The effect of foam core density at various slenderness ratios on axial strength of sandwich panels with glass-FRP skins

In this study, the effect of the density of a polyisocyanurate (PIR) foam core on the behavior of axially loaded sandwich panels with glass fibre reinforced polymer (GFRP) skins are examined, for different panel heights. Thirty-six test specimens with a cross-sectional foam core area of 100 × 50 mm2 and symmetrical 100 mm wide GFRP skins were fabricated with heights of 750, 1000, 1250, and 1500 mm to examine various slenderness ratios (kLe/r). Three PIR foam core materials with densities of 32, 64 and 96 kg/m3 were used. An out-of-straightness assessment was first conducted to ensure that eccentricities were within acceptable limits. All samples were tested to failure in axial compression with pinned end conditions. It was shown that doubling and tripling the core density led to increases in peak load of 71 and 170%, respectively, due to the enhanced composite action and reduced shear deformations. On the other hand, slenderness had insignificant impact on peak loads, contrary to what one would expect from Euler's theory. The reason being the variety of governing failure modes. Columns with low (kLe/r) of 22-25 failed largely due to localized single skin buckling, while those with high (kLe/r) of 51-61 failed primarily by global buckling followed by secondary core shear failure with skin debonding. Columns with intermediate (kLe/r) experienced a combination of localized and global failure modes.