THREE DIMENSIONAL SIMULATION OF MOISTURE DIFFUSION IN THICK COMPOSITES

摘要

Long term moisture exposure has been shown to affect the mechanical performance ofpolymeric composite structures. This reduction in mechanical performance must beaccommodated for during product design in order to ensure long term structure survival. Inorder to determine the long-term moisture effects on composite components, representativeparts are commonly tested after having been exposed to an accelerated moisture conditioningenvironment. Accelerated moisture conditions are established in order to rapidly drivemoisture into test specimens simulating worst-case long term exposure scenarios. Currentlyaccepted methodologies for analyzing the time required to condition specimens are limited,allowing only simple geometry and an assumption that diffusivity rates are independent of theflow path or direction. Therefore, a more advanced finite element method is desired. In thecurrent work, a three dimensional model is developed and implemented in commercial finiteelement code. The parametric study has been conducted for complex shapes, moisturediffusion pathways, and varying moisture and temperature conditions. Finite element resultsare validated with a one-dimensional analytical model and experimental results. The ultimategoal for this research is to determine exposure times for accelerated conditioning that producethe most accurate moisture distribution with the part and minimize over-conditioning of thelaminate.