Abstract: A viscoplastic constitutive model which considers the cyclic deformation behavior with mean strain is presented.In the model,a memory papameter q of strain amplitude which considers the effect of mean strain is proposed,the evolution equations of back stresses are formulated,and an appropriate definition of nonproportionality is introduced.Moreover,the evolution equations of isotropic deformation resistance which has fading memory on the cyclic deformation behavior of previous history are deveopled.The model is applied to the constitutive modelling of the effect of mean strain of 1Cr18Ni9Ti stainless steel.The predictions show that the model is reasonable for the effect.

Key words: effect of mean strain, cyclic viscoplast icity, const itutive equations