Compressive behavior of soft lattice structures and their application to functional compliance control

Lattice structures are advantageous in terms of their high specific stiffness and strength, and have been applied to the design of lightweight structures owing to the recent development of additive manufacturing (AM). The unique design flexibility of AM has enabled the fabrication of a functionally graded lattice (FGL) by gradually changing the lattice size and enhancing structural efficiency of lattice structures. Although FGLs have been generally designed to reduce the compliance (i.e., to increase the stiffness), this study aims to develop soft polymeric lattices to widen the range of compliance for the development of FGLs. To develop soft lattice structures, various lattices were designed and fabricated using a photo-polymerization type 3D printer and photo-curable polyurethane resin. Compression tests were conducted on these lattices, and their deformation behaviors were analyzed experimentally. The effects of various lattice design parameters and the curing time were also investigated, and the resulting changes in the compliance were analyzed. As a consequence, the compressive stiffness can vary widely, within a range of 10−3 to 102 N/mm. Two types of FGLs, which enabled the self-positioning and self-guided moving functions, were then developed by varying the lattice direction, strut diameter and curing time effectively.