Mechanical property optimization of functionally graded multi-morphology lattice structures

Functionally graded lattice structures have drawn considerable attention in engineering applications owing to their excellent mechanical properties. This study fabricated functionally graded multi-morphology 316 L stainless steel lattices via laser powder bed fusion (LPBF), based on the triply periodic minimal surface (TPMS) lattice structure, including volume fraction gradient structures (with cosine and cosine-squared functions as gradients), unit cell size gradient structures (with 4 mm and 5 mm unit cell sizes as gradients), hybrid lattice structures (with Gyroid and Diamond structures as gradients), and two uniform structures (with 4–5 mm unit cell sizes). Quasi-static compression tests combined with digital image correlation (DIC) measurements were used to investigate the lattices’ deformation mechanisms along the gradient-aligned (Z-axis, the building direction is parallel to the gradient variation direction) and gradient-perpendicular (X-axis, the building direction is perpendicular to the gradient variation direction) directions, and analyze their load-bearing capacity and energy absorption. Experimental results show: under the same volume fraction, 4 mm unit cell specimens have better deformation resistance and load-bearing capacity than 5 mm ones; hybrid lattices outperform unit cell size and volume fraction gradient structures in comprehensive mechanical properties (elastic modulus, yield strength, plateau stress); Z-axis gradient specimens deform layer-by-layer from the minimum volume fraction region, while X-axis ones show overall co-deformation for uniform load distribution; gradient type and direction impact energy absorption, with Z-axis hybrid lattices achieving the highest energy absorption (66.81 MJ/m³), providing a reference for high-performance energy-absorbing structure design.