Topology optimized lattice core effects on the flexural behavior of Ti-6Al-4V sandwich structures produced by electron beam powder bed fusion (EB-PBF)

Abstract

Metal sandwich structures are utilized in aerospace applications that require high specific flexural strength and temperature resistance. Conventional fabrication methods, which involve joining operations (e.g. brazing, welding, bonding) to attach face sheets to a core structure, limit the geometric complexity that can be produced economically with sufficient quality. New additive manufacturing (AM) technologies, such as electron beam powder bed fusion (EB-PBF), present the ability produce a monolithic sandwich structure from Ti-6Al-4V with novel topology optimized cores. For this investigation, five lattice core geometries were selected, three triply periodic minimal surface (TPMS) types: Gyroid, Diamond, and Primitive, and two strut types: Octet and Kelvin. To demonstrate the unique capability of AM to optimize structures, two methods for functionally grading the core densities were applied based on a 4-point bend simulation. One grading method used a compliance minimization strategy (density-based), and the other a von Mises stress minimization strategy. After using waste powder from another additive process to produce 15 novel sandwich structures, the flexural properties were determined by ASTM C393 4-point bend experiments. This research revealed that the continuous grading of the core densities successfully delayed flexure yielding without increasing weight, and the TPMS core geometries exhibited a higher resistance to core buckling. The stress minimization strategy provided superior performance, while the Diamond core geometry attained the highest flexure yield stress. This work serves as a valuable contribution in the design for additive manufacturing of metal sandwich products, and highlights the sustainability of the EB-PBF process.