Mr. Ifan Dafydd Profile

Ifan Dafydd

at Imperial College London

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Proceedings Article | 27 March 2018 Paper

Damage severity assessment in composite structures using ultrasonic guided waves with chirp excitation

Ifan Dafydd, Zahra Sharif Khodaei

Proceedings Volume 10598, 105980D (2018) https://doi.org/10.1117/12.2299647

KEYWORDS: Composites, Transducers, Ultrasonics, Wave propagation, Laser Doppler velocimetry, Waveguides, Structural health monitoring, Signal detection, Signal to noise ratio, Visualization

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This paper explores the feasibility of using ultrasonic guided Lamb waves to characterise the type and through thickness severity of damage present in composite plate-like structures. Two cases were considered, the first compared isolated subsurface delaminations between plies whilst the second case looked at more complicated barely visible impact damages caused by a low velocity impactor. In this study, the ultrasonic guided Lamb waves were generated by a surface mounted piezoelectric transducer and were sensed by a Laser Doppler Vibrometer. This allowed full wavefield imaging of the Lamb wave interaction with damage without the need for a previously acquired damage free baseline signal. In order to save time and improve the signal to noise ratio, the narrowband toneburst signals are reconstructed from a singular chirp response and a post-processing algorithm. Both cases showed similar results in that the first symmetric mode, S₀, which is dominant at higher frequencies, caused mode conversions when interacting with the defects whilst the first anti-symmetric mode, A₀, dominant at lower frequencies, mainly caused a change in phase and amplitude across the defects. Both cases also showed that as the damaged area got more severe, the effects of the damage on both modes became more pronounced.

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