3D printed bending-stretching coupled non-self-similar hierarchical cellular topology under in-plane loading

Ultralight hierarchical metamaterial is a type of promising structure in aerospace and transportation applications owing to the high stiffness/strength to density ratio. Though some hierarchical topologies with distinct in-plane configurations have been reported, the topology with superior mechanical behaviors under plastic deformation is urgent to be tailored. The present study develops a novel bending-stretching coupled Non-Self-Similar Hierarchical Topology (NSSHT) via additive fabricating methodology, and gives an insight into the mechanical responses and energy absorption capacities. It is identified that the softening post initial peak stress is triggered by the bending of the oblique membrane in the first order unit cell when edge length ratio (gamma) is low, while by the initial rotation of second order unit cell when gamma is high. Compared to the quasi-static measurements, the dynamic specific initial peak stress of NSSHT with uniform wall thickness (eta = 1) was enhanced up to 131.9%. The deformation modes at distinct stress stages are different under quasi-static and dynamic loads. For specific energy absorption capacity, the NSSHT with non-uniform wall thickness behaves better, and the majority is dissipated at stress enhancement stage. The developed novel hierarchical structures enable to provide a wider spectrum of choices for tailoring high-performance lightweight components.