Abstract: In this paper, an unified elastic-viscosic-plastic theory which can compute the change of elastic, viscosic and plastic stale of each point in the body is proposed. The theory is based on the laws of the thermodynamics and the pseudo elastic postulate. In the paper, the constitutive equations and variational principles are deduced. From which, the finite element method of both space and time may be easily formulated. Note that, by choosing the material parameters properly, the plastic constitutive equations currently used may be given.

Key words: the first and second laws of thermodynamics, pseudo elastic postulate