechanical behavior of vertebrae after simulated mild fracture and to identify the determinants of this postfracture behavior. Twenty-one human L(3) vertebrae were analyzed for bone mineral density (BMD) by dual-energy X-ray absorptiometry (DXA) and for microarchitecture by micro-computed tomography (µCT). Mechanical testing was performed in two phases: initial compression of vertebra to 25% deformity, followed, after 30?minutes of relaxation, by a similar test to failure to determine postfracture behavior. We assessed (1) initial and postfracture mechanical parameters, (2) changes in mechanical parameters, (3) postfracture elastic behavior by recovery of vertebral height after relaxation, and (4) postfracture plastic behavior by residual strength and stiffness. Postfracture failure load and stiffness were 11%?±?19% and 53%?±?18% lower than initial values (p?=?.021 and p?mechanical behavior explained by the initial values. Both initial and postfracture mechanical behaviors were significantly correlated with bone mass and microarchitecture. Vertebral deformation recovery averaged 31%?±?7% and was associated with trabecular and cortical thickness (r?=?0.47 and r?=?0.64; p?=?.03 and p?=?.002, respectively). Residual strength and stiffness were independent of bone mass and initial mechanical behavior but were related to trabecular and cortical microarchitecture (|r|?=?0.50 to 0.58; p?=?.02 to .006). In summary, we found marked variation in the postfracture load-bearing capacity following simulated mild vertebral fractures. Bone microarchitecture, but not bone mass, was associated with postfracture mechanical behavior of vertebrae. PMID:20928886

Wegrzyn, Julien; Roux, Jean-Paul; Arlot, Monique E; Boutroy, Stéphanie; Vilayphiou, Nicolas; Guyen, Olivier; Delmas, Pierre D; Chapurlat, Roland; Bouxsein, Mary L

2011-04-01

317

A nonlinear fracture mechanics approach to the growth of small cracks  

NASA Technical Reports Server (NTRS)

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.

Newman, J. C., Jr.

1983-01-01

318

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)

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 influence of bone quality, i.e., mineralization, water content, osteon size, area and number, microdamage and crystallinity differed between different locations, age groups and fracture mode. Fracture toughness was also significantly correlated with clinical parameters such as cortical index and Singh index, significance level being dependent upon bone location, fracture mode and age. Several mechanistic models to predict how bone microstructure influences bone fracture toughness were proposed based on experimental results and available literature.

Yeni, Yener Nail

319

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

NASA Technical Reports Server (NTRS)

Fractography and metallographic sectioning were used to investigate the influence of microstructure on the fracture mechanism and fracture toughness (KIC) of normal interstitial and extra low interstitial (ELI) Ti-5Al-25Sn at 20 K (-423 F) and 77 K (-320 F). Plates of each grade 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 dispersed beta phase and in the ordering of the alpha matrix. The ELI alloys were tougher than the normal interstitial plates. KIC of the furnace-cooled ELI plate was 25% lower than that of the air-cooled ELI material. Variations in cooling rate had no influence of KIC of the normal interstitial alloys. Fractography showed that a large portion of the fracture surfaces were covered with elongated dimples. Metallographic sections of specimens deformed at 77 K showed that these features form at the intersections of slip bands or deformation twins with grain or twin boundaries. Ordering and higher interstitial levels increase the local strain in slip bands resulting in void nucleation at lower macroscopic strains and lower KIC values.

Van Stone, R. H.; Low, J. R., Jr.; Shannon, J. L., Jr.

1978-01-01

320

Type II odontoid fracture from frontal impact: case report and biomechanical mechanism of injury.  

PubMed

The authors report a case of Type II odontoid fracture from a frontal impact sustained in the crash of a late-model motor vehicle. They discuss the biomechanical mechanisms of injury after considering patient demographic data, type and use of restraint systems including seatbelt and airbags, crash characteristics, and laboratory-based experimental studies. Multiple factors contributed to the Type II odontoid fracture: the patient's tall stature and intoxicated state; lack of manual three-point seat belt use; obliqueness of the frontal impact; and the most likely preflexed position of the head-neck complex at the time of impact, which led to contact of the parietal region with the A-pillar roof-rail area of the vehicle and resulted in the transfer of the dynamic compressive force associated with lateral bending. Odontoid fractures still occur in individuals involved in late-model motor vehicle frontal crashes, and because this injury occurs secondary to head impact, airbags may not play a major role in mitigating this type of trauma to an unrestrained occupant. It may be more important to use seat belts than to depend on the airbag alone for protection from injury. PMID:15871490

Yoganandan, Narayan; Baisden, Jamie L; Maiman, Dennis J; Pintar, Frank A

2005-04-01

321

Mechanisms Predisposing Penile Fracture and Long-Term Outcomes on Erectile and Voiding Functions  

PubMed Central

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.

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

2014-01-01

322

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

PubMed

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

Daxini, S D; Prajapati, J M

2014-01-01

323

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

PubMed Central

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.

Daxini, S. D.; Prajapati, J. M.

2014-01-01

324

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

PubMed

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

Dimas, Leon S; Buehler, Markus J

2014-06-01

325

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

NASA Technical Reports Server (NTRS)

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.

Hardrath, H. F.

1974-01-01

326

Use of adjoint methods in the probabilistic finite element approach to fracture mechanics  

NASA Technical Reports Server (NTRS)

The adjoint method approach to probabilistic finite element methods (PFEM) is presented. When the number of objective functions is small compared to the number of random variables, the adjoint method is far superior to the direct method in evaluating the objective function derivatives with respect to the random variables. The PFEM is extended to probabilistic fracture mechanics (PFM) using an element which has the near crack-tip singular strain field embedded. Since only two objective functions (i.e., mode I and II stress intensity factors) are needed for PFM, the adjoint method is well suited.

Liu, Wing Kam; Besterfield, Glen; Lawrence, Mark; Belytschko, Ted

1988-01-01

327

Strength prediction of unidirectional composites with a circular hole using fracture mechanics  

NASA Astrophysics Data System (ADS)

The results of a numerical study that suggests the applicability of a fracture mechanics approach to predicting the strength of off-axis unidirectional composite laminates with a circular cut-out are presented. The veracity of the approach was based only on the set of test results in Zein and Reifsnider (1990), due to the scarcity of experimental tensile strength data on such specimens in the literature. It was observed that for the off-axis unidirectional laminate considered, AS4/3502 graphite-epoxy, there was fairly good agreement between the predicted and experimental strengths.

Ang, H. E.; Gao, Y. L.; Tan, C. L.

1992-07-01

328

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

NASA Technical Reports Server (NTRS)

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.

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

1982-01-01

329

Alteration of Fractured Rocks Due to Coupled Chemical and Mechanical Processes: High-Resolution Simulations and Experimental Observations  

NASA Astrophysics Data System (ADS)

Engineering activities such as enhanced geothermal energy production and improved oil recovery techniques are heavily dependent on the permeability of the subsurface, while others such as CO2 sequestration and nuclear waste disposal rely on the efficiency of rock formations as transport barriers. In either case fractures provide the main pathways for fluid flow and transport, especially in rocks with lower matrix porosity. Laboratory experiments aimed at quantifying the chemo-mechanical responses of fractures have shown a range of results, some of which contradict simple conceptual models. For example, under conditions favoring mineral dissolution, where one would expect an overall increase in permeability, experiments show that permeability increases under some conditions and decreases under others. Recent experiments have attempted to link these core-scale observations to the relevant small-scale processes occurring within fractures. Results suggest that the loss of mechanical strength in asperities due to chemical alteration may cause non-uniform deformation and alteration of fracture apertures. However, due to the lack of direct micro-scale measurements of the coupled chemical and mechanical processes that lead to alteration of contacting fracture surfaces, our ability to predict the long-term evolution of fractures is still limited. To explore the processes that control permeability evolution, I developed a computational model that uses micro-scale surface roughness and explicitly couples dissolution and elastic deformation to calculate local alterations in fracture aperture under chemical and mechanical stresses. A depth-averaged algorithm of fracture flow is used to model reactive transport and chemical alteration of the fracture surfaces. Then, I deform the resulting altered fracture-surfaces using an algorithm that calculates the elastic deformation. The results of the model are compared with flow-through experiments conducted on fractured limestone. The fracture apertures are mapped before and after the experiments. These detailed aperture measurements are used as input to the new coupled model. The experiments cover a wide range of transport and reaction conditions; some exhibited negligible reaction-induced deformation and formation of distinct dissolution channels and others more uniform dissolution and measurable deformation caused by dissolution. Simulation results predict these general trends and the small-scale details in regions of contacting asperities.

