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1.
《International Journal of Plasticity》2006,22(6):1026-1061
We analyze plane strain deformations of a representative volume element (RVE) to evaluate effective thermophysical parameters of a particulate composite comprised of two perfectly bonded heat conducting elasto-thermo-visco-plastic constituents. It is assumed that the composite is also isotropic and its response elasto-thermo-visco-plastic. Effective values of material parameters so computed are compared with those obtained from either existing micromechanics models or the rule of mixtures or both. It is found that values computed from the rule of mixtures differ at most by 10% from those obtained by using the RVE. Effective stress versus effective strain curves obtained by analyzing simple shearing and axisymmetric deformations of the RVE and of the homogenized material, and also those obtained in plane strain deformations involving loading/unloading/reloading are found to be very close to each other. Time histories of the effective plastic strain at two neighboring points, one in each constituent, are quite different. The effective stress computed by the rule of mixtures from the average effective stress in each constituent and its volume fraction is very close to that obtained from surface tractions acting on the specimen boundaries. The average effective stress in a constituent is computed from the effective plastic strain averaged over that constituent. This also holds for a composite comprised of three constituents. 相似文献
2.
In this study, effects of typical texture components observed in rolled aluminum alloy sheets on shear band formation in plane strain tension/compression and bending are systematically studied. The material response is described by a generalized Taylor-type polycrystal model, in which each grain is characterized in terms of an elastic–viscoplastic continuum slip constitutive relation. First, a simple model analysis in which the shear band is assumed to occur in a weaker thin slice of material is performed. From this simple model analysis, two important quantities regarding shear band formation are obtained: i.e. the critical strain at the onset of shear banding and the corresponding orientation of shear band. Second, the shear band development in plane strain tension/compression is analyzed by the finite element method. Predictability of the finite element analysis is compared to that of the simple model analysis. Third, shear band developments in plane strain pure bending of a sheet specimen with the typical textures are studied. Regions near the surfaces in a bent sheet specimen are approximately subjected to plane strain tension or compression. From this viewpoint, the bendability of a sheet specimen may be evaluated, using the knowledge regarding shear band formation in plane strain tension/compression. To confirm this and to encompass overall deformation of a bent sheet specimen, including shear bands, finite element analyses of plane strain pure bending are carried out, and the predicted shear band formation in bent specimens is compared to that in the tension/compression problem. Finally, the present results are compared to previous related studies, and the efficiency of the present method for materials design in future is discussed. 相似文献
3.
The stereoimaging technique is an accurate, high-resolution means of measuring the in-plane displacements resulting from the deformation of a specimen so that the corresponding components of the strain tensor can be computed independently of the stresses. The example used in this paper is a fatigue-cracked specimen of a microscopically homogeneous experimental powder-metallurgy aluminum alloy, analyzed to determine the displacement and strain fields accompanying the opening of the fatigue crack. The displacement measurements are processed by a computer program which compensates for measurement fluctuations in the displacement data by smoothing, and derives the strain magnitudes. The principal strains and the maximum shear strain are determined using Mohr's circle, and the latter strain is then used to estimate the plastic-zone size. The crack-opening mode may be inferred from the displacement map, and the state of stress (plane stress or plane strain) inferred by applying the in-plane compatibility equation. 相似文献
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An in-plane shear specimen made of dual phase steel designed for ductile fracture studies is presented and then analyzed experimentally
and numerically. In the experiment, digital image correlation (DIC) technique is utilized to measure the deformation of the
specimen. Based on the implicit nonlinear FE solver Abaqus/Standard, numerical analysis of the specimen is performed by using
plane stress and solid elements respectively. The elongation of the specimen’s gauge length and the shear strain distribution
within the shear zone are compared between the experimental and numerical results and a general good agreement is obtained.
Thereafter, based on calculated results, the stress state of the shear zone is investigated in detail. It is shown that the
shear stress is dominant within the shear zone despite of the emergence of normal stresses. The deformation is concentrated
in the shear zone, where the incipient fracture is most likely to occur. The stress triaxiality and the Lode parameter at
the fracture initiation are found to be maintained at a relatively low level, which implies that the stress state achieved
by the specimen is close to pure shear. The present study demonstrates that the proposed in-plane shear specimen is suitable
for investigation of the fracture behavior of high strength materials under shear stress states. 相似文献
6.
