Department of Materials Physics and Chemistry, School of Materials Science and Engineering, Northeastern University, Shenyang 110819, P. R. China.
Key Laboratory for Anisotropy and Texture of Materials, Ministry of Education, Northeastern University, Shenyang 110819, P. R. China.
ACS Biomater Sci Eng. 2021 Oct 11;7(10):4819-4827. doi: 10.1021/acsbiomaterials.1c00956. Epub 2021 Sep 20.
Mollusk shells generally consist of several macro-layers with different microstructures. To explore the specific role that different macro-layers play in the overall mechanical properties of shells, the microstructures, hardness distribution, and three-point bending behavior in the deep-sea shell were investigated. It is found that the shell presents a hierarchical structure comprising three layers in thickness, that is, the outer, middle, and inner layers, which exhibit homogeneous, prismatic, and nacreous structures, respectively. Among them, the homogeneous structure in the outer layer is harder, which is beneficial for the shell to enhance resistance to wear and perforation. Furthermore, both the bending strength and fracture energy for group Up (loading from outer to inner surfaces) are far higher than those for group Down (loading from inner to outer surfaces), indicating that the inner nacreous layer is not only stronger but also tougher. Cracks tend to deflect at the interfaces in nacreous structure, and nacreous structure is thereby more resistant to breakage. Hence, the nacreous structure in the inner layer could protect the shell from breaking catastrophically in the deep sea with high pressure. In brief, the combination of a harder outside layer and a tougher inside layer provides an effective protective structure for the deep-sea shell, and the excellent environment adaptability of shell can thus be interpreted in terms of its ingenious microstructure arrangement.
软体动物的贝壳通常由几个具有不同微观结构的宏观层组成。为了探究不同宏观层在贝壳整体力学性能中所起的具体作用，研究了深海贝壳的微观结构、硬度分布和三点弯曲性能。结果表明，贝壳呈现出厚度为三层的层状结构，分别为外层、中层和内层，其分别呈现出均匀、棱柱和珍珠层结构。其中，外层的均匀结构更硬，有利于增强贝壳的抗磨损和穿孔能力。此外，组 Up（从外表面向内表面加载）的弯曲强度和断裂能均远高于组 Down（从内表面向外表面加载），表明内层珍珠层不仅更强韧。在珍珠层结构中，裂纹倾向于在界面处发生偏折，因此珍珠层结构更能抵抗断裂。因此，内层的珍珠层结构可以保护贝壳在深海高压环境下不发生灾难性破裂。总之，更硬的外层和更坚韧的内层的结合为深海贝壳提供了有效的保护结构，贝壳的优异环境适应性可以从其巧妙的微观结构排列来解释。
