循环荷载下大孔隙红砂岩的动力响应及损伤研究

为探究循环荷载下不同孔隙率红砂岩的动力特性和损伤规律,采用SHPB冲击实验系统,选取了2组不同孔隙率的红砂岩进行循环冲击实验,分析大孔隙率红砂岩的动力波形,本构曲线及损伤度,得到不同孔隙率红砂岩的变形模量、峰值应力、峰值应变及损伤度的变化规律。结果表明:不同孔隙率的红砂岩试件在循环荷载下的应力时程基本一致,随着循环次数的增加,岩石经历了孔隙闭合-裂隙开展-应力硬化-应变软化直至破坏的阶段,其变形模量和峰值应变呈现出先减小,再增大,再减小的趋势,峰值应力与速度呈正相关的关系。随着循环次数的递增,孔隙率大的岩石的峰值应力下降趋势大于孔隙率小的岩石,并且损伤累积使岩石在冲击破坏前表现出了较明显的塑性特征,不同孔隙率红砂岩的损伤度变化趋势基本是先增大后减小,孔隙率大的岩石累计损伤度大于孔隙率小的岩石,其损伤裂纹基本都是从透射杆端部开始,随着裂纹的产生扩展直至破坏。

Study on dynamic response and damage of red sandstone with large porosity under cyclic loading

In order to explore the dynamic characteristics and damage laws of red sandstone with different porosity under cyclic loading, two groups of red sandstone with different porosity are selected for cyclic impact test by SHPB impact test system. The dynamic waveform, constitutive curve and damage degree of red sandstone with large porosity are analyzed. The law of change of deformation modulus, peak stress, peak strain and damage degree of red sandstone with different porosity were obtained. The results show that under cyclic impact loading, characteristics of stress history are basically the same for red sandstone with different porosity. With the increase of the number of cyclic loads, the rock has gone through four stages which are pore closure, crack development, stress hardening and strain softening to failure. Its deformation modulus and peak strain appears to decreasing first, then increasing, then decreasing. There is a positive correlation between peak stress and velocity. With the increase of the number of cycles, the peak stress of the rock with large porosity decreases more than that of the rock with small porosity, and the damage accumulation makes the rock show a better performance before impact failure, obvious plastic characteristics. The damage degree of red sandstone with different porosity increases first and then decreases, and the cumulative damage degree of the rock with large porosity is greater than that of the rock with small porosity. The damage cracks are generated basically from the end, with the crack generation and expansion until the failure.