Abstract:

Objective Air permeability affects the comfort of shue upper materials. Before making footwear products, it is necessary to test the air permeability of the sample upper materials. In order to study the influence of organizational structure on the air permeability of warp-knitted jacquard upper materials, it is necessary to explore a method for predicting the air permeability of warp-knitted jacquard upper materials. It is also necessary to verify the feasibility of data simulation research methods to improve the efficiency of shoe upper materials from design to production and then to final application, and reduce unnecessary waste of resources and time.

Method The experimental samples were selected from different functional areas of the jacquard upper material. The front and back sides of the wear resistance zone were with dense surface and solid bottom (sample A), and the front and back sides of the breathable zone were with mesh surface and solid bottom (sample B1). sample B2 was obtained by adjusting the positive and negative orientation of sample B1. The fabric structure of each sample was observed by Nikon E100 microscope, and then the geometric model of the fabric sample structure was established by Solidworks three-dimensional modeling software. The geometric model of the sample was imported into Workbench finite element analysis software for model preprocessing and meshing, combined with geometric model and computational fluid dynamics. Fluent, a fluid analysis software, was adopted to calculate the permeability behavior of the fabric. In order to verify the feasibility of the simulation data, the permeability of the sample was tested by YG46IE-III automatic permeability meter, and the simulation results were compared with the experimental results.

Results Speed cloud chart showed that the closer to the yarn model, the more blocked the airflow and the smaller the air flow rate. The pores in the coil were smaller than the gap at each longitudinal interval of the fabric, so the air flow rate between the pores in the coil was found much smaller than the air flow rate at the longitudinal interval. In addition, the flow velocity of model A is more uniform, while the air velocity at the grid of model B1 is much larger than that at the surrounding meshless due to the existence of the grid. In summary, under the same conditions, the air permeability of the mesh fabric B1 was larger than that of the mesh fabric A, that is, the air permeability B1 > A. When the air flows from the mesh surface, much air was accumulated at the mesh due to the large pores, and the flow rate of the air at the mesh is much larger than that of the same surface layer without mesh, resulting in uneven distribution of air flow rate in the spacer layer. When the air contacted the bottom layer of the fabric through the spacer layer, which was subjected to resistance, thus reducing the air flow rate. When the air flowed from the non-grid surface of the fabric, the air had to flow uniformly from the inlet boundary. After passing through the spacer layer to the grid, the flow rate became larger, so the overall flow rate became larger. In summary, the air permeability B2 > B1.

Conclusion Due to the complicated preparation process of warp-knitted jacquard upper material, in order to better study its air permeability and save the time consumed by sample preparation and test performance, this research attempts to use numerical simulation method to predict the air permeability of warp-knitted jacquard upper materials. The results show that the simulation results are similar to the experimental results, and the error is less than 20%. Therefore, this method is feasible. However, there are still some shortcomings. For example, the model establishment process ignores its actual friction factors, so the simulation results are greater than the actual results. Secondly, the upper material structure of warp-knitted jacquard is very complex, and the modeling process is cumbersome. It is necessary to develop better procedures for jacquard fabric modeling to save time and cost.

Key words: warp-knitted jacquard, shoe upper material, air permeability, numerical simulation, computational fluid dynamics