Showing papers in "Journal of Engineering Materials and Technology-transactions of The Asme in 2002"
TL;DR: In this paper, the authors examined the relationship between elastic strain energy, inelastic strain energy and cohesive energy, the latter encompassing the work of fracture and other energy consuming mechanisms within the fracture process zone, and showed that the plastic energy in the material surrounding the crack is not accounted in the cohesive energy.
Abstract: Cohesive Zone Models (CZMs) are being increasingly used to simulate fracture and fragmentation processes in metallic, polymeric, and ceramic materials and their composites. Instead of an infinitely sharp crack envisaged in fracture mechanics, CZM presupposes the presence of a fracture process zone where the energy is transferred from external work both in the forward and the wake regions of the propagating crack. In this paper, we examine horn the external work flows as recoverable elastic strain energy, inelastic strain energy, and cohesive energy, the latter encompassing the work of fracture and other energy consuming mechanisms within the fracture process zone. It is clearly shown that the plastic energy in the material surrounding the crack is not accounted in the cohesive energy. Thus cohesive zone energy encompasses all the inelastic energy e.g., energy required for grainbridging, cavitation, internal sliding, surface energy but excludes any form of inelastic strain energy in the bounding material.
185 citations
Metz1
TL;DR: Estrin et al. as mentioned in this paper proposed a cellular dislocation-based model for all hardening stages in large strain deformation and implemented it into the viscoplastic self-consistent polycrystal model to predict hardening curves corresponding to different proportional loading paths.
Abstract: A recent strain hardening model for late deformation stages (Estrin, Y., Toth, L.S., Molinari, A., and Brechet, Y., Acta Materialia, 1998, A dislocation-based model for all hardening stages in large strain deformation, Vol. 46, pp. 5509-5522) was generalized for the 3D case and for arbitrary strain paths. The model is based on a cellular dislocation arrangement in which a single- phase material is considered as a composite of a hard skeleton of cell walls and soft cell interiors. An important point in the approach is the evolution of the volume fraction of the cell walls which decreases with the deformation and gives rise to a plateau-like behavior (Stage IV) followed by a drop-off (Stage V) of the strain hardening rate observed at large strains. The hardening model was implemented into the viscoplastic self-consistent polycrystal model to predict hardening curves corresponding to different proportional loading paths. The calculated curves were evaluated to elucidate the path dependence of hardening.
180 citations
TL;DR: In this article, a three-dimensional residual stress mapping of an aluminum 2024-T3 arcan specimen, butt-welded by the friction stir technique, was performed by neutron diffraction results indicate that the residual stress distribution profiles across the weld region are asymmetric with respect to the weld centerline.
Abstract: Three-dimensional residual stress mapping of an aluminum 2024-T3 arcan specimen, butt-welded by the friction stir technique, was performed by neutron diffraction Results indicate that the residual stress distribution profiles across the weld region are asymmetric with respect to the weld centerline, with the largest gradients in the measured residual stress components occurring on the advancing side of the weld, with the longitudinal stress, σ L , oriented along the weld line, as the largest stress Within the region inside the shoulder diameter, the through-thickness stress, σ Z , is entirely compressive, with large gradients occurring along the transverse direction just beyond the shoulder region In addition, results indicate a significant reduction in the observed residual stresses for a transverse section that was somewhat closer to the free edge of an Arcan specimen Microstructural studies indicate that the grain size in the weld nugget, is approximately 64 microns, with the maximum extent of the recrystallized zone extending to 6 mm on each side of the weld centerline Outside of this region, the plate material has an unrecrystallized grain structure that consists of pancake shaped grains ranging up to several mm in size in two dimensions and 10 microns in through-thickness dimension
144 citations
TL;DR: In this article, the authors present results from a molecular dynamics simulation study to characterize the motion and velocity of edge dislocations at high strain rate and the interaction and fate of the moving edge dislocation with slacking fault tetrahedra in Cu using an EAM interatomic potential.
