Pummelos as Concept Generators for Biomimetically Inspired Low Weight Structures with Excellent Damping Properties

• Published in: Advanced engineering materials 2010-12, Vol.12 (12), p.B658-B663
• Main Authors: Fischer, Sebastian F., Thielen, Marc, Loprang, Ruth R., Seidel, Robin, Fleck, Claudia, Speck, Thomas, Bührig-Polaczek, Andreas
• Format: Article
• Language: English
• Subjects: Damping; Foams; Fruits; Impact resistance; Investment casting; Maxima; Mechanical analysis; Mechanical properties
• ISSN: 1438-1656; 1527-2648; 1527-2648
• DOI: 10.1002/adem.201080065

Natural materials often exhibit excellent mechanical properties. An example of outstanding impact resistance is the pummelo fruit (Citrus maxima) which can drop from heights of 10 m and more without showing significant outer damage. Our data suggest that this impact resistance is due to the hierarchical organization of the fruit peel, called pericarp. The project presented in the current paper aims at transferring structural features from the pummelo pericarp to engineering materials, in our case metal foams, produced by the investment casting process. The transfer necessitates a detailed structural and mechanical analysis of the biological model on the one hand, and the identification and development of adequate materials and processes on the other hand. Based on this analysis, engineering composite foam structures are developed and processed which show enhanced damping and impact properties. The modified investment casting process and the model alloy Bi57Sn43 proved to be excellent candidates to make these bio‐inspired structures. Mechanical testing of both the natural and the engineering structures has to consider the necessity to evaluate the impact of the different hierarchical features. Therefore, specimens of largely varying sizes have to be tested and size effects cannot be ignored, especially as the engineering structures might be upscaled in comparison with the natural role model. All in all, the present results are very promising: the basis for a transfer of bio‐inspired structural hierarchical levels has been set. This paper shows the approach how natural hierarchical structures can be transferred to technical components: There should be specialists, who analyze the natural role model to highlight the structure–function relationship. With the help of this input, the engineer can transfer the focused structures. Before the structure transfer, the engineer has to point out a suitable production process and an appropriate material. The material scientists have to find the right test methods and specimen dimensions to identify the effect of different hierarchical levels. All these presented aspects are conducted with results for every section of the structure transfer. Beside the procedure of a structure transfer, the paper presents an aspect of bio‐inspired devices beyond the lotus effect. Newly security components with high damping could be generated from our research.