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Glass fiber-reinforced polymer composites have promising applications in infrastructure, marine, and automotive industries due to their low cost, high specific stiffness/strength, durability, and corrosion resistance. Polyurethane (PU) resin system is widely used as matrix material in glass fiber-reinforced composites due to their superior mechanical behavior and higher impact strength. Glass fiber-reinforced PU composites are often manufactured using pultrusion process, due to shorter pot life of PU resin system. In this study, E-glass/PU composites are manufactured using a low-cost vacuum-assisted resin transfer molding process. A novel, one-part PU thermoset resin system with a longer pot life is adopted in this study. Tensile, flexure, and impact tests are conducted on both the thermoset PU neat resin system and E-glass/PU composites. A three-dimensional finite element model is developed in a commercial finite element code to simulate the impact behavior of E-glass/PU composite for three different energy levels. Finite element model is validated by comparing it with experimental results.

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Hybrid fibre-reinforced polymer composites have extensive applications due to their high strength, cost effectiveness, improved product performance, low maintenance and design flexibility. However, moisture absorbed by composite components plays a detrimental role in both the integrity and durability of hybrid structure because it can degrade the mechanical properties and induce interfacial delamination failures. In this study, the moisture diffusion characteristics in two-phase hybrid composites using moisture concentration-dependent diffusion method have been investigated. The two phases are unidirectional S-glass fibre-reinforced epoxy matrix and unidirectional graphite fibre-reinforced epoxy matrix. 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 during the diffusion process. A user-defined subroutine was developed to implement this method into commercial finite element code. Three-dimensional finite element models were developed to investigate the moisture diffusion in hybrid composites. A normalization approach was also integrated in the model to remove the moisture concentration discontinuity at the interface of different material components. The moisture diffusion in the three-layer hybrid composite exposed to 45℃/84% relative humidity for 70 days was simulated and validated by comparing the simulation results with experimental findings. The developed model was extended to simulate the moisture diffusion behaviour in an adhesive-bonded four-layer thick hybrid composite exposed to 45℃/84% relative humidity for 1.5 years. The results indicated that thin adhesive layers (0.12-mm thick) did not significantly affect the overall moisture uptake as compared with thick adhesive layers (0.76-mm thick).