Effect of non-linear tension-compression loading reversal on the hardening behavior and initiation fracture strain of a cold-rolled TRIP780 steel sheet

Abstract

This work examines the influences of non-linear pre-forming paths on the ductile behavior and damage evolution of a cold-rolled transformation-induced plasticity (TRIP) steel. Two non-linear pre-forming paths, i.e. tension followed by compression (TC) and compression followed by tension (CT), were designed to reveal the Bauschinger effect and fracture ductility. The experimental results demonstrated that the fracture strain was strongly affected by the loading path and magnitude of pre-forming. A single-surface plasticity model accounting for a non-associated Hill’ 48 plastic flow potential was developed by combining a Voce-Swift isotropic hardening law and a mixed non-linear kinematic (NLK) hardening rule. The experimental strain-stress curves of pre-formed specimens were utilized to calibrate the model parameters. The proposed model well predicted the hardening anisotropy, Bauschinger effect, permanent softening and transient behavior of specimens undergoing TC and CT pre-forming strategies. In addition, the influence of non-linear TC and CT pre-forming loading paths on the initiation fracture strain were modeled and investigated through a Hosford-Coulomb fracture criterion. The results showed that the proposed non-associated and mixed hardening model can describe the hardening behavior under TC and CT non-linear deformation. It is also found that the Hosford-Coulomb fracture model is capable to provide reasonable prediction on the fracture strain under different non-linear pre-forming loading paths even though a larger scatter for the TC deformation. These results also confirm that the ductility of the TRIP780 increases under a TC or CT non-linear pre-forming.