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Frederic Barlat - One of the best experts on this subject based on the ideXlab platform.
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calibration of a Strain Path change model for a dual phase steel
International Journal of Mechanical Sciences, 2021Co-Authors: Diane Herault, Sandrine Thuillier, Shinyeong Lee, Pierreyves Manach, Frederic BarlatAbstract:Abstract Dual phase steels are largely used to form automotive structural parts by deep drawing involving complex loading Paths, which influence the material mechanical behavior and formability, as well as subsequent service life. The aim of this paper is to investigate the calibration of a Strain Path change model from an experimental database involving simple shear tests. The enhanced Homogeneous Anisotropic Hardening (e-HAH) is an advanced constitutive model that can take account of the Strain Path change influence on the material behavior by using a stress-based indicator. The performance of such a model depends highly on the material parameter identification and the experimental database. The mechanical behavior of a dual phase steel DP600 is first characterized under different linear Strain Paths, uniaxial and biaxial tension and simple shear, in order to quantify the initial anisotropy. Then, the influence of Strain Path changes on the material behavior is investigated during sequences involving simple shear, uniaxial tension and compression. Finally, the parameters of e-HAH model are identified and the influence of the experimental database on the optimised parameters is highlighted with the use of different Strain Paths and different Strain ranges.
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a crystal plasticity model for describing the anisotropic hardening behavior of steel sheets during Strain Path changes
International Journal of Plasticity, 2018Co-Authors: Hwigeon Kim, Frederic Barlat, Chong Soo Lee, Yongmoon Lee, Shakil Bin Zaman, Youngung JeongAbstract:Abstract In the present study, a viscoplastic self-consistent crystal plasticity model (VPSC-RGBV), which accounts for various microstructural features, including the accumulation and annihilation of dislocations due to slip activity and latent hardening originated from interactions between gliding dislocations on different slip planes, is described. The simulation results of the VPSC-RGBV model are compared with those of a macro-mechanical distortional plasticity model, the so-called homogeneous anisotropic hardening (HAH), and experimental data pertaining to metals undergoing complex loading histories. The differences between the simulated and experimental results under non-proportional loading, including 1) the stress-Strain curve, 2) instantaneous r-value after Strain-Path change, and 3) yield surface evolution, are discussed. Finally, potential improvements are suggested for VPSC-RGBV model.
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mechanical behavior of low carbon steel subjected to Strain Path changes experiments and modeling
Acta Materialia, 2016Co-Authors: Wei Wen, Gabriela Vincze, M. Borodachenkova, Frederic Barlat, E.f. Rauch, C.n. Tome, José GrácioAbstract:The mechanical response of a low carbon steel under complex Strain Path changes is analyzed here in terms of dislocation storage and annihilation. The mechanical tests performed are cyclic shear and tensile loading followed by shear at different angles with respect to the tensile axis. The material behavior is captured by a dislocation-based hardening model, which is embedded in the Visco-Plastic Self-Consistent (VPSC) polycrystal framework taking into account the accumulation and annihilation of dislocations, as well as back-stress effects. A new and more sophisticated formulation of dislocation reversibility is proposed. The simulated flow stress responses are in good agreement with the experimental data. The effects of the dislocation-related mechanisms on the hardening response during Strain Path changes are discussed.
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Mechanical behavior of Mg subjected to Strain Path changes: Experiments and modeling
International Journal of Plasticity, 2015Co-Authors: M. Borodachenkova, Gabriela Vincze, Carlos N. Tomé, Frederic Barlat, E.f. Rauch, José GrácioAbstract:Two-step tension tests with reloads along different directions are performed on rolled Mg alloy sheet at room temperature. The experimental yield stress at reloading is systematically lower than before unloading. Such a behavior is captured by a microstructure-based hardening model accounting for dislocation reversibility and back-stress. This formulation, embedded in the Visco-Plastic Self-Consistent (VPSC) model, links the dislocation density evolution throughout the deformation with hardening. The predicted results agree well with the experimental data in terms of flow stress response and texture evolution. The effects of texture anisotropy and back-stress on the mechanical response during the Strain Path change are discussed.
