Multiaxial non-crimp fabrics: Characterisation of manufacturing capability for composite aircraft primary structure applications

Abstract

Carbon composite reinforcement fabrics aimed at flight critical aircraft structure application were designed and the capability of the process used to manufacture them examined. Studies of the LIBA multiaxial non-crimp fabric manufacturing process focused on the effect of changes to four manufacturing parameters using an experimental design process to design the fabrics and analyse the results. The composite properties measured included microstructural features of the fibre tows and resin distribution, and mechanical performance both in-plane and their damage resistance and tolerance characteristics. Nine pairs of Toray T300 carbon based LIBA multiaxial non-crimp fabrics were manufactured and converted to composite laminates. Processing was accomplished using the interleaved Resin Film Infusion processing route with commercial Fiberdux 914 matrix resin. All the fabrics were of the same reinforcement type, consisting of 816 g/m2 of fibre; 376 g/m2 oriented along the fabric length (0°) and 220 g/m2 oriented in each of the ±45° directions. Differences between the nine pairs of fabrics were restricted to the settings of four manufacturing parameters; stitch course (needle penetrations/cm); stitch tension, 00 tension and 0° coverage (amount of constraint on the 0° material provided by the stitch). Three settings were used for each of the parameters; each representing the upper and lower limits, and standard setting. Microstructural characterisation of the laminates indicated large differences in both resin distribution and levels of 0° fibre crimp caused by the changes in manufacturing parameter settings. In-plane and damage resistance and tolerance tests on their composites allowed relationships between manufacturing settings, microstructure and engineering properties to be deduced. It was found that selected in-plane properties could be increased by as much as 17% relative to standard production materials, although a wide range of influence was observed. For damage resistance and tolerance characteristics, reductions in impact damage area (C-scan) of between 13-50% are expected across a range of energies. Manufacturing settings to maximise the impact force for delamination initiation were found to minimise the impact damage areas. Similarly the same settings maximised both the Mode I propagation strain energy release rate and the Compression After Impact strength of the materials. It was found that polyester knitting yarn was largely responsible for the control of the damage resistance and tolerance characteristics together with the mean size of the resin areas and layers within the composite. The manufacturing/microstructure/property relationships identified provide those wishing to exploit these materials with design guidelines to tailor fabric structure and performance characteristics for the intended application. Above all else the results highlight the need for precision in specifying and controlling the manufacturing process in order to repeatably produce the desired performance. Further work on the same materials could be used to provide a link to processing characteristics such as permeability for liquid resin moulding processes and ability to conform to complex curved surfaces.