Fatigue Strength of Composite Materials Considering Hygrothermal Degradation

Felipe A. Acosta, Ruth Roman, Miguel A. Pando, Luis A. Godoy


Fiber-reinforced polymer composites (FRP) constitute an attractive alternative in the construction industry to conventional materials such as steel and concrete. However, understanding of the influence of environmental conditions in their long-term mechanical behavior is of vital importance to ensure their implementation. The main objective of this project is to assess the effect of hygrothermal exposure on the fatigue performance of glass/vinyl-ester composites. Two types of laminates (uniaxial and biaxial) and vinyl-ester neat resin are investigated. The specimens are immersed in distilled water at 40°C [104°F] for periods of times ranging from 50 days to 500 days. Fatigue tests are performed at a stress ratio (R) of 0.1 and a frequency of 5 Hz. Three stress levels are evaluated: 70%, 50% and 30% of the unaged ultimate tensile strength. Using Epaarachchi and Clausen methodology, a fatigue life prediction model is proposed that incorporates the hygrothermal conditioning effect on the fatigue life. The aging specimens show a decrease in fatigue life compared to the as-received specimens. The higher fatigue life degradation occurred in the uniaxial laminate samples. Fatigue life time predictions of vinylester neat resin samples based on exposure time show a better correlation than the results based on moisture absorption. In the case of laminate specimens, both approaches show good correspondence with experimental results.

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