Flax and glass FRP-XPS insulation sandwich panels under in-plane and out-of-plane bending

To meet a growing demand for good insulating properties of walls and tighter building envelopes, structural insulated panels (SIPs) have been developed for decades. This kind of sandwich structure commonly uses polystyrene as a core layer, skinned with two sheet layers. In recent years, fibre-reinforced polymer (FRP) has been applied innovatively as this structural sheet, which has higher strength-to-weight ratio compared to traditional board materials such as oriented strand board, steel, or concrete. In this chapter, flax FRP (FFRP)– and glass FRP (GFRP)–skinned extruded polystyrene (XPS) foam sandwich panels were fabricated. Specifically, three types of XPS foam cores with thicknesses of 40, 50, and 80 mm, along with FFRP and GFRP face sheets with different thicknesses, were considered as the experimental variables. Out-of-plane and in-plane bending tests were conducted to evaluate the structural performance of the SIPs. In terms of the out-of-plane bending test, it showed that 1.51 times thicker FFRP face sheets provided equivalent mechanical properties of FRP-skinned sandwich panel as GFRP sheets. In in-plane bending tests, the foam core only showed a stabilisation function. It was also observed that, compared with GFRP-skinned XPS foam panels, FFRP-skinned XPS foam panels offered better compatibility between XPS foam and face sheet. Meanwhile, face wrinkling occurred when the thickness of FFRP face sheet was decreased, and only in the case of face wrinkling failure did the foam core thickness have an effect on the load capacity of the FRP-skinned panel structure.