We would like to congratulate Mr. Torben Marhenke
The department would like to congratulate Torben Marhenke on successfully passing his PhD oral exam!
Torben held his presentation about:
„Experimental and model-based investigations of non-destructive material testing of wood-based composite materials through ultrasound“
on wednesday, September 2nd, 2020 at the Department of Dynamics and Vibration and successfully passed his oral exam.
Wood-based materials are created by cutting wood to smaller elements and bonding it together afterwards. Since the middle of the last century wood-based materials have been used as alternatives to solid wood and are used primarily in the construction and furniture industries. Due to the assembly of individual structural elements, wood-based materials present the risk of air inclusions or unglued areas, which are summarized under the term delamination. Delamination leads to a reduced strength of the materials and can lead to serious consequences when using wood-based materials as construction materials. In order to detect delaminations, ultrasonic transmission measurements are currently being utilized in the industry.
The subject of this thesis is the scientific investigation of non-destructive material testing using ultrasound on the basis of experiments and models. Although wood-based materials have been used for several decades and technical experience values exist, there is a lack of engineering knowledge about the mechanical behavior of this material. According to the current state of the art, there is only one complete set of parameters for describing wood-based materials as orthotropic materials. Within the scope of this work, several methods for the non-destructive determination of the nine mechanical equivalent parameters are described. Runtime measurements and model updating enable the online detection of mechanical parameters during the production process.
Analytical and numerical models are created on the basis of the determined mechanical parameters. These models are used to investigate the influence of density profiles, flow effects and delaminations on the sound transmission behavior of wood-based materials. Experimental measurements verified the models and provide additional insights into the transmission properties.
In this thesis the optimization of the delamination detection is done with regard to the improvement of reliability, improvement of the defect resolution and determination of the defect position. By changing the measurement setup and adapting the transmitted signal the system's susceptibility to errors can be minimized. The application of the re-radiation method enables the detection of defects in the single-digit millimeter range as well as the determination of the depth of the defect by means of a sound reconstruction. A prerequisite for the application of the re-radiation method was the development of a novel measurement setup. Instead of channel-wise transmitter/receiver pairs, linear transmitters and a high-resolution receiver are used.