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3D Printing of Biomimetic Composites with Improved Fracture Toughness

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Document pages: 37 pages

Abstract: Recent researches show that material microstructural designs mimicking biomaterials offer an effective way to design tougher materials. To reveal the underlying microstructure-toughness relationship, five bioinspired material microstructures are investigated experimentally, including the brick-and-mortar, cross-lamellar, concentric hexagonal, and rotating plywood microstructure. The feature sizes of microstructures are controlled to be one order smaller than the specimen size, providing better pictures of how crack resistance interacts with heterogeneity. Fracture theories are further used to analyze the toughening mechanisms and find the design criteria of different microstructures. Results show that the rotating plywood structure presents a "J " shaped R-curve, while other structures show "Γ " shaped R-curves. The "J " shaped R-curve gives a larger critical energy release rate and tolerates a longer crack, thus preferable for crack arresting. By contrast, the "Γ " shaped R-curve provides a larger critical failure stress, which is beneficial for producing stiffer and stronger materials. Moreover, combined experimental results and theoretical analysis suggest that heterogeneity improves toughness by 1) creating stiffness variations to slow down crack propagation and prevent crack penetration and 2) guiding cracks along weak interfaces to promote progressive damage. Our results shed new light on the structure-property relationships which will facilitate the design of tougher and better crack resistant composites.

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