Strain analysis of a glass-fibre-reinforced polyester under dynamic loads
Abstract
Strain on fibreglass-reinforced polyester was analysed for different types of stress-strain patterns to determine the existence of a critical point on the respective diagrams. This critical point defines the maximum strain value prior to a steep and abrupt increase that causes failure. «Useful life» should, therefore, be regarded to be the number of cycles associated with the critical point rather than the number associated with failure. The tests conducted in this study showed that the number of critical point cycles was around 95% of the yield point cycles. The degradation rate of the material tested under different loads was found with an analytical model applied to the most common strain pattern. The model proposed also showed that the stress ratio, R, was related to elastic modulus degradation. When studied for load state values of 10 to 16% of the ultimate tensile strength (UTS), material life expectancy was found to be 104 to 107 cycles. No fatigue limit appeared for these values, however. Immersion of the material in water and subsequent drying under ambient conditions was found not affecting either deformation or deformation-related variables. Finally, a model was developed to predict life expectancy from the maximum strain values.
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References
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