# Quality Tests of Hybrid Joint-Clinching and Adhesive--Case Study
## 3 Results
### Results of Bonding Strength  
Strength tests were conducted for all the prepared specimens. Figure 12 shows examples of force-displacement plots for specimens from each measurement series, while the results are summarised in Table 8. The view of exemplary samples after breaking is shown in Figure 9, while the loaded samples during the strength tests are shown in Figure 13. \begin{table}
\begin{tabular}{c c c c c} \hline  & \(\mathbf{H_{II}\ (\%)}\) & \(\mathbf{H_{III}\ (\%)}\) & \(\mathbf{H_{IV}\ (\%)}\) & \(\mathbf{H_{V}\ (\%)}\) \\ \hline Average & 63.4 & 49.9 & 38.7 & 28.6 \\ Deviation & 5.27 & 4.30 & 3.31 & 3.67 \\ T-student coefficient 10\% & 1.67 & 1.67 & 1.67 & 1.67 \\ Confidence interval L\({}_{0,1}\) & 8.78 & 7.18 & 5.53 & 6.11 \\ \hline \end{tabular}
\end{table} 
Table 6: Pulse heights on the flaw detector screen—determination of measurement errors in the defect area (the complete set of results are available in the Appendix A, Table 11). \begin{table}
\begin{tabular}{c c c c} \hline  & **Series 1** & **Series 2** & **Series 3** \\ \hline Min & 1.784 & 1.843 & 1.802 \\ Max & 3.307 & 3.383 & 3.212 \\ Average & 2.572 & 2.654 & 2.513 \\ Standard deviation & 0.432 & 0.466 & 0.389 \\ \hline \end{tabular}
\end{table} 
Table 7: Ultrasonic measure of joint quality R for the first three measurement runs (the complete set of results are available in the Appendix A, Table 12). \begin{table}
\begin{tabular}{c c c c c} \hline  & \(\mathbf{H_{II}\ (\%)}\) & \(\mathbf{H_{III}\ (\%)}\) & \(\mathbf{H_{IV}\ (\%)}\) & \(\mathbf{H_{V}\ (\%)}\) \\ \hline Average & 69.8 & 58.8 & 50.0 & 41.6 \\ Deviation & 1.03 & 2.08 & 0.98 & 1.97 \\ T-student coefficient 10\% & 1.66 & 1.67 & 1.67 & 1.67 \\ Confidence interval L\({}_{0,1}\) & 1.72 & 3.47 & 1.64 & 3.29 \\ \hline \end{tabular}
\end{table} 
Table 5: Pulse heights on the flaw detector screen—determination of measurement errors in the defect area (the complete set of results are available in the Appendix A, Table 11). Figure 12: Example force vs. distance plots for (**a**) first test series, (**b**) second test series, (**c**) third test series, and (**d**) fourth test series. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Series 1** & **Series 2** & **Series 3** & **Series 4** \\  & **(N)** & **(N)** & **(N)** & **(N)** \\ \hline Min & 476 & 1085 & 1486 & 965 \\ Max & 622 & 1247 & 1749 & 1082 \\ Average & 551.64 & 1166.86 & 1617.1 & 1013.08 \\ Standard deviation & 44.41 & 44.00 & 79.09 & 34.91 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Shear force obtained during strength tests (the complete set of results are available in the Appendix A, Table A4). Figure 13: Example view of samples after shear test for: (**a**) first test series, (**b**) second test series, (**c**) third test series, and (**d**) fourth test series. The force vs. displacement diagrams are typical for an elastic adhesive. Stresses gradually build up after reaching the maximum value and there is a gradual decrease after breaking the connection. For a thicker layer of glue (third test series), it can be seen that the high stress value is maintained for about 2 mm displacement. The nature of the diagram is typical for hybrid and flexible adhesives [29; 30] with higher elongation; for structural adhesives, the nature of the diagram is different [31; 32]. Structural adhesives decrease more rapidly after reaching the maximum value, similar to clinching. The thickness of the adhesive after tearing was measured during the tests. The thickness measurements were performed using the Karl Deutsch KD2050 leptoscope ([PERSON], Wuppertal, Germany). The average thickness of the adhesive in the first and second test series was 161 micron meters on one surface. In the third test series, however, the average adhesive thickness was 20.3 microns.