Third‐Invariant Model for Rate‐Dependent Soils

Abstract

A theory of viscoplasticity for frictional materials is developed in which first and third invariants of stress and strain are used instead of the more conventional second invariants. Rate effects are incorporated directly into the expression for the flow surface so that the numerical algorithm for a plasticity subroutine can be used. The usual concepts of strain‐ and strain rate‐hardening viscoplasticity are used, except that a non‐associated flow rule is required to control dilatation. For two sandy materials, detailed comparisons are made of theoretical and experimental stress‐strain data for both static and dynamic paths.