Advanced moisture modeling of polymer composites

Long-term moisture exposure has been shown to affect the mechanical performance of polymeric composite structures. This reduction in mechanical performance must be considered during product design in order to ensure long-term structure survival. In order to determine the long-term moisture effects on composite components, representative parts are commonly tested after having been exposed to an accelerated moisture conditioning environment. Accelerated moisture conditions are established in order to rapidly drive moisture into test specimens simulating worst-case long-term exposure scenarios. Currently, accepted methodologies for analyzing the time required to condition specimens are limited, allowing only simple geometry and an assumption that diffusivity rates are independent of the flow path or direction. Therefore, a more advanced finite element method is desired. In this study, a three-dimensional model is developed and implemented in commercial finite element code. The parametric study has been conducted for three-dimensional shapes, moisture diffusion pathways, and varying moisture and temperature conditions. Finite element results are validated with a one-dimensional analytical model and experimental results. A user-subroutine was implemented in commercial finite element code to calculate the moisture content. The ultimate goal for this research is to determine the exposure time for accelerated conditioning that produces the most accurate moisture distribution with the part and minimize over-conditioning of the laminate.