Mechanical convergence of lattice materials across topologies, constituent materials, and deformation regimes

Additively manufactured lattice metamaterials provide exceptional strength-to-weight ratios, yet their mechanical properties critically depend on specimen size. A core design challenge is therefore defining a minimum representative volume—the smallest cell array that yields bulklike, size-invariant properties—to ensure reliable performance. While often discussed, this critical scale has never been rigorously established for architected lattices. Here, through integrated experiments and numerical simulations on metallic (AlSi10Mg) and polymeric (ABS) lattices spanning multiple topologies (simple cubic, body-centred cubic, and octet-truss) and a broad range of strut slenderness ratios, encompassing bending-dominated, stretching-dominated, and transitional deformation regimes, we establish the first systematic general convergence criterion. We show that a 5 × 5 × 5 cell array ensures convergence of elastic modulus and strength, independent of topology, material, or absolute scale. Crucially, while this threshold is general, it is found that the deformation regime plays a previously unreported role in governing the pathway to convergence as array size increases. Stretching-dominated architectures converge earlier than bending-dominated ones, and lattices exhibiting simultaneous bending, stretching, and shear achieve the earliest convergence of all. Across deformation regimes, strength stabilizes prior to modulus and failure modes evolving from boundary-driven collapse to progressive, bulk-like failure. These material-independent design rules eliminate the need for exhaustive size-scaling studies, accelerating the development of reliable lightweight lattice metamaterials for advanced engineering applications.