Three-dimensional stress states at crack tip induced by shear and anti-plane loading

It was known for a long time that shear and anti-plane fracture modes are coupled. It means that shear or anti-plane loading of an elastic plate with a through-the-thickness crack also generates a coupled three-dimensional anti-plane or shear singular stress state, respectively. These singular stress states (or coupled fracture modes) are currently largely ignored in theoretical and experimental investigations as well as in standards and failure assessment codes of structural components, in which it is implicitly assumed that the intensities of these modes as well as other three-dimensional effects are negligible in comparison with the stress field generated by the primary modes (modes I, II and III). In this paper we provide an overview of recent theoretical studies carried out by the authors, which demonstrate that the account for these coupled modes can totally change the classical (two-dimensional) view on many fracture phenomena. In particular, this relates to a generation of the coupled modes by non-singular (in two-dimensional sense) shear and anti-plane stress fields. The theoretical results indicate the existence of a strong plate thickness effect on the intensity of the coupled modes, which can significantly influence fracture conditions.