Fracture toughness analysis of helical fiber-reinforced biocomposites

Many biological materials contain nanofibers of helical shape to achieve multiple biological functions and superior mechanical properties. In this paper, we establish a microstructure-based crack-bridging model to investigate how the chiral morphologies of nanofibers contribute to the fracture properties of these natural nanocomposites. By using a cohesive interfacial model, the force–displacement relation for a helical nanofiber during pullout is first derived. It is found that the fracture toughness of biological materials is sensitive to the chiral morphology of fibers, suggesting a strategy to attain superior strength, toughness and elasticity. We discover an optimum helical angle that maximizes the toughness. A scaling law is provided to predict the macroscopic fracture toughness of helical fiber-reinforced nanocomposites in terms of microscopic geometric and mechanical parameters. This work not only sheds light on the toughening mechanisms of biological materials but also offers inspirations for design and optimization of advanced composites.