循环荷载条件下原煤力学性质及损伤演化规律

对原煤试样分别进行了常规加载和循环荷载条件下的单轴和三轴力学强度试验,借助声发射技术,系统研究了单轴循环荷载及三轴循环荷载条件下原煤的损伤演化规律并对比分析。常规循环荷载试验结果显示:从循环初始至结束,煤岩内部损伤过程具有明显的3阶段,即初始损伤阶段,微裂纹扩展萌生稳定增长阶段,裂纹贯通破坏阶段;定量分析了应变峰值、卸载刚度及损伤变量在循环荷载过程中的变化规律,单轴循环试验初始损伤阶段的损伤程度较大,第3阶段损伤变量变化显著;三轴循环试验损伤过程中第1阶段最显著,而在损伤第3阶段,煤样临近破坏时损伤变量略微升高,与单轴试验损伤变量显著增加的情况不同;循环应力上限处声发射现象最强烈,说明循环过程中应力上限时的内部损伤程度最大。分级循环荷载试验结果显示:分级荷载增加初期应变回滞环较密集,声发射现象显著,试样破坏时声发射计数最大;各级循环也具有损伤不同阶段特征,达到损伤稳定阶段的损伤变量近似值与均值压力呈指数型变化关系。

Mechanical properties and damage evolution of coal under cyclic loading conditions

The uniaxial and triaxial strength tests on raw coal samples under cyclic load conditions were conducted using acoustic emission technology to systematically study and compare the damage evolution characteristics under single and triaxial cyclic loading conditions.During the whole process of cyclic loading，the rock internal damage process is divided into three stages，namely the initial damage stage，the micro-crack initiation and evolution stably stage，and the destruction stage.The peak strain，unloading stiffness and damage variable in the process of cyclic loading were quantitatively analyzed.The uniaxial cyclic test shows the most significant damage in the first stage and the triaxial cyclic test also shows significant damage in the first stage，while the third stage is not significant.The upper limit of the cyclic stress shows a stronger acoustic emission phenomenon，indicating the most intense internal damage occurs around the cyclic stress upper limit.Incremental step uniaxial cyclic loading tests show the damage variable under stable damage stage and the mean stress is in an exponential relationship.The damage variable value slightly elevates when approaching destruction under the triaxial cyclic loading condition，which shows a great diversity under uniaxial cyclic loading.