Lode-dependent anisotropic-asymmetric yield function for isotropic and anisotropic hardening of pressure-insensitive materials. Part II: Stress invariant-based coupled quadratic and non-quadratic function

This research couples a Lode-dependent anisotropic-asymmetric (LAA) frame (Lou and Yoon, 2023. International Journal of Plasticity, 166, 103,647) with a stress-invariant-based coupled quadratic-non-quadratic (CQN) anisotropic hardening function to analytically characterize the anisotropic-asymmetric hardening of sheet metals under uniaxial tension and uniaxial compression. Experiments are conducted for AA2A12-O under uniaxial tension, uniaxial compression, equibiaxial tension, plane strain tension and shear. Anisotropy is investigated by conducting the experiments along different loading directions from the rolling. The flow curves are obtained from these experimental data at distinct stress states and loading directions. The plastic hardening is represented by the CQN-coupled LAA function to verify its accuracy. The CQN-coupled LAA model is also utilized to represent the plastic flow of DP980 under uniaxial tension, uniaxial compression, shear and plane strain tension along different loading directions as well as equibiaxial tension. The application to AA2A12-O and DP980 demonstrates that the CQN-coupled LAA function is capable of modeling plastic hardening behaviors under uniaxial tension, uniaxial compression, equibiaxial tension and equibiaxial compression and dramatically improving the prediction accuracy of flow curves under plane strain tension.