Study on fracture pattern of open surface-flaw in gabbro

A series of experimental studies are carried out to investigate the propagation of an open surface-flaw in gabbro samples under compression load. A new fracture pattern is observed where an anti-wing crack (its growth direction is opposite to that of wing crack) is induced at a distance away from the flaw tip in the region of compression stress zone. The wing crack appears at the later stage. Besides, the stress for crack initiation is strongly affected by the inclined angle α of the pre-existing flaw. The stress for crack initiation decreases when the flaw angle increases (30°≤aα≤ 75°). Besides, the outburst phenomenon always appears at the flaw tips when the flaw angle equals about 45°, which may be an important parameter for the problem of the rock outburst. The initiation angle of the anti-wing crack is between 135° and 145° from the flaw plane. The growth of the anti-wing crack turns to the loading direction when the crack growth length equals about half of the flaw length. The results of acoustic emission (AE) support the observations from the experiments. The anti-wing crack pattern can be observed in all the specimens containing an open surface-flaw. However, the growth mechanisms of the anti-wing crack are not fully investigated up to now. A further study would be carried out in the future.