Abstract: In copper and other face centered cubic metals, high-energy particle irradiation produces hardening and shear localization. Post-irradiation microstructural examination in Cu reveals that irradiation has produced a high number density of nanometer sized stacking fault tetrahedra. The resultant irradiation hardening and shear localization is commonly attributed to the interaction between stacking fault tetrahedra and mobile dislocations, although the mechanism of this interaction is unknown. In this work, we present results from a molecular dynamics simulation study to characterize the motion and velocity of edge dislocations at high strain rate and the interaction and fate of the moving edge dislocation with slacking fault tetrahedra in Cu using an EAM interatomic potential. The results show that a perfect SFT acts as a hard obstacle for dislocation motion and although the SFT is sheared by the dislocation passage, it remains largely intact. How-ever, our simulations show that an overlapping, truncated SFT is absorbed by the passage of an edge dislocation, resulting in dislocation climb and the formation of a pair of less mobile super-jogs on the dislocation.
113 citations
TL;DR: In this article, the authors developed an indentation model based on the theory of mechanism-based strain gradient plasticity to study the effect of the indenter tip radius on indentation hardness.
Abstract: The micro-indentation experiments have shown that the indentation hardness depends not only on the indentation depth hut also on the indenter tip radius. In fact, the indentation hardness displays opposite dependence on the indentation depth h for a sharp, conical indenter and for a spherical indenter, decreasing and increasing, respectively, with increasing h. We have developed an indentation model based on the theory of mechanism-based strain gradient plasticity to study the effect of indenter tip radius. The same indentation model captures this opposite depth dependence of indentation hardness, and shows the opposite depth dependence resulting from the different distributions of strain and strain gradient underneath a conical indenter and a spherical indenter. We have also used the finite element method to study the indentation hardness for a spherical indenter as well as for a conical indenter with a spherical tip. It is established that the effect of indenter tip radius disappears once the contact radius exceeds one half of the indenter tip radius.
107 citations
TL;DR: Cavitation shotless peening as discussed by the authors uses a submerged high speed water jet with cavitation to modify surfaces in the same way as shot peening, where no solid body collisions occur in this peening process.
Abstract: Cavitation impact, which normally produces severe damage in hydraulic machinery, can be used to modify surfaces in the same way as shot peening. Cavitation impact enables the surface of a material to be peened without the use of shot, thus it is called cavitation shotless peening. As there are no solid body collisions occurring in this peening process. the roughness of the peened surface should be less than that produced by shot peening. This characteristic makes it suitable for peening soft metals. In order to demonstrate the improvement of the fatigue strength of aluminum alloy be this process, specimens were subjected to the process, and then tested in a rotating bending fatigue test. Cavitation impacts were produced and controlled by using a submerged high speed water jet with cavitation, i.e., a cavitating jet. It was revealed that the fatigue strength of an aluminum alloy specimen treated by this peening process was 50% stronger than that of a specimen without peening.
105 citations
TL;DR: In this article, a large experimental database, made of tension-internal pressure tests and biaxial compressive tests, was used to study the behavior of a Cu-Al-Be Shape Memory Alloy (SMA) under proportional and nonproportional loadings.
Abstract: This paper is concerned with the mechanical behavior of a Cu-Al-Be Shape Memory Alloy (SMA). A large experimental database, made of tension-internal pressure tests and biaxial compressive tests, is reported. Particular attention is paid to the behavior of the material under multiaxial proportional and nonproportional loadings. Moreover, these two types of complementary tests allow for the determination, on the one hand, of the shape of the initial surface of transformation onset and, on the other hand, of the initial direction of the transformation strain rate. A generalized macroscopic J 2 -J 3 criterion to describe the transformation onset is proposed and identified.
95 citations
TL;DR: In this article, the authors examined existing multiaxial fatigue models to determine their suitability at estimating fatigue damage in Ti-6Al-4V under complex, multi-xial loading with an emphasis on long-life conditions.
