On the Thermostatic Behavior of Elastomers

Abstract

When a thermally expansible homogeneous isotropic elastic continuum is deformed isothermally, the mechanical work done on the body is partly stored as internal energy, partly converted to heat. In the range of strain up to about 10 percent (which is typical of natural rubber), the internal energy storage exceeds the work done so that heat must be added to the sample. Beyond the strain of 10 percent, heat is increasingly liberated. An equivalent statement conveys the information that, if the sample be stretched adiabatically, there is an initial temperature drop, then subsequent rise. In the limit of large strain, the ratio of internal energy stored to work done approaches a limiting value which depends on the thermal coefficient of expansion, the absolute temperature, and a parameter m which is related to the temperature coefficient of the shear modulus. In this paper, general expressions for internal energy, entropy, enthalpy, etc., are presented in terms of the strain energy function and its temperature coefficient.