Abstract
Diatom frustules, with their hierarchical three-dimensional patterned silica structures at nano to micrometer dimensions, can be a paragon for the design of lightweight structural materials. However, the mechanical properties of frustules, especially the species with pennate symmetry, have not been studied systematically. A novel approach combining in situ micro-indentation and high-resolution X-ray computed tomography (XCT)-based finite element analysis (FEA) at the identical sample is developed and applied to Didymosphenia geminata frustule. Furthermore, scanning electron microscopy and transmission electron microscopy investigations are conducted to obtain detailed information regarding the resolvable structures and the composition. During the in situ micro-indentation studies of Didymosphenia geminata frustule, a mainly elastic deformation behavior with displacement discontinuities/non-linearities is observed. To extract material properties from obtained load-displacement curves in the elastic region, elastic finite element method (FEM) simulations are conducted. Young’s modulus is determined as 31.8 GPa. The method described in this paper allows understanding of the mechanical behavior of very complex structures.
Highlights
Biomimetics and bioinspired materials are emerging fields for learning design strategies from nature and applying them to synthetic structures
Diatoms are one of the surprisingly elegant example of nature’s sophisticated design skills, demonstrating how organisms build refined structures based on a bottom-up approach and simple components
Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies conformed the hierarchical structures of the Didymosphenia geminata frustule determined with nano-X-ray computed tomography (XCT)
Summary
Biomimetics and bioinspired materials are emerging fields for learning design strategies from nature and applying them to synthetic structures. Diatoms are one of the surprisingly elegant example of nature’s sophisticated design skills, demonstrating how organisms build refined structures based on a bottom-up approach and simple components Their hard porous shell, known as frustule, is composed mainly of amorphous bio silica which possesses remarkably organized and hierarchical 3D porous exoskeleton structures at the nano, submicrometer, and micrometer scales [8,9,10,11]. Atomic force microscopy (AFM) nanoindentation measurements of frustules revealed that Young’s modulus and hardness values are varying significantly, from 7 to hundreds of GPa, and from 1 to 12 GPa, respectively, depending on the location where the measurement was performed [27,32] These findings support that the mechanical performance is related to the amorphous bio silica itself and to the hierarchical 3D morphology of porous exoskeleton structures at the nano, submicrometer to micrometer scales of the frustule. The method described here holds a great potential to understand the mechanical behavior of complex structures such as in biomaterials, catalysts, and other porous or skeleton materials
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