Mechanical response of functionally graded lattices with different density grading strategies

This paper explains the quasi-static compressive behaviour of functionally graded lattices made of polyamide PA11 by multi jet fusion (MJF). The effects of various unit cell topologies such as body-centred cubic (BCC), rhombic dodecahedron (RD), and octet (OT) unit cells, as well as different stacking configurations were examined to achieve bi-directional and uni-directional grading in the lattice structures. Moreover, the strut diameters of the lattices were changed to obtain different relative density grading. The experimental results showed that topology grading played a dominant role in tuning the deformation patterns, stress-strain curves, and the energy absorption capacity of the lattice structures. Based on the numerically simulated results obtained from the validated finite element models, a semi-empirical formula was subsequently developed to predict the plateau stress of the studied FG lattices. Further numerical studies on the effects of the loading direction and the cell arrangement showed that the specific plateau stress and specific energy absorption capacity of the lattices compressed along the loading direction (z) were higher than those when they were compressed in the lateral (x) direction. Additionally, the cell arrangement predominately affected the deformation patterns and stress-strain curves. The findings of this study revealed that desired crushing performance of lattice structures can be achieved through functional grading of cell topologies, and it can be further enhanced by incorporating strut diameter grading.