基于NSCB冲击试验的不同层理间距砂岩能量演化及损伤特性

Energy evolution and damage characteristics of sandstone with different bedding spacing based on NSCB impact test

采用分离式霍普金森压杆试验系统(SHPB),对层理间距6、8、10 mm的直切槽半圆砂岩试件(NSCB)进行动态冲击试验,利用高速相机记录其破坏形态,分析砂岩在不同层理间距条件下的应力、应变响应特征,能量演化特性以及各阶段的能量演化持续时间,并对其损伤特性进行分析。利用离散格子弹簧模型(DLSM)模拟不同层理间距条件下砂岩试件的动态断裂过程,分析其层理间岩石基质的应力、应变、能量演化及损伤特性,并根据动能演化曲线分析其总动能和损失动能耗散情况。结果表明:砂岩动态断裂形态和应力、应变特性受层理间距改变影响明显。当层理间距增大时次生裂纹减少,裂纹扩展速度增大,同时应力、应变峰值增大。能量演化各阶段持续时间均随裂纹扩展速度增大而缩短,可释放弹性应变能峰值随层理间距增大而减小,总吸收能和耗散能峰值则不断增大。层理间距较大时,损伤曲线增长速率在前期较大,后期衰减减小,层理间岩石基质越远离切缝中线,后期损伤累积速度衰减明显。层理间岩石基质的应力、应变及能量演化曲线峰值随层理间距增大而降低,其相关性随岩石基质远离切缝中线而减弱。

In this study,the split Hopkinson pressure bar test system(SHPB)is used to carry out dy⁃namic impact tests on straight⁃cut semicircular sandstone specimens(NSCB)with bedding spacings of 6 mm,8 mm and 10 mm,and a high⁃speed camera is used to record the failure pattern and analyze the sandstone.The stress and strain response characteristics,energy evolution characteristics and the energy evolution duration of each stage are analyzed under different bedding spacing conditions,and the damage characteristics are analyzed.The discrete lattice spring model(DLSM)was used to simulate the dynamic fracture process of sandstone specimens under different bedding spacing conditions,and the stress,strain,energy evolution and damage characteristics of the rock matrix between the beddings are analyzed,and the total kinetic energy is explored according to the kinetic energy evolution curve and loss of kinetic energy dissipation.The results show that the dynamic fracture morphology and stress and strain characteristics of sandstone are significantly affected by the change of the bedding spacing.The secondary cracks decrease with the increase of bedding spacing;the stress and strain peaks increase with the crack propagation speeding up.The duration of each stage of energy evolution decreases with the in⁃crease of crack propagation speed;the peak value of releasable elastic strain energy decreases with the increase of bedding spacing,and the peak value of total absorbed energy and dissipation energy increases continuously.When the interlayer spacing increases,the growth rate of the damage curve is higher in the initial stage,while the attenuation decreases in the later stages.The peak values of stress,strain and en⁃ergy evolution curves of the rock matrix between beddings decrease with the increase of the bedding spacing,and their correlations weaken as the rock matrix moves away from the centerline of the kerf.