单轴分级循环加载条件下砂岩疲劳变形特性与损伤模型研究

Fatigue deformation characteristics and damage model of sandstone subjected to uniaxial step cyclic loading

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.

Fatigue deformation damage evolution process and the relationship between stress- strain curve characteristics under step cyclic loading conditions were analyzed through uniaxial step cyclic compression test on two groups of sandstone samples using MTS electro-hydraulic servo testing machine. The theoretical model between axial strain and the number of cycles un- der step cyclic loading conditions was proposed. An evolution equation of damage index which can evaluate the damage extent of rock was established under fatigue conditions. The results show that the theoretical model can be served as failure criterion of rock subjected to step cyclic loading. The correlation coefficient between experimental and theoretical values exceeds 98 ~. The fatigue life can be predicted through the inverse function of the theoretical model. Evolu- tion equation of damage index can measure the level of fatigue damage of rock subjected to fa- tigue loading. Upper limit stress of fatigue cycles is the key factor affecting the fatigue life of rock. As the upper limit stress increase, the fatigue life of rock decreases by geometric pro- gression.