Flexural Behavior of Ti-6Al-4V TPMS Lattice Sandwich Structure produced by Electron Beam Powder Bed Fusion

Metallic sandwich structures are highly valued in the aerospace industry due to their high specific flexural strength and temperature resistance. However, traditional manufacturing processes for metallic joining of face sheets to a core structure (e.g. brazing) severely limit the final geometry that can be economically produced, and the structures are fraught with defects that limit the structural performance and durability. This presentation demonstrates the capability of electron beam powder bed fusion (EB-PBF) additive manufacturing to produce monolithic Ti-6Al-4V sandwich structures containing novel topology optimized core geometries. In this investigation, a triply periodic minimal surface (TPMS) Diamond lattice was applied to a sandwich core, and then the thickness was functionally graded using two different optimization strategies in order to satisfy a 4-point bend load case: 1) a compliance (density-based) minimization strategy, and 2) a Von Mises stress-based minimization strategy. The flexural behavior of the graded sandwich structures was compared with a uniform Diamond lattice topology in static 4-point bend experiments according to standard test method ASTM C393 for short beam core shear. Empirical data showed the density-graded core achieved a 19% load increase over the uniform core, while the stress-graded core further enhanced load capacity by 50% and exhibited a higher resistance to damage. Post-fracture analysis was performed by scanning electron microscopy and optical microstructural analysis where these revealed a superior monolithic sandwich structure, but with orthotropic properties relative to the build direction. This work is important to any materials and process engineer or designer to consider for future applications of additive metal sandwich structures.