Compressive fatigue characteristics of octet-truss lattices in different orientations

Abstract

Octet-truss lattice materials have excellent potential for use as lightweight structures due to their high strength and stiffness, but low relative density. Octet-truss lattice specimens fabricated by stereolithography technique with a photopolymer resin were studied in this research. The unit cell orientation effects on the compressive fatigue behaviors of octet-truss lattices were studied using experimental analysis and computer simulation. A detailed comparison was made between the failure modes of static and fatigue failures, and the deformation mechanisms of lattices in different orientations under compressive cyclic load were determined. Both the static mechanical properties and fatigue properties of octet-truss lattices are highly dependent on the lattice orientation. When normalized with respect to their orientation-dependent Young’s moduli, the fatigue endurance of lattices in different orientations conforms very well (R 2 = 0.88) to a single S-N curve described by a power law. Finally, the differences in fatigue performance between lattices in different orientations were explained and a simple compression–compression fatigue mechanism was determined. Highlights Compressive fatigue behaviors of octet-truss lattice structures in three different unit cell orientations were investigated and compared in this research. Orientation-Z structure has the best resistance to fatigue failure in comparison to other orientations. The absolute S–N curves of lattices in different orientations were normalized by their Young’s moduli into a curve that can be expressed by one single power law. The mechanism of compressive fatigue failure of octet-truss lattice structures in different orientations was determined. Comparing with fatigue crack initiation and propagation in struts, cyclic ratchetting made dominant contribution to the compressive fatigue failure. The differences between the fatigue resistances of lattices in three orientations were explained by comparing the mechanical response in the finite element model.