Shape adaptive structures by 4D printed polymers

As additive manufacturing, also known as three-dimensional (3D) printing, grows, creeping up in printing technologies. It is not about how long it takes for a part to be printed; but rather the fact that 3D printing fabricates static matters, 4D printing involves specifically designed geometries with active materials that can transform from one state to another under external stimuli. Recently, some researchers employed 4D printing combined with active materials like shape memory polymers (SMPs) to propose innovative means for crafting custom-designed self-folding structures. In many applications, 4D printed polymers experience static and dynamic loadings. This paper investigates static and dynamic behaviors of 4D printed objects under thermo-mechanical loadings. Fused deposition modeling (FDM) as a filament-based printing method is employed to fabricate SMP objects. Experiments are conducted to study static and dynamic responses of the 4D printed polymers. A macroscopic constitutive model is developed to predict thermo-mechanical behaviors of the printed SMPs. Governing equations are also established to simulate deformation mechanism and shape recovery of 4D printed structures. In this respect, a finite element formulation is developed based on the non-linear Green-Lagrange strain tensor and solved by implementing iterative Newton-Raphson scheme. The accuracy of the computational approach is checked with experimental results. It is shown that the structural-material model is capable of replicating the main features observed in the experiments. This research is likely to advance the state of the art SMP 4D printing, and provide pertinent results and computational tool that are instrumental in the design of adaptive structures with shape recovery features.