Effect of Anisotropy on Mixed Mode Crack Extension Behavior in Granite

This paper describes an experimental investigation of the effect of anisotropy on mixed mode crack propagation in granite by the use of asymmetric three-point bend specimens. Acoustic emission techniques were employed during the fracture tests to detect the onset of kinked crack extension. In order to characterize the fracture strength anisotropy, uniaxial tension tests and Brazilian tests were conducted, and fracture strength was measured as a function of direction with respect to the anisotropy. Based on the fracture strength data, the results of the mixed mode fracture tests were analyzed with regard to the fracture angle by means of linear elastic fracture mechanics. It is shown that the concept of a critical tensile stress at a characteristic distance, modified to account for the anisotropy of fracture strength, can explain the observed extension behaviors of mixed mode cracks.