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a crystallographic dislocation model for describing hardening of polycrystals during Strain Path changes application to low carbon steels
International Journal of Plasticity, 2013Co-Authors: K Kitayama, Frederic Barlat, E.f. Rauch, José Grácio, C.n. TomeAbstract:Abstract Polycrystal aggregates subjected to plastic forming exhibit large changes in the yield stress and extended transients in the flow stress following Strain Path changes. Since these effects are related to the rearrangement of the dislocation structure induced during previous loading, here we propose a crystallographically-based dislocation hardening model for capturing such behavior. The model is implemented in the polycrystal code VPSC and is applied to simulate Strain Path changes in low carbon steel. The Path changes consist of tension followed by shear at different angles with respect to the preload direction, and forward simple shear followed by reverse shear. The results are compared to experimental data and highlight the role that directional dislocation structures induced during preload play during the reload stage.
Viggo Tvergaard - One of the best experts on this subject based on the ideXlab platform.
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use of abrupt Strain Path change for determining subsequent yield surface experimental study with metal sheets
Acta Materialia, 2000Co-Authors: Toshihiko Kuwabara, Mitsutoshi Kuroda, Viggo Tvergaard, K NomuraAbstract:A basic idea for a method for determining the subsequent yield surface in the vicinity of a current loading point by using an abrupt Strain Path change has been proposed recently by Kuroda and Tvergaard (Acta mater., 1999, 47, 3879). The proposed method is applied to real experimental studies. In a biaxial tensile testing apparatus, a cruciform specimen is used, with the Strains measured by a biaxial-Strain gauge. Then, with the hydraulic pressure of two sets of opposing hydraulic cylinders servo-controlled independently, the testing apparatus can be used to prescribe an abrupt change of the Strain Path. Both a cold-rolled steel sheet and an aluminum alloy sheet are investigated. The differences between the yield surface shapes found by the Strain Path change procedure and the shapes found by probing the yield points from the elastic region are shown and discussed for different cases.
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effect of Strain Path change on limits to ductility of anisotropic metal sheets
International Journal of Mechanical Sciences, 2000Co-Authors: Mitsutoshi Kuroda, Viggo TvergaardAbstract:Abstract Localized necking in thin metal sheets is analyzed by using the M–K-model approach, and the effect of a number of different non-proportional Strain Paths prior to the occurrence flow localization are considered. The analyses account for plastic anisotropy, using four different anisotropic plasticity models to fit a set of experimental data for cold-rolled steel sheet. The predicted forming limit diagrams show strong dependence on whether or not the load on the sheet is removed between two load steps on a non-proportional Strain Path. This dependence is investigated in detail for one of the anisotropic plasticity models, and it is shown that elastic Straining plays a large role, as the stresses quickly move from one point of the yield surface to another. When the load is removed between steps, the stress point moves in a different manner, which results in quite different flow localization response.
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use of abrupt Strain Path change for determining subsequent yield surface illustrations of basic idea
Acta Materialia, 1999Co-Authors: Mitsutoshi Kuroda, Viggo TvergaardAbstract:Abstract For elastic–plastic materials, a new method is proposed for determining the shape of the subsequent yield surface in the vicinity of a current loading point. A proportional Strain Path is prescribed until the loading point of interest has been reached, then an abrupt Strain Path change is prescribed, which makes the stress point move quickly along the yield surface. It is assumed that a closed-loop testing machine is used for the experiment, so that the Strain Path can be prescribed according to Strain gauge measurements. Relative to the standard method of determining yield surface shapes by probing in many different stress directions from the elastic region, using some chosen plastic Strain offset, the main advantage of the proposed method is that elastic unloading is not needed prior to tracing the yield surface. The method is illustrated here by a few analyses, first for the simplest flow theory of plasticity, and subsequently for crystal plasticity, using the Taylor model to represent a polycrystal.
Odd Sture Hopperstad - One of the best experts on this subject based on the ideXlab platform.
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a combined isotropic kinematic and distortional hardening model for aluminum and steels under complex Strain Path changes
International Journal of Plasticity, 2018Co-Authors: Jisheng Qin, Bjorn Holmedal, Odd Sture HopperstadAbstract:Abstract In this work, a new model is proposed for predicting stress transients caused by Strain Path changes. The model is formulated in stress space, where a second order tensor, i.e., the microstructure stress deviator, is used to memorize and model the evolution history of the microstructure. Both its direction and magnitude are used to transiently distort the yield surface and to modify the work hardening. Orthogonal Strain-Path changes are handled by yield surface distortions, while Bauschinger effects are described by a kinematic hardening formulation. The model is calibrated to, and captures well, earlier published experiments for commercial pure aluminum, an extra deep drawing quality steel and a dual-phase steel. The proposed model describes qualitatively the response to double Strain-Path changes in low carbon steels. Efforts are made to design a relatively simple model as compared to the high complexity of the experiments, applying simple mathematical sub-models with straightforward interpretations and enabling a numerically stable implementation.
