Comparison of Ti-6Al-4V TPMS Sandwich Structures Functionally Graded by Compliance and Stress Minimization Strategies

Metallic sandwich panels are widely used in aerospace applications demanding high specific flexural strength and elevated-temperature capability. Conventional joining of face sheets to cores (e.g., brazing) restricts geometric complexity and introduces void-related defects. This work demonstrates electron beam powder bed fusion (EB-PBF) of monolithic Ti-6Al-4V sandwich structures featuring topology-optimized cores, thereby eliminating interfacial joins and expanding design freedom. Five lattice core architectures were investigated: two strut-based (Octet, Kelvin) and three TPMS-based (Gyroid, Diamond, Primitive). For each core, two thickness grading strategies derived from 4-point bend simulations were applied, a compliance (density-based) minimization, and a von Mises stress minimization, alongside a uniform-thickness baseline. Flexural performance was evaluated by 4-point bend experiments per ASTM C393. Results showed that functional grading of core thickness delayed the onset of flexural yielding, while TPMS cores exhibited superior resistance to core buckling compared to strut-based lattices. The stress-minimization grading strategy consistently delivered higher maximum load and flexural modulus than compliance-based grading. Among the architectures, the TPMS Diamond core achieved the highest maximum load and flexural yield stress. These findings highlight the potential of EB-PBF to produce integrated, defect-resistant sandwich structures and underscore the value of stress-informed grading with TPMS geometries for maximizing flexural performance.