Investigation of torsional properties of surface- and strut-based lattice structures manufactured using multiJet fusion technology

Lattice structures have proven to have excellent mechanical properties in several loading conditions for a wide range of applications and additive manufacturing enables to fabricate these intricate as well as complex structures with exceptional accuracy. However, studies of mechanical properties of these structures in response to torsional and other complex loading are very limited. In this study, three different structures namely gyroid, primitive, and vertical-inclined were designed in cylindrical shape samples and additively manufactured using MultiJet fusion technology. Torsion tests until failure of structures were performed to study mechanical properties including torsional stiffness, energy absorption, and failure modes of structures. In addition, a new method of calculating polar moment of inertia is established taking the non-uniform cross section of the structures into account for accurate calculation of torsional properties. Experimental results indicate that the surface-based gyroid and primitive structures have superior torsional stiffness, energy absorption capacity, and ultimate strength compared to the strut-based vertical-inclined structure. Gyroid structure has almost 9% higher torsional stiffness value than primitive structure and nearly two times higher stiffness than vertical-inclined structure. However, primitive structure showed superior energy absorption capacity of 8 J/mm³ withstanding a large amount of plastic deformation. In contrast, both gyroid and vertical-inclined structures had lower energy absorption capacity values of 3.72 J/mm³ and 2.27 J/mm³, respectively. Lastly, failure mode of structures revealed that both gyroid and vertical-inclined failed in a brittle manner with fractures at an angle to their longitudinal axis while primitive structure showed ductile mode of failure with fracture perpendicular to its longitudinal axis.