Incorporation of asymmetric yield and hardening behaviour in axisymmetric elastoplastic problems

摘要

Within the context of total deformation plasticity, an axisymmetric model is developed for materials with asymmetric yield and hardening behaviours. The model employs the variable material properties (VMP) method which is an axisymmetric method of analysis widely used for problems such as pressure vessels. The original VMP method is applicable only to materials with symmetric hardening behaviour. In this study, the VMP method is extended to materials with asymmetric yield and hardening to examine the importance of considering the asymmetry within elastoplastic analyses. The asymmetric and isotropic Cazacu-Barlat yield criterion is employed. For residual stress calculations, actual unloading stress-strain curves obtained from experiments are directly incorporated into the proposed method. The results of the proposed model are first compared to the experimental results from a cylindrical magnesium specimen loaded under internal pressure and axial push/pull. The results are in very good agreement for the load cases where the stress state is uniaxial; the results deviate slightly for multi-axial stress states. An extensive comparison is made between the proposed asymmetric solution results and the results of symmetric solutions. The symmetric solutions adopt von Mises yield criterion and a symmetric hardening rule, e.g., isotropic and kinematic. The residual stress field results demonstrate that, for asymmetric materials, the results obtained from a symmetric solution can be significantly different under biaxial loading, and consideration of an asymmetric yield criterion along with an asymmetric hardening model is necessary. The loading and unloading responses of a thick-walled cylinder under internal pressure obtained from the proposed model are compared to those obtained from the LS-DYNA, MAT124 model. It is shown that the stress distributions are substantially different both after loading and unloading reversals. (C) 2016 Elsevier Ltd. All rights reserved.