A STUDY ON THE SIGNIFICANCE OF THE CHOSEN STRESS MEASURE IN FINITE STRAIN PLASTICITY

The choice of the specific stress measure used in eulerian formulation s of finite deformation plasticity theory depends on the stress tensor employed for the definition of the hyperelastic law and its work conj ugate rate of deformation used in the dissipation functional, The expo nential algorithm proposed in [1] is based on the Kirchhoff stress ten sor tau and the spatial rate of deformation tensor d as work conjugate variables. The formulation of the yield function in terms of Kirchhof f stresses, however, is questionable on physical grounds. Experimental evaluations of yield stresses. strength properties or the post-yieldi ng and post-failure behavior measured from the deformed configuration result in yield and failure stresses to be interpreted as Cauchy stres ses sigma = tau/J, where J is the jacobian determinant. Consequently, a direct calibration of yield or failure stresses and of hardening or softening characteristics of the material reauires the use of Cauchy s tresses in the formulation of the yield function and of the hardening law.