The present research work has studied the fatigue behaviour of matrices and fibre-composites based upon modified epoxy polymers. The basic epoxy polymer has been modified with (a) nano-silica particles, (b) micrometre-rubber particles, and (c) both of these additives, to give a ‘hybrid’ modified epoxy. These modifications have been undertaken in order to try to increase the cyclic fatigue resistance of the fibre-composite material. The experimental work has used a linear elastic fracture mechanics (LEFM) approach to firstly ascertain the fatigue properties of the epoxy polymer matrices. Secondly, the unmodified (i.e. control) and the modified epoxy resins were used to fabricate glass fibre reinforced plastic (GFRP) composite laminates by a resin infusion under flexible tooling (RIFT) manufacturing method. Tensile cyclic fatigue tests were performed on these composites, during which the degree of matrix cracking and stiffness degradation were also monitored. The fatigue life of the GFRP composite was significantly increased due to the presence of the nano-silica particles and/or micro-rubber particles. Suppressed matrix cracking and a reduced crack propagation rate in the modified matrix of the fibre-composite were observed to contribute towards the enhanced fatigue life of the composites containing the nano-silica particles and/or micro-rubber particles. The theoretical studies employed an extended finite element method, coupled with a cohesive zone model, to predict the fatigue behaviour of the fibre composites based upon the unmodified (i.e. control) and modified epoxy polymer matrices. A ‘user element subroutine’ has been developed in Abaqus to incorporate the extended finite element method and a mathematical model has been proposed to evaluate the constitutive laws for the cohesive zone model to simulate the growth of fatigue cracks. A fatigue degradation strategy based on the ‘Paris law’ (determined from the fatigue tests on the matrix materials) has been adopted to change the constitutive law for the cohesive zone model as a function of the number of fatigue cycles that have been accumulated. The theoretical predictions for the fatigue behaviour have been compared to the experimental results, and very good agreement between the theoretical and experimental results was found to exist.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:550199 |
| Date | January 2012 |
| Creators | Babu, Jibumon B. |
| Contributors | Kinloch, Anthony ; Taylor, Ambrose |
| Publisher | Imperial College London |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/10044/1/9507 |
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