Thermodynamics of linear reversible deformation

The change in internal energy of a body on stretching can be determined by means of deformation calorimetry. Theoretically the changes in thermodynamic properties on stretching can be deduced from Hooke's law and the Thomson expression dQ = β₀TL df, which gives the amount of heat dQ absorbed when the force is changed from f to f+df; β₀ is the linear expansion coefficient of the isotropic specimen, T the absolute temperature, and L the length of the deformed specimen. This has been demonstrated here for the deformation of a metal, and of isotropic and oriented polyethylene.