煤样循环加卸载的滞回环及其力学特性

Hysteresis loop and mechanical characteristics of coal sample during cyclic loading and unloading

为研究煤样循环加卸载中滞回曲线的演化规律,利用RMT-150型岩石伺服试验机对煤样进行循环加卸载实验,分析循环加卸载实验获得的应力-应变曲线、循环次数与滞回环面积、残余变形、阻尼比、动态弹性模量。研究结果表明:循环加卸载轴向应力-应变曲线在荷载卸载处弹性变形较快,塑性变形较小;加载曲线ε1随着σ1变化趋势不明显,卸载曲线ε1随着σ1变化趋势较为平缓;随着循环次数增加,单个循环的能量耗散在增加,累计耗散也在逐渐增加;煤的阻尼比与循环次数呈负相关关系,动态弹性模量与循环次数呈正相关关系,且两者前期变化速率较快,推测前期煤样损伤速度较快;单个循环残余变形先减小后增大,增大起始值可作为判断煤样发生损伤破坏的损伤阈值。

This paper describes an investigation into the evolution law of hysteretic curve during cyclic loading and unloading of coal samples by running cyclic loading and unloading experiments on coal samples using RMT-150 rock servo testing machine and analyzing the stress-strain curve,number of cycles,area of hysteretic loop,residual deformation,damping ratio and dynamic elastic modulus obtained from cyclic loading and unloading tests.The results show that there is a faster elastic deformation of the axial stress-strain curve under cyclic loading and unloading,and a smaller plastic deformation at load unloading.The loading curveε1 has no obvious trend withσ1,while the unloading curveε1 shows a gentle trend withσ1.The dissipated energy increases with the increase of the number of cycles,with the energy dissipation of a single cycle increasing and the cumulative dissipation gradually increasing.The damping ratio of coal has a negative correlation with the number of cycles,while the dynamic elastic modulus has a positive correlation with the number of cycles.The change rate of both is faster in the early stage,so it is speculated that the damage rate of coal sample is faster in the early stage.The single cyclic residual deformation sees an initial decrease and a subsequent increase,and the increase of the initial value can be used as the damage threshold value to judge the damage of coal sample.