Cellular metal lattices with hollow trusses

Abstract

Cellular metal lattice truss structures are being investigated for use as multifunctional load supporting structures where their other functionalities include thermal management, dynamic load protection and acoustic damping. A simple method for making lattice structures with either solid or hollow trusses is reported. The approach involves laying up collinear arrays of either solid wires or hollow cylinders and then alternating the direction of successive layers. The alternating collinear assembly is metallically bonded by a brazing process. The dimensions of the cylinders, the wall thickness of hollow truss structures and the spacing between the trusses enable independent control of the cell size and the relative density of the structure. The process has been used to create stainless steel lattices with either square or diamond topologies with relative densities from 0.03 to 0.23. The through thickness elastic modulus of these lattice truss structures is found to be proportional to relative density. The square topology has twice the stiffness of the diamond oriented trusses. The peak compressive strengths of both topologies are similar and is controlled by plastic buckling. The structural efficiency of hollow truss structures with a fixed cell size is approximately proportional to the relative density unlike equivalent structures made from solid trusses whose peak strength has been predicted to scale with the cube of the relative density. The experimental data for hollow trusses lie between predictions for trusses with built-in and pin-jointed nodes consistent with experimental observations of constrained node rotation. The use of hollow trusses increases the resistance to buckling offsetting the usually rapid drop in strength as the relative density decreases in cellular systems where truss buckling controls failure. The low relative density hollow truss structures reported here have the highest reported specific peak strength of any cellular metal reported to date.