| The pneumatic technology,which has been regarded as a significant manufacturing method for combining micro-scale filament into meso-scale yarn,has been widely used in textile manufacturing field.As one of the most important application,pneumatic splicing is employed to combine two separated yarn constituted of numerous filaments into a knotless one.Research on pneumatic splicing is of great significance for improving the appearance of yarns and enhancing the intrinsic properties of yarns.In order to understand the complex dynamic behavior of the splicing process,this study firstly presents a numerical model for simulating the splicing behavior of multi-filaments by adopting a one-way Fluid-structure interaction algorithm.In this model,the airflow in splicing chamber of three-dimensional compressible viscous gas was controlled by realizable k-? turbulence model.The flexible filament was dispersed into a digital chain constituted of continuous truss elements.The aerodynamic force,which converted by the airflow velocity where distribute in the nodes of the flexible filament model,was applied to each node of truss by employing the equation summarized from Buckingham Pi Theorem.Finally,the explicit dynamics algorithm was used to calculate the displacement and deformation of the filaments subjected to the external force containing contact force and aerodynamic force.Meanwhile,a visual experimental platform including a PCO.1200hs high-speed camera,a transparent splicing chamber,an air pressure regulator,a filter,an air compressor and a cold light source was designed to record the motion behavior of flexible filaments during the splicing process.Then,the axial aerodynamic drag coefficient Cl and the normal aerodynamic drag coefficient Cn in the numerical model were measured respectively according to the actual test samples.At this stage,their numerical values were firstly reasoned by the aerodynamic equation combing with experimental measurement data(airflow drag and the length of yarn)and simulation data(airflow velocity,density)to acquire drag coefficient formulas by curve fitting.These formulas were introduced into numerical model to simulate the motion of filament and the results have a good consistency of the high-speed camera sequence photos.Furthermore,the motion of single filament in splicing chamber was analyzed combining with the 3D motion path extracted from numerical model and the cotton yarn was replaced by polyester draw texturing yarn which used in latter splicing experiments to obtain corresponding drag coefficient formulas and similar filament motion.Finally,the joint forming mechanism during pneumatic splicing process was analyzed by the combination of numerical simulation and visualization experiments.The filament portion which placed in the homolateral and contralateral position of rotating channel with respect to orifices exhibit totally different motion characteristics.The bending deformation of the homolateral filaments subjected to the impinging of jet-flow and the subsequent retracting will result in the separation of the two yarns.Meanwhile,the contralateral filaments are trying to wind around the yarn in the opposite direction to generated contact-friction force.It is the competition between the separation force exerted on the homolateral filaments and the contact-friction force formed by the winding of the contralateral filaments that determines whether the splicing joint can finally be formed successfully.In addition,the overlapping length(OL),which was considered as an important configuration parameter in the splicing process,has been found to have a more pronounced effect on the movement of contralateral filaments for the longer length of contralateral filaments contribute to longer staying time to form complex entanglements and stronger contact-friction force. |
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