A taxonomy of shape-changing behavior for 4D printed parts using shape-memory polymers

4D printing (4DP) combines the use of additive manufacturing (AM) to produce freeform components with stimuli-responsive materials, so that the printed parts can transform over a calculated duration of time. This paper provides a collective review of the transformational behavior of 4D printed parts that can be achieved using shape-memory polymers (SMPs). Using the process of 4DP, flat-packed structures can be printed and activated by external stimuli to transform into fully deployed functional structures. The paper provides designers and engineers with an understanding of the possibilities of shape-changing behaviors that can be realized using 4DP, where examples of existing work are referenced. From this knowledge, designers and engineers are able to implement suitable design strategies using computer-aided-design (CAD) to better control the shape-change behavior. We summarize our findings using a taxonomy of shape-changing behaviors that can be categorized according to basic, complex, and combined behaviors.