Additive manufacturing of functionally graded thickness in TPMS lattice structures with optimised mechanical strength

Additively manufactured (AM) triply periodic minimal surface (TPMS) lattice structures are widely used because of their superior mechanical strength-to-weight ratio, high surface area, and design freedom for engineered porosity. Additionally, the complex geometry, design flexibility, and no need for sacrificial support renders AM as the ideal processing approach for TPMS structures. This study aims to establish a gradient-based optimisation method to design and fabricate TPMS structures with functionally graded thickness for mechanical strength and mass constraints. Ti-6Al-4V lattice beams were fabricated through laser powder bed fusion (L-PBF) and investigated through flexural testing with digital image correlation and finite element analysis (FEA). Findings show that the graded beams redistributed regions of high stress to maintain a more uniform strain distribution across the beam, allowing these beams to withstand prolonged higher loads. Specifically, the graded beams were able to withstand on average a 35% higher load as compared to the beams with uniform thickness. The presented design method effectively combines design optimisation and AM constraints to generate functionally graded lattice structures with superior mechanical strength. Findings from this study can be seamlessly applied to mechanical products that benefit from higher stiffness-to-weight ratios, and other TPMS applications such as heat exchangers.