FIFTH CANADIAN CONFERENCE ON NONDESTRUCTIVE ... - IAEA

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MATERIALS EFFECTS ON ACOUSTIC EMISSION DURING DEFORMATION AND
FRACTURE
M. Nabit Ba&6im
Univzuity o (j Wa.ni.toba.
Winnipeg, Manitoba, Canada
ABSTRACT
The technique of acoustic emission is increasingly used for nondestructive
testing of large structures. Because of its passive nature in detection of
the stress wave emissions which occur during plastic deformation and/or crack
propagation, it is possible to monitor large areas by using a relatively low
number of transducers. While the application of the technique is being
perfected, understanding of the nature and origin of acoustic emission is
less clear due to the complexity of quantifying the nature of the acoustic
sources and the effect of the medium where the stress waves are propagating.
In this investigation, models describing the origin of acoustic emission in
terms of dislocations are reviewed. The effect of attenuation on the stress
waves is examined and the extent of acoustic emission activity from a
specific material is related to its microstructure. A comprehensive analysis
of the nature of acoustic emission as observed in a typical application is
thus presented.
1. INTRODUCTION
Considerable effort has taken place in recent years to use acoustic emission
as a nondestructive testing method for evaluation of the integrity of
structures and components. The bulk of this effort has been directed to
applications involving large structures, namely pressure vessels, nuclear
reactors...etc where flaw localization is the main concern and evaluation of
the severity of these flaws is the primary goal of the application of the
technique. Commercially available systems, which are equipped with very
sophisticated digital processing techniques including micro-processors are
available for performance of such tests. The application of acoustic
emission is usually conducted during proof tests of these structures and
record.-, of performance of the acoustic emission activity, in terms of
acoustic emission parameters such as total ringdown count, count rate, peak
amplitude and energy of the signals are obtained. As well, the position of
the flaw is determined from the differences in time of arrival to several
transducers positioned at various locations on the structures. Bassim(l) and
and Houssny-Eman(2) have summarized the different techniques used for