Ameli, Pasha

330

Vertically Oriented Femoral Neck Fractures: Mechanical Analysis of Four Fixation Techniques  

Microsoft Academic Search

Objective: Femoral neck fractures inyoung individuals are typically high angled shear fractures. These injuries are difficult to stabilize due to a strong varus displacement force across the hip with weight bearing. The purpose of this study was to compare the biomechanical stability of four differing fixation techniques for stabilizing vertical shear femoral neck fractures. Methods: Vertical femoral neck fracture stability

Arash Aminian; Fan Gao; Wasyl W. Fedoriw; Li-Qun Zhang; David M. Kalainov; Bradley R. Merk

2007-01-01

331

Short-Timescale Chemo-Mechanical Effects and their Influence on the Transport Properties of Fractured Rock  

Microsoft Academic Search

Anomalous changes in permeability are reported in fractures circulated by fluids undersaturated with respect to the mineral\\u000a host. Under net dissolution and net removal of mineral mass, fractures may alternately gape or seal, depending on the prevailing\\u000a mechanical and chemical conditions. The influence on transport properties is observed to be large, rapid, and irreversible:\\u000a Permeabilities may change by two orders

Derek Elsworth; Hideaki Yusuhara

332

Short-Timescale Chemo-Mechanical Effects and their Influence on the Transport Properties of Fractured Rock  

Microsoft Academic Search

Anomalous changes in permeability are reported in fractures circulated by fluids undersaturated with respect to the mineral\\u000a host. Under net dissolution and net removal of mineral mass, fractures may alternately gape or seal, depending on the prevailing\\u000a mechanical and chemical conditions. The influence on transport properties is observed to be large, rapid, and irreversible:\\u000a Permeabilities may change by two orders

Derek Elsworth; Hideaki Yasuhara

2006-01-01

333

Deformation limits on two-parameter fracture mechanics in terms of higher order asymptotics  

NASA Astrophysics Data System (ADS)

This report addresses the limitations of two-parameter fracture mechanics. We performed an asymptotic analysis of the general power series representation of the crack tip stress potential in an elastic plastic material that obeys a Ramberg-Osgood constitutive law. Expansion of the power series over a substantial number of terms yields. only three independent coefficients for low. and medium-hardening materials. The first independent The second and third independent coefficients, K2 and K4 are a function of geometry and loading level. A two-parameter theory implies that the crack tip stress fields have two degrees of freedom, but the asymptotic analysis implies that three parameters are required to characterize near-tip conditions. Thus two-parameter fracture theory is a valid engineering model only when there is an approximately unique relationship between K2 and K4. We performed elastic-plastic finite element analyses on several geometries and evaluated K2 and K4 as a function of deformation level. A reference,two-parameter solution (which gives a unique relation between K2 and K4) was provided by the modified boundary layer (MBL) geometry. Results indicate that the near tip stresses in all but the deeply cracked SENT (a/W-.5.O.9) and SENT (a/W-0.9) lend themselves to a two-parameter characterization. However, the deeply cracked SENT and SENT specimens maintain a high level of constraint to relatively large deformation levels. Thus single-parameter fracture mechanics is fairly robust for these high constraint geometries, but two-parameter theory is of little value when constraint loss eventually occurs.

Crane, D. L.; Anderson, T. L.

1994-09-01

334

Strain rate effects on the mechanical properties and fracture mode of skeletal muscle.  

PubMed

The present study aimed to characterize the mechanical response of beagle sartorius muscle fibers under strain rates that increase logarithmically (0.1mm/min, 1mm/min and 10mm/min), and provide an analysis of the fracture patterns of these tissues via scanning electron microscopy (SEM). Muscle tissue from dogs' sartorius was excised and test specimens were sectioned with a lancet into sections with nominal length, width, and thickness of 7, 2.5 and 0.6mm, respectively. Trimming of the tissue was done so that the loading would be parallel to the direction of the muscle fiber. Samples were immediately tested following excision and failures were observed under the SEM. No statistically significant difference was observed in strength between the 0.1mm/min (2.560±0.37MPa) and the 1mm/min (2.702±0.55MPa) groups. However, the 10mm/min group (1.545±0.50MPa) had a statistically significant lower strength than both the 1mm/min group and the 0.1mm/min group with p<0.01 in both cases. At the 0.1mm/min rate the primary fracture mechanism was that of a shear mode failure of the endomysium with a significant relative motion between fibers. At 1mm/min this continues to be the predominant failure mode. At the 10mm/min strain rate there is a significant change in the fracture pattern relative to other strain rates, where little to no evidence of endomysial shear failure nor of significant motion between fibers was detected. PMID:24863204

Shapiro, Michael; Tovar, Nick; Yoo, Daniel; Sobieraj, Micheal; Gupta, Nikhil; Branski, Ryan C; Coelho, Paulo G

2014-06-01

335

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

SciTech Connect

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.

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

1982-06-01

336

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

SciTech Connect

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.

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

1998-04-01

337

Processing and Mechanical Properties of High Temperature/ High Performance Composites. Mechanism-Based Constitutive Laws and Design. Book 1.  

National Technical Information Service (NTIS)

This document discusses the following: (1) Materials selection and innovation in design; (2) Elasto-plastic analysis of interface layers for fiber-reinforced metal-matrix composites; (3) Modeling of anisotropic behavior of weakly bonded fiber reinforced M...

A. G. Evans F. A. Leckie

1994-01-01

338

Strain hardening, fracture and toughening mechanisms in self-assembling gels  

NASA Astrophysics Data System (ADS)

Polymer gels based on triblock copolymers in a midblock-selective solvent are excellent model systems for studying fundamental features of network mechanics. We use a series of acrylic triblock gels that exhibit both a concentration dependent ``structural'' gelation phenomenon and a temperature dependent ``dynamic'' gelation phenomenon. Dynamic gelation is controlled by the exchange kinetics of endblock between different aggregates, and is strongly temperature dependent because of an underlying glass transition of the endblock aggregates. Structural gelation is controlled by midblock chains which form a percolated network of endblock aggregates above a critical concentration. The focus of this talk is on the non-linear mechanical response of these materials, including strain hardening and fracture in both extension and in shear. We also discuss the design of high toughness ionically crosslinked gels with a type of double network structure.

Shull, Kenneth

2010-03-01

339

A hybrid-dimensional approach for an efficient numerical modeling of the hydro-mechanics of fractures  

NASA Astrophysics Data System (ADS)

of subsurface fluid flow requires accounting for hydro-mechanical coupling between fluid-pressure variations and rock deformation. Particularly, flow of a compressible fluid along compliant hydraulic conduits, such as joints, fractures, or faults, is strongly affected by the associated deformation of the surrounding rock. We investigated and compared two alternative numerical modeling approaches that describe the transient fluid-pressure distribution along a single deformable fracture embedded in a rock matrix. First, we analyzed the coupled hydro-mechanical problem within the framework of Biot's poroelastic equations. Second, in a hybrid-dimensional approach, deformation characteristics of the surrounding rock were combined with a one-dimensional approximation of the fluid-flow problem to account for the high aspect ratios of fractures and the associated numerical problems. A dimensional analysis of the governing equations reveals that the occurring physical phenomena strongly depend on the geometry of the hydraulic conduit and on the boundary conditions. For the analyzed geometries, hydro-mechanical coupling effects dominate and convection effects can be neglected. Numerical solutions for coupled hydro-mechanical phenomena were obtained and compared to field data to characterize the fractured rock in the vicinity of an injection borehole. Either approach captures convection, diffusion, and hydro-mechanical effects, yet the hybrid-dimensional approach is advantageous due to its applicability to problems involving high-aspect-ratio features. For such cases, the modeling of pumping tests by means of the hybrid-dimensional approach showed that the observed inverse-pressure responses are the result of the coupling between the fluid flow in the fracture and the rock deformation caused by fluid-pressure variations along the fracture. Storage capacity as a single parameter of a fracture is insufficient to address all aspects of the coupling.

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

2014-02-01

340

Stability-based classification for ankle fracture management and the syndesmosis injury in ankle fractures due to a supination external rotation mechanism of injury.  

PubMed

The aim of this thesis was to confirm the utility of stability-based ankle fracture classification in choosing between non-operative and operative treatment of ankle fractures, to determine how many ankle fractures are amenable to non-operative treatment, to assess the roles of the exploration and anatomical repair of the AITFL in the outcome of patients with SER ankle fractures, to establish the sensitivities, specificities and interobserver reliabilities of the hook and intraoperative stress tests for diagnosing syndesmosis instability in SER ankle fractures, and to determine whether transfixation of unstable syndesmosis is necessary in SER ankle fractures. The utility of stability based fracture classification to choose between non-operative and operative treatment was assessed in a retrospective study (1) of 253 ankle fractures in skeletally mature patients, 160 of whom were included in the study to obtain an epidemiological profile in a population of 130,000. Outcome was assessed after a minimum follow-up of two years. The role of AITFL repairs was assessed in a retrospective study (2) of 288 patients with Lauge-Hansen SE4 ankle fractures; the AITFL was explored and repaired in one group (n=165), and a similar operative method was used but the AITFL was not explored in another group (n=123). Outcome was measured with a minimum follow-up of two years. Interobserver reliability of clinical syndesomosis tests (study 3) and the role of syndesmosis transfixation (study 4) were assessed in a prospective study of 140 patients with Lauge-Hansen SE4 ankle fractures. The stability of the distal tibiofibular joint was evaluated by the hook and ER stress tests. Clinical tests were carried out by the main surgeon and assistant, separately, after which a 7.5-Nm standardized ER stress test for both ankles was performed; if it was positive, the patient was randomized to either syndesmosis transfixation (13 patients) or no fixation (11 patients) treatment groups. The sensitivity and specificity of both clinical tests were calculated using the standard 7.5-Nm external rotation stress test as reference. Outcome was assessed after a minimum of one year of follow-up. Olerud-Molander (OM) scoring system, RAND 36-Item Health Survey, and VAS to measure pain and function were used as outcome measures in all studies. In study 1, 85 (53%) fractures were treated operatively using the stability based fracture classification. Non-operatively treated patients reported less pain and better OM (good or excellent 89% vs. 71%) and VAS functional scores compared to operatively treated patients although they experienced more displacement of the distal fibula (0 mm 30% vs. 69%; 0-2 mm 65% vs. 25%) after treatment. No non-operatively treated patients required operative fracture fixation during follow-up. In study 2, AITFL exploration and suture lead to equal functional outcome (OM mean, 77 vs. 73) to no exploration or fixation. In study 3, the hook test had a sensitivity of 0.25 and a specificity of 0.98. The external rotation stress test had a sensitivity of 0.58 and a specificity of 0.9. Both tests had excellent interobserver reliability; the agreement was 99% for the hook test and 98% for the stress test. There was no statistically significant difference in functional scores (OM mean, 79.6 vs. 83.6) or pain between syndesmosis transfixation and no fixation groups (Study 4). Our results suggest that a simple stability-based fracture classification is useful in choosing between non-operative and operative treatment of ankle fractures; approximately half of the ankle fractures can be treated non-operatively with success. Our observations also suggest that relevant syndesmosis injuries are rare in ankle fractures due to an SER mechanism of injury. According to our research, syndesmotic repair or fixation in SER ankle fracture has no influence on functional outcome or pain after minimum one year compared with no fixation. PMID:23205893

Pakarinen, Harri

2012-12-01

341

Pivoting system fracture in a bileaflet mechanical valve: a case report.  

