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Characterisation of Impact Damage in Carbon Fibre Reinforced Plastics by 3D X-Ray Tomography
[Thesis]. Manchester, UK: The University of Manchester; 2012.
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Abstract
Carbon fibre reinforced plastics (CFRP's) are finding increased used as structural materials in many transport applications, particularly next generation commercial aircraft. The impact damage tolerance of these materials is relatively poor compared to conventional aircraft materials such as aluminium. As a result there is a concerted research effort to improve the damage tolerance of these materials. Understanding the microstructural mechanisms of damage can help to design improved materials. Three-dimensional X-Ray computed tomography (CT) allows these damage mechanisms to be identified and quantified non-destructively. However, a lack of published work in the field means no consistent methodologies for imaging or quantifying damage in CFRP's using X-Ray tomography exist. This thesis provides several novel methodologies for imaging and quantifying impact damage using X-Ray CT. A dual energy imaging methodology was developed to overcome the reduction in CT image quality caused by the high aspect ratio of CFRP structures. This approach resulted in a 66% increase in signal-to-noise ratio, and a 109% increase in contrast-to-noise ratio. The development of a methodology for quantifying impact damage in CFRP based on thresholding the in-plane damage area showed good agreement with ultrasonic C-scan results, and allowed correlations between impact energy, damage area and compression-after-strength to be made. Region of interest (ROI) algorithms for high magnification imaging of impact damage in CFRP plates were investigated. These algorithms were not developed by the author, but further understanding of their effectiveness and practical applications is presented in this work. Finally, a novel X-Ray tomographic imaging technique using interferometry was applied to imaging impact damage in CFRP's. This method was developed by a research group in Switzerland at the \emph{Centre Suisse d'Electronique et de Microtechnique} (CSEM) in Zurich. The work in this thesis presents the first application of the technique to image impact damage in CFRP.