長期間海水に浸漬させた平織CFRP積層板の強度劣化特性評価

抄録

The influence of long-term seawater immersion on the mechanical properties of plain woven CFRP laminates was evaluated by static tensile and tension fatigue tests. These tests were carried out on the CFRP immersed different time under seawater: 2566 hours and 4967 hours. The mechanical properties of the specimen for 2566 hours immersion decreased drastically; the tensile strength, the elastic modules and the fatigue strength at 10⁶ cycles reduced by 21.3%, 12.3% and 30.7% compared with those of no immersion specimen, respectively. On the other hand, after 4967 hours immersion, it was found that the mechanical properties decreased slightly. From observation of the Scanning Electron Microscopy (SEM), it was clear that morphology of the fiber/matrix interface varied with the immersion time. However, there was a small difference on the interface fracture surface between 2566 hours and 4967 hours. These results indicated that degradation of the fiber/matrix interface progressed dramatically by 2566 hours, and after that, interface degradation gradually converged. Damage growth behavior under fatigue loadings was investigated by non-destructive inspections using soft X-ray photography and ultrasonic inspection. At first, matrix cracks occurred along 90° and ±45° fiber directions. After that, delamination occurred originating from the matrix crack. Then, these damages expanded as the number of cycles increased, and finally, the specimen broke as the longitudinal fiber in the 0°/90° layers damaged.