What 438.000 test cycles tell me about the health of an aircraft structure

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Author: ReMAP-PhD Agnes Broer

“Aircraft are nowadays made of lightweight fiber-reinforced composite material. Damage in composite materials is usually internal and not immediately visible on the outside. According to strict maintenance schedules, aircraft structures are therefore extensively inspected using various non-destructive techniques. These manual inspections cost a lot of time and money. I investigate the possibilities of the usage of permanently installed sensors on composite aircraft structures to increase maintenance efficiency, thus increasing aircraft availability.”

The senses of an aircraft

“Some examples of Structural Health Monitoring (SHM) are available, but sensor data cannot be used yet to substitute interval-based classical inspection tasks. To make inspections of the structure of an aircraft more efficient, state-of-the-art sensor technologies and AI-modelling could help. In ReMAP we develop a methodology, resulting in models that can tell whether there is damage, where the damage is, what damage that is and how severe the damage is. Additionally, predictions of the remaining useful lifetime of the structures based on machine learning methods will take place. In the future, maintenance engineers can apply this methodology and determine if further inspection or repair of an aircraft structure is required. But models need data, lots of data. And that is where I, and the whole ReMAP- SHM-team, come in. In ReMAP we use data from five state-of-the-art sensor technologies. I investigate the data from sensors that respond to light and sound (namely optical fiber and acoustic emission sensors) and how we can fuse data to obtain a better image of the damage. I see it as the eyes and ears of an airplane. By combining both senses you get better insight.”

The forces on an aircraft

“The tests I now perform in the Aerospace Structures & Materials Laboratory of the Faculty of Aerospace Engineering at TU Delft simulate the forces on an aircraft wing. An airplane that goes up and down, caused by for instance turbulence or a bumpy landing, causes a cyclic load on the material. The connection between two elements, in this case a stiffener and skin panel, is a critical point. Because of the cyclic loading, damage may occur between these two elements. I test, all the way up to final failure, how that load influences such damage. As expected this space grows and becomes larger as I observed with the sensors.”

Yes! The eyes and ears are a good start

“The first result of an extensive test period of 438.000 cycles show that combining the two senses does indeed improve damage diagnostics. Yet, it now already appears that additional sensor techniques such as lamb waves or digital image correlation may improve damage diagnostics even more. So fusing SHM-data has clear benefits for the data driven approach of condition based maintenance of aircraft as being done in ReMAP. I will continue the research this coming two years to further explore data fusion for SHM and Condition Based Maintenance.”

Acknowledgement: For this SHM research the composite panels are designed by Embraer (PT) and manufactured by SME Optimal Solutions (PT). The sensors are provided by Cedrat Technologies (FR) and Smartec SA (CH) and are very carefully placed on these panels by scientifically based criteria from the University in Patras (GR). École National Supérieure d’Arts et Métiers (FR) developed the data acquisition software. The University of Patras executes test cycles in parallel.

The research and the results are published at EWSHM2020.

Paulo Rupino Cunha

Paulo Rupino Cunha

Assistant Professor of Information Systems with Habilitation and former head of the IS Group at the Faculty of Science and Technology of the University of Coimbra, Portugal. Director of Informatics and Systems Lab of Instituto Pedro Nunes (IPN), a non-profit association for Innovation and Technology Transfer.

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