Evaluation of stress state on the mechanical properties of 3D printed metallic lattice structures fabricated via laser powder bed fusion for orthopedic applications

Abstract

The ability to change the design parameters of metallic lattice structures provides the control to optimize the interconnected porosity size to promote osseointegration and manipulate stiffness values to mimic bone, ideal for minimizing stress shielding. These benefits have caused a widespread proliferation of 3D printed porous metallic scaffolds in orthopedic implants, specifically Laser Powder Bed Fusion (LPBF). Once implanted, these devices experience complex stress states under physiological loading. To design these structures to mimic the mechanical behavior of bone, their performance under these conditions must be understood. The characterization of 3D printed metallic lattice structures’ compressive mechanical properties is well established, but the mechanical behavior of these structures under additional loading conditions requires further exploration. This research aims to define a method for characterizing LPBF metallic lattice structures’ mechanical properties in various physiologically relevant loading conditions and determine the stress state’s pure impact on the design parameters of metallic lattice structures to optimize the design process for practical applications. To achieve this goal, Ti6Al4V and Co28Cr6Mo metallic lattice structures were fabricated via LPBF, and monotonic tensile, compressive, compressive shear, and torsion testing was conducted to determine the mechanical behavior. The findings showed that sample geometry and test setup significantly impacted the mechanical properties of metallic lattice structures, which led to the design of a universal sample geometry that enabled the utilization of a single sample for tensile, compressive, and torsional testing. The impact of the stress state’s effect on sheet-based, strut-based, stochastic, and functionally graded metallic lattice structures was characterized.