The Methods of Specifying the Properties of Viscoelastic Materials

Abstract

Seven methods (Voigt model, Maxwell model, operator equation, mechanical impedance function, creep curve, relaxation curve, and dynamic modulus function) of specifying viscoelastic behavior are discussed. A number of exact relations between these methods of specification are worked out in detail. The majority of these relations are simple enough to be of practical value although a few are too cumbersome. Approximate relationships between the creep curve, the relaxation curve, Maxwell model, and Voigt model are discussed; and numerical examples show the magnitude of errors introduced by the approximation to be small even in quite unfavorable cases. A consideration of the practical utility and physical meaning of the various methods of specification distinguishes between (1) those of general descriptive value and those of direct experimental value; (2) those useful in a phenomenological study of mechanical behavior and those more suited to a formulation of molecular theory. A summary of the present molecular theories is presented together with their interpretation in terms of the Voigt and Maxwell specifications.