Abstract: Many critical engineering components are routinely subjected to cyclic multiaxial stress states, which may include non-proportional loading and multidimensional mean stresses. Existing multiaxial fatigue models are examined to determine their suitability at estimating fatigue damage in Ti-6Al-4V under complex, multiaxial loading, with an emphasis on long-life conditions. Both proportional and non-proportional strain-controlled tension/ torsion experiments were conducted on solid specimens. Several multiaxial fatigue damage parameters are evaluated based on their ability to correlate the biaxial fatigue data and uniaxial fatigue data with tensile mean stresses (R>-1) to a fully-reversed (R=-1) uniaxial baseline. Both equivalent stress-based models and critical plane approaches are evaluated. Only one equivalent stress model and two critical plane models showed promise for the range of loadings and material considered.
82 citations
TL;DR: In this article, a framework coupling continuum elasto-viscoplasticity with three-dimensional discrete dislocation dynamics is presented, where the elastic response is governed by the classical Hooke's law and the viscoplastic behavior is determined by the motion of curved dislocations in a 3D space.
Abstract: We present a framework coupling continuum elasto-viscoplasticity with three-dimensional discrete dislocation dynamics. In this approach, the elastic response is governed by the classical Hooke 's law and the viscoplastic behavior is determined by the motion of curved dislocations in a three-dimensional space. The resulting hybrid continuum-discrete framework is formulated into a standard finite element model where the dislocation-induced stress is homogenized over each element with a similar treatment for the dislocation-induced plastic strain, The model can be used to investigate a wide range of small scale plasticity phenomena, including microshear bands, adiabatic shear bands, stability and formation of dislocation cells, thin films and multiplayer structures. Here we present results pertaining to the formation of deformation bands and surface distortions under dynamic loading conditions and show the capability of the model in analyzing complicated deformation-induced patterns.
81 citations
TL;DR: In this article, the authors present experimental results on the instrumented Vickers micro-indentation and compression of solutionized Ni-rich NiTi single crystals at room temperature.
Abstract: We present experimental results on the instrumented Vickers micro-indentation and compression of solutionized Ni-rich NiTi single crystals. The tests are conducted at room temperature where the solutionized Ti-50.9 at percent Ni material is 18 degrees above A f and the solutionized Ti-51.5 at percent Ni material is more than 100 degrees above A f Aside from elastic deformation, it is discovered that dislocation motion and a reversible stress-induced martensitic transformation influence the micro-indentation response of Ti-50.9 at percent Ni, while the micro-indentation of Ti-51.5 at percent Ni only induces irreversible dislocation motion. The effect of the surface normal orientation on material hardness was negligible in the Ti-51.5 at percent Ni and followed trends anticipated by the activation of favorable slip systems in the Ti-50.9 at percent Ni. Compression tests on the identical Ti-50.9 at percent Ni samples revealed deformation by coupled stress-induced martensite and plastic flow, depending on the crystallographic orientation. The trends in hardness with surface normal orientation were not commensurate with the orientation dependence of the uniaxial compressive transformation or yield strength. The ramifications of the results in terms of comparing micro-indentation and macrocompression and the interactions between plasticity and the stress-induced martensitic transformation are discussed.
74 citations
TL;DR: In this article, a three-dimensional finite element analysis for the cold expansion process in two aluminum alloys, 2024-T351 and 7050-T7451, is developed for the hole expansion, elastic recovery, and finish reaming.
Abstract: A three-dimensional finite element analysis is developed for the cold expansion process in two aluminum alloys, 2024-T351 and 7050-T7451. The entire cold working process including hole expansion, elastic recovery, and finish reaming is simulated. Both isotropic hardening and kinematic hardening models are considered in the numerical calculations. The results suggest that a three-dimensional nature exists in the residual stress fields surrounding the hole. There are significant differences in residual stresses at different sections through the thickness. However, residual stress at the surface is shown to remain the same for the different plastic hardening models after the hole has recovered and finish reaming has been performed. The reaming of the material around the hole has slight effect on the maximum value and distribution of residual stresses. A comparison has been drawn between the FEA of average through thickness strain and a previous experimental investigation of strain that utilized neutron diffraction and modified Sachs boring on a 7050 aluminum specimen containing a cold expanded hole, The different methods show very good agreement in the magnitude of strain as well as the general trend. The conclusions obtained here are beneficial to the understanding of the phenomenon of fatigue crack initiation and growth at the perimeter of cold worked holes.
