3D-Printed Soft and Hard Meta-Structures with Supreme Energy Absorption and Dissipation Capacities in Cyclic Loading Conditions

The main objective of this article is to introduce novel 3D bio-inspired auxetic meta-structures printed with soft/hard polymers for energy absorption/dissipation applications under single and cyclic loading–unloading. Meta-structures are developed based on understanding the hyper-elastic feature of thermoplastic polyurethane (TPU) polymers, elastoplastic behavior of polyamide 12 (PA 12), and snowflake inspired design, derived from theory and experiments. The 3D meta-structures are fabricated by multi-jet fusion 3D printing technology. The feasibility and mechanical performance of different meta-structures are assessed experimentally and numerically. Computational finite element models (FEMs) for the meta-structures are developed and verified by the experiments. Mechanical compression tests on TPU auxetics show unique features like large recoverable deformations, stress softening, mechanical hysteresis characterized by non-coincident compressive loading–unloading curve, Mullins effect, cyclic stress softening, and high energy absorption/dissipation capacity. Mechanical testing on PA 12 meta-structures also reveals their elastoplastic behavior with residual strains and high energy absorption/dissipation performance. It is shown that the developed FEMs can replicate the main features observed in the experiments with a high accuracy. The material-structural model, conceptual design, and results are expected to be instrumental in 3D printing tunable soft and hard meta-devices with high energy absorption/dissipation features for applications like lightweight drones and unmanned aerial vehicles (UAVs).