Quasi-static crushing of DMLS-produced Ti6Al4V hierarchical honeycombs

Abstract

• Surface morphology and compressive performance of DMLS printed Ti6Al4V vertex-based hierarchical honeycombs are characterised. • Distinct deformation and collapse mechanisms are observed for quasi-static in-plane crushing of three levels of hierarchical honeycombs. • Surface roughness increased monotonically with hierarchical order. • Second-order hierarchical configurations achieve the highest failure loads under quasi-static loading. Honeycombs excel at absorbing energy during quasi-static crushing events. Adding hierarchical structures to these designs improves their effectiveness. Hierarchical structures are best built using additive manufacturing technologies. There is, however, limited experimental data on their crush-resistance. This renders it difficult to improve and validate current theoretical and numerical models on the deformation behaviour of hierarchical honeycombs. This study aims to design vertex-based hierarchical honeycombs and examine their surface quality and mechanical behaviour for quasi-static crushing scenarios. Zero-, first-, and second-order hierarchical honeycombs were designed and fabricated using direct metal laser sintering technology. The Ti6Al4V specimens were quasi-statically crushed using the MTS Criterion TM , Model 43 universal testing machine to evaluate the deformation behaviour of honeycomb topologies with different levels of hierarchy. Surface roughness analysis revealed that the average surface roughness ( Ra ) increased with the order of hierarchy, with lower Ra values on top flat surfaces compared to side inclined surfaces. Mechanical testing showed deformation occurred primarily through beam bending, with pronounced buckling under y-direction loading. The load drop after peak values was attributed to fracture at the vertices of the walls. The sequential collapse of the hierarchical honeycombs under compression began with the lowest order of hierarchy, involving bending, buckling, Poisson’s ratio lateral expansion, and sliding along inclined and horizontal lines. Zero-order hierarchical honeycombs exhibited the lowest failure loads, while second-order hierarchical honeycombs had the highest. The design-to-experiment test approach was employed to predict the performance benefits of hierarchical honeycombs, providing valuable insights and highlighting design limitations to address crash-worthy additively manufactured hierarchical lattice structures.