Moisture Absorption Characterization and Mechanical Properties of CFRP Under the Combined Effects of Seawater and Continuous Bending Stress

Composite structures are susceptible to the combined effect of seawater aging and stress load in the marine environment. This paper investigates the moisture absorption and mechanical properties of CFRP immersed in seawater at 70 °C and subjected to sustained bending. The moisture absorption process of CFRP in a moisture-force coupling environment was characterized, and the effect of moisture-force coupling on the bending and tensile properties of laminates was studied. The results show that the maximum moisture content and diffusion coefficient of the sample decrease with the increase of the sustained bending stress level. It is found that the Fick model can better describe the water diffusion process of thicker samples than the Langmuir model. The bending stress causes the post-curing rate of the sample to slow down, and the duration becomes longer. The tensile strength of the sample at a 10.5% stress level exceeds the initial value of 8.62% after immersion for 2016 h. The sustained bending stress aggravated the degradation of the flexural properties. The sample under 30% bending stress decreased by 18.08% after immersion for 2016 h, while the unstressed sample only decreased by 11.90%. An empirical prediction model based on the Fick model and experimental data is proposed to describe the degradation of bending strength, verified by the existing literature data.