Influence of Evolution in Anisotropy During Strain Path Change on Failure Limits of Sheet Metals

Effects of evolution in anisotropy during plastic deformation under strain path changes on the formability and failure were investigated in the present study. The evolution in anisotropic property of the extra deep drawing steel was considered by implementing the non-quadratic anisotropic yield function Yld2000-2d as a function of effective plastic strain, and the corresponding forming behaviour in two-step forming processes was analysed. For the strain path effect, pre-strain was applied under biaxial mode using Marciniak in-plane stretch forming set-up, followed by the secondary deformation using the out-of-plane stretch forming tool. For failure prediction of the proposed two-step forming, different failure limit approaches were investigated. First, a strain based forming limit diagram (FLD), proposed as the Marciniak–Kuczynski model was modified to include the evolution in anisotropic yield function. The dynamic shift in FLD was also determined by taking strain path change into consideration. In addition, the influence of evolution of yield function on the strain path independent failure limit criteria was also assessed in terms of stress based forming limit diagram. Finally, the prediction accuracy of the failure limit criteria was compared among different models in terms of failure location and limiting dome height (LDH). It was observed that the incorporation of evolution in anisotropic yield surface improved the prediction of formability in terms of the LDH and strain distribution for the investigated material.