TL;DR: Kim et al. as discussed by the authors developed an analytical model for drilling burr formation based on the principle of energy conservation and metal cutting theory, and the results showed good agreement with the model.
Abstract: Author(s): Kim, Jinsoo; Dornfeld, David | Abstract: An analytical model for drilling burr formation was developed. The model holds for ductile materials that do not show catastrophic fracture during the plastic deformation of workpiece material for burr formation. The proposed burr formation mechanism was based on the observation of behavior of workpiece materials during drilling of low alloy steel. The model was based on the principle of energy conservation and metal cutting theory. Experimental validation was done, and the results showed good agreement with the model. Based on the model, the effects of several important parameters on burr formation was investigated.
TL;DR: In this paper, the effects of shot-peening on the fretting fatigue behavior of titanium alloy, Ti-6Al-4V, were investigated using X-ray diffraction analysis, which measured a maximum compressive stress of 800 MPa at the surface, which reduced to zero at a depth of 188mm.
Abstract: The effects of shot-peening on the fretting fatigue behavior of titanium alloy, Ti-6Al-4V were investigated. Specimens were shot-peened as per AMS 2432 standard. X-ray diffraction analysis measured a maximum compressive stress of 800 MPa at the specimen surface, which reduced to zero at a depth of 188mm. The compensatory residual tensile stress in the specimen was estimated using a curve fitting technique, the maximum value of which was found to be 260 MPa at a depth of 255mm. Fretting fatigue tests were conducted at room temperature at a cyclic frequency of 200 Hz. Scanning electron microscopy of the shot-peened fretting fatigue specimens showed that the crack initiated at a point below the contact surface, the depth of which was in the range of 200 ‐300 mm. Finite element analysis of the fretting fatigue specimens was also conducted. Fatigue life diagrams were established for the fretting fatigue specimens with and without shotpeening, and were compared to those under the plain fatigue condition, i.e. without fretting. Shot-peening improved the fretting fatigue life of Ti-6Al-4V; furthermore, it moved the crack initiation site from the fretting contact region to a region inside the specimen. Moreover, stress analysis showed that the fatigue failure of shot-peened specimens was caused by the compensatory tensile residual stress.@DOI: 10.1115/1.1448323#
TL;DR: In this article, the authors give an update of recent developments of gradient plasticity as this was advanced by Aifantis and co-workers in the early eighties to address dislocation patterning and chear band problems, and elaborate on two specific issues of current interest: size effects and plastic heterogeneity.
Abstract: The purpose of this two-purt article, is first to give an update of recent developments of gradient plasticity as this was advanced by Aifantis and co-workers in the early eighties to address dislocation patterning and chear band problems, and then to elaborate on two specific issues of current interest: size effects and plastic heterogeneity. In Part I, a brief review of gradient dislocation dynamics as providing a direct motivation for the simplest form of gradient plasticity is given. Then, a more general phenomenological formulation of gradient plasticity is given and used to interpret size effects. In Part H, wavelet analysis is used as a potential tool to describe plastic heterogeneity at very fine scales for which experimental results are not available, as well as for providing another means to interpret size effects through the derivation of scale-dependent constitutive equations.
TL;DR: In this article, the deformation failures of aluminum honeycomb materials in dynamic compression, static shear and static tearing are characterized, including complete curves of compression and shear stress-strain relations in the three principal directions.
Abstract: Large deformation failures of aluminum honeycomb materials in dynamic compression, static shear and static tearing are characterized in this comprehensive experimental study. Two low density honeycomb materials that make up the Offset Deformable Barrier (ODB) used in vehicle crash test were tested. Material characterization methods, including one for studying material tearing, have been developed. The honeycomb material data under large deformation, including complete curves of compression and shear stress-strain relations in the three principal directions, are presented and analysed. Honeycomb material tearing strength, defined as tearing force per unit tearing length, is introduced. Strain-rate dependence of honeycomb materials under dynamic loading is investigated. Local failure mechanisms of honeycombs in compression, shear, and indentation punch tests and their relations with the hulk properties of the materials are studied in detail. The results of this research may be used to improve the material fidelity of finite element simulations of the ODB.
