Design, optimization and additive manufacturing of an innovative bike helmet using auxetic metastructures

• Innovative helmet with auxetic TPU liner and PETG outer shell for better energy absorption. • Impact analyses conducted in both experiments and FE simulations. • Taguchi DOE method optimizes auxetic structure to minimize helmet deceleration in impacts. Safety helmets with high energy absorption are crucial for bike riders and represent a significant priority for the sports industry. This study proposes an innovative design of a mountain bike helmet with an auxetic re-entrant metastructure made out of thermoplastic polyurethane (TPU) for its liner and a thin layer of Polyethylene Terephthalate Glycol (PETG) for its outer shell. The metastructure is designed in SolidWorks software and the impact test is simulated according to the conditions of the EN 1078 standard in Abaqus software. Finite element modeling utilizes input data from the compression tests on 3D-printed TPU specimens. The Taguchi design of experiment (DOE) is used to find the optimal cell geometry of the metastructure and minimize the deceleration during impact tests. A fused deposition modeling (FDM) 3D printer manufactures the entire liner integrally. Two different impact test scenarios, flat anvil and kerbstone anvil, are performed on the manufactured helmet. A comparison of experimental and finite element results shows good accuracy of the numerical model. In addition to a customized helmet liner tailored to individual head shapes and sizes, the proposed liner provides low deceleration during impacts.