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Title: Fatigue of composite materials
Author: Dyer, K. P.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 1997
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A study has been undertaken of fatigue in glass fibre reinforced composites. Two matrix resins were tested; an isophthalic polyester and a polyurethane-vinyl-ester, which was designed to have superior properties, including toughness and resistance to hydrolytic attack. Three different types of glass fibre fabrics were used for reinforcement, a conventional woven roving and two novel stitch-bonded cloths. The resins and cloths were combined into eight lay-ups in order to consider the effects of matrix, cloth and lay-up on fatigue strength and lifetime. The fatigue study was extended to evaluate the micromechanisms that occur in these composites during fatigue and how damage accumulated throughout the sample lifetime. This involved measuring stiffness changes during fatigue cycling combined with microscopic study of the samples. The damage mechanisms that occurred were similar to those seen by previous authors on different materials and from this, it was concluded that the same mechanisms occur independent of material and lay-up but these parameters affect the point in the specimen lifetime at which the damage occurs. After the data had been obtained, two experimental models were compared against data obtained in the S-N and damage accumulation studies to evaluate whether existing models would predict the behaviour of these composites. It was found that modelling of the linear portion of the S-N curve was fairly accurate but the damage accumulation model was not suitable. The composites were also fatigue tested in various environments and compared against the results obtained in air. Distilled water, sea water and dilute HCl were chosen as being the most likely encountered in the service of these materials. It was found that distilled water and sea water have minimal effect on fatigue in these composites during the short lifetimes used in this study, but it is suggested that the effect would increase with lifetime. The dilute HCl acid also had a smaller than expected effect. This study was backed with various tests which studied methods of water transport into these materials and the effects of the environments on matrix and fibre properties. Finally, initial studies have been made into methods of fabricating these materials into composite tubes with the aim of studying their properties in torsion and possibly tension-torsion.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available