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modeling Strain Path changes in aluminum and steel
International Journal of Solids and Structures, 2017Co-Authors: Jisheng Qin, Bjorn Holmedal, Kai Zhang, Odd Sture HopperstadAbstract:Abstract The present paper evaluates two phenomenological plasticity models which account for the influence of Strain-Path change (SPC) on the stress-Strain behavior. The HAH model (Barlat et al., 2014) is modified to capture SPC transients observed in aluminum, i.e., hardening stagnation after reverse SPCs and permanent softening after orthogonal SPCs. Predictions by the HAH model are compared to the MHH model (Manik et al., 2015), which was originally developed for aluminum. The MHH model turned out to be directly applicable to an extra deep drawing quality (EDDQ) steel without any modifications. The MHH model predicts the stress-Strain behavior after single SPCs slightly better than the HAH model for both aluminum and steel. It can also capture correctly R-value transients in aluminum after purely orthogonal SPCs. However, only the HAH model can capture transients after double SPCs qualitatively for low carbon steels. The applicability of these advanced continuum plasticity models to aluminum and steel and the differences in their mathematical formulation are discussed.
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Strain Path change induced transients in flow stress work hardening and r values in aluminum
International Journal of Plasticity, 2015Co-Authors: Tomas Manik, Bjorn Holmedal, Odd Sture HopperstadAbstract:Abstract Commercially pure aluminum with random texture was preStrained either by rolling or by uniaxial compression, and then tested in uniaxial tension to study the transients in flow stress, work hardening and r -value induced by the Strain-Path change. New experimental results are reported on the variation of the r -value and the permanently reduced work hardening subsequent to the Strain-Path change. A continuum plasticity model was developed that can reproduce the observed behavior. The model applies a second-order “delayed pointer” tensor to represent the microstructural anisotropy and was implemented into the finite element software LS-DYNA. The model was calibrated to the experimental data, and a simulation of early Strain localization subsequent to an orthogonal Strain-Path change was compared to Strain fields measured by a digital image correlation technique.
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an evaluation of a combined isotropic kinematic hardening model for representation of complex Strain Path changes in dual phase steel
European Journal of Mechanics A-solids, 2009Co-Authors: V Tarigopula, Odd Sture Hopperstad, M Langseth, A H ClausenAbstract:Abstract This paper aims at evaluating an elastoplastic constitutive model which accounts for combined isotropic-kinematic hardening for complex Strain-Path changes in a dual-phase steel, DP800. The capability of the model to reproduce the transient hardening phenomena under two-stage non-proportional loading has been assessed through numerical simulations of sequential uniaxial tension and notched tension/shear tests. Finite element simulations with shell elements were performed using the explicit non-linear FE code LS-DYNA. Numerical predictions of the stress–Strain response were compared to the corresponding experimental data. The results from the experiments demonstrated that prior plastic deformation has certainly influenced the subsequent work-hardening behaviour of the material under biaxial or shear deformation modes. Furthermore, the numerical simulations from the two-stage uniaxial tension–notched tension and uniaxial tension–shear tests predicted the general trends of the experimental results such as transitory hardening and overall work hardening. However, some discrepancies were found in accurately describing the transient hardening behaviour subsequent to Strain Path changes between the experiments and numerical simulations.
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elastic plastic behaviour of dual phase high strength steel under Strain Path changes
European Journal of Mechanics A-solids, 2008Co-Authors: V Tarigopula, Odd Sture Hopperstad, M Langseth, A H ClausenAbstract:Abstract The elastic-plastic behaviour of dual-phase, high-strength steel sheets under two-stage Strain-Path changes has been investigated. Three different loading sequences, namely monotonic, 45° tensile Path changes and orthogonal tensile Path changes complied by sequences of simple uniaxial tensile tests, were analysed at room temperature. From the experiments, it was found that there is a considerable reduction of the initial flow stress over the Strain-Path changes. The transient softening phenomenon is observed to be a function of orientation, and the period of the transient behaviour following the Strain-Path change is lengthened with the amount of pre-Strain. A constitutive model is adopted that includes combined isotropic and kinematic hardening and is capable of describing the marked transient softening behaviour after the pre-Straining. The experimental stress–Strain behaviour subsequent to the Strain Path change is predicted with reasonable accuracy, while the model fails to accurately describe the transient, deformation-induced anisotropy in the plastic flow.
