Effect of nickel and copper shells on mechanical properties of advanced lightweight TPU metamaterials during uniaxial compression

This study explores the impact of metallic shells by electroforming method on the mechanical behavior of thermoplastic polyurethane (TPU)-based lattice structures. First, the TPU lattice structures were printed by additive manufacturing technique. Then layers of Ni and Cu as a thin shell were dressed on the TPU lattice structures in the electroforming baths of Ni and Cu solutions. Finally, uniaxial compression tests achieved on the samples. Results demonstrated substantial enhancements in mechanical performance attributable to these metallic coatings. Notably, the Ni-coated lattice structure (Ni-LS) exhibited a peak yield strength of 4.55 MPa, marking a 1.08-fold improvement over the Ni-Cu-LS structures and a 1.35-fold increase relative to the Ni-Cu-Ni-LS variant. Furthermore, the energy absorption density of the coated structures was elevated by nearly sixfold compared to the uncoated TPU lattice, with multi-layer coatings providing additional gains. These results underscore the potential of Ni and Cu-coated TPU lattices to deliver exceptional strength-to-weight ratios and enhanced energy absorption capabilities.