An assessment of methods to determine the directional moisture diffusion coefficients of composite materials

An assessment was made of methods of determining the directional moisture diffusivities in a unidirectional carbon–fibre/epoxy composite with a distinctly anisotropic microstructure. Experimental data were collected for samples cut from 25 mm thick panels in three orthogonal directions during conditioning in water and humid environments. Using the full 3D Fickian solution and an optimisation process on the full data set was the best method of determining the diffusivities. Diffusivity across the fibres was 40% and through thickness diffusivity was 13% of that along fibres, which was found to be close to that of the unreinforced resin. A critical analysis was made of methods of approximating the 3D Fickian solution.