Mitsutoshi Kuroda - One of the best experts on this subject based on the ideXlab platform.
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use of abrupt Strain Path change for determining subsequent yield surface experimental study with metal sheets
Acta Materialia, 2000Co-Authors: Toshihiko Kuwabara, Mitsutoshi Kuroda, Viggo Tvergaard, K NomuraAbstract:A basic idea for a method for determining the subsequent yield surface in the vicinity of a current loading point by using an abrupt Strain Path change has been proposed recently by Kuroda and Tvergaard (Acta mater., 1999, 47, 3879). The proposed method is applied to real experimental studies. In a biaxial tensile testing apparatus, a cruciform specimen is used, with the Strains measured by a biaxial-Strain gauge. Then, with the hydraulic pressure of two sets of opposing hydraulic cylinders servo-controlled independently, the testing apparatus can be used to prescribe an abrupt change of the Strain Path. Both a cold-rolled steel sheet and an aluminum alloy sheet are investigated. The differences between the yield surface shapes found by the Strain Path change procedure and the shapes found by probing the yield points from the elastic region are shown and discussed for different cases.
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effect of Strain Path change on limits to ductility of anisotropic metal sheets
International Journal of Mechanical Sciences, 2000Co-Authors: Mitsutoshi Kuroda, Viggo TvergaardAbstract:Abstract Localized necking in thin metal sheets is analyzed by using the M–K-model approach, and the effect of a number of different non-proportional Strain Paths prior to the occurrence flow localization are considered. The analyses account for plastic anisotropy, using four different anisotropic plasticity models to fit a set of experimental data for cold-rolled steel sheet. The predicted forming limit diagrams show strong dependence on whether or not the load on the sheet is removed between two load steps on a non-proportional Strain Path. This dependence is investigated in detail for one of the anisotropic plasticity models, and it is shown that elastic Straining plays a large role, as the stresses quickly move from one point of the yield surface to another. When the load is removed between steps, the stress point moves in a different manner, which results in quite different flow localization response.
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use of abrupt Strain Path change for determining subsequent yield surface illustrations of basic idea
Acta Materialia, 1999Co-Authors: Mitsutoshi Kuroda, Viggo TvergaardAbstract:Abstract For elastic–plastic materials, a new method is proposed for determining the shape of the subsequent yield surface in the vicinity of a current loading point. A proportional Strain Path is prescribed until the loading point of interest has been reached, then an abrupt Strain Path change is prescribed, which makes the stress point move quickly along the yield surface. It is assumed that a closed-loop testing machine is used for the experiment, so that the Strain Path can be prescribed according to Strain gauge measurements. Relative to the standard method of determining yield surface shapes by probing in many different stress directions from the elastic region, using some chosen plastic Strain offset, the main advantage of the proposed method is that elastic unloading is not needed prior to tracing the yield surface. The method is illustrated here by a few analyses, first for the simplest flow theory of plasticity, and subsequently for crystal plasticity, using the Taylor model to represent a polycrystal.
C.n. Tome - One of the best experts on this subject based on the ideXlab platform.
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mechanical behavior of low carbon steel subjected to Strain Path changes experiments and modeling
Acta Materialia, 2016Co-Authors: Wei Wen, Gabriela Vincze, M. Borodachenkova, Frederic Barlat, E.f. Rauch, C.n. Tome, José GrácioAbstract:The mechanical response of a low carbon steel under complex Strain Path changes is analyzed here in terms of dislocation storage and annihilation. The mechanical tests performed are cyclic shear and tensile loading followed by shear at different angles with respect to the tensile axis. The material behavior is captured by a dislocation-based hardening model, which is embedded in the Visco-Plastic Self-Consistent (VPSC) polycrystal framework taking into account the accumulation and annihilation of dislocations, as well as back-stress effects. A new and more sophisticated formulation of dislocation reversibility is proposed. The simulated flow stress responses are in good agreement with the experimental data. The effects of the dislocation-related mechanisms on the hardening response during Strain Path changes are discussed.
