Analyzing the rules of fracture and damage, and the characteristics of the acoustic emission signal of a gypsum specimen under uniaxial loading

Abstract

In order to study the mechanism of rock bursts in a mined-out area of a gypsum mine, in this paper acoustic emission testing of the uniaxial compression of gypsum and sandstone samples is carried out. The case of rupture of the specimen is observed, and the load axial deformation curve and acoustic emission parameters are obtained for the whole process of specimen rupture. The similarities and differences between the gypsum and sandstone samples are determined in terms of their mechanical properties, their damage evolution laws and frequency band energy distributions, and the instantaneous energy characteristics of their acoustic emission. The results show that the main fracture morphology of gypsum is 'eight'-type, and the macroscopic fracture morphology of sandstone is mainly of partial 'Y'-type and inverted Y-type. The intensity and uniformity of the gypsum and sandstone of the medium are different; because the gypsum is more uniform, it does not show as much variation as sandstone, instead suddenly increasing and decreasing. The maximum value of the damage variable D of gypsum reached 1, but the maximum value of D of the sandstone only reached 0.9. The frequency band of the maximum energy of gypsum and sandstone gradually decreased across the the four stages of rupture, while the maximum energy percentage increased gradually. From the stage where damage gradually increases to the stage of integral fracture of the specimen, the instantaneous energy showed a certain degree of increase. With an increase in the strength of the sample, the maximum energy percentage of the two materials corresponding to each phase gradually increases, and from the stage where damage gradually increases to the stage of integral fracture of the specimen, the value of instantaneous energy obviously increases. The results indicate that gypsum mines will also experience rock bursts, as coal mines do, but the intensity will be different. Therefore, using the three indicators, the frequency band of the maximum energy, the maximum energy percentage, and the maximum instantaneous energy, the rupture of the sample can be predicted, which can be used to improve the accuracy and efficiency of early warning systems for rock bursts in gypsum mines.