砂岩在低频循环荷载作用下的疲劳和损伤特性试验研究

EXPERIMENTAL STUDY OF FATIGUE DAMAGE PROPERTIES OF SANDSTONE SAMPLES UNDER CYCLIC LOADING WITH LOW FREQUENCIES

针对砂岩岩样,探讨围压作用时不同频率轴向循环荷载下的疲劳损伤特性,研究频率对砂岩岩样的疲劳力学性质的影响。采用的试验设备是MTS–815岩石和混凝土试验系统,试验围压分别为2,10和40 MPa,施加的循环荷载频率分别为0.1,1.0,3.0 Hz。岩样为汶川地区的干砂岩,试样平均直径为48.9 mm,高度与直径之比为2∶1。试验结果表明:(1)在相同围压作用下,频率对岩样的残余变形、疲劳刚度和破坏模式有很大影响,频率越高,破坏时的残余轴向应变越大,破坏次数越多,岩样的初始刚度越大;(2)提出的疲劳损伤变量D可以描述岩样在循环荷载作用下的疲劳损伤过程。

The fatigue damage properties of intact sandstone samples subjected to axially cyclic loads with different frequencies at confining stress state were investigated,and influence of frequency on dynamic mechanical features of sandstone was studied. The apparatus employed was the MTS–815 rock and concrete test system,three levels of confining pressure(2,10 and 40 MPa) and three sets of frequencies(0.1,1.0 and 3.0 Hz) were applied. The dry sandstone samples were extracted from Wenchuan with average diameter of 48.9 mm and the ratio of height to diameter of 2∶1. Results demonstrated that:(1) The frequency has a strong influence on residual deformation,fatigue stiffness and failure mode under the same confining pressure. The higher the frequency,the bigger the residual axial strain and the more number of cycles at failure,and the larger the initial stiffness.(2) The damage variable D proposed could describe the fatigue damage process of sandstone samples under dynamic cyclic loading.