Additive manufacturing-enabled shape transformations via FFF 4D printing
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ARTICLE Additive manufacturing-enabled shape transformations via FFF 4D printing Abishera Ravichandra Rajkumar and Kumar Shanmugama) Department of Mechanical and Materials Engineering, Khalifa University of Science and Technology, Masdar Institute, Masdar City, Abu Dhabi, UAE (Received 21 June 2018; accepted 3 October 2018)
Fused-filament-fabrication (FFF) is a commonly used and commercially successful additivemanufacturing method for thermoplastics. Depending on the FFF process parameters, the internalstrains along print direction, thermal-gradient across layers, and anisotropy introduced during layerby-layer build-up can significantly affect the macroscopic properties, dimensional stability, and structural performance of the final part. Conversely, these factors can be optimized to result in unique, controllable thermally actuated shape-transformations. This work aims at quantifying and understanding the underlying mechanisms that drive the thermally actuated shape-transformation in three commonly used thermoplastics fabricated by the FFF method namely, poly-lactic-acid (PLA), highimpact-polystyrene (HIPS), and acrylonitrile-butadiene-styrene (ABS). Initially, the release of internalstrains is analyzed for unidirectionally printed samples experimentally and computationally, employing a thermoviscoelastic-viscoplastic constitutive model. Subsequently, two basic initial (as-printed) configurations, namely, a beam and a circular-disc are chosen to study the 1D to 2D and 2D to 3D shape-transformations, respectively. The effect of process parameters such as the printing speed, print path, and infill density on the shape transformation behavior is investigated systematically. Finally, the results are applied to demonstrate shape-transformations for application in morphing-structures and/or as an alternative, simplified process in fabricating curved-components.
I. INTRODUCTION
Emergence of novel processes and materials in the field of 3D printing has revolutionized the industry from being a mere prototyping technique to increasingly become a full-scale manufacturing solution, called additive manufacturing.1–7 Fused filament fabrication (FFF) or fused deposition modeling (FDM) is a commonly used additive manufacturing technique to fabricate 3-dimensional thermoplastic objects. The FFF uses a continuous thermoplastic filament fed through a heated, moving extruder head where the material is melted and extruded continuously bead-by-bead to form a layer and layer-by-layer to form the final part. This process results in anisotropy, thermal gradients, and internal stresses/strains in the final fabricated parts. Over the years, the anisotropic material behavior of FDM components has been extensively studied.8–11 In the FDM process, the semimolten material is deposited in a directional manner resulting in anisotropic material behavior. The anisotropic character of the 3D-printed part is primarily the result of the build direction and the bead angle. During the FFF process, the sequential deposition of material beads and layers cause the
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