New materials and processes in aerospace engineering
Discover the expert speech of Prof. Philippe Lours, director of International Affairs à IMT Mines Albi & founder of the Master Aerospace Materials Design, Manufacturing & Innovation Management (AeroMat-Innovation), and Prof. Étienne Copin, Vice-director of Master AeroMat-Innovation.
What are some of the latest innovations in aircraft materials engineering?
Accelerated by the covid19 crisis, the objective for reducing aviation emission and struggling against climate change speeds up today both incremental and disruptive innovation in aeronautics all over the world in technology companies and research laboratories. We could mention various ones such as zero fuel aircraft, advanced materials including composites, smart robotics or automation, 3D printing and structural health monitoring.
Today focus is placed on developing health monitoring systems, embedded within the materials, for optimising maintenance checks. In the case of “smart materials”, this is the material itself which reacts to its environment and can be probed to obtain valuable information. In both cases, i.e. extrinsic or intrinsic system, the challenge is to be able to manufacture the required architecture.
What are the benefits and challenges of composites materials?
There are many interests in using composites, materials with generally higher specific engineering properties than metals. They can be formed into complex shapes in one-piece designs, thereby reducing assemblies. They also have high impact resistance, thermostability, damage tolerance and they resist better to fatigue and corrosion than metals do. With composites, you can reduce both the cost and weight of aircraft. However, we need to improve the recycling of composite materials and maybe vibrational damping properties as well so as to ensure better passenger comfort in aircraft.
Another new topic in composites is a more extensive use of thermoplastic matrix instead of thermosets. This could be positive in terms of recyclability because a thermoplastic can be remelted, allowing to recover the reinforcements like carbon fibers more easily. The challenge would be to functionalize composites by embedding sensors inside. Another way to boost composites use is to develop self-healing materials.
At last, ceramic matrix composites are very good materials because they have low density, high hardness and high thermal and chemical resistance. Constitutive materials such as graphene and carbon nanotubes can also be used to improve electrical properties and resistance to fracture and damage of composites.
Today over 50% of modern aircraft are made of polymer base composites. In particular where and how will composites materials be used in the aircraft of the future?
First, composites replaced secondary structures, that do not have to sustain high loads, giving both weigh and cost reduction. Today aircrafts primary structures are made of composites as well, in this case essentially for lightweighting reasons. Most of the skin can be manufactured with high performance composites. Many interiors are also made of composites, along with some large parts of the fuselage, the engine fan etc. Today, the limitation for increasing the ratio of composites is related to the temperature resistance and mechanical strength for critical components. Indeed, made of polymers, they can’t resist high temperatures and in some critical parts, high strength, ductility and resistance to fracture are required.
What are some other promising new materials?
There is also considerable research on advanced metal alloys and coatings in propulsion systems for increasing the turbine inlet temperature. The optimisation of engine materials, leading to an increase of engine efficiency, results in drastic fuel saving and emission reduction. However current systems are hitting the temperature limit of current materials. Hence there is a need for investigating new materials with higher temperature resistance properties, including new alloys, inter-metallics and advanced coating systems along with ceramic matrix composites already mentioned.
What is lightweighting in aerospace design?
Lightweighting is the weight reduction of aircrafts resulting from using low density materials such as composites, new aluminium alloys containing lithium and, possibly in the future, magnesium alloys. This is of utmost importance because using lighter materials enables to reduce fuel consumption as less energy is required to compensate for gravity. Choosing the right material is one way to decrease the weight. Another way is to optimize existing designs to reduce the quantity of material needed, getting new structures, circa 30% lighter for instance, which successfully sustain the same loads. This is where new processes such as additive manufacturing are useful because they allow to produce complex geometries with optimized shape and a sparingly recourse to materials, which could not be manufactured cost effectively - if not at all - with conventional processes. In some cases, they can be even more resistant than their standard counterparts.
What can additive manufacturing bring to the aircraft industry?
In Additive Manufacturing, parts are printed out directly from a 3D file with no need for tooling, which provides a great deal of freedom in the design of parts. As mentioned earlier, it can help to produce lightweight parts with optimised design. It can also potentially bring many other benefits for the aerospace industry in the future: rapid prototyping, personalisation on demand, optimised function approach in the conception phase, reduction of lead time, increased buy-to-fly ratio and mitigation of risks in the supply chain for the production phase, advanced repairs, spare parts on demand/on site during the maintenance phase.