Speaker
Description
In recent years, 4D printing has gained significant attention in the material modeling community. Unlike classical 3D Fused Deposition Modeling (FDM), 4D printing incorporates the dimension of time to the printing process. Recent publications have focused on characterizing printed materials, predicting their time-dependent behavior, and investigating the influence of infill patterns on the shape memory effect. Current investigations reveal that the direction of the stored strain held in printed structures strongly correlates with the print orientation. This work focuses on characterizing of the printed material and the quantification of the imposed recovery strain during the printing process and its subsequent shape-changing capability. Shape Memory Polymers (SMPs) are a subcategory of smart materials that have the capability to store an externally imposed shape, which can be recovered with an activation trigger, most commonly temperature. This trigger facilitates for the formation and breakup of cross links in the material, allowing for the capture of entropic deformation energy. During printing, this effect is imposed locally to the filament influenced by parameters such as temperature and printer speed. This research emphasizes a new more precise approach to modeling the material behavior and describing the recovery strain. An intermediate configuration is employed to predict the recovery after activation of the programmed state. By mixing free energy functions for both low and high temperatures, the model becomes adaptable for various types of polymers, though its currently limited to mostly amorphous polymers due to the complexity introduced by crystallization. Uniaxial tensile tests are used to capture the elastic properties of the printed samples, extended with strain recovery test to measure the stored strain that is imposed in the printing process on the filament. The imposed strain is assumed to be constant at each point, where the magnitude of the strain depends on the layer orientation angle around the vertical print axis. This constant recovery strain is linked to the printing parameters, storing the orientation as an internal field. Future research will extend this approach to more complex orientations and material behaviors, such as crystallization and visco-elastoplastic materials.
