Skin‐Layer Effects on Out‐of‐Plane Compression and Energy Absorption of 3D ‐Printed TPU Honeycombs

ABSTRACT 3D‐printed thermoplastic polyurethane (TPU) honeycombs have potential applications in lightweight cushioning and energy‐absorbing structures due to their flexibility, designability, and large‐deformation capability. This study investigates the out‐of‐plane compressive behavior of 3D‐printed hexagonal TPU honeycombs with and without skin layers. Quasi‐static compression tests were conducted to validate the finite element model, and numerical simulations were then used to analyze the effects of wall thickness‐to‐length ratio, cell angle, and loading rate on load‐carrying and energy absorption performance. The experimental and numerical nominal stress‐compression ratio curves showed consistent trends and comparable magnitudes, indicating that the model could capture the main compressive response of the TPU honeycombs. The wall thickness‐to‐length ( t / l) ratio was the dominant geometric parameter. When t / l increased from 0.025 to 0.225, the peak stress of unskinned honeycombs increased from 1.31 to 4.44 MPa, while the specific energy absorption (SEA) increased slightly from 3.71 to 3.80 J·g −1 . For skinned honeycombs, the peak stress increased from 0.34 to 15.71 MPa, and the SEA increased from 2.75 to 10.58 J·g −1 . The cell angle had a limited effect within θ = 100° ~ 140°, whereas increasing the loading rate raised the nominal stress level and SEA in the numerical cases. Skin layers mainly increased the mean crushing stress, while their effect on SEA depended on t / l . Under the baseline condition, the mean crushing stress of the skinned honeycomb increased by 64.10% compared with the unskinned honeycomb; when t / l = 0.225, it increased by 319.68%, and SEA increased from 3.80 to 10.58 J·g −1 . These results clarify that skin layers do not uniformly improve all energy absorption indices; instead, they primarily enhance mean crushing stress, while the improvement in SEA depends on the wall thickness‐to‐length ratio.