Characteristic Behaviors Of CFRP And GFRP At Cryogenic Temperature Under Static And Cyclic Loadings
Free (open access)
S. Kubo, K. Okubo & T. Fujii
Characteristic behaviors of plain-woven Carbon Fiber Reinforced Plastics (CFRP) at cryogenic temperature were investigated under static and cyclic loading. The test results were compared with those of Glass Fiber Reinforced Plastics (GFRP). Tensile behaviors of monofilaments were also evaluated. The test results showed that two knee-points appeared in the stress-strain curve of GFRP under static load, while that of CFRP was almost linear. Both strength and failure strain of the CFRP at cryogenic temperature were lower than those of CFRP at room temperature, because the epoxy resin was brittle at cryogenic temperature. At cryogenic temperature, the knee-point was also shown in the SN curve of GFRP of the fatigue test but that was not shown in the S-N curve of CFRP. The elastic modulus of CFRP at cryogenic temperature suddenly decreased in the final stage of fatigue, while such change was not observed at room temperature. The thermal fatigue test where no cyclic loads were applied to the specimen was also conducted in order to investigate the damage progression due to temperature change. After the thermal fatigue test, the residual strength of the CFRP and GFRP were measured at room temperature. The change in residual strength was explained by the difference of the coefficient of thermal expansion. This paper also mentioned that, at cryogenic temperature, the stiffness reduction under cyclic loading was related to the local thermal stress by thermal cyclic fatigue. It should be said that the carbon fiber was failed with accompanying critical crack propagation of the matrix due to the brittle of resin at cryogenic temperature. Keywords: fiber reinforced plastics, cryogenic temperature, coefficient of thermal expansion, residual strength, stiffness reduction.
fiber reinforced plastics, cryogenic temperature, coefficient of thermal expansion, residual strength, stiffness reduction.