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Title: Design and formulation of a bespoke self-healing agent for repair of multifunctional fibre reinforced polymers
Author: Imperiale, Vita
ISNI:       0000 0004 2746 4948
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2014
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The aim of this investigation was to design a bespoke self-healing agent (SHA) formulation in order to achieve a fully autonomous healing functionality, which provides effective and timely in-situ repair of FRP composite laminates. The preliminary phase of the design process consisted of the identification of the SHA requirements, the choice of epoxy resins as the most suitable chemistry and, finally, the selection of the best candidate species, amongst the many commercially available. Numerous formulations were then generated by the combination of the above components. Therefore, an initial downselection process, with chemical and physical properties characterisation was necessary to consider only a limited number of formulations for mechanical properties characterization. A Mode I fracture toughness test was considered as a means of final selection, the adhesive function being one of the most important functional requirements. Finally, the recovery of residual compressive strength after impact (CAI) was used as a validation method, which was able to demonstrate and quantify the self-healing recovery within a FRP laminate. A very low viscosity epoxy based formulation with a slightly higher fracture toughness than the host composite matrix and good degree of reactivity was selected as having the best overall performance. Adhesion, as a function of time and temperature, was further assessed in this formulation. It was demonstrated that a certain degree of load bearing ability can be achieved after limited reaction extent with full recovery of load bearing ability after 6 hours at 25°C. An ageing assessment of SHA demonstrated that after seven days exposure to 60°C the formulation possessed excellent adhesive properties. The novel integration of a two-part SHA, with the components segregated within different hollow glass fibres for a fully autonomous process, required the development of a suitable manufacturing and design of the FRP laminate. The damaged and self-healed samples achieved 93% of the strength relative to the initial pristine configuration. Besides an increase in the failure load, self-healing generated a significant change in the stress-strain characteristics, which restored a degree of linearity up to failure, and a reduction in the differential strains (and hence increased buckling resistance). The bleeding of the SHA from storage in the HGF to effect healing can be implied from ultrasonic C-scan analysis, where images of self- healing samples possessed fragmented and less defined delamination contours compared to the image of damaged samples without SHA within hollow glass fibres. This investigation has demonstrated that a fully autonomous recovery of a significant proportion of compressive strength in a CFRP is possible via self-healing. For the first time it has been demonstrated that a bespoke multi-component SHA is able to bleed from embedded HGF, self-mix and react to allow recovery of up to 93% of compressive strength, notwithstanding the presence of remaining damage within the CFRP laminate
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available