An experimentally verified criterion for propagation across unbounded frictional interfaces in brittle, linear elastic materials

Understanding how a propagating fracture interacts with existing fractures, lithologic boundaries and other material interfaces is essential to the interpretation of fracture network geometries. In this paper, a first order analysis of the stresses near a mode I fracture impinging upon a frictional interface oriented normal to the growing fracture results in a simple criterion that predicts whether a growing fracture will terminate at or cross the interface. The analysis uses the linear elastic fracture mechanics solution for the stresses near a fracture tip to determine the compressive stress required to prevent slip along the interface at the moment when the stress on the opposite side of the interface is sufficient to initiate a fracture. A series of experimental investigations designed to assess the conditions required for crossing are presented and shown to be consistent with the criterion. Using data from previously published experiments, the criterion is shown to accurately predict the occurrence of compressional crossing in nine different brittle materials including three types of synthetic materials and six types of natural rock.