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Strain Fields (strain + field)
Selected AbstractsA Polycrystalline Approach to the Cyclic Behaviour of f.c.c. Alloys , Intra-Granular HeterogeneityADVANCED ENGINEERING MATERIALS, Issue 9 2009Xavier Feaugas For several decades, the plastic deformation mechanisms of f.c.c. metals under cyclic loading have received considerable attention. The extensive work on this subject has gradually lead to the identification of the physical processes to be included in a formal scheme of fatigue behavior. Accordingly, we propose a review of the physical mechanisms of plastic deformation in f.c.c. metals and alloys to define the state-of-the-art and motivate future studies. The aim is to demonstrate the importance of a good knowledge of the heterogeneous nature of deformation at the intra-granular scale in defining a physical model of cyclic behavior. A large characterization of the different stages associated with the evolution of heterogeneous dislocation structures during tensile and cyclic loadings is given for an austenitic stainless steel AISI 316L. A unified view of these various structures is proposed in the form of a modified Pedersen's map [,max,=,f(,pcum), where ,max is the maximum plastic strain and ,pcum the cumulative plastic strain] in the case of tensile loading and different kinds of cyclic loading: uni-axial and multi-axial tests under stress or strain amplitude control. The specificities of each domain defined in the map are discussed in terms of long-range internal stresses in order to formalize, in a simple composite scheme, the intra-granular stress,strain field. The importance of taking into account this scheme and the nature of the different dislocations populations in a polycrystalline model is illustrated. [source] Large eddy simulation of passive scalar in complex turbulence with flow impingement and flow separationHEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 5 2001Ken-ichi Abe Abstract In order to reveal unknown characteristics of complex turbulent passive scalar fields, large eddy simulations in forced convection regimes have been performed under several strain conditions, including flow impingement and flow separation. By using the simulation results, relations between the dynamic and scalar fields are carefully examined. It is then confirmed that the scalar is transported by a large vortex structure near the examined regions wherever the mean shear vanishes, although in the high-shear regions, the scalar transport is governed by a coherent structure due to the high shear strain. In addition, a priori explorations are attempted by processing the data, focusing on the derivation of a possible direction for modeling algebraically the passive scalar transport in a complex strain field. The a priori tests suggest that an expanded form of the GGDH model introducing a quadratic product of the Reynolds stresses is promising for general flow cases. © 2001 Scripta Technica, Heat Trans Asian Res, 30(5): 402,418, 2001 [source] Flat boundaries and their effect on sand testingINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 8 2010G. Marketos Abstract A study of the effect of the use of flat boundaries on the stressing of a sample of an idealized granular material with no applied shear is presented. Discrete element method (DEM) data of 1D compression were analysed and the local strain field inside the sample was investigated as the sample was stressed. A best-fit strain was seen to best describe the material behaviour free from boundary effects. The individual particle displacements were probed, providing insight into the behaviour of particles adjacent to the boundaries. In addition, the porosity and force distribution inside the sample were observed, allowing for estimates of the width of a boundary region to be made. This region, non-representative of far-field material behaviour, will affect the behaviour of a granular sample in DEM or laboratory tests, with local porosity differences leading to a change in the transport properties of the sample, and force distribution changes leading to a bias in the location of grain cracking or crushing events for sufficiently high stress levels. Nevertheless, the largest effect of the boundary region was a severe underestimation of the stiffness of a granular material. Copyright © 2009 John Wiley & Sons, Ltd. [source] Numerical studies of shear banding in interface shear tests using a new strain calculation method,INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 12 2007Jianfeng Wang Abstract Strain localization is closely associated with the stress,strain behaviour of an interphase system subject to quasi-static direct interface shear, especially after peak stress state is reached. This behaviour is important because it is closely related to deformations experienced by geotechnical composite structures. This paper presents a study using two-dimensional discrete element method (DEM) simulations on the strain localization of an idealized interphase system composed of densely packed spherical particles in contact with rough manufactured surfaces. The manufactured