In underground engineering, such as mining engineering and deep tunnel engineering, the rock is often loaded and unloaded repeatedly. The strength of rock under cyclic load is lower than that under static load. To obtain the fracture response of the rock, the three-point bending tests of notched granite beams under cyclic loading and unloading were carried out with Electro-hydraulic Servo Material Test System. The acoustic emission technology was adopted to monitor the acoustic emission events of sample in the process of fracture. It is revealed that the fracture toughness of granite under cyclic loading and unloading is lower than that under static loading. Based on the acoustic emission energy obtained from monitoring, the damage evolution during cyclic loading and unloading was analyzed. The fracture mode of granite samples is analyzed by the RA value-average frequency correlation method. And the Felicity ratio during the loading and unloading cycle was calculated to evaluate the severity of initial damage of the material. It is revealed that Kaiser effect appears only in the elastic deformation stage of cyclic loading unloading bending. The Holmquist–Johnson–Cook damage constitutive model and Weibull distribution were used to establish the heterogeneous granite model. And the three-point bending of the model under cyclic loading and unloading was simulated to disclose the crack growth mechanism of rock. The study may provide some references for rock instability control in geotechnical engineering construction.

中文翻译：

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循环加卸载条件下缺口花岗岩梁断裂特性的试验与数值研究

在地下工程中，如采矿工程、深部隧道工程，岩石经常反复装卸。循环荷载作用下岩石的强度低于静荷载作用下的强度。为获得岩石的断裂响应，利用电液伺服材料试验系统对带槽口的花岗岩梁进行了循环加卸载的三点弯曲试验。采用声发射技术监测样品在断裂过程中的声发射事件。结果表明，花岗岩在循环加载和卸载下的断裂韧性低于静态加载下的断裂韧性。基于监测得到的声发射能量，分析了循环加载和卸载过程中的损伤演化。采用RA值-平均频率相关法分析花岗岩样品的断裂方式。并计算了装卸循环过程中的 Felicity 比率，以评估材料初始损坏的严重程度。结果表明，凯撒效应仅出现在循环加载卸载弯曲的弹性变形阶段。使用 Holmquist-Johnson-Cook 损伤本构模型和 Weibull 分布建立非均质花岗岩模型。并对模型在循环加载和卸载下的三点弯曲进行了模拟，揭示了岩石裂纹扩展机制。该研究可为岩土工程施工中岩石失稳控制提供一定的参考。并计算了装卸循环过程中的 Felicity 比率，以评估材料初始损坏的严重程度。结果表明，凯撒效应仅出现在循环加载卸载弯曲的弹性变形阶段。使用 Holmquist-Johnson-Cook 损伤本构模型和 Weibull 分布建立非均质花岗岩模型。并对模型在循环加载和卸载下的三点弯曲进行了模拟，揭示了岩石裂纹扩展机制。该研究可为岩土工程施工中岩石失稳控制提供一定的参考。并计算了装卸循环过程中的 Felicity 比率，以评估材料初始损坏的严重程度。结果表明，凯撒效应仅出现在循环加载卸载弯曲的弹性变形阶段。使用 Holmquist-Johnson-Cook 损伤本构模型和 Weibull 分布建立非均质花岗岩模型。并对模型在循环加载和卸载下的三点弯曲进行了模拟，揭示了岩石裂纹扩展机制。该研究可为岩土工程施工中岩石失稳控制提供一定的参考。使用 Holmquist-Johnson-Cook 损伤本构模型和 Weibull 分布建立非均质花岗岩模型。并对模型在循环加载和卸载下的三点弯曲进行了模拟，揭示了岩石裂纹扩展机制。该研究可为岩土工程施工中岩石失稳控制提供一定的参考。使用 Holmquist-Johnson-Cook 损伤本构模型和 Weibull 分布建立非均质花岗岩模型。并对模型在循环加载和卸载下的三点弯曲进行了模拟，揭示了岩石裂纹扩展机制。该研究可为岩土工程施工中岩石失稳控制提供一定的参考。