Additive manufactured semi-plate lattice materials with high stiffness, strength and toughness

Closed-cell materials, such as plate-lattices, are attracting increasing attention as a result of their potential to achieve the theoretical upper bounds for isotropic elasticity and strain energy storage (the Hashin-Shtrikman upper bounds) (Berger et al., 2017). However, their complex meso-geometries, especially their enclosed structures, make most of additive manufacturing methods impossible to undertake, due to difficulties associated with removing the Supporting material. To overcome this, plate-lattices with small holes located in the plates, termed semi-plate lattices, have been manufactured at the centimeter scale using a multi-jet printing plastic 3D printer combined with a wax removing process. Experimental compression tests on the resulting specimens have shown that semi-plate lattice structures offer an enhanced stiffness, strength and a much-improved energy absorption capability compared with their truss-based lattice counterparts. Numerical predictions agree well with the experimental data and show that the plate topology have higher stress contours with more homogeneous stress distribution. The Mode I fracture toughness of the semi-plate lattices has also been investigated. The fracture toughness of both the semi-plate lattices and the truss lattices has been shown to increase linearly with relative density and the square root of the cell size. The introduction of holes in semi-plate lattices plays a significant role in controlling the propagation of cracks in terms of both speed and direction. Compared with metal foams, the additively manufactured semi-plate lattices are lighter and stronger, whilst offering an equivalent fracture toughness. By using additive manufacturing with different constituent materials, such as alloys and ceramics, semi-plate-based lattice materials can be manufactured to offer greater potential in engineering design than traditional truss-based lattice materials.