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UBC Theses and Dissertations

Natural weathering of glass fibre reinforced plastics and degradation of their properties : an exploratory multivariate analysis Nezafatkhah, Sina


In this research, different sets of glass/polyester composite material test pieces were used to evaluate the degradation processes induced by natural weathering. Reinforced and unreinforced polyester samples were fabricated and aged in a semi-arid climatic condition in Kelowna, British Columbia, Canada, for all seasons of a year, consisting of a dry/sunny summer, and a cold/cloudy winter. Reinforced composite plates, manufactured under an open-mould hand-layup process, were produced in eight different configurations, varying in their fibre preform architecture, the application of surface coating, and their initial curing state. Unreinforced polyester samples, on the other hand, were only different in their initial curing condition. To study the weathering induced changes in the material properties, not only were the natural degrading agents monitored during the ageing period, but also properties, such as surface hardness, surface roughness, and flexural strength were seasonally measured. Using PCA as an exploratory and multivariate data analysis tool, the correlations were determined between the natural climatic agents and their resultant changes in the material properties. Among the climatic agents, UV radiation, relative humidity, and the depth of snow cover were found as the most affecting agents. The architecture of fibre preform proved to be the most influential factor among the design and processing variables, followed by the surface coating application, and selection of an appropriate initial curing state. Gradual curing in the ambient condition was found to improve the ageing behaviour of GFRP composites, compared to curing at elevated temperatures, as partially cured samples demonstrated less significant sensitivity to photodegradation. Finally, the internal structure of aged samples was morphologically inspected to validate the ageing induced degradation mechanisms. Internal defects, such as weakened interfacial adhesions, cracks along the gel coat interface, and expanded bubbles, were clearly seen in the aged samples using micro-CT inspections.

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