TL;DR: In this paper, a phenomenological, polycrystalline version of a nonlocal crystal plasticity model is formulated, where the presence of geometrically necessary dislocations (GNDs) at, or near, grain boundaries is modeled as elastic lattice curvature through a curl of the elastic part of the deformation gradient.
Abstract: A phenomenological, polycrystalline version of a nonlocal crystal plasticity model is formulated. The presence of geometrically necessary dislocations (GNDs) at, or near, grain boundaries is modeled as elastic lattice curvature through a curl of the elastic part of the deformation gradient. This spatial gradient of an internal state variable introduces a length scale, turning the local form of the model, an ordinary differential equation (ODE), into a nonlocal form, a partial differential equation (PDE) requiring boundary conditions. Small lattice elastic stretching results from the presence of dislocations and from macroscopic external loading. Finite deformation results from large plastic slip and large rotations. The thermodynamics and constitutive assumptions are written in the intermediate configuration in order to place the plasticity equations in the proper configuration for finite deformation analysis.
TL;DR: In this paper, an ellipsoid with uniform nonlinear properties is embedded in an infinite homogeneous matrix and an approximate solution is obtained by approaching the matrix behavior with an affine response.
Abstract: Averaging models are proposed for viscoplastic and elastic-viscoplastic heterogeneous materials. The case of rigid viscoplastic materials is first discussed. Large deformations are considered. A first class of models is based on different linearizations of the nonlinear local response. A second class of models is obtained from approximate solutions of the nonlinear Eshelby problem. In this problem, an ellipsoid with uniform nonlinear properties is embedded in an infinite homogeneous matrix. An approximate solution is obtained by approaching the matrix behavior with an affine response. Using this solution of the nonlinear Eshelby problem, the average strain rate is calculated in each phase of the composite material, each phase being represented by an ellipsoid embedded in an infinite reference medium. By adequate choices of the reference medium, different averaging models are obtained (self-consistent scheme, nonlinear Mori Tanaka model…). Finally, elasticity is included in the modelling, but with a restriction to small deformations.
TL;DR: In this paper, the authors present experimental measurements of the through-thickness distribution of residual stress in a ceramic-metallic functionally graded material (FGM) and further present an error analysis and optimization of the residual stress measurement technique.
Abstract: This paper presents experimental measurements of the through-thickness distribution of residual stress in a ceramic-metallic functionally graded material (FGM). It further presents an error analysis and optimization of the residual stress measurement technique, Measurements are made in a seven-layered plate with a base of commercially pure titanium and successive layers containing an increasing proportion of titanium-boride, reaching 85% titanium-boride in the final layer. The compliance method is employed to determine residual stress, where a slot is introduced using wire electric-discharge machining and strain release is measured as a function of increasing slot depth. Strain release measurements are used with a back-calculation scheme, based on finite element simulation, to provide residual stresses in the FGM. The analysis is complicated by the variation of material properties in the FGM, but tractable due to the flexibility of the finite element method. The Monte Carlo approach is used for error analysis and a method is described for optimization of the functional form assumed for the residual stresses. The magnitude and variation of the resulting residual stress distributions and several aspects of the error analyses are discussed.
TL;DR: In this paper, a multiple slip dislocation-density based crystalline formulation has been coupled to a kinematically based scheme that accounts for grain-boundary (GB) interfacial interactions with dislocation densities.
