Analysis on warning signs of damage of coal samples with different water contents and relevant damage evolution based on acoustic emission and infrared characterization

In order to explore warning signs of buckling failure of coal samples of bursting liability with different water contents in a process of damaging these coal samples, coal samples from a coal seam of bursting liability were collected as object of this study. Uniaxial compression tests of naturally watery, naturally water-absorbing and saturated coal samples were conducted respectively. Systems of acoustic emission (AE), average infrared radiation temperature (AIRT) and infrared thermography (IRT) were applied to monitoring. Variables of overall damage and surface damage of coal samples and their evolution law were determined by the accumulative AE energy count and infrared radiation energy respectively to reveal the internal relation between overall damage and surface damage of coal sample with different water contents in condition of uniaxial compression. Research results showed: the higher the water content of a coal sample was, the clearer the temperature difference of abnormal infrared points would be. This indicated that the higher the water content of a coal sample was, the earlier the appearance of its external buckling failure would be than its internal structural buckling failure. Appearance of AE signals of coal samples was earlier than that of abnormal infrared points, while appearance of abnormal infrared points was earlier than that of structural buckling failure. This indicated that internal damage of coal samples appeared earlier than their external damage and the internal buckling failure was earlier than the external buckling failure. Though the growth rate of surface damage was high, surface damage was lower than overall damage on the whole. Compared with surface damage, overall damage was in clear stages with early warning signs. Surface damage is consistent with overall damage. According to comprehensive comparative analysis, the combination of infrared and AE methods could reflect warning signs of structural buckling of coal samples. Appearance of AE signals was earlier than that of abnormal infrared points, indicating warning signs of structural buckling of coal. Appearance of abnormal infrared points is an important basis for prediction of structural buckling of coal.