Department of Materials Physics and Chemistry, School of Material Science and Engineering, Northeastern University, Shenyang 110819, China.
Department of Mechanical and Industrial Engineering, Ryerson University, 350 Victoria Street, Toronto, Ontario M5B 2K3, Canada.
Sci Rep. 2017 Jan 17;7:40043. doi: 10.1038/srep40043.
Natural structural materials with intricate hierarchical architectures over several length scales exhibit excellent combinations of strength and toughness. Here we report the mechanical response of a crossed-lamellar structure in Cymbiola nobilis shell via stepwise compression tests, focusing on toughening mechanisms. At the lower loads microcracking is developed in the stacked direction, and channel cracking along with uncracked-ligament bridging and aragonite fiber bridging occurs in the tiled direction. At the higher loads the main mechanisms involve cracking deflection in the bridging lamellae in the tiled direction alongside step-like cracking in the stacked direction. A distinctive crack deflection in the form of "convex" paths occurs in alternative lamellae with respect to the channel cracks in the tiled direction. Furthermore, a barb-like interlocking mechanism along with the uneven interfaces in the 1st-order aragonite lamellae is also observed. The unique arrangement of the crossed-lamellar structure provides multiple interfaces which result in a complicated stress field ahead of the crack tip, hence increasing the toughness of shell.
具有复杂多层次结构的天然结构材料在强度和韧性方面表现出优异的结合。本文通过逐级压缩试验研究了 Cymbiola nobilis 贝壳的交错层状结构的力学响应，重点研究了增韧机制。在较低的载荷下，在堆叠方向上会产生微裂纹，而在平铺方向上会产生通道裂纹以及未开裂韧带桥接和方解石纤维桥接。在较高的载荷下，主要的机制包括在平铺方向的桥接层中出现的裂纹偏转以及在堆叠方向上出现的阶跃状裂纹。在交替层中会出现一种独特的以“凸”形路径形式的裂纹偏转，相对于平铺方向上的通道裂纹。此外，还观察到在一阶方解石层中存在着棘爪状互锁机制以及非均匀的界面。交错层状结构的独特排列提供了多个界面，从而在裂纹尖端前方产生了复杂的应力场，从而提高了贝壳的韧性。
