低温岩石冲击破碎分形特征与断口形貌分析

通过霍普金森压杆（SHPB）动态冲击试验，研究负温状态下红砂岩的动态力学性能，分析不同负温对岩石强度性能、分形维数及耗散能的影响，并结合微观断口形貌剖析较低负温下岩石动态力学性能劣化的原因.研究表明，较低的负温会使红砂岩出现"冻伤"，在高应变率加载下岩石会迅速丧失承载能力，动态力学强度急剧下降，这与静载实验中岩石强度随温度降低逐渐增大的趋势有着较大的差异；冻结岩石试件的耗散能W_L与分形维数D呈正相关性，且与宏观破坏特征有着密切的联系，即耗散能越大，岩石破碎越严重，相应分形维数也越大，但分形维数与耗散能的增速比存在阈值；断口形貌分析结果显示，较低的负温会使红砂岩内部组成物质间界面处生成大量裂纹，这些裂纹尖端塑性变形能力差，在高应变率加载下极易失稳扩展发生低应力脆性破坏，而胶结物由于组成矿物成分复杂更易受负温影响，因此在动荷载和负温双重作用下往往是胶结物处先产生破坏，进而引起红砂岩整体破裂. 

Study on Fractal Characteristics and Fracture Mechanism of Frozen Rocks

Through the dynamic impact test of pressure bar (SHPB), the dynamic mechanical properties of red sandstone under negative temperature were studied, and the influences of different negative temperature on rock strength properties, fractal dimension and dissipated energy were analyzed, and the reasons for the deterioration of rock dynamic mechanical properties under low negative temperature were analyzed in combination with micro-fracture morphology.The research shows that low negative temperature will cause "frostbite" of red sandstone. Under high strain rate loading, the rock will quickly lose its bearing capacity and its dynamic mechanical strength will drop sharply.The dissipated energy W_L of frozen rock specimen is positively correlated with the fractal dimension D, and closely related to the macroscopic failure characteristics. In other words, the greater the dissipated energy is, the more seriously the rock is broken, and the greater the corresponding fractal dimension is.Fracture morphology analysis shows that the lower negative temperature can make the red sandstone interface between internal material generate a large number of cracks, the crack tip poor, to instability under high strain rate loading low stress brittle fracture the composition of cement more susceptible to negative temperature effect, so the dynamic load and negative temperature cement, cause the collapse of the red sandstone as a whole.