Numerical investigation of energy absorption behaviour of additively manufactured functionally graded lattice structures for automotive crash box applications

In the quest to improve crash safety in automotive structures, lightweight energy absorbing lattice architectures have gained considerable attention. This study presents a combined numerical and experimental investigation of additively manufactured uniform and functionally graded (FG) lattice structures for automotive crash-box applications. Four lattice topologies Body-Centered Cubic (BCC), Body-Centered Cubic with vertical stiffeners (BCCz), Octet Truss, and Re-entrant Auxetic are evaluated under quasi-static and dynamic loading conditions. The novelty lies in the comparative analysis of multiple lattice topologies and the development of functionally graded Re-entrant auxetic lattices under identical loading conditions. Parametric models with varying unit cell size, strut thickness, and re-entrant angle are developed and analysed using finite element simulations. Among all configurations, the Re-entrant Auxetic lattice shows superior deformation stability and specific energy absorption behaviour. Uniform lattices with different packing factors and FG lattices with layer-wise density variation are further investigated under quasi-static compression and impact loading. The functionally graded re-entrant auxetic lattice exhibited approximately 17.9% higher specific energy absorption (SEA) than the corresponding uniform lattice, indicating improved crashworthiness performance. Finally, the optimized FG lattice is integrated into a crash box, which absorbs more energy (72,343 J vs. 69,654 J) and has a higher specific energy absorption (38.54 vs. 37.39 kJ/kg) than the uniform-lattice crash box, with a smoother force response, although at the cost of a higher peak crushing force and a lower crash force efficiency (0.61 vs. 0.72). These results indicate the potential of FG lattices for lightweight automotive crashworthiness applications.