Nanofibre bridging as a toughening mechanism in carbon/epoxy composite laminates interleaved with electrospun polyamide nanofibrous veils

Electrospun thermoplastic nanofibres have a large potential for the interlaminar toughening of composite laminates. They can easily be placed in resin rich interlayers between reinforcing plies prior to laminate production and require no dispersion into the matrix resin. Although there are many expected benefits, the research on composite laminates enhanced with electrospun thermoplastic nanofibres is still very limited and a thorough understanding of the toughening mechanism is still missing. This article provides thorough insights into the micromechanisms that lead to the interlaminar toughening of carbon/epoxy composite laminates interleaved with electrospun polyamide nanofibrous veils. The main mechanism leading to a higher interlaminar fracture toughness, both under Mode I and Mode II loading conditions, was the bridging of (micro)cracks by PA nanofibres. The effectiveness of the nanofibre bridging toughening mechanism is dependent on a good load transfer to the nanofibres. Crack propagation under Mode II loading conditions resulted in much higher improvements than under Mode I loading due to an optimal loading of the nanofibres along their fibre direction in the plane of the nanofibrous veil. In Mode I crack propagation, however, the loading of the nanofibres is less optimal and was shown to be dependent on both the primary reinforcement fabric architecture, as well as on the presence of a carbon fibre bridging zone.