Isotropic bodies — Thermodynamic potential

Abstract

A very difficult problem of the theory of thermoelastic transformations is the one of determining the nature of the thermodynamic potential, J. This problem is both theoretical and experimental: first of all theoretical, since it is necessary to set up by analytical, geometrical, kinematical, physical, etc., considerations some kind of dependence of J upon fundamental parameters; then experimental, since only experience may establish or overturn a proposed scheme. Also, experience may suggest modifications. Hooke’s Law, which implies identification of J with a quadratic form in the linearized ε _rs and in T, represents a solution of the problem in first approximation, but it fails if the deformations are not sufficiently small, even though they remain in the elastic range. Nor may it be said, for certainly it is not true, that the same form of thermodynamic potential is valid for every elastic body in the case of large strain.