Thermal Conductivity of Carbon Fibre Fabrics and Multi-Scale Composites with Heat Transfer Simulations for RFI Manufacturing

Title: Thermal Conductivity of Carbon Fibre Fabrics and Multi-Scale Composites with Heat Transfer Simulations for RFI Manufacturing
Authors: Yang, Yue
Date: 2013
Abstract: Composites are increasingly used in aerospace applications where performance is the foremost priority of industry. Research on carbon nanotube (CNT)-reinforced polymers conducted in the past decade showed promising results for the improvement of mechanical, thermal and electrical properties of composites. This thesis was undertaken in the context of a larger project, the main goal of which is to develop a complete solution for the manufacturing of carbon fibre-epoxy composites using CNT-reinforced epoxies, referred to as multi-scale composites. This thesis focuses on the thermal aspect of this project under three topics: 1) thermal conductivity of dry carbon fibre fabrics for understanding heat diffusion in composites and similar fabric materials 2) thermal conductivity of CNTreinforced polymers and composites for determining the effect of parameters including CNT addition, and 3) modelling of heat transfer during composite manufacturing for ensuring that their temperature distribution remains controlled. In-plane k rip and through-thickness k rtt thermal conductivity data were measured for two dry carbon fibre fabrics as a function of fibre volume fraction Vf . Results showed that k rip varies linearly with Vf whilst k rtt varies in an exponential recovery trend with Vf . An existing analytical model was used successfully for predicting k rip and simulations developed for predicting k rtt values demonstrated that k rtt depends on the evolution of heat conduction paths in the through-thickness direction as a result of improvements in the fibre contact network. A procedure was developed for manufacturing composites using the RFI process. Thirty-two composites and multi-scale composite plates were manufactured and characterised for investigating the effects of eleven material and manufacturing parameters on fibre volume fraction, porosity, k rip and k rtt . Results showed that the effect of using multi-walled CNT-reinforced epoxy on thermal conductivity of composites is negligible at 0.3% CNT loading. However, this reduced the porosity of the composites significantly. Results also showed that using fabrics with higher surface densities led to a slight increase in k cip . A heat transfer model coupled with cure kinetics was developed for predicting temperature profiles of the laminate during RFI manufacturing. The model was validated experimentally and eleven simulation cases were run for investigating the effects of five material and manufacturing parameters on temperature profiles in the laminate. Results showed that the epoxy resins used in this project combined with the cure cycle recommended by the manufacturer are well-suited for manufacturing laminates with a typical thickness of approximately 5 mm as well as thick laminates of 15 mm to 20 mm.
CollectionThèses, 2011 - // Theses, 2011 -