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Title: Online chemical analysis of plasma treated carbon fibre reinforced polymer surfaces
Author: Thomson, James
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2017
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Carbon fibre reinforced polymer (CFRP) is a type of composite structural material, with higher specific strength and fatigue resistance than many metals. CFRP is used to lighten structures, such as aircraft. Aircraft structures comprise multiple components which require reliable joints, with 5km of joints per Airbus A350XWB. These are currently reinforced using rivets, clips and clasps, which tend to diminish CFRP's weight reduction capacity, and introduce unwelcome local stresses. Adhesive joints are preferred in terms of overall specific strength and even stress distribution, but comprehensive monitoring of CFRP surface chemistry during joining is imperative for long-term joint integrity. In particular, mould release agents required for CFRP component formation interfere with chemical adhesion so that a pre-bonding surface treatment is required. In this study a long arc generator (LARGE) plasma source was used for surface treatment. In order to understand the surface characteristics, a range of different parameters were evaluated using goniometry of water droplets, X-ray photoelectron spectroscopy (XPS) and 'pull off' mechanical joint strength testing. The temperature and active species present in the plasma plume were investigated by IR emission spectroscopy indicating that temperatures exceeding 2000K and that species such as hydroxyl radicals were present at different plasma lengths. Plasma treatment to increased surface energy, oxidised the surface and enabled stronger adhesion between CFRP and other surfaces. XPS showed that decreasing the treatment distance from the plasma source would increase the amount of silicon oxygen bonds formed from ~50% in untreated samples to over 80% in samples treated at 2cm. Peaks were also observed using Raman microscopy associated with the polydimethylsiloxane (PDMS) based release agents, and its oxidation, which correlated with the spectra of treated samples analysed with XPS to R2 values of up to 0.97. CFRP was formed using four different release agents, two liquid - Frekote and Marbocote, and two solid - Super Release Blue and Tygavac. Raman spectroscopy showed that the solid release agents created a more consistent surface chemistry before plasma treatment. Online analysis was developed for quality control for certification of adhesive joints using a Raman spectroscopic approach as a characterising tool. The near-line system revealed that directly after treatment, fluorescence obscures the Raman signal. Principal component analysis (PCA) driven soft independent modelling of class analogy (SIMCA) was used to differentiate samples based on their plasma treatment parameters. The Raman probe system along with the SIMCA modelling developed here can be used as an inspection technique, able to indicate the treatment parameters used on the CFRP to an 81.25% assignment accuracy.
Supervisor: Martin, Philip Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available