# Sewater Effect on Fatigue Behaviour of Notched Carbon/Epoxy Laminates
## 1 Introduction
They observed a significant effect on the variation of the mechanical properties of the material. [PERSON] et al. [22] analysed the response of CFRP laminates immersed in seawater and observed that fatigue durability is strongly affected by the stress ratio and the deterioration of the fibre/matrix interface strength. According to [PERSON] and [PERSON] [23], the coupling between mechanically induced microcracks in the composite and the suction of water into the capillary channels has an important role in the fatigue life of the component. Similar conclusions have been found by [PERSON] et al. [4] who reported a significant reduction in the fatigue lifetime due to seawater ageing. [PERSON] et al. [24] evaluated the effect of seawater absorption on fatigue damage accumulation in a GFRP laminate and reported a strong influence of water absorption on the damage accumulation of such materials under cyclic loading. In the study by [PERSON] [25], who compared the fatigue behaviour of dry and saturated glass/epoxy samples, it was observed that there was a smaller lifetime expectancy at higher strain rates for wet samples, while at lower strain levels the fatigue strength increased. [PERSON] et al. [3] analysed the effect of moisture ingress on the bending fatigue of laminated composites and concluded that the lifetime expectancy was significantly reduced, more precisely from 80% of the ultimate flexural strength (UFS) to 65% of the ultimate flexural strength. [PERSON] et al. [26] investigated the degradation of critical components made of polymer matrix composites for naval applications immersed in distilled and seawater. They noted a significant reduction in transverse strength for the water-immersed composites when compared to the control samples. The negative effect of environmental factors, such as seawater, on the physical and mechanical properties of composite materials has been addressed by many authors [3; 27; 28]. Another important aspect in the design of composite laminates subjected to cyclic loading is the existence of geometric discontinuities. There are several engineering structures where it is necessary to introduce holes to accommodate electrical wires, bolt and river holes, and access holes for routing of cables and hydraulic pipes, or for assembly and maintenance purposes, which can cause high-stress gradients, speeding up the fatigue-crack growth rates [29; 30]. These holes or notches produce stress concentration effects and can therefore affect the structural integrity. Although composite materials have high specific strength and high specific stiffness, they are not isotropic, so the stress distribution is dependent on the loading orientation [31]. [PERSON] et al. [32] studied the effect of the central hole size on the strength of composite laminates subjected to tension/compression. An interesting outcome was that the specimens with open holes developed transverse cracks in the top layer from the notch boundary. Furthermore, at higher applied stresses, the cracks also emanated from the free edges. [PERSON] et al. [33] evaluated the low-velocity impact response of holed GFRP laminates. They observed that there was a significant influence on fatigue life in notched samples compared to the control samples. However, according to the authors' knowledge, there are no studies addressing the fatigue response of composite components with holes immersed in seawater. For this purpose, fatigue tests were carried out for different immersion times (0, 30 and 60 days) into seawater, using specimens produced from carbon/epoxy composites containing open holes. The difference observed in the fatigue life between immersion into natural and artificial seawater was also be analysed. The fatigue life results are discussed in terms of S-N curves, and the damage evolution is evaluated in terms of stiffness modulus.