PubMed

A leaflet escape occurred in a low profile bileaflet mechanical prosthesis manufactured by TRI-Technologies that had been implanted for 3 years in the mitral position of a 32 year old patient. The escaped leaflet had embolized and was subsequently located by an abdominal computerized axial tomography scan and ultrasound in the terminal portion of the aortic bifurcation. The embolized leaflet was removed 3 months after valve replacement surgery. In an attempt to determine the cause of the escape the retrieved embolized leaflet was investigated. Techniques employed included visual examination aided by stereo-microscopy, x-ray imaging and scanning electron microscopy. One of the ears had fractured and was missing from the leaflet. Chipping was observed at the leaflet ear position on both the inflow and outflow surfaces. Visual and SEM observations found fractographic river-lines that indicated an apparent origin at the inflow surface of the ear nearest to the straight 'B-datum' line or coaptation edge. The origin seemed to be in the radius between the leaflet ear and the leaflet body. SEM observation of the remaining intact ear showed wear marks on both the inflow and outflow sides of the leaflet ear that corresponded to the suspected origin of fracture. It is believed that the use of boron alloyed pyrolytic carbon material and the leaflet's homogeneous monolithic structural design were factors that contributed to this adverse event. PMID:19165769

Zhang, Hongbo; Deng, Xiaoyan; Cianciulli, Tomás Francisco; Zhang, Ze; Chappard, Daniel; Lax, Jorge Alberto; Saccheri, Maria Cristina; Redruello, Hector Jorge; Jordana, Jorge Luis; Prezioso, Horacio Alberto; King, Martin; Guidoin, Robert

2009-08-01

342

FAVOR: A new fracture mechanics code for reactor pressure vessels subjected to pressurized thermal shock  

SciTech Connect

This report discusses probabilistic fracture mechanics (PFM) analysis which is a major element of the comprehensive probabilistic methodology endorsed by the NRC for evaluation of the integrity of Pressurized Water Reactor (PWR) pressure vessels subjected to pressurized-thermal-shock (PTS) transients. It is anticipated that there will be an increasing need for an improved and validated PTS PFM code which is accepted by the NRC and utilities, as more plants approach the PTS screening criteria and are required to perform plant-specific analyses. The NRC funded Heavy Section Steel Technology (HSST) Program at Oak Ridge National Laboratories is currently developing the FAVOR (Fracture Analysis of Vessels: Oak Ridge) PTS PFM code, which is intended to meet this need. The FAVOR code incorporates the most important features of both OCA-P and VISA-II and contains some new capabilities such as PFM global modeling methodology, the capability to approximate the effects of thermal streaming on circumferential flaws located inside a plume region created by fluid and thermal stratification, a library of stress intensity factor influence coefficients, generated by the NQA-1 certified ABAQUS computer code, for an adequate range of two and three dimensional inside surface flaws, the flexibility to generate a variety of output reports, and user friendliness.

Dickson, T.L.

1993-04-01

343

FAVOR: A new fracture mechanics code for reactor pressure vessels subjected to pressurized thermal shock  

SciTech Connect

This report discusses probabilistic fracture mechanics (PFM) analysis which is a major element of the comprehensive probabilistic methodology endorsed by the NRC for evaluation of the integrity of Pressurized Water Reactor (PWR) pressure vessels subjected to pressurized-thermal-shock (PTS) transients. It is anticipated that there will be an increasing need for an improved and validated PTS PFM code which is accepted by the NRC and utilities, as more plants approach the PTS screening criteria and are required to perform plant-specific analyses. The NRC funded Heavy Section Steel Technology (HSST) Program at Oak Ridge National Laboratories is currently developing the FAVOR (Fracture Analysis of Vessels: Oak Ridge) PTS PFM code, which is intended to meet this need. The FAVOR code incorporates the most important features of both OCA-P and VISA-II and contains some new capabilities such as PFM global modeling methodology, the capability to approximate the effects of thermal streaming on circumferential flaws located inside a plume region created by fluid and thermal stratification, a library of stress intensity factor influence coefficients, generated by the NQA-1 certified ABAQUS computer code, for an adequate range of two and three dimensional inside surface flaws, the flexibility to generate a variety of output reports, and user friendliness.

Dickson, T.L.

1993-01-01

344

Mechanism of diffusion-controlled brittle fracture. Final report, April 1, 1987--July 31, 1991  

SciTech Connect

Two generation of UHV testing systems were developed, one for testing pre-cracked specimens at constant displacement and the other at constant load, and they were supplemented by a computer-controlled potential-drop system for measurement of crack-growth rates. The latter system was also developed during this project. Experiments were carried out on the alloy Cu-8%Sn which was used as a model system for the phenomenon of diffusion-controlled fracture by intergranular decohesion resulting from the ingress of an embrittling element from a free surface as the result of an applied stress. The cracking phenomenon found earlier in alloy steels, and shown to be due to surface-adsorbed sulfur, was reproduced in the Cu-Sn alloy. This provided verification of the earlier proposed mechanism for the cracking phenomenon in the alloy steels, known as stress-relief cracking, and it also provided support for the hypothesis that the phenomenon was of a generic nature. In conjunction with the experimental work, the development of a quantitative theory of this class of brittle fracture, which we have termed ``dynamic embrittlement,`` was begun.

McMahon, C.J.

1991-10-01

345

Statistical distribution of natural fractures and the possible physical generating mechanism  

NASA Astrophysics Data System (ADS)

We have fitted field measurements of fracture spacings (from the vicinity of Lake Strom Thurmond, Georgia, U.S.A.) to the Weibull, Schuhmann and fractal distributions. The fracture spacings follow a fractal and Weibull distribution which implies that they were formed as a result of a repetitive fragmentation process. The limited variation of the fracture density with orientation in the study area suggests that the stress distribution generating these fractures may be uniform.

Boadu, F. K.; Long, L. T.

1994-06-01

346

3D Thermo-mechanical modelling of a stretched continental lithosphere containing localized low-viscosity anomalies (the soft-point theory of plate break-up)  

NASA Astrophysics Data System (ADS)

We present numerical models of extensional visco-elasto-plastic 3D continental lithosphere containing weaker areas within its mantle section. We aim at understanding the 3D crustal structure of volcanic passive margins that is characterized by both across-strike and along-strike finite strain gradients, with maxima around central igneous complex or their feeding magma reservoirs. It is suggested that localized hot melting zones within the lithosphere act as mechanical soft points and result in the local focusing of extension. To test this hypothesis 3D thermo-mechanical models of extensional continental lithosphere containing thermally induced soft points are implemented. Results show that crustal extension initiates and is focused over soft points in the mantle, reproducing the tectonic segmentation and zig-zag pattern of VPMs (volcanic passive margins).

Gac, Sébastien; Geoffroy, Laurent

2009-04-01

347

Action of recombinant human BMP-2 on fracture healing in rabbits is dependent on the mechanical environment.  

PubMed

The utility of recombinant human bone morphogenetic protein-2 (rhBMP-2) in inducing bone formation in fractures of bone is well known. However, the influence of the mechanical environment on the actions of rhBMP-2 on fracture healing is not clear. An experimental model of fractures of the tibia in rabbits was developed and utilized to investigate the role of mechanical environment on rhBMP-2 action. A 1 mm osteotomy gap was stabilized by either a low- or high-stiffness fixator (LSF or HSF, respectively), and local treatment with rhBMP-2 in an absorbable collagen sponge (ACS) was evaluated. The results of the investigation were analysed by both histomorphometry and biomechanics. The LSF caused an increase in mineralized periosteal callus compared to HSF, the rhBMP-2 in ACS accelerated fracture healing only in the LSF group but not in the HSF group. The area of mineralized tissue in interfragmentary callus was determined by fixation stiffness and not by BMP treatment. rhBMP-2 caused higher bone resorption in the endosteal callus during the late stages of fracture healing, but these histological differences did not affect the mechanical properties. Biomechanical evaluation showed only differences at 3 weeks between LSF-rhBMP-2 and LSF-ACS. The bending and torsional properties were higher in the rhBMP-2/ACS group compared to ACS alone at 3 weeks. PMID:20209659

Cuenca-López, María D; Peris, José L; García-Roselló, Mireia; Atienza, Carlos; Prat, Jaime; Becerra, José; Andrades, José A

2010-10-01

348

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

NASA Technical Reports Server (NTRS)

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.

Herring, H. W.

