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Monitoring the Crack Growth by Measurement of Diffracted Lamb Waves

This article presents an application of ultrasonic Lamb waves to monitor the growth of a crack in an aluminum plate subject to mechanical fatigue. PZT sensors were fixed on both sides of the zone where a crack is expected to appear. The study was conducted by theoretical and experimental approaches. The diffraction Fresnel-Kirchhoff approximation was used to establish an estimate for the attenuation measured as a function of the crack length. A finite element program was equally used to estimate the propagation attenuation and the time of flight. The time of flight was compared with the value obtained considering simple ray propagation by diffraction on the crack’s tip. Finally the obtained data were compared with those obtained experimentally.