surface is made up of regular or irregular triangular asperities with varying slopes. A new simple method of strain calculation is used in this study to generate strain field inside a simulated direct interface shear box. This method accounts for particle rotation and captures strain localization features at high resolution. Results show that strain localization begins with the onset of non-linear stress,strain behaviour. A distinct but discontinuous shear band emerges above the rough surface just before the peak stress state, which becomes more expansive and coherent with post-peak strain softening. It is found that the shear bands developed by surfaces with smaller roughness are much thinner than those developed by surfaces with greater roughness. The maximum thickness of the intense shear zone is observed to be about 8,10 median particle diameters. The shear band orientations, which are mainly dominated by the rough boundary surface, are parallel with the zero extension direction, which are horizontally oriented. Published in 2007 by John Wiley & Sons, Ltd. [source] Addressing volumetric locking and instabilities by selective integration in smoothed finite elementsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 1 2009Nguyen-Xuan Hung Abstract This paper promotes the development of a novel family of finite elements with smoothed strains, offering remarkable properties. In the smoothed finite element method (FEM), elements are divided into subcells. The strain at a point is defined as a weighted average of the standard strain field over a representative domain. This yields superconvergent stresses, both in regular and singular settings, as well as increased accuracy, with slightly lower computational cost than the standard FEM. The one-subcell version that does not exhibit volumetric locking yields more accurate stresses but less accurate displacements and is equivalent to a quasi-equilibrium FEM. It is also subject to instabilities. In the limit where the number of subcells goes to infinity, the standard FEM is recovered, which yields more accurate displacements and less accurate stresses. The specific contribution of this paper is to show that expressing the volumetric part of the strain field using a one-subcell formulation is sufficient to get rid of volumetric locking and increase the displacement accuracy compared with the standard FEM when the single subcell version is used to express both the volumetric and deviatoric parts of the strain. Selective integration also alleviates instabilities associated with the single subcell element, which are due to rank deficiency. Numerical examples on various compressible and incompressible linear elastic test cases show that high accuracy is retained compared with the standard FEM without increasing computational cost. Copyright © 2008 John Wiley & Sons, Ltd. [source] Two-level multiscale enrichment methodology for modeling of heterogeneous platesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 9 2009Caglar OskayArticle first published online: 15 JUN 200 Abstract A new two-level multiscale enrichment methodology for analysis of heterogeneous plates is presented. The enrichments are applied in the displacement and strain levels: the displacement field of a Reissner,Mindlin plate is enriched using the multiscale enrichment functions based on the partition of unity principle; the strain field is enriched using the mathematical homogenization theory. The proposed methodology is implemented for linear and failure analysis of brittle heterogeneous plates. The eigendeformation-based model reduction approach is employed to efficiently evaluate the non-linear processes in case of failure. The capabilities of the proposed methodology are verified against direct three-dimensional finite element models with full resolution of the microstructure. Copyright © 2009 John Wiley & Sons, Ltd. [source] A posteriori error estimation for extended finite elements by an extended global recoveryINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 8 2008Marc Duflot Abstract This contribution presents an extended global derivative recovery for enriched finite element methods (FEMs), such as the extended FEM along with an associated error indicator. Owing to its simplicity, the proposed scheme is ideally suited to industrial applications. The procedure is based on global minimization of the L2 norm of the difference between the raw strain field (C,1) and the recovered (C0) strain field. The methodology engineered in this paper extends the ideas of Oden and Brauchli (Int. J. Numer. Meth. Engng 1971; 3) and Hinton and Campbell (Int. J. Numer. Meth. Engng 1974; 8) by enriching the approximation used for the construction of the recovered derivatives (strains) with the gradients of the functions employed to enrich the approximation employed for the primal unknown (displacements). We show linear elastic fracture mechanics examples, both in simple two-dimensional settings, and for a three-dimensional structure. Numerically, we show that the effectivity index of the proposed indicator converges to unity upon mesh refinement. Consequently, the approximate