Assessment of out-of-plane ply waviness in carbon-fibre reinforced plastics : comparing different non-destructive evaluation modalities

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Gomes, Rylan C.V.V. and Mohseni, Ehsan and Tunukovic, Vedran and Maes, Vincent and Contino, Matteo and Pierce, S. Gareth and Burnham, Kenneth and Vithanage, Randika K.W. and MacLeod, Charles N. and Munro, Gavin and O'Hare, Tom (2026) Assessment of out-of-plane ply waviness in carbon-fibre reinforced plastics : comparing different non-destructive evaluation modalities. NDT and E International, 160. 103630. ISSN 0963-8695 (https://doi.org/10.1016/j.ndteint.2026.103630)

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Abstract

Out-of-plane waviness (ply wrinkles) reduces tensile and compressive strength in Carbon Fibre Reinforced Polymers (CFRPs), with maximum out-of-plane ply angle governing failure mechanisms. This study comparatively evaluates three Non-Destructive Evaluation (NDE) techniques: Eddy Current Array Testing (ECAT), Phased Array Ultrasonic Testing (PAUT) and X-ray Digital Tomosynthesis (DT) for detecting and characterising ply wrinkles across three parameters: amplitude, wavelength, and maximum out-of-plane ply angle. Nine unidirectional CFRP coupons containing induced ply wrinkles of controlled amplitudes (0.13 -1.31 mm) were inspected, addressing a critical gap in comparative NDE performance for sub-2 mm amplitude defects in thin laminates. PAUT achieved the highest overall characterisation success rate of 96.3% (26/27 measurements) and a detection success rate of 88.9% (8/9 samples). Critically, PAUT achieved 100% success in characterising maximum out-of-plane ply angle - the parameter governing compressive/tensile failure across all samples, including the lowest amplitude wrinkle (0.13 mm). However, systematic overestimation in wrinkle amplitude characterisation occurred (+55.3% mean percentage error). ECAT achieved an equivalent 88.9% detection success and 33.3% characterisation success, successfully measuring wrinkle wavelength (100%) but unable to quantify wrinkle amplitude or out-of-plane ply angle from complex impedance data alone, positioning it as a rapid automated screening tool. X-ray DT achieved 88.9% detection and characterisation success, with moderate overestimation in wrinkle amplitude characterisation (+24.8%). However, complete detection and characterisation failure occurred on the lowest amplitude ply wrinkle. A critical finding establishes that reliable characterisation requires ply wrinkle amplitudes ≥0.32 mm across all techniques, with implications for the wrinkle parameter hierarchy in manufacturing quality control.

ORCID iDs

Gomes, Rylan C.V.V. ORCID logoORCID: https://orcid.org/0009-0004-9937-7322, Mohseni, Ehsan ORCID logoORCID: https://orcid.org/0000-0002-0819-6592, Tunukovic, Vedran ORCID logoORCID: https://orcid.org/0000-0002-3102-9098, Maes, Vincent, Contino, Matteo, Pierce, S. Gareth ORCID logoORCID: https://orcid.org/0000-0003-0312-8766, Burnham, Kenneth, Vithanage, Randika K.W. ORCID logoORCID: https://orcid.org/0000-0002-1023-2564, MacLeod, Charles N. ORCID logoORCID: https://orcid.org/0000-0003-4364-9769, Munro, Gavin and O'Hare, Tom;
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