Abstract
In order to study the fatigue strength and failure characteristics of coal samples, a series of multilevel cyclic loading tests were carried out. The test results show that: (1) When the confining pressure corresponds to 0, 5 and 10 MPa, the fatigue strength of coal samples at a frequency of 0.5 Hz is slightly larger than that with a frequency of 0.25 Hz. (2) For fatigue failure, the circumferential strain is more sensitive than that of axial strain. (3) In the condition of conventional compression test, it is favorable for larger scale cracks to growth and rapid development when the broken degree of coal samples is low. In the long-term cyclic loading test, it is beneficial to produce small cracks. The coal sample is more broken in this case.
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