Three-point Bending of Sandwich Beams with FRP Facing and PP Honeycomb Core

Abstract

In this study, two sets of sandwich beams were tested in three-point bending. The sandwich panels were fabricated in a wet layup process. The facing component was made of either polyethylene terephthalate (PET) fiber-reinforced polymer (FRP), or glass fiber reinforced polymer (GFRP). The facing thickness was 3 mm for both PET FRP and GFRP. Polypropylene (PP) in honeycomb structure form, with a density of 80 kg/m3, was used as the core component among all tested beams. The sandwich beam dimensions were consistent at 1,200 mm length, 78 mm width, and 82 mm height. While testing each sandwich beam, the applied load, overall beam deflection, and facing strain were captured at mid-span. The resulting data were processed to produce load-deflection, moment-curvature, and load-strain diagrams. At peak load, bond failure between the walls of the cylindrical tubes within the honeycomb structure occurred; therefore, the failure mode for all tested sandwich beams was attributed to shear failure. The load-deflection relation was nonlinear in both sets, which was derived from the thermoplastic component (PET FRP facing and/or PP core). A nonlinear analytical model was developed and compared to the experimental testing data. The method used for experimental testing and analytical modelling was outlined in this study. The experimental matrix, testing results, and analytical model indicated that the nonlinearity of the sandwich beam's load-deflection relation stems from the facing and core components. In contrast, the nonlinearity of moment-curvature and load-strain relation stems solely from the facing component.