BEM analysis of a cylindrical three-point bend specimen with a chevron crack for fracture toughness test of rock

The stress intensity factor along the periphery of a chevron crack in a cylindrical three point bend specimen (CB) is evaluated by BEM for the establishment of a rock fracture toughness test using CB specimens. So far, in the test, the stress intensity factor is assumed to be constant along the front edge of the crack and is evaluated by the compliance method. It is revealed by the present analysis that the stress intensity factor takes a minimum value at the center of the front edge so that the crack growth during the fracture toughness test makes the front edge of the crack concave. It is also shown that the stress intensity factor evaluated by the compliance method is larger than that of the concave crack with a homogeneous distribution of the stress intensity factor along the front edge. This implies that the fracture toughness test leads to overestimation.