4D-Printed Negative Poisson's Ratio Honeycomb Structures With Multi-Stage Deformation Characteristics

The traditional re-entrant hexagonal honeycomb (TRH) structure exhibits a negative Poisson's ratio and lightweight characteristics. Low plateau stress and insufficient energy absorption remain major limitations. Inspired by the staggered arrangement and rectangular cell-wall features of onion epidermal cells, this study introduced vertical, horizontal, and diagonal reinforcing cell walls into the TRH structure. A 4D-printed negative Poisson's ratio honeycomb structure with multi-stage deformation characteristics is constructed and denoted as the MSH structure. Deformation modes under quasi-static compression are analyzed. Energy absorption behavior is evaluated. Regulation mechanisms of key cell wall parameters are investigated. Reconfigurability under thermomechanical training is also examined. Results indicate that higher plateau stress is achieved when vertical and horizontal cell walls are simultaneously added to form rectangular substructures. A pronounced dual-stress-plateau response is exhibited. Plateau stress is effectively tuned by cell wall thickness. The inclined cell wall mainly governs the first plateau stress. The horizontal cell wall mainly governs the second plateau stress. Programmability and reconfigurability are enabled under thermomechanical training. Energy absorption (EA) and specific energy absorption (SEA) are actively tuned over a wide range. The structure also shows good resistance under repeated impacts. Application potential in adaptive protective systems is indicated.