The advent of additive manufacturing technology empowers precise control of multi-material components or specific defects in lightweight lattice metamaterials, however, fracture mechanics and toughening design strategies in such metamaterials remain enigmatic. By incorporating theoretical analysis, numerical simulation, and experimental investigation, our study reveals that stretch-bend synergistic strut deformations caused by bi-material components or topology defects contribute notably tougher lattice structures surpassing its ideal single-material lattices. A peak fracture energy at a critical modulus ratio was found in a designed bi-material lattice composed of triangular soft struts and hexagonal stiff struts, which originates from the shift of fracture modes at crack tip from strut bending to stretching dominated failure modes as the modulus of soft struts increases, where the compromise in competition between bending-enhanced and stretching-weakened energy dissipations of struts deformations results in the maximized fracture energy. A parametric design protocol was proposed to optimize fracture energy of bi-material lattices through tuning the modulus ratio and relative density. Furthermore, the concept of stretch-bend synergistic toughening can also be applied to make tougher single-material lattices with specific topological defects. Our findings not only provide physical insights into directing crack propagation but also provide quantitative guidance to optimize fracture resistance within low-density tough lattice metamaterials.

中文翻译：

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双材料晶格超材料的断裂力学


增材制造技术的出现使得能够精确控制多材料组件或轻质晶格超材料中的特定缺陷，然而，此类超材料中的断裂力学和增韧设计策略仍然是个谜。通过结合理论分析、数值模拟和实验研究，我们的研究表明，由双材料成分或拓扑缺陷引起的拉伸弯曲协同支柱变形明显有助于超越其理想的单材料晶格的更坚韧的晶格结构。在由三角形软支柱和六角形刚性支柱组成的设计双材料晶格中发现了临界模量比处的峰值断裂能，其源于裂纹尖端的断裂模式从支柱弯曲到拉伸主导失效模式的转变作为模量软支柱的数量增加，其中支柱变形的弯曲增强和拉伸减弱的能量耗散之间的竞争折衷导致断裂能最大化。提出了一种参数化设计方案，通过调整模量比和相对密度来优化双材料晶格的断裂能。此外，拉伸弯曲协同增韧的概念也可用于制造具有特定拓扑缺陷的更坚韧的单一材料晶格。我们的研究结果不仅为引导裂纹扩展提供了物理见解，而且还为优化低密​​度坚韧晶格超材料内的断裂阻力提供了定量指导。