Noncontact measurement of guided ultrasonic wave scattering for fatigue crack characterization

P. Fromme

doi:10.1117/12.2009460

19 April 2013 Noncontact measurement of guided ultrasonic wave scattering for fatigue crack characterization

P. Fromme

Proceedings Volume 8692, Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2013; 86921N (2013) https://doi.org/10.1117/12.2009460
Event: SPIE Smart Structures and Materials + Nondestructive Evaluation and Health Monitoring, 2013, San Diego, California, United States

Abstract

Fatigue cracks can develop in aerospace structures at locations of stress concentration such as fasteners. For the safe operation of the aircraft fatigue cracks need to be detected before reaching a critical length. Guided ultrasonic waves offer an efficient method for the detection and characterization of fatigue cracks in large aerospace structures. Noncontact excitation of guided waves was achieved using electromagnetic acoustic transducers (EMAT). The transducers were developed for the specific excitation of the A₀ Lamb mode. Based on the induced eddy currents in the plate a simple theoretical model was developed and reasonably good agreement with the measurements was achieved. However, the detection sensitivity for fatigue cracks depends on the location and orientation of the crack relative to the measurement locations. Crack-like defects have a directionality pattern of the scattered field depending on the angle of the incident wave relative to the defect orientation and on the ratio of the characteristic defect size to wavelength. The detailed angular dependency of the guided wave field scattered at crack-like defects in plate structures has been measured using a noncontact laser interferometer. Good agreement with 3D Finite Element simulation predictions was achieved for machined part-through and through-thickness notches. The amplitude of the scattered wave was quantified for a variation of angle of the incident wave relative to the defect orientation and the defect depth. These results provide the basis for the defect characterization in aerospace structures using guided wave sensors.

Citation Download Citation

P. Fromme "Noncontact measurement of guided ultrasonic wave scattering for fatigue crack characterization", Proc. SPIE 8692, Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2013, 86921N (19 April 2013); https://doi.org/10.1117/12.2009460

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