Investigation of fine-scale flows in composites processing

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Anticipated growth in global air passengers by 90% over the next 20 years presents both challenges and opportunities. High fuel costs and environmental pressures mean there has been a real focus on operating economics and this has led to an unprecedented growth in composite materials, which offer a lightweight alternative. Successful production of carbon composites brings its own challenges however, in that it requires the use of autoclaves to minimise gaps (void defects) in the polymer resin material that encapsulates the fibres. This makes the process costly, energy-hungry and slow.Lower capital and operating costs, flexible processing infrastructure, a broader supply chain and a greener manufacturing process represent the big gains that could be made through development of effective out-of-autoclave (OOA) manufacturing processes. Indeed, the High Value Manufacturing Catapult has recently identified OOA manufacturing solutions as a key area for economic growth to ensure a UK presence in next-generation aircraft wings, aero propulsion technologies, and structural light-weighting technologies necessary to help the government achieve carbon-reduction and emissions targets.This project will develop experimental techniques and numerical tools to simulate void processes, in order to produce improved material designs for composite manufacture in out-of-autoclave conditions. The processes we intend to analyse use semi-impregnated carbon fibre reinforcement, where the polymer is applied in such a way that dry and saturated regions are present at the start of processing. Two processes will be studied: (i) vacuum bag processing, where consolidation is by atmospheric pressure (low pressure slowly evacuates entrapped gasses, suitable for larger parts such as wing skins), and (ii) using a mechanical press (high pressure fast process collapses voids, suitable for smaller parts such as automotive structures). The advantage of a semi-impregnated material format is that toughened polymers with higher process viscosity can be used, and once the modelling approach is established, it can be extended to resin infusion processes with minor modifications to the model geometry and boundary conditions.The first stage of this project is to address a fundamental need to be able to understand and model the processes that form and remove voids, so that these processes may be designed quickly in a cost-effective manner in a virtual environment. Once this jump in understanding is made and suitable tools created, the second stage is to create tailored materials to minimise formation of void defects for either the vacuum or press-based routes using manual and automatic optimisation. With the UK currently boasting a £2.3bn composite market, and looking to grow this to £12bn by 2030, the findings of this research will contribute to a vitally important and growing sector of the UK economy.