围压条件下砂岩循环冲击损伤的力学与超声分析

采用带围压装置的φ100mm霍普金森压杆系统，对砂岩试样进行了单轴冲击和4MPa、20MPa围压条件下的循环冲击试验，并对每次冲击前后的砂岩试样进行超声纵波检测，分析了砂岩在冲击荷载循环作用下的应力、应变特征，定义了砂岩试样的屈服-弹性比用以描述围压下试样应力应变曲线的弹塑性特征，采用纵波波速定义了砂岩试样的冲击损伤并分析了循环冲击试验中砂岩试样纵波波速和应力应变之间的关系。分析发现：在围压作用下，应力－应变曲线呈现典型的弹塑性特征。随着冲击荷载循环作用次数的增加，砂岩试样屈服应力、峰值应力降低，屈服应变、峰值应变增加。随着循环冲击作用次数的增加，砂岩试样的应力、应变特征与纵波波速之间存在良好的相关关系。较低围压状态下累计损伤度明显高于较高围压下砂岩的累积损伤，砂岩循环冲击损伤具有明显的围压效应。研究结果对地下工程的建设和防护有一定的指导意义。

Mechanical and ultrasonic analysis on damage of sandstone under cyclical impact loading with confining pressure

Based on a φ100-mm-diameter split Hopkinson pressure bar with confining pressure apparatus, cyclical impacting with confining pressure of 4 MPa and 20 MPa for sandstone specimens were performed as well as uniaxial impact tests. Meanwhile, the ultrasonic longitudinal wave test was executed before and after each impact. The stress-strain properties of sandstone under cyclical impact were analyzed, whose relationship with longitudinal wave velocity (Vp) in sandstone was analyzed based on impact damage defined by Vp as well. The yield-elastic-ratio was defined to analyze the elastic-plastic characteristics of sandstones under confining pressure. The results show that, the stress-strain curves under confining pressure present a typical elastic-plastic feature. With the increase of cyclical impact times, yield stress and peak stress of sandstone sample reduce while yield strain and peak strain increase. The accumulative damage under lower confining pressure is apparently higher than that under higher confining pressure. The cyclical impact damage of sandstone shows an obvious confining pressure effect. Results of this paper have a guiding significance to the underground construction and protection.