چكيده لاتين
Additive manufacturing, as one of the emerging technologies in the production of components, has gained significant attention among researchers and industries. One of the widely used methods in this technology is material extrusion, which is favored due to its simplicity, material diversity, minimal waste, and applicability in various fields. This method is particularly important for the production of thermoset polymer components because these materials exhibit high resistance to heat and chemicals after curing. One approach to enhancing the mechanical properties of these materials is the use of fibers. Unlike continuous fibers, short fibers are suitable for this process due to their ability to improve mechanical properties while also being easier to integrate into processes and creating isotropic properties in the components. In this research, a novel method for 3D printing short fiber-reinforced thermoset composite parts via material extrusion is presented. The inks used in this process must be capable of flowing while also maintaining their shape upon exiting the nozzle and being deposited on the build platform, without spreading. Unlike existing methods, this technique improves the rheological properties of the ink without any additives; instead, it achieves this by controlling the time elapsed since the mixing of the two polymer components with the resulting properties. For the resin used, the mixture becomes suitable for printing after three hours, and adding 5% fibers reduces this time to 2.5 hours. This method does not use any external energy sources, such as UV light, for ink curing during the printing process, which results in reduced energy waste. Given the physical nature of these materials, an extruder system was designed and built for printing high-viscosity inks. This mechanism is based on a power transmission screw, allowing it to generate significant force within a limited space and with low torque. To examine anisotropy caused by printing in different directions, samples made from pure resin were printed at 0°, 45°, and 90° angles and subjected to tensile testing. The results indicated that the samples exhibited nearly isotropic behavior, with the print direction having little effect on elastic modulus, ultimate strength, and elongation at break. The effect of secondary curing was also investigated in this study, showing that while it did not significantly impact the elastic modulus, it increased the ultimate strength by up to 16%. The influence of increasing the number of printed layers with different configurations showed that the variation in mechanical properties was less than 10%, and the behavior remained nearly isotropic. This increase in the number of layers did not reduce the mechanical properties, indicating that interlayer adhesion was well achieved. Additionally, the impact of ink preparation parameters for printing short fiber composites, including fiber content, mixing time, and mixing speed, was examined. In this study, 50-micron glass fibers were used. To reduce the number of experiments from 27 to 9, the Taguchi method was employed in the design of experiments. The results demonstrated that the use of 5% by weight of short fibers can increase the ultimate strength by 19.5%, and using 20% by weight of fibers results in a 29% increase in elastic modulus. In all experiments, the DIC method was used to measure strain. Moreover, it was shown that this method can successfully produce parts with various structures, even without support.
