de Obaldia Enrique Escobar, Jeong Chanhue, Grunenfelder Lessa Kay, Kisailus David, Zavattieri Pablo
Lyles School of Civil Engineering, Purdue University, West Lafayette, IN 47907, USA.
Department of Chemical and Environmental Engineering, University of California, Riverside, Riverside, CA 92521, USA.
J Mech Behav Biomed Mater. 2015 Aug;48:70-85. doi: 10.1016/j.jmbbm.2015.03.026. Epub 2015 Apr 6.
Many biomineralized organisms have evolved highly oriented nanostructures to perform specific functions. One key example is the abrasion-resistant rod-like microstructure found in the radular teeth of Chitons (Cryptochiton stelleri), a large mollusk. The teeth consist of a soft core and a hard shell that is abrasion resistant under extreme mechanical loads with which they are subjected during the scraping process. Such remarkable mechanical properties are achieved through a hierarchical arrangement of nanostructured magnetite rods surrounded with α-chitin. We present a combined biomimetic approach in which designs were analyzed with additive manufacturing, experiments, analytical and computational models to gain insights into the abrasion resistance and toughness of rod-like microstructures. Staggered configurations of hard hexagonal rods surrounded by thin weak interfacial material were printed, and mechanically characterized with a cube-corner indenter. Experimental results demonstrate a higher contact resistance and stiffness for the staggered alignments compared to randomly distributed fibrous materials. Moreover, we reveal an optimal rod aspect ratio that lead to an increase in the site-specific properties measured by indentation. Anisotropy has a significant effect (up to 50%) on the Young's modulus in directions parallel and perpendicular to the longitudinal axis of the rods, and 30% on hardness and fracture toughness. Optical microscopy suggests that energy is dissipated in the form of median cracks when the load is parallel to the rods and lateral cracks when the load is perpendicular to the rods. Computational models suggest that inelastic deformation of the rods at early stages of indentation can vary the resistance to penetration. As such, we found that the mechanical behavior of the system is influenced by interfacial shear strain which influences the lateral load transfer and therefore the spread of damage. This new methodology can help to elucidate the evolutionary designs of biomineralized microstructures and understand the tolerance to fracture and damage of chiton radular teeth.
许多生物矿化生物体已经进化出高度定向的纳米结构来执行特定功能。一个关键例子是在大型软体动物石鳖（Cryptochiton stelleri）的齿舌齿中发现的耐磨棒状微观结构。这些牙齿由一个软质核心和一个硬壳组成，该硬壳在刮擦过程中所承受的极端机械载荷下具有耐磨性。这种卓越的机械性能是通过由α - 几丁质包围的纳米结构磁铁矿棒的分级排列实现的。我们提出了一种组合仿生方法，其中通过增材制造、实验、分析和计算模型对设计进行分析，以深入了解棒状微观结构的耐磨性和韧性。打印出由薄的弱界面材料包围的硬六边形棒的交错配置，并用立方角压头进行力学表征。实验结果表明，与随机分布的纤维材料相比，交错排列具有更高的接触电阻和刚度。此外，我们揭示了一个最佳的棒纵横比，该纵横比导致通过压痕测量的特定部位性能增加。各向异性对平行和垂直于棒的纵轴方向的杨氏模量有显著影响（高达50%），对硬度和断裂韧性有30%的影响。光学显微镜表明，当载荷平行于棒时，能量以中位裂纹的形式耗散，当载荷垂直于棒时，能量以横向裂纹的形式耗散。计算模型表明，在压痕早期阶段棒的非弹性变形会改变抗穿透性。因此，我们发现系统的力学行为受界面剪切应变影响，界面剪切应变影响横向载荷传递，进而影响损伤扩展。这种新方法有助于阐明生物矿化微观结构的进化设计，并了解石鳖齿舌齿对断裂和损伤的耐受性。
