ASSOCIATIVE VERSUS NONASSOCIATIVE POROUS VISCOPLASTICITY BASED ON INTERNAL STATE-VARIABLE CONCEPTS

A general constitutive framework for porous viscoplasticity is used to study the role of specific void growth models in both associative and non-associative viscoplastic flow rules. Three particular model frame works for porous viscoplasticity are identified, denoted as associativ e, nonassociative and partially coupled. The structure of a specific m odel framework is defined by the nature of the inelastic flow rule (as sociative versus non-associative) and the specific dependence of the y ield function on the first overstress invariant (pressure). As distinc t from the great majority of existing models for flow of porous viscop lastic media, this work considers the physically based models which em ploy internal state variables to represent evolving internal structure . Some applications are examined using Bammann's internal state variab le viscoplastic model in the context of the three model frameworks. Co pyright (C) 1996 Elsevier Science Ltd