动静组合加载下长径比对岩样峰值应力与破坏形态影响研究

Study on the influence of aspect ratio on peak stress and failure mode of rock samples under the combined dynamic and static loading

为了探究动静组合加载条件下岩样长径比对其强度及破坏形态的影响,先基于岩石动力学理论,阐释了SHPB试验中应力波传播的基本规律。随后,采用ANSYS/LS-DYNA有限元软件,对6组不同长径比试样开展了动静组合加载数值模拟,深入分析其应力-应变响应与破坏形态的演化规律。研究结果表明:动静组合加载下试样应力-应变曲线大致分线弹性阶段、破坏阶段与峰后阶段;长径比越大,破坏阶段的“上凹”现象越显著;当长径比n>0.8时,应力-应变曲线峰后阶段出现回弹。围压相同时,不同轴压下试样峰值应力总体上随长径比的增大而增大。轴压在20 MPa条件下,当围压低于一定阈值时,大长径比试样峰值应力会更高;而当围压大于该阈值,峰值应力与长径比关系不甚明显;围压的增加会抑制长径比对峰值应力的影响。在不同动静组合加载条件下,试样均以剪切破坏为主,端面边缘易出现碎块脱落,侧面可观测到剪切裂纹;随着长径比的增大,试样破坏程度逐渐降低,其侧面剪切裂纹数量也趋于减少。

To investigate the effect of aspect ratio on the strength and failure mode of rock sample under the com⁃bined dynamic and static loading conditions,the basic law of the stress wave propagation in split⁃Hopkinson pres⁃sure bar(SHPB)test was initially elucidated based on the rock dynamics theory.Subsequently,the ANSYS/LS⁃DYNA finite element numerical simulations were conducted on six groups of rock samples with different aspect ratios under the combined static and dynamic loading.The evolution laws of stress⁃strain responses and failure patterns were further analyzed.The results show that the stress⁃strain curves of the rock samples under the combined static and dynamic loading can be roughly divided into linear elastic stage,failure stage and post⁃peak stage.As the as⁃pect ratio n increases,the concave phenomenon at the failure stage becomes more obvious,and the stress⁃strain curve rebounds at the post⁃peak stage once the aspect ratio n exceeds 0.8.When confining pressure is constant,the peak stresses of rock samples under different axial compression generally increase with the increase of the aspect ratio.When the axial compression is set as 20 MPa,a threshold of the confining pressure exists,where the peak stress of larger aspect ratio of rock sample is higher as the confining pressure is below it.However,it hardly varies with the aspect ratio when the confining pressure is over this threshold.An increase in the confining pressure can suppress the effect of the aspect ratio on the peak stress.Under the combined different static and dynamic loading,the rock samples mainly exhibit shear failure,with fragments falling off at the edge of the end faces and shear cracks observed on the sides.As the aspect ratio increases,the failure degree of rock samples gradually decreases and the number of lateral shear cracks tends to decrease.