In order to examine the fatigue process of granite, a series of Westerly granite specimens were subjected to a cyclic loading test under the uniaxial compression with maximum 140 and 160MPa at room temperature. The development of microcracks within the specimens stressed to different characteristic stages was observed microscopically and their growth patterns were analyzed using image analysis technique. As a result, with increasing loading cycles, the number and the population of microcracks within the specimen increased. At the first stage of loading, many intragranular cracks generated. During the quasistable middle stage, many microcracks preferentially elongated parallel to the loading direction and grew into transgranular cracks. With further loading, cracks gradually widened, and some of them grew into intergranular cracks. It was estimated that the generation and growth of these intergranular cracks induced the rock fatigue failure.
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