Abstract:

Objective Warp knitted jacquard spacer fabrics are widely used in sports shoes. In order to ensure the comfort of sports shoes, mesh is usually formed in the shoe-upper materials to improve the air permeability, but the mesh inevitably affects the tensile properties of fabrics, and in actual wearing. The shoe-upper materials endure long-term cyclic tensioning and eventually produce irreversible deformation, but this phenomenon is rarely explored up to date. Therefore, it is necessary to study the factors affecting the cyclic tensile properties of shoe-upper materials and optimize the design of the jacquard structure, aiming to achieve a better balance between the permeability and mechanical properties of the material and improve its service life.

Method The study selected warp knitted jacquard spacer fabrics with different jacquard layer structures commonly used in shoe-upper materials as samples, and tensile break experiments were conducted on MTS Exceed Model E43 to determine the tensile limit range. Three sets of constant load schemes were designed based on application scenarios, and 200 cyclic tensile tests were carried out on MARK-10 tensile tester to compare and analyze the influence of jacquard layer structure on the tensile properties of fabrics. Tensile break test was carried out after cyclic stretching to compare the mechanical properties of the samples before they were gone through the cyclic tensile test.

Results The tensile break results showed that the breaking strength of the same fabric in the wale direction was greater than that in the course direction, while the breaking elongation at break in the wale direction was smaller than that in the course direction, which was due to the chain stitch limiting the fabric elongation. When other conditions are kept the same, the sample with jacquard layer structure only consisting of solid structures has the highest breaking strength and the lowest elongation at break in both directions. Based on this, for every 25% increase in mesh structure, the breaking strength in the wale direction decreases by 8.60%-11.60%, and the breaking strength in the course direction decreases by 28.54%-31.24%. When two samples have the same composition percentage of solid structure and mesh structure in the jacquard layer, a greater number of continuous courses in the wale direction represents a larger mesh size, which reduces the breaking strength of the fabric. This is because the solid structure has more yarns under tensile and can bear lager external force. Most of the fabric deformation occurred at the initial stage of cyclic tension, and the residual deformation generated in the first cycle is the largest, accounting for 58.38% - 66.52% of the total residual deformation. With the increase of the number of cycles, the residual deformation gradually accumulates, and the increment gradually decreases. The cyclic tensile properties of fabrics differed greatly in wale and course directions. Under the same loading conditions, the residual deformation produced by cyclic tensile was much larger in the wale direction than in the course direction, which is because the tensile strength of the fabric in the course direction is much less than that in the wale direction, and the elongation at break in the course direction is larger, so that the deformation produced by stretching in the course direction is much larger too. Under the same loading conditions and basic structure, the sample with a greater percentage of solid structure in the jacquard layer has a less residual deformation, indicating that it has a lower degree of deformation and excellent cyclic tensile resistance. When two samples have the same ratio of solid structure to mesh structure composition of the jacquard layer, the cyclic tensile resistance of the fabric could be improved by changing the arrangement of the mesh structure to increase the number and length of underlaps and reduce the number of continuous courses in the wale direction to reduce the mesh size.After cyclic stretching, the breaking strength of the fabric in both directions is significantly decreased, and the sample with the least percentage of solid structure in the jacquard layer shows most significantly.

Conclusion The composition percentage of solid structure and mesh structure in the jacquard layer is the main factor affecting the tensile properties and cyclic tensile resistance of shoe-upper materials. Increasing the percentage of solid structure and changing the arrangement of mesh can affect its tensile property. The fabric with jacquard layer only consisting of solid structure has the best tensile property. The tensile property of the fabric in the wale direction is obviously better than that in the course direction, so in practical application, it should be avoided to make the fabric transverse and the force direction the same.

Key words: warp knitted spacer fabric, shoe-upper material, jacquard, jacquard layer structure, tensile property