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In order to study the influence of loading mode and impact velocity on coal crack propagation law, asymmetric semi-circular bend specimens were used to develop test and numerical simulation with multiple impact speeds under three loading modes of mode Ⅰ, mode II and mixed mode Ⅰ-Ⅱ under impact loading. The effects of loading mode and impact velocity on the dynamic fracture propagation process, crack initiation time and failure form of coal samples were studied. The results show that the crack of coal sample is linear under mode Ⅰ dynamic loading; under mode II and mixed mode Ⅰ-Ⅱ loading, the crack is in the form of a curve extending to the upper left; under three different loading modes, the crack initiation time of coal sample decreases with the increase of impact velocity, and its influence gradually weakens, the crack initiation time of coal samples under mode II loading is significantly longer than the other two loading methods; the destruction degree of coal samples increases with the increase of impact velocity, the impact of mode Ⅰ loading is small, and the mixed mode Ⅰ-Ⅱ and mode II loading is large.

Uniaxial compression was performed on frozen and untreated frozen coal samples under natural and natural saturated conditions. The strength and deformation characteristics of coal samples were analyzed, and the AE characteristics and damage evolution were analyzed during the loading process. The result shows that the compressive strength of natural and saturated coal samples after low-temperature freezing decrease by 13.93% and 25.02%, respectively. The deformation characteristics and hit rate evolution are basically unchanged, but the slope of the stress-strain curve decrease during the compaction stage. The maximum hit rate increases by 10.20% and 22.45%, respectively. The damage evolution of coal samples in the three conditions can be divided into initial damage stage, slow damage stage, fast damage stage and post-peak damage stage, but the post-peak damage stage is significantly shortened after low-temperature freezing treatment. The damage evolution of coal samples at the peak load is obviously different after low temperature freezing treatment, and it rises in multiple steps in the natural state, while it rises in a single step after freezing treatment. The damage grows faster, the corresponding damage is more severe, and the coal sample is more broken.