The Future is Remanufacturing: Composites for Life

Composites based on continuous fibre prepreg sheet laminates are a mature technology - widely used in the aviation industry for key structural components, However, the future horizon for composite development now lies in providing lightweight thick-section composite parts aimed at replacing metal components predominantly within the automotive sector. High thermal tolerance, thick section composites that are tough and durable could now offer a viable metal replacement technology for an expanding range of sub-chassis applications, particularly wheels, suspension, braking systems gear casings, rotor shrouds and components within the engine compartment.
Historically, monolith-type, thick-section parts have typically been made from aluminium or steel, and exceptionally with thermoset composites - but these have fundamental drawbacks when used for thick-section moulding. Thermoplastic discontinuous fibre tapes offer a tantalising alternative to traditional thermosets. Thermoplastic composites (TPC) based on e.g. PEEK and high-performance Nylons have the potential to offer a viable lightweight aluminium replacement option, with superior toughness and fatigue performance - both critical considerations for both automotive and aviation applications. The excellent formability and high flow characteristics mean parts can be produced quickly and cheaply with part counts into the 100,000's, making this class of composites uniquely suited to the volume demanded by the automotive industry, whilst also being capable of being used in thick section mouldings .
The recent development of Polyether ether ketone (PEEK) carbon fibre moulding compounds at Exeter showed that this material achieves a bulk modulus of ~40GPa when hot-pressed, which, whilst short of the ~70GPa offered by aluminium, is a marked improvement over previous offerings. Recent advances in manufacturing approach pioneered by the University of Exeter have seen the achievable modulus reliably pushed above 70GPa - directly on par with Aluminium, and, most excitingly, a technique by which controlled, localised orientation might be achieved through the use of pre-consolidated charges, exploiting the high viscosity of the material during manufacture. This technique could revolutionise the TPC sector, allowing the simple manufacture of thick-section components with the optimised design properties previously found only in multiaxial ATL processes. The new "pre-charges" route being proposed, will simplify manufacture, and remove the barriers to rapid volume production, similar to the advent of prepregs and SMC in the 1970's, that made possible the controlled, mass-manufacture of high performance composites in the aviation and automotive industries.

A base line improvement in properties together with the removal of manufacturing barriers, could change the current emphasis on thermosets to thermoplastics, which is highly important environmentally. Recycling of most types of thermosets is not commercially viable, despite extensive research into the area. Thermoplastic based systems have the potential to solve the recycling issue, with the ability to melt and re-press components without performance implications greatly improving the recyclability of the material - a characteristic that has long eluded thermoset CFRP's. Moreover, this trait lends itself exceptionally well to in-situ repair and damage healing. The viability of remanufacture and remoulding of composites needs to be established for all of the most common TPC's available. The study will both consider the remanufacture of components (closed loop recycling), and also the viability of 'shape change' with TPC's, i.e. the extent to which materials can be reprocessed like metals through re-melting and reforming multiple times. The future vision is for manufacturers to include recycling/remanufacture instructions as part of standard materials datasheets.

1) The Industrial partners: All partners will benefit directly by keeping abreast of the latest research on this class of composites, and continued links with the University. Each partner also stands also to benefit directly: Victrex plc are the world leading producers of PEEK. PEEK TPCs are a particular focus for the project, where Victrex stand to gain if the market and usage of TPCs grow through increased sales. Heightened appreciation of potential benefits of TPCs could bring about a paradigm shift in the composites industry, via a move away from non-recyclable non-reusable thermosets in favour of the more sustainable option of TPCs. Royal Tencate Composites are leading makers of TP moulding compounds and TP - coated tapes and would similarly benefit from the increased market. Meggitt plc are Tier 1 - 2 suppliers, predominantly to the aviation industry. Their position relies on technical excellence, and the ability to offer world beating products that are lighter, perform better, and are more sustainable than rival offerings. Meggitt recognises the rising importance of TPCs in previously unthought-of applications, such as wheels. Composites-For-Life will only strengthen this position. Boeing and Leonardo Helicopters as airframe makers can see the advantages and are exploring TPCs as candidate materials for potential metal/thermoset replacement. The advantages of lower weight, improved toughness, improved fatigue life and a far reduced requirement for post manufacture processing (shot-blasting, peening, anti- corrosion coating, anodization, or painting), make TPCs attractive in themselves, and in addition, offer an answer to the sustainability and disposal issue. Another very important advantage is the ability to "heal" components, a facet of interest to their military customers offering the prospect of fast turn-round repair. The National Composites Centre (NCC) recognise the growing importance of TPCs to their member organisations and wish to offer capability in the area, as evidenced by their recent investment in TPC technology. It is critical for the NCC to stay abreast of the latest science in the area (see support letter), where the NCC will directly benefit in this regard as a project partner.
2) The wider industrial and scientific communities: The flow of publications, presentations and seminars planned (see NCC support letter), will heighten awareness and provide new knowledge concerning the manufacture and recyclability of TPCs, and also the extent to which re-moulding and healing is possible, supported by scientific data. This will allow informed decisions to be made regarding materials selection, and create a foundation of research for a new, sustainable, manufacturing route for TP moulding compounds. Currently, only a few specialist manufacturers can process DFMCs. It is hoped that this programme will open up the field by making the manufacture and processing information available to all, for the first time.
3) Society: Environmental benefits include lower density than aluminium and steel, meaning, when used in automotive and aviation, reduced through-life fuel consumption and reduced CO2. Lightweighting is also critical to electric vehicles, increasing range and economy. As important are the toughness and fatigue properties of TPCs, being far tougher than thermosets, - a major drawback of these materials. TPCs can also be used to mould thick-sections - difficult or impossible with thermosets. TPCs can therefore access previously unattainable application areas for composites, offering further weight savings. Fatigue life is a x10 higher than aluminium, where TPCs do not suffer corrosion, further adding to overall safety and potentially reducing inspection and maintenance schedules. TPCs do not need any post-mould surface treatment, whereas Aluminium parts post-forging are machined, cleaned, shot peened and then glass bead overpeened to inhibit fatigue cracks it is then anodised, and painted with an epoxy.