Coupled fracture modes in three-dimensional fracture mechanics

Shear and anti-plane loadings of an elastic plate with a through-the-thickness crack generate various singular stress states: primary fracture modes (conventional fracture mode II and III), corner singularities, and coupled fracture modes. Two latter 3D singular states are largely ignored in theoretical and experimental investigations as well as in the current standards and failure assessment codes. It is often implicitly assumed that all three-dimensional effects are negligible and the actual three-dimensional stress state can be adequately approximated by stress components found, for example, from the corresponding classical solutions of the plane theory of elasticity. In this paper we provide an overview of recent 3D studies carried out by the authors, which demonstrate that the account for these coupled modes can totally change the classical view of many fracture phenomena. In particular, this relates to a generation of the coupled fracture modes by shear and anti-plane loading with KII = 0 and KIII = 0, respectively. In these cases the coupled fracture modes dominate the near crack tip stress field and are capable to initiate brittle fracture. In addition, the intensities of the coupled modes are significantly influenced by the thickness of the plate, the effects of which are also disregarded in the classical Linear-Elastic Fracture Mechanics.Andrei Kotousov, Paolo Lazzarin and Filippo Bert