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.