Plastic instability in complex strain paths predicted by advanced constitutive equations

The present paper aims at predicting plastic instabilities under complex loading histories using an advanced sheet metal forming limit model. The onset of localized necking is computed using the Marciniak-Kuczinslcy (MK) analysis [I] with a physically-based hardening model and the phenomenological anisotropic yield criterion Yld2000-2d [2]. The hardening model accounts for anisotropic work-hardening induced by the microstructural evolution at large strains, which was proposed by Teodosiu and Hu [3]. Simulations are carried out for linear and complex strain paths. Experimentally, two deep-drawing quality sheet metals are selected: a bake-hardening steel (BH) and a DC06 steel sheet. The validity of the model is assessed by comparing the predicted and experimental forming limits. The remarkable accuracy of the developed software to predict the forming limits under linear and non-linear strain path is obviously due to the performance of the advanced constitutive equations to describe with great detail the material behavior. The effect of strain-induced anisotropy on formability evolution under strain path changes, as predicted by the microstructural hardening model, is particularly well captured by the model.open1134Nsciescopu

Mechanical behavior of low carbon steel subjected to strain path changes: Experiments and modeling

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. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.11158Ysciescopu

Mechanical behavior of Mg subjected to strain path changes: Experiments and modeling

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. (C) 2014 Elsevier Ltd. All rights reserved.112619Ysciescopu

Study on plastic flow localization prediction using a physically-based hardening model

The present paper aims at a detailed analysis of sheet metal formability using the physically-based hardening model accounting for the evolution of the anisotropic work-hardening induced by the microstructural evolution at large strains of Teodosiu and Hu (1995) [9]. The onset of localized necking is simulated by an advanced sheet metal forming limit model which connects, through the Marciniak-Kuczinsky analysis, the respective microstructural hardening model with the phenomenological anisotropic yield criterion Yld2000-2d (Barlat et al., 2003) [17]. Linear and complex strain paths are taken into account. The selected material is a DC06 steel sheet. An exhaustive study on the evolution of internal variables of the microstructural hardening model under such loadings is presented. The origin of the increase/decrease of formability under specific strain path changes is discussed. (C) 2011 Elsevier B.V. All rights reserved.X1132sciescopu

Sheet metal forming limit predictions based on advanced constitutive equations

The present paper aims at analysing the strain and stress-based forming limits predicted by an advanced sheet metal forming limit model. The onset of localized necking is simulated through the Marciniak-Kuczinsky (MK) analysis [1]., which connects the physically-based hardening model accounting for the evolution of the anisotropic work-hardening induced by the microstructural evolution at large strains of Teodosiu and Hu [2] with the phenomenological anisotropic yield criterion Yld2000-2d (Barlat et al., 2003) [3] Linear and complex strain paths are taken into account. The selected material is a DC06 steel sheet. The validity of the model is assessed by comparing the predicted and experimental forming limits. The remarkable accuracy of the developed software on predicting the forming limits is obviously due to the performance of the advanced constitutive equations applied on M-K theory, able to describe with great detail the material behaviour. The effect of the strain-induced anisotropy predicted by the microstructural hardening model on the evolution of formability under strain path changes is particularly aimed it.X111sciescopu

Analysis of sheet metal formability through isotropic and kinematic hardening models

The present paper aims at analysing the sheet metal formability through several isotropic and kinematic hardening models. Specifically, a special attention is paid to the physically-based hardening model of Teodosiu and Hu (1995), which accounts for the anisotropic work-hardening induced by the microstructural evolution at large strains, as well as to some more conventional hardening models, including the isotropic Swift strain-hardening power law, and the Voce saturation strain-hardening law, combined with a non-linear kinematic hardening described by the Armstrong-Frederick law. The onset of localized necking is simulated by an advanced sheet metal forming limit model which connects, through the Marciniak-Kuczinsky analysis, the hardening models with the anisotropic yield criterion Y1d2000-2d (Barlat et al., 2003). Both linear and complex strain paths are taken into account. The selected material is a DC06 steel sheet. The validity of each model is assessed by comparing the predicted forming limits with experimental results carefully obtained on this steel. The origin of discrepancy in the predicted results using different hardening models is thoroughly analyzed. (C) 2011 Elsevier Masson SAS. All rights reserved.X111816sciescopu

Modelling the plastic behaviour of metals under complex loading conditions

Aluminium alloys and low carbon steel exhibit a transient work-hardening rate when the strain path is abruptly modified. The underlying physical mechanisms are latent hardening in the case of cross-loading and massive disappearance of the dislocations pertaining to prestrain when the loading stress is reversed. The modelling approach previously proposed for strain reversal is extended to cross-loading. In the model, the work-hardening rate is controlled by the evolutionary laws of three dislocation densities related to forward, backward and cross-loading. A parameter which measures the amplitude of the strain path change is incorporated in this approach. It is believed that these three densities are sufficient to model many cases consisting of two stage strain paths.X112539sciescopu

Microstructural effects on yield surface evolution in cubic metals using the viscoplastic phi-model

Polyaystalline yield surfaces of metals are a good way to characterize the anisotropy of plastic deformation. The evolution of these surfaces is impossible to accurately reproduce without taking into account the evolution of the material microstructure such as texture development. In this paper, a numerical computation of yield surfaces using the viscoplastic phi-model is proposed. Results concerning face-centered cubic metals subjected to a plane strain compression test are presented. The influence of several mechanical parameters (strain hardening, strain rate sensitivity coefficient and accumulated deformation) on subsequent yield surfaces evolution is studied. The analysis of the change in the shape and size of the yield surfaces shows that the results depend strongly on the parameter phi which controls the strength of the interactions in the polycrystal. In addition, the predictions are compared to the widely used viscoplastic self-consistent model as well as to experimental yield loci taken from the literature for various aluminum alloy sheets. A fairly good qualitative agreement between our phi-model results and the experimental ones is found. The probable links between the parameter phi and the microstructural features such as the stacking fault energy and the grain size of the polycrystal are also briefly discussed. (C) 2010 Elsevier Ltd. All rights reserved.X111618sciescopu