F. Yasmeen R. Balcaen M.A. Sutton D. Debruyne S. Rajan H.W. Schreier 《Experimental Mechanics》2018,58(7):1115-1132
In practice, out-of-plane motions usually are not avoidable during experiments. Since 2D–DIC measurements are vulnerable to parasitic deformations due to out-of-plane specimen motions, three-dimensional digital image correlation (StereoDIC or 3D–DIC) oftentimes is employed. The StereoDIC method is known to be capable of accurate deformation measurements for specimens subjected to general three-dimensional motions, including out-of-plane rotations and displacements. As a result, there has been limited study of the deformation measurements obtained when using StereoDIC to measure the displacement and strain fields for a specimen subjected only to out-of-plane rotation. To assess the accuracy of strain measurements obtained using stereovision systems and StereoDIC when a specimen undergoes appreciable out of plane rotation, rigid body out-of-plane rotation experiments are performed in the range ?400?≤?θ?≤?400 using a two-camera stereovision system. Results indicate that (a) for what would normally be considered “small angle” calibration processes, the measured normal strain in the foreshortened specimen direction due to specimen rotation increases in a non-linear manner with rotation angle, with measurement errors exceeding ±1400με and (b) for what would normally be considered “large angle” calibration processes, the magnitude of the errors in the strain are reduced to ±300με. To theoretically assess the effect of calibration parameters on the measurements, two separate analyses are performed. First, theoretical strains due to out-of-plane rigid body rotation are determined using a pinhole camera model to project a series of three-dimensional object points into the image plane using large angle calibration parameters and then re-project the corresponding sensor plane coordinates back into the plane using small angle calibration parameters. Secondly, the entire imaging process is also simulated in order to remove experimental error sources and to further validate the theory. Results from both approaches confirmed the same strain error trends as the experimental strain measurements, providing confidence that the source of the errors is the calibration process. Finally, variance based sensitivity analyses show that inaccuracy in the calibrated stereo angle parameter is the most significant factor affecting the accuracy of the measured strain. 相似文献
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Based on [1], the stress structures of the smooth region and shear lip of the specimens have been investigated in the paper.
The characteristics of the stress structure in the smooth region have been found that the variable z can separated out; the
stresses in the midsection can be obtained by the plane strain FEM results or HRR structure modified by the stress triaxiality.
The effects of load level and thickness on the stress structure can be reflected by the distribution of CTOD along the thickness
direction. The obtained expressions of the stresses are very simple and visualized. The analyses of the stress structure in
the shear lip show that the stresses can be obtained by different methods of interpolation to a certain precise degree.
A new degree parameter of the plane strain state has been put forward and studied. The parameter can reflect relatively well
the variation of the kind and thickness of the specimen as well as the load level. The fracture parameter has also been investigated
to be sure that it can be obtained by modified CTOD with the stress triaxiality. 相似文献
9.
Based on[1],the stress structures of the smooth region and shear lip of thespecimens have been investigated in the paper.The characteristics of the stress structure inthe smooth region have been found that the variable z can separated out;the stressesin the midsection can be obtained by the plane strain FEM results or HRR structuremodified by the stress triaxiality.The effects of load level and thickness on the stressstructure can be reflected by the distribution of CTOD along the thickness direction.The obtained expressions of the stresses are very simple and visualized.The analysesof the stress structure in the shear lip show that the stresses can be obtained bydifferent methods of interpolation to a certain precise degree.A new degree parameter of the plane strain state has been put forward andstudied.The parameter can reflect relatively well the variation of the kind andthickness of the specimen as well as the load level.The fracture parameter has alsobeen investigated to be sure that it can be obta 相似文献
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An abnormal stress peak was measured in the specimen response in a Kolsky tension bar experiment. Efforts in changing specimen
gage length and applying Teflon tape on the threads of both the specimen and the adapters have been conducted to address this
stress peak which was found to be pseudo. The pseudo stress peak was caused by the interfacial impact of the threads on the
specimen and the bar ends and must be removed from the intrinsic stress response of the specimen material. Higher impact speeds
result in higher amplitudes in the peak stress. The peak stress can be significantly reduced by applying Teflon tape on the
threads. At a certain strain rate, it becomes more efficient to minimize the peak stress by simultaneously using a specimen
with a shorter gage length and applying Teflon tape on the threads. 相似文献
12.
