This paper aims to investigate the potential for 4D deformation of the smallest building blocks of the material extrusion additive manufacturing (MEAM) process: single extrudates produced with a single material. In contrast to previous 4D printing approaches where property-variations are realised across multiple layers or with complex composites, this study hypothesises that residual strain varies from top-to-bottom within a single printed extrudate and that this offers an opportunity to achieve controllable 4D printing with the smallest possible resolution (single lines in a single layer).
The influences of bed temperature, printing temperature, printing speed, extrusion width, extrusion thickness and activation temperature are quantified in terms of residual strain and 4D curvature.
An almost fourfold variation in curvature was achieved, printing speed and layer thickness greatly affected 4D deformation: the maximum curvature was increased by >600% compared to the minimum curvature when varying printing speed. In addition to rigorous parametric characterisation, a case study demonstrates the 4D deformation of a flat single-layer lattice into a 3D self-formed stent structure comprised of intricate single-extrudate struts. A separate case study demonstrates the resilience of the method by showing results to translate to alternative materials, with alternative printing hardware and with a different 4D activation procedure.
This study successfully proves a new way to achieve intricate 3D structures with the MEAM process, which would be impossible without 4D deformation due to their intricacy and the need for support material. The findings are also relevant to research into undesired warping due to the quantification of residual strain.
