Moisture Diffusion Behavior Of 3D Woven Composites And Meso-scale Modeling

Polymer-matrix composites have excellent comprehensive properties. However, moisture is expected to degrade their mechanical properties due to matrix plasticization and moisture introduced micro-scale defects. Moisture diffusion properties will be an important indicator for evaluating their durability. In this paper, the moisture absorption behaviors of 3D woven composites(3D WCs) were studied experimentally and theoretically. The FEM model and theoretical model for their moisture diffusions were established as well.The neat epoxy, unidirectional composite(UD) and 3D WC specimens of the same material system were prepared in the laboratory and their moisture weight gain curves were obtained by moisture uptake experiments. Fick's law and Langmuir equations were used to get the moisture properties of neat epoxy and UD. These values were compared with the diffusivities deduced by two-phase diffusion model. Interphase was proved to promote moisture diffusion. A new diffusivity prediction model considered interphase effect was built afterwards.Meso-scale FE model of 3D WC considered its weave structure was built in commercial FE software ABAQUS. The moisture properties of resin-rich region and bundle in 3D WC were calculated from the experimental data of neat epoxy and UD. The two-stage phenomenon was successfully simulated by the use of ABAQUS's custom subroutine USDFLD. It is also the first combinative application of Langmuir model and FE method.A meso-scale FE model will not be satisfied for 3D WCs with different weave structures. A sandwich model was proposed here for engineering application. Through conducting serials simplifications and equivalences, the water uptake of 3D woven composite with local heterogenic moisture properties was predicted by a sandwich structure with constant diffusivity. The results of experiment, FE method and sandwich model are all in good agreement. Actually, this method is also valid for any other laminated structures or materials with non-constant diffusivities.