error converges to the exact error, indicating that the error indicator is valid. Additionally, the numerical examples suggest a novel adaptive strategy for enriched approximations in which the dimensions of the enrichment zone are first increased, before standard h - and p -adaptivities are applied; we suggest to coin this methodology e-adaptivity. Copyright © 2008 John Wiley & Sons, Ltd. [source] Accurate eight-node hexahedral elementINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 6 2007Magnus Fredriksson Abstract Based on the assumed strain method, an eight-node hexahedral element is proposed. Consistent choice of the fundamental element stiffness guarantees convergence and fulfillment of the patch test a priori. In conjunction with a ,-projection operator, the higher order strain field becomes orthogonal to rigid body and linear displacement fields. The higher order strain field in question is carefully selected to preserve correct rank for the element stiffness matrix, also for distorted elements. Volumetric locking is also removed effectively. By considerations of the bending energy, improved accuracy is obtained even for coarse element meshes. The choice of local co-ordinate system aligned with the principal axes of inertia makes it possible to improve the performance even for distorted elements. The strain-driven format obtained is well suited for materials with non-linear stress,strain relations. Several numerical examples are presented where the excellent performance of the proposed eight-node hexahedral is verified. Copyright © 2007 John Wiley & Sons, Ltd. [source] On the numerical treatment of initial strains in biological soft tissuesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 8 2006E. Peña Abstract In this paper, different methodologies to enforce initial stresses or strains in finite strain problems are compared. Since our main interest relies on the simulation of living tissues, an orthotropic hyperelastic constitutive model has been used to describe their passive material behaviour. Different methods are presented and discussed. Firstly, the initial strain distribution is obtained after deformation from a previously assumed to be known stress-free state using an appropriate finite element approach. This approach usually involves important mesh distortions. The second method consists on imposing the initial strain field from the definition of an initial incompatible ,deformation gradient' field obtained from experimental data. This incompatible tensor field can be imposed in two ways, depending on the origin of the experimental tests. In some cases as ligaments, the experiment is carried out from the stress-free configuration, while in blood vessels the starting point is usually the load-free configuration with residual stresses. So the strain energy function would remain the same for the whole simulation or redefined from the new origin of the experiment. Some validation and realistic examples are presented to show the performance of the strategies and to quantify the errors appearing in each of them. Copyright © 2006 John Wiley & Sons, Ltd. [source] Vibration and stability control of robotic manipulator systems consisting of a thin-walled beam and a spinning tip rotorJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 10 2002Ohseop Song Vibration and stability feedback control of a robotic manipulator modeled as a cantilevered thin-walled beam carrying a spinning rotor at its tip is investigated. The control is achieved via incorporation of adaptive capabilities that are provided by a system of piezoactuators, bonded or embedded into the host structure. Based on converse piezoelectric effect, the piezoactuators produce a localized strain field in response to an applied voltage, and as a result, an adaptive change of vibrational and stability response characteristics is obtained. A feedback control law relating the piezoelectrically induced bending moments at the beam tip with the appropriately selected kinematical response quantities is used, and the beneficial effects of this control methodology upon the closed-loop eigenvibration characteristics and stability boundaries are highlighted. The cantilevered structure modeled as a thin-walled beam, and built from a composite material, encompasses non-classical features, such as anisotropy, transverse shear, and secondary warping, and in this context, a special ply-angle configuration inducing a structural coupling between flapping-lagging and transverse shear is implemented. It is also shown that the directionality property of the material of the host structure used in conjunction with piezoelectric strain actuation capability, yields a dramatic enhancement of both the vibrational and stability behavior of the considered structural system. © 2002 Wiley Periodicals, Inc. [source] Gliding dislocations in Bi2Te3 materialsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2009N. Peranio Abstract In Bi2Te3, dislocations were found with an uniquely high mobility at room temperature. The gliding dislocations were analysed and their effect on the thermoelectric properties is discussed. The