Investigation of fine-scale flows in composites processing

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.

Economic and environmental benefits are envisaged from this research. The global market for composite products in 2013, across all sectors, had a value of US $68.1bn. The overall market is expected to grow at around 6.5% over 7 years to about $105.8bn in 2020 and government consultation with the UK composites supply chain has shown that the UK has the opportunity to grow its current £2.3bn composite product market to £12bn by 2030. However, this can only be achieved through a sustained and pro-active program of research and development.

Carbon composite materials are in demand, particularly by the aircraft and automotive industries where lightweight alternatives to metal are needed to create aircraft and vehicles that are more fuel efficient and environmentally friendly (a 10% reduction in car weight improves fuel economy by 6-8%). To minimise structural defects during manufacture of these vehicles, current processes require the use of autoclaves, which introduces challenges with respect to slow manufacturing, high equipment acquisition costs, expensive tooling, energy intensive processes, restricted component size, and a supply chain tied to autoclaves. An aim of this research is therefore to identify ways in which effective carbon composites can be produced in an out-of-autoclave (OOA) environment, thereby circumventing these issues and enabling lower-cost, greener manufacturing of carbon composites.

The primary outputs of this work will be:
(i) validated software suitable for modelling resin flows in composites manufacturing, and capable of predict void content as a function of material and manufacturing process
(ii) new experimental techniques for monitoring those processes that will be able to help refine existing manufacturing techniques
(iii) new composite material microstructures that will produce consistent void contents when using a broad range of cheap, out-of-autoclave techniques

As industrial partners on this project, SHD Composites and Dantec Dynamics will have immediate access to these outputs, together with Rolls-Royce and BAe Systems. Quarterly updates to the industrial partners will take place through technical review meetings, aimed at improving the uptake and understanding of the developed tools, whilst capturing partner technical requirements. The software developed during this project will also be packaged in a suitable form to allow members at the National Composites Centre (NCC) (including Leonardo, Airbus, GE, GKN and QinetiQ) to conduct virtual modelling of a manufacturing process. A Software Specialist is currently being recruited as part of the Simulation of new manufacturing processes for composites structures Platform Grant (EP/P027350/1) and will be available to help package the project outputs into a user friendly format. We envisage that the software will be arranged to start from an initialised microstructure of a composite material, and then predict a likely void content at the end of the process, given a set temperature-pressure profile. Support for uptake of this software will be provided by Kratz, who has recently been awarded a Researcher in Residence placement at the NCC, and will be available for day-to-day testing. A workshop will also be held at the NCC for industry dissemination of project outputs.

In addition, since experimental fluid mechanics is an area under threat in the UK, the upskilling of two PDRAs in this area will be of benefit to industry through their subsequent employment.