Effect Of Seawater Aging On Bending Fatigue Of 3D Orthogonal Woven Carbon /glass Fiber Hybrid Composite

The hybrid fiber composites applied in marine engineering currently concentrate on laminated structures.However,some deficiencies of physical and mechanical properties,such as resistance to delamination,damage tolerance and impact property,limited its practical application.The 3D orthogonal hybrid woven composites had given it more advantages over the laminated hybrid composites to in-plane and interlaminar property.Therefore,the study on the bending fatigue performance of 3D orthogonal hybrid fiber reinforced polymer composites during long-term service in the marine environment is of great significance for expanding the application range of marine engineering composites.In this paper,a 3D orthogonal carbon/glass fiber hybrid composite(3DOHCs)is designed and prepared.Compared with the laminated carbon/glass fiber hybrid composite(LMHCs),the damage evolution and mechanism of the two composites were investigated under bending fatigue load before and after seawater aging.Before seawater aging,the static three-point bending test was performed on the 3DOHCs,LMHCs and 3D orthogonal carbon fiber composite(3DOCFCs).The result shows that the 3DOHCs has higher bending strength and modulus than the LMHCs.The modulus of the 3DOHCs was lower than that of the 3DOCFCs.However,the failure strain and strength of the 3DOHCs were higher than those of the 3DOCFCs.The bending strength of 3DOHCs shows a positive hybrid effect.It is because 3DOCFCs with the top layer of carbon fiber is more prone to failure than 3DOHCs with the top layer of glass fiber under bending load.The bending fatigue life of the 3DOHCs was carried out three-point bending fatigue test under 50%,55% and 60% of the maximum stress loading.The fatigue damage evolution images of 3DOHCs at different stages were captured under55% stress level by the Super-high magnification lens zoom 3D microscope.It indicates that the bending fatigue process of the 3D hybrid composite was mainly characterized by compressive failure.Before and after seawater aging,a transverse fiber bundle tension test was used to qualitatively characterize the bond strength at the interface of carbon fiber/matrix(C/M)and glass fiber/matrix(G/M).The interface strength testing results were statistically analyzed by Weibull distribution.After aging,the strength decline rates of epoxy resin,carbon fiber,glass fiber,C/M and G/M are 11.3%,2.65%,5.66%,17.22%,14.37%,respectively.The results indicated that the degradation of the matrix and interface performance contributed to the attenuation of the bending fatigue performance of3 DOHCs after aging in seawater,and the descending of interface property played a dominant role.Drying treatment after seawater immersed the bending fatigue property of3 DOHCs will basically be restored,which is concerned with the hygroscopic expansion of the matrix.After moisture absorption,the matrix expansion causing residual stress similar to thermal expansion stress,which reduces interface strength and bending fatigue performance of the composite.After drying,the expansion of the matrix is eliminated due to the evaporation of water molecules in the matrix.The interface and matrix return to the original state and the properties of the composite are recovered.The S-N curve suggests that the bending fatigue life for the 3DOHCs were significantly higher than those of the LMHCs at the same stress levels before and after seawater aging.It indicates that the 3D hybrid composite shows better fatigue performance than LMHCs.Figure 35,table 11,reference 123.