3D printing of a cycling helmet with bioinspired structure and biomaterial: design, additive manufacturing, and FEM validation

This thesis work was carried out in collaboration with Mondragon Unibertsitatea, precisely with the research groups of the Departments of Additive Manufacturing and Composite Materials. The objective was to move away from the widespread creation of a Polystyrene (EPS) foam helmet and focus on new material, the Low Weight Polylactic Acid (PLA LW): biodegradable, biocompatible, obtaining a lightweight and 3D printed helmet with a bio-inspired structure (beetle structure), able to absorb a high amount of energy during the impact. Quasi-static compression tests on EPS samples of a generic helmet and samples of PLA LW with the beetle structure were carried out, to establish the differences between the two materials and calculate the specific stress. The PLA LW specific stress values were in an intermediate range between the EPS in the software CES Edupack, and the analyzed EPS sample of a generic helmet: a valid reason to continue to carry out tests on the PLA LW with the beetle structure. The following step was to create the helmet structure with Grasshopper (Rhinoceros plug-in) based on the head scan realized with a 3D Sense 2 Scanner and print the helmet. The printer was a Raise Pro 2 with a double extruder: the first for the PLA LW filament, the second for the water-soluble Polyvinyl Alcohol (PVA). The latter was used for the supports and removed with a dive at the end of printing. Dynamic tests with Hoytom HM-D Testing Machine were performed to analyze the energy absorbed by the EPS and PLA LW with beetle structure helmet models with and without Thermoplastic Polyurethane (TPU) cover. The models were also validated with the Finite Element Method (FEM) in Abaqus through explicit dynamic steps. Finally, further simulations were executed to evaluate the head injury criteria and, in particular, the value of head acceleration, the only parameter considered during a real test and mentioned by the legislation BS EN 1078. What has been achieved in the physical tests is almost equal absorbed energy of EPS and PLA LW with TPU cover; in FEM analysis these values are slightly higher for PLA LW with bioinspired structure compared to EPS. The acceleration of the head is lower in the case of the structure bio-inspired with PLA LW, and the objective of not reaching the value of 220g is confirmed.