单轴压缩下炭质板岩的应变速率效应及声发射特性

Strain Rate Effect and Acoustic Emission Characteristics of Carbonaceous Slates in Uniaxial Compression

摘要:

为了探究应变速率对炭质板岩单轴力学特性和声发射特征的影响，开展了4组不同准静态应变速率（8.50×10^-6s^-1、1.70×10^-5s^-1、1.70×10^-4s^-1和3.34×10^-4s^-1）下的单轴压缩试验，并同时监测了加载过程的声发射信号。基于试验数据，总结分析了应变速率对炭质板岩应力-应变关系、能量耗散及声发射特征的影响规律，探讨了应变速率的影响机制。同时，基于加载过程中耗散能密度的演变规律，提出了将耗散能曲线平直段起点作为炭质板岩闭合应力σ_cc、平直段终点作为扩容应力σ_cd的特征应力确定方法。结果表明：在准静态应变速率范围内，炭质板岩的弹性模量和峰值强度随应变速率的增大均先增大后减小，在应变速率1.7×10^-4s^-1时达到最大值；闭合应力、起裂应力和扩容应力与峰值应力的比值基本在0.37、0.55和0.74左右，不随应变速率发生变化；应变速率对声发射信号影响显著，随应变速率增加，0~50kHz内的主频率占比逐渐增加，而100~250kHz内的主频率占比逐渐减小，炭质板岩的破坏形式逐渐由张拉破坏变为剪切破坏。

Abstract:

To investigate the strain rate effect and acoustic emission characteristics of carbonaceous slates， a series of uniaxial compression tests were conducted at four different quasi-static strain rates （8.50×10^-6s^-1， 1.70×10^-5s^-1， 1.70×10^-4s^-1， and 3.34×10^-4s^-1）， and the acoustic emission signal was measured simultaneously. Based on the test results， the effects of strain rate on the stress-strain relationship， energy dissipation， and acoustic emission characteristics were analyzed， and the mechanism of these strain rate effects was explored. In addition， the closing stress σ_cc and the crack damage stress σ_cd were determined based on the evolution of dissipative energy density during loading； the closing stress σ_cc was defined as the starting point of the flat section of the dissipative energy curve， and the crack damage stress σ_cd was defined as the end point. The results show that in the quasi-static strain rate range， the elastic modulus and peak strength of carbonaceous slates first increase and then decrease with the strain rate， reaching their maximum values at the rate of 1.7×10^-4s^-1. The ratio of closure stress， crack initiation stress， and crack damage stress to the peak stress were about 0.37， 0.55， and 0.74， respectively， which do not change with the strain rate. The strain rate also has a significant impact on the acoustic emission signal. With the increase of strain rate， the proportion of main frequency in the range of 0~50 kHz increases and that in the range of 100~250 kHz gradually decreases. The failure mode also gradually changes from tensile failure to shear failure.