Flexural performance of high strength-to-weight ratio strut-based and surface-based lattice-structured Inconel-718 parts manufactured by laser powder bed fusion

Lightweight parts consisting of lattice structures can be easily fabricated by additive manufacturing and are becoming potential choices for aerospace and other applications. Lattice structures can be strut-based, surface-based, or planar-based. The present work studied and compared the flexural load-bearing capacity and the strength-to-weight ratio of three-point bending specimens with lattice structures of a new strut-based unit cell named BLS_2 and three existing surface-based unit cells. The BLS_2 was designed by adding different angular and prismatic beam combinations to maximize the unit cell’s Maxwell number and give stretch-dominant behavior. The surface-based unit cells studied were triply periodic minimal surfaces (TPMS) unit cells, namely, Gyroid, Schwarz primitive, and Schwarz diamond. All specimens were made by Inconel 718 using a laser powder bed fusion machine. A finite element simulation based on the maximum equivalent strain damage model was developed in LS-Dyna and was validated by experimental results. Among the TPMS structures, the Schwarz diamond gave the highest flexural stiffness, followed by Schwarz primitive and Gyroid. On the other hand, Schwarz primitive has the highest stiffness to relative density ratio, followed by Schwarz diamond and Gyroid. A mixed-mode transgranular fracture was observed in all the specimens in the SEM study of fracture surfaces. The Gyroid specimen showed a ductile to brittle transition due to the high balling effect during manufacturing. The BLS_2 lattice structure gave a higher strength-to-weight ratio than all the TPMS lattice structures due to BLS_2’s high Maxwell number and negligible Laves and delta phases in its microstructure.