A model of anisotropy evolution of sheet metals

Conventional plasticity models assume that shapes of yield surfaces are remain fixed throughout plastic deformation. However, some experiments show that anisotropy is changing with increasing plastic strain. This paper proposes a constitutive model that describes the evolution of anisotropy, both for the stress directionality and r-values, of sheet metals. The evolution of anisotropy is expressed by the change of the yield function as a function of the effective plastic strain. The anisotropy model is validated by comparing the experimental data on AA6022-T43 aluminium sheet (after Stoughton, T. B. and Yoon, J. W., Int J Plasticity 25 (2009) 1777-1817). This model is incorporated into the Yoshida-Uemori kinematic hardening model to describe both the Bauschinger effect and the anisotropy evolution.