Degradation mechanism for mechanical property of carbon fiber reinforced epoxy composite under simulated seawater absorption coupled with flexural load

Property evolution of carbon fiber reinforced epoxy composite used in marine environment was investigated in this paper. The moisture absorption and flexural properties of carbon fiber composite laminate were studied under the combined pretreatment condition of simulated seawater and three-point flexural load. An in-situ observation system was used during mechanical test to analyze damage initialization and development on dry and wet composites. Theoretical analysis considering hydro-mechanical coupling was conducted, based on experimental data, moisture simulation and stress analysis. Stress distribution under flexural load was discussed using finite element method, and its effects on moisture diffusion and failure process were analyzed based on the theoretical and experimental results. It demonstrates that moisture absorption of composites is inhibited as flexural load is applied during moisture absorption. It is attributed to compressive stress concentration of composite on the loading region. The retention of flexural property shows slight increase under moisture coupled with flexural load, which is resulted from decreased moisture content. Failure process of composite during three-point flexural test after immersion is different from that of dry composite, especially for the position and number of crack formation and propagation. Weakened interlaminar interface and more large cracks are found after immersion coupled with flexural load, which are explained based on water degradation and initial damage at stress concentration region. It denotes that more attentions should be paid on failure process of wet composite structure in marine field.