Hybrid auxetics: Postponing failure with elastomer infiltration of Ti-6Al-4V lattices

This work examines how a soft elastomeric phase can be used to reinforce and delay the failure of additively manufactured metal lattice structures with auxetic geometry. A novel hexaround unit-cell was designed to ensure printability of Ti-6Al-4V via laser powder-bed fusion. Once infiltrated with a compliant polyurethane, these hybrid lattices showed a pronounced delay in strut-level failure and shear-band formation. Microtomography coupled with in-situ compression experiments confirmed that nodal cracking commonly observed in unfilled lattices is mitigated by the polymer phase. While hybrid lattices exhibited comparable or slightly increased stiffness only at large deformations, their enhanced integrity and stress redistribution suggest promise for crashworthiness and impact applications requiring high ductility or energy absorption. We discuss how the stiffness ratio between filler and metallic skeleton determines the extent of improvement, offering design guidelines for next-generation hybrid lattices. This is the first in-situ tomographic evidence that a compliant matrix can defer the critical shear-band in an additively manufactured metal auxetic lattice.