Design and assessment of functionally graded lattices

Lattice structures are architectures of interest for lightweight applications in different fields such as aerospace, biomedical, automotive and structural engineering. Their properties, such as strength to weight ratio, specific strength and energy absorption can be potentially tailored or generally improved by functionally grading. In this study differently graded lattice structures based on Body Centered Cubic (BCC) unit cell, which has a simple basic geometry that can be advantageous for easier 3D printing and a wider use in industry were considered. Linearly graded and symmetrically linearly graded geometries were modelled with a similar value of average relative density in order to compare their structural behaviour with a uniform BCC lattice structure. The different geometries of the graded lattices were 3D printed with stereolithography (SLA), which allowed to obtain a good geometrical accuracy and superficial finish. The printed models were subjected to compression tests and main parameters, specifically, stiffness and energy absorption capability were evaluated. The results obtained showed that, in particular, the proposed symmetrical functional grading allowed a moderate increase of stiffness and a more noticeable improvement of energy absorption capability with respect to a uniform structure, which was higher when the load was applied perpendicularly to the grading direction.