1 Nano-Modified Sandwich Composites under Dynamic Loading Conditions

The aim of this paper is to investigate the influence of nano-structures, mostly intercalated form, on sandwich composites under impact loadings. To achieve such goal, a set of sandwich composites plates made of fiberglass/nano-modified epoxy face sheets and polystyrene foams was prepared. The polystyrene core was 25 mm thick and the face sheets were made of eight layers of woven fabric glass fibers and nano-modified epoxy ( 0.8 mm of thickness). The epoxy system was made of bisphenol A resin and an amine hardener, i.e. RemLam M and HY956, from Hunstman Inc. The fiber volume fraction used was around 65%, while the nanoclay content varied from 0 wt % to 10 wt%. The nanoclay used in this research was organic modified montmorillonite produced by Southern Clay Inc. (Cloisite 30B). Once the sandwich composites planes were prepared, they were submitted to low velocity impact tests using a drop weight tower. The energies applied ranged from 5 Joules to 75 Joules. Two sets of experiments were performed, i.e. high velocity + low mass and low velocity + high mass. Damage caused by the two groups of experiments and peak forces measured were dissimilar. The results show that the addition of 5 % on nanoclay with respect to the epoxy system weight leads to a more efficient energy absorption and a different failure modes. Two transition failure modes, from upper face sheet cracking + core indentation to upper face sheet tearing + core crushing, and upper face sheet tearing + core crushing to lower face sheet and core debonding, appears to overshadow the nanoclay effect, as they seems to be infective in these two conditions. I