Department of Materials Engineering, Indian Institute of Science, Bangalore, India.
Department of Materials Engineering, Indian Institute of Science, Bangalore, India.
J Mech Behav Biomed Mater. 2018 Feb;78:96-107. doi: 10.1016/j.jmbbm.2017.10.018. Epub 2017 Oct 18.
Nacre achieves excellent mechanical properties with a relatively simple hierarchical structure. Analyses suggest that a significant gain in toughness is realized with a modest reduction in strength, with increasing levels of hierarchy. This study probes the role of different hierarchical length scales in governing the strength and modulus of nacre using a combination of bulk compression tests, microindentation and nanoindentation tests. The variability in the measured properties is assessed through Weibull analyses. The transition from elastic deformation is characterized using spherical indentation tests at the micro and nano scales together with a Herztian analysis. The modulus of the organic phase at different scales was deduced using indentation data and appropriate micromechanical models. The results show a minimal influence of length scales on elastic-plastic transitions, suggesting that initiation of plasticity occurs through a common biomineral sliding mechanism across length scales. However the ultimate strengths follow the trends of models for hierarchical materials, with the strength reducing by a factor of ~2 with each increase in level of hierarchy. The modulus of the organic phase was higher at the lowest scale, in contrast to an earlier study, indicating that confinement significantly modifies the effective properties of the organic.
珍珠母具有相对简单的层次结构，可实现优异的机械性能。分析表明，随着层次结构的增加，在强度略有降低的情况下，韧性显著提高。本研究使用体压缩试验、微压痕和纳米压痕试验相结合的方法，探讨了不同层次长度尺度在控制珍珠母强度和模量方面的作用。通过威布尔分析评估了测量性能的可变性。使用球形压痕试验在微观和纳米尺度上以及赫兹分析来表征从弹性变形到塑性变形的转变。使用压痕数据和适当的细观力学模型推导出不同尺度下有机相的模量。结果表明，长度尺度对弹塑性转变的影响很小，这表明塑性的开始是通过跨越长度尺度的共同生物矿滑动机制发生的。然而，最终强度遵循分层材料模型的趋势，每增加一个层次，强度就会降低约 2 倍。与早期的研究相反，有机相的模量在最低尺度时更高，这表明约束显著改变了有机相的有效性能。
