Effects of random and controlled irregularity in strut lattice structure of PA12 on compression anisotropy

Lattice structures have attracted significant attention as novel energy-absorbing structures; however, regular lattice structures have anisotropic energy-absorbing properties. To make the energy absorption properties isotropic, the irregularization of the lattice structures may be effective. However, the irregularity effect on the energy absorption amount is unclear. Therefore, in this study, irregularities were introduced into the lattice structures comprising struts, and the irregularity effects on the isotropy of the compressive properties and amount of energy absorption were investigated. The lattice structures were designed using a three-dimensional Voronoi partitioning method, and the irregularities of the structures were controlled by the Voronoi seed point distribution. The designed lattice structures were fabricated by powder bed fusion with recycled PA12 powder. In the compressive deformation behavior of the lattice structures with small irregularities, steep stress drops were observed with the generation of failure bands. However, local strut rupture occurred continuously in the lattice structure with large irregularities, and the flow stress undulated gently. From these behavioral characteristics, energy absorption was calculated and discussed concerning the irregularities, redefined quantitatively using the coefficient of variation (CV) for the cell volume distribution. The energy absorption anisotropy decreases sharply for CV above 0.1, and such lattice structures can be considered almost isotropic. Thus, even if the structure is incompletely random, it is isotropic with a certain level of irregularity. In contrast, the average energy absorption between structures with equivalent CV decreases monotonically until CV below 0.35 and then saturating. The results indicate that irregular lattice structures with controlled CV are isotropic and absorb energy more efficiently than random lattice structures designed without planning. Thus, irregularity control is evidently important in designing lattice structures with higher isotropic energy absorption.