Fracture behavior under compression loading of surface-cleaned metallic lattice structures

Lattice structures are porous materials with interconnected porosity and non-stochastic pore distribution that present unique properties. Recently, additive manufacturing (AM) has driven attention to the production of lattice structures since it provides a direct-from-CAD production, tailoring their mechanical properties by controlling their unit cell type, pore size, strut size, and porosity. However, the mechanical behavior of these structures is yet to be understood, as surface post-processing is needed for the biomedical application (ASTM F3335) and manufacturing deviations and defects imply different results from the CAD projected models. In this work, three different types of Ti-6Al-4 V ELI lattice structures were projected and produced by powder bed fusion AM technique. The surface structures were cleaned using pickling, and as-built and pickled structures were compared using scanning electron microscopy (SEM), optical microscopy (OM), and Archimedes’ principle. Mechanical compressive tests were conducted on the surface-cleaned lattice structures, and fractured surfaces were analyzed by SEM. Finally, finite element analysis (FEA) was made to understand the stress distribution during compression. The results show that pickling is successful in removing adhered powder particles from lattice structures’ outer and inner surfaces, as it also reduces surface roughness and defects, which may act as stress raisers. The compressive tests along with fracture analysis show that fracture behavior cannot be predicted using Maxwell’s criterion in 3D and FEA can be a better tool to predict fracture behavior. These results show that classifications of lattice structures made by AM in stretch or bending-based need further research.