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Biologically Inspired Materials and Structures

Biological concepts and systems can inspire technological innovations. It can be of great value to analyse the principles behind natural structures and assess them with regard to suitable parameters in order to create novel technological materials and structures.

One well-known example are self-cleaning surfaces, emulating the surface of the lotus leaf. Nano- and microscopic structuring of the surface can also be used for passive anti-ice surface technologies for aviation, leading to energy-efficient de-icing concepts.1

Not only biological surfaces like those of lotus leaves, but biological materials as a whole are often structured in a hierarchical way over many orders of magnitude. This principle also determines the properties of wood, which played a major role as construction material in aviation in the past, and that might become interesting again in another form through an innovative densification process.

“Natural” features of wood are often acting as origins for failure under mechanical load. Their number can be drastically reduced by a novel two-step treatment.2 After partial removal of lignin, the wood is hot-pressed, resulting in a highly densified structure. The cellulose fibres are well aligned, facilitating the formation of hydrogen bonds between neighbouring cellulose molecules. Together with the reduction of defects, this results in an increased toughness and in a more than tenfold rise in tensile strength compared to natural wood. The values for strength are then similar to those of aluminium alloys. Laminates fabricated of this anisotropic material are potentially applicable to innovative structures in aviation.

 

1Bauhaus Luftfahrt. (2011). The Future Technology Radar. Project Report, Munich. ID: 621103-12 WP1-D1.2
2Song, J., Chen, C., Zhu, S., Zhu, M., Dai, J., Ray, U., … Hu, L. (2018). Processing bulk natural wood into a high-performance structural material. Nature, 554, pp. 224–228. doi: 10.1038/nature25476

  • Hierarchical organisation of biological materials: Wood as an example for hierarchical composition. The specific organisation of the individual components over several length scales results in remarkable properties.Hierarchical organisation of biological materials: Wood as an example for hierarchical composition. The specific organisation of the individual components over several length scales results in remarkable properties.
  • Mechanical properties of densified wood: Comparison of specific tensile strengths and specific Young’s moduli of natural and densified wood, glass fibre reinforced polymers (GFRP), and two alloys common in aviation (Al2024 and Ti6Al4V).Mechanical properties of densified wood: Comparison of specific tensile strengths and specific Young’s moduli of natural and densified wood, glass fibre reinforced polymers (GFRP), and two alloys common in aviation (Al2024 and Ti6Al4V).