真三轴不同循环加卸载模式下砂岩的能量演化规律

Energy evolution of sandstone under different cyclic loading and unloading modes in true triaxial mode

  • 摘要: 为阐明不同循环加卸载模式对砂岩能量演化的影响,利用自主研发的TAWZ-5000/3000岩石真三轴试验系统开展不同路径下真三轴循环加卸载试验。通过应力-应变曲线分析砂岩力学特性,得到砂岩弹性能密度、耗散能密度与输入能密度之间的线性函数关系。结果表明:(1)不同循环加卸载模式下,滞回环随最大主应变的增加呈现不同的演化特征;相同模式下,增加循环次数不会改变滞回环的变化趋势。(2)不同路径下岩样的破坏强度和最大主应力峰谷值应变均表现出明显的路径依赖特性。等幅循环加卸载模式下岩石峰值强度最低,其次是分级循环加卸载模式,梯级循环加卸载模式的峰值强度最高。(3)等幅循环加卸载模式下岩样能量密度更大,最大主应力方向输入能密度和耗散能密度初期迅速下降后逐渐趋向平稳,而弹性能密度保持不变;另外2种模式下最大主应力方向输入能密度、弹性能密度和耗散能密度随循环次数的增加呈“正相关”增长趋势。中、小主应力方向的能量密度远小于最大主应力方向。

     

    Abstract: To clarify the impact of different cyclic loading and unloading modes on the energy evolution of sandstone, triaxial cyclic loading and unloading tests were conducted using the self-developed TAWZ-5000/3000 rock true triaxial testing system along different paths. By analyzing the stress-strain curves, the mechanical characteristics of sandstone were evaluated, revealing a linear functional relationship between the elastic energy density, dissipated energy density, and input energy density of the sandstone. The results indicate that: (1) Under different cyclic loading and unloading modes, the hysteresis loops exhibited distinct evolutionary characteristics with an increase in the maximum principal strain; under the same mode, increasing the number of cycles did not change the trend of hysteresis loop variation. (2) The failure strength and peak-to-valley strain of rock samples under different paths showed significant path dependence. The peak strength was lowest in the equal-amplitude cyclic loading and unloading mode, followed by the graded cyclic loading and unloading mode, with the stepped cyclic loading and unloading mode showing the highest peak strength. (3) In the equal-amplitude cyclic loading and unloading mode, the energy density of rock samples was greater, with the input energy density and dissipated energy density in the direction of major principal stress rapidly declining and then stabilizing, while the elastic energy density remained constant; under the other two modes, the input energy density, elastic energy density, and dissipated energy density in the direction of major principal stress exhibited a positive correlation growth trend with an increase in the number of cycles. The energy density in the directions of minor and intermediate principal stresses was significantly lower than that in the direction of major principal stress.

     

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