Linear Superposition in Visco?Elasticity and Theories of Delayed Effects

Abstract

Writers on elastic after-working or "visco-elasticity" have given a formula expressing the stress-history as an integral involving the strain-history linearly. If this is to be based directly on experiment, linear superposition is a necessary physical datum; but it is not sufficient, and examples are given to demonstrate this. Necessary and sufficient conditions are established in this paper, and expressed in physical as well as in mathematical terms; they may admit physical verification in some degree. Histories both with and without beginning are considered.