Four-dimensional (4D) printing through FDM: Effect of infill density and bed temperature on shape memory properties in different thermo-mechanical programming conditions

This study investigates the impact of key parameters in fused deposition modeling (FDM), i.e., infill density and bed temperature, on the shape memory properties of four-dimensional (4D) printed shape memory polymer (SMP). Two thermo-mechanical programming methodologies, namely programming during printing (PDP) and programming after printing (PAP), are used to examine their effects too. Increasing the infill percentage greatly improves the ability of the material to regain its original shape. This is achieved by increasing the amount of material and minimizing gaps between layers, which helps to build up the pre-strain, which causes shape morphing. On the other hand, higher bed temperatures decrease the shape recovery by slowing down cooling, decreasing residual strain, and minimizing thermal stresses. Compared to PAP samples, PDP samples show a significant 40 % increase in shape memory index (SMI), indicating the considerable influence of FDM printing rather than post-printing programming process.