Adjustable mechanical performances of 4D-printed shape memory lattice structures

Lattice structures are widely used due to their inherent advantages. With the development of smart devices, there is a growing demand for programmable, adjustable, and reconfigurable performances. However, a significant limitation of traditional lattice structures is that their shape, function, and performance cannot be changed after fabrication. In order to address this issue, we conducted experimental and simulated investigations on the shape memory effect, adjustable mechanical performances, and their deformation mechanism using the shape memory programming method. Two bending-dominated lattice structures, namely four curved bars lattice structure (FCBL) and sinusoidal wave horseshoe lattice structure (SWHL), were taken as examples. Results show that the deformation modes of both structures are switched from a bending-dominated mode to a stretching-dominated one after programming while exhibiting distinct bending sections. FCBL displays a 'C' shape with one bending section, whereas SWHL exhibits an 'S' shape with two bending sections. These deformation modes significantly enhance the tensile moduli by 480.9% (FCBL) and 1546% (SWHL), and change their Poisson's ratio from -0.29 to 0.25 (FCBL) and -0.31 to 0.43 (SWHL), respectively. The modulus and Poisson's ratio of FCBL and SWHL are well reproduced by the finite element modeling, providing a reference for designing the tunable mechanical performances of lattice structures.