1971-01-01

349

Statistical distribution of natural fractures and the possible physical generating mechanism  

Microsoft Academic Search

We have fitted field measurements of fracture spacings (from the vicinity of Lake Strom Thurmond, Georgia, U.S.A.) to the Weibull, Schuhmann and fractal distributions. The fracture spacings follow a fractal and Weibull distribution which implies that they were formed as a result of a repetitive fragmentation process. The limited variation of the fracture density with orientation in the study area

F. K. Boadu; L. T. Long

1994-01-01

350

Determination of Some Parameters for Fatigue Life in Welded Joints Using Fracture Mechanics Method  

NASA Astrophysics Data System (ADS)

In this work, the parameters stress intensity factor (SIF), initial and final crack lengths ( a i and a f), crack growth parameters ( C and m), and fatigue strength (FAT) are investigated. The determination of initial crack length seems to be the most serious factor in fatigue life and strength calculations for welded joints. A fracture mechanics approach was used in these calculations based on SIF which was calculated with the finite element method (FEM). The weld toe crack was determined to be equal to 0.1 mm, whereas the weld root crack's length was varied depending on the degree of the weld penetration. These initial crack length values are applicable for all types of joints which have the same crack phenomenon. As based on the above calculated parameters, the new limits of FAT for new geometries which are not listed yet in recommendations can be calculated according to the current approach.

Al-Mukhtar, A. M.; Biermann, H.; Hübner, P.; Henkel, S.

2010-12-01

351

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

NASA Technical Reports Server (NTRS)

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.

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

1976-01-01

352

The use of a coherent gradient sensor in dynamic mixed-mode fracture mechanics experiments  

NASA Astrophysics Data System (ADS)

T HE USE of a coherent gradient sensing (CGS) apparatus is explored in dynamic fracture mechanics investigations. The ability of the method to quantify mixed-mode crack tip deformation fields accurately is tested under dynamic loading conditions. The specimen geometry and loading follow that of Lee and Freund who gave the theoretical and numerical mixed-mode K values as a function of lime for the testing conditions. The CGS system's measurements of KI and KII are compared with the predicted results, and good agreement is found. The method is used to measure K beyond the time domain of the known solution; it is seen that a shift from primarily mode II deformation to primarily mode I deformation occurs.

Mason, J. J.; Lambros, J.; Rosakis, A. J.

353

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

NASA Technical Reports Server (NTRS)

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.

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

1986-01-01

354

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

NASA Technical Reports Server (NTRS)

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.

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

2003-01-01

355

Magnesium alloys as body implants: fracture mechanism under dynamic and static loadings in a physiological environment.  

PubMed

It is essential that a metallic implant material possesses adequate resistance to cracking/fracture under the synergistic action of a corrosive physiological environment and mechanical loading (i.e. stress corrosion cracking (SCC)), before the implant can be put to actual use. This paper presents a critique of the fundamental issues with an assessment of SCC of a rapidly corroding material such as magnesium alloys, and describes an investigation into the mechanism of SCC of a magnesium alloy in a physiological environment. The SCC susceptibility of the alloy in a simulated human body fluid was established by slow strain rate tensile (SSRT) testing using smooth specimens under different electrochemical conditions for understanding the mechanism of SCC. However, to assess the life of the implant devices that often possess fine micro-cracks, SCC susceptibility of notched specimens was investigated by circumferential notch tensile (CNT) testing. CNT tests also produced important design data, i.e. threshold stress intensity for SCC (KISCC) and SCC crack growth rate. Fractographic features of SCC were examined using scanning electron microscopy. The SSRT and CNT results, together with fractographic evidence, confirmed the SCC susceptibility of both smooth and notched specimens of a magnesium alloy in the physiological environment. PMID:22075121

Choudhary, Lokesh; Raman, R K Singh

2012-02-01

356

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

USGS Publications Warehouse

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) tensile stresses of magnitude greater than the pressure in the slit are concentrated along the free surface. The relative surface displacements over a shallow vertical slit are downward over the slit and upward to both sides of this area. The tensile stress acting parallel to the free surface over a shallow vertical slit is concentrated in two maxima adjacent to a point of very low stress immediately over the slit. The solution is used to estimate the length-to-depth ratio at which igneous sills have gained sufficient leverage on overlying strata to bend these strata upward and form a laccolith. The pronounced mode II stress intensity associated with shallow horizontal slits explains the tendency for some sills to climb to higher stratigraphie horizons as they grow in length. The bimodal tensile stress concentration over shallow vertical slits correlates qualitatively with the distribution of cracks and normal faults which flank fissure eruptions on volcanoes. The solution may be used to analyze surface displacements and tilts over massive hydraulic fractures in oil fields and to understand the behavior of hydraulic fractures in granite quarries. ?? 1979.

Pollard, D. D.; Holzhausen, G.

1979-01-01

357

Fracture mechanics tests to characterize bonded glass\\/epoxy composites: Application to strength prediction in structural assemblies  

Microsoft Academic Search

This paper presents results from a study of assemblies composed of glass fibre reinforced epoxy composites. First, tests performed to produce mixed mode fracture envelopes are presented. Then results from tests on lap shear and L-stiffener specimens are given. These enabled failure mechanisms to be examined in more detail using an image analysis technique to quantify local strain fields. Finally

Peter Davies; Jeffrey Sargent

2003-01-01

358

Fracture mechanics behavior of a Ni?Fe superalloy sheath for superconducting fusion magnets. Part 1. property measurements  

Microsoft Academic Search

A seamless extruded conduit for superconductor cabling was fabricated and subjected to mechanical tests. The conduit is made of a nickel-iron alloy having aging and thermal contraction characteristics comparable with Nb3Sn conductors. The conduit in liquid helium at 4 K retains its ductility and offers high strength, toughness, and fatigue resistance. Specimens with surface cracks in tension offer substantial fracture

R. L. Tobler; I. S. Hwang; M. M. Steeves

1997-01-01

359

Effect of the thermal cycle on the hot ductility and fracture mechanisms of a C–Mn steel  

Microsoft Academic Search

Transverse cracking on the surface of continuously cast steel products has been one of the main problems of this stage in steelmaking for many years. The incidence of this problem has been found in microalloyed steels as well as in some plain carbon steels containing residual elements. In this work, the hot ductility and fracture mechanisms of a C–Mn steel

J. Calvo; A. Rezaeian; J. M. Cabrera; S. Yue

2007-01-01

360

Fracture mechanics investigation regarding the effects of cracks on the structural integrity of a BWR-core shroud  

Microsoft Academic Search

As a consequence of core shroud intergranular stress corrosion cracking (IGSCC) detected in the course of inservice inspections, a fracture mechanics analysis was carried out to evaluate the effects of postulated cracks on the structural integrity. In this study, critical crack sizes and crack growth were calculated. Due to the comparatively low stress acting on the core shroud during normal

D Beukelmann; J Schäfer; W Lehmann

1999-01-01

361

Research challenges arising from current and potential applications of dynamic fracture mechanics to the integrity of engineering structures  

Microsoft Academic Search

Following several decades of contentiousness, the general framework of dynamic fracture mechanics is now generally agreed upon. While some basic issues remain unresolved, many successful practical applications have been made. Examples are provided in this paper that are drawn from the transport of fluids in gas pipelines, and of people in aircraft and aerospace vehicles. These examples illustrate that the

M. F. Kanninen; P. E. O'Donoghue

1995-01-01

362

Characterisation of recharge processes and groundwater flow mechanisms in weathered-fractured granites of Hyderabad (India) using isotopes  

Microsoft Academic Search

In order to address the problem of realistic assessment of groundwater potential and its sustainability, it is vital to study the recharge processes and mechanism of groundwater flow in fractured hard rocks, where inhomogeneties and discontinuities have a dominant role to play. Wide variations in chloride, ?18O and 14C concentrations of the studied groundwaters observed in space and time could

B. S. Sukhija; D. V. Reddy; P. Nagabhushanam; S. K. Bhattacharya; R. A. Jani; Devender Kumar

2006-01-01

363

Theoretical and user`s manual for pc-PRAISE: A probabilistic fracture mechanics computer code for piping reliability analysis  

Microsoft Academic Search

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

D. O. Harris; D. D. Dedhia; S. C. Lu

1992-01-01

364

Theoretical and user's manual for pc-PRAISE: A probabilistic fracture mechanics computer code for piping reliability analysis  

Microsoft Academic Search

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

D. O. Harris; D. D. Dedhia; S. C. Lu

1992-01-01

365

Fracture toughness and fracture mechanisms of PBT\\/PC\\/IM blends: Part V Effect of PBT-PC interfacial strength on the fracture and tensile properties of the PBT\\/PC blends  

Microsoft Academic Search

To investigate the effect of PBT-PC interfacial strength on the fracture toughness and toughening mechanisms of the PBT\\/PC system, a series of PBT\\/PC blends with different content of in situ formed PBT-PC copolymers were made by melt blending. The in situ copolymer was separately prepared via reactive blending of the PBT and PC in the presence of a transesterification catalyst

Jingshen Wu; Ke Wang; Demei Yu

2003-01-01

366

Carpal fractures.  

PubMed

Carpal fractures are exceedingly rare clinical entities and are often associated with concomitant injuries. In this review, we focus on fractures of the carpus, excluding the scaphoid, and provide an update on the current consensus as to mechanism, diagnosis, management, outcomes, and complications after such injuries. PMID:24679911

Suh, Nina; Ek, Eugene T; Wolfe, Scott W

2014-04-01

367

The injury mechanisms of osteoporotic upper extremity fractures among older adults: a controlled study of 287 consecutive patients and their 108 controls.  

