Mirkhalaf M, Barthelat F
Department of Mechanical Engineering, McGill University, 817 Sherbrooke Street West, Montreal, Quebec, Canada H3A 2K6.
Department of Mechanical Engineering, McGill University, 817 Sherbrooke Street West, Montreal, Quebec, Canada H3A 2K6.
J Mech Behav Biomed Mater. 2016 Mar;56:23-33. doi: 10.1016/j.jmbbm.2015.11.010. Epub 2015 Dec 1.
The remarkable mechanical performance of biological materials such as bone, nacre, and spider silk stems from their staggered microstructure in which stiff and strong reinforcements are elongated in the direction of loading, separated by softer interfaces, and shifted relative to each other. This structure results in useful combinations of modulus, strength and toughness and therefore is increasingly mimicked in bio-inspired engineering composites. Here, we report the use of a simple and versatile technique based on doctor-blading to fabricate staggered composites of microscopic alumina tablets with high alignment in a chitosan matrix. Tensile tests on these nacre-like materials show that the modulus and strength of the composite films are enhanced by the incorporation of ceramic tablets, but only up to 15vol% after which all properties degrade. This phenomenon, also reported in the past for most of nacre-like materials, composed of micro/nano tablets, obtained from different techniques, has been limiting our ability to produce large volumes of high-performance nacre-like materials. Examination of the structure of the films revealed that at lower tablet concentrations the tablets are well-aligned and well dispersed thorough the volume of the film. At 15vol% and beyond, we observed tablet misalignment and clustering. In order to investigate the impact of these imperfections on material performance we developed large scale finite element models representative of the structure of the composite films. These models show that the mechanical performance significantly degrades with tablet misalignment, and especially at high tablet concentrations. The simulations along with the SEM images therefore quantitatively explain the experimental trends, e.g. the degradation of mechanical properties at high tablet contents.
诸如骨骼、珍珠母和蜘蛛丝等生物材料卓越的力学性能源于其交错的微观结构，其中坚硬且强壮的增强体沿加载方向拉长，由较软的界面分隔，并相互错开。这种结构产生了模量、强度和韧性的有益组合，因此在受生物启发的工程复合材料中越来越多地被模仿。在此，我们报告了一种基于刮刀法的简单通用技术的应用，用于在壳聚糖基质中制备具有高度排列的微观氧化铝片交错复合材料。对这些类珍珠母材料进行的拉伸试验表明，复合薄膜的模量和强度通过掺入陶瓷片而得到提高，但仅在达到15体积%之前如此，之后所有性能都会下降。这种现象过去在大多数由不同技术制备的由微/纳米片组成的类珍珠母材料中也有报道，一直限制着我们生产大量高性能类珍珠母材料的能力。对薄膜结构的检查表明，在较低的片浓度下，片排列良好且在整个薄膜体积中分散均匀。在15体积%及以上时，我们观察到片排列不齐和聚集现象。为了研究这些缺陷对材料性能的影响，我们开发了代表复合薄膜结构的大规模有限元模型。这些模型表明，随着片排列不齐，尤其是在高片浓度下，力学性能会显著下降。因此，模拟结果与扫描电子显微镜图像一起定量地解释了实验趋势，例如在高片含量下力学性能的下降。
