Natural materials achieve balanced mechanical properties such as material strength and toughness through ingeniously designed microstructures. For instance, nacre shell, containing 95 vol.% mineral platelets and 5 vol.% organic matrices in a staggered arrangement (also known as the brick-and-mortar architecture), exhibits comparable stiffness and strength but 3000 times higher toughness than the monolithic minerals. Although scientists and researchers are mimicking these microstructures in Nature in the synthetic materials, the rigorous fracture mechanics theory for such materials containing predominant heterogeneity is still missing.
Recent study by Prof. Xiaoding Wei’s group in the Department of Mechanics and Engineering Science at Peking University establishes a multiscale analytical framework for a mode I crack propagation in nacreous composites by adopting the “fishnet” scheme. This approach reveals that due to the microstructural effects, the mathematical formulae for the mode I crack in staggered composites turn out to coincide with those for the mode III crack in homogenous ideal elastic-plastic media. The fracture analysis provides rigorous solutions to the plastic zone size and the crack resistance curve (also known as the R-curve) for nacreous composites (see Figure 1). The findings in this study deepen our understanding of the unique fracture mechanics of composites containing sophisticated micro-architectures and help the design of novel bio-inspired materials.
Figure 1. Schematic of the process zone in front of the Mode I crack in nacreous composites containing brick-and-mortar microstructures.
This work has been published in the Journal of the Mechanics and Physics of Solids (https://doi.org/10.1016/j.jmps.2020.104157). The research was supported by the National Key R & D Program, the National Natural Science Foundation of China, China Postdoctoral Science Foundation and Beijing Innovation Center for Engineering Science and Advanced Technology at Peking University.