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The moisture diffusion behavior of two-part thermoset polyurethane neat resin, woven E-glass fiber-reinforced polyurethane face sheet, closed-cell rigid polyurethane foam core and their corresponding sandwich specimens was investigated in this study. The vacuum-assisted resin transfer molding process was used to manufacture the polyurethane sandwich panels. Open-edge moisture diffusion experiment was conducted for sandwich panel and its constituents by immersing each type of samples in distilled water at room temperature for nearly seven months. Moisture diffusivities and solubility for neat resin, face sheet and foam core specimens were characterized according to the experimental analysis. The moisture diffusion behavior for closed-cell polyurethane foam was found to deviate significantly from classical Fick's law, and a multi-stage diffusion model was thus proposed to explain this deviation using a time-dependent diffusivity scheme. A user-defined subroutine was developed to implement this scheme into the commercial finite element analysis code ABAQUS. A three-dimensional dynamic finite element model was developed to predict the moisture diffusion behavior in neat resin, face sheet, foam core and sandwich specimens. This finite element model was then validated by comparing simulation results with experimental findings.

Composite materials are increasingly used in applications of civil infrastructure and building materials. The new generations of two-part thermoset polyurethane resin systems are desirable materials for infrastructure applications. This is due to high impact resistance, superior mechanical properties, and reduced volatile organic compounds when compared to the conventionally used resin systems such as vinyl ester and polyester. Glass fiber-reinforced two-part polyurethane composites and low-density polyurethane foam are used to design and manufacture composite structural insulation panels using vacuum assisted resin transfer molding process for temporary housing applications. Using these types of composite panels in building construction will result in cost-efficient, high-performance products due to inherent advantages in design flexibility. Use of core-filled composite structures offers additional benefits such as high strength, stiffness, lower structural weight, ease of installation and structure replacement, and higher buckling resistance than the conventional panels. Energy efficiency is known to be inherently better with the core-filled composite panel than in a metallic material. The panels can be designed to resist the required loads, and the study aims to evaluate the ability of lab scale tests and models to predict part quality in full-scale parts. Furthermore, it discusses the manufacturing challenges. Flexural tests and energy consumption evaluations were performed on these structural components. Finite element simulation results were used to validate the flexural experiment findings.

This study investigated the effect of moisture absorption on the mechanical performance of polyurethane sandwich composites. The core material was a closed cell polyurethane foam. Face sheets were made of E-glass/polyurethane composite laminates. Vacuum-assisted resin transfer molding process was used to manufacture specimens for testing. The foam core, laminates, and sandwich composites were submerged in salt water for prolonged periods of time. Mechanical property degradation due to moisture absorption for each constituent was evaluated. Compression test was performed on the foam core samples. Laminates were evaluated by three-point bending tests. The interfacial bond strength in the sandwich structure was evaluated by double cantilever beam mode-I interfacial fracture test. The testing results revealed that the effect of salt water exposure on the compressive properties of the foam core is insignificant. The flexural modulus of polyurethane laminates degraded 8.9% and flexural strength degraded 13.0% after 166 days in 50% salinity salt water at 34°C conditioning. The interfacial fracture toughness of polyurethane sandwich composites degraded 22.4% after 166 days in 50% salinity salt water at 34°C conditioning.