Endochronic description of plastic anisotropy in sheet metal

It is shown in this paper that an extended form of Hill's quadratic yield c riterion for anisotropic sheet metal can be derived from an endochronic the ory of plasticity. The extended form considers the combined isotropic-kinem atic hardening and the 'anomalous behavior' observed in the anisotropic pla stic behavior of sheet metals can be accounted for by the concept of kinema tic hardening. This form of anisotropic endochronic theory can accommodate the usual requi rement of normality between the plastic strain rate and the yield function. In addition, the theory leads naturally to the expressions for back stress es. This work provides an additional example to show that the form of the i ntrinsic time is directly related to the form of the yield function. It is suggested that the coefficients of the quadratic yield function be de termined from the yield stresses obtained from a set of tension tests. (C) 1999 Elsevier Science Ltd. All rights reserved.