Effect of a little water absorption on the long-term durability of advanced composites and how to improve the life

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Even under the normal condition where the relative humidity is 60% or lower, a little water in the atmosphere penetrates into advanced composites such as CFRP and accelerates the fatigue degradation under cyclic loading. The present study revealed that we must pay a lot of attention to long-term degradation due to a little water absorption. The mechanism on the relationship between a little water and degradation at the fiber/matrix interface is a key for the long-term durability for advanced fiber composites.The effect of protection from water penetration during fabrication process on the static and fatigue properties was studied for plain woven CFRP. The static strength and fatigue life were examined when the humidity condition changed at each stage; mixing, lamination, storage and testing stage. The experimental results showed that the static strength and fatigue life of plain woven CFRP were significantly improved even when the material was protected from water penetration during th … More e lamination stage. The protection from water penetration during the lamination stage improved the resistance of crack growth and interfacial shearing strength at the interface between fiber and matrix. Such improvement of fiber/matrix interfacial properties contributed to the improvement the static strength and fatigue life of plain woven CFRP improve.How to observe and characterize the fatigue degradation of advanced composites under cyclic loading was also focused using the thermo-elastic image techniques for composites. The experimental results showed the damage initiation points were widely scattered in the materials due to its woven structure. In order to obtain accurate damage information, thermo-elastic damage analysis (TDA) was developed and used. The present study well demonstrated that the progressive fatigue degradation was well characterized by analyzing the thermo-views taken simultaneously during fatigue. The fatigue life of woven fabric composites was significantly extended by using spread tows as well. The flat tows reduce the crack initiation occurring in the transverse yarns. Less