Q&A – Mark Summers
Mark Summers, Head of Technology (Manufacturing, Materials, & Structures) at the Aerospace Technology Institute, UK, talks to Gary Peters about the use of graphene and composites in aerospace, and recent INSIGHT paper, Graphene Exploitation materials applications in aerospace.
When and why did the report start, and how long did it take to complete?
The Aerospace Technology Institute’s (ATI) stakeholders requested a review to understand the technology challenges and opportunities, barriers to implementation, and exploitation opportunities through three key industry implementation timescales. The INSIGHT paper was generated in partnership with the Graphene Institute and its technology partners. The document was published in January 2018, around 12 months from the initial consultation exercise.
What, in your opinion, are the key findings?
The exploitation of graphene in aerospace applications is in its infancy and as understanding of graphene materials develops, it is anticipated that the scope of potential applications will continue to expand. This INSIGHT paper highlights some of the potential benefits of graphene for aerospace from analysis of the current state technology, against the ATI’s view of future industry needs. The graphene material application analysis has identified opportunities for improved fuel efficiency, aircraft performance and cost, and reduced environmental impact.
Graphene has multiple exploitation opportunities within the sector. These relate to architecture enhancements, product technologies, and manufacturing enablers. Key potential applications were identified as:
- Reducing manufacturing costs – Exploitation of the thermal properties of graphene enhanced materials to reduce the cure times of resin-based materials, resulting in lower manufacturing costs for carbon fibre (CFRP) materials. The resulting graphene enhanced components could behave in a multifunctional way, acting as structural components and heatsink and/or electrically conductive devices. These multifunctional properties could in turn lead to lower parts count and reduced manufacturing times.
- Advanced materials and surface coatings – The use of graphene enhanced CFRP in structures could facilitate increased or equivalent performance at lower mass, in turn improving aircraft efficiency, burning less fuel, and creating cleaner aircraft with lower emissions. In the near term, graphene will be added to the resin in thermoset CFRP to form a hybrid system, where the fibre provides the stiffness whereas graphene improves properties such as inter-laminar shear strength and damage tolerance, allowing a reduction in ply-thickness. Graphene may be used as the main reinforcement for stiffness in high performance polymers, such as polyether ether ketone, to produce small parts and pipes that replace metal equivalents. The potential for graphene to be used as a coating could offer corrosion resistance due to its physical properties. Being an atomic scale structure, it has potential in coating materials to reduce drag, and by exploiting its conductivity and thermal properties could be used in de-icing systems and lightning strike protection.
- Novel heat management – The extremely high thermal conductivity of graphene (6,000Wm-1K-1) makes it an ideal heat spreader to minimise heat spots, particularly for batteries and electronics. Such heat spreaders may be formed from compressed graphene sheets or through addition to a polymer or rubber. Additionally, graphene could add EMI shielding to the packaging, while reducing weight compared to traditional metal components.
- Advanced flight deck avionics – 2D layered materials such as graphene, boron nitride and tungsten disulphide are stacked to form van der Waal solids, which can behave as novel electronic devices just a few atoms thick. The atom thin nature of these devices means that they are transparent. In the simplest form, graphene on a polymer substrate can be used as a flexible transparent conductor, which can then be combined with organic electronics to provide a new generation of head-up displays, directly integrated into the windscreen of an aircraft
- Novel energy harvesting – The growing use of aircraft smart sensors leads to a demand to develop either passive sensors, such as those mentioned under communication and antenna systems above, or energy harvesting to locally power the system. The addition of graphene to oxide thermoelectric materials has increased their thermal operating window and figure of merit (ZT), allowing this new cheaper, lighter, and less toxic generation of materials that operate uniformly over a wide range of temperature differences such as those that might occur during a flight.
What are the challenges of upscaling its use and implementation?
The material supply capacity and cost/kg are critical to ensure the widespread adoption of graphene across the sector. Multiple methods of graphene production exist, but if only a fraction of the applications were to be realised for large commercial aircraft, current supply incorporating embedded process verification could not meet the global needs at a commercially viable price point. The sector needs to be convinced that a viable raw material supply chain exists, with dual supply capabilities, to consider new graphene enhanced components for safety critical applications. Considerable material screening is required by the industry’s end users. The work will optimise and functionalise candidate graphene materials for potential applications, initiating the high cost and lengthy qualification process (for more see Materials World June 2018).
Graphene is one of many 2D materials that have been developed from initial studies almost 20 years ago. Additives in material are already commonplace, enabling products such as high-performance alloy steels and toughened carbon fibres. The aerospace sector has reviewed other material additives such as carbon nanotubes that disperse through the CFRP resin. The popularity of graphene research and potential benefits of a single layer atomic structure or multi-layer graphene nanoplatelets has generated significant interest at a point in time where CFRP materials are being utilised in higher quantities across the whole airframe, system components, and propulsion solutions.
Where is graphene being used currently in the aerospace sector?
