Time-dependent elastoplastic constitutive model

The subloading surface model does not premise that the stress exists on the yield surface and thus describes a plastic deformation even when the stress exists inside the yield surface. The measure describing the degree that the stress approaches the yield surface or goes out from the surface is involved in this model. It is extended so as to describe the time-dependent deformation behavior of materials by allowing the stress to go out from the yield surface and considering the fact that a plastic deformation requires time to occur, although an elastic deformation is induced momentarily. Further, based on it, the constitutive equation of soils is formulated by taking the secondary consolidation phenomenon into account.