Revealing the strain rate-dependent asymmetric deformation mechanisms of TWIP steel by crystal plasticity modeling

In this study, the strain rate-dependent tension-compression asymmetric (TCA) plastic behavior of twinning-induced plasticity (TWIP) steel is investigated by developing a dislocation density-based crystal plasticity model. This model incorporates strain rate effects on dislocation mechanisms, with particular emphasis on the interactions between different types of dislocations and twins. By integrating the crystal plasticity finite element (CPFE) model with experimental tests, the TCA plastic behavior of TWIP steel and the underlying micro-mechanisms were systematically explored. The study reveals that, with random initial crystal orientations, TWIP steel exhibits a higher flow stress during compression than tension. Moreover, dynamic loading, compared to quasi-static loading, exacerbates the difference between compression and tension. The TCA plastic behavior is primarily attributed to differences in texture evolution under varying loading conditions. A quantitative analysis was further conducted to examine the influence of back stress, dislocation-twin boundaries (TB) interactions, twining mechanisms, and initial texture on strain rate-dependent TCA plastic behavior. Our findings show that, when back stress and the influence of dislocation types in dislocation-TB interactions are excluded, the stress levels during tensile and compressive deformation under quasi-static loading are nearly identical. Similarly, when twinning mechanisms are not considered, the stress difference between tensile and compressive deformation under quasi-static and dynamic loading is minimal.