Energy absorption and deformation of Re-entrant Bi-material tubular metamaterials

• Dual-material additive manufacturing of PLA–TPU ensures stable, controllable deformation without cracking. • The novel metamaterial exhibits 90%, 88%, and 91% improvements in stiffness, total and specific energy absorption. • The novel metamaterial retains 60% energy and 98.9% height after cyclic compression. This study presents a novel bi-material re-entrant tubular (BRT) metamaterial fabricated via dual-material additive manufacturing, in which a rigid PLA core is encapsulated by a flexible TPU shell. This configuration effectively integrates the high stiffness of PLA with the elasticity of TPU, enabling a stable and controllable collapse process without cracking. The soft–hard coupling ensures efficient stress transfer and coordinated deformation, mitigating stress concentrations and preventing premature failure. Compared with single-material re-entrant tubular (RT) structures, the bi-material BRT metamaterial exhibits substantial mechanical enhancement, with stiffness, total energy absorption, and specific energy absorption increased by 90%, 88%, and 91%, respectively. Parametric analyses reveal that increasing the PLA core thickness significantly improves structural stiffness, plateau stress, and energy absorption capacity, with specific energy absorption enhanced by up to 67%. However, excessive PLA thickness may weaken interfacial adhesion and induce delamination or brittle fracture, highlighting the importance of optimal thickness matching between soft and rigid layers to balance stiffness and ductility. Under cyclic compression, the BRT metamaterial retains over 60% of its initial energy absorption capacity even at 100% strain after four loading cycles, exhibiting pronounced secondary stability and adaptive deformation. The structure recovers 98.9% of its original height, demonstrating excellent geometric stability and recoverability. This research provides an effective design strategy for future multi-material metamaterials with tunable mechanical properties.