Endochronic description of plastic anisotropy in sheet metal

It is shown in this paper that an extended form of Hill|s quadratic yield criterion for anisotropic sheet metal can be derived from an endochronic theory of plasticity[ The extended form considers the combined isotropic kinematic hardening and the {anomalous behavior| observed in the anisotropic plastic behavior of sheet metals can be accounted for by the concept of kinematic hardening[ This form of anisotropic endochronic theory can accommodate the usual requirement of normality between the plastic strain rate and the yield function[ In addition\ the theory leads naturally to the expressions for back stresses[ This work provides an additional example to show that the form of the intrinsic time is directly related to the form of the yield function[ It is suggested that the coe.cients of the quadratic yield function be determined from the yield stresses obtained from a set of tension tests[