Non-linear viscoelastic behavior of some polymers and their composites.

Abstract

Constant load creep data were obtained for four plastics: polyethyline, polypropylene, nylon, and polycarbonate. Viscoelastic responses of these materials proved to be non-linear in both time and stress. An empirical creep equation, based on a time dependent retardation rate constant, was developed to characterize the creep behavior and good correlation was obtained for various stress levels. By assuming the developed relationship to be an equation of state, creep behavior of simple composites of plastics was predicted with good results when viscoelastic responses of the components were similar. The importance of stress-time history is demonstrated by using the creep equation to estimate mechanical behavior in other modes of testing. The concept of a retardation spectrum and its application to the materials studied is considered.