Effects of carbon nanotube modified adhesive layer on low velocity impact and flexural properties of cork core sandwich structures

The traditional method of manufacturing sandwich structures using a structural adhesive to achieve face-sheets to core bonding maintains widespread use. Most research addressing experimental performance of sandwich structures focuses on core and face-sheet related parameters, and only marginal attention is directed to the mechanical properties of the thin, low content, adhesive layer – it usually suffices that it can provide effective face-sheet/core bonding. The present work studies sandwich structures with a cork agglomerate core and resin infusion processed skins consisting of +/-45° glass fibre fabric reinforced epoxy resin. A polyurethane structural adhesive was used to assemble the structure. The focus of the study was the influence on sandwich performance with respect to a modification of the adhesive with multiwall carbon nanotubes, exploring the possibility of an increase in both shear and adhesion strength of the modified adhesive. The sandwich structure was evaluated with respect to four-point bending and low velocity impact tests. In addition, scanning electron microscopy analysis was used to examine the adhesive layer morphology. The results were analysed to determine how the addition of ca. 0.4 wt.% of carbon nanotubes to the adhesive effectively influenced failure behaviour and damage events in both flexural and impact testing.