MACANTA:Multifunctional hierarchical advanced composite aerostructures utilising the combined properties of different carbon nanotube (CNT) assemblies

The advent of carbon-fibre composite passenger aircraft, such as the Boeing 787 and the Airbus A350, has been primarily driven by the need to reduce structural weight. Higher operating efficiencies per revenue passenger kilometre also contribute to a reduction in environmental impact where 1 kg of fuel saved equates to a reduction of 3.15 kg of CO2 emissions. Indeed the European Union has set ambitious aircraft emission reduction targets by 2050 as the level of commercial air traffic is set to continue doubling every fifteen years. The high specific strength and stiffness, and corrosion and fatigue resistance of carbon-fibre composite materials, make them highly suitable for lightweight aerostructures. In laminated form, these superior properties are tempered by the material's relatively low through-thickness strength and fracture toughness which makes composite structures susceptible to impact damage. Carbon-fibre composites also have low electrical conductivity which necessitates the need for additional measures to ensure adequate lightning strike protection. The industry has adopted the use of a fine metallic mesh incorporated into the aerodynamic surfaces. This approach adds unnecessary weight to the structure as well as increasing manufacture and maintenance complexity. Composite materials also have low thermal conductivity which impacts on the design of anti-icing systems.

In recent years, a number of research groups have explored the unique properties of nanoparticles dispersed in resin or introduced between lamina interfaces, to address these limitations. The use of carbon nanotubes (CNTs) especially, generated much excitement due their phenomenal structural and transport properties. The results to date have been highly variable and have fallen well short of expectations. This is partly due to a lack of interdisciplinary collaboration where fundamental questions, requiring input from chemists, physicists, material scientists and research engineers, were not adequately investigated. The proposed research in MACANTA aims to rectify this by bringing together a team with highly complementary expertise to increase the fundamental understanding of the influence of physical and chemical characteristics of different CNT assemblies in pursuit of developing multifunctional composites which mitigate the known shortcomings as well as providing additional functionality.

A unique aspect of MACANTA is the emphasis on understanding and exploiting the different forms of CNT assemblies to best serve specific functions and integrated within a single structure. The team has the unique capability of producing very high quality CNTs, produced as highly-aligned 'forests'. These may be harnessed in this form and strategically placed between plies to increase through-thickness fracture toughness. Beyond simply dispersing within the matrix, they may also be 'sheared' to produce aligned buckypaper, drawn into very thin webs or spun into yarns, where their respective electrical and thermal conductivity will be investigated. These CNT assemblies will be assessed for improving lightning strike protection and providing anti-icing capability. The piezoresistive property of CNT webs will also be explored for in-situ structural health monitoring of adhesively bonded composite joints.

The successful completion of the research proposed in MACANTA will culminate in the manufacture of a set of demonstrator multifunctional composite panels. They will represent a significant advancement in the state-of-the-art and provide a competitive advantage to interested stakeholders. It will also provide an ideal training platform for the development of skills of three postdoctoral researchers and two associated PhD students funded by QUB.

The UK aerospace industry is the second largest, after the USA's, contributing £24 billion to the economy and supporting over 230,000 jobs. The sector faces new challenges in delivering lower development, manufacturing and operational costs, compounded by increasing global competition for market share. The advent of carbon-fibre composite passenger aircraft, to reduce structural weight, has placed additional pressures, especially on the civilian sector, to maintain its competitiveness and innovative advantage. Competition in the design, development and manufacture of advanced composite structures, from the rest of Europe, South America and the Far East, not to mention a developing supply-chain capability in North Africa, means that the UK has to maintain its drive towards incessant innovation. MACANTA, has the potential to lead to a disruptive technology in the development of the next generation of composite aerostructures. By exploiting the unique properties of different carbon nanotube (CNT) assemblies, integrated within a composite structure, MACANTA aims to deliver a multifunctional capability overcoming current known limitations of low electrical and thermal conductivity and through-thickness fracture toughness when compared to traditional aluminium alloys used in aircraft structures. Addressing these limitations will mitigate the need for additional measures which add weight and maintenance complexity to the structure. Moreover, MACANTA will explore additional functionality beyond these shortcomings, such as the introduction of structural health monitoring at critical adhesively bonded joints. By being at the forefront of innovation and actively seeking expedient exploitation routes, the industry will be well positioned to strengthen its global share of airframe development and manufacture. From a product end-user perspective, i.e. primarily airline operators, the emergence of multifunctional composites will deliver enhanced operational efficiencies which will contribute to a reduced environmental impact.

The School of Mechanical and Aerospace Engineering is committed to further strengthening the research capability, knowledge and skills in the area of nano-enhanced composites and to this end has funded the establishment of a very-high-specification CNT production facility. The quality of commercially available CNTs is not reliable and this has compromised a number of research programmes. Bombardier Aerospace Belfast, in recognition of the substantial potential of this research in delivering step changes in its future composite nacelles and wing programmes, has pledged generous in-kind contributions, as outlined in the Statement of Support. Other companies, with a UK footprint, involved in the production of composite aerostructures, including GKN Aerospace (see Statement of Support), Agusta-Westland, Spirit Aerosystems (Prestwick), BAE Systems and Airbus are additional potential beneficiaries of technologies developed in MACANTA. The developed composite functionality will further be relevant to other sectors, including the automotive (e.g. Jaguar Land Rover, Nissan UK, Bentley, Formula 1 constructors) and wind energy industries (Vestas). Carbon-fibre composite manufacturers Hexcel and Cytec have each provided Statements of Support which attest to the high relevance of the proposed research.

With two PhD Students and three PDRAs involved in the research, the programme will provide multidisciplinary skills to a cohort of researchers and engineers. Queen's University Belfast is an exemplar institution in Knowledge Transfer partnerships, with 350 over 15 years, 80% with SMES, resulting in 400 subsequent graduates placements and generating an annual income of £1.8 Million as a sustaining consequence. MACANTA will be seeking to use this well established knowledge exchange route to local and national supply chain SMES and Tier 1 and 2 companies.