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Gewählte Master / Diploma Thesis:

Elisabeth Fizek (2015): How much can wood move? Using wood as an bio-inspired actuator.
Master / Diploma Thesis - Institut für Holztechnologie und Nachwachsende Rohstoffe, BOKU-Universität für Bodenkultur, pp 71. UB BOKU obvsg

Data Source: ZID Abstracts
Nature represents various examples of materials that can autonomously change their shape in response to external stimuli. This master thesis is intended to generalize wooden bio-inspired actuators, which respond to surrounding humidity changes. The resulting bending movement is based on the biomimetic model of conifer cones, which open when dried and close when wet. The first part of this thesis presents the current knowledge on structure-function relationships of pine cones, and the functionality of compression wood tissues. Then, the employed research approach, as well as results and discussions are presented. Ten bilayers consisting of compression and normal wood of Pinus sylvestris were prepared and exposed to various climates. Half of the samples were glued with phenol-resorcinol-formaldehyde (PRF) resin, while with the other half casein glue was used. Bilayers were exposed to various humidity cycles and the extent of movement as well as the actuating forces were measured. It was found that the exhibited movements and forces are considerable. The PRF- bilayers showed higher amounts of bending and forces than the casein-glued bilayers. A certain linear-proportionality of the movements during adsorption and desorption was also observed. Through time lapse recordings the time spans necessary to reach various degrees of curvatures were determined. It became apparent that the wooden bilayers are able to quickly respond to rising humidity changes. Finally, the experimental data were compared with an adapted form of Timoshenko´s theory, which is originally used for calculating curvature and forces of bimetals during temperature change. This comparison revealed that the employed Timoshenko´s theory is able to model curvatures and forces of the wood bilayers responding to humidity changes. The determined results indicate strong reproducibility, and a range of technical applications are seen for such bio-inspired wooden bilayers.

Beurteilende(r): Wimmer Rupert

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