Experimental analysis of mixed mode crack propagation in brittle rocks: The effect of non-singular terms

The fracture behavior of Neyriz marble is investigated both experimentally and theoretically by using two different test configurations: (1) the center cracked circular disk specimen subjected to mode I loading, and (2) the edge cracked triangular samples under mixed mode loading. The experimental results show that there is a noticeable difference between the values of mode I fracture resistance obtained from these two test configurations. The aim of this paper is to justify this difference by using a modified maximum tangential stress criterion which takes into account the effects of non-singular stress terms (T-stress, A3 and B3) in addition to the singular terms. The same criterion is then extended to estimate the mixed mode fracture resistance of triangular specimen from the mode I fracture resistance obtained from the circular specimen. It is also shown that the criterion provides better estimates for the experimental data when uses A3 in the calculation of the fracture process zone length.