title: Analysis of high frequency guided wave scattering at a fastener hole with a view to fatigue crack detection.
abstract: The scattering of high frequency guided ultrasonic waves by a fatigue crack at the side of a fastener hole has been studied. The guided wave pulse consists of the superposition of the two fundamental Lamb modes A0and S0above the cut-off frequencies of the higher modes. The scattered field was simulated using a three-dimensional finite difference algorithm with a staggered, Cartesian grid for the limited area of interest around the hole and an analytical phase angle correction for the additional, variable propagation distance. Experimentally, the modes were selectively excited using a standard ultrasonic wedge transducer and measured using a laser interferometer, resulting in good spatial resolution. The scattered field was measured and simulated for an undamaged hole, a small, part-thickness quarter-elliptical fatigue crack, and a through-thickness fatigue crack. Good agreement was found and a significant influence of the fatigue cracks on the scattered field was observed. The complex difference of the scattered field due to additional scattered waves at the fatigue cracks of variable depth and length was evaluated. This allows for the prediction of high frequency guided wave sensitivity for fatigue crack detection at fastener holes, a significant maintenance problem for ageing aircraft.
authors.affiliation: Department of Mechanical Engineering, University of Applied Sciences, 1705 Fribourg, Switzerland. Electronic address: bernard.masserey@hefr.ch.
authors.forename: Bernard
authors.initials: B
authors.lastname: Masserey
authors.affiliation: Department of Mechanical Engineering, University College London, London WC1E 7JE, United Kingdom. Electronic address: p.fromme@ucl.ac.uk.
authors.forename: Paul
authors.initials: P
authors.lastname: Fromme
keywords: Finite difference method; Lamb waves; Laser measurement; Scattering