A mixed hardening model combined with the transformation-induced plasticity effect

A mixed isotropic-kinematic hardening model considering the transformation-induced plasticity (TRIP) effect was proposed for TRIP steels in this study. Besides the nonlinear Chaboche backstress and linear Prager-Ziegler backstress, a third backstress that depicts the contribution of TRIP effect to the kinematic hardening was presented. The TRIP effect was modeled using an equivalent plastic strain and a stress triaxiality coefficient as the variant. Forward-reverse shear experiments were performed for a cold rolled TRIP780 steel. A new clamper was designed to reduce the buckling during reverse shear. Cyclic loading-unloading-reloading uniaxial tension experiments were conducted and the degradation of elastic modulus with the plastic strain was discussed. Micro-indentation tests were performed to check the true elastic modulus. U-bending springback simulation was performed with the new hardening model combined with the Yoshida's elastic modulus. The results showed that the investigated TRIP780 steel has prominent kinematic hardening behavior, Bauschinger effect, transient hardening and permanent softening during forward-reverse shear deformation. The percentage of the third backstress component due to the TRIP effect in the total backstress reaches 31% at 0.25 plastic strain. Springback simulation with the proposed hardening model combined with the degradation of elastic modulus is more precise than the isotropic model.