Programmed Out-of-Plane Curvature to Enhance Multimodal Stiffness of Bending-Dominated Composite Lattices

What is it about?

Lattice-based materials are attracting wide attention from the scientific community due to their ability to achieve unprecedented multifunctional properties with an application-specific tailorable feature. The microstructure of such materials can be conceived as a periodic network of connecting elementary structural components (cell walls) such as beams and plates. The effective macroscale properties of lattice materials are strongly dependent on the repeating unit cell level geometry, which has been investigated widely for improving the specific stiffness of lattice materials. Conventional bending-dominated lattices exhibit less specific stiffness compared to stretching-dominated lattices while showing high specific energy absorption capacity. In this article, we propose to improve the specific stiffness of bending-dominated lattices by introducing elementary-level out-of-plane curvature through a multi-level hierarchical framework. The influence of curvature in the elementary beams is investigated here on the effective in-plane and out-of-plane elastic properties of lattice materials. The elementary cell walls with out-of-plane curvature are modeled based on 3D degenerated shell finite elements. Subsequently, the cell wall deflections are integrated with unit cell level mechanics in an efficient semi-analytical framework to obtain the lattice-level effective elastic moduli. The results reveal that the effective in-plane elastic moduli of lattices with curved isotropic cell walls can be significantly improved without altering the lattice-level relative density significantly (up to 847.33% and 1098.54% for Young’s modulus and shear modulus, respectively), while the effective out-of-plane elastic properties reduce due to the introduction of curvature. To address this issue, we further propose laminated composite cell walls with out-of-plane curvature which can lead to holistic improvements in the in-plane and out-of-plane elastic properties. The proposed curved composite lattice materials would lead to improving the in-plane specific stiffness of bending-dominated lattices to a significant extent along with narrowing the disparity between in-plane and out-of-plane stiffness, while maintaining the multi-functional advantages such as high energy absorption capability, more ductile behavior and aversion of any sudden failure.

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