SHAPE MEMORY PROPERTIES OF 4D PRINTED PARTS UNDER CYCLIC LOADING: EFFECTS OF INFILL CHARACTERISTICS AND STIMULUS CONDITIONS

4D printing has spurred growing interests since its recent emergence, as it enables the fabrication of dynamic structures with reconfigurability over time when exposed to external stimuli, which is not feasible using 3D printing. The current literature on 4D printing is mainly focused on developing new materials and investigating the time-evolving properties of the printed parts, whereas the influences of process parameters on stimuli-response behaviors of 4D printed parts are not adequately explored, especially under cyclic loadings. In this study, experimental analyses are conducted to investigate the effects of infill strategies and stimulus conditions on the shape memory properties of 4D printed thermo-responsive parts. Specifically, cyclic thermo-mechanical tests are performed under different operating temperatures to investigate the shape programmability and recovery characteristic of specimens printed with various infill patterns. The results indicate that specimens printed with the rectilinear pattern exhibit better shape programmability under cyclic thermo-mechanical loadings than polygonal patterns. In addition, the decrease in shape fixity ratios over multiple cycles is also observed for all considered infill patterns. The comparative studies suggest that the increase in operating temperature within the vicinity of the material's glass transition temperature can improve the cyclic shape memory property.