A multiscale nonlinear fracture model for staggered composites to reveal the toughening effect of process zone

Abstract

The attainment of both strength and toughness is a vital requirement for most structural materials. Unfortunately, these properties are generally mutually exclusive in synthetic materials. Natural structural materials defeat the conflict of strength versus toughness, and provide design motifs for the high-performance materials. However, there still lacks a deep understanding of the toughening mechanisms in bioinspired composites. This paper presents a microstructure-based nonlinear fracture mechanics model for staggered composites, to investigate the toughening effect of the nonlinear deformation in the process zone. Firstly, a nonlinear stress–strain relationship of staggered composites is derived, to capture the plastic deformation of the matrix. Then, a multiscale nonlinear fracture mechanics model incorporating the effect of crack bridging and process zone is established based on the above constitutive relation and HRR theory. Finally, the model is used to reveal the influence of geometric and constitutive parameters. The results demonstrate that the process zone leads to a tremendous contribution to the overall toughness. And the crack resistance curve is rising with crack extension due to the increase of the process zone. What is more, there still exists an optimal balance between toughness, stiffness, and strength in biological materials. These results can provide guidelines for the design of high-performance composites.