## 2 Material and Methods
### Experimental Studies
#### 2.1.2 Experimental Parameters and Design  
The test plate was 2 mm thick and was composed of the 2024-T4 aluminum alloy. The rivets, which had diameters of 4 mm [18], were round-head rivets composed of the LY10 aluminum alloy. The two plates overlapped and were connected by rivets. The plate and rivet dimensions are shown in Figure 2 in which (a) depicts the specimen model and (b) shows the rivet model. In the specimen model, c is the edge distance, a is the row spacing, t is the rivet spacing, W is the plate width, and L is the lap length. The perpendicular edge distance is considered the same as the parallel direction in this model.  
Figure 1: Stress condition of lap plate: (**a**) Single-rivet small section joint (**b**) double-row rivet small section joint.  
The rivet arrangement labeling format is shown in Figure 3. As an example, for specimen 5-3-122-8-12-10, the \"5\" indicates that there are five rivets, the \"3\" means that there are three rows of rivets, the\"122\" shows that, from left to right, the three rows of rivets contained one, two, and two rivets, the \"8\" denotes the edge distance, the \"12\" represents the rivet spacing, and the \"10\" denotes the row spacing. The unit of edge distance, rivet spacing, and row spacing is mm.  
To analyze the effects of the number of rivets, the number of rows, the rivet arrangement, the row spacing, the edge distance, and the rivet spacing on the lap joint strength, 41 sets of riveted lap joint tests were conducted. Each set was tested three times. The experimental design scheme is shown in Table 1.  
\begin{table}
\begin{tabular}{c c c} \hline
**Rivet Number Effect** & **Rivet Spacing Effect** & **Row Spacing Effect** \\ \hline
1-1-1-16-0-0 & 8-4-2222-8-8-10 & 6-3-222-8-12-8 \\
2-1-2-10-16-0 & 8-4-2222-8-10-10 & 6-3-222-8-12-10 \\
3-2-21-10-16-10 & 8-4-2222-8-12-10 & 6-3-222-8-12-12 \\
4-2-22-10-16-10 & 8-4-2222-8-14-10 & 6-3-222-8-12-14 \\
5-2-2-23-8-10-10 & 8-4-2222-8-16-10 & 6-3-222-8-12-16 \\
6-2-33-8-10-10 & 8-4-2222-8-18-10 & 6-3-222-8-12-18 \\
7-3-331-8-10-10 & 8-4-2222-8-20-10 & 6-3-222-8-12-20 \\
8-3-332-8-10-10 & 8-4-2222-8-22-10 & \\
9-3-333-8-10-10 & 8-4-2222-8-24-10 & \\ \hline
**Rivet Arrangement Effect** & **Rivet Edge Distance Effect** & **Row Number Effect** \\ \hline
6-3-132-8-10-10 & 8-4-2222-4-12-10 & 3-1-3-8-10-10 \\
6-3-213-8-10-10 & 8-4-2222-6-12-10 & 6-2-33-8-10-10 \\
6-3-123-8-10-10 & 8-4-2222-8-12-10 & 9-3-333-8-10-10 \\
6-3-333-8-10-10 & 8-4-2222-10-12-10 & 12-4-3333-8-10-10 \\
6-3-323-8-10-10 & 8-4-2222-12-10 & \\
6-2-33-8-10-10 & 8-4-2222-14-12-10 & \\ \hline \end{tabular}
\end{table}
Table 1: Experimental design scheme.  
Figure 3: Rivet arrangement labeling format.  
Figure 2: Riveted sample dimensions: (**a**) sample and (**b**) rivet.  
[PERSON] and [PERSON] [19] investigated the increases in the dynamic strengths of joints with increases in the loading speed during tensile tests. They found that the effect of the loading speed on the peak load was more significant when the loading speed was in the 0.5-2 or 10-30 mm/min ranges, and it was less significant when the loading speed was in the 2-10 mm/min range. Therefore, the tensile tests in this study were performed using a CMT4304 electronic universal testing machine at a loading speed of 3 mm/min. To eliminate the eccentric effect of the lapped specimens, an eccentric collet was used for the tests.