Shear wave caustics and the shadows of surface breaking cracks |
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Authors: | J. R. Brewster and K. H. G. Ashbee |
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Affiliation: | * The University of Tennessee, Department of Materials Science and Engineering, Knoxville, TN 37916, USA |
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Abstract: | A refinement to the detection of defects in rods and pipes by means of their ultrasonic shadows is presented. It has been previously shown that in standard non-destructive test configurations ultrasonic waves inside cylindrical test objects form caustics, surfaces of high sound intensity. Here it is demonstrated that when a crack edge crosses a caustic the diffraction of sound around the defect is enhanced, which allows the point at which this intersection occurs to be detected. Because the caustic is a well-defined geometric entity the position of the crack edge is now known. This effect presents a novel method of sizing defects that extend in from the surface. Experiments were performed in water immersion using 5 MHz sound. The test specimens were 76 mm diameter aluminium cylinders into which slots were cut to act as artificial defects. |
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Keywords: | caustics NDE defect sizing diffraction |
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