In situ Wear Study Reveals Role of Microstructure on Self-Sharpening Mechanism in Sea Urchin Teeth

H. D. Espinosa; A. Zaheri; H. Nguyen; D. Restrepo; M. Daly; M. Frank; J. McKittrick

Matter 1 (2019) 1246-1261

Animals’ teeth have evolved to provide food procurement, mastication, and protection. These functions, directly linked to survival of many living animal species, require superior hardness and abrasion resistance in the animal’s dentition system. Such resistance typically emerges from damage tolerance and sharpness preservation during the organism’s life span. An example is the sea urchin tooth, which through gradients in mechanical properties together with exploitation of microstructural features achieves such functionality. Using contact mechanics, dimensional analysis, and a novel in situ scanning electron microscopy experimental methodology, conditions for tooth deformation and wear, via a self-sharpening mechanism consisting in plate chipping, were imaged and quantified. Nonlinear finite-element modeling of the self-sharpening mechanism provided insight into the synergy between constituent material properties and tooth microstructural elements. The findings reported here should inspire the design of novel tools used in machining operations, e.g., cutting and grinding, as well as in mining and tunnel boring. The teeth of animals play a crucial role in their survival, and, like other body parts, they adapted to the host’s habitat to maximize their functionality. Superior performance in the sea urchin dentition system was hypothesized to emerge from sharpness preservation during the organism’s life span. In this work, a novel in situ scanning electron microscopy experimental methodology was employed to visualize a mechanism for sharpness preservation and to quantify conditions for its activation. Nonlinear finite-element modeling, incorporating experimentally measured nanoscale properties of constituents and interfaces, provided insight into synergistic effects between tooth architecture and material properties leading to sharpness preservation. The reported findings have the potential to influence the design of tools for mining, boring, and machining operations, e.g., cutting and grinding. The self-sharpening of the sea urchin tooth was previously hypothesized but never visualized. Through a novel in situ SEM experiment, such visualization in three dimensions become possible. Moreover, when in situ experimental measurements were combined with nonlinear finite-element analysis, the synergy between tooth microstructural features and mechanical properties of constituents responsible for the observed self-sharpening mechanism was ascertained. Such insight of material architecture and properties is readily transferable to composite material design.