Poynting Effects in Soft Elastic Materials: A Review of Recent Results

Abstract

The celebrated experiments of J. H. Poynting in 1909 have given rise to a vast literature regarding an interesting feature of the nonlinear response of soft solids. Poynting conducted a series of experiments on metal wires and found that loaded wires lengthen when twisted. Thus to maintain a constant length in such experiments, a compressive axial force would need to be applied at the ends of the specimen. This is the classical (positive) Poynting effect. Another example of such an effect arises when a soft material specimen is being laterally sheared or rotated between two platens. The necessity to apply a compressive lateral normal force in order to maintain the relative distance between the platens is also often referred to as a Poynting-type effect. Both effects are inherently nonlinear phenomena. In recent years, a large body of experimental and theoretical work on the Poynting effect has been carried out. In particular, a reverse Poynting effect has been investigated where the cylinder contracts under torsion unless a tensile axial force is applied or in the case of the lateral shear problem, the platens tend to draw together laterally unless a tensile lateral normal force is applied. The purpose of the present article is to review recent research findings on both of these effects for soft materials.