Gradient-dependent model for moisture diffusion in a polymer matrix composite laminate

This study presents a new diffusion model named the gradient-dependent model. It is based on the strain-dependent model, a modification of Fick's diffusion model, and is employed to solve penetrant diffusion in a 2D-infinite plate with finite thickness. An immersion test is performed and analyzed for studying moisture diffusing through the surfaces of a polymer matrix composite laminate into the material and the induced in-plane expansion is measured. The hygric expansion is proportional to the moisture concentration, which can be derived from the gradient-dependent model involving parameters standing for the hygric property of the material. By fitting the theoretical solution of the hygric expansion to the data, the parameters for locating the penetrant front can be obtained and they are very important in describing the hygric behavior of the material.