Fatigue Strength of Fiber Reinforced Plastics Degraded by Environmental Exposure
Norio TAKEDA, Tomohiro NARUSE and Masaaki IWASA
Abstract:This article shows the environmental degradation in the fatigue strength of a glass fiber / unsaturated polyester composite, and proposes how to improve the environmental durability of the composite. First, the specimens of the composite are exposed to high temperature and in some cases moisture for long periods of time, and then the reduction in the fatigue strength of them is evaluated by performing fatigue tests. Next, to clarify the degradation of the matrix resin and the effect of the degradation on the fatigue strength of the composite, two viscoelastic properties, namely storage modulus and loss tangent, of the matrix resin are measured with DMA (Dynamic Mechanical Analyzer) before and after environmental exposure. In addition, the specimens broken in the fatigue tests are observed with SEM (Scanning Electron Microscope) in order to investigate the debonding of the interface between the fibers and the matrix resin and the effects of the debonding on fatigue strength. In the case of the composite, the fatigue strength of the composite is reduced by exposing it in high-temperature and moist environment. The reduction occurs especially in the low-cycle fatigue range, and hence it can be caused by the environmental degradation in the fatigue strength of the matrix resin rather than the interface. Since the degradation is easily confirmed by measuring the loss tangent of the matrix resin, measuring the loss tangent could be utilized to improve the environmental durability of the fatigue strength of the composite. Key Words:FRP, Degradation, Environment, Fatigue strength, Viscoelastic propertis