International Journal of Mechanical Sciences 326 (2026) 111885

Keywords:4D printing ,Shape-memory ,Programming ,Reconfigurable ,Gradient metamaterials, Energy absorption

Programmable energy-absorbing metamaterials that combine broad load regulation with reusability remain  difficult to realize, because most existing architectures exhibit fixed post-fabrication responses and mainly  provide a single dominant load plateau. In this study, a 4D-printed gradient corrugated plate-tube (CorTube)  metamaterial is proposed by integrating gradient sequencing with shape-memory polylactic acid. Quasi-static  compression experiments and finite-element simulations show that the gradient design transforms relatively  concentrated collapse in homogeneous units into staged progressive collapse in the assembled structure, thereby  generating separated load plateaus over a broader stress range. A mechanism-based interpretation further reveals  that different gradient parameters play distinct roles in redistributing local activation events. The tube spacing  mainly controls the onset and stability of the first plateau, the corrugation angle mainly governs the collapse  sequence and plateau separation, and tube diameter serves mainly as a secondary tuning parameter. Among the  tested designs, the angle-gradient CorTube exhibits the best overall performance, reaching a total specific energy  absorption of 1.088 J/g, which is an 8-fold enhancement relative to the best homogeneous CorTube unit  structure. Besides, it also generates two additional load plateaus at 4.76 and 10.72 MPa. The structure further  recovers its original shape within 5 s at 80  ◦ C after large deformation. And cyclic tests show that the linear regime  and the first load plateau remain nearly unchanged throughout six compression cycles, exhibiting excellent  repeatability. The second and third load plateaus are highly stable during the first three cycles but gradually  degrade from the fourth cycle onward due to accumulated local damage. The structure fully recovers its original  shape within 5 s at 80  ◦ C, demonstrating reusable early-stage performance over six cycles and stable multi-  plateau behavior for at least three cycles. Finally, a scaled UAV landing buffer prototype using four type2  CorTube units was designed and tested, confirming the engineering feasibility of multi-stage buffering and  thermal reusability. These results demonstrate that combining gradient architecture with shape-memory  reconfiguration provides an effective route to lightweight, multi-cycle reusable, and mechanically adaptive  energy-absorbing metamaterials for protective and buffering applications.

Zhao Peng, Chengjun Zeng, Wei Zhao, Jinsong Leng, Yanju Liu

Programming energy absorption via 4D-printed reconfigurable gradient metamaterials.pdf