PubMed

The risk factors for falls in older adults are well known but knowledge on the direct injury mechanisms that result in various osteoporotic fractures has been very sparse. The purpose of this study was therefore to clarify the injury mechanisms of osteoporotic upper extremity fractures of older adults and to compare these mechanisms with those of the control fallers, and in this way to obtain reliable insight into the etiology and pathogenesis of upper extremity fractures and thus to enable fracture prevention. One hundred and twelve patients with a fresh fracture of the proximal humerus, 65 patients with an elbow fracture, 110 patients with a wrist fracture and 108 controls (no fracture, or a fracture other than the case fracture) were interviewed and examined between September 1995 and December 1997. The inclusion criteria of the subjects were that the patient was 50 years of age or older at the time of the accident, and that the fracture/injury had occurred as a result of low-energy trauma (typically a fall from standing height or less) within a week before the interview and examination. In 97% of patients with a proximal humerus or elbow fracture, and in all patients (100%) with a wrist fracture, the fracture was a result of a fall. In the control group this figure was 93%. In a polychotomous logistic regression analysis the intergroup differences in the fall directions (adjusted by gender, age and functional capacity) were statistically highly significant (chi 2 = 43.6, d.f. = 15, p < 0.001). Most of the patients with a proximal humerus fracture or elbow fracture reported that they had fallen 'obliquely forward' (43% and 38%) or 'to the side' (29% and 26%), whereas in the wrist fracture group the main fall direction was also 'obliquely forward' (34%) but the other fall directions (i.e., 'forward', 'to the side', 'obliquely backward' and 'backward') were quite equally represented (13-19%). The odds ratio (OR) for an obliquely forward fall resulting in a proximal humerus fracture was 3.5 [95% confidence interval (CI) 1.4-9.2), as compared with the fall directions of the controls and the 'obliquely backward' fall direction. In a logistic regression analysis the patients with a wrist fracture managed to break their fall (e.g., with an outstretched arm) more frequently than the patients in the other groups (OR 3.9; 95% CI 2.0-7.3). The patients with a proximal humerus fracture, in turn, managed to break their fall less frequently than the controls (OR 0.33; 95% CI 0.14-0.80). The same was true of the patients with an elbow fracture, although the difference was not significant (OR 0.49%; 95% CI 0.19-1.3). As objective evidence for a direct fall-induced impact on the fracture site, 68% of patients with a proximal humerus fracture revealed a fresh subcutaneous hematoma on the shoulder/upper arm, while such a hematoma was rare in the controls (2%) (p < 0.001). Correspondingly, 62% of patients with an elbow fracture showed a similar hematoma on the elbow area, while this was seen in none of the controls (p < 0.001). In patients with a wrist fracture a hand/wrist hematoma was seen in 58% of the victims, as compared with 18% of the controls (p < 0.001). The study shows that the most typical osteoporotic upper extremity fractures of older adults have their specific injury mechanisms. A great majority of these fractures occur as a result of a fall and a subsequent direct impact of the fractured site. Effective fracture prevention could be achieved by minimizing the obvious risk factors of falling and reducing the fall-induced impact force with injury site protection. PMID:11199185

Palvanen, M; Kannus, P; Parkkari, J; Pitkäjärvi, T; Pasanen, M; Vuori, I; Järvinen, M

2000-01-01

368

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

PubMed Central

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.

Hohenwarter, A.; Pippan, R.

2013-01-01

369

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

NASA Technical Reports Server (NTRS)

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.

Gangloff, Richard P.; Kim, Sang-Shik

1993-01-01

370

A generation mechanism of triboelectricity due to the reaction of mechanoradicals with mechanoions which are produced by mechanical fracture of solid polymer  

Microsoft Academic Search

Mechanical fracture of solid polymer under vacuum at 77K can, in principle, produce both mechanoradicals and mechanoanions which are formed by homolytic and heterolytic scission of carbon-carbon bonds in the polymer main chain. The production of mechanoanions was claimed by a detection of tetracyanoethylene (TCNE) anion radical (TCNE-), which was observed by electron spin resonance (ESR) spectroscopy using the electron

M. Sakaguchi; H. Kashiwabara

1992-01-01

371

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

NASA Astrophysics Data System (ADS)

Large sand intrusions often exhibit conical morphologies analogous to magmatic intrusions such as saucer-shaped or cup-shaped sills. Whereas some physical processes may be similar, we show with scaled experiments that the formation of conical sand intrusions may be favoured by the pore-pressure gradients prevailing in the host rock before sand injection. Our experiments involve injecting air into a permeable and cohesive analogue material to produce hydraulic fractures while controlling the pore pressure field. We control the state of overpressure in the overburden by applying homogeneous basal pore pressure, and then adding a second local pore pressure field by injecting air via a central injector to initiate hydraulic fractures near the injection point. In experiments involving small vertical effective stresses (small overburden, or high pore fluid overpressure), the fracturing pressure ( ?fract) is supralithostatic and two dipping fractures are initiated at the injection point forming a conical structure. From theoretical considerations, we predict that high values of ?fract are due to strong cohesion or high pore fluid overpressure distributed in the overburden. Such conditions are favoured by the pore pressure/stress coupling induced by both pore pressure fields. The dips of cones can be accounted for elastic-stress rotation occurring around the source. Contrary to magmatic chamber models, the aqueous fluid overpressure developed in a parent sandbody (and prevailing before the formation of injectites) may diffuse into the surrounding overburden, thus favouring stress rotation and the formation of inclined sheets far from the parent source. For experiments involving higher vertical effective stresses (thick overburden or low pore fluid overpressure), the fracturing pressure is lower than the lithostatic stress, and a single fracture is opened in mode I which then grows vertically. At a critical depth, the fracture separates into two dilatant branches forming 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.

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

2012-01-01

372

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

NASA Astrophysics Data System (ADS)

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.

Sommer, Silke

2010-06-01

373

Modeling Fractures in Thermal Systems: Thermal-Mechanical Feedback and Vein Formation  

NSDL National Science Digital Library

Barb Dutrow, Department of Geology & Geophysics, Louisiana State University Topic: Mineralogy, Petrology, fracture formation Course type: Upper level undergraduate course Description In many geologic systems, ...

374

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

PubMed

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 velocity, sequential movement patterns, higher elbow-flexion to knee-extension strength ratios, higher seat-to-handle velocity during the initial drive, or higher shoulder angle excursion may result in RSF. Gearing may indirectly affect rib loading. Increased risk may be due to low calcium, low vitamin D, eating disorders, low testosterone or use of depot medroxyprogesterone injections. Injury management involves 1-2 weeks cessation of rowing with analgesic modalities followed by a slow return to rowing with low-impact intensity and modified pain-free training. Some evidence shows injury prevention strategies should focus on strengthening the serratus anterior, strengthening leg extensors, stretching the lumbar spine, increasing hip joint flexibility, reducing excessive protraction, training with ergometers on slides or floating-head ergometers, and calcium and vitamin D supplementation. Future research should focus on the epidemiology of RSF over 4-year Olympic cycles in elite rowers, the aetiology of the condition, and the effectiveness of RSF prevention strategies for injury incidence and performance in rowing. PMID:21985212

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

2011-11-01

375

Fracture-mechanics data deduced from thermal-shock and related experiments with LWR pressure-vessel material  

SciTech Connect

Pressurized water reactors (PWRs) are susceptible to certain types of hypothetical accidents that can subject the reactor pressure vessel to severe thermal shock, that is, a rapid cooling of the inner surface of the vessel wall. The thermal-shock loading, coupled with the radiation-induced reduction in the material fracture toughness, introduces the possibility of propagation of preexistent flaws and what at one time were regarded as somewhat unique fracture-oriented conditions. Several postulated reactor accidents have been analyzed to discover flaw behavior trends; seven intermediate-scale thermal-shock experiments with steel cylinders have been conducted; and corresponding materials characterization studies have been performed. Flaw behavior trends and related fracture-mechanics data deduced from these studies are discussed.

Cheverton, R.D.; Canonico, D.A.; Iskander, S.K.; Bolt, S.E.; Holz, P.P.; Nanstad, R.K.; Stelzman, W.J.

1982-01-01

376

Probability of pipe fracture in the primary coolant loop of a PWR plant. Volume 5. Probabilistic fracture mechanics analysis. Load Combination Program Project I final report  

SciTech Connect

The primary purpose of the Load Combination Program covered in this report is to estimate the probability of a seismic induced LOCA in the primary piping of a commercial pressurized water reactor (PWR). Best estimates, rather than upper bound results are desired. This was accomplished by use of a fracture mechanics model that employs a random distribution of initial cracks in the piping welds. Estimates of the probability of cracks of various sizes initially existing in the welds are combined with fracture mechanics calculations of how these cracks would grow during service. This then leads to direct estimates of the probability of failure as a function of time and location within the piping system. The influence of varying the stress history to which the piping is subjected is easily determined. Seismic events enter into the analysis through the stresses they impose on the pipes. Hence, the influence of various seismic events on the piping failure probability can be determined, thereby providing the desired information.

Harris, D.O.; Lim, E.Y.; Dedhia, D.D.

