Energy criterion of in-plane fracture propagation in geomaterials with rotating particles

Abstract

In-plane propagation of tensile fractures (Mode I cracks), shear fractures/bands (Mode II cracks) and compaction bands (Mode I anticracks) is routinely observed in geomaterials in the presence of high compressive stress. While the in-plane propagation of tensile cracks is expected, the mechanics of inplane propagation of shear cracks is not clear. We propose a unified criterion of in-plane growth of these types of fractures based on the assumption that the grains are able to undergo independent relative rotations. The relative rotations break the binder between the grains even in the presence of high compressive stress. An asymptotic model is developed for long fractures showing that the energy release rate is controlled by the conventional Mode I and II stress intensity factors. The proposed unified criterion of fracture growth compares the energy release rate with the specific fracture energy consisting of three terms: the fracture energy of the bonds (present in all three types of fracture), specific energy of shear (for shear fractures/bands) and specific energy of compaction (for compaction bands). We developed estimates for all three components of the specific fracture energy.