Architected LPBF metallic metamaterials with enhanced torsional performance for bionic applications

The confluence of additive manufacturing, computational design and biomimetic engineering can bring a paradigm change in the metamaterial application space. However, lattice metamaterials have largely been investigated using uniform unit-cell architectures and are often designed agnostic of the dominant loading mode. Under torsion, unlike axial loading, the highest apparent shear stresses occur near the outer circumference; therefore, failure of peripheral load-bearing unit cells can strongly compromise structural integrity. In this study, we present a field-grading methodology to improve the torsional performance of laser powder bed fusion (LPBF) Ti–6Al–4V lattice structures. A simple cubic (SC) unit cell was radially graded to obtain a field graded simple cubic (FGSC) lattice with increased material allocation in the high-shear peripheral region while maintaining matched nominal relative density. Under quasi-static torsion, FGSC lattices exhibited up to 30% higher apparent shear strength than uniform SC lattices at matched measured relative density, 22% on average, together with up to 169% longer torsional fatigue life among the tested densities. The structures followed Gibson–Ashby-type power-law scaling, albeit with constants that differ from classical idealized lattices. Finite element analysis showed that radial grading lowers the mean apparent stress amplification relative to an equivalent solid bar and reduces the radially binned 99th-percentile von Mises stress by 18% on average. Principal-stress analysis identified the strut junctions as the fatigue-critical, tensile-constrained sites. Owing to their tunable stiffness, open porosity, and prospective drug-loading capacity, the proposed field graded cellular architectures offer a promising route toward damage-tolerant implantable devices.