冷加载循环作用下煤样强度特性研究

为研究煤样强度与冷加载周期、表面裂隙宽度和裂隙体积变化量之间的关系，实验采用液氮作为制冷剂，对水饱和煤样进行1~5周期循环浸泡冷加载，使煤样原生裂隙结构发生损伤，通过拟合多项式揭示周期、表面裂隙宽度和裂隙体积变化量作为损伤因子对裂隙结构的损伤规律，构建损伤判据。结果表明:煤样随着循环冷加载周期的增加，表面裂隙宽度由微观向细观和宏观演化；循环冷加载4个周期为煤样冻裂和抗压的强度极限，2个周期为煤样裂隙饱和水吸附能力极限；冷加载对煤样的原生裂隙结构作用显著，使裂隙在膨胀拉应力作用下发生扩展，同时水结冰体积膨胀，对裂隙结构损伤产生了重要作用。

Study on characteristic of coal sample strength under cyclic cold loading

In order to investigate the relationship of coal sample strength with cold loading cycle, surface fissure width (SFW) and fissure volume variation (FVV), the liquid nitrogen was applied as refrigerant in the test to implement cyclic cold loading on water saturated coal samples for 1 to 5 cycles, which damaged the protogenic fissure structure of coal samples. Through fitting polynomial, the damage mechanism of fissure structure caused by damage factors, which consisted of cycle, SFW and FVV, was revealed, then the damage criterion was built up. The results showed that: with the increase in cycle of cyclic cold loading on coal samples, SFW evolves from micro level to meso and macro level. The limits of frost crack and compressive strength for coal samples emerge after 4 cycles of cyclic cold loading, and the limit of saturated water absorption arrives after 2 cycles. Cold loading plays an important role on the protogenic fissure structure of coal samples, which causes the propagation of fissure under expansive tensile stress. At the same time, the volume expansion during water icing plays an important role in damage of fissure structure.