抄録
To examine the fatigue process of granite, fine-grained Westerly granite specimens were subjected to the cyclic loading test at room temperature under uniaxial compression with maximum stress 160MPa, almost 80% of the estimated peak stress, and a series of specimens stressed to six characteristic stages classified by the number of loading cycles were retrieved. The development of microcracks in the tested specimens was observed microscopically and their growth patterns were investigated using the image analysis technique. The results were as follows. With increasing loading cycles, the number and the population of microcracks within the specimen increased. Intragranular cracks generated at the first stage of loading, most of them occurring around the biotite or muscovite grains especially in quartz grains. Many cracks preferentially elongated parallel to the loading direction and grew into transgranular cracks. It was confirmed that during the quasi-stable middle stage microcracks generated and elongated but did not grow into intergranular cracks across the grain boundaries. With further cycles, the newly generated cracks gradually widened, and some of them grew into intergranular cracks. It was estimated that the generation and growth of these intergranular cracks induced rock failure. The decrease in strength was caused by the increase in crack population and preferentially orientated microcracks, and a different mechanism for the failure process of fatigue was indicated compared to monotonic compression.