Abstract: A multiple slip dislocation-density based crystalline formulation has been coupled to a kinematically based scheme that accounts for grain-boundary (GB) interfacial interactions with dislocation densities. Specialized finite-element formulations have been used to gain detailed understanding of the initiation and evolution of large inelastic deformation modes due to mechanisms that can result from dislocation-density pile-ups at GB interfaces, partial and total dislocation-density transmission from one grain to neighboring grains, and dislocation density absorption within GBs. These formulations provide a methodology that can be used to understand how interactions at the GB interface scale affect overall macroscopic behavior at different inelastic stages of deformation for polycrystalline aggregates due to the interrelated effects of GB orientations, the evolution of mobile and immobile dislocation-densities, slip system orientation, strain hardening, geometrical softening, geometric slip compatibility, and localized plastic strains. Criteria have been developed to identify and monitor the initiation and evolution of multiple regions where dislocation pile-ups at GBs, or partial and total dislocation density transmission through the GB, or absorption within the GB can occur. It is shown that the accurate prediction of these mechanisms is essential to understanding how interactions at GB interfaces affect and control overall material behavior.
TL;DR: In this paper, a semi-analytical/numerical approach is proposed to enforce a zero traction condition at select collocation points on a surface, where the image segment, with proper selection of its Burgers vector components, annuls the undesired shear stresses on the surface.
Abstract: Recent advances in 3-D dislocation dynamics include the proper treatment of free surfaces in the simulations. Dislocation interaction and slip is treated as a boundary-value problem for which a zero-traction condition is enforced at the external surfaces of the simulation box. Here, a new rigorous method is presented to handle such a treatment. The method is semi-analytical/numerical in nature in which we enforce a zero traction condition at select collocation points on a surface. The accuracy can be improved by increasing the number of collocation points. In this method, the image stress-field of a subsurface dislocation segment near a free surface is obtained by an image segment and by a distribution of prismatic rectangular dislocation loops padding the surface. The loop centers are chosen to be the collocation points of the problem. The image segment, with proper selection of its Burgers vector components, annuls the undesired shear stresses on the surface. The distributed loops annul the undesired normal stress component at the collocation points, and in the process create no undesirable shear stresses. The method derives from crack theory and falls under generalized image stress analysis whereby a distribution of dislocation geometries or entities (in this case closed rectangular loops), and not just simple mirror images, are used to satisfy the problem's boundary conditions (BCs). Such BCs can, in a very general treatment, concern either stress traction or displacements.
TL;DR: In this paper, the deformation and recrystallization textures of 99.99% pure copper sheets were simulated using the rate sensitive relaxed constraints model and the evolution of the texture was discussed based on the strain energy release maximization model.
Abstract: A study has been made of the deformation and recrystallization textures of 99.99% pure copper sheets which were cross rolled by 82 and 96% reduction in thickness and recrystallized in a salt bath at 450°C for 1h. The deformation texture was approximated by the {011} orientation as the major component and {001} as a minor component. These deformation texture components were well simulated using the rate sensitive relaxed constraints model. The {001} orientation was calculated to be metastable while the {011} orientation was located in the middle of the rotation path between the stable orientations in two cross rolling directions. The recrystallization texture in the center layer of the 96% cross-rolled copper sheet was approximated by {86 50 9} for each rolling direction. The evolution of the recrystallization texture was discussed based on the strain energy release maximization model.
TL;DR: In this article, two bending training methods have been applied on NiTi wires, one based on the martensite deformation and the other based on thermal cycling under constant bending curvature.
Abstract: The two-way shape memory effect (TWSME), has been studied in a near-equiatomic NiTi commercial alloy. Two bending training methods have been applied on NiTi wires. One is based on the martensite deformation and the other on thermal cycling under constant bending curvature. The efficiency of each method has been evaluated with better results of TWSME in the martensite deformation method. Finite element simulation has been performed on wires, in the pure bending mode, in order to calculate the maximum tensile strain in the transversal section of the wire. These simulations have allowed us to compare our results with the TWSME data obtained in prior studies under the tensile mode.
TL;DR: In this article, simple shear and torsion of single crystal copper were analyzed by employing experiments, molecular dynamics simulations, and finite element simulations in order to focus on the kinematic responses and the apparent yield strengths at different length scales of the specimens.
