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利用MTS815电液伺服试验机对两组砂岩试样进行了单轴分级循环加卸载试验,分析了分级循环加卸载应力-应变曲线特征和分级循环加卸载下岩石疲劳损伤演化过程,建立了循环加卸载条件下轴向应变与循环数目之间的理论模型,并推导了评价岩石损伤程度的损伤变量演化方程.结果表明:理论模型可以作为岩石循环加卸载条件下的破坏准则,试验结果与理论值之间相关度超过98%,同时,其逆函数可以实现对岩石疲劳寿命的预测;疲劳损伤演化方程可以衡量循环加卸载过程中疲劳损伤的发展水平;疲劳循环上限应力值是决定岩石疲劳寿命的关键因素,随着上限应力的提高,岩石的疲劳寿命呈现几何级数下降.
The MTS815 electro-hydraulic servo testing machine was used to uniaxially graded cyclic loading and unloading test on the two sandstone samples. The characteristics of stress-strain curve of cyclic loading and unloading and the evolution of fatigue damage under graded cyclic loading and unloading were analyzed. The theoretical model between the axial strain and the number of cycles under unloading conditions is deduced and the evolution equation of the damage variables is deduced.The results show that the theoretical model can be used as the failure criterion under the cyclic loading and unloading conditions and the experimental results are in agreement with the theoretical values The correlation coefficient is more than 98%. Meanwhile, the inverse function can predict the fatigue life of rock. The fatigue damage evolution equation can measure the development level of fatigue damage in cyclic loading and unloading process. The upper fatigue limit value of fatigue cycle determines the fatigue life of rock As the key factor, with the increase of the upper stress, the fatigue life of rock shows a geometric decline.