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概要

Nonlinear ultrasonic imaging technique is applied for detection and sizing of tight cracks. Tight crack su rfaces are clapped and rubbed repeatedly by high-powered burst waves, thus higher and sub-harmonics are ge nerated. By using a band-pass or high-pass filter, the second and higher harmonic components are extracted from the received signals and the amplitude map is constructed. We can make the ultrasonic images of the cracked surface itself, by focusing the ultrasonic beams on peaks of rugged cracked surface, and receiving the backscattered transverse wave. The amplitude mapping of the second and higher harmonics generated at the tight crack surface by a high-powered tone-burst wave pulser gives us clear images of tight crack surf aces. We can evaluate the depth of the tight cracks with the B-scan images of second and higher harmonics.

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