탄소섬유 함유 PDMS 혼합액의 유동가시화 실험에 관한 연구

Abstract

Material property of polymer composite can be improved by the additive alignement inside the composite. In particular, when anisotropic additives are used in polymer composite, they tend to improve or decrease material property depending on the aligned direction. This additive alignment is accomplished by stirring the polymer composite, sonification and magnetic fields to sort the additives, or injection of polymer composites. This additive alignments is used as a way to improve the material property of polymer composite and in this study, research on the additive alignment of polymer composite inside the injection mold is performed. Firstly, additive alignment in the orifice channel is calculated by computational fluid dynamics(CFD). Additive alignment, which occurs after passing through an orifice channel, was calculated and analyzed in different initial additive locations. The additive alignment by CFD showed different trends depending on the initial location of the additive. Also, additives located around the wall of the channel and on the center of the channel showed different alignment. In addition, the shear stress direction that occurs after passing through the orifice channel was calculated and the shear stress direction showed a concentric shape similar to the additive alignment distribution observed in the actual orifice channel. Based on these CFD results, a method was devised to analyze the additive in the image before conducting the flow visualization. For this purpose, the additive alignment angle analysis code was written and the validity was analyzed using an image consisting of random line and an actual flow visualization image. As a result of the analysis, the code can analyze the additive alignment in the images with smaller error and more faster spead compared to the Hough transform. To analyze the additive alignment in the flow channel, additive alignment from parallel and perpendicular channel was analyzed. For this purpose, a 3D printed mold was used and visualized depending on the thickness of the flow channel and the flow rate. Analysis using the code showed that both parallel and perpendicular flow paths tend to increase the additive alignment as the flow rate increased and flow channel thickness decreased. Also, additives flowing in the parallel channel were aligned in a similar direction to the flow direction close to the channel wall by distribution of shear stress occurring within the flow channel. But in the center of the channel, additives show more random alignment. The additive alignment shown at the perpendicular channel showed similar additive alignment compared to the flow direction. But, the tendency of the additive flow is changed at the convex corner. Based on this result, the flow channel angle is changed and the additive alignment is analyzed. Flow visualization images taken at the flow channel at the location of channel angle change were also analyzed. However, the additive alignment according to the channel angle did not significantly affect the alignment angles that flow within the polymer composite. But, the additive flow tendency with channel angle change show at the flow rate was increased the flow rate in the convex region. Based on these results, the orifice channel analyzed by CFD was flow visualized. Additive alignment, which occurs after passing orifice channel, has been visualized, showing additive alignment that is perpendicular to the flow direction at the center of channel, unlike previously studied parallel channel or angle change channel. At the channel wall regions, the alignment tended to be aligned similar to the flow direction. Also, as flow channel thickness gets, the higher the additive alignment angle. This additive alignment was caused by the extended shear stress generated by the orifice channel and have similar distribution with the shear stress direction analyzed by CFD and additive alignment that occurred after orifice pass. In addition, it has been confirmed that the additive alignment angle tends to gradually decrease along the flow. This reduction in additive alignment affected by the shear stress generated within the flow channel.