Anisotropic distortional hardening based on deviatoric stress invariants under non-associated flow rule

An anisotropic distortional hardening (ADH) model is developed under non-associated flow rule by evolving the analytical asymmetric Yoon2014 yield criterion (Hu and Yoon, 2021). The deviatoric stress invariants in the proposed hardening model are analytically expressed. Then, the evolving equations are imposed to describe Bauschinger effect and transient behavior. The anisotropic parameters in yield function can be directly expressed with the four hardening curves along 0 degrees, 45 degrees, 90 degrees and equi-biaxial directions under the proportional loadings. Most importantly, nonlinear strain paths are incorporated in the model. Permanent softening & strengthen, work-hardening stagnation & overshooting behaviors during strain path changes have also been taken into account in the proposed model. The corresponding parameters for these characteristics are relatively independent, although optimization is required for the parameter identifications. The effectiveness and accuracy of the proposed ADH model have been compared with the kinematic hardening models for SPCC material. The constitutive description for 780R AHSS from the proposed model has also been compared with the YU model (Yoshida et al., 2015) under tension-compression along RD, DD and TD. The accuracy of the proposed model under complex strain paths has also been verified by comparing with the results predicted from the eHAH model (Barlat et al., 2013) for EDDQ and DP780. In addition, a plastic potential function is developed based on the form of the proposed model for non-associated flow rule. The accuracy has been verified by applying it to 780R AHSS, EDDQ and DP780.