4D printing of polymer-based smart structures by thermal activation

• Main Author: Teoh, Joanne Ee Mei
• Other Authors: Chua Chee Kai
• Format: Theses and Dissertations
• Language: English
• Published: 2018
• Subjects: DRNTU::Engineering::Mechanical engineering::Prototyping
• Online Access: http://hdl.handle.net/10356/74351
• Institution: Nanyang Technological University

4D printing is an emerging technology and presents a significant advancement over 3D printing. By leveraging on additive manufacturing of shape memory materials, this technology can enable controlled shape recovery of complex structures leading to a broad range of disruptive commercial applications including product design, industrial manufacturing and biomedical implementation. 4D printing has attracted significant attention from both the research community and industry. Commercial computer aided design software tools are available to design and simulate shape recovery. However, there is limited research on systematic design for shape recovery of complex structures fabricated using shape memory materials. This research is aimed to establish a systematic design methodology for 4D printing using polymer based shape memory materials by thermal stimulation. Polymer shape memory material provides key advantages in terms of low temperature deposition and fabrication. In addition, different polymer based composite shape memory materials can be synthesised, formulated and customised to achieve different thermomechanical properties, leading to the practical choice of using thermal stimulus where glass transition temperature can be used as the controllable parameter for shape recovery. In this research, three design guidelines have been developed. Firstly, (1) quantifying the relationship between smart structure design and mechanical fracture characteristics during shape setting; and (2) allocating multimaterials at different levels of design to obtain complex response behaviours. Secondly, a thorough understanding of heat transfer in 4D smart structures in relation to their self-response behaviours. Lastly, to explore the feasibility of printing and programming crossfolded smart structures as well as to characterize crossfolded structures. The systematic design methodology was established using computer aided design, finite element simulation and empirical analysis. ANSYS software was used to perform computer aided design and finite element simulation of single-material structures to analyse shape recovery characteristics of complex structures. It was also used to establish critical design guidelines and material parameters that significantly impact the shape recovery performance including response rate and recovery path. Different shape recovery structures including cross-folding were investigated. Stress relief feature were also designed and analysed to establish guidelines for reducing fracture during both programming and shape recovery stages. Experiments using fabricated test samples were used to perform correlation and validation of results obtained from computer aided design and finite element simulation. We have established design guidelines and material parameters that impact the controlled multistage response of 4D printed structures. These parameters included printed thickness, stress relief features and material properties. By optimising these parameters, we have demonstrated repeatable shape recovery performance of complex single-material and multimaterial structures, an example was the self-morphing artificial orchid flower which was thermally activated to blossom.