A study on stress-corrosion cracking using single fiber model specimen (degradation properties of GFRP caused by water absorption)

Recently the crack propagation properties of GFRP on the stress corrosion cracking (S.C.C) are investigated, and the threshold stress intensity factor K_ICC is verified in some environmental solution. From the investigation, it was found that GFRP reinforced by C glass fiber has a superior acid resistance. However the microscopic crack propagation mechanisms caused by the material corrosion are not verified, and the microscopic mechanisms are necessary to assure the durability. Therefore the degradation mechanisms of the inner fiber and the matrix and the fiber/matrix interface should be quantified. In this study, the degradation of the fiber strength and the fiber/matrix interfacial shear strength are investigated using a single fiber composite previously immersed into environmental solutions, distilled water and acid solution. The effects of solution diffusion into the matrix resin on the fiber strength and the interfacial shear strength have been evaluated as a function of immersion time by fragmentation test in the room air. It is found that the diffusion of distilled water influences the degradation earlier than the acid solution. And the diffusion behavior is confirmed by Fickian diffusion analysis. The calculated concentration distribution showed that the water concentration around the fiber is saturated much earlier than the saturation of the acid ion due to the lower diffusion coefficient. Furthermore the crack propagation mechanisms are discussed based on the degradation estimated by the fragmentation test.