## 4 Experimental Verification  
In order to verify the correctness of the hoop structure simulation, the welding test under the same conditions was carried out, and the residual stress of the specimen was measured by the blind hole method. In the test, the inner and outer cylinder was Q345R steel. The inner diameter of the plywood  
Figure 8: Distribution of circumferential residual stress in the weld around the inner tube weld.  
Figure 7: Distribution of circumferential residual stress around the weld of the hoop structure.  
was 1800 mm, the thickness of the plywood was 12 mm, the width of the weld was 14 mm, and the length of the pipe is 1 m. A V groove shall be adopted for the welding joint, and the angle of the weld groove shall be 40\({}^{\circ}\). The welding current was 460 A, the arc voltage was 30 V, the welding speed was 10 mm/s, and the diameter of the welding wire was 4 mm. During the welding process, electrode arc welding is used as the base, and submerged arc welding is used to fill and cover the surface.  
Due to the large experimental materials, non-destructive residual stress detection is inconvenient. Therefore, the YC-III type static program-controlled resistance strain gauge and ZDL-II type residual stress drilling device were used to test the residual stress of the laminate by the blind hole method (Figure 9). After the laminate was wrapped and welded, in the stable area of the weld, strain gauges were respectively pasted in the \(\Phi\) values of 2\({}^{\circ}\), 5\({}^{\circ}\), 10\({}^{\circ}\), 15\({}^{\circ}\), 45\({}^{\circ}\), and 90\({}^{\circ}\) directions. Then, we used the drilling device to drill the blind hole with the hole diameter of 1.5 mm and the depth of 2.0 mm, and we measured the corresponding strain value. The residual stress value was calculated according to the principle of stress release. The calculation formula was:  
\[\sigma_{1,2}=\frac{E(\varepsilon_{1}+\varepsilon_{2})}{4A}\pm\frac{E}{4B}\sqrt {\left(\varepsilon_{1}-\varepsilon_{2}\right)^{2}+\left[2\varepsilon_{2}- \left(\varepsilon_{1}+\varepsilon_{2}\right)\right]^{2}}, \tag{4}\]  
\[\theta=\frac{1}{2}\text{tg}^{-1}\frac{2\varepsilon_{2}-\left(\varepsilon_{1} +\varepsilon_{3}\right)}{\varepsilon_{3}-\varepsilon_{1}}. \tag{5}\]  
Subsequently, the strain release systems \(A\) and \(B\) were modified with the shape-strain specific energy parameter, and the correction formula was [36]:  
\[A(\mu\varepsilon/MPa)=\left\{\begin{array}{ll}-0.341163&S(10^{-8})\leq 2.00417 \\ -0.005223\times S-0.330356&S(10^{-8})>2.00417\end{array}\right., \tag{6}\]  
\[B(\mu\varepsilon/MPa)=\left\{\begin{array}{ll}-0.763261&S(10^{-8})\leq 2.00417 \\ -0.0219526\times S-0.719503&S(10^{-8})>2.00417\end{array}\right.. \tag{7}\]  
The stresses at the measuring points in the x and y directions were:  
\[\sigma_{x,y}=\frac{\sigma_{1}+\sigma_{2}}{2}\pm\frac{\sigma_{1}-\sigma_{2}}{ 2}\cos 2\theta. \tag{8}\]  
The comparison between the test results and the finite element calculation results are shown in Table 3 and Figure 10. It is worth noting that because the experimental specimen is large, there would be a certain deviation in the residual stress measured at the corresponding point according to the angle. Therefore, the residual stress distribution trend was used as the verification standard here. It can be seen from the figure that the distribution trend of the residual stress on the outer surface of the hoop structure is basically consistent with the numerical simulation results, which can show the reliability of the finite element calculation.  
Figure 9: \(Cont.\)