Quasi-static indentation and impact in glass-fibre reinforced polymer sandwich panels for civil and ocean engineering applications

Sandwich structures comprising glass-fibre reinforced polymer faces and low-density core constitute an efficient and versatile constructive system for civil and ocean engineering structures. However, being multilayered with relatively soft core materials, they are particularly susceptible to damage under concentrated loads. Whilst numerous studies exist on the indentation and impact behaviour of sandwich composites, the great majority considers the thin-skinned laminates used by the aeronautical industry. To mitigate the lack of studies on the significantly thicker and more robust civil and ocean engineering sandwich laminates, the quasi-static indentation and low-velocity impact behaviour of such panels is experimentally studied. Three types of core materials (polyurethane and polyethylene terephthalate foams and end-grain balsa) and five different indenters, of varying shape (hemispherical versus flat) and diameter (10, 20 and 30 mm), are considered. Flat and larger indenters required higher loads and energies for first damage and perforation. The first damage and peak resistance values of the polyethylene terephthalate panels were, respectively, 15 and 8% higher than in the polyurethane panels; for the balsa panels, such figures were 20 and 10%. The polyurethane panels showed the highest energy absorption capacity. Predictions of first damage resistance given by two analytical models (for flat and hemispherical indenters) were assessed against the gathered experimental data. The obtained predictions were reasonably accurate, but indicate a need for further calibration, mainly concerning the effects of core material.