Comments on "on the Stability of Shear Cracks and the Calculation of Compressive Strength" by J. K. Dienes

The factor (1/2)(O+I) multiplying 2w appears (o-I) (o-3I) > • (2-•)3⁄4•/2 (l-v) c (1) because the body is assumed to be linearly elastic, and Scr denotes the crack surface (his equation (13), where • is the Poisson ratio, (which Dienes denotes as S in the body of his • is the shear modulus, and 2•c23⁄4 is the "surpaper but as S i in his Appendix A, in which S face energy" of the fracture) seems untenable. It denotes the sum of both the crack surfaces S i implies that O must exceed 3T for the crack to and the external surface S o of the body). Since grow, whereas elementary physical understanding of the frictional work increment is given by the the problem convinces one that a crack of suffivariation of the quantity ciently low surface energy will grow if o is