The cost of manufacturing high quality composite components can be significantly reduced by using Out of Autoclave (OOA) processes if they can achieve final parts with a finish quality as high as that obtained using an autoclave process. Much research has been carried out recognising that regardless of the reinforcement fibre orientation, manufacturing of preimpregnated (prepregs) carbon components is much affected during its forming stage by fibre deformation and failure modes.This work sought to reduce wrinkling in the moulding of prepregs by introducing slip layers within the lay-up. Three types of slip layers were used: a dry fabric, a resin rich layer and a resin film. In order for the slip layers to be fully incorporated into the final laminate the resin content within the slip layer must be adjusted prior to crosslinking. In the case of dry fabric layer, additional resin must be introduced and in the case of a resin rich layer and resin film layer, excess resin has to be removed. The laminates used in the project were based on 2/2 twill and unidirectional carbon prepregs. These were manufactured by either Resin Infusion (RI) or Vacuum Bagging (VB). Resin adjustments were made at the same time.The 2/2 twill and unidirectional carbon prepregs were first characterised by Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Thermal Analysis (DMTA) before RI and VB. Dry 2/2 twill and unidirectional carbon fabrics and/or Resin Film (for VB) or fabrics and Epoxy Resin (for RI) were introduced in several plybooks and then cured. Final parts were either made of 2/2 twill carbon or unidirectional carbon. The parts were used to investigate the relationship between individual plies during the consolidation of a plybook. The first characterisations were done on flat laminates. Also two moulds were manufactured and used to produce new parts for further characterisations. The first, an aluminium mould was machined using a Computer Numerical Control (CNC). The second mould was a fan blade, made using chopped strand mats. The final parts had 3, 4 or 6 plies. These parts were characterised using Optical Microscopy (OM), Scanning Electron Microscopy (SEM), and Torsion testing. The results provide a first step towards understanding how the friction at a ply/ply level can be influenced by the "starving" or the "enriching" of resin in a plybook during its consolidation. The work showed that in OOA manufacturing, the friction at a ply/ply level can be controlled by introducing Resin Film, Dry or Resin Rich Fabrics in a prepreg plybook. It was demonstrated that introducing lubrication to control ply friction during forming can result in quality part as high as that obtained from a traditional composite forming process. As the final parts were made using a fixed die mould and a vacuum bag, most of the plies in the layups could deform individually and accommodate interply shear. Torsion testing on a number of a random selection of samples showed negligible effects on shear stresses, strengths and modulus within the parts were negligible. It is argued that the flexibility of the vacuum bag could have had an impact on the layups during forming. The plies could conform to the mould easier. This work has potential for other applications. For example in match die moulding, introducing wet lubrication could improve interply shear during forming and help in improving accuracy and geometrical conformity of final parts. Furthermore, developing techniques to control friction during forming in OOA can be attractive to industries which could not afford to invest in this OOA prepreg technology. OOA processing times have become very attractive to industries such as the sporting good, automotive, wind energy and transportation. These industries could explore the opportunity presented by the work in this EngD thesis.
|Date of Award||31 Dec 2015|
- The University of Manchester
|Supervisor||James Methven (Supervisor)|
- prepreg, composite, DSC, DMA, SEM, resin rich
- characterisation, CFRC, mould manufacturing, slip layers,