In order to further study the characteristics of crack evolution in different granites, uniaxial compression acoustic emission experiments were carried out on granites and fine-grained granites. It is found that by comparing the event rate, cumulative event number, energy rate and cumulative energy, the crack initiation ability of fine-grained granite is weaker than that of granite in the unstable crack growth stage, and the brittle character is stronger in the post-peak failure stage. The proportion of high-amplitude AE signals in granite is about twice that of fine-grained granite, and the proportion of high-amplitude AE signals in granite is more, and the damage is more intense. The AF value of fine-grained granite is higher than that of granite before the main fracture occurs, and the fine-grained granite has a higher proportion of tension cracks before the main fracture occurs. It is found that the inflection point of "fluctuation increasing- fluctuation decreasing" can be used as the critical failure precursor point of the sample. The evolution law of different types of AE signals in each stage of the sample is analyzed, and it is found that a large number of low amplitude and medium frequency AE signals appear in the granite in the stable crack expansion stage, indicating that more damage will be accumulated in the granite at this stage.

In order to further study the precursor temporal signals of damage in water-saturated and dry sandstones, as well as the dynamic sensitivity changes of acoustic and thermal signals, uniaxial compression tests were conducted on sandstones with different water content states, with real-time monitoring of internal acoustic emission (AE) signals and surface thermal infrared (TIR) signals. Research has shown that during the damage process of water-saturated and dry sandstones, TIR anomalies appear first, followed by AE anomalies. The time lag between the first appearances of TIR and AE anomalies in water-saturated sandstone is shorter than that in dry sandstone, indicating the detrimental effect of water. This time lag is of great significance for determining the degree of internal and external damage and the precursor of instability failure in rock samples. The order of sensitivity indicators for acoustic and thermal signals in water-saturated sandstone is as follows: combined acoustic-thermal signal > TIR signal > AE signal; for dry sandstone, it is: combined acoustic-thermal signal > AE signal > TIR signal. The sensitivity of the combined acoustic-thermal signal is significantly higher than that of individual acoustic or thermal signals. Therefore, in practical engineering, it is necessary to analyze the coupling of acoustic and thermal signals when analyzing the precursors of instability.