Abstract: International Society for Rock Mechanics ( ISRM ) proposed in 1995 a new type of rock fracture toughness specimen——cracked chevron notched Brazilian disk ( CCNBD ), the previous analytical and numerical studies of the dimensionless stress intensity factor, which is an important mechanicel parameter, does not take into account the effects of finite notch width. Since the minimum chevron notch width is limited by the size of the cutting wheels used to produce it and can not be zero, as the specimen size get small enough, the notch width would become large in relation to the sample size. Our 3D BEM(Boundary Element Method) calculation shows that the larger the notch width is, the bigger the error makes for the dimensionless stress intensity factor. To the standard CCNBD specimen suggested by ISRM, this paper determines the minimum dimensionless stress intensity factor to be 0.954 which is 13.6 % larger than the value 0.84 given by ISRM; and the tread of the curve is changed when the crack is short, this could make the failure of the experiment. We recommend that a full 3D numerical analysis taking into effect of the notch width to be done whenever determine the dimensionless stress intensity factor.

Key words: cracked chevron notched Brazilian disc(CCNBD), dimension stress intensity factor, fracture Toughness, notch width, FRANC3D