glide of dislocations was induced by heating with a focused electron beam at 120 keV, external stresses were not applied. The dislocations were bowed out in the glide direction and were only pinned at the surface of the samples. Stereomicroscopy combined with image simulations yielded basal plane dislocations with a density of 109 cm,2 and Burgers vectors of type ,110,. Video sequences showing the glide of single dislocations and groups of dislocations were recorded. Isolated dislocations showed a high mobility in ±,110, direction at a velocity of 10,100 nm s,1. Dislocation dipoles were pinned and did not glide. Dislocations equidistantly arranged within the same glide plane showed a collective movement. Dislocations piled up in different glide planes were fixed and acted as barriers for gliding dislocations. The motion of dislocations was attributed to residual shear stresses of about 10 MPa, and their glide directions depended on the sign of the Burgers vector. Attractive and repulsive forces of dislocations directly visualise the forces due to the elastic strain fields of other dislocations. The relevance of phonon scattering on dislocations in Bi2Te3, particularly due to their high mobility and density, was confirmed by two inspections: (i) Dislocations decrease the lattice thermal conductivity due to phonon scattering on the elastic strain field. The phonon mean free path was estimated to about 800 µm at 3 K and agreed with published data. (ii) The dislocation resonance theory of Granato and Lücke predicts an interaction between phonons and dislocations acting as oscillating strings. The attenuation of ultrasound was estimated and was compared with published data. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Mapping full field deformation of auxetic foams using digital speckle photographyPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11 2008Fu-pen Chiang Abstract Measuring strain in foam presents a number of challanges. In the case of polymeric foam, the material is so soft that a conventional strain gage is not applicable because the rigidity of gage and its associated glue is stronger than the foam itself. Transducers such as clip gage, etc. may not be suitable either because the strain field may not be uniform within the gage length. Thus it is desirable that a non-contact and full field strain measurement technique be available. In this paper we introduce a speckle photography technique that is non-contact and can measure the full field deformation of a foam specimen. We use the natural texture of the pattern. Digitized images of the foam specimen under different loads are "compared" using a special algorithm called CASI, to yield deformation maps of the specimen. Examples of applying this technique to testing PVC foam composites are presented in the paper. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Stranski,Krastanow growth of stacked GaN quantum dots with intense photoluminescencePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003K. Hoshino Abstract Multiple-layer stacked GaN quantum dots (QDs) with intense photoluminescence (PL) have been grown by the Stranski,Krastanow growth mode in metalorganic chemical vapor deposition. Scanning transmission electron microscopy (STEM) analysis shows that the vertical aligned QDs are formed, which results from a strain field induced by buried islands. We have also investigated PL spectra at room temperature. The PL intensity increases with increasing number of the stacked layer. This indicates that the carriers can be injected into each layer of GaN quantum dots. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Spectrally-resolved nonlinear spectroscopy of in-plane anisotropy in uniaxially-strained GaN epilayersPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2005Satoru Adachi Abstract Spectrally-resolved four-wave mixing technique has revealed the internal structures of excitons in uniaxially strained gallium nitride films. Nonlinear response of four-wave mixing on the oscillator strength highlights the polarized excitons, and therefore allows us to map out the uniaxial strain field and the resultant anisotropic exchange splitting. Such a measurement gives a kind of crystalline analysis achieved in X-ray diffraction spectroscopy as well as information of the exciton fine structures including their temporal dynamics. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Tools for multiaxial validation of behavior laws chosen for modeling hyper-elasticity of rubber-like materialsPOLYMER ENGINEERING & SCIENCE, Issue 2 2002L. Chevalier We present an experimental approach to discriminate hyper-elastic models describing the mechanical behavior of rubber-like materials. An evaluation of the displacement field obtained by digital image correlation allows us to evaluate the heterogeneous strain field observed during these tests. We focus on the particular case of hyper-elastic models to simulate the behavior of some rubber-like materials. Assuming incompressibility of the material, the hyper-elastic potential is determined from tension and compression tests. A biaxial loading condition is obtained in a