ARE LARGE DIFFERENTIAL STRESSES REQUIRED FOR STRAIGHT FRACTURE PROPAGATION PATHS

Fracture growth geometries in linear elastic materials are sensitive t o the ratio between the remote differential stress, or T-stress, and t he fracture driving stress. Two mechanically interacting fractures fol low straighter paths for greater values of this ratio. We demonstrate that the degree of curvature that develops between two mechanically in teracting fractures is also controlled by such factors as sub-critical fracture growth and fracture surface roughness. Sub-critical fracture growth limits the development of fracture curvature by decreasing the fracture driving stress needed for propagation. Fracture surface roug hness can affect the development of fracture curvature by limiting the magnitude of the shear displacement discontinuity that can be accommo dated along the fracture. Thus, propagation paths for two mechanically interacting fractures can be quite straight even in the presence of s mall to moderate differential stresses. Consequently, the absence of f racture curvature does not necessarily imply a high differential stres s state.