1981-06-01

377

Effect of roughness and material strength on the mechanical properties of fracture replicas  

SciTech Connect

This report presents the results of 11 rotary shear tests conducted on replicas of three hollow cylinders of natural fractures with JRC values of 7.7, 9.4 and 12.0. The JRC values were determined from the results of laser profilometer measurements. The replicas were created from gypsum cement. By varying the water-to-gypsum cement ratio from 30 to 45%, fracture replicas with different values of compressive strength (JCS) were created. The rotary shear experiments were performed under constant normal (nominal) stresses ranging between 0.2 and 1.6 MPa. In this report, the shear test results are compared with predictions using Barton`s empirical peak shear strength equation. observations during the experiments indicate that only certain parts of the fracture profiles influence fracture shear strength and dilatancy. Under relatively low applied normal stresses, the JCS does not seem to have a significant effect on shear behavior. As an alternative, a new procedure for predicting the shear behavior of fractures was developed. The approach is based on basic fracture properties such as fracture surface profile data and the compressive strength, modulus of elasticity, and Poisson`s ratio of the fracture walls. Comparison between predictions and actual shear test results shows that the alternative procedure is a reliable method.

Wibowo, J.; Amadei, B.; Sture, S. [Univ. of Colorado, Boulder, CO (United States)] [and others

1995-08-01

378

Hydromechanical interactions in a fractured carbonate reservoir inferred from hydraulic and mechanical measurements  

Microsoft Academic Search

Hydromechanical coupled processes in a shallow fractured carbonate reservoir rock were investigated through field experiments coupled with analytical and numerical analyses. The experiments consist of hydraulic loading\\/unloading of a water reservoir in which fluid flow occurs mainly inside a heterogeneous fracture network made up of vertical faults and bedding planes. Hydromechanical response of the reservoir was measured using six pressure–normal

F. Cappa; Y. Guglielmi; P. Fénart; V. Merrien-Soukatchoff; A. Thoraval

2005-01-01

379

Fracture Mechanics in Low-Cycle Loading and in the Presence of High Strain Gradient.  

National Technical Information Service (NTIS)

The fracture criterion for variable low-cycle loading was developed based on the concept of cumulative damage. The study of fracture stability in high strain gradient field is based on the argument that couple-stress becomes significant in such fields. An...

F. D. Ju Y. C. Hsu

1971-01-01

380

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

NASA Technical Reports Server (NTRS)

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.

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

1971-01-01

381

Mechanical modeling of tectonic deformations  

SciTech Connect

Finding oil traps is based essentially on interpreting seismic data. The interpretation is often difficult; the geologist generally is faced with several possible solutions because structures are not always clearly defined. Rock mechanics are used to retain only the kinematic solutions that are stable at all times. All the possible evolutions are no longer equally probable. Two different methods were used. Elasto-plastic behaviors (limestones, sandstones, etc.) are satisfactorily taken into account within a finite element code. It must be able to model the great displacement and large deformations that occur on a geological time scale. In an experimental approach, conditions of structural deformation are recreated in laboratories using physical models. Results of the numerical modeling have to be calibrated against these experiments. A sedimentary basin has been modeled in this way. This basin has been numerically modeled. Sedimentation is modeled by a gradual activation of the meshing. The plastic strain is computed at each time step of the deformation. Large values are located along lined zones corresponding to the faults observed on physical models. The creation and propagation of faults are modeled correctly. Moreover, the authors check that the spacing of the faults depends on the thicknesses of the layers. Viscous behaviors of salt domes are better taken into account by a finite differences code. Mushroom diapirs and balloon diapirs have been modeled in this way. Other parameters such as the spacing between salt domes may be studied, too.

Julien, P. (TOTAL C.F.P., Paris (France))

1990-05-01

382

Deferoxamine restores callus size, mineralization and mechanical strength in fracture healing after radiotherapy  

PubMed Central

Background Therapeutic augmentation of fracture site angiogenesis with Deferoxamine (DFO) has proven to increase vascularity, callus size and mineralization in long-bone fracture models. We posit that the addition of DFO would enhance pathological fracture healing in the setting of radiotherapy in a model where non-unions are the most common outcome. Methods Sprague-Dawley rats (n = 35) were divided into 3 groups. Fracture (Fx), radiated fracture (XFx) and radiated fracture + DFO (XFxDFO). Groups XFx and XFxDFO received a human equivalent dose of radiotherapy (7 Gy/day × 5 days = 35 Gy) 2 weeks prior to mandibular osteotomy and external fixation. The XFxDFO group received injections of DFO into the fracture callus after surgery. Following a 40-day healing period, mandibles were dissected, clinically assessed for bony-union, imaged with Micro-CT, and tension tested to failure. Results Compared to radiated fractures, metrics of callus size, mineralization and strength in DFO treated mandibles were significantly increased. These metrics were restored to a level demonstrating no statistical difference from control fractures. In addition we observed an increased rate of achieving bony unions in the XFxDFO treated group when compared to XFx (67% vs. 20% respectively). Conclusions Our data demonstrate near total restoration of callus size, mineralization, and biomechanical strength, as well as a 3-fold increase in the rate of union with the use of DFO. Our results suggest that the administration of DFO may have the potential for clinical translation as a new treatment paradigm for radiation induced pathologic fractures. Level of Evidence Animal study, not gradable for level of evidence.

Donneys, Alexis; Ahsan, Salman; Perosky, Joseph E.; Deshpande, Sagar S.; Tchanque-Fossuo, Catherine N.; Levi, Benjamin; Kozloff, Ken M.; Buchman, Steven R.

2013-01-01

383

At the moment of occurrence of a fragility hip fracture, men have higher mechanical properties values in comparison with women  

PubMed Central

Background It is well established that males have lower fracture risk in comparison with females, which suggests a higher bone resistance in men. The aim of our study was to find out if in older patients with hip fragility fractures, gender has also an impact on trabecular bone material behaviour, specifically to determine whether trabecular mechanical properties under compressive loading differ between men and women who suffered a fragility hip fracture. Methods Femoral epiphyses were consecutively collected during hip replacement surgery due to proximal femur fragility fracture. Trabecular bone cylinders were drilled and submitted to uniaxial compression tests and mechanical properties were assessed. Results Seventy-three patients, 55 women (mean age 81 years and standard deviation of 7 years) and 18 men (mean age 81 years and standard deviation of 8 years) were evaluated. The ultimate stress of trabecular bone was significantly higher in men than in women: the median values and the interquartile range (IQR) were respectively 8.04(5.35-10.90) MPa vs. 4.46(3.02-7.73) MPa, (p-value?=?0.005). The same difference between male and female was observed in the Young’s modulus: 293.68(166.67-538.18) MPa vs. 174.26(73.07-322.28) MPa, (p-value?=?0.028), and also in the energy to failure: 0.25(0.07-0.42) MJ/m3 vs. 0.11(0.05-0.25) MJ/m3, (p-value?=?0.058). These differences were also verified after adjusting the analysis for age in a multivariate model analysis. Conclusions Our observations demonstrated that, even in a population who suffered a fragility hip fracture, men still have higher trabecular bone mechanical properties in comparison with women.

2013-01-01

384

Model for toughness curves in two-phase ceramics: 1. Basic fracture mechanics  

SciTech Connect

A fracture mechanics model is presented for the toughening of ceramics by bridging from second-phase particles, resulting in toughness curve (T-curve) behavior. It is assumed that the second-phase particles are in a state of residual thermal expansion dilatational mismatch relative to the matrix. In the long-crack region, these stresses augment frictional sliding stresses at the interphase boundaries, enhancing the crack resistance; in the short-crack region, the same stresses drive the crack, diminishing the crack resistance. The principal manifestation of these countervailing influences is a reduced sensitivity of strength to initial flaw size, i.e., an increased flaw tolerance. In seeking to incorporate these key physical elements, the authors' model opts for mathematical simplicity by assuming uniformly distributed stresses in two bridging domains: in the first, at small crack-wall separations, a constant opening stress; in the second, at larger separations, a constant closing stress. The uniform crack-plane distributions allow for simple closed-form solutions of the crack K-field equations, and thence an analytical formulation for the T-curve. Indentation-strength data on a reference Al[sub 2]O[sub 3]/Al[sub 2]TiO[sub 5] ceramic composite are used to demonstrate the main theoretical predictions and to calibrate essential parameters in the T-curve formulation.

Lawn, B.R.; Padture, N.P.; Braun, L.M.; Bennison, S.J. (National Inst. of Standards and Technology, Gaithersburg, MD (United States). Ceramics Div., Materials Science and Engineering Lab.)

1993-09-01

385

COMPARISON OF THE TRADITIONAL STRENGTH OF MATERIALS APPROACH TO DESIGN WITH THE FRACTURE MECHANICS APPROACH  

SciTech Connect

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.

Z. Ceylan

2002-04-30

386

Low Magnitude Mechanical Signals Reduce Risk-Factors for Fracture during 90-Day Bed Rest  

NASA Technical Reports Server (NTRS)

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,

Muir, J. W.; Xia, Y.; Holquin, N.; Judex, S.; Qin, Y.; Evans, H.; Lang, T.; Rubin, C.

2007-01-01

387

Development of fracture mechanics data for two hydrazine APU turbine wheel materials  

NASA Technical Reports Server (NTRS)

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.

Curbishley, G.

1975-01-01

388

A review of path-independent integrals in elastic-plastic fracture mechanics, task 4  

NASA Technical Reports Server (NTRS)

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.

Kim, K. S.

