High strain rate mechanical behavior of Ti-6Al-4V octet lattice structures additively manufactured by selective laser melting (SLM)

Dynamic mechanical response of additively manufactured 12 mm x 8 mm size octet lattice structures of Ti-6Al-4V was investigated. Cylindrical specimens composed of a single unit cell of 36 trusses and 13 nodes sandwiched between two support plates were built using selective laser melting. The radius of the trusses was incrementally varied from 0.1 mm to 0.5 mm. The interior of the trusses and nodes examined using electron microscope was found to be fully densified with no porosity of other defects and demonstrated a uniform microstructure throughout the lattice composed of acicular martensitic needles. High strain rate compression of these lattices was conducted using split-Hopkinson pressure bar at a displacement rate of 7500 mm/s corresponding an effective strain rate of similar to 1000 s(-1). The peak compressive strength and energy absorption capacity of the lattices were found to vary almost linearly with relative density of the cell, which increased proportional to the square of the truss radius. Specific strength and absorption however were found to be significantly higher in the lattice with smallest truss radius. The dynamic compression was recorded using a high speed camera at 100,000 fps capture rate and provided insight into the deformation processes: the initial elastic wave loading, the inertia driven continued loading followed by relaxation for elastic strain recovery. These mechanisms which significantly diversified with the truss radius are presented.