“New materials play a central role in almost all innovations in aerospace,” says René Alderliesten, associate professor in the Structural Integrity & Composites group at the Faculty of Aerospace Technology. “They carry new aerodynamic designs such as Blended Wing Body aircraft, they enable lightweight and safe storage of alternative fuels such as hydrogen, and they minimize waste when an aircraft is decommissioned at the end of its life.” But the history of new materials paints a bleak picture: For both carbon fiber composites and fibrous metal laminates, almost thirty years passed between the first laboratory tests and their introduction into space. “Even if we had a design of the perfect sustainable aircraft on paper now, we would not be able to fly it by 2050,” said Nathan Eskue, associate professor in the same group. “Certification is the critical path and it needs to be accelerated.”
The so-called test pyramid is the basis for aviation safety. New materials have to undergo countless tests – from (a lot of) testing of general material properties to (a lot of) testing of sub-components to (a few) large integrated tests on board aircraft. Many of these tests are destructive – samples of the material are subjected to forces until they break or deform. This data is input to models that predict whether a future series of components, integrated into the whole, will meet the specifications. “The pyramid is a proven method, but the development in new materials is lightning fast,” says assistant professor John-Allen Pascoe, also from the same group. “Today, we can 3D-print components, optimize the placement and orientation of advanced fibers and implement detailed microstructures. To apply these techniques, we need to certify hundreds or even thousands of different materials for each innovative component we want to use in an aircraft. If you can not certify it, you can not fly it, so it puts a huge brake on our design freedom. ”
Three pillars of smart certification
The three professors have made it their group mission to develop a smart certification approach that reduces the time to certification by at least ten years. Alderliesten: “We want to make all the destructive tests superfluous and certify individual components as soon as they are manufactured.” Their solution consists of the three pillars of physics, production process monitoring and simulation-based acceptance. With both Alderliesten and Pascoe as experts in material fatigue and structural integrity, and Eskue an expert in process monitoring and artificial intelligence (AI), they have all the necessary expertise in-house.
“With deep insight into the underlying physics, we want to understand how core material properties translate under load into mechanical properties such as elongation, bending and cracking,” says Pascoe. “And with the use of sensors during and after the manufacturing process, we can accurately monitor and control the condition of the components – both their microstructure and any minor defects.” Next, AI plays a central role in determining whether or not these defects are acceptable. Using physics and sensor data as input, the AI models predict whether a component meets the specifications if tested. “The three pillars are very closely intertwined,” says Eskue, “We use the physics and sensor data to build the AI models and ensure that they can be explained – not a kind of black box. Conversely, AI can help find missing pieces in physics theories. and determine which sensors we still need to develop. “
Corresponding security level
“Our approach sounds very logical, but it requires a completely different nature of research and science,” says Alderliesten. “We have already worked out the broad lines of smart certification, but there are still thousands of challenges to tackle.” Perhaps the most difficult nut to crack is industrial adoption, as everything new in aviation must at least be able to provide a similar level of security. Pascoe: “In the field of metal aircraft, we have fifty to a hundred years of experience and an enormous amount of test data on how metals behave under all possible conditions. If we want to use new materials, we have to demonstrate that they are just as safe. ” The same is true of their approach to smart certification – they need to demonstrate that it is at least as safe as the test pyramid. They therefore work closely with industry – the manufacturers of materials, components and aircraft. Alderliesten: “We let them apply our approach in their own production process, so that they themselves experience that it guarantees safety while saving time and money.”
Towards sustainable aviation
Researchers are currently developing simulation-based acceptance models for some production processes. Then they will generalize their results so that it can be applied more quickly to each new material and every other production process. There will certainly be preliminary breakthroughs – which researchers will celebrate profusely – but it may be another decade or so before society notices their radically different approach to certification. Eskue: “Progress will be painfully slow at first, but once it starts to spin, it can go really fast. And because all that testing is not scalable, even small steps forward are worth more than the effort. The more tests we can safely eliminate, the faster we will see new, sustainable aircraft in the sky.