循环荷载作用下石膏质岩的疲劳特性试验研究

 利用MTS 815岩石力学测试系统、声发射系统、环境扫描电镜开展石膏质岩循环荷载作用下的疲劳试验，探讨循环荷载条件对其疲劳损伤特性的影响。结果表明：石膏质岩循环荷载作用下的疲劳损伤特征明显，塑性特性显著。其疲劳试验的应力–应变全过程曲线具有如下形状特征：加载曲线可分为“近线性”的弹性特征段和“呈压扁状”的塑性特征段，塑性特征段滞后效应明显，卸载曲线呈现近线性特征。循环荷载条件对石膏质岩疲劳损伤特性影响显著，疲劳试验过程的声发射信息演化规律及微观结构变化特征能够较好地揭示其疲劳损伤演化过程及宏观破裂特征：循环应力水平高、上限应力大、加载频率低，疲劳试验的应力–应变全过程曲线越饱满疏松、加卸载的滞回环面积越大，声发射信息越强烈而集中、声发射率指标越高，试样的疲劳损伤速率快，每次循环产生的塑性应变量大，微观结构越破碎，试样的疲劳寿命越短。

Experimental study of fatigue characteristics of gypsum rock under cyclic loading

The fatigue tests of gypsum rock were conducted using the dynamic test system MTS 815，acoustic emission system and environmental scanning electron microscope to investigate the impact of cyclic loading on the fatigue damage characteristics of gypsum rock. The shapes of cyclic stress-strain curves of gypsum rock are different from ones of other rocks. The loading curves can be divided into a nearly linear segment with elastic characteristics and a plastic characteristics segment with depressed shapes，which show that the strains lag behind the stresses. The unloading curves exhibit largely the elastic characteristics as the curve shapes are approximately linear. The cyclic loading conditions have obvious influence on the fatigue damage properties of gypsum rock. The damage process and the macroscopic failure characteristics were revealed from the AE information and microstructure characteristics. Under the higher stress level，the larger stress upper limit and the lower loading frequency，the cyclic stress-strain curves are sparser with the larger areas of hysteretic loop in each cycle and the more AE information occur with higher AE rates. In this case，the fatigue damage rate is higher，the plastic strains are larger and the more microstructures are broken in each cycle.