AE Activities and Fatigue Limits on Rocks under Cyclic Compressive Loading

本研究对OGINO凝灰岩、Akiyoshi大理岩和Kimachi砂岩进行了疲劳和单轴压缩试验，并对声发射进行了监测，在单轴压缩试验结果的基础上，利用Kaizer效应确定了3种岩石的屈服应力。最大应力占岩石单轴抗压强度的一定比例，最小应力始终保持在1MPa左右，根据疲劳试验结果估算了岩石的疲劳极限。通过对各种岩石的疲劳极限与屈服应力的比较，发现岩石的疲劳极限并不总是与其屈服应力相对应。因此，为了确定岩石的疲劳极限，必须进行疲劳试验。疲劳试验期间的上限应变行为与蠕变试验期间的上限应变行为相似，并分为三个区域，分别对应于蠕变中的第一、第二和第三蠕变区域。另一方面，当最大应力较高时，声发射事件的累积次数与加载循环次数成正比，然后试样失效。在最大应力较低的情况下，声发射活动变得激烈之前，试样的失败。AE事件累积次数的增长点并不对应于二级区向三级区的过渡点，而是在三级区。

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.