Effects of Hygrothermal Aging on the Flexural Properties of Cross-Ply and Angle-Ply CFRP Composite Laminates

In this study, the influences of the aging period and temperature on the flexural properties of CFRP laminates were investigated experimentally and numerically. Samples with cross-ply (CP) and angle-ply (AP) layups were prepared and immersed in water tanks with different temperatures (30 ℃ and 50 ℃). Three-point bending tests were performed for unaged, 15, and 35 days-aged composite laminates. SEM, optical, and Fourier transform infrared spectroscopy were employed to investigate the morphology, chemical structures, and failure mechanisms. It was found that the water molecule uptake mainly existed among the matrix and fiber–matrix interface. As a result, the CP laminates showed a buckling-driven delamination failure at the compressive surface, while debonding and kinking failure appeared for AP laminates. A higher temperature or longer immersion period worsens the laminate performance. For CP samples aging for 35 days, the flexural strength showed a 32.8% reduction at 30 ℃ and a 40.6% reduction at 50 ℃. However, the reduction of flexural strength of AP samples was 29.7–31.1% at both temperatures, which was insensitive to the temperature. A finite element model was also developed, and the numerical results showed that the differences in flexural properties reduction were due to the distinct load-carrying mechanisms.