Structural Behaviour of Sandwich Panels Constructed of Foam Cores and Flax FRP Facings

Abstract

In this study, the flexural behaviour of sandwich panels constructed of flax fibre-reinforced polymer (FRP) facings and closed cell polyisocyanurate foam cores was examined. A total of nine sandwich beam specimens (1200 mm long and 150 mm wide) made of 75 mm thick foam were prepared and tested under three-point bending. The parameters of the study were core density and facing thickness. Three different foam densities (32, 64, and 96 kg/m3) were used as well as three different facing thicknesses: one, two and three layers of a bidirectional flax fabric (400 g/m2). A bio-based epoxy resin was used to make FRPs. Several different failure mechanisms were observed during the testing, including: delamination, shear, crushing of the top face, tensile rupture of bottom face, and several combinations of these failures. It was observed that the shear and delamination failures occurred mainly in the low-density foam specimens, delamination and crushing of the compression face occurred mainly in the medium-density foam specimens, and that tensile rupture of the bottom face occurred in the high-density foam core specimens. As the tensile rupture of the bottom face occurred, it was concluded that the flax FRP facings reached full capacity in these cases and the foam did not cause premature failure.