1985-01-01

389

A review of path-independent integrals in elastic-plastic fracture mechanics  

NASA Technical Reports Server (NTRS)

The objective of this paper is to review 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. The P-I integrals considered are the J-integral by Rice (1968), the thermoelastic P-I integrals by Wilson and Yu (1979) and Gurtin (1979), the J-integral by Blackburn (1972), the J(theta)-integral by Ainsworth et al. (1978), the J-integral by Kishimoto et al. (1980), and the Delta-T(p) and Delta T(p)-asterisk integrals by Alturi et al. (1982). The theoretical foundation of the P-I integrals is examined with an emphasis on whether or not the path independence is maintained in the presence of nonproportional loading and unloading in the plastic regime, thermal gradient, and material inhomogeneities. The simularities, difference, salient features, and limitations of the P-I integrals are discussed. Comments are also made with regard to the physical meaning, the possibility of experimental measurement, and computational aspects.

Kim, Kwang S.; Orange, Thomas W.

1988-01-01

390

Development of Probabilistic Fracture Mechanics Analysis Code for Pipes with Stress Corrosion Cracks  

NASA Astrophysics Data System (ADS)

Risk-Informed integrity management methodologies have been developed for Japanese nuclear power plants. One of the issues of concern is the reliability assessment of piping with flaws due to stress corrosion cracking (SCC). Therefore, the probabilistic fracture mechanics analysis code has been developed, which can perform the reliability assessment for austenitic stainless steel piping with flaws due to SCC. This paper describes technical basis of this code. This method is based on Monte-Carlo technique considering many sample cases in a piping section, where the initiation and growth of cracks are calculated and piping failures, including leaks and rapture, are evaluated. A notable feature is that multiple cracks can be treated, consequently, assessment of coalescence of cracks and intricate break evaluation of piping section have been included. Moreover, the in-service inspection (ISI) and integrity evaluation by Fitness-for-Service (FFS) code are integrated into the analysis, and the contribution to failure probability decrease can be assessed. Key parameters are determined on a probability basis with the designated probability type throughout the procedure. Size, location and time of crack initiation, coefficients of crack growth due to SCC and factors for piping failure are included in those parameters. With this method the reliability level of the piping through the operation periods can be estimated and the contribution of various parameters including ISI can be quantitatively evaluated.

Machida, Hideo; Arakawa, Manabu; Yamashita, Norimichi; Yoshimura, Shinobu

391

Thermomechanical fatigue life prediction in gas turbine superalloys: A fracture mechanics approach  

SciTech Connect

A model is presented that was developed to predict thermomechanical fatigue crack initiation and estimate mode I crack growth of gas turbine hot section gas path superalloys. The model is based on a strain energy density fracture mechanics approach modified to account for thermal exposure and single crystal anisotropy. Thermomechanical fatigue crack initiation and small crack growth is modeled by employing an initial material defect size. Model capability was quantified by applying the model to two hot section gas path superalloys: uncoated MAR-M509 and MCrAlY overlay coated PWA 1480. Thermomechanical fatigue model stresses were obtained from nonlinear finite element analysis of thermomechanical fatigue specimen strain-temperature history. Nonlinear stress-strain behavior was predicted using unified viscoplastic constitutive models. Model thermomechanical fatigue life predictions were in good agreement with observed uniaxial thermomechanical fatigue specimen lives. Thermomechanical fatigue cracking effects captured by the model included coating thickness, single crystal anisotropy, cycle waveshape, dwell, and thermal exposure. 45 refs.

Nissley, D.M. [United Technologies Corp., East Hartford, CT (United States)

1995-06-01

392

Determination of the elastic-plastic fracture mechanics Z-factor for alloy 182 weld metal flaws  

Microsoft Academic Search

One of the ways that the ASME Section XI code incorporates elastic-plastic fracture mechanics (EPFM) in the Section XI Appendix C flaw evaluation procedures for circumferential cracks is through a parameter called Z-factor. This parameter allows the simpler limit-load (or Net-Section-Collapse) solutions to be used with a multiplier from EPFM analyses. This paper shows how 3-D finite element (FE) analyses

Do-Jun Shim; Gery M. Wilkowski; David L. Rudland

2011-01-01

393

Fracture mechanism and toughness of the welding heat-affected zone in structural steel under static and dynamic loading  

Microsoft Academic Search

Due to the influence of the welding thermal cycle, the toughness of structural steel generally degenerates. Recently, the\\u000a intercritically reheated coarse-grained heat-affected zone (IC CG HAZ) was found to demonstrate the worst toughness in welded\\u000a joint, which was associated with its fracture mechanism. In this article, two IC CG HAZs of a structural steel were prepared\\u000a by welding thermal-cycle simulation

H. Qiu; H. Mori; M. Enoki; T. Kishi

2000-01-01

394

Fracture mechanics assessment of PWR vessel integrity incorporating dynamic crack arrest data above 220 MPa radical m  

SciTech Connect

The present rules and criteria regarding the PTS issue, as established by the US Nuclear Regulatory Commission (NRC), are the PTS rule (Code of Federal Regulations, 1985) and Nuclear Regulatory Guide 1.154 (Regulatory Guide 1.154, 1987). The PTS rule specifics screening criteria in the form of limiting values of reference nil ductility temperature (RT{sub NDT}) of the reactor pressure vessel. Also, the PTS rule requires that a plant specific safety analysis must be performed for any plant that a utility seeks to operate beyond the screening criteria. Nuclear Regulatory Guide 1.154 provides guidance for utilities on how to perform the plant specific analysis. It references the IPTS study as an acceptable methodology for performing the probabilistic fracture mechanics portion of the plant specific analysis and specifies that the frequency of vessel failure due to PTS shall not exceed 5 {times} 10{sup {minus}6} failures per reactor year. Since the IPTS Program was completed, the Heavy Section Steel Technology (HSST) Program has conducted several large specimen fracture mechanics experiments which demonstrated that prototypical reactor pressure vessel steels are capable of arresting a crack propagating in the cleavage mode at fracture toughness values considerably above 220 MPa{radical}m, the implicit limit of the American Society of Mechanical Engineers (ASME) Code and the maximum value included in the IPTS studies. The purpose of this paper is to investigate the potential impact of the enhanced crack arrest data on the results of probabilistic fracture mechanics analyses. 12 refs., 5 figs.

Dickson, T.L.; Cheverton, R.D.

1991-01-01

395

The effect of tempering temperature on the mechanical properties and fracture morphology of a NiCrMoV steel  

Microsoft Academic Search

The present study focuses on the mechanical properties and the fracture morphology of a NiCrMoV steel with a specific composition. All specimens were austenitized at 870 °C for 1 h, followed by oil quenching, and then tempered at temperatures in the range of 200–600 °C. The results of tensile testing indicated that the yield strength (YS) and ultimate tensile strength (UTS) decreased with

A. Salemi; A. Abdollah-zadeh

2008-01-01

396

Research paper Thermal-mechanical modeling of cooling history and fracture development in inflationary basalt lava flows  

Microsoft Academic Search

Thermal-mechanical analyses of isotherms in low-volume basalt flows having a range of aspect ratios agree with inferred isotherm patterns deduced from cooling fracture patterns in field examples on the eastern Snake River Plain, Idaho, and highlight the caveats of analytical models of sheet flow cooling when considering low-volume flows. Our field observations show that low-volume lava flows have low aspect

Simon A. Kattenhorn; Conrad J. Schaefer

397

Fatigue properties and fatigue fracture mechanisms of SiC whiskers or SiC particulate-reinforced aluminium composites  

Microsoft Academic Search

Fatigue properties and fracture mechanisms were examined for three commercially fabricated aluminium matrix composites containing SiC whiskers (SiCw) and SiC particles (SiCp) using a rotating bending test. The fatigue strengths were over 60% higher for SiCw\\/A2024 composites than that for the unreinforced rolled material, while for the SiCp\\/A357 composites, fatigue strengths were also higher than that for the unreinforced reference

Chitoshi Masuda; Yoshihisa Tanaka

1992-01-01

398

Fracture mechanics data for 2024-T861 and 2124-T851 aluminum  

NASA Technical Reports Server (NTRS)

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.

Pionke, L. J.; Linback, R. K.

1974-01-01

399

Strengthening mechanisms and fracture surface characteristics of silicate glass matrix composites with inclusion of alumina particles of different particle sizes  

NASA Astrophysics Data System (ADS)

Strengthening mechanisms of silicate glass by the inclusion of alumina particles of different volume fractions and different particle sizes are reported. The formulas of three responsible strengthening mechanisms, based on inclusion/crack interactions and interfacial elemental diffusion, were deduced; these include crack deflection, crack bridging and interdiffusion. The strength of the glass/alumina composites increased with inclusion fraction, but followed strengthening mechanisms that varied with alumina particle size. Crack deflection and bridging mechanisms dominated in strengthening for the glass/alumina (at mean particle size of 6 ?m) composites while interdiffusion mechanism played a major role in the glass/alumina (at mean particle size of 1 ?m) composites. The theoretical deduction of strengthening mechanisms depending on the particle size of alumina inclusions was demonstrated by the experimental strength data and fracture surface characteristics of the glass/alumina composites.

Chen, Minghui; Zhu, Shenglong; Wang, Fuhui

2013-03-01

400

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

Microsoft Academic Search

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 (KIC) measurements of Fe–base, Ni–base, and Co–base hardfacings were performed

B. V. Cockeram

1998-01-01

401

Mechanical behavior of polycrystalline ceramics: Brittle fracture of SiC-Si3N4 materials  

NASA Technical Reports Server (NTRS)

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.

Ceipold, M. H.; Kapadia, C. M.; Kelkar, A. H.

