In order to reduce the wear and tear of Z-yarn implantation into the preform, the frictional behavior of Z-yarn during implantation into the preform was studied. According to the actual implantation conditions of Z-yarns, we designed a guiding array clamping device and a tensile force sensor to study the changes of tensile strength of Z-yarns at different implantation positions and implantation times, results show that the tensile strength of Z-yarns decreases significantly after 25 implantations at the position of 4 N friction force, and it's necessary to replace Z-yarns in time to avoid their fracture in the preform. The use of unadulterated solvent dimethyl silicone oil applied to the Z-yarns, can significantly reduce their wear, the tensile strength of Z-yarns after 60 implantations is only 5.6% lower than that of Z-yarns after 10 implantations. Design the tension control system, and when the tension is 0.46 N, the tensile strength of Z-yarns during implantation is 34.2% higher than without tension. Meanwhile, the relationship between the normal force applied to Zyarn and the implantation length and fiber bundle width are established by combining Hertzian theory and experimental data, and the friction coefficient algorithm during Z-yarn implantation is derived by combining Howell's equation, which solves the problem that the fiber friction coefficient cannot be measured due to the complicated working condition of Z-yarn implantation.The frictional wear mechanism of yarn during Z-yarn implantation into the preform is revealed, and a method to reduce yarn wear and increase its continuous implantation number is proposed.
To further improve the Z-direction tensile properties of flexible oriented 3D braided composites, we proposed a new process for twisting Z-fibers. We found a pattern of increasing and then decreasing tensile strength after twisting fibers with different K-numbers, and the four bundles of 3K fiber with 20 twists/m had the strongest tensile performance, which increased by 29.06% compared with the untwisted. Scanning electron microscopy was used to observe the twisting morphology and hairiness statistics of fiber bundles to analyze the reasons for this phenomenon. In order to increase the theoretical research on twisted fiber bundles, the relationships between the twist of fiber bundles and the tensile strength of fiber bundles, the length of fiber bundles, and the elongation of fiber bundles were established by using the idea of the least square method, and the prediction of fiber bundle strength was realized by twisting, length, and elongation purpose. The geometric model of the twisted fiber bundle was established, and the relationships between axial strain and radial strain of fiber bundles, axial strain and Poisson's ratio were realized. Combined with finite element simulation, the stress distribution position of the twisted fiber bundle was predicted. Finally, combined with the flexible-oriented three-dimensional weaving method, we selected the fiber with a twist of 20 twists/m as the Z-direction fiber, and completed the Z-direction performance enhancement of the composite material and, compared with the untwisted fiber, the tensile strength was increased by 60.9%.
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