Biological materials are often composed of relatively weak constituents yet have evolved complex, hierarchical structures that allow them to achieve remarkable mechanical properties. In biological systems that need to survive impact scenarios, convergent evolution has resulted in design motifs which appear repeatedly in organisms that come from vastly different areas of the natural world. In this work, the structure-property relationships of two systems, the horse hoof wall and the jackfruit, are examined as sources of inspiration for impact resistance. The horse hoof wall, capable of withstanding large, repeated, dynamic loads, has been touted as a candidate for impact-resistant bioinspiration. However, the scientific community’s understanding of this biological material and its translation into engineered designs is incomplete. A model of the hoof wall's viscoelastic response was developed and the role of hydration, strain-rate, and impact energy on the material's response were elucidated. Post-impact fractography identified hierarchical failure mechanisms of the unique hoof structure. Multi-material 3D printed designs based on the hoof's meso/microstructure were fabricated and exhibited advantageous energy absorption and fracture control relative to control samples.
In-situ microCT suggest that the hollow tubules in the hoof wall may be a progressive failsafe mechanism meant to absorb energy from biaxial lateral compression. These results also highlight behavior variations that arise from different loading orientations, hydrations, and locations within the hoof wall. Toughening mechanisms such as tubule crack deflections, tubule bridging, tubule arresting, and fiber bridging are also visualized providing valuable context to previous studies.
The jackfruit is the largest fruit on Earth reaching 50 kgs and falls from heights of up to 50 m. To survive such large impact energies, the layered structure of the jackfruit includes a series of collapse mechanisms that absorb energy and mitigate damage. Quasi-static, viscoelastic, and dynamic tests are performed on the different layers of the fruit to establish an understanding of the fruit’s mechanical behavior. The structures are then replicated using 3D printing to show that the architectures identified in the jackfruit can be utilized in engineered materials to improve their impact resistance.