Fatigue durability test of quasi-isotropic carbon/epoxy laminates in marine environment

Fiber-reinforced polymer (FRP) composites are utilized as a substitute material for metal structures in maritime industries. The durability of composites depends on varying harsh marine environments. The continuous exposure of FRPs to the harsh marine environment affects their static and dynamic properties. In this study, the impact of moisture absorption on the fatigue characteristics of autoclave-cured quasi-isotropic carbon/epoxy laminates is examined. Specimens were aged in artificial seawater under ambient, sub-zero, and humid conditions for 365 d. The fatigue test was conducted at different stress levels on aged laminates. The S-N curve, stiffness degradation, damage accumulation, and rate of damage growth using energy dissipation method were evaluated based on the experimental results. The results showed that fatigue property of quasi-isotropic carbon/epoxy specimens largely depends on aging conditions. The S-N curve of aged specimens showed a greater fatigue life at higher stress levels than the pristine specimen. Under different aging conditions and varying stress levels, specimens exhibited a standard damage curve. A total of 60–70% damage was developed during the initial stages of fatigue loading. The presence of moisture, multiple cracks, and interphase debonding between fibers and matrix were responsible for the reduction in fatigue life of quasi-isotropic carbon/epoxy specimens.