multiaxial testing machine and model predictions are compared with experimental results. [source] Origin of the in situ stress field in south-eastern AustraliaBASIN RESEARCH, Issue 3 2004Mike Sandiford The in situ stress field of south-eastern Australia inferred from earthquake focal mechanisms and bore-hole breakouts is unusual in that it is characterised by large obliquity between the maximum horizontal compressive stress orientation (SHmax) and the absolute plate motion azimuth. The evolution of the neotectonic strain field deduced from historical seismicity and both onshore and offshore faulting records is used to address the origin of this unusual stress field. Strain rates derived from estimates of the seismic moment release rate (up to ,10,16 s,1) are compatible with Quaternary fault,slip rates. The record of more or less continuous tectonic activity extends back to the terminal Miocene or early Pliocene (10,5 Ma). Terminal Miocene tectonic activity was characterised by regional-scale tilting and local uplift and erosion, now best preserved by unconformities in offshore basins. Plate-scale stress modelling suggests the in situ stress field reflects increased coupling of the Australian and Pacific Plate boundary in the late Miocene, associated with the formation of the Southern Alps in New Zealand. [source] Deformation Field around the Stress Induced Crack Area in Sandstone by the Digital Speckle Correlation MethodACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 3 2009Yonghong ZHAO Abstract: The deformation field around sub-cracks was calculated using the digital speckle correlation method. First, the uni-axial compression tests on sandstone samples containing a pre-fabricated fracture were made. Photomicrographs showing the characteristics of the sub-crack development were taken using a scanning electron microscope (SEM). From these photomicrographs, the real-time images showing the initiation, growth and coalescence of sub-cracks and micro-cracks in the sandstone specimens were obtained and the effects of loading level as well as grain boundaries on the development of cracks were analyzed. Second, the intensity images of the sandstone specimen surface were captured from the observations of the SEM corresponding to different loading levels. Then correlation computation was carried out for the sequential pairs of intensity images to evaluate the displacement components, as well as the strain field. The results show that the deformation varies in different areas separated by sub-cracks during rock damage processes. [source] Strain field measurements of rubber by image analysis and design criteria for laminated rubber bearings (LRB)EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 4 2004Chamindalal Sujeewa Lewangamage Abstract Although seismic isolation rubber bearings in bridges and buildings have proven to be a very effective passive method for reducing earthquake-induced forces, a detailed mechanical modeling of the rubber that is used in bearings under large strains has not been established. Therefore, a 3D model of failure behavior and the design criteria for the safety evaluation of seismic isolation bearings have not yet been developed. This paper presents: (1) correlation-based template-matching algorithms to measure large strain fields of continua; (2) a failure criterion for rubber; and (3) the design criteria for the safety evaluation of laminated algorithms, data-validation algorithms were developed and implemented to eliminate possible unrealistic displacement vectors present in the measured displacement field. The algorithms were successfully employed in the strain field measurement of LRB and rubber materials that are subjected to failure. The measured local strains for rubber material at failure were used to develop a failure criterion for rubber. The validity of the proposed criterion was evaluated by applying it to the LRB; the criterion was introduced into a 3D finite element model of LRB, compared with the experimental results of bearings failure, and verified. Finally, design criteria are proposed for LRB for the safety evaluation. Copyright © 2003 John Wiley & Sons, Ltd. [source] Study of Fatigue Damage Micromechanisms in a Duplex Stainless Steel by Complementary Analysis TechniquesADVANCED ENGINEERING MATERIALS, Issue 9 2009Ahmed El Bartali The low-cycle fatigue (LCF) damage micromechanisms are studied in a duplex stainless steel at room temperature using complementary analysis techniques. Surface damage is observed in real-time with an in-situ microscopic device during a low-cycle fatigue test. Slip systems activated in each grain in each phase are identified from SEM photographs and EBSD measurements. The surface relief appeared at the end of the test is measured with an interferometric profilometer. Displacement and strain fields on the microstructural scale are calculated using DIC technique from surface images taken during cycling. Observations were combined to analyse damage mechanisms from slip marking appearance to strain localisation and crack initiation. [source] Fatigue damage analysis in a duplex stainless steel by digital