Hervin, Flora Louise;
(2023)
Guided wave propagation and scattering in anisotropic composite structures.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
Carbon fibre reinforced polymer (CFRP) laminates are widely used for aerospace applications as they reduce the weight of structures whilst maintaining mechanical strength. Composites have highly anisotropic material properties and high in-plane strength but poor interlaminar strength, making them vulnerable to barely visible impact damage (BVID) caused by low velocity impacts. Composite damage is multi-modal, consisting of fibre breakage, matrix cracking, and delaminations, with delaminations causing the most significant strength reduction. Guided ultrasonic waves, often generated using a sparse network of sensors bonded to a structure, provide a promising structural health monitoring (SHM) technique for composites. Guided waves propagate along a structure, with energy throughout the entire thickness, making them ideal for rapid, long-range inspection of large areas. In anisotropic materials wave energy is focused along the high stiffness (fibre) directions, resulting in higher amplitude and wave speed in these directions. Waves launched away from the fibre direction are steered towards the fibres. These anisotropic effects could lead to inaccuracies in damage localization if not accounted for. Propagation of the fundamental, flexural (A0) guided wave mode was investigated in an undamaged unidirectional CFRP panel. Anisotropic effects including the directionality of wave velocities, skew angles, and beam spreading were quantified through both finite element simulations and experiments, achieving good agreement with predictions obtained from dispersion curves. Scattering of the A0 mode at an artificial delamination was studied for a quasiisotropic CFRP plate layup. Wave-trapping on top of the delamination, and strong forward scattering at the delamination exit was found. Significantly different scattering behaviour was observed to that of a magnet target, often used to develop SHM systems. Scattering around both damage targets was found to be directionally dependent, with higher amplitudes in the fibre directions of the outermost laminae. Implications for the SHM of composites were discussed.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Guided wave propagation and scattering in anisotropic composite structures |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2023. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Mechanical Engineering |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10173199 |
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