Fracture toughness characteristics of additively manufactured Ti-6Al-4V lattices

Metallic lattice structures are well known for having high specific elastic moduli and strength. However, very little is understood about their resistance to fracture. In this work Ti-6Al-4V lattice structures are additively manufactured by selective laser melting and their fracture toughness characteristics are investigated. Resistance to fracture was determined under Mode-I loading at static rates using an extended compact tension (EC(T)) specimen, modified to contain lattice cells. The lattices consist of octet cells with a 3.5 mm edge length and relative densities ranging from 25% to 56%. Toughness is shown to increase by a power law with relative density and this trend was also obtained with finite element models. A new functional grading optimisation methodology is also presented for increasing fracture toughness. The size optimisation results in a functionally graded lattice whereby lattice truss diameters become the design variables. After size optimisation, initiation fracture toughness increases by up to 37%.

Automated summary

Metallic lattice structures are known for their high specific elastic moduli and strength, but their resistance to fracture is not well understood. In this study, Ti-6Al-4V lattice structures were additively manufactured using selective laser melting, and their fracture toughness characteristics were investigated under Mode-I loading. The results showed that toughness increases with relative density in a power law manner, and a new functional grading optimisation methodology was introduced to increase fracture toughness. After size optimisation, initiation fracture toughness was improved by up to 37%.