轴压影响下砂岩循环冲击力学性质及损伤演化特征

采用能够施加轴压的霍普金森压杆系统对砂岩试样进行循环冲击试验,分析循环冲击过程中试样的应力-应变曲线变化规律,并使用波速测量装置监测单次冲击后试样的纵波波速值,探讨轴压影响下砂岩试样循环冲击损伤演化特征。结果表明,轴压0 MPa、15 MPa、25 MPa、35 MPa时,采用相同速度发射子弹,试样分别在第19次、9次、6次、4次发生宏观破坏。不同冲击次数后试样动态应力-应变曲线形态有所区别,主要体现在峰后曲线斜率、峰值应力等方面。在本次实验所施加的轴压范围内,试样破坏所需的循环冲击次数随着轴压增加而减少,平稳发展阶段累积损伤变量及首次冲击产生的损伤变量值均有所降低。轴压作用改变了试样内部微裂隙闭合或扩展程度,对循环冲击试样累积损伤发展趋势产生显著影响,轴压与循环冲击产生耦合损伤,共同影响岩石动态力学性质。

Mechanical Properties and Damage Evolution Characteristics of Sandstone Under Cyclic Impact with Axial Compression

The cyclic impact tests on sandstone specimens was carried out by using Split Hopkinson Pressure Bar (SHPB) by applying axial compression to analyze the variation law of stress-strain curve of the specimens during the cyclic impact, and the longitudinal wave velocity of the specimens after a single impact was monitored by a wave velocity measuring device to discuss the damage evolution characteristics of sandstone specimens under cyclic impact with axial compression. The results show that when the bullets were fired at the same speed with the axial compression at 0 MPa, 15 MPa, 25 MPa and 35 MPa, respectively, macro fracture can be observed in the specimens at the 19th, 9th, 6th and 4th times of impact. The dynamic stress-strain curves of the specimens after different numbers of impact were different especially in the slope of the curved line after the peak and the peak stress. Within the range of applied axial compression in this experiment, the numbers of cyclic impact required for the specimen damage decreased with the increasing of the axial compression, and both the value of cumulative damage variables at the stable development stage and the damage variables at the first time of impact decreased. Axial compression changes the degree of micro-fracture closure or propagation in the specimen, which has a significant impact on the development of cumulative damage in the specimens under cyclic impact. The coupling damage generated by axial compression and cyclic impact can also affect the dynamic mechanical properties of sandstones.