On the nonlinear anelastic behavior of AHSS

It has been widely observed that the loading/unloading behavior of metals which have previously undergone plastic deformation is nonlinear. Furthermore it shows a hysteresis behavior upon further unloading/reloading cycles. The origin of this nonlinearity is attributed to additional dislocation based micro mechanics which contribute to the total reversible strain, referred to as anelastic strain. Compared to a FE model prediction using only elastic contribution to reversible strain the actual springback will be larger. In this work the unloading behavior of DP800 AHSS is analyzed in detail and a mixed physical-phenomenological model is proposed to describe the observed nonlinearity for different levels of pre-strain. This one dimensional uniaxial model is generalized to a 3D constitutive model incorporating elastic, anelastic and plastic strains. The performance of the model is evaluated by comparing the predicted cyclic unloading/reloading stress-strain curves with the experimental ones. It is shown that by incorporating aneiastic behavior in the model the prediction of the cyclic behavior of the material is significantly improved. (C) 2017 Elsevier Ltd. All rights reserved.