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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.

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.

This paper presents the evaluation of an innovative low-cost small-scale prototype deck panel under monotonic and fatigue bending. This new system introduces a trapezoidal-shaped polyurethane foam core with a thermoset polyurethane resin that has a longer pot life to facilitate the infusion process. The proposed panel exhibited a higher structural performance in terms of flexural stiffness, strength, and shear stiffness. The panels consist of two glass fiber-reinforced polymer (GFRP) facings with webs of bidirectional E-glass-woven fabric that are separated by a trapezoidal-shaped low-density polyurethane foam. The GFRP panels were manufactured using a one-step vacuum-assisted resin transfer molding process. The specimens studied were constructed in the Composite Manufacturing Laboratory in the Mechanical and Aerospace Engineering Department at Missouri University of Science and Technology. Small-scale prototype deck panels were tested both statically and dynamically in four-point bending to investigate their flexural behavior. The ultimate bearing capacity of the proposed sandwich panels was determined from compression crushing tests. In addition, the load-deflection behavior of the proposed panel was investigated under three loading conditions: compression, static flexure, and dynamic flexure. The initial failure mode for all panels was localized outward-compression skin wrinkling of the top facing. The ultimate failure was caused by local crushing of the top facing under the loading point due to excessive compressive stresses. First-order shear deformation theory was used to predict the panel deformation in the service limit state. In general, the analytical results were found to be in good agreement with the experimental findings. individual papers. This paper is part of the Journal of Bridge Engineering, © ASCE, ISSN 1084-0702/04015033 (13)/$25.00. © ASCE 04015033-1 J. Bridge Eng. J. Bridge Eng., 2016, 21(1): 04015033 Downloaded from ascelibrary.org by Missouri University of Science and Technology on 02/26/16. Copyright ASCE. For personal use only; all rights reserved. © ASCE 04015033-2 J. Bridge Eng. J. Bridge Eng., 2016, 21(1): 04015033 Downloaded from ascelibrary.org by Missouri University of Science and Technology on 02/26/16. Copyright ASCE. For personal use only; all rights reserved. © ASCE 04015033-4 J. Bridge Eng. J. Bridge Eng., 2016, 21(1): 04015033 Downloaded from ascelibrary.org by Missouri University of Science and Technology on 02/26/16. Copyright ASCE. For personal use only; all rights reserved. © ASCE 04015033-5 J. Bridge Eng. J. Bridge Eng., 2016, 21(1): 04015033 Downloaded from ascelibrary.org by Missouri University of Science and Technology on 02/26/16. Copyright ASCE. For personal use only; all rights reserved. © ASCE 04015033-6 J. Bridge Eng. J. Bridge Eng., 2016, 21(1): 04015033 Downloaded from ascelibrary.org by Missouri University of Science and Technology on 02/26/16. Copyright ASCE. For personal use only; all rights reserved. © ASCE 04015033-8 J. Bridge Eng. J. Bridge Eng., 2016, 21...

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.