Abstract: We analyze simple shear and torsion of single crystal copper by employing experiments, molecular dynamics simulations, and finite element simulations in order to focus on the kinematic responses and the apparent yield strengths at different length scales of the specimens. In order to compare torsion with simple shear, the specimens were designed to be of similar size. To accomplish this, the ratio of the cylinder circumference to the axial gage length in torsion equaled the ratio of the length to height of the simple shear specimens (0.43). With the [110] crystallographic direction parallel to the rotational axis of the specimen, we observed a deformation wave of material that oscillated around the specimen in torsion and through the length of the specimen in simple shear. In torsion, the ratio of the wave amplitude divided by cylinder circumference ranged from 0.02 ‐0.07 for the three different methods of analysis: experiments, molecular dynamics simulations, and finite element simulations. In simple shear, the ratio of the deformation wave amplitude divided by the specimen length and the corresponding values predicted by the molecular dynamics and finite element simulations (simple shear experiments were not performed) ranged from 0.23‐0.26. Although each different analysis method gave similar results for each type boundary condition, the simple shear case gave approximately five times more amplitude than torsion. We attributed this observation to the plastic spin behaving differently as the simple shear case constrained the dislocation activity to planar double slip, but the torsion specimen experienced quadruple slip. The finite element simulations showed a clear relation with the plastic spin and the oscillation of the material wave. As for the yield stress in simple shear, a size scale dependence was found regarding two different size atomistic simulations for copper (332 atoms and 23628 atoms). We extrapolated the atomistic yield stresses to the order of a centimeter, and these comparisons were close to experimental data in the literature and the present study. @DOI: 10.1115/1.1480407#
TL;DR: In this paper, a method for determination of minimum sample size required to estimate the fatigue life has been presented, which is based on the analysis of the variance of error which arises due to scattered nature of fatigue life data.
Abstract: A method for determination of minimum sample size required to estimate the fatigue life has been presented. No functional relationship between stress and fatigue life other than log normal and Weibull distribution function of fatigue life has been assumed. The method is based on the analysis of the variance of error which arises due to scattered nature of the fatigue life data. An example of the application of the presented method is also given.
TL;DR: This paper introduces nonlinear kinematic constitutive equations consistent with ratchetting modeling into the distortional model of subsequent yield surfaces proposed by Kurtyka, T., and Zyczkowski, M.
Abstract: Many theoretical studies have been made to describe multiaxial ratchetting and most of them have been concentrated on the location of the yield domain, not on its shape. In this paper; we introduce nonlinear kinematic constitutive equations consistent with ratchetting modeling into the distortional model of subsequent yield surfaces proposed by Kurtyka, T., and Zyczkowski, M. We use an efficient polycrystalline model to simulate complex tests including yield surface detections in order to get some reference predictions to use in the development of the constitutive laws introduced into the distoritional model. The distortional model is thus qualitatively identified with the polycrystalline model and then quantitatively identified with the experimental results on a type 316L stainless steel. It gives promising results.
TL;DR: In this paper, finite element analyses were conducted of hierarchical particulate composites with high volume fractions of particles of irregular shape, and the results were close to the Hashin-Shtrikman lower formula in a stiffness versus concentration plot and in stiffness loss map.
Abstract: Concentrated suspensions of inclusions occur in asphalt and dental composite resins. Concentrated suspensions are also of use in achieving a combination of high stiffness and loss (the product E tan δ), desirable in damping layer and structural damping applications. For realizable particulate microstructures, analytical solutions for monodisperse inclusion morphologies such as spherical, random fibrous and platelet, are valid only in the case of a dilute concentration of inclusions. Finite element analyses were conducted of hierarchical particulate composites with high volume fractions of particles of irregular shape. For particle volume concentration 40 percent or less, the results are close to the Hashin-Shtrikman lower formula in a stiffness versus concentration plot and in a stiffness loss map. For larger concentration, stiffness is higher and E tan δ is lower. The irregular particle shape therefore enhances stiffness at a given concentration, and reduces damping layer performance.
