Development and fracture toughness characterization of a nylon nanomat epoxy adhesive reinforcement

The potential of an electrospun nylon nanofibrous mat as adhesive carrier and reinforcing web in adhesive bonding has been proven by the authors in a previous work. In that work, a pre-preg nanomat was developed using a low-viscosity epoxy resin for composite hand lay-up, in order to favour wetting of the nanofibres and to minimize air entrapment. However, the resin for hand lay-up exhibited a poor bonding performance when compared to the one typical of epoxy adhesives. The present work is therefore aimed at developing a laboratory route to add an electrospun polymeric nanomat to a two-part epoxy adhesive joint. Three different adhesives with increasing viscosity have been preliminarily evaluated regarding the entrapment of air after curing. The most promising one has been used to manufacture a small-size, Al-alloy double cantilever beam joint and compare the performance with and without the nanomat. Three different precracking procedures have also been developed and evaluated, namely fatigue precracking (A), razor blade tapping (B) and nanomat exfoliation (C). The results indicate that the fracture toughness of the nanomat-reinforced adhesive joint is similar to the neat adhesive one at the beginning of the propagation but it becomes much higher as the crack advances.