image correlation techniqueFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 2 2008A. EL BARTALI ABSTRACT Strain field measurements by digital image correlation today offer new possibilities for analysing the mechanical behaviour of materials in situ during mechanical tests. The originality of the present study is to use this technique on the micro-structural scale, in order to understand and to obtain quantitative values of the fatigue surface damage in a two-phased alloy. In this paper, low-cycle fatigue damage micromechanisms in an austenitic-ferritic stainless steel are studied. Surface damage is observed in real time, with an in situ microscopic device, during a low-cycle fatigue test performed at room temperature. Surface displacement and strain fields are calculated using digital image correlation from images taken during cycling. A detailed analysis of optical images and strain fields measured enables us to follow precisely the evolution of surface strain fields and the damage micromechanisms. Firstly, strain heterogeneities are observed in austenitic grains. Initially, the austenitic phase accommodates the cyclic plastic strain and is then followed by the ferritic phase. Microcrack initiation takes place at the ferrite/ferrite grain boundaries. Microcracks propagate to the neighbouring austenitic grains following the slip markings. Displacement and strain gradients indicate probable microcrack initiation sites. [source] The evolution of the stress,strain fields near a fatigue crack tip and plasticity-induced crack closure revisitedFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 1 2004L. G. ZHAO ABSTRACT The evolution of the stress,strain fields near a stationary crack tip under cyclic loading at selected R -ratios has been studied in a detailed elastic,plastic finite element analysis. The material behaviour was described by a full constitutive model of cyclic plasticity with both kinematic and isotropic hardening variables. Whilst the stress/strain range remains mostly constant during the cyclic loading and scales with the external load range, progressive accumulation of tensile strain occurs, particularly at high R -ratios. These results may be of significance for the characterization of crack growth, particularly near the fatigue threshold. Elastic,plastic finite element simulations of advancing fatigue cracks were carried out under plane-stress, plane-strain and generalized plane-strain conditions in a compact tension specimen. Physical contact of the crack flanks was observed in plane stress but not in the plane-strain and generalized plane-strain conditions. The lack of crack closure in plane strain was found to be independent of the material studied. Significant crack closure was observed under plane-stress conditions, where a displacement method was used to obtain the actual stress intensity variation during a loading cycle in the presence of crack closure. The results reveal no direct correlation between the attenuation in the stress intensity factor range estimated by the conventional compliance method and that determined by the displacement method. This finding seems to cast some doubts on the validity of the current practice in crack-closure measurement, and indeed on the role of plasticity-induced crack closure in the reduction of the applied stress intensity factor range. [source] Physics-based GPS data inversion to estimate three-dimensional elastic and inelastic strain fieldsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2010Akemi Noda SUMMARY The Earth's crust is macroscopically treated as a linear elastic body, but it includes a number of defects. The occurrence of inelastic deformation such as brittle fracture at the defects brings about elastic deformation in the surrounding regions. The crustal deformation observed through geodetic measurements is the sum of the inelastic deformation as source and the elastic deformation as effect. On such a basic idea, we created a theory of physics-based strain analysis with general source representation by moment tensor, and developed an inversion method to separately estimate 3-D elastic and inelastic strain fields from GPS data. In this method, first, the optimum distribution of moment density tensor is determined from observed GPS data by using Akaike's information criterion. Then, the elastic and inelastic strain fields are obtained from the optimum moment tensor distribution by theoretical computation and direct conversion with elastic compliance tensor, respectively. We applied the inversion method to GPS horizontal velocity data, and succeeded in separately estimating 3-D elastic and inelastic strain rate fields in the Niigata,Kobe transformation zone, central Japan. As for the surface patterns of total strain, the present results of 3-D physics-based inversion analysis accord with the previous results of 2-D geometric inversion analysis. From the 3-D patterns of the inverted elastic and inelastic strain fields, we revealed that the remarkable horizontal contraction in the Niigata,Kobe transformation zone is elastic and restricted near the surface, but the remarkable shear deformation is