Few shear test techniques exist that cover the range of strain rates from static to dynamic. In this work, a novel specimen geometry is presented that can be used for the characterisation of the shear behaviour of sheet metals over a wide range of strain rates using traditional tensile test devices. The main objectives during the development of the shear specimen have been 1) obtaining a homogeneous stress state with low stress triaxiality in the zone of the specimen subjected to shear and 2) appropriateness for dynamic testing. Additionally, avoiding premature specimen failure due to edge effects was aimed at. Most dimensional and practical constraints arose from the dynamic test in which the specimen is loaded by mechanical waves in a split Hopkinson tensile bar device. Design of the specimen geometry is based on finite element simulations using ABAQUS/Explicit. The behaviour of the specimen is compared with the more commonly used simple shear specimen with clamped grips. Advantages of the new technique are shown. The technique is applied to Ti6Al4V sheet. During the high strain rate experiments high speed photography and digital image correlation are used to obtain the local shear strain in the specimen. Comparison of experimental and numerical results shows good correspondence. 相似文献
13.
Plastic size effects in single crystals are investi-gated by using finite strain and small strain discrete dislo-cation plasticity to analyse the response of cantilever beam specimens. Crystals with both one and two active slip sys-tems are analysed, as well as specimens with different beam aspect ratios. Over the range of specimen sizes analysed here, the bending stress versus applied tip displacement response has a strong hardening plastic component. This hardening rate increases with decreasing specimen size. The hardening rates are slightly lower when the finite strain discrete disloca-tion plasticity (DDP) formulation is employed as curving of the slip planes is accounted for in the finite strain formulation. This relaxes the back-stresses in the dislocation pile-ups and thereby reduces the hardening rate. Our calculations show that in line with the pure bending case, the bending stress in cantilever bending displays a plastic size dependence. How-ever, unlike pure bending, the bending flow strength of the larger aspect ratio cantilever beams is appreciably smaller. This is attributed to the fact that for the same applied bend-ing stress, longer beams have lower shear forces acting upon them and this results in a lower density of statistically stored dislocations. 相似文献
14.
The stress field for the three-dimensional plasticity fracture problem is formulated by reducing the formulation to a system of singular integral equations. This will be referred to as the Singular Integral Operators Method (SIOM).An application is given to the determination of the stress field for a double notched tensile specimen in the case of plane stress and plane strain. 相似文献
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The plane strain elastic-plastic state at a crack tip is determined for compact tension, bend, double edge-cracked and centre-cracked specimens using a finite element method with triangular constant-strain elements. The solutions are found to differ by 10 to 30 per cent at the ASTM-limit as regards fracture surface displacement, normal stress and plastic zone size. In order to bring the boundary layer solution for the crack problem into agreement with the solution for a specific specimen one has to modify this solution. The modification consists of an addition to the boundary tractions for the boundary layer problem of tractions corresponding to the non-singular, constant second term in a series expansion of the normal stress parallel to the crack plane. 相似文献
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《International Journal of Solids and Structures》2014,51(21-22):3752-3761
Large-scale thin-walled structures with a low weight-to-stiffness ratio provide the means for cost and energy efficiency in structural design. However, the design of such structures for crash and impact resistance requires reliable FE simulations. Large shell elements are used in those simulations. Simulations require the knowledge of the true stress–strain response of the material until fracture initiation. Because of the size effects, local material relation determined with experiments is not applicable to large shell elements. Therefore, a numerical method is outlined to determine the effect of element size on the macroscopic response of large structural shell elements until fracture initiation. Macroscopic response is determined by introducing averaging unit into the numerical model over which volume averaged equivalent stress and plastic strain are evaluated. Three different stress states are considered in this investigation: uniaxial, plane strain and equi-biaxial tension. The results demonstrate that fracture strain is highly sensitive to size effects in uniaxial tension whereas in plane strain or equi-biaxial tension size effects are much weaker. In uniaxial and plane strain tension the fracture strain for large shell elements approaches the Swift diffuse necking condition. 相似文献
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Split Hopkinson pressure bar experiments on soils are often carried out using a rigid steel confining ring to provide plane strain conditions, and measurements of the circumferential strain in the ring can be used to infer the radial stress on the surface of the specimen. Previous experiments have shown evidence of irregular electromagnetic interference in measurements of radial stress, which obscures the signals and impedes analysis. The development of robust constitutive models for soils in blast and impact events relies on the accurate characterisation of this behaviour, and so it is necessary to isolate and remove the source of interference. This paper uses an induction coil to identify the source of the anomalous signals, which are found to be due to induced currents in the gauge lead wires from the movement of magnetised pressure bars (martensitic stainless steel, 440C). Comparative experiments on sand and rubber specimens are used to show that the deforming soil specimen does not make a significant contribution to this activity, and recommendations are made on reducing electromagnetic interference to provide reliable radial stress measurements. 相似文献