Functionally graded octet lattice structure for enhancing multifunctional mechanical performance using localized material distribution

Localized buckling instabilities often limit the mechanical performance of lattice structures, limiting their potential for lightweight applications. Although functional grading is promising, controlling buckling at fixed relative density is non-trivial because the same geometric adjustments that delay local failure also redistribute loads and can sharpen collapse in the weaker regions. In this study, utilizing design freedom of additive manufacturing, we introduce a mechanics-guided novel approach to functionally graded octet lattice structures, methodically modified to overcome local buckling phenomena and enhance multifunctional performance. Lattice structures were designed by precisely varying strut dimensions, geometry, and spatial arrangement to achieve functionally graded configurations. Our comprehensive experimental and numerical investigations systematically analyzed how variations in geometry influence mechanical behavior, while maintaining constant relative density across all configurations. The graded designs improved peak load, compression modulus, and energy absorption by 40%, 50%, and 31%, respectively, relative to a uniform octet. An investigation of the deformation pattern of the structure under compression load reveals that these gains, together with crashworthiness metrics, provide information regarding the stability of the plateau region and a more progressive propagation of local buckling rather than an abrupt localized collapse. Finite element analysis (FEA) validates that added vertical members shift bending away from early-buckling regions, and proves the strength above the upper limit of an analytical model. This work provides a route to tune the buckling-critical response and improves the strength, stiffness, and energy absorption.