Acoustic emission during high-temperature frictional sliding

Summary

Acoustic emissions during high temperture frictional sliding in faulted granite were detected with a piezoelectric transducer plced outside the furnace and pressure vessel. Suitable choice of materials allowed the transmission of signals sufficiently large for measurement and analysis. Acoustic emissions were also monitored during the fracture runs at room temprature and could be compared with earlier studies. As observed previously, the emission rate increased dramatically prior to failure and the Ishimoto-Iida relationship between emission amplitude,A, and number of emissions,N(A), of amplitude,A. i.e., LogN(A)=K′−(b+1)logA, was followed. The constant,b, was typically about 1.4, higher than the value of 1 or less indicated by previous experimental and theoretical studies.

Acoustic emissions were detected during frictional sliding at all temperatures from 25 °, to 700°C. The activity began at low stresses and acceerated as the stress increased. During slidin the emission rate was nearly constant (with large counts during stick-slip events) at a level which decreased with increasing temperature. This apparent decrease may be explained by a real decrease in the number of emissions or by an increase in attenuation at higher temperatures.

The power-law relationship between amplitude and emission rate seemed to hold for sliding as for fracture. Highb-values, between 1.2 and 2.1, are in agreement with earlier studies and are little affected by temperature within the scatter of the measurements. Where the number of emissions allowed its measurement, theb-value of emissions during loading prior to slip was consistently, although only slightly higher than that during steady sliding.