Effect of strain rate difference between inside and outside groove in M−K model on prediction of forming limit curve of Ti6Al4V at elevated temperatures

The influence of initial groove angle on strain rate inside and outside groove of Ti6Al4V alloy was investigated. Based on the evolution of strain rate inside and outside groove, the effect of strain rate difference on the evolution of normal stress and effective stress inside and outside groove was also analyzed. The results show that when linear loading path changes from uniaxial tension to equi-biaxial tension, the initial groove angle plays a weaker role in the evolution of strain rate in the M−K model. Due to the constraint of force equilibrium between inside and outside groove, the strain rate difference makes the normal stress inside groove firstly decrease and then increase during calculation, which makes the prediction algorithm of forming limit convergent at elevated temperature. The decrease of normal stress inside groove is mainly caused by high temperature softening effect and the rotation of groove, while the increase of normal stress inside groove is mainly due to strain rate hardening effect.