Effect of loading rate on Kaiser effect of sandstone under tensile stress
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Abstract:
The paper aims at recognizing the Kaiser effect characteristics of rock tensile failure process with the change of loading rate and acquiring the mechanism and criteria. Firstly, the relationship between Kaiser point stress, loading rate, acoustic emission (AE) parameters were studied. Then, the RFPA2D software was used to simulate the test process from the perspective of micro-crack development. The mechanism of the difference between the Kaiser effect induced by the change of loading rate during the test was analysed. Finally, the spectral characteristics of the Kaiser point under tensile stress was obtained by wavelet analysis and the judging criteria for macroscopic phenomena was quantified. The results show that the KE characteristic parameters of sandstone positively correlated with loading rate. There are great differences in Kaiser point of each parameter, especially in that of the cumulative energy. The faster the loading speed, the weaker the regularity of the rock crack propagation path. Changes of the trend of the crack competition results in the uniformity of the cracking energy distribution, which affect the obviousness and identification accuracy of the Kaiser effect. The frequency of the Kaiser point is mainly concentrated within the range of 0 kHz to 312.50 kHz with normal distribution, accounting for 41.73%, and the maximum value distributes around 300 kHz. The frequency range of Kaiser point shows a constant tightening trend with the change of loading rate, which can be used as the basis for reasonable selection of experimental loading rate for different rocks. The results can provide reference for the stability monitoring, early warning and forecasting work of rock mass roof or compartment rock under bending stress.
