Time–temperature superposition of large-strain shear properties of the ethylene–propylene copolymer system

Abstract

The principle of time temperature superposition for some mechanical properties of polymers is well known, particularly where strains are on the order of 1% or less. For large strains the simple data transformation techniques are not useful, probably because of morphological changes in the polymer. Morphological changes have the effect of changing the mechanical properties, thus necessitating a shift on the verticle axis as well as horizontal axis where mechanical properties are plotted on the ordinate and strain rate, e.g., is plotted on the abscissa. By the Rouse and Zimm theories of flexible chain polymer molecules a relationship is shown between a verticle shift and a horizontal shift, thereby making it unnecessary to determine the exact nature of morphological changes in the polymer when strained. Six polymers were strained to the fracture point and the shear modulus and fracture strength data were used to demonstrate the technique of simultaneous verticle and horizontal transformation of data.