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

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.