BEM CALIBRATION OF THE SHORT ROD SPECIMEN FOR FRACTURE-TOUGHNESS TEST OF ROCK

The results of numerical calibration of a standard short-rod rock specimen with a chevron crack used in the ISRM suggested method are reported, where the boundary element method was used to compute compliance, the stress intensity factor based on the compliance and the distribution of the local stress intensity factor along the crack front edge for various crack depths. The local stress intensity factor is never uniform for a straight front edge of the crack. The change of the shape of the front edge during the fracture toughness test was computed for two cases. In the first case, crack growth resistance is independent of crack growth and, in the second case, crack growth resistance increases with crack growth. Based on the results of the calibration, the validity of the ISRM suggested method for the measurement of rock fracture toughness is discussed.