Intermediate configurations and the description of viscoelastic-plastic material behaviors

The paper starts from the general constitutive equation of a simple material with memory. The concept of an intermediate configuration is based on the idea of local unloading: A given strain process is continued under the condition of vanishing stress; its asymptotic limit is introduced as the unrecoverable part of the total strain. By assumption, the present value of the unrecoverable strain depends on the history of the total strain; this functional dependence is rate-independent, if the unrecoverable strain corresponds to the plastic strain in the usual sense. A viscoelastic-plastic material can be defined by means of a relaxation functional, which relates the recoverable part of the strain history to the actual stress tensor. (orig.)