AGH UST-designed sensors to detect damage in aircraft composites

Carbon fibre-reinforced thermoplastic composites replace metals in aircraft constructions with increasing frequency. What speaks to the advantage of composites is their durability and lower mass compared to metals, which translates into reduced fuel consumption. This not only entails savings for airlines, but also reduces the negative impact of flights on the environment by cutting down on carbon dioxide emissions. The manufacturing of composites is also not environmentally neutral – it requires energy and resources. To reduce this consumption, we have to prolong the life cycle of composite parts, which can be achieved through the optimisation of the production, control, and maintenance methods. This is exactly the goal of a consortium made up of 16 European companies from the aviation industry and scientific institutions, including the AGH University of Science and Technology in Krakow.

The idea behind this joint project named “GENEX” is to create a network of composite manufacturers, airlines, and entities responsible for the maintenance of aircraft using modern technologies. One of the key elements of this vision is the monitoring system of composite parts in airplanes, which will provide a constant data stream reporting on their status during their operational life. This is precisely the portion of the project in which the AGH UST scientists are involved. Their task is to design piezoelectric sensors integrated with the structure of the composites.

Damage detection using ultrasounds

To detect and locate unwanted changes that occur in the structure of the composites, our engineers will use ultrasounds. ‘We will try to send a wave from one point to receive it in another. The properties of such a wave are shaped when it interacts with the structure of the composite on the path from the receiver to the transmitter. We can determine its features for an undamaged element by conducting experimental measurements or by referring to its digital model. All future discrepancies can point to potential damage to the composite structure’, describes Dr hab. (Eng.) Paweł Paćko, Professor at the Faculty of Mechanical Engineering and Robotics.

The team will have to face problems that stem from the anisotropic structure of composite materials. In such structures, the properties of ultrasound waves vary depending on the direction of their propagation. When designing the senor specs, scholars will rely on the so-called ‘comb-type composite transducers’ made of piezoelectric fibres. These devices are capable of emitting, receiving, and processing acoustic waves. ‘The chief advantage of this type of transducers, compared to their traditional ultrasound counterparts, is their plasticity and the possibility to integrate them with the composite structure. Our job will be to design the devices in such a way that their construction is able to “capture” the status of the composite from a specific direction’, the scientist explains.

Hot spots in planes

The task of manufacturing the devices with the parameters specified by the AGH UST scholars will be assigned to the Smart Material GmbH company (Germany), one of the project partners.

Professor Tadeusz Stepinski from the Faculty of Mechanical Engineering and Robotics who supervises the work carried out at the AGH UST sums it up like this: ‘An ideal situation would be if we could create a network of sensors in an airplane, which would be parallel to the human nervous system. When we feel pain, it’s a signal that something’s wrong with our body. Although the devices we plan to use are characterised by small size and could easily be incorporated into the composite structure, they require a power supply. Meanwhile, we are already placing so many cables in airplanes, significantly increasing their weight. Therefore, we are forced to limit the number of sensors, focusing on the areas prone to substantial stress that can damage the material.’

Digital twins to the rescue

Collecting data on damage to the composite structure is one thing. However, as mentioned in the introduction to this article, the key to the success of this project is the effective transfer, processing, and practical use of these data by producers, airlines, and maintenance companies. The holistic vision of this project is truly remarkable.

The initiators want to create digital twins, that is, mathematical and numerical models of the composites used in aircaft construction. Using solutions from the area of the Internet of Things, they will be constantly updated with information regarding the wear of the materials, collected by the monitoring system equipped with piezoelectric sensors. With the help of IT tools, including artificial intelligence, scientists will be able to locate those parts and their impact on safety, simultaneously reducing the number of regular and costly ground-based inspections. Digital twins will also provide relief to maintenance companies. Using augmented reality technology and equipping engineers with special goggles, they will be able to locate the spots that require their attention, displaying guidelines to facilitate repairs. Finally, using data on material wear, composite manufacturers will be able to expand the life cycle of their products by introducing the necessary control mechanisms and modifications into the production process.

Institutions and companies participating in the project

Coordination of the “GENEX” project – ITAINNOVA – Instituto Tecnológico de Aragón (Spain). The remaining partners, in addition to the AGH UST and Smart Material GmbH, include: Asociación de Investigación Metalúrgica del Noroeste (Spain), Deutsches Zentrum fur Luft- und Raumfahrt (Germany), Fundación CIDETEC (Spain), Innovation in Research & Engineering Solutions (Belgium), Research Center for Non Destructive Testing GmbH (Austria), École Nationale Supérieure d’Arts et Métiers (France), Altran Innovación SL (Spain), Ingrid Cloud AB (Sweden), Centre Suisse d’Électronique et de Microtechnique (Switzerland), GMI Aero (France), AERNNOVA Engineering Division (Spain), EASN Technology Innovation Services BVBA (Belgium) oraz Ziegler Aerospace Limited (Great Britain).