Quantitative measurements of acoustic emission related to its microscopic mechanisms

A method for the quantitative measurements of the acoustic emission is worked out. Its performance is analyzed with regard to the transducer loss and the ultrasonic attenuation in the specimen. This method is actually applied to the tension tests of pure aluminium specimens. The power spectrum of the acoustic emission is obtained over a wide range of 100 kHz to 4 MHz. The total power attains a peak of 5 pW at the beginning of the plastic deformation and decreases to 0.3 pW with the increase of the deformation. The autocorrelation function for the acoustic emission is given as a monotonically decreasing function. This result reveals that the elastic energy of the acoustic emission is radiated not oscillatorily but in the form of random pulses. Mean value of the pulse widths is estimated to change from 0.6 to 0.2 μsec in the early stages of the deformation. This change is shown to be attributable to the increase of the density of dislocations in the material.Subject Classification: 35.10.