MIXED MODE FRACTURE TOUGHNESS OF CRACKED SPECIMENS MADE OF NANOMODIFIED EPOXY RESIN

In the present work the effects of nanoclay addition on fracture behaviour of an epoxy resin under mixed mode (I plus II) loadings are studied by analysing the results from Single Edge Notch Bending (SENB) specimens. The results allow to conclude that, for weight contents lower than 5 wt.%, nanomodification significantly enhances the fracture toughness of the epoxy resin upon the entire range of mixed mode loadings, the improvements being dependent on the mode mixity ratio. Experimental results are later compared to the theoretical predictions based on different, well acknowledged, mixed mode fracture criteria. The results from specimens made of pure epoxy are well predicted, almost independently of the approach used for the synthesis. Conversely, as far as the results from specimens made of nanomodified polymer are concerned, the agreement with theoretical predictions is much poorer. This can be thought of as linked to the emergence, of different damaging mechanisms due to nanomodification depending on the mode mixity.