循环载荷下煤样力学特性和损伤演化规律试验研究

Experimental study on mechanical characteristics and damage evolution law of coal samples under cyclic load

为探索循环应力下煤样的力学特征和损伤演化规律,利用TAW-2000压力机和SH-Ⅱ声发射系统对煤样进行循环载荷试验。结果表明:随着循环峰值应力的增加,循环峰值轴向应变、径向应变和塑性变形均呈线性增长。煤样破碎成多个块体且形状各异。随着循环应力的增大,曲线出现明显的迁移效应。随着循环峰值应力增大,体应变不断增长且呈现离散-密集-离散的特征。通过弹性模量大幅度变化和达到峰值可以一次和二次预判煤样的破断;通过泊松比波动和稳定增长可以一次和二次预判煤样的破断。随着循环应力的增大,声发射计数在不断增大。第7次循环后声发射计数增长较快,煤样进入明显的塑性阶段。循环加卸载前期损伤程度较低,呈现缓慢增长的趋势,当达到塑性分界点时,损伤变量呈现台阶式增长。加载阶段声发射能量增长趋势为先缓慢后快速再极速,卸载阶段声发射能量增长较缓慢且平稳,通过声发射能量的异常增长也可预判煤样即将失稳破坏。加卸载响应比分为典型的4个阶段,整体呈现"U"型变化。

In order to explore the mechanical characteristics and damage evolution of coal samples under cyclic load,using the TAW-2000 press machine and SH-II acoustic emission（ AE） system was used. The cyclic load test results show that： with the increase of coal cycle peak stress,peak cyclic axial strain,radial strain and plastic deformation showed linear growth.The coal sample is broken into many blocks with different shapes.With the increase of cyclic stress,the curve shows obvious migration effect.With the increase of cyclic peak stress,the volume strain increases continuously,the curves are discrete-intensive-discrete. Through the elastic modulus and the peak value large change,the coal sample can be broken at one time and two times,and the coal sample can be broken at one time and two times by the Poisson ratio fluctuation and steady growth.With the increase of the cyclic stress,the AE count increases continuously,and the AE count increases rapidly after a certain point,and the coal sample reach the obvious plastic stage. In the early stage of cyclic loading and unloading,the damage degree is low,showing a slow growth trend.When the plastic boundary point is reached,the damage variable shows a stepwise growth.The loading stage of AE energy growth trend is first slow after fast speed again,the unloading stage of AE energy growth has been relatively slow and steady,the abnormal growth of the AE energy can also predict the coal sample to failure.The loading and unloading response score is typically four stages,showing a U type change overall.