## 2 Test Content and Methods
### NOL Ring Preparation and Performance Test Methods  
NOL ring tensile and shear tests adopt the national standard of the People's Republic of China, \"Mechanical Properties Test Method for Filament Winding Reinforced Plastic Ring Specimens,\" code name GB/T1458-2008 [25].  
\begin{table}
\begin{tabular}{c c c c} \hline
**Level** & **Winding Angle (A)** & **Fiber (B)** & **Resin (C)** \\ \hline
1 & 45\({}^{\circ}\) & T-700 12k & HBV-SL-03-01 \\
2 & 30\({}^{\circ}\) & SYT49s 12k & HBV-SL-03-02 \\
3 & 0\({}^{\circ}\) & TZT700s 12k & HBV-SL-03-03 \\
4 & 45\({}^{\circ}\) & SYT49s 12k & HBV-SL-03-03 \\
5 & 30\({}^{\circ}\) & TZT700s 12k & HBV-SL-03-01 \\
6 & 0\({}^{\circ}\) & T-700 12k & HBV-SL-03-02 \\
7 & 45\({}^{\circ}\) & TZT700s 12k & HBV-SL-03-02 \\
8 & 30\({}^{\circ}\) & T-700 12k & HBV-SL-03-03 \\
9 & 0\({}^{\circ}\) & SYT49s 12k & HBV-SL-03-01 \\ \hline \end{tabular}
\end{table}
Table 2: NOL loop winding orthogonal test table \(L9(3^{3})\).  
To prepare tensile-shear specimens, the following steps were taken: firstly, a release agent was applied to the winding mold, and the pipe was wrapped to its full length and full wall thickness; then, it was cured in the curing furnace and demolded; finally, the wet-wound pipe was cut according to size, manually polished, and numbered. Because there is a large dispersion in the preparation process of NOL ring winding, nine horizontal tests were selected for tensile and shear tests. Twenty-one groups of tests mentioned in the article required a total of 252 NOL rings to prepare tensile-shear specimens. Tensile tests were performed on a universal testing machine at a loading speed of 2 mm/min, while shear tests were performed at a loading speed of 1 mm/min. The test temperature was 23 \({}^{\circ}\)C and the humidity was 55%. The tensile-shear test is shown in Figure 3.  
The tensile strength of NOL rings was calculated according to the following formula [25]:  
\[\sigma_{t}=\frac{p_{b}}{2\times Lh}, \tag{1}\]  
where \(\sigma_{t}\) is the tensile strength of NOL rings, in MPa; \(p_{b}\) is the failure load, in N; \(L\) is the width of the sample, in mm; and \(h\) is the thickness of the sample, in mm.  
The shear strength of NOL rings was calculated according to the following formula [25]:  
\[\tau_{s}=\frac{3\times p_{b}}{4\times Lh}, \tag{2}\]  
where \(\tau_{s}\) is interlaminar shear strength, in MPa; \(p_{b}\) is the failure load, in N; \(L\) is the width of the sample, in mm; and \(h\) is the thickness of the sample, in mm.  
Discretization was calculated according to the following formula [25]:  
\[C_{\
u}=\frac{S^{2}}{\overline{\chi}}, \tag{3}\]  
Figure 3: (**a**) NOL ring tensile test; (**b**) NOL ring shear test.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Test Number** & **Curing Times** & **Heating Rate** \\ \hline
2 & 2 & 1 min/\({}^{\circ}\)C \\
3 & 3 & 1 min/\({}^{\circ}\)C \\
4 & 1 & 2 min/\({}^{\circ}\)C \\
5 & 1 & 3 min/\({}^{\circ}\)C \\ \hline \hline \end{tabular}
\end{table}
Table 3: NOL ring samples of different curing systems.  
where \(C_{v}\) is the discrete value of nine groups of data at each level, \(S^{2}\) is the variance of nine groups of data at each level, and \(\overline{X}\) is the mean value of nine groups of data at each level.