Using built-in sensors to automatically characterize damage using ultrasound waves and artificial intelligence - this is the goal of the new DFG research group FOR3022, which involves the Leibniz Institute for Materials Engineering - IWT and the University of Bremen.
Hybrid materials are increasingly used in the aerospace industry. This is because composite materials offer special functional properties that meet the increasing technical and economic requirements of these industries. Due to their hybrid structure, composite materials made of fibre-reinforced plastics with metal foils - so-called fibre-metal laminates - have significant advantages over aluminium, which continues to be the standard material in the aerospace industry. For this reason, fibre-metal laminates are increasingly being used on aircraft parts that are particularly susceptible to impacts such as bird strikes. This can result in damage such as the detachment of adhesives, so-called delamination, as well as cracks that are not visible from the outside.
Long preparation time for the new project
In order to better understand and reliably diagnose damage in such hybrid materials, a newly established DFG research group FOR3022 "Ultrasonic Monitoring of Fibre Metal Laminates Using Integrated Sensors" has recently been dedicated to the investigation, characterization and diagnosis of damage in fibre metal laminates. The now realized research project is preceded by a long preparation phase. The initial ideas for this major project were developed within the former central scientific institution "Integrated Solutions in Sensorial Structure Engineering - ISIS" of the University of Bremen.
In a first phase, the research association will devote three years to this project. The research group is supported by the German Research Foundation (DFG) with a funding volume of 2.7 million euros. In addition to Leibniz-IWT, the University of Bremen with its Department of Computer Science (PD Dr. Stefan Bosse) and Electrical Engineering (Professor Walter Lang) as well as the Fibre Institute (Professor Axel Herrmann), the German Aerospace Center (DLR) and the Helmut Schmidt University of Hamburg (HSU) are involved in the research project. Professor Michael Sinapius from the Institute for Adaptronics and Functional Integration at the TU Braunschweig is coordinating the project.
Every damage leaves its fingerprint
"With the new research group, we want to gain new insights into the interactions of impact damage and ultrasonic waves in fibre-metal laminates," says Axel von Hehl, head of the Lightweight Materials Department at Leibniz-IWT and member of the MAPEX Center for Materials and Processes at the University of Bremen. "The aim of the first phase is in particular the damage characterization. This means: We want to capture and identify the fingerprint of a specific damage". Such damage changes the propagation of ultrasonic waves that are to be used for damage detection. In contrast to medical or diagnostic technology, so-called guided ultrasound waves are used here. These propagate in thin-walled components, such as aircraft fuselage skins. In order to know exactly which damage classes are involved in each individual case, the scientists use the high-resolution X-ray microscope available at the MAPEX Center. By assigning the damage classes to the measured ultrasonic signals, the ultrasonic testing procedure is trained until it enables reliable damage identification.
A diagnostic system for impact damage
To enable damage monitoring during operation at a later date, the scientists are also working on integrating sensors into the material. These sensors are intended to detect and characterize so-called impact damage during operation and thus provide information about the extent of damage. "The information has to be obtained and derived from a large amount of raw data, which can only be achieved by automated procedures and the use of artificial intelligence methods," explains Stefan Bosse from the Department of Computer Science.
In a possible second three-year funding phase of the research group, the findings gained so far in damage characterisation will be used to investigate damage development. This would allow more precise statements to be made about the extent of damage and the resulting need for action. On this basis, the sensors installed are to be used in the long term as a reliable diagnostic system for impact damage to aircraft.