TL;DR: In this article, an intermediate modeling of polycrystalline plasticity is proposed for rigid viscoplatic large deformations, based on the use of a bicrystal as the elementary local element representing the polycrystal.
Abstract: In this paper, intermediate modeling of polycrystalline plasticity is proposed for rigid viscoplatic large deformations. This approach is based on the use of a bicrystal as the elementary local element representing the polycrystal. The local homogenization is obtained by considering the bicrystal volume-averaging and the jump conditions at the assumed planar interface between the two crystals. Two interaction laws based on Taylor and Sachs type assumptions are proposed. These bicrystal-based averaging schemes are different from the classical Taylor and Sachs models since they allow for stresses and strains to vary from one single crystal to the other, We simulate uniaxial tension and compression as well as plane strain compression tests. Results in terms of stress-strain curves are shown in comparison to those of the pure Taylor and Sachs models. We also show results for texture evolution and discuss their comparison with the experimental measurements.
TL;DR: In this paper, a three-dimensional model was established to determine the calibration coefficients for integral hole-drilling, and the relationship between calibration coefficients and plate thickness was investigated over a wide range of plate thickness.
Abstract: One of the important factors affecting the accuracy of stress values obtained from holedrilling method is the calibration coefficient. A three-dimensional model was established to determine the calibration coefficients for integral method. The constraint conditions and loading conditions during hole-drilling can be simulated more realistically with this method. With this new model, coefficients ā i,j and b i,j could be determined within one computation procedure. The relationship between calibration coefficients and plate thickness was investigated over a wide range of plate thickness. It has been found that the calibration coefficients determined in this work may vary with thickness of plates and the thickness range for thin plates was thus well defined. The calibration coefficients can thus be extended to measure the residual stresses of either thin or thick plates. Comparison of calibration coefficients with those determined by other studies was also conducted.
TL;DR: In this paper, a stochastic dislocation dynamics (SDD) model is developed to investigate dislocation elide through dispersal obstacles, and the model accounts for the dynamics of the flight process between successive meta-stable dislocations under various dray mechanism using discrete dislocations dynamics.
Abstract: A stochastic dislocation dynamics (SDD) model is developed to investigate dislocation elide through dispersal obstacles. The model accounts for: 1) the dynamics of the flight process between successive meta-stable dislocations under various dray mechanism using discrete dislocation dynamics, and 2) thermal activation processes for meta-stable pinned dislocations using a stochastic force. The integration of the two processes allows one to examine the transient regime of dislocation motion between obstacle-controlled motion and drag-controlled motion. Result pertaining to the stress-strain rate behavior in copper are obtained. The stress and temperature dependence of the average dislocation velocity show obstacle-controlled region below the critical resolved shear stress (CRSS) and drag controlled region above the CRSS, which is in good qualitative agreement with experimental data. In the transient region right below the CRSS, negative temperature sensitivity is observed due to the competition between the drag effects in dislocation flight process and thermal activation process.
TL;DR: In this article, the in situ shear response of the matrix in polymer matrix composites (PMC) has been studied and a plot of tangent shear modulus vs shear strain was derived using the Halpin-Tsai equations.
Abstract: The in situ shear response of the matrix in polymer matrix composites (PMC) has been studied. Torsion tests were performed on solid cylinders of unidirectional glass fiber reinforced/vinylester and unidirectional carbon fiber reinforced/vinylester composites. The composite specimens were subjected to a uniform rate of twist. From the composite stress-strain curve, a plot of tangent shear modulus vs shear strain was derived. Then, using the Halpin-Tsai equations, the in situ matrix shear modulus was determined. The in situ matrix properties obtained from glass/vinylester and carbon/vinylester composites were found to be different. In addition, the properties of the in situ matrix were found to be a function of fiber volume fraction and the elastic properties of the reinforcing fiber. The behavior of the insitu matrix as a function of the fiber volume fraction was explained by using a three cylinder interphase model The validity of the interphase model in predicting the composite shear modulus was studied by comparison of results against a conventional 2 cylinder model.