Additive manufacturing and mechanical testing of functionally-graded steel strut-based lattice structures

Functionally graded materials have been increasingly considered for many applications, spanning from aerospace to biomedicine, because directional mechanical or physical features are provided. Recent developments of additive manufacturing technologies allow to pursue new challenging metal structures, possibly designed on a case-by-case basis. Nevertheless, many studies in the literature have already pointed out the need for accurately defining the manufacturing limits of the technologies as well as the correlation between the geometries and the mechanical performance. In this frame, this paper is aimed at manufacturing and testing steel functionally graded strut-based lattice structures to map their mechanical properties as a function of the grading approach (uniform, size-graded and rod-graded) and the fractional density (15 %, 25 % and 35 %), even computing the calibration parameters to check the reliability of the usual Gibson-Ashby scaling laws. Results showed strut distortion and deviation from the designed geometry in samples with the lowest fractional density (15 %) and at thinner layers of the rod-graded geometries. Size-graded structures demonstrated higher mechanical properties, regardless of the fractional density.