Modeling and characterization of shape memory properties and decays for 4D printed parts using stereolithography

The integration of shape memory materials into additive manufacturing has added a new dimension of time to conventional 3D printing and enabled innovative product designs with high tailorability and adaptability. To date, most studies on shape memory effects mainly adopt experimental approaches to characterize the material responsiveness to various stimulation conditions considering a single thermomechanical loading cycle. The information regarding the cyclic shape memory behaviors as well as the potential additive manufacturing-induced impacts on the achieved shape memory performance is limited. In this paper, the shape memory behaviors of the stereolithography printed thermo-responsive structures are theoretically modeled by jointly considering the influences from both the printing process and the shape memory process. The cyclic shape memory effects are analytically characterized and experimentally validated using methacrylate copolymers under iterative thermomechanical loadings. Meanwhile, case studies are presented to provide insights into shape memory behaviors upon the impacts of various levels of critical process parameters. The results indicate an exceptional prediction accuracy of 96.24% and 95.73% for the established shape fixity and recovery models, respectively. It is also observed that the printing process parameters, including layer thickness and scan speed, have considerable impacts on the shape memory performance of the printed parts. (c) 2021 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).