The mode I interlaminar fracture toughness of carbon fiber/epoxy resin composite with freezing after water absorption

Abstract

In this study, the effect of freezing after water absorption on the mode I interlaminar fracture toughness of carbon fiber reinforced plastics (CFRP) was investigated. Plain woven carbon fiber was used as reinforcement. Epoxy resin was used as the matrix. A water absorption test was conducted at 90°C for up to 500 hours. After water absorption, the specimens were kept at -15°C, -79°C and -198°C. The fracture surfaces of specimens were observed by using a scanning electronic microscope (SEM). Double cantilever beam tests were conducted at room temperature after water absorption and freezing. As a result, the following conclusions were obtained. CFRP can absorb a lot of water at an elevated temperature. At 90°C, the rate of water absorption is about 1.5%. The fracture toughness of water-absorbed CFRP is greater than that of virgin CFRP material in the case that the water absorbed ratio is more than 0.9%. This is because the resin becomes ductile due to water absorption. In the case of freezing, at which the water absorption ratio is less than 0.9%, the fracture toughness only almost increases. However, in the case of 1.5%, the fracture toughness increases by about 50%. This is also because of the interface between the fiber and the matrix.