# Study on Denoising Method of Weld Defect Signal Based on SSA-VMD-WPD
## 2 Materials and Methods
### Experimental Equipment and Test Blocks
#### 2.1.2 Experimental Specimen  
According to the typical characteristics of defect occurrence in practical work, crack defects were commonly found near the surface, lack of fusion defects often occurred at the groove, and lack of penetration defects typically appeared at the bottom of V-groove welds or in the middle of X-groove welds, porosity defects occurred more randomly, and slag inclusion defects also tended to appear randomly [27; 28; 29]. The specific process parameters of the test specimens are provided in Table 2. The test material was high-quality, low-carbon steel 20#, which is commonly employed in the production of various steel rivets, bolts, and welded structural components. It is characterized by its low strength, good toughness, plasticity, and weldability. The elemental composition of the material is detailed in Table 3. Each test specimen was pre-fabricated with weld defects, including slag inclusions, lack of fusion, lack of penetration, porosity, and crack defects, all located within the weld seam. These defects were varied in length, height, depth within the weld seam, and distance from the center of the weld seam to simulate diverse defect scenarios, as depicted in the design diagram of the test specimens in Figure 2a. The detection report of the specimens was obtained through defect inspection processes, detailing the types of defects, their horizontal and depth positions within the weld seam, defect lengths, and distances of defect deviation from the center of the weld seam. Physical illustrations of the test specimens are provided in Figure 2b.  
\begin{table}
\begin{tabular}{c c c} \hline \hline  & Probe frequency & 5 MHz \\  & Number of Formation Elements & 32 \\  & Center distance & 0.6 mm \\
**Probe parameters** & Wafer Length & 10.00 mm \\  & Probe Size & 19.2 \(\times\) 10 mm \\  & Probe Type & line matrix \\  & & Maximum working voltage: 200 V \\  & Incentives & Maximum repetition frequency: 10 KHz \\  & & Long-term working conditions: 5 KHz 100 V \\  & Wedge Angle & 37.00\({}^{\circ}\) \\
**Wedge parameters** & Wedge speed of sound & 2330 m/s \\  & Center height & 12.80 mm \\  & Horizontal distance & 26.00 mm \\ \hline \hline \end{tabular}
\end{table}
Table 1: Main Parameters of Probes and Wedges.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Weld Type** & **Flat Plate Butt Weld** \\ \hline Welding method & Argon arc welding + manual arc welding \\ Test block material & 20\# \\ Specification size & 400 mm \(\times\) 400 mm \(\times\) 30 mm, 400 mm \(\times\) 400 mm \(\times\) 20 mm \\ \multicolumn{2}{c}{Bevel form} & X-type, V-type \\ \multicolumn{2}{c}{Defect type} & Slag, unfused, imperfect, porosity, cracks \\ \hline \hline \end{tabular}
\end{table}
Table 2: Test block parameters.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Carbon Content** & **Silicon Content** & **Manganese** & **Sulfur** & **Phosphorus** \\ \hline
0.17–0.23\% & 0.15–0.40\% & 0.6–1.00\% & \(\leq\)0.010\% & \(\leq\)0.025\% \\ \hline \hline \end{tabular}
\end{table}
Table 3: 20# Elemental Composition.