Effect of FFF process parameters on density and mechanical properties of PET-G and carbon fiber reinforced PET-G composites
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Date
2021
Authors
Sharma, Kaushal
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Abstract
Fused Filament Fabrication (FFF) is an emerging additive manufacturing processes because of its low cost, simplicity of the process and capability to use a broad range of thermoplastic materials and reinforced polymer composites. Despite many studies focused on optimization of print parameters, the mechanical properties of optimized printed specimens are inferior to those manufactured by conventional methods such as extrusion, compression molding, and injection molding. Moreover, reason for this low mechanical properties has not been elucidated by correlating it with the microstructure of printed specimens. While past studies have focused on mainly on polymers, such studies on reinforced composites are very limited. Hence, the objective of this research is to develop this knowledge by studying the effect of the print parameters (layer thickness (L.H.), nozzle diameter (N.D.), and nozzle temperature (T)) on microstructure characterized by void fraction/density and relate it to the mechanical properties carbon fiber reinforced PET-G composites. The void fraction decreased, density/modulus/yield strength of the printed composite increased with decrease in the L.H., increase in the N.D., and increase in the T. As the N.D./L.H. increased for a given T, the pressure applied on the printed bead increased resulting in increased spread of the molten bead (i.e., increase in width) and in reduction in void fraction. For a given N.D./L.H. ratio, the void fraction decreased with increase in T due to reduction in viscosity. The effect of print parameters on the pure PET-G was similar to that on composites but, less pronounced due to difference in viscosity. The density, modulus and the yield strength of composites, printed using optimized print conditions, were higher than those of PET-G due to lower void fraction as well as high modulus and preferential orientation (along print direction) of carbon fibers. The maximum density of the composite was 99.5% of the density of the compression moulded composite. The modulus and yield strength were 101% and 107% respectively of that of compression moulded specimens. The higher properties, despite lower density, is believed to be difference in fiber orientation. The maximum density of PET-G was 99.2% of the density of the PET-G filament. The modulus and the yield strength of the 3D printed PET-G were 98% and 85.5% of that of filament, respectively. Based on these results it can be concluded that lowest possible L.H., Highest possible N.D., and highest possible T results in least void fraction and maximum modulus and yield strength.
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Keywords
Mechanical properties, Fused filament fabrication, Density