1972-01-01

402

FRACTURE MECHANICAL MEASUREMENTS WITH COMMERCIAL STAINLESS STEELS AT 4 K AND WITH CP-TITANIUM AT 173 K  

SciTech Connect

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 MPasq root(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.

Nyilas, A. [Cryogenic Engineering and Materials Expertise, CEME, 76297 Stutensee (Germany); Mitterbacher, H. [Linde AG, Engineering Division, Materials Technology, 82049 Pullach (Germany)

2010-04-08

403

Development of a balanced experimental-computational approach to understanding the mechanics of proximal femur fractures.  

PubMed

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

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

2014-06-01

404

Petrophysical and Mechanical Properties of Fractured Aquifers in the Northern Newark Basin: Implications for Carbon Sequestration  

NASA Astrophysics Data System (ADS)

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 distinct sedimentary layers and strike predominantly SSE-NNW. In the Palisades sill breakouts are absent but the wellbore is consistently enlarged by up to 4 inches in the SE-NW direction (nominal hole diameter is 8.5 in). Drilling-induced tensile fractures and drilling-enhanced natural fractures appear in the tensile quadrants striking NE-SW. Preliminary analysis of sonic wavefields also suggest the NE orientation of the fast shear azimuth. For a vertical borehole these factors indicate maximum horizontal stress in the NE-SW direction, and are consistent with earthquake focal plane solutions and previous stress direction estimates in the Newark Basin. Borehole images also provide an excellent tool to describe natural fracture distribution and orientation. Combined with other petrophysical data such as core-calibrated density log, elastic moduli and stress-induced shear-wave anisotropy indicator, they allow to constrain geomechanical properties of the formation and to predict fracture behavior for potential CO2 injection conditions.

Zakharova, N. V.; Goldberg, D.; Collins, D.; Olsen, P. E.

2012-12-01

405

Flaw preparations for HSST program vessel fracture mechanics testing: mechanical-cyclic pumping and electron-beam weld-hydrogen-charge cracking schemes  

SciTech Connect

The purpose of the document is to present schemes for flaw preparations in heavy section steel. The ability of investigators to grow representative sharp cracks of known size, location, and orientation is basic to representative field testing to determine data for potential flaw propagation, fracture behavior, and margin against fracture for high-pressure-, high-temperature-service steel vessels subjected to increasing pressurization and/or thermal shock. Gaging for analytical stress and strain procedures and ultrasonic and acoustic emission instrumentation can then be applied to monitor the vessel during testing and to study crack growth. This report presents flaw preparations for HSST fracture mechanics testing. Cracks were grown by two techniques: (1) a mechanical method wherein a premachined notch was sharpened by pressurization and (2) a method combining electron-beam welds and hydrogen charging to crack the chill zone of a rapidly placed autogenous weld. The mechanical method produces a naturally occurring growth shape controlled primarily by the shape of the machined notch; the welding-electrochemical method produces flaws of uniform depth from the surface of a wall or machined notch. Theories, details, discussions, and procedures are covered for both of the flaw-growing schemes.

Holz, P.P.

1980-06-01

406

Application of small specimens to fracture mechanics characterization of irradiated pressure vessel steels  

SciTech Connect

In this study, precracked Charpy V-notch (PCVN) specimens were used to characterize the fracture toughness of unirradiated and irradiated reactor pressure vessel steels in the transition region by means of three-point static bending. Fracture toughness at cleavage instability was calculated in terms of elastic-plastic K{sub Jc} values. A statistical size correction based upon weakest-link theory was performed. The concept of a master curve was applied to analyze fracture toughness properties. Initially, size-corrected PCVN data from A 533 grade B steel, designated HSST Plate O2, were used to position the master curve and a 5% tolerance bound for K{sub Jc} data. By converting PCVN data to IT compact specimen equivalent K{sub Jc} data, the same master curve and 5% tolerance bound curve were plotted against the Electric Power Research Institute valid linear-elastic K{sub Jc} database and the ASME lower bound K{sub Ic} curve. Comparison shows that the master curve positioned by testing several PCVN specimens describes very well the massive fracture toughness database of large specimens. These results give strong support to the validity of K{sub Jc} with respect to K{sub Ic} in general and to the applicability of PCVN specimens to measure fracture toughness of reactor vessel steels in particular. Finally, irradiated PCVN specimens of other materials were tested, and the results are compared to compact specimen data. The current results show that PCVNs demonstrate very good capacity for fracture toughness characterization of reactor pressure vessel steels. It provides an opportunity for direct measurement of fracture toughness of irradiated materials by means of precracking and testing Charpy specimens from surveillance capsules. However, size limits based on constraint theory restrict the operational test temperature range for K{sub Jc} data from PCVN specimens. 13 refs., 8 figs., 1 tab.

Sokolov, M.A.; Wallin, K.; McCabe, D.E.

1996-12-31

407

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

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.

Ghoniem, N. M.

2003-07-14

408

The Mechanisms of Dispersion Strengthening and Fracture in Al-based XD (TM) Alloys  

NASA Technical Reports Server (NTRS)

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.

Aiken, R. M., Jr.

1990-01-01

409

Mechanical characterization of a CO2 fractured reservoir by means of microseismicity induced by high pressure injection tests  

NASA Astrophysics Data System (ADS)

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 (?). 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.

De Simone, Silvia; Soler, Joaquim; Carrera, Jesus; Slooten, Luit Jan; Ortiz, Gema

2014-05-01

410

Fracture mechanics and statistical modeling of ternary blends of polylactide/ethylene-acrylate copolymer /wood-flour composites  

NASA Astrophysics Data System (ADS)

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 amorphous grade. The semicrystalline blends showed decreased tensile strength and modulus with increased impact modifier content. In contrast, the ductility, elongation at break, and energy to break increased significantly. Mechanisms of toughening of PLA with EAC included impact modifier debonding, fibrillization, crack bridging and matrix shear yielding resulting in a ductile behavior. Increasing the EAC content in PLA/wood-flour composites enhanced the impact strength and elongation at break, but reduced the tensile modulus and strength of the composites. Composites with fine wood particles showed greater improvement in elongation at break than those with coarse particles; an opposite trend was observed for impact strength, tensile modulus and tensile strength. Numerical optimization produced two scenarios based on materials compositions to produce composites with similar mechanical properties as unfilled PLA. These optimization solutions were successfully validated experimentally. The crack initiation (Jin) and complete fracture (Jf) energies of unmodified PLA/wood-flour composites showed the deleterious effect of wood fiber incorporation into the plastic matrix by significantly decreasing the fracture toughness of PLA as the wood flour content increased. By contrast, impact modification of wood plastic composites with EAC significantly increased both the resistance to crack initiation (Jin) and complete fracture (Jf). Microscopic morphological studies revealed that the major mechanisms of toughening was through the EAC existing as separate domains in the bulk matrix of the composites which tended to act as stress concentrators that initiated local yielding of the matrix around crack tips and enhanced the toughness of the composites.

Afrifah, Kojo Agyapong

411

A partitioned model order reduction approach to rationalise computational expenses in nonlinear fracture mechanics  

PubMed Central

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.

Kerfriden, P.; Goury, O.; Rabczuk, T.; Bordas, S.P.A.

2013-01-01

412

Study of the Mechanism of Dynamic Ductile Fracture of Two-Phase Materials.  

National Technical Information Service (NTIS)

Dynamic ductile fracture of two phase material have been investigated in two stages. The first stage is a model study where an idealized two phase material, single crystal Cu SiO2, was used to study the initiation and growth of voids, the dislocation morp...

M. Taya I. W. Hall H. S. Yoon

1986-01-01

413

Effect of adhesive layer elasticity on the fracture mechanics of a blister test specimen  

Microsoft Academic Search

An analytical model of a blister type specimen for evaluation of adhesive bond strength is developed. The model accounts for shear deformation of both the plate and the adhesive layer in order to determine the extent to which a blister specimen may be considered to be a mixed mode fracture specimen. A method for relating the results of numerical stress

D. P. Updike

1976-01-01

414

Contact-induced Damage in Ceramic Coatings on Compliant Substrates: Fracture Mechanics and Design  

Microsoft Academic Search

Simple explicit relations are presented for the onset of com- peting fracture modes in ceramic coatings on compliant sub- strates from Hertzian-like contacts. Special attention is given to a deleterious mode of radial cracking that initiates at the lower coating surface beneath the contact, in addition to traditional cone cracking and quasiplasticity in the near- contact area. The critical load

Young-Woo Rhee; Hae-Won Kim; Yan Deng; Brian R. Lawn

2001-01-01

415

VOIDS GROWTH AND COALESCENCE FRACTURE MECHANISM OF DUCTIL IRON COMPUTATIONAL STUDY BY DISCRETE ELEMENT METHOD  

Microsoft Academic Search

The micromechanics of fracture by growing and coalescence of voids is described using the discrete element method (DEM) for micro-porous metal- matrix material (Ductile Iron). The study was developed in 2D series of representativ e volume elements (RVE) of a pseudomicrostructure of the reference material. In the RVEs, the stress vs strain, damage energy, elastic strain energy response and the

Rubén Galiano Batista; Ignacio Iturrioz

416

Mechanical characterization of thick polysilicon films: Young's modulus and fracture strength evaluated with microstructures  

Microsoft Academic Search

Young's modulus and the fracture strength of thick polysilicon films were evaluated with surface micromachined test structures. The polysilicon films were deposited in an epitaxial reactor and were about 10.5 µm thick. Four different processing schemes of doping and annealing were used and thus four different sets of test structures were micromachined. A micromanipulator system developed at Uppsala University was