Fracture behavior of fibrous network materials: Crack insensitivity and toughening mechanism.

• Fibrous network materials are found to be insensitive to the crack when the crack length is less than a critical length. • The critical length of crack is three times as much as the average length of fiber segments. • Fiber re-orientation contributes to the enhancement of the crack resistance of the fibrous network materials. A 3D numerical model is established to characterize the fibrous network materials and the fracture behavior is investigated through the finite element method (FEM) analysis. The numerical results show that fibrous network material is insensitive to the crack when the crack length is less than a critical value, which is three times as much as the average length of fiber segments in the fibrous network. In addition, the toughening mechanism of the fibrous network material is revealed based on the FEM simulations. Due to the damage accumulation of bonds near the crack tip, the fibers around the crack tip are reoriented and become perpendicular to the crack path, which can further inhibit the crack propagation, and the deformation mode changes from bending-dominated deformation to tensile-dominated deformation, with the loading capacity of the fibrous network materials enhanced. The results in this paper demonstrate that the fibrous network materials show damage-tolerance to the small crack under the critical crack length, and the fibrous network formed by brittle fibers can exhibit ductile behaviors by controlling the microstructure and relative density, which is useful for the design and optimization of fibrous network materials. Image, graphical abstract [ABSTRACT FROM AUTHOR]