Poisson's ratio in linear viscoelasticity - A critical review

Poisson's ratio is an elastic constant defined as the ratio of the lateral contraction to the elongation in the infinitesimal uniaxial extension of a homogeneous isotropic body. In a viscoelastic material Poisson's ratio is a function of time (or frequency) that depends on the time regime chosen to elicit it. It is important as one of the material functions that characterize bulk behavior. This paper develops the linear theory of the time- or frequency-dependent Poisson's ratio, and it reviews work on its experimental determination. The latter poses severe difficulties in view of the high accuracy required. Thus, reliable information on the viscoelastic Poisson's ratio is as yet rather scanty. The paper also reports on attempts to measure the Poisson's ratio of a viscoelastic material as a function of temperature. Lateral contraction in creep and at constant rate of extension receives attention as well.