Study on the damage behavior of CFRP under cyclic hygrothermal-fatigue loading

Addressing the research gap where most existing studies focus on the coupling of constant hygrothermal conditions and static loads, with insufficient investigation into the damage mechanism of carbon fiber-reinforced polymers (CFRPs) under the synergistic effect of alternating hygrothermal environments and dynamic loads, this study investigated the damage behavior of carbon fiber-reinforced vinylester composite laminates under the coupling effect of cyclic hygrothermal conditions (30°C/85% RH to 60°C/95% RH) and tension-compression fatigue loading with four stress amplitude levels. Gravimetric weighing, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) were employed to characterize the moisture absorption behavior and macro-microscopic damage features, while compressive property tests were conducted to analyze the evolution of mechanical performance. The results show that: The moisture absorption curve of CFRPs conforms to the Fickian diffusion model under pure hygrothermal aging; however, fatigue loading accelerates matrix hydrolysis by promoting moisture absorption (with no significant effect on thermal oxidation), leading to an increase in moisture absorption rate and deviation from the Fickian model; this coupled effect significantly reduces the compressive properties of CFRPs, and the degree of performance degradation intensifies with the extension of aging time and the increase in fatigue stress amplitude.