Catastrophic brittle fracture is encountered in many engineering contexts, including transportation, infrastructure, and bio-medical devices, bringing with it significant societal costs. Now that tools such as 3D printers allow facile construction of structures with complex geometries and nearly arbitrary patterns, the potential exists for new structural designs that have improved failure characteristics. However, challenges still exist in designing architected materials with superior fracture properties and optimized functionalities. Nature provides some examples of geometric motifs associated with improved failure characteristics. Here, we take inspiration from bamboo, a functionally graded material, with a number of useful properties: it is lightweight, flexible, and possesses a high specific toughness. Bamboo has heterogeneous structural features, including density gradients and voids. We 3D print architected materials with a gradient pattern of voids, which can be seen in natural bamboo’s axi-symmetric longitudinal section. The void patterns demonstrate crack blunting, leading to higher fracture energy during bending-induced fracture. Three-point bending experiments and finite element analysis are used to explain the observed behavior. We show that gradient void patterns in brittle solids can lead to approximately seventy times increase in fracture energy relative to a solid specimen with no voids. We also conduct low-energy impact tests of larger specimens, showing potential for impact mitigation and crack trapping.
2025-04-09 09:00:00
