Complex Materials, Department of Materials, ETH Zürich, 8093 Zürich, Switzerland.
Complex Materials, Department of Materials, ETH Zürich, 8093 Zürich, Switzerland
Proc Natl Acad Sci U S A. 2018 Dec 11;115(50):12698-12703. doi: 10.1073/pnas.1805094115. Epub 2018 Nov 26.
The nacreous layer of mollusk shells holds design concepts that can effectively enhance the fracture resistance of lightweight brittle materials. Mineral bridges are known to increase the fracture resistance of nacre-inspired materials, but their role is difficult to quantify due to the lack of experimental systems where only this parameter is controllably varied. In this study, we fabricate tunable nacre-like composites that are used as a model to experimentally quantify the influence of the density of mineral bridges alone on the fracture properties of nacre-like architectures. The composites exhibit a brick-and-mortar architecture comprising highly aligned alumina platelets that are interconnected by titania mineral bridges and infiltrated by an epoxy organic phase. By combining experimental mechanical data with image analysis of such composite microstructures, an analytical model is put forward based on a simple balance of forces acting on an individual bridged platelet. Based on this model, we predict the flexural strength of the nacre-like composite to scale linearly with the density of mineral bridges, as long as the mineral interconnectivity is low enough to keep fracture in a platelet pullout mode. Increasing the mineral interconnectivity beyond this limit leads to platelet fracture and catastrophic failure of the composite. This structure-property correlation provides powerful quantitative guidelines for the design of lightweight brittle materials with enhanced fracture resistance. We illustrate this potential by fabricating nacre-like bulk composites with unparalleled flexural strength combined with noncatastrophic failure.
软体动物贝壳的珍珠层具有设计理念，可以有效地提高轻质脆性材料的抗断裂能力。众所周知，矿物桥可以提高珍珠层启发材料的抗断裂能力，但由于缺乏仅可控制该参数变化的实验系统，其作用难以量化。在这项研究中，我们制备了可调谐的珍珠层状复合材料，将其用作模型来实验定量地研究仅矿物桥密度对珍珠层状结构的断裂性能的影响。该复合材料具有砖-泥结构，由高度取向的氧化铝薄片组成，这些薄片通过钛矿矿物桥相互连接，并被环氧树脂有机相渗透。通过将实验力学数据与这种复合材料微观结构的图像分析相结合，提出了一个基于作用在单个桥接薄片上的力的简单平衡的分析模型。基于该模型，我们预测珍珠层状复合材料的弯曲强度与矿物桥的密度呈线性关系，只要矿物的连通性足够低，以使断裂处于薄片拔出模式。超过该极限增加矿物的连通性会导致薄片断裂和复合材料灾难性失效。这种结构-性能相关性为设计具有增强抗断裂能力的轻质脆性材料提供了有力的定量指导。我们通过制备具有无与伦比的弯曲强度和非灾难性失效的珍珠层状块状复合材料来说明这种潜力。