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an elasto plastic self consistent model with hardening based on dislocation density twinning and de twinning application to Strain Path changes in hcp metals
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2015Co-Authors: Milovan Zecevic, Irene J. Beyerlein, Marko Knezevic, C.n. TomeAbstract:Abstract In this work, we develop a polycrystal mean-field constitutive model based on an elastic–plastic self-consistent (EPSC) framework. In this model, we incorporate recently developed subgrain models for dislocation density evolution with thermally activated slip, twin activation via statistical stress fluctuations, reoriented twin domains within the grain and associated stress relaxation, twin boundary hardening, and de-twinning. The model is applied to a systematic set of Strain Path change tests on pure beryllium (Be). Under the applied deformation conditions, Be deforms by multiple slip modes and deformation twinning and thereby provides a challenging test for model validation. With a single set of material parameters, determined using the flow-stress vs. Strain responses during monotonic testing, the model predicts well the evolution of texture, lattice Strains, and twinning. With further analysis, we demonstrate the significant influence of internal residual stresses on (1) the flow stress drop when reloading from one Path to another, (2) deformation twin activation, (3) de-twinning during a reversal Strain Path change, and (4) the formation of additional twin variants during a cross-loading sequence. The model presented here can, in principle, be applied to other metals, deforming by multiple slip and twinning modes under a wide range of temperature, Strain rate, and Strain Path conditions.
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a polycrystal plasticity model for predicting mechanical response and texture evolution during Strain Path changes application to beryllium
International Journal of Plasticity, 2013Co-Authors: Irene J. Beyerlein, Marko Knezevic, Donald W Brown, Thomas A Sisneros, C.n. TomeAbstract:Abstract A polycrystalline material, deformed to large plastic Strains and subsequently reloaded along a distinct Strain Path, exhibits a change in flow stress and hardening behavior. Such changes upon reloading depend on the level of mechanical anisotropy induced by texture and sub-grain microstructure developed during prior loading. In order to comprehend such material behavior, we extend a previously developed rate- and temperature-sensitive hardening law for hexagonal single crystals that accounts explicitly for the evolution of dislocation densities by including the effects of reverse dislocation motion and de-twinning on Strain hardening and texture evolution. The law is implemented within a visco-plastic self-consistent polycrystalline model and applied to simulate macroscopic behavior of polycrystalline beryllium during Strain-Path changes. We show that the model successfully captures the mechanical response and evolution of texture and twin volume fraction during pre-loading in compression and subsequent cross-reloading in compression along two orthogonal directions at two different Strain rates. These predictions allow us to elucidate the role played by various slip and twin mechanisms, de-twinning, and reverse dislocation motion on Strain hardening and texture evolution of beryllium during Strain-Path changes. The model is general and can be applied to any metal deforming by slip and twinning.
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a crystallographic dislocation model for describing hardening of polycrystals during Strain Path changes application to low carbon steels
International Journal of Plasticity, 2013Co-Authors: K Kitayama, Frederic Barlat, E.f. Rauch, José Grácio, C.n. TomeAbstract:Abstract Polycrystal aggregates subjected to plastic forming exhibit large changes in the yield stress and extended transients in the flow stress following Strain Path changes. Since these effects are related to the rearrangement of the dislocation structure induced during previous loading, here we propose a crystallographically-based dislocation hardening model for capturing such behavior. The model is implemented in the polycrystal code VPSC and is applied to simulate Strain Path changes in low carbon steel. The Path changes consist of tension followed by shear at different angles with respect to the preload direction, and forward simple shear followed by reverse shear. The results are compared to experimental data and highlight the role that directional dislocation structures induced during preload play during the reload stage.
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Experiments and Modeling of Low Carbon Steel Sheet Subjected to Double Strain Path Changes
Metallurgical and Materials Transactions A, 2013Co-Authors: Gabriela Vincze, Frederic Barlat, E.f. Rauch, C.n. Tome, M.c. Butuc, José GrácioAbstract:Low carbon steel was deformed under double Strain Path changes consisting in three successive tension tests carried out in different directions with respect to the material symmetry axes. The influences of the Strain amounts and severity of Strain Path change in the reloading yield stress and subsequent Strain hardening were investigated in detail. The trends captured using the homogeneous anisotropic hardening approach, which is based on a homogeneous yield function, are in good agreement with the experimental results.
