Modeling and Simulation of Moisture Diffusion in Hybrid Fiber-Reinforced Polymer Composites

Hybrid fiber-reinforced polymer composites have extensive applications due to their high strength, corrosion resistance, low maintenance and design flexibility. However, moisture absorbed by composite components plays a detrimental role in the integrity and durability of hybrid structure since it can degrade the mechanical properties and induce interfacial delamination failures. In the current study, the moisture diffusion characteristics in two-phase (unidirectional S-glass fiber reinforced epoxy matrix/unidirectional graphite fiber reinforced epoxy matrix) hybrid composites using moisture concentration-dependent diffusion method have been investigated. In the moisture concentration-dependent diffusion method, the diffusion coefficients are not only dependent on the environmental temperature, but also dependent on the nodal moisture concentration due to the internal swelling stress built in the diffusion process. A user-defined subroutine is developed to implement this method into a commercial finite element code. Three dimensional finite element models have been developed to investigate the moisture diffusion in hybrid composites. Also, normalization approach is integrated in the modeling to remove the moisture concentration discontinuity at the interface of different material components. The moisture diffusion in the 3 layer hybrid composite exposed to 45 /84% relative humidity for 70 days is simulated and validated by comparing with available experimental findings. The developed model has been extended to simulate the moisture diffusion behavior in adhesive-bonded 4 layer thick hybrid composite structure. The results indicate that adhesive layer plays a role in resisting the moisture diffusion process in hybrid composites owing to its low diffusivity in this study. Copyright 2013 by Aurora Flight Sciences.