Investigation of the Resin Film Infusion Process for Multi-scale Composites Based on the Study of Resin Flow, Void Formation and Carbon Nanotube Distribution
Creators: name: Baril-Gosselin, Simon
Publisher: name: Université d'Ottawa / University of Ottawa
Year: 2018
Subjects: Polymer-matrix Composites
Manufacturing
Resin Film Infusion

description: The aerospace industry is steadily increasing its use of polymer-matrix composites (PMCs) in airframe structures as it seeks to benefit from the high specific in-plane strength of laminated structural PMCs. However, PMC laminates suffer from low interlaminar shear strength due to their weaker polymer-matrix. Minimising risks of delamination is of paramount importance towards improving the safety of PMC structures. Multi-scale composites that are reinforced by both continuous fibres and nano-particles were identified as a potential solution for improving toughness and reducing risks of delamination in PMCs. An important challenge in the fabrication of multi-scale PMCs is to ensure that nano-particles are dispersed uniformly within the matrix. This is only achieved through minimal filtration of nano-particles during processing. The short resin flow lengths enabled by the resin film infusion (RFI) process make this process a prime candidate for the fabrication of multi-scale PMCs. The main objective of this thesis is to validate the possibility of using out-of-autoclave RFI for fabricating multi-scale carbon fibre composites featuring epoxy resins modified with carbon nanotubes (CNTs). The work is accomplished in 5 phases. In phase 1, preliminary work investigates the fabrication of PMCs with and without CNTs, using out-of-autoclave RFI. Results show that the types of reinforcement and matrix have strong effects on the porosity and interlaminar strength of PMCs. These results ushered the need for more thorough investigation and understanding of the RFI process, beyond what is available in the literature. Phases 2 to 4 focus on understanding how the choices of materials and types of stacking configuration can affect parts made using RFI. Phase 2, the in-situ characterisation of resin saturation during RFI is performed. Results enable a detailed analysis of the way in which resin flows around and inside yarns. Phase 3 consists in the characterisation of void formation during RFI. Two types of voids are observed: flow-induced voids resulting from either the merging of resin flow fronts or the drainage from capillary action; and gas-induced voids resulting from resin volatiles going out of solution and remaining in the resin matrix. In this work, the greatest source of porosity was caused by volatiles. In phase 4, the distribution and filtration of CNTs during RFI processing is characterised. Results show that processing choices can limit filtration and that clustering of CNTs prevents a uniform dispersion of CNTs in PMCs. Finally, the possibility of using RFI for making a multi-scale PMC demonstrator part is investigated. The work culminated with the successful fabrication of a delta-stringer panel. This thesis makes several important contributions to the knowledge pertaining to multi-scale PMC processing and performance, and to RFI. Firstly, it provides a robust description of RFI processing beyond was it available in literature, through in-situ observations of resin flow and void formation. Secondly, it assesses the viability of RFI for producing multi-scale PMCs featuring CNTs. In-situ observations of RFI processing enabled the identification of mechanisms leading to a loss of CNT dispersion during processing, partly explaining the minimal improvements in the interlaminar properties of composites observed when adding CNTs to the matrix. Thirdly, the fabrication of a delta-stringer panel made of a multi-scale PMC was successful, making it the first validation of the scalability of out-of-autoclave RFI processing for manufacturing multi-scale PMCs. The work presented herein contributed to the dissemination of knowledge; one conference paper was presented at ICCM20 (20th International Conference on Composite Materials), and another was presented at CANCOM2017 (10th Canadian-International Conference on Composites), and one journal article written in collaboration with project partners was submitted to Composites Science and Technology.