Impact resistant hierarchically structured materials based on fruit walls and nut shells

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Fruit walls as well as nut and seed shells typically perform a multitude of functions. One of these consists in the direct or indirect protection of the seeds from mechanical damage or other negative environmental influences This qualifies such biological structures as role models for the development of new materials and components that protect commodities and/or persons from damage caused for example by rough handling or crashes. Our goal is to improve the mechanical properties of metal foam based components by altering their structure on various hierarchical levels inspired by features and principles important for the impact and/or puncture resistance of our role models, rather than by tuning the properties of the bulk material. For this we have established various investigation methods which combine mechanical testing with different imaging methods. We identified different structural hierarchies to be especially important for the mechanical deformation and failure behaviour of the biological role models. We abstracted and transferred these into corresponding structural principles and thus designed hierarchically structured bio-inspired metal foams. After the successful production of first metal based bio-inspired structures by investment casting during the 1st project period, the process has been modified and optimised within the last two years in order to realise more complex and more reliable structures, by implementing and combining different hierarchical structural elements as well as by minimising casting defects. To evaluate the structural effects, we applied similar investigation methods and mechanical testing experiments as those used for the biological role models. In the applied for project phase 3 we will further pursue this goal by gaining an even deeper quantitative understanding of the form-structure-function relationship of the biological concept generators on deeper hierarchical levels and level overarching, and by abstracting these findings and transferring them in bio-inspired metal foams and composite foam-based structures with further improved damping properties and puncture resistance.