AE Activities and Fatigue Limits on Rocks under Cyclic Compressive Loading

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In this study, fatigue and uniaxial compression tests were done on OGINO tuff, Akiyoshi marble and Kimachi sandstone with monitoring AE (acoustic emission) activity.The yieldind stresses of three kinds of rocks are determined by Kaizer's effect, based on the results obtained with the uniaxial compression tests. Also, the fatigue limits of the rocks are estimated from the results obtained with the fatigue tests where the maximum stress takes a prescribed percentage of the uniaxial compressive strength of the rock and the minimum stress alwasys keeps about 1MPa. From the comparison of the fatigue limit with the yielding stress on each rock, it is found that the fatigue limit of the rock doesn't always correspond to its yielding stress. Accordingly, it is necessary to perform the fatigue tests in order to determine the fatigue limit of a rock.The behavior of the upper strain during fatigue tests is similar to that during creep test and is classified into three regions that correspond to primary, secondary and tertiary creep regions in creep.On the other hand, as the maximum stress is higher, the cumulative number of AE events is proportional to the number of the loading cycles and then specimen is failed. In case that the maximum stress is lower, AE activity becomes vigorous just prior to the failure of the specimen. The increasing point of the cumulative number of AE events doesn't correspond to the transitional point from secondary to tertiary region, and is found out in tertiary region.