Location of the Sources of Acoustic Emission in Thin-Wall Objects of Spherical Shape
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LOCATION OF THE SOURCES OF ACOUSTIC EMISSION IN THIN-WALL OBJECTS OF SPHERICAL SHAPE V. R. Skal’s’kyi,1,2 E. P. Pochaps’kyi,1 B. P. Klym,1 and O. H. Simakovych1
UDC 620.179.17
We obtain solutions of the problem of finding the coordinates of acoustic-emission sources in thin-wall spherical objects in a Cartesian coordinate system by using an antenna with three transducers. We study the possibilities of removing the ambiguities in the determination of locations of the sources of elastic acoustic-emission waves by this antenna. The obtained results are verified by the results of computer simulation of an actual spherical object. The measurement errors are estimated. Keywords: acoustic emission, detection of acoustic-emission sources, thin-wall spherical objects, coordinates of the source.
Urgency and the State of the Problem The acoustic emission (AE) method is fairly extensively used for the monitoring of the initiation and development of defects in structural elements, which makes it possible to prevent their premature failures. As one of the most important components of this type of engineering diagnostics, we can mention the determination of the coordinates of the site of fracture because this enables one to concentrate inspection in a small area and, thus, increase its reliability. Note that nucleating or developing defects emit elastic AE waves in the material. Their monitoring makes it possible to find the coordinates of the source by using an acoustic antenna of primary transducers by analyzing the differences between the times of arrival (DTA) of elastic waves to each of these transducers. The number of АЕ transducers (AET) required for the detection of a source depends on the geometry of the object of investigation but, as a rule, acoustic antennas contain four AET [1]. The works devoted to the determination of the coordinates of AE sources in the plane are known [1–8]. This approach can also be used for the detection of sources in small areas of the sphere for which it is possible to neglect the curvature. Since the error of calculations increases with the area of diagnostics, this method is inapplicable to small spherical objects of monitoring. The methods used for the detection of AE sources on spherical surfaces based on the use of preliminarily specified schemes of location of the AET were considered in [9]. The actual objects of monitoring, due to the complexity of their structure, can impose certain restrictions on the scheme of mounting of piezoelectric transducers. Thus, it might be necessary to use schemes with arbitrarily located AET. In this case, it is necessary to have a proper procedure of finding the coordinates of АЕ sources with regard for the possibility of degenerate cases (and their analysis) with an aim to develop the algorithm of testing. The problems of determination of the coordinates of АЕ sources on the spherical surfaces were considered in [10–13]. To solve them, the authors of the cited works used a modified polar coordinate system introduced on the surface of the sphere. The ob
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