## 2 Materials and Methods
### Tensile Shear Test  
The test results of different clamping distances under a shear force are summarized in Table 4. It can be seen that the shear strengths of the 25 mm, 50 mm, and 100 mm clamping distances are reduced by 3.44%, 9.25%, and 14.08% compared with the clamping distance of 10.5 mm. In terms of peak and overall elongation, the peak and overall elongation of the 25 mm clamping distance increased by 64.20% and 83.03% when compared with the 10.5 mm clamping distance. In comparison to the 25 mm clamping distance, the peak and overall elongation of the 50 mm clamping distance increased by 55.58% and 42.13%. Comparing the 50 mm clamping distance, the peak and overall elongation of the 100 mm clamping distance increased by 33.27% and 110.86%. In short, the junction shear strength decreases and the peak and overall elongation increase dramatically with the distance between clamps. It is worth noting that while the overall elongation growth was chaotic, the elongation growth with the peak decreases gradually. Figure 10: Failure modes of the junction subjected to uniaxial tension under various clamping distances: (**a**) 10.5 mm, (**b**) 25 mm, (**c**) 50 mm, (**d**) 100 mm. The plots of the shear stress-elongation of the junctions under different clamping distances are shown in Figure 11. It can be found that the peak and overall elongation both increase significantly with the distance between clamps. The majority of the tests showed similar results, and the peak strength varied only a little between samples with the same clamping distance. Firstly, the shear stress increased linearly before reaching its maximum value; then, it reached its maximum yield strength, and the strain-softening phenomenon appeared. The stress was reduced and then entered the major deformation stage, where the stress essentially stayed the same. Lastly, it entered the strain hardening stage, where the stress was raised and the sample was destroyed. The shear stress-strain behaviors became more similar to the standard tensile curve of the HDPE material strip as the distance between the clamps increased. However, there were differences in the failure area post-peak. Long deformation from the commencement of failure to complete failure is required for the test curve with a distance between clamps of 10.5 mm. The failure arises very suddenly when the distance between clamps is increased to 100 mm, but the two failure modes of the test curves of 25 mm and 50 mm both exist, which explains the problem of disordered overall elongation growth. The failure modes of the samples under a shear force are shown in Figure 12. The results in Figure 12 indicate that the test procedure was characterized by apparent elongation deformation and a thin neck phenomenon of the strip. The two strips had no separation at the welding area, and the failures occurred at the connection between the welding junction and the strip. The welded junction is unlikely to fail when subjected to a shear force, and the actual shear strength of the junction should be higher than the shear yield stress obtained in the tests. It can also be found that the failure modes of the samples with a distance of 10.5 mm between the clamps were the ductile failure at the connection between the welded junction and the strip, and the increase in elongation caused the strip to separate from the junction (Figure 12a). Brittle failure appeared at the connection when the distance between the clamps was increased to 25 mm or 50 mm. The sample displayed a sudden general fracture failure after the elongation reached a specific degree (Figure 12b,c). When the clamping distance was increased to 100 mm, the sample failed as a result of a sudden brittle failure of the entire connection (Figure 12d). The reason for analyzing these fracture modes can be attributed to the characteristics of the welded junction. Two strips of ultrasonic spot welding form the welded junction, and the perforated area creates a weak area and is prone to stress concentration.