Abstract This study is aimed at exploring the effect of the lower limit of cyclic stress (LLCS) on the loading and unloading failure process of sandstone. First, cyclic loading and unloading experiments were performed on sandstone samples under different stress paths. Furthermore, the variations of mechanical properties and acoustic emission (AE) signals of samples during cyclic loading and unloading were analyzed. The results show that the equivalent residual strain produced by a single loading and unloading with a low LLCS is larger than the residual strain produced by that with a high LLCS. Under cyclic loading and unloading, the loading elastic moduli of samples grow as the number of cycles increases. In the loading failure stage, the loading elastic modulus under a high LLCS is greater than that under a low LLCS. In the 2nd and 3rd stages, the AE counts, main frequency signals and high-amplitude signals generated under loading and unloading with a high LLCS all account for smaller proportions than those generated under loading and unloading with a low LLCS. Low-frequency and high-amplitude signals appear in both the third stage and the loading failure stage under a low LLCS, while they only appear in the loading failure stage under a high LLCS. In the 2nd and 3rd stages, the b value first grows and then decreases under a low LLCS, while it keeps rising under a high LLCS. A high LLCS is conducive to suppressing the axial deformation of sandstone and reducing the amount of damage caused during a single loading and unloading. This study boasts theoretical reference value for the monitoring of coal rock stability and the prevention of dynamic disasters.

中文翻译：

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循环加卸载循环应力下限对砂岩力学性能及声发射的影响研究

摘要 本研究旨在探讨循环应力下限（LLCS）对砂岩装卸破坏过程的影响。首先，对不同应力路径下的砂岩样品进行了循环加载和卸载实验。此外，还分析了样品在循环加载和卸载过程中的力学性能和声发射（AE）信号的变化。结果表明，低LLCS的单次加载和卸载产生的等效残余应变大于高LLCS的残余应变。在循环加载和卸载下，样品的加载弹性模量随着循环次数的增加而增加。在加载失效阶段，高LLCS下的加载弹性模量大于低LLCS下的加载弹性模量。在第二和第三阶段，高LLCS加载和卸载时产生的AE计数、主频信号和高幅度信号都比低LLCS加载和卸载时产生的比例要小。低频高幅信号出现在低LLCS下的第三阶段和加载失败阶段，而它们只出现在高LLCS下的加载失败阶段。在第 2 和第 3 阶段，b 值在低 LLCS 下先增长然后下降，而在高 LLCS 下则保持上升。较高的LLCS有利于抑制砂岩轴向变形，减少单次装卸过程中的损伤量。该研究对煤岩稳定性监测和动力灾害防治具有理论参考价值。高LLCS加载和卸载时产生的主频信号和高幅度信号都比低LLCS加载和卸载时产生的比例要小。低频高幅信号出现在低LLCS下的第三阶段和加载失败阶段，而它们只出现在高LLCS下的加载失败阶段。在第 2 和第 3 阶段，b 值在低 LLCS 下先增长然后下降，而在高 LLCS 下则保持上升。较高的LLCS有利于抑制砂岩轴向变形，减少单次装卸过程中的损伤量。该研究对煤岩稳定性监测和动力灾害防治具有理论参考价值。高LLCS加载和卸载时产生的主频信号和高幅度信号都比低LLCS加载和卸载时产生的比例要小。低频高幅信号出现在低LLCS下的第三阶段和加载失败阶段，而它们只出现在高LLCS下的加载失败阶段。在第 2 和第 3 阶段，b 值在低 LLCS 下先增长然后下降，而在高 LLCS 下则保持上升。较高的LLCS有利于抑制砂岩轴向变形，减少单次装卸过程中的损伤量。该研究对煤岩稳定性监测和动力灾害防治具有理论参考价值。