A nonlinear viscoelastoplastic rheological model based on nishihara's model

A new nonlinear viscoelastoplastic rheological model is proposed to perfectly describe the global creep behavior in this paper. The present model is based on Nishihara's model by adding two additional elements: one is the nonlinear viscoplastic element which is used to define the onset of the tertiary creep stage; the other is the plastic element describing the instantaneous plastic deformation. Firstly, a three-dimensional model is formulated on the basis of its one-dimensional form. Then, the identification of rheological parameters is investigated in detail. Moreover, the parameter sensibility analysis is performed. The experimental results of triaxial creep test are used to verify the validity of the model. It is shown that the proposed nonlinear viscoelastoplastic rheological model can be used to perfectly describe three creep stages at multiple deviatoric stress levels with a set of rheological parameters.