A new method for establishing elastic-viscoplastic constitutive model of clay

摘要

In this paper, three existing elastoplastic constitutive models, i.e. Cam-clay model, subloading surface model and superloading surface model, are improved to predict the time-dependent behavior of clay. In the new models, the yield function of the original elastoplastic constitutive model is used as a static yield surface, which is regarded as a reference dynamic yield surface at the strain rate of common tests (10~(-7)-10~(-5)s~(-1)). A relative overstress relation is used to obtain the dynamic loading surface at any strain rate based on the static yield surface. Therefore, a dynamic equilibrium condition, using stress, viscoplastic strain and viscoplastic strain rate as state variables, is adopted as a convergence criteria. Two material parameters about the rate sensitivity are added into the original models, which can be determined by triaxial compression tests with different strain rates. Each original elastoplastic constitutive model can be regarded as a special case of the corresponding elastic-viscoplastic model in a certain strain rate. The new models have been implemented into ABAQUS by a stress integration algorithm using Newton-Raphson iteration. The numerical results show that the models can reproduce the time-dependent behavior of clays such as rate sensitivity and creep in addition to the deformation behavior as predicted by the original elastoplastic models.