单轴循环冲击下花岗岩力学特性与损伤演化机理

Mechanical property and damage evolution mechanism of granite under uniaxial cyclic impact

摘要:

为研究循环冲击荷载下黑云母花岗岩的动态力学特性,利用改进的分离式霍普金森压杆,选取4种不同的入射波应力幅值对花岗岩试样进行等幅循环冲击,并对相关机理和试验现象进行探析.结果表明:入射波应力幅值为110.57和90.48 MPa时,随着冲击次数的增加,岩样的峰值应力逐渐降低,最大应变、平均应变率和损伤值均呈现增大趋势；入射波应力幅值为70.82 MPa时,花岗岩的峰值应力随着冲击次数的增加表现出先增强后降低的特性,而最大应变、平均应变率与损伤值则表现出相反规律；入射波应力幅值降为50.69 MPa时,岩样的力学性质基本不变,岩样未见明显的损伤.此外,研究还发现基于岩样静态压缩应力-应变曲线推求的静态裂纹起裂应力,经强度增长比例系数放大后可得到动态裂纹起裂应力,籍此能较好地解释上述循环冲击试验中所观测到的现象.

Abstract:

To study the dynamic mechanical properties of biotite granite under cyclic impact loading, four different stress amplitudes of incident wave were selected to cyclically strike the rock samples on a modified split Hopkinson pressure bar (SHPB). The related mechanism and experimental phenomenon were analyzed. Results showed that when the stress amplitudes of incident wave were 110.57 and 90.48 MPa, the peak stresses of the rock samples decreased gradually with an increase in the number of impacts, while the maximum strain, average strain rate, and damage value all increased. When the stress amplitude of incident wave was 70.82 MPa, the peak stress of the sample first increased and then decreased as the number of impacts increased, while the opposite law occurred for the maximum strain, average strain rate, and damage value. As the stress amplitude of incident wave dropped to 50.69 MPa, the mechanical properties of the rock sample were basically unchanged, and no obvious damage was detected inside the rock sample. Besides, it was found that the static crack initiation stress determined based on the static compressive stress-strain curve could be extended to the dynamic loading state by multiplying a strength increase factor, which could well explain the phenomenon observed in the cyclic impact test.