The compressive and shear response of titanium matrix composite lattice structures

Abstract

A method has been developed for fabricating millimeter cell size cellular lattice structures with square and diamond collinear truss topologies from 240 μm diameter Ti–6Al–4V-coated SiC monofilaments (titanium matrix composite (TMC) monofilaments). Lattices with relative densities in the range 10–20% were manufactured and tested in both compression and shear. Because of the very high strength of the TMC monofilaments, the compressive strengths of both topology lattices were dominated by elastic buckling of the constituent struts. However, under shear loading, some of the struts are subjected to tensile stresses and failure is then set by tensile fracture of the monofilaments. Analytical expressions are derived for the elastic moduli and strength of both lattice topologies and the predictions are compared with measurements over the range of relative densities investigated in this study. Excellent agreement between the measurements and predictions is observed. The specific shear strength of the TMC lattices is superior to all other cellular materials investigated to date, including carbon fiber-reinforced polymers (CFRP) honeycombs. Their compressive properties are comparable to CFRP honeycombs. The TMC lattices have a brittle response and undergo catastrophic failure at their peak load. They appear most promising as candidates for the cores in sandwich structures intended for elevated temperature and multifunctional applications where their limited ductility is not a significant constraint.