## 3 Results and Discussion
### Effect of Wet WindingTension  
For wet winding, failure data of NOL rings with different winding tensions are sorted in Figure 8. When the winding tension varies between 70 and 130 N, the failure load of composite materials decreases as the winding tension increases. The NOL ring with a winding tension of 70 N has the highest tensile strength and shear strength, which are 2453 and 43 MPa, respectively, and the NOL ring with a winding tension of 130 N has the lowest tensile strength and shear strength, which are 2143 and 38 MPa, respectively.  
Figure 9 shows the relationship between winding tension and resin content in NOL ring samples. It can be seen that the resin content decreases with increasing winding  
Figure 8: NOL ring failure load with different winding tension.  
Figure 7: NOL ring failure load of different resins.  
tension. The content of NOL ring resin is the highest (21.3%) when the tension is 70 N and the lowest (18.9%) when the tension is 130 N.  
During the preparation of NOL rings, carbon fibers are combined with resin by siphoning, and the amount of resin bound in this way is limited by the type and cross-sectional area of the fiber tows. After the fiber bundles are fully impregnated with resin, the excess resin will be stored between the fiber bundles due to the wet winding process. This part of the resin is weakly bound to the fiber tows, and the resin will be extruded under the winding tension, and the resin content of the composite decreases. As the fiber winding tension increases, the effect of the unit winding tension on the decrease in resin content is weakened. This is because the distance between fiber bundles decreases as the resin content decreases, the pressure required for the macroscopic flow of resin increases, and the increase in winding tension gradually decreases the increase in resin flow. Although the increase in winding tension decreases the resin content, the process damage to the fibers also increases, so the strength of the composite decreases at higher winding tensions due to process limitations.  
Resin content was converted to fiber volume content, and empirical formulas exist for fiber volume content and winding tension.  
\[V_{f}=\frac{V_{0}-V_{\infty}}{1+\frac{T_{f}}{T_{0}}}+V_{\infty}+k, \tag{8}\]  
where \(T_{f}\) and \(V_{f}\) are the current fiber volume content and current winding tension, respectively, \(V_{0}\) and \(T_{0}\) are the initial fiber volume content and initial winding tension, respectively, \(V_{\infty}\) is the ultimate fiber volume content, and \(k\) is the correction factor.  
Figure 10 shows the microstructure of composite materials and the schematic diagram of resin-rich regions arranged in hexagons. It is shown that the volume content of the ultimate fibers inside the composite can reach 90.7%. However, it is impossible for carbon fibers to reach the ideal arrangement limit in the resin matrix in engineering, and there must be resin-rich areas in the composite materials. Generally, the fiber volume content ranges from 60 to 80%. Therefore, 0.8 is taken as the ultimate fiber volume content in this paper, and \(k\) is taken as \(-0.25\) after correction with the actual measurement results. The comparison in Figure 8 shows that the predicted fiber volume content of composite materials is in good agreement with the actual measured results.  
Figure 9: NOL ring resin content with different tension.