Crashworthiness capability comparison of a 3D Greek cross fractal structure additively manufactured with polyamide and thermoplastic polyurethane

Abstract Designers are continuously searching for materials or meta-structures, also inspired by nature, that exhibit favourable strength-to-weight ratios, substantial heat transfer capabilities, and efficient energy absorption. One particular example includes fractal geometries, which usually consist of intricate three-dimensional geometrical structures and are challenging to produce through traditional manufacturing methods. In this regard, this study analyses the performance of a three-dimensional cross-based fractal structure (3D-CFS) designed for energy absorption and manufactured using polymeric materials. Mathematically, the geometry is obtained using a 3D Greek cross repeated in the 3D space according to the fractal principle. Owing to the intricate final structure, samples are fabricated using an Additive Manufacturing system based on powder bed fusion with a laser beam and infrared light. The study is carried out using two polymeric materials, polyamide and thermoplastic polyurethane, and the mechanical response of the structure is analysed under dynamic compression tests. The tested geometries consisted of samples with a single 3D-CFS cell, various volume fractions and a configuration with multiple cells that emulated a possible layout for linear helmet application. The findings indicate that the 3D-CFS is a promising geometry for eventual implementation into shock absorption applications, specifically in personal protective equipment (PPE) usage.