A Macroscale Biomimetic Composite Duplicating the Deformation Mechanisms of Nacre
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A Macroscale Biomimetic Composite Duplicating the Deformation Mechanisms of Nacre Deju Zhu and Francois Barthelat1 1 Department of Mechanical Engineering, McGill University 817 Sherbrooke Street West, Montreal, QC H3A 2K6, Canada ABSTRACT This article presents the first man-made material based on the structure of nacre that successfully duplicates the mechanism of tablet sliding. This material was made of millimeter size PMMA tablets arranged in columns and held by fasteners. Strain hardening was provided by tablet waviness, delaying localization and leading to strains at failure 3-5 times greater than bulk PMMA. Analytical and finite element models successfully captured the locking mechanisms, enabling a rigorous design and optimization of similar composites based on different materials or at different length scales. This work demonstrates how key features and mechanisms in natural nacre can be successfully harnessed in engineering materials. Interestingly, the development of this model material and of its associated models also unveiled two new mechanisms, the effect of free surfaces and “unzipping”. Both mechanisms may be relevant to natural materials such as nacre or bone. INTRODUCTION Materials produced by nature exhibit remarkable properties which are attracting the attention of engineers, material scientists, chemist and zoologists in search of inspiration for novel material designs [1]. Often made of materials with relatively poor structural qualities, biological materials achieve their performance through intricate microstructures finely tuned over millions of years of evolution [2]. Elucidating the structure-properties relationships in these materials is a challenging task, but is nevertheless an essential step for a successful biomimetic “transfer of technology” from natural to man-made materials and systems. Nacre from mollusk shells, also known as mother of pearl, is now identified as an excellent model for highperformance materials offering attractive combinations of stiffness, strength and toughness [3]. Nacre is a highly mineralized material made of 95% of the mineral calcium carbonate, which comes in the form of microscopic polygonal tablets closely stacked to form a dense, threedimensional brick wall [4]. The remaining constituents are proteins and polysaccharides, which form an organic matrix concentrated at the interfaces between the tablets [5]. The unique architecture and mechanisms of nacre and how they lead to its impressive mechanical performance have motivated the development of numerous “artificial nacres” over the past 20 years. Various fabrication techniques were employed, including layer by layer deposition [6], colloidal assembly [7] and ice-templated sintering of alumina powders [8]. While these materials display structures which closely resemble nacre, none could truly duplicate its mechanism of tablet sliding. In this article a novel composite is presentedwhich is based on millimeter size PMMA tablets, constructed following the brick and mortar arrangement of natural nacre in a two
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