4D-printed shape memory polymer: Modeling and fabrication

Additive manufacturing (AM), as one of the most powerful manufacturing methods, is fabricating a three-dimensional (3D) structure using computer-aided design (CAD) data by adding material layer by layer. In contrast to traditional manufacturing processes that start from raw block material and remove waste materials, the AM process can demonstrate better aspects such as freedom of design, reduced postprocessing, and waste reduction. With emerging smart materials such as shape memory polymers, the 3D printing technology has upgraded to a technology that is called four-dimensional (4D) printing, in which the fourth dimension expresses time. In this technology, by using active materials, the printed structure can reshape its configuration and also change its mechanical properties in the presence of external stimuli such as temperature, magnetic field, and/or electric field. The fabrication and modeling of 4D-printed structures are considered due to their extensive applications in various areas such as biomedical and robotic. In this chapter, initially based on thermomechanical properties of smart materials, the constitutive modeling is presented for the shape memory feature. Subsequently, the fabrication of 4D-printed elements based on the FDM process is described, and a simple finite element method (FEM) is introduced to predict their self-morphing features. Finally, the fabricated self-morphing and adaptive structures are presented and the proposed model is calibrated based on them. Following model calibration, some smart structures such as grippers, adaptive dynamic structures, and smart composites are presented as case studies, and their behavior under external stimuli is investigated.