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Material Characterisation and Interface Optimisation of Recycled Carbon Fibre Composites

Howarth, Jack (2012) Material Characterisation and Interface Optimisation of Recycled Carbon Fibre Composites. PhD thesis, University of Sheffield.

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Abstract

Composites manufactured from a novel non-woven veil of recycled carbon fibre were tested in longitudinal tension, 3-point bend and short beam shear to assess their mechanical properties with respect to other commonly available materials. It was found that their mechanical properties were intermediate between ‘high-end’ unidirectional pre-preg and ‘low-end’ chopped strand mat, and similar to that of other short-fibre reinforced plastics. A range of oxygen plasma treatments were carried out on the fibres to improve interfacial performance of the composites. It was found that treatment at an intermediate plasma power of 20 W resulted in the greatest improvement in tensile strength of a 10⁰ off-axis composite. Samples were manufactured from either 2 individual veils (IV) or from 2, 10-layer ‘pre-forms’ (PF). Both exhibited similar improvements in 10⁰ off-axis strength. Thus shadowing of the fibre within the plasma did not appear to be significant. Overtreatment at higher plasma powers (35 and 50 W for IV and 50 W for PF) resulted in a significant reduction in tensile strength and failure strain. X-ray Photoelectron Spectroscopy (XPS) showed that plasma treatment at 20 W resulted in the highest level of oxygen functionality on the fibre surface, correlating with the best interfacial performance. Plasma treatment at 10 and 35 W resulted in slightly elevated surface oxygen content, however the off-axis tensile properties of 10 W treated samples were not significantly improved compared to the untreated control. The poor mechanical performance of the over-treated samples can be attributed to either an overly strong interface resulting from increased adhesion or damage to the fibres as a result of the treatment process. There were large variations in fibre wettability across treatments, such that no discernible pattern was present between wettability and interfacial performance. XPS and ToF-SIMS analysis showed that there was almost complete coverage of the veil by the binder in the veil-making process, and that silicon contamination on the fibre itself is likely silica based, and that silicon present in the binder is PDMS.

Item Type: Thesis (PhD)
Academic Units: The University of Sheffield > Faculty of Engineering (Sheffield) > Materials Science and Engineering (Sheffield)
Identification Number/EthosID: uk.bl.ethos.574066
Depositing User: Mr Jack Howarth
Date Deposited: 14 Jun 2013 13:12
Last Modified: 12 Oct 2018 09:18
URI: http://etheses.whiterose.ac.uk/id/eprint/4042

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