Influence of geometrical defects in the elastic-plastic failure of lattice materials

Foams and microlattices are examples of hybrid materials, being composites of material and space. In structural applications they offer several advantages, notably high weight-specific strength and stiffness, with the architecture of the internal structure strongly influencing the mechanical property – density relationship. The deviation from architectural homogeneity has a similarly strong influence on the mechanical properties of these materials, particularly in cases when the constituent cell walls or ligaments are subjected to tensile deformations. Here we report the effect of geometrical imperfections on the tensile failure and Mode I fracture toughness of ductile 2D cellular solids. Hexagonal honeycomb architectures are fabricated with controlled imperfections of three types: hard inclusions, missing ligaments, and deviation from periodicity. Two types of materials are used, with tensile ductility in the range of ≈5% and ≈20% respectively. We report the influence of geometrical imperfections on the mechanical properties (tensile ductility and resistance curves) for both types of materials, and compare them with the predictions of FE calculations