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Title: Static and fatigue behaviour of fibre composites infused with rubber- and silica nanoparticle-modified epoxy
Author: Awang Ngah, Shamsiah
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2013
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Delamination has been recognised as the primary defect in composite structures, which can lead to rapid deterioration of the structure. This is because delamination is barely visible damage, and the presence of delamination crack growth between the fibre-matrix layered structure can severely reduce the load bearing capability without being noticed. The present work investigates the matrix toughening approach via the addition of a second phase copolymer and rigid silica nanoparticles in an attempt to enhance the delamination resistance in Glass Fibre (GF) composites. This investigation includes the analysis of the structure/property relationships of toughened epoxy matrices and their corresponding GF composites under quasi-static and fatigue loading conditions. The toughness performance and the toughening mechanisms of the modified epoxies and their corresponding composites are the main theme of this thesis. This investigation revealed a positive correlation between the interlaminar fracture toughness of GF composites and the toughness of the matrix phase. A large toughness increase was observed when using rubber-modified and core-shell rubber (CSR)-modified epoxy matrices. The use of a silica nanoparticle-modified matrix only showed a marginal toughness increase, and in some epoxy systems, the addition of silica nanoparticles was detrimental to the composite toughness. In the hybrid-modified matrix, the largest toughness increase was observed, indicating the presence of a synergistic effect between the rubber particles and silica nanoparticles. The toughening mechanisms in the rubber-modified epoxy were rubber particle cavitation and plastic void growth, whereas in the CSR-modified epoxy the toughening mechanisms were cavitation of the rubbery core and shear deformation in the polymer matrix. In the silica nanoparticle-modified epoxy, debonding of the nanoparticles and subsequent void growth were evident, but the energy dissipation was small and not sufficient to contribute to the large toughness increase. In addition, the silica nanoparticles increased the matrix stiffness and caused the matrix to be less adhered to the fibre surface, thus promoting a fibre-matrix interfacial failure. The fatigue performance of the GF composites with toughened matrices was analysed in terms of fatigue crack growth and fatigue threshold. The addition of rubber particles and silica nanoparticles reduced the fatigue crack growth rate and increased the fatigue threshold values. The fatigue threshold was further increased when using the hybrid-modified matrix suggesting a synergistic toughening effect in the threshold region. Microscopy analysis revealed there were no appreciable difference in the toughening mechanisms between the fatigue and quasi-static fracture behaviour.
Supervisor: Taylor, Ambrose Sponsor: Majlis Amanah Rakyat (MARA) (Malaysia) ; Government of Malaysia
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available