The high cost of raw materials, high labour costs and lengthy cycle times have limited the use of conventional ply-based composites in the automotive industry. This thesis seeks to identify the potential of using low cost discontinuous fibre composites (DFCs) for structural applications. Properties of DFCs are governed by the degree of homogeneity of the reinforcement and discontinuities at the fibre ends, which cause stress concentrations; thereby limiting the mechanical performance of the material. This work focuses on material characterisation of laminates moulded from discontinuous carbon fibre preforms manufactured by a robotic spray process. Through the culmination of this work, a suitable design methodology for automotive applications has been identified. Design procedures for aerospace have also been considered. An analytical model has been developed to determine the tensile stiffness and strength of a discontinuous carbon fibre preform composite. The model can be used within automotive and aerospace design methodologies to define material properties, but a number of other factors must be considered. Areal mass of the preform has been identified as the governing factor in achieving target compaction levels. Poor homogeneity in thin parts prevents the ability to achieve high volume fractions, which determines mechanical performance. It has been demonstrated that the matrix has a greater influence on the properties of DFCs when compared to continuous fibre composites. Toughened resins were particularly effective in improving tensile strength of DFCs that exhibited poor homogeneity. Damage tolerance of DFCs has been evaluated through open-hole and compression after impact testing. Higher property retention was observed compared to continuous fibre equivalents. Greater damage tolerance of DFCs could lead to increased weight-saving in structural applications. However, current safety factors based on conventional laminates may be too conservative and could lead to over-engineering thus limiting the potential of the material.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:594708 |
| Date | January 2013 |
| Creators | Kirupanantham, Giridharan |
| Publisher | University of Nottingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://eprints.nottingham.ac.uk/13801/ |
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