Abstract Biological materials such as silk, nacre, and bone have superior mechanical properties due to their well-designed microstructures with dissimilar, namely soft and bulk, composites. It is widely believed that the unique microstructures result in high strength and toughness via a normal-shear-stress-coupling mechanism. Microcrack initiation in biological materials play a crucial role in triggering such a mechanism, and therefore further investigation of its initiating condition and microcrack propagation are needed. In this study, we first describe a staggered model from biological material and illustrate the effects under different microcrack patterns. We employ a Fast Fourier Transform based (FFT-based) homogenization method with linear elasticity and non-local damage theory to investigate the stress distribution and load transmission, as well as the microcrack propagation due to different structural designs of soft matrix geometry. The major implication of this paper is that the design of soft matrix geometry determines the microcrack initiating patterns and impacts the local transmission mechanism of biocomposites. This research provides insights into design strategies for microstructures to trigger normal-shear-stress-coupling behavior for biocomposites to achieve high toughness and strength.

中文翻译：

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微裂纹模式控制生物复合材料的机械强度

摘要 丝绸、珍珠层和骨等生物材料由于其精心设计的微观结构具有不同的复合材料，即柔软的和块状的，因此具有优异的机械性能。人们普遍认为，独特的微观结构通过法向剪切应力耦合机制产生高强度和韧性。生物材料中的微裂纹萌生在触发这种机制中起着至关重要的作用，因此需要进一步研究其启动条件和微裂纹扩展。在这项研究中，我们首先描述了生物材料的交错模型，并说明了不同微裂纹模式下的影响。我们采用基于快速傅立叶变换（基于 FFT）的均质化方法和线性弹性和非局部损伤理论来研究应力分布和载荷传递，以及由于软基体几何结构的不同结构设计而导致的微裂纹传播。本文的主要含义是软基质几何结构的设计决定了微裂纹的起始模式并影响了生物复合材料的局部传输机制。这项研究为微观结构的设计策略提供了见解，以触发生物复合材料的法向剪切应力耦合行为，以实现高韧性和强度。