Exploring Anisotropy and Residual Stress in Fused Filament Fabrication for 4D Printing

Abstract

Fused Filament Fabrication (FFF) is an extrusion-based additive manufacturing technique that can build 3D objects in successive layers, offering viable and affordable 3D printing solutions that produce minimum waste. There are two barriers that prevent the advanced application of FFF: The performance and geometric precisions of FFF printed products are prone to the anisotropy and residual stresses arising from the printing process, and objects with complex geometries must be printed with the aid of support structures. The thesis addresses these challenges by exploring the anisotropy and residual stress in FFF, whereby FFF printed objects can self-transform into desired shapes when triggered by heat – a process known as 4D printing. The research project utilises the residual stress and anisotropy as the morphing principle to initiate and control the shape transformation of the 4D printed structures. A broad range of FFF printing materials, including acrylonitrile butadiene styrene (ABS), Wood-Plastic Composite (WPC), and shape memory polymer (SMP), are explored. Initial research focuses on the experimental investigations on the anisotropic mechanical performance of 3D printed WPC and numerical modelling of the residual stress and geometric defects in 3D printed ABS. The results indicate that the raster angles and printing patterns are the key parameters influencing the anisotropic tensile and flexural properties of 3D printed WPC, and the residual stress and distortion of 3D printed ABS. Based on these findings, the FFF printed components can be programmed with desired anisotropic behaviours and built-in residual stresses through the design of printing patterns and control of the printing process. An FFF-based 4D printing framework for simulating and manufacturing heat-responsive self-morphing structures is developed. 4D printing prototypes of ABS, WPC, and SMP that can morph from flat printed shapes into various forms are presented.