Brittle fracture of three-dimensional lattice structure

Abstract

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, KIC, 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 different 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 significant 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.