The staggered structure is prominent in high-performance biological materials such as nacre, spider silk or bone. It consists of stiff and strong elongated inclusions aligned with the direction of loading. This structure leads to useful combinations of stiffness, strength and toughness, and it is therefore increasingly mimicked in bio-inspired composites. The modulus and strength of natural and bio-inspired composites are typically predicted using the shear lag model, where inclusions carry tensile stress and interfaces carry shear stresses. In this work, we have used a simple doctor blade technique to make thin film of nacre-like materials, which we tested in tension. Strength and modulus increase up to 10–15 % volume concentration of mineral reinforcement after which they degrade. Finite element analyses of staggered microstructure over a wide range of arrangement and concentrations revealed new trends which can explain the experimental results. For example the stiffness of the material can degrade in higher mineral concentrations if the tablets lack interface in the matrix. The results show that materials with combination of stiffness, strength and energy absorption can be achieved when there is an overlap between the tablets the distance between them is small in the transverse direction. This is identical with the microstructure of nacre where mineral tablets are divided by a very thin organic layer. The results suggest new approaches to simultaneously optimize modulus, strength and toughness in this class of composites.
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This work was supported by the Fonds de recherche du Québec – Nature et technologies and by the Natural Sciences and Engineering Research Council of Canada. SMMV was partially supported by a McGill Engineering Doctoral Award.
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