In-situ investigations of tensile and fracture behavior of 316 L stainless steel lattice struts fabricated by laser powder bed fusion

Lattice materials, fabricated using additive manufacturing, offer a lightweight alternative to traditional bulk structural components while meeting mechanical performance requirements. Despite these advantages, the complex geometry of lattice structures and additive manufacturing processes introduce defects that can significantly impact the mechanical properties of individual struts of lattices. This study investigates the mechanisms through which fabrication-induced defects influence the tensile response and fracture behavior of 316 L stainless steel lattice struts manufactured by laser powder bed fusion in horizontal and vertical orientations. In-situ tensile testing within an X-ray computed tomography instrument was conducted to visualize and analyze the evolution of the three-dimensional structure during the test. Horizontally built struts exhibited geometric irregularities, such as irregular cross-sections, dripping effects, and strut warping, primarily due to limited support of loose powder during fabrication. These irregularities created regions with reduced cross-sections that served as sites for fracture initiation, resulting in less ductility. Meanwhile, vertically built struts exhibited uniform cross-sections, but displayed a higher fraction of porosity, characterized by spherical pores near the surface. These pores acted as sites for strain localization, with cracks initiating and propagating near them. However, the absence of reduced cross-sections in vertically built struts delayed fracture and provided higher ductility.