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Composite polymeric materials have exhibited significant advantages when operating in hostile conditions such as the marine environment. However, there is a lack of information concerning three-dimensional variations induced by prolonged exposure to seawater in composite structures and their impact on fatigue performance. Thus, this study aims to investigate the effects of long-term exposure to natural seawater on both the fatigue strength and three-dimensional chemical changes of GFRP laminates. Fatigue tests were conducted under uniaxial cyclic loading at a stress ratio R=0.1, considering three groups of specimens: a control group not immersed in natural seawater, a group immersed for 230 days in natural seawater, and a group immersed for 910 days in natural seawater. After the tests, fracture surfaces were analysed using scanning electron microscopy (SEM) and energy-dispersive spectrometry (EDS). SEM examination revealed the microstructural occurrence of fibre-matrix debonding, reducing the load transfer between the fibre and matrix, contributing to the fatigue life decrease in immersed specimens. The fatigue results revealed that the reduction in fatigue life of the specimens immersed for 230 days was approximately 66% of that observed in the control specimens increasing to 95% when the immersion period extended to 910 days. Moreover, the effect of immersion time on the chemical structure of various regions within the specimens was assessed using Fourier-transform infrared (FTIR) spectroscopy. The main findings suggest the existence of a concentration gradient within the laminate and that regions near permeable surfaces are more vulnerable to chemical changes compared to regions located further away, even after reaching saturation.
Vidinha et al. (Fri,) studied this question.