Strain Rate Dependences of Dynamic Fracture Toughness and Fracture Energy of Rocks

This paper considers dynamic rock fracture from the viewpoint of the force and energy limiting criteria formulated from the concepts of the structural-temporal approach. For each limiting criterion set at a given fracture time, the incubation time is calculated as a key constant material characteristic within the proposed approach which depends on the scale and is the main measure of the material response. Experimental literature data on three-point bending are used to discuss the strain rate dependences of rock fracture toughness with varying specimen notch length and fracture work. Using the dynamic fracture of coal and granite as an example, it is shown that the incubation time determined by the force criterion is independent of the specimen notch length. Comparison is made of the marble incubation times obtained from the strain rate dependences of fracture toughness and fracture work.