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非均匀应力下含不同缺陷形态砂岩损伤破坏特征及能量演化规律

Damage characteristics and energy evolution of sandstone with defect of different geometric profiles under heterogeneous loads

  • 摘要: 为探索非均匀应力对岩石损伤破坏的影响及分区演化规律, 对含缺陷砂岩在非均匀应力作用下的力学响应特征与能量演化规律进行研究, 剖析非均匀应力作用下岩石的强度与变形特性, 结合声发射特征参数与岩石破坏形态, 深入分析不同缺陷形态砂岩的损伤演化阶段及特征, 并探寻全过程的能量转化机制。研究结果表明, 低应力区域下应力−应变曲线阶段与试样整体曲线高度契合, 砂岩的残余应力波动特征与高、低应力区域曲线高度一致; 砂岩整体承载能力越高, 应力区域间峰值差值越大。高应力区域圆形缺陷砂岩峰值处呈现低应力高变形, 梯形与矩形缺陷砂岩峰值处呈现高应力低变形; 低应力区域初期变形场易交叉, 梯形缺陷砂岩径向变形最大, 圆形缺陷砂岩轴向变形最大、矩形缺陷砂岩最小。高应力区域应变曲线“内收”, 低应力区域“外扩”。矩形和圆形缺陷砂岩声发射振铃计数呈“先增后减再增”趋势, 梯形缺陷砂岩则呈“持续上升、多点突增”趋势, 整体呈“密集−稀疏−再密集”变化特征。初始阶段矩形缺陷形态砂岩产生较多剪切裂纹, 圆形和梯形缺陷砂岩较少, 并随着应力的增加, 3种缺陷形态试样中剪切裂纹呈现增长趋势, 砂岩破裂模式以剪切破坏为主。高应力区域剪切裂纹数量多且易形成连通裂纹, 低应力区域裂纹较少且多为拉伸裂纹。高应力区域“效能”占比高于低应力区域, 低应力区域弹性变形能占比高于高应力区域, 其中含圆形缺陷砂岩最为显著。高应力区域耗散能稳定增长, 低应力区域增长减缓; 耗散能积聚曲线在高应力区域呈“加速、匀速、减速”趋势, 低应力区域耗散能呈“先加速后减速再加速”趋势。研究成果为非均匀应力条件下围岩控制提供了一定的基础。

     

    Abstract: To study the influence of non-uniform stress on rock damage, failure and the evolution law of damage zones, the mechanical response characteristics and energy evolution law of sandstone with defects under non-uniform stress were studied. The results show that the stress-strain curve stage in the low-stress area is highly consistent with the overall curve of the specimen, and the residual stress fluctuation characteristics of sandstone are highly consistent with the curves in the high and low stress areas. The higher the overall bearing capacity of sandstone, the greater the peak difference between stress areas. It is also found that in the high-stress area, circular defect sandstone shows low stress and high deformation at the peak, while trapezoidal and rectangular defect sandstone shows high stress and low deformation at the peak. In the low-stress area, the initial deformation field is prone to intersect, and trapezoidal defect sandstone has the largest radial deformation, circular defect sandstone has the largest axial deformation, and rectangular defect sandstone has the smallest. In the high-stress area, the strain curve contracts inward, while it expands outward in the low-stress zone. The acoustic emission ring count of sandstone with rectangular and circular defects shows a first increasing, then decreasing, and final increasing trend, while that of trapezoidal defect sandstone shows a continuous increase and sudden increases at multiple points, showing an overall dense-sparse-dense change pattern. In the initial stage, sandstone with rectangular defect generates more shear cracks, while sandstone with circular and trapezoidal defects generates fewer cracks. With the increase of stress, the number of shear cracks in the three defect shapes of specimens shows an increasing trend, and the failure mode of sandstone is mainly shear failure. In the high-stress area, there are more shear cracks and they are more likely to form coalesced cracks, while in the low-stress area, there are fewer cracks and they are mostly tensile cracks. The efficiency proportion in the high-stress area is higher than that in the low-stress area, and the proportion of elastic deformation energy in the low-stress area is higher than that in the high-stress area, especially in the specimen with circular defect shape. Energy dissipation in high-stress regions shows a steady increase, while growth in low-stress regions slows. The dissipation energy accumulation curve in high-stress zone shows a sequential trend of acceleration, uniform speed and deceleration trend, while the dissipation energy of the low-stress zone shows a sequential trend of acceleration, deceleration and acceleration trend.

     

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