单轴循环加卸载作用下红砂岩变形损伤及能量演化

Deformation Damage and Energy Evolution of Red Sandstone under Uniaxial Cyclic Loading and Unloading

利用RYL-600型微机控制剪切流变仪对红砂岩试件开展低频率单轴循环加卸载试验,研究该条件下红砂岩的疲劳变形、损伤特性及能量演化规律.研究结果表明:1)该红砂岩应力上限疲劳破坏门槛值在75%~85%之间,且疲劳寿命随应力上限增加而急剧减少.2)低频单轴循环加卸载条件下红砂岩轴向变形呈现3个阶段,开始阶段应变量较小但增速很大,稳定阶段应变逐步缓慢增长,破坏阶段应变量和应变增速都快速增大;3个阶段中滞回环密集度呈现出典型的疏-密-疏特征,单个滞回环形状表现出“胖-瘦-胖”的发展规律,且其面积随应力上限增加而增大.3)损伤发展过程呈现起始阶段、稳定扩展阶段和加速破坏阶段的3阶段特征;应力上限越高,损伤发展越快;3个阶段中,循环次数占据疲劳寿命最小部分的加速破坏阶段产生绝大部分的损伤增量.4)弹性能随循环次数增加先增大后保持稳定,但临近破坏时因材料弹性减弱而减小;耗散能在循环开始时较大,然后随循环次数增加先减小而后趋于稳定,临近破坏时又急剧增大至近4倍,岩石破坏伴随耗散能的急剧增大.5)岩石内部应力调整反映在滞回环演化中,滞回环面积越大,单次塑性变形越大,损伤程度越高,能量耗散越严重.

Low frequency uniaxial cyclic loading and unloading experiments on red sandstone were carried out to study the fatigue deformation,damage characteristics and energy evolution of red sandstone by using RYL-600 microcomputer controlled shear rheometer.The experiment results are as follows.The threshold value of fatigue failure stress of the red sandstone is between 75%and 85%and the fatigue life decreases sharply with the increase of upper stress.Under the condition of low-frequency uniaxial cyclic loading and unloading,the axial deformation of red sandstone is divided into three stages.In the initial stage,strain is small but grows rapidly;in the stable stage,strain gradually increases slowly;in the near failure stage,strain and strain increment increases rapidly.In the three stages,the ed damage stage.The higher the upper limit of stress is,the faster the damage develops.In the three stages,the accelerated failure stage,which occupies the smallest part of fatigue life,produces the majority of damage increment.The number of elastic energy cycles first increases and then remains stable.However,it decreases with the decrease of material elasticity in accelerated damage stage.The initial value of dissipated energy is large,and then it decreases with the increase of cycle number and then tends to be stable.When it is close to failure,it increases sharply by nearly 4 times,indicating that the rock failure must be accompanied by the sharply increase of dissipated energy.The internal stress adjustment of rock is reflected in the evolution of hysteretic loop.The larger the hysteretic loop area is,the larger the single plastic deformation is,the higher the damage degree is,and the more serious the energy dissipation is.