Shape Adaptive Structures by 4D Printing

This paper introduces a 4D printing method to program shape memory polymers (SMPs) during fabrication process. Fused deposition modeling is employed to program SMPs during depositing the material. This approach is implemented to fabricate complicated polymeric structures by self-bending features without need of any post-programming. Experiments are conducted to demonstrate feasibility of one-dimensional (1D)-to 2D and 2D-to-3D self-bending. It is shown that 4D printed plate structures can transform into 3D curved shell structures by simply heating. A 3D macroscopic constitutive model is developed to predict thermo-mechanical behaviors of the printed SMPs. Governing equations are also established to simulate programming mechanism during printing process and shape change of self-bending structures. In this respect, a finite element formulation is developed considering von-Kármán geometric non-linearity 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.