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.

Prediction of the Deterioration of FRP Composite Properties Induced by Marine Environments

“…The classification societies' rules prescribe the procedure for obtaining S-N curves for composite materials. Various authors have reported results obtained in modeling S-N curves for composites [29,34,35] and the prediction of the fatigue life of composite structures [27,43,44]. A failure model for groups of similar glass/polyester composites, such as the ones used in this research, can be defined in the form:…”

“…where N is the number of fatigue life cycles, δ u is the ultimate tensile strength (UTS) value, δ max is the maximal tensile stress occurring in the loaded structure, and α and β are experimental data fitting coefficients [44]. Using material data for design purposes obtained previously or by other researchers for similar material types and configurations is acceptable according to the classification societies' rules.…”