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This work aims to develop a greater understanding of fracture behaviour of a three-dimensional lattice structure. Octet-truss lattice was used in this study due to its high strength to density ratio and great potential in the advanced lightweight structure applications. The fracture toughness, K IC , was found to be almost isotropic while the modulus and strength were highly dependent on the model size and lattice orientation. The converged solution for the modulus and strength were obtained when model width is large compared to cell.The modulus can be varied by 20% and the strength can be doubled when lattice orientation was changed. The validity of linear elastic fracture mechanics(LEFM) was examined on dierent model geometries including single edge notch tension(SENT), compact tension(CT), single edge notch bending(SENB) and thumbnail crack model. It shows that the LEFM can be adequately used in the structures with linear crack fronts. In the thumbnail crack model, the curved crack front generates more complexity in the structure ahead of the crack tip which results in a signicant discrepancy in measured toughness compared to the models with linear crack fronts. Moreover, great fracture performance was exhibited in the lattices, where an increase in fracture load was observed during the crack growth.

Experimentation has been performed to measure the fracture behaviour of three-dimensional lattices manufactured using a Selective Laser Melting (SLM) technique. Specimens have been designed using a compact tension (CT) geometry with different lattice orientations and fabricated from a relatively brittle Aluminum alloy. The toughness has been measured and an increase in fracture resistance has been observed during crack extension. The influence of lattice orientation has been demonstrated, which shows that a change in orientation will result in a different crack path, but the effect on toughness is small. Finally, the significance of specimen size on toughness measurement has been investigated using finite element (FE) analysis. The results show that the experimentally measured result have overestimated the fracture toughness of the lattice specimens by approximately 10% due to the insufficiently large specimen size.