Experimental and Theoretical Study of Fracture Paths in Brittle Cracked Materials Subjected to Pure Mode II Loading

Crack growth path was investigated experimentally, numerically and theoretically using two test specimens subjected to pure mode II loading. The specimens were (a) the center cracked circular disc (CCCD) specimen subjected to diametral compression often called the Brazilian disc and (b) the diagonally loaded square plate (DLSP) specimen containing inclined center crack and subjected to pin loading. A few CCCD and DLSP specimens made of two brittle materials (i.e. marble rock and PMMA) were tested under pure mode II conditions. It was observed that the fracture initiation directions and the fracture paths for the tested specimens differed significantly and grew in two different trajectories. However, it was shown that the experimentally observed fracture paths for both specimens can be predicted theoretically very well by using the incremental crack growth method. Several finite element analyses were performed to simulate the whole fracture trajectories of the tested CCCD and DLSP specimens. At each increment, the direction of fracture initiation for the tip of growing crack was determined using the fracture parameters (i.e. stress intensity factors and T-stress) based on the modified maximum tangential stress (MMTS) criterion. The main difference in the fracture trajectory was found to be related to the magnitude and sign of the fracture parameters (which depend strongly on the specimen geometry and loading configuration) and also the type of tensile or compressive loading in the CCCD and DLSP samples.