inelastic and extends over the upper crust. [source] Geomechanical simulation to predict open subsurface fracturesGEOPHYSICAL PROSPECTING, Issue 2 2009Helen Lewis ABSTRACT Geomechanical simulation of the evolution of a geological structure can play an important role in predicting open fracture development for all stages in that structure's development. In this work, three such geomechanical simulations are used to predict the evolving stress and strain fields, including dilational and compactional changes in the rock fabric in developing fault and fold systems. Their consequences for open fracture development and flow are addressed. These simulated stress and strain fields show considerable spatial and temporal heterogeneity that is consistent with deformation patterns observed in both natural examples and in laboratory-deformed analogues. But the stress and strain states that develop are neither co-axial nor do they bear a simple relationship to one another. The dilational and compactional strains, manifest as open fracturing or sealing, represent some significantly increased or significantly decreased flow rates. However, open-fracture predictions based on such geomechanical simulations are extremely difficult to validate with any degree of confidence as there is little direct evidence of sub-surface fracture distributions. In this context we also discuss possible integration of seismic anisotropy measurements, as an independent measure of open fracture alignment, to support the geomechanically derived fracture predictions. The focus of this work is on volumetric strains in fault zone evolution, though folding is also addressed. [source] Direct Evidence for Cation Non-Stoichiometry and Cottrell Atmospheres Around Dislocation Cores in Functional Oxide InterfacesADVANCED MATERIALS, Issue 22 2010Miryam Arredondo Long-range strain fields associated with dislocation cores at an oxide interface are shown to be sufficient enough to create significant variations in the chemical composition around the core (Cottrell atmospheres). Such stress-assisted diffusion of cations towards the cores is proposed to significantly impact the properties of nanoscale functional devices. The figure shows a Z-contrast image of a single dislocation core at an oxide interface. [source] Strain localization in soft rock,a typical rate-dependent solid: experimental and numerical studiesINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 11 2005A. R. Bhandari Abstract Strain localization developing inside soft rock specimens is examined through experimental observation and numerical simulation. In the experimental study, soft rock specimens are sheared at different strain rates under plane strain conditions and deformation and strain localization characteristics are analysed. Transition of localization mode from highly localized mode for higher strain rate to distributed and diffused mode of strain localization for lower strain rates was observed. In the numerical study, simulations of plane strain compression tests are carried out at different strain rates by using an overstressed-type elasto-viscoplastic model in finite element computations. The role of strain rates on setting gradients of strain fields across shear band is clarified. The probable mechanism for transition of localization mode is discussed. Copyright © 2005 John Wiley & Sons, Ltd. [source] Strain localization in sand: an overview of the experimental results obtained in Grenoble using stereophotogrammetryINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 4 2004Jacques Desrues Abstract Experimental results are presented from the extensive program of drained plane strain compression tests on sand carried out in Grenoble over the last two decades. Systematic analysis of photographs of the deforming specimen allowed for measuring deformations and determining strain fields throughout the test, that is: prior to, at, and after the onset of strain localization. The principles, details and accuracy of the procedure are described, as well as its suitability to properly depict the patterns of deformation. Findings concerning the occurrence and progression of strain localization are discussed. The issues of shear band orientation and thickness are addressed, as well as temporary and persistent complex localization patterns, and the volumetric behaviour inside a band after its formation. The influence of such variables as initial state of the sand (effective stress and relative density), specimen size and slenderness, as well as grain size, is discussed. Copyright © 2004 John Wiley & Sons, Ltd [source] Semi-analytical elastostatic analysis of unbounded two-dimensional domainsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 11 2002Andrew J. Deeks Abstract Unbounded plane stress and plane strain domains subjected to static loading undergo infinite displacements, even when the zero displacement boundary condition at infinity is enforced. However, the stress and strain fields are well behaved, and are of practical interest. This causes significant difficulty when analysis is attempted using displacement-based numerical methods, such as the