Comments on chevron bend specimen for determining fracture toughness of rock

Based on a number of tests on different rocks, Suggested Methods for Determining the Fracture Toughness of Rock (SMs) was reviewed. The advantages of SMs are obvious, but some problems are also discovered. A serious one is that the nonlinear corrected fracture toughness of chevron bend specimens, K C CB , is less than the uncorrected one, K CB , for hard rock like granite, marble and others. The reason is discussed and the proposal is given.