Structure-property dependence of nonwoven veils for composite interleaves

Abstract

This thesis discusses the use of nonwoven textiles to increase the interlaminar fracture toughness (IFT) of carbon fibre reinforced polymers (CFRPs), which are increasingly used in primary aerospace structures and automotive applications. The study builds upon earlier work that revealed a relationship between coverage of an interleaving veil, determined by its areal density and fibre morphology, and mode I and mode II IFT. Accordingly, a systematic investigation into the influence of different nonwoven veils used as interleaves on the IFT of carbon/epoxy composites is presented here. The dependence of IFT on the fibre type of microfibre veils was found to differ depending on the mode of loading, such that for mode I an increase in IFT with increasing coverage was dependent on veil fibre type, where polymer fibres showed higher increases than inorganic fibres, whereas for mode II, the increase in IFT showed considerable insensitivity to fibre type. Through investigation of veils with a range of areal density and coverage, for both mode I and mode II, IFT was found to increase to a plateau above a mean coverage of about 3. Analysis of fracture surfaces using SEM revealed curled veil fibres that were absent from the original veil and are consistent with a significant energy absorbing mechanism. Investigation of the influence of nanofibres electrospun onto low-coverage carbon fibre veils, which allowed coverage to be increased with a limited increase in areal density, showed no increase in IFT above that achieved with the low-coverage carbon fibre veil alone. The relationship between coverage (for veils with coverage up to 3) and an increase in IFT to a plateau was not found to exist for nanofibre veils. Although nanofibre veils at high coverages could provide some interlaminar toughening, as found in the literature when using pre pregs, these may not be suitable for resin infusion processes, and could not compete with the superior toughening provided by microfibre veils.

Date of Award	21 Dec 2022
Original language	English
Awarding Institution	The University of Manchester
Supervisor	William Sampson (Supervisor) & Prasad Potluri (Supervisor)