finite-element method. To circumvent this difficulty problems of this nature are often changed subtly before analysis to limit the displacements to finite values. Such a process is unsatisfactory, as it distorts the solution in some way, and may lead to a stiffness matrix that is nearly singular. In this paper, the semi-analytical scaled boundary finite-element method is extended to permit the analysis of such problems without requiring any modification of the problem itself. This is possible because the governing differential equations are solved analytically in the radial direction. The displacement solutions so obtained include an infinite component, but relative motion between any two points in the unbounded domain can be computed accurately. No small arbitrary constants are introduced, no arbitrary truncation of the domain is performed, and no ill-conditioned matrices are inverted. Copyright © 2002 John Wiley & Sons, Ltd. [source] Upper and lower bounds for natural frequencies: A property of the smoothed finite element methodsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 2 2010Zhi-Qian Zhang Abstract Node-based smoothed finite element method (NS-FEM) using triangular type of elements has been found capable to produce upper bound solutions (to the exact solutions) for force driving static solid mechanics problems due to its monotonic ,soft' behavior. This paper aims to formulate an NS-FEM for lower bounds of the natural frequencies for free vibration problems. To make the NS-FEM temporally stable, an ,-FEM is devised by combining the compatible and smoothed strain fields in a partition of unity fashion controlled by ,,[0, 1], so that both the properties of stiff FEM and the monotonically soft NS-FEM models can be properly combined for a desired purpose. For temporally stabilizing NS-FEM, , is chosen small so that it acts like a ,regularization parameter' making the NS-FEM stable, but still with sufficient softness ensuring lower bounds for natural frequency solution. Our numerical studies demonstrate that (1) using a proper ,, the spurious non-zero energy modes can be removed and the NS-FEM becomes temporally stable; (2) the stabilized NS-FEM becomes a general approach for solids to obtain lower bounds to the exact natural frequencies over the whole spectrum; (3) ,-FEM can even be tuned for obtaining nearly exact natural frequencies. Copyright © 2010 John Wiley & Sons, Ltd. [source] Analysis of micro fracture in human Haversian cortical bone under transverse tension using extended physical imagingINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 8 2010É. Budyn Abstract We propose a procedure to investigate local stress intensity factors at the scale of the osteons in human Haversian cortical bone. The method combines a specific experimental setting for a three-point bending millimetric specimen and a numerical method using the eXtended Finite Element Method (X-FEM). The interface between the experimental setting and the numerical method is ensured through an imaging technique that analyses the light microscopy observations to import the geometrical heterogeneity of the Haversian microstructures, the boundary conditions and appearing crack discontinuities into the numerical model. The local mechanical elastic Young's moduli are measured by nano-indentation, and the Poisson ratios are determined by an imaging technique of the stress,strain fields. The model is able to access three scales of measurement: the macro scale of the material level (mm), the micro scale inside the Haversian material for stress,strain fields (10,100µm), and the sub-micro scale for the crack opening profiles (1,10µm ) and fracture parameters (stress intensity factors). The model is applied to several patients at different aging stages. Copyright © 2009 John Wiley & Sons, Ltd. [source] Integration of geometric design and mechanical analysis using B-spline functions on surfaceINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 14 2005Hee Yuel Roh Abstract B-spline finite element method which integrates geometric design and mechanical analysis of shell structures is presented. To link geometric design and analysis modules completely, the non-periodic cubic B-spline functions are used for the description of geometry and for the displacement interpolation function in the formulation of an isoparametric B-spline finite element. Non-periodic B-spline functions satisfy Kronecker delta properties at the boundaries of domain intervals and allow the handling of the boundary conditions in a conventional finite element formulation. In addition, in this interpolation, interior supports such as nodes can be introduced in a conventional finite element formulation. In the formulation of the mechanical analysis of shells, a general tensor-based shell element with geometrically exact surface representation is employed. In addition, assumed natural strain fields are proposed to alleviate the locking problems. Various numerical examples are provided to assess the performance of the present B-spline finite element. Copyright © 2005 John Wiley & Sons, Ltd. 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