Abstract
A microscopical, photoelastic technique has been used to investigate the distributions of stress and strain around a crack in a highly elastic material, natural rubber. The finite strains encountered in such a material give rise to a distortion of the principal-stress map, an effect which has no parallel in classical elasticity and which leads to a complex dependence of the stresses upon the external constraint. The strain energy at a point is however simply related to the external constraint when the latter is expressed in terms of a stored energy parameter T, which is defined. The same parameter is shown to govern the distortion of the stress field. The decay of strain energy in a direction perpendicular to the crack axis is much more gradual when the strains are finite, but the rate of decay along the axis in the elastomer is similar, both in form and magnitude, to that predicted by infinitesimal-strain theory.