Geometric determinants of monotonic and fatigue performance in additively manufactured TPMS lattice structures: Decomposing scale effects

Additively-manufactured lattice structures are increasingly used in biomedical, automotive, and aerospace applications, where scale strongly influences structural integrity. In TPMS gyroid lattices, even though scaling involves simultaneous changes in unit-cell size and wall thickness, their combined effects on manufacturing fidelity and mechanical performance remain unclear. This study investigates these effects in AlSi10Mg gyroid lattices under monotonic and fatigue loading by decomposing scale into three cases: variation in scale, variation in unit-cell size at constant wall thickness, and variation in wall thickness at constant unit-cell size. As-printed geometric deviations altered key attributes governing mechanical performance, including relative density, slenderness, and surface-to-volume ratio. Wall thickness showed the strongest influence on geometric deviation, whereas unit-cell size showed comparatively stable geometric fidelity. Monotonic properties were governed primarily by relative density and slenderness. Fatigue behaviour was controlled by the coupled effects of relative density and surface-to-volume ratio, reflecting a competitive damage mechanism between deformation mode and surface roughness. Both yield strength and fatigue limit decreased with increasing unit-cell size or decreasing wall thickness, with mechanical performance showing greater sensitivity to unit-cell size than to wall thickness. Decomposing scale effects offers a clearer interpretation of geometry–process–performance relationships beyond trends observed for individual geometric parameters.