MODE I FRACTURE ASSESSMENT OF U-NOTCHED ROCK SPECIMENS USING MTS-FEM CRITERION

In this paper, the fracture behavior of U-notched rock specimens under pure mode I loading has been investigated by means of a new criterion. The proposed approach is based on the maximum tangential stress (MTS) criterion which states that the onset of fracture takes place when the maximum tangential stress at the critical distance from the notch border attains a critical value. Due to the relatively large critical distance in quasi-brittle materials such as rock, the classical MTS criterion which considers only the first or singular terms of the stress series expansion around the notch border cannot provide an accurate estimation for the onset of fracture in rock-type notched samples. Therefore, it is proposed in this paper that the tangential stress component is determined directly form finite element (FE) analysis. Since the proposed approach is a combination of MTS criterion and the FE method, it is named the MTS-FEM criterion. In order to evaluate the MTS-FEM criterion, the experimental results reported in the previous studies for U-notched samples were employed. The comparison between the fracture loads predicted by MTS and MTS-FEM criteria and those reported in the previous studies revealed that the MTS-FEM criterion not only can provide more accurate estimates than the MTS criterion, but also in good agreements with the experimental results (less than 13%).