Toughening by interpenetrating lattices

•Separate lattices can be interwoven to significantly increase their toughness •The sub-lattice properties can be tuned via topology and optimized for toughness •The toughening effect can be explained using a crack-bridging model As structural lattice metamaterials become more accessible through 3D printing, there is a need to better understand their fracture behavior, which sets practical limits for engineered structures. Lattices face a problem of decreasing toughness as their density and cell size decrease. Recently discovered interpenetrating lattices, made by weaving two or more physically separate lattices through the same volume, offer a potential path to significantly improve fracture toughness by increasing the fracture process zone size and inducing unique contact and friction toughening mechanisms. Interpenetrating lattices possess a steeply rising resistance-curve behavior, with the final toughness associated with catastrophic fracture an order of magnitude greater than the initiation toughness needed to begin advancing a crack. Remarkably, the interpenetrating lattice’s toughness in certain topologies can be five times greater than its corresponding, fully dense solid base material, and the toughening effect can be tailored by controlling the mechanical mismatch of the constituent sub-lattices. As structural lattice metamaterials become more accessible through 3D printing, there is a need to better understand their fracture behavior, which sets practical limits for engineered structures. Lattices face a problem of decreasing toughness as their density and cell size decrease. Recently discovered interpenetrating lattices, made by weaving two or more physically separate lattices through the same volume, offer a potential path to significantly improve fracture toughness by increasing the fracture process zone size and inducing unique contact and friction toughening mechanisms. Interpenetrating lattices possess a steeply rising resistance-curve behavior, with the final toughness associated with catastrophic fracture an order of magnitude greater than the initiation toughness needed to begin advancing a crack. Remarkably, the interpenetrating lattice’s toughness in certain topologies can be five times greater than its corresponding, fully dense solid base material, and the toughening effect can be tailored by controlling the mechanical mismatch of the constituent sub-lattices.