Evaluation of facings and sandwich properties of carbon fiber/epoxy-PVC foam sandwich composites: Comparison of VARI co-cure and precure manufacturing methods

The manufacturing process of sandwich composites using vacuum-assisted resin infusion (VARI) can be achieved in a one-step infusion process (co-cure). The purpose of this study is to evaluate the properties of the facing and sandwich composites manufactured by the VARI co-cure method. The sandwich composite was fabricated by VARI co-cure and precure for comparison using carbon fiber-epoxy as the facing and PVC foam as the core material. Thickness measurement, fiber volume fraction test, and tensile test were conducted to evaluate the facing properties. The flexural properties of the sandwiches and the effect of different plies on the facing and sandwich properties were also analyzed. The thickness of the co-cure facing is thicker and more varied than the precure. In addition, for the co-cure sandwich, the vacuum bag side (upper) facing has higher thickness and thickness variation than the mold side (lower) facing. The tensile strength of the co-cure facing is lower than the precure facing, which is 433–490 MPa (upper) and 455–521 MPa (lower) compared to 467–538 MPa (precure). The flexural and shear rigidity of the co-cure sandwich is affected by the side of the facing (upper/lower) exposed to tension or compression normal stress as a result of differences in facing properties on both sides. The specific flexural stiffness of the co-cure sandwich was lower by 17.09–45.19 MN-cm 5 /g compared to the precure of 16.86–46.83 MN-cm 5 /g due to a combination of increased flexural rigidity and the addition of density to the co-cure sandwich. Increasing facing plies from 2 to 6 plies results in an increase in facing thickness (166%) and thickness variation (477%), an increase in the fiber volume fraction of facing (11%), resulting in an increase in tensile modulus (12%) and strength (14%) of facing as well as increased stiffness of flexural (339%) and shear (42%) of sandwich.