3-DIMENSIONAL, FINITE DEFORMATION, VISCOPLASTIC CONSTITUTIVE MODELS FOR POLYMERIC MATERIALS

A general methodology for developing three-dimensional. finite deforma tion, viscoplastic constitutive models for polymeric materials is pres ented. The development begins with the presentation of a one-dimension al spring and dashpot construction which exhibits behavior typical of polymeric materials, namely strain-rate dependence, stress relaxation, and creep. The one-dimensional construction serves as a starting poin t for the development of a three-dimensional, finite deformation, visc oplastic constitutive model which also exhibits typical polymeric beha vior. Furthermore, the three-dimensional constitutive model may be eas ily generalized to incorporate an arbitrary number of inelastic proces ses, representing (inelastic) microstructural deformation mechanisms o perating on different time scales. Strain-rate dependence, stress rela xation, and creep phenomena are discussed in detail for a simple versi on of the constitutive model. Test data for a particular polymer is us ed to validate the simple model. It is concluded that the methodology provides a flexible approach to modeling polymeric materials over a wi de range of loading conditions.