アコースティック・エミッションの定量的解析法

抄録

A novel method for the quantitative measurement of acoustic emission is worked out. The performance of the method is analyzed with regard to transducer loss and ultrasonic attenuation in the specimen. The magnitude of the error in the measurements is shown to be negligible for purposes of the present discussion. This method is actually applied to tension tests of pure aluminium specimens. The power spectrum of the acoustic emission for plastic deformation of the specimen is obtained quantitatively over a wide range from 100 kHz to 4 MHz. The total acoustic emission power attains a peak of 5 pW at the beginning of plastic deformation and decreases to 0. 3 pW as strain increases. The autocorrelation function, which is the Fourier transform of the power spectrum, is given as a monotonically decreasing function of τ. This shows that the elastic energy of the acoustic emission is radiated not in oscillatory form but in the form of random pulses. The mean value of the pulse width is estimated to be about 0. 6 μsec in the early stages of deformation and is observed to decrease gradually to less than 0. 2 μsec with deformation. This value is considered to correspond to the average dwell time of the elementary source events producing the acoustic emission. The change of the dwell time is attributed to an increase of the density of dislocations in the material. It is concluded that this quantitative method is a powerful tool for research on acoustic emission mechanisms in connection with dislocation kinetics.