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Abstract

Sea urchin spines combine extreme lightweight construction with impact resistance and improved mechanical strength although being made of presumably brittle calcium carbonate (calcite). Lance and pencil sea urchins (Phyllacanthus imperialis and Heterocentrotus mammillatus) are of particular interest as they exhibit large and mechanical very stable spines and the constructional concepts of these spines was translated into graded porous alumina ceramics derived from starch-blended slip casting. A high level of porosity (>30 vol%) is identified as the important element for graceful failure in polycrystalline alumina and graded porosity, i.e., layers of higher and lower density, can significantly improve the impact resistance of the material giving raise to what we refer to as cascading graceful failure: a mechanical response of porous materials with curved layers of graded porosity that maintains a high level of compressive strength even after the linear elastic threshold is surpassed and local structural collapse occurs.