Axial compressive behaviour of flax and glass FRP-XPS insulation sandwich panels

Sandwich structures made up of flax fibre–reinforced polymer (FFRP) skins and balsa wood (BW) cores were investigated under axial compression test and three-point bending test. The influences of the core thickness and the number of FFRP layers on the axial compression and flexural behaviour (in-plane and out-of-plane) of FFRP-BW sandwich structures were examined. The test results indicated that using two-layer FFRP as the skins of the FFRP-BW sandwich structure can achieve significantly higher compression strength and out-of-plane flexural stiffness than FFRP-BW with one-layer FFRP skins. As the core thickness increased, the in-plane bending strength and compression strength of the sandwich structures decreased by 31.7–50.1% and 20.5–39.7%, respectively. Regarding the out-of-plane flexural stiffness, the increase of the core thickness led to the increase of 61.5–103.0% and 64.9–150.2% in the FFRP-BW sandwich structures with one-layer and two-layer FFRP laminates, respectively.