Thick section composites
Thick section composites
Thick section composites
From a research perspective, composites based on continuous fibre prepreg laminates are a mature technology – widely used and supported by many centres of academic excellence across the world. The future horizon for composite development now lies in providing lightweight, thick-section composite parts rather than skin structures. This is assuredly the next frontier growth-area for the wider application of composites, where the mass scale of production envisaged means that the demand for recyclability will be even more pressing.
Key Research Aspects:
Exeter has perfected a methodology for reliably moulding thick-section (>50mm) composite componentry, using discontinuous PEEK Carbon Fibre prepreg tapes, and thereby allow the use of composites in a whole range of new application areas.
Making thick section composite components – JEC article - Tackling the barriers to the widespread utilisation of thermoplastic composites, the team has perfected a metholdogy for reliably moulding thick section (>50mm) composite componentry, using discontinuous PEEK carbon fibre prepreg tapes, and therby allow the use of composites in a whole range of new applications.
Exeter has developed a manufacturing technique that allows controlled, localised fibre orientation through the use of pre‐consolidated charges. This technique offers control of fibre orientation in all three axes, an advantage that could revolutionise the TPC sector where aligned fibre pre-charges could now be used to augment component properties in the exact areas required, allowing designers the freedom to exactly specify the size, type, orientation and the fibre volume-fraction in differing regions of the same component. Because the pre-charges are pre-made, each pre-charge can have its own specific formulation, so that where e.g. optimised stiffness, tensile strength, or toughness is required within a singular component, these features can be designed-in and easily manufactured. The image shows a quarter section of the AW129 helicopter wheel. The diagram shows how oriented pre-charges have been used to optimise properties beyond that achievable by an isotropic monolith. Assembly is simply a matter of arranging the appropriate pre-charges within the tool, and re-melting, and consolidating the component.
The simple answer to recycling composites lies in the use of thermoplastic resins as the matrix material, such as PEEK, polypropylene (PP) derivatives, and high-performance Nylons. Thermoplastic-based systems have the potential to revolutionise the sector in this regard, with the prospect of being able to melt and re-press components without performance implications, and without the removal of the resin matrix - a characteristic that has long eluded thermoset CFRP’s. Moreover, this ability to reprocess the material lends itself exceptionally well to in-situ repair and damage healing. Another critical advantage of TPCs is their inherent toughness and damage tolerance. TPCs offer a vision of multi-life components that can be reconditioned or remanufactured many times over whilst maintaining their mechanical properties. The development of thick section composites with in-built recyclability is a central research theme at Exeter. The only limitation to TPC adoption has been that, until recently, TPCs (Thermoplastic Composites) have not been able to deliver the requisite mechanical performance for structural applications, these are now within reach for TPCs, where, PEEK/Carbon moulding compounds achieve a bulk modulus of ~40GPa, which is a marked improvement over previous offerings and now rivals equivalent thermosets. Recent advances in manufacturing approach pioneered by Exeter have seen the achievable modulus reliably pushed above 70GPa – directly on par with Aluminium.
Metal free brake pads - - Phenolic composite brake pad backing plates are a disruptive idea that has yet to find acceptance, which is surprising considering they are 75-percent lighter, inert and corrosion-free, thermally insulating and have superior damping properties – just the characteristics required for electric vehicle braking duty cycles. Read more about the research carried out in this area in the latest brake report article.
Working with Industry to find solutions to real-world needs is central to Exeter’s approach, characterised by multi-partner initiatives developing thick-section parts, alongside Meggitt PLC – a T1 airframe parts maker, in collaboration with Leonardo and Boeing, where the demonstrator part was a full composite version of the AW189 helicopter wheel. Exeter also partner raw materials suppliers: Victrex PLC trialling commercial and developmental grades of PAEK plastics, Toray – global composite raw materials manufacturer of PEEK/CF tapes to specification. This will includes cut tapes manufactured from Victrex PEEK grades including trial batches of developmental materials, plus uncut rovings, allowing Exeter to experiment with cutting angle and length factors. Further collaborations involving Chinese automotive giant Geely and Bentley motors UK, also focused on thick-section PEEK composites for metal replacement in electric vehicles.
Exeter specialises in PEEK utilisation, its composites, additive manufacturing, recycling and chemistry, where this expertise and facilities led to a multi-million pound collaboration with Victrex PLC – the world-leading chemical company producing most of the worlds PEEK. Exeter has specialist facilities for processing high temperature polymers in particular, including injection moulding, and 2 state-of-the-art thermoplastic 80 Tonne hot presses, equipped with rapid cooling. Also all types of mechanical testing, a polymer analysis suite (DSC, DMA, Thermal conductivity, melt-flow, porosity, rheometry, CT & SEM) – specifically targeting high performance plastics.
Full-stop is an Innovate UK funded project supporting the acceleration towards zero-emissions vehicles, through the development of enhanced lighter braking systems. Full-stop utilises the latest advances in high temperature tolerant composite materials, to deliver a foundation braking system (callipers/discs and pads) with a 60% weight saving, whilst still performing to the highest rating for these safety-critical components.
Project lead: Freeman Automotive Ltd/EBC Brakes
These two Innovate UK funded projects looked at different components of the braking system, aiming to develop a new type of automotive braking system for future low carbon vehicles. The aim was to deliver a lightweight and cost-effective alternative to heavy metal componentry such as grey cast iron. Both projects brought together knowhow from the world of automotive friction materials, car brake system design, and the composites industry.
Partners: Freeman Automative Ltd/EBC Brakes, European Friction Industries, Hexion, Caterham Cars, University of Exeter and Hexcel (Brake-thru only)
This project's aim is to develop a new lightweight wheel technology for aircraft. The new wheels will utilise some of the latest advances in materials engineering.
Requirements in this sector are formidable, where wheels must survive a series of industry-specific tests including extended roll life, roll-on-rim, combined load and burst tests in order to be viable. If achieved, the 25+% potential weight savings would put UK tier 1 suppliers in a world-leading position.
Partners: Meggitt Aerospace Ltd, Victrex Manufacturing Ltd, TenCate Advanced Composites Ltd, Oxford Advanced Surfaces Ltd, University of Exeter
Y. Wang, L. Savage, (2017) Manufacturing of pre-impregnated discontinuous CF/PAEK composite. (ICCM 21) Xi'an, China August 20-25.