Karas, Busra (2022) Additive Manufacturing of Carbon Fibre Reinforced Polymer Composites. PhD thesis, University of Sheffield.
Abstract
Additive manufacturing (AM) of carbon fibre reinforced thermoplastic composites can offer advantages over traditional carbon fibre manufacture through improved design freedom and reduction in production time and cost. However state-of-the-art fused deposition modelling (FDM) approaches for the production of carbon fibre composites, generally possess high porosity compared to conventionally manufactured advanced composites. On the other hand, the addition of fibre to the polymer powder bed fusion processes such as selective laser sintering (SLS) creates drawbacks such as poor fibre distribution in the powder feedstock, high porosity and low strength in the final parts. The reason for low-performance composites in AM processes is the lack of heat and pressure application. The traditional manufacturing processes for advanced composites improve the consolidation of the layers with autoclave machines or hot press processes, whereas in AM processes, compaction is not ideal to sustain the complexity of final geometry. In this study, the development of a novel alternative to the current composite AM based on sheet lamination, named composite fibre additive manufacturing (CFAM), is presented with the aim of reducing component porosity. This approach involves selectively inkjet printing a binder and polymer powder onto discontinuous carbon fibre sheets which are then compressed and heated to form net shape components. Using CFAM, complex-shaped discontinuous carbon fibre reinforced nylon composite parts were successfully manufactured for the first time. First of all the effect of process parameters such as applied pressure level, compaction time, and the volume of printed ink on the mechanical and microstructural properties of final parts was investigated to benchmark the process. Further investigation focused on polymer morphology to understand the effect of crystallinity on the CFAM final part properties. Additionally, a combination of hybrid layers involving continuous and discontinuous carbon fibre was examined with the aim of improving the mechanical properties. Finally, complex-shaped drone frames were manufactured to investigate the dimensional tolerances. The geometric accuracy and the load-carrying performance of the final products produced with the CFAM and other AM processes are examined and compared. The results demonstrate a correlation between the amount of pressure applied and the percentage of porosity and fibre volume fraction in the final parts. By providing an optimum level of pressure, the voids which can act as crack propagators, reduce significantly (1.5%). Hence more consolidated parts with relatively higher tensile strength and stiffness were obtained. Interaction between the crystallization process of thermoplastic matrix material in CFAM and resultant part properties was established using a new approach based on elements of DSC analysis, which provides a new level of understanding into the polymer behaviour under the different processing conditions. Finally, the end-use product performance of CFAM was found to be superior compared to the other composite AM techniques. The innovative fabrication process established in this thesis achieved the rapid production of high-performance discontinuous carbon fibre reinforced polymer parts with flexibility in material composition.
Metadata
Supervisors: | Mumtaz, Kamran and Fairclough, Patrick |
---|---|
Related URLs: | |
Keywords: | Additive manufacturing; composites; sheet lamination; mechanical testing; X-ray CT tomography |
Awarding institution: | University of Sheffield |
Academic Units: | The University of Sheffield > Faculty of Engineering (Sheffield) > Mechanical Engineering (Sheffield) |
Depositing User: | Dr Busra Karas |
Date Deposited: | 21 Dec 2022 16:11 |
Last Modified: | 22 Nov 2023 10:26 |
Download
Final eThesis - complete (pdf)
Embargoed until: 21 December 2024
Please use the button below to request a copy.
Filename: Karas_AM of CFRP_Final Thesis.pdf
Export
Statistics
Please use the 'Request a copy' link(s) in the 'Downloads' section above to request this thesis. This will be sent directly to someone who may authorise access.
You can contact us about this thesis. If you need to make a general enquiry, please see the Contact us page.