3D printing thermoplastic polyurethane hierarchical cellular foam with outstanding energy absorption capability

In this paper, 3D printing is combined with supercritical CO₂ foaming technology as a novel strategy for the manufacture of thermoplastic polyurethane (TPU) lightweight hierarchical structure, which has the advantages of high specific strength of microcellular foam and free design of 3D printing structure at the same time. More critically, the microstructure of the hierarchical structure presents a shell and core structure similar to the turtle shell, with the thickness of the shell layer and the size of the core layer's cells adjustable with 3D printing parameters, leading to changes in the mechanical properties of the printed foam. In further energy absorption tests, the hierarchical cellular honeycomb with high specific strength exhibits enhanced the specific energy absorption (SEA) by 9.56% compared with the unfoamed honeycomb. In addition, the SEA of TPU hierarchical cellular honeycomb can be adjusted in the range of 0.214–0.377 J/cm³ by changing the printing parameters, with the maximum energy absorption efficiency up to 0.383. Combined with the advantages of 3D printing personalization make the hierarchical cellular foam promising for a broad range of applications in fields such as personal shielding, energy absorption, and transportation.