Graphene has been incorporated into many research platforms to understand the potential benefits. Projects supported by the National Aerospace Technology Exploitation Programme have explored the potential application for non-structural components. Platforms such as the University of Central Lancashire, UK, graphene drone are attempting to demonstrate the reality of graphene benefits through physical flight demonstration. The ATI is not aware of any safety critical, series production components that are in service on large passenger aircraft.
Do you think that graphene will truly take off and change the aerospace sector of the future?
Graphene, and other 2D materials, have the potential to provide significant benefits that will reduce cash operating costs for the airline industry. If the early stage research matures into viable product technologies and topology optimised structures/components with multifunctional properties, disruption will have significant impact on fuel efficiency, performance, cost, and passenger experience. Early opportunities such as the development of thermally efficient composite mould tools, could provide substantial ‘off aircraft’ cost savings and high rate capabilities for the industry.
What are the biggest challenges facing the composite sector?
Industry has recognised the need to evolve a different approach to the use of CFRP in aircraft design and manufacture. Traditional design techniques have led to the development of components that are not topologically optimised, often constrained by the processes and methodologies that have been practiced for decades in metallic products. Future high value design, verification and validation, and routes to certification need to consider the performance characteristics of CFRP 2D and 3D materials that will impact whole aircraft fuel efficiency, cost, environment and operational needs. The expense of CFRP raw materials, processing and manufacturing often restrict widespread adoption, as traditional metallic materials are more cost effective. Manufacturers are seeking to reduce production costs by the reduction of complex infrastructure and high energy processing needs (e.g. autoclaves) through the development of new materials.
How has the use of composites in the aerospace sector evolved over the last 10 years?
The civil aerospace industry has consistently increased the use of CFRP on aircraft programmes over the last four decades, to the point that it is now commonplace for aircraft to have more than 50% material usage (by weight) across airframe, propulsion and systems elements combined. The materials change from aluminium to carbon fibre has been driven by performance, fuel efficiency, and in-service support benefits. The series production architecture has evolved from traditional metallic design, not topologically optimised, therefore not maximising composite material mechanical properties. In recent years, cost and rate have become critical drivers to the sector that is resulting in significant technology innovations that reduce recurring costs through efficient manufacturing processes and optimised structure architecture.
How do you think it will evolve moving forward?
The ATI forecasts the total value of aircraft deliveries between 2016–2035 to exceed US$6.3 trillion. Within this predicted market growth, CFRP usage is going to substantially increase over the next decade due to new aircraft sales, wider adoption of the material in incremental development programmes, and new platform entrants. The opportunities for material formulation and manufacture, equipment suppliers and component manufacturers are rapidly evolving. This could enable new and enhanced end-to-end value chains to be established locally and internationally, linked to productivity and the logistics needs of end users.
What makes composites suited to use in the aerospace sector, and other forms of transport?
CFRP has several benefits when compared to traditional materials such as aluminium and alloy steel. The airline industry has identified that CFRP aircraft are able to remain in service for longer intervals due to the properties described below:
- Strength to weight ratio – CFRP has a high strength to weight ratio that enables fuel efficiency improvements to be realised through the reduction of structural mass. Clearly, this is a benefit for the aviation industry, but also provides opportunities for the automotive industry to offset the weight gain of an all-electric drivetrain.
- High tensile strength – CFRP has an extremely high tensile strength, often considered superior to non-matrix structure materials. This benefit has clear structural integrity advantages but can also be considered as an issue for applications where rigidity is a hinderance where flexure is required (e.g. aircraft wings).
- Fatigue and damage tolerance – CFRP has an excellent resistance to impact damage, and the ability to perform consistently over a high number of cycles without material degradation.
- Low coefficient of thermal expansion – CFRP is less likely to be affected by temperature changes, enabling higher manufacturing tolerances to be attained, and less impact by environmental conditions on each aircraft mission.
- Corrosion resistance – CFRP resists oxidation much better than untreated alloys. This is particularly important considering the array of environmental conditions an aircraft is exposed to on each mission.
- Thermal conductivity – Some applications within the whole aircraft require high levels of thermal management. CFRP has been proven to be an excellent heat insulator.
What do you think will be the dominant material used in the aerospace sector over the coming years, and why?
CFRP usage within the composites sector will continue to expand over the next decade and beyond, as the aerospace market grows and composites replace other materials in structures. It is likely that pre-impregnated material usage will significantly reduce in favour of dry fibre out of autoclave materials. This will facilitate the need to reduce manufacturing recurring costs and enable unprecedented build rates.
Thermoplastic materials will start to become more widespread, displacing thermoset materials over time. For metals the raw material will change in many applications from a billet to additive manufacturing powders or wire. The move towards additive manufacturing could eliminate conventional manufacturing processes such as forging and casting. Development of and hybrid manufacturing capabilities will enable dissimilar materials to be incorporated into a single unitised structure or multi-functional component.
Mark Summers is Head of Technology (Manufacturing, Materials, & Structures) at the Aerospace Technology Institute (ATI), UK. He is responsible for the ATI’s manufacturing, materials, and structures strategic research programme, and his role globally is to undertake a strategic advisory role representing the ATI and UK aerospace sector internationally.