Fracture of Honeycombs Produced by Additive Manufacturing

Lattice materials, such as honeycombs, are remarkable in their ability to combine high stiffness, strength and toughness at low density. In addition, the recent and pervasive development of additive manufacturing technologies makes it easier to produce these cellular materials and opens new possibilities to improve their properties by implementing small modifications to their microstructure. Such developments open new opportunities towards the design of new classes of architectured materials. For example, recent computational studies have shown that honeycombs with lattice density gradients have a fracture energy under tensile loading up to 50% higher than their uniform counterparts. The aim of this study is to provide experimental evidence for these promising numerical results. To achieve this, single-edge notched tension specimens, with a honeycomb lattice structures, were manufactured by stereolithography using a ductile polymer resin. The performances of three different honeycombs were compared: (i) a uniform sparse lattice, (ii) a uniform dense lattice, and (iii) a gradient lattice with alternating bands of sparse and dense lattices. The results indicated that specimens with a density gradient may achieve a work of fracture per unit volume that is up to 79% higher than that of a uniform lattice.