Microcrack patterns control the mechanical strength in the biocomposites

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. (C) 2017 Elsevier Ltd. All rights reserved.