Analyse spectrale et energétique d'une source ultrasonore en mouvement — application à l'Emission acoustique de l'aluminium soumis à déformation plastique

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Abstract

The strain and grain size dependence of continuous acoustic emission spectra is investigated over a frequency range of 0.6.–3.3 MHz in pure aluminium (99.99%). The plot of the emitted energy versus strain exhibits a maximum whose position depends on measurement frequency and grain size.

To explain the experimental results a model of an elementary event is developed. This model is based on a moving ultrasonic source whose dynamical characteristics are similar to those of the perturbation produced by the “start and stop” motion of a dislocation. Analysing the position of the emitted energy maximum and the following energy decrease allows one to relate the mean free path of dislocations to the grain size and amount of plastic deformation.

The observed geenral tendency is an enhancement of higher frequencies of continuous emission spectra as deformation proceeds; this appears as the result of a decrease in the duration of the elementary event, that is in the dislocation motion length.

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