DFG research project at Paderborn University extended
The use of polymers in general, and in particular in modern metal-plastic hybrid components, fibre composites and lightweight design has become increasing established due to the high degree of flexibility and lower cost of these materials. Polymers are also increasingly being used in ultrasonic measurement systems for, for example, flow measurements and parking aids, because they can be more easily deformed and cured than metallic components. In addition, polymers also provide thermal and electrical insulation. For the simulation-based design of such measurement systems or components, it is essential to know the mechanical and acoustic properties of the polymers used. However, the material parameters specified by the manufacturer are often not accurate enough. That’s why, since 2019 and under the leadership of Professor Bernd Henning of Paderborn University and Professor Carolin Birk of the University of Duisburg-Essen, scientists have been working on a research project to accurately determine the relevant mechanical properties using special measurement systems. The project has now been extended by the German Research Foundation (DFG) for a further two and a half years and will be funded with a total of approximately €580,000 until 2025.
“By comparing transmission measurements of specimens with a simulation model using numerical algorithms, we can accurately determine the mechanical properties of the specimens. In established approaches to date, such acoustic properties can be determined only by destroying the specimen. Depending on how well the specimen withstands this, you can then calculate its parameters. We only sonicate the specimen, so it remains fully intact,” explains Dmitrij Dreiling, a scientist in the Department of Electrical Engineering and Information Technology.
Usually, in such transmission measurements, continuous sound excitation is used to transmit sound through the specimen from one side, and the measurement signal is then received and analysed on the other side of the specimen. With this type of excitation, however, the sensitivity to shear motion in the specimen is low. The project participants have therefore developed several set-ups for alternative material characterisation, which they have validated through simulations and measurements. The use of segmented transducers to segment the sound excitation has proven successful. Notably, it has significantly improved the determination of the shear parameters of polymer specimens. “However, new challenges arise from segmenting the sound excitation,” says Dreiling. In particular, according to the scientist, the transmitter and receiver must be precisely aligned during the measurement, in order to ensure simulation equivalence. To avoid any uncertainty, a segmented transducer, which divides up the ultrasonic frequency, is to be used as the transmitter and receiver. Dreiling: “This places significantly greater demands on system characterisation and signal processing. We therefore also plan to investigate the optimal specimen geometry, the temperature dependence of the specimens and the modelling of the damping properties with regard to their validity and applicability.