循环冲击荷载下轴压对花岗岩动力学特性的影响

Influence of axial pressure on dynamic mechanical properties of granite under cyclic impact loading

为研究循环冲击荷载下轴压对花岗岩动态力学特性的影响,利用改进的动静组合式SHPB装置对5种轴压σA(0,30,60,90和120 MPa)下的花岗岩试样进行等幅循环冲击.结果表明:在相同的循环冲击荷载下,试样的总循环冲击次数随轴压的增加呈现先增加后减小的趋势,在σA=60 MPa时达到最大.5种轴压下的试样都表现为典型Ⅱ型应力-应变曲线.σA=0,30,90和120 MPa下试样的平均应变率和峰值应变随着冲击次数的增加而增加,峰值应力和弹性模量趋势相反,σA=0和120 MPa试样的力学参数劣化速率较快;σA=60 MPa下试样的平均应变率和峰值应变随着冲击次数的增加呈现先减小后增加的趋势,峰值应力和弹性模量则相反,其动力学参数劣化速率较慢.结合静态压缩声发射能量计数可以发现,当轴压超过起裂应力时,轴压对循环冲击荷载下岩石动力学特性的影响由强化向劣化效应转变.

To study the influence of axial pressure on the dynamic mechanical properties of granite under cyclic impact loading,a modified dynamic and static combined SHPB system was adopted to perform equal-amplitude cyclic impact on granite samples under five axial pressures(σA=0,30,60,90 and 120 MPa).Experimental results show that under the same cyclic impact loading,the total number of cyclic impacts of the samples first increased and then decreased with the increase in axial pressure,and it reached maximum when σA=60 MPa.The samples under five axial pressures all exhibited typical Ⅱ-type stress-strain curves.The average strain rate and peak strain of the samples under σA=0,30,90 and 120 MPa increased with the increase in the impact number,while the peak stress and elastic modulus were opposite.The dynamic mechanical parameters of the samples deteriorated faster under σA=0 and 120 MPa.The average strain rate and peak strain of the samples under σA=60 MPa showed a trend of decreasing and then increasing with the increase in the impact number,while it was opposite for peak stress and elastic modulus,and the dynamic mechanical parameters deteriorated slowly.Combined with the acoustic emission energy count in static compression,it can be found that when the axial pressure exceeded the crack initiation stress,the influence of axial pressure on the rock dynamic characteristics converted from strengthening to deterioration under cyclic impact loading.