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Peculiarities of Elastic Waves Generated by Fatigue Tensile Fractures

In the case of fracturing of rocks in subcritical stress state, the stress release due to fracturing could be accompanied by stress increase near the fracture tips, so the rock deformation near the tips could also generate elastic waves (so called "stopping-phase"). Results of experimental modeling of elastic wave generations by fatigue tensile fractures are considered. The model sample consisted of elastic layer made of rubber and fragile layer made of paraffin, the layers were bounded. The elastic layer was stretched and fixed, so the fragile layer was under static tension and started fracturing by tensile fractures. First fractures appeared in visually intact material, later fractures were preceded by a cloud of small "micro" fractures. The fracturing generated elastic waves, which had two components: one corresponded to fracturing of the fragile layer and had characteristic frequency 5-10 kHz; another one had frequency 100-300 Hz, opposite onset and corresponded to tension of elastic layer. It was concluded that tensile fractures in stressed rocks could be considered as a kind of a double-source of elastic waves: one source is the fracture itself, another source is an area of deformations due to stress increase in the vicinity of the fracture tips.