SOME GENERAL-PROPERTIES OF SOLID POLYMER INELASTIC DEFORMATION-BEHAVIOR AND THEIR APPLICATION TO A CLASS OF CLOCK MODELS

Results of macroscopic experiments on the inelastic deformation behavi or of solid polymers are used to establish general properties. They in clude nonlinear rate sensitivity in the inelastic range in monotonic l oading and the transition from primary, to primary and secondary, and to primary and secondary and tertiary creep as the creep stress level increases beyond :he quasilinear region. Consistent with the notion of a solid it is presumed that a nonzero stress can be sustained at rest . The rest stresses at which relaxation tests terminate form the relax ation boundary. It is suggested that this relaxation boundary has the appearance of a nonlinear stress-strain curve. These properties are us ed as criteria in evaluating some types of ''clock'' models where ordi nary time in the kernels of linear viscoelastic integral representatio ns is replaced by a transformed time. It is a function of either the i nvariants of strain or the invariants of stress. It is shown that thes e models cannot reproduce the change in the creep properties as stress level increases. Creep always terminates. For large times asymptotic solutions hold linear rate sensitivity and a linear relaxation boundar y are predicted. Nonlinear rate sensitivity can be modeled before the asymptotic solution is reached. (C) 1998 The Society of Rheology.