Hygrothermal ageing and damage of sandwich composites

The aim of this work was to analyse the durability of sandwich panels with a honeycomb aluminium core and composites skins based on epoxy resin and carbon-glass fibres. Ageing tests have been developed and the mechanical properties after ageing were evaluated. In particular the specimens were edge-sealed on all sides to prevent the water ingress in the core and submitted to this cycle: in water at 50°C for 1h, heating in dry air at 70°C for 3h, spraying with hot water at 70°C for 3h, heating in dry air at 70°C for 18h. They were then subjected to compression (edgewise and flatwise) and bending. Moreover, the sandwiches were subjected hot-wet conditions (at 70°C in distilled water for 3 and 5 weeks) and tested to flatwise tension test: the bond between core and skins was evaluated. Undamaged specimens simulated the ingress of water by diffusion and specimens with perforated surface simulated the direct ingress of water due to defects. This work showed a decrease of bending properties of 20% for specimens with fibres oriented at 90°and of about 50% for those at 0°. A reduction of the compression moduli due to ageing was found: 43-51% for the edgewise and 59% for flatwise. Moreover, the flatwise tension tests under hot-wet conditions (70°C-100% urs) showed a decrease of the Young’s modulus (63% after 5 weeks), while the tensile strength was halved.