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Modern engineering applications require advanced materials that are stronger, tougher, and lighter. Nature offers various structural architectures to achieve superior mechanical properties. Inspired by bone with a spongy soft-core and a compact hard-shell, this study introduces architected multi-material lattices with tunable mechanical properties such as stiffness, strength, and energy absorption. The architected lattices are fabricated via multi-material fused filament fabrication. The hard polylactic acid (PLA) shell of the lattice struts maintains the stiffness, while the soft thermoplastic polyurethane (TPU) core enhances toughness and energy absorption capacity. The microstructural and mixed-mode fracture characteristics of the PLA-TPU interfaces were examined since the interfacial microstructure and adhesion are crucial to stress transfer in multi-phase composite materials. This study explores the flexural behavior of the multi-material struts and reveals two distinct failure modes depending on the volume fraction of the soft-core through 3-point bend tests. This study demonstrates the bio-inspired design on a hexagonal planar lattice with a strut thickness-to-length ratio of 0.3. Tunable stiffness, strength, and energy absorption are achieved by varying the core-to-strut thickness ratio. Compression test results show that the architected lattices exhibit an energy absorption capacity that is about 2–3 times greater than that of the constituent single-phase lattices.
Yavaş et al. (Thu,) studied this question.