# Quality Tests of Hybrid Joint-Clinching and Adhesive--Case Study
## Materials and Methods  
### Samples  
The plates used in this study were made of DC01 cold-rolled low-carbon steel. These sheets are used for the production of car body parts and household appliance parts. The chemical composition of the DC01 sheet, according to EN 102130, is shown in Table 1. The sheet has a tensile strength TS below 280 MPa.  
Figure 2: Joints used in car body repair; 1—veld; 2—adhesive; 3—classic rivet.  
It was assumed that the samples used in the study should be as close as possible to the materials used in industrial conditions, so the thickness of the glued sheet was set at 0.7 mm. The adhesives available on the market are characterised by different bonding strengths, ranging from 2 MPa to 30 MPa. Due to the small thickness of the sheet and the relatively low tensile strength of DC01, it was decided to use strips of metal sheet with a width of 17 mm, which--assuming an area for bonding of 17 \(\times\) 20 mm for different adhesives--gives bonding stresses in the sheet from 57 MPa for the weakest adhesives to 855 MPa for the strongest adhesives. In addition to the adhesive bonding, the sheet metal clinching will be utilised, the maximum stress of the specimens will be higher. This means that if a thin plate thickness is used, an adhesive with relatively low shear strength should be used. A hybrid adhesive was chosen, which has a lower strength than epoxy and methacrylate adhesives, but its setting time is shorter, and according to the manufacturer, the surface preparation does not significantly affect the quality of the bond. The bonding tests were performed using high-strength adhesive (Figure 3).  
Before starting the tests, a series of specimens were prepared with different surface preparation. In the first case, the sheet was only degreased; in the second one, it was sand-blasted with EK40 electrocorundum (P.P.H. REWA, KOLUSZKI, Poland) and degreased, while in the third case, the surfaces of the sample were treated with P80 sandpaper. The aim of this work was to select the surface preparation for bonding in further studies. The roughness parameters were examined and evaluated in all the samples. The arithmetic  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Designation**} & **Numerical** & \multirow{2}{*}{**C [\%] Classification**} & \multirow{2}{*}{**Mn [\%].**} & \multirow{2}{*}{**P [\%]**} & \multirow{2}{*}{**S [\%]**} & \multirow{2}{*}{**Si**} & \multirow{2}{*}{**Ti**} & \multirow{2}{*}{**Al**} & \multirow{2}{*}{**Nb**} \\ \cline{1-1} \cline{6-11}  & & & & & & & & & & \\ \hline DC01 & 1.033 & \(\leq\)0.12 & \(\leq\)0.6 & \(\leq\)0.045 & \(\leq\)0.045 & - & - & - & - \\ \hline \hline \end{tabular}
\end{table}
Table 1: Chemical composition (%).  
Figure 3: Comparison of ruptured specimens; (a) high-strength adhesive; (b) hybrid adhesive used in tests.  
mean deviation of the roughness profile (\(\rm R_{a}\)) and the arithmetic mean of the absolute values of the height of the five highest peaks of the roughness profile and the depth of the five lowest roughness profile pits in the segmental segment (\(\rm R_{z}\)) were investigated. All of the measurements were taken in accordance with the EN ISO 4287 and EN ISO 4288 standards. For the degreased surface, the roughness \(\rm R_{a}\) parameter was 0.49 \(\rm\upmu\)m, and \(\rm R_{z}\) was 2.6 \(\rm\upmu\)m; for the blasted surface, \(\rm R_{a}\) was 2.46 \(\rm\upmu\)m, and \(\rm R_{z}\) was 14.4 \(\rm\upmu\)m; while for the surface sanded with P80 grit paper, \(\rm R_{a}\) was 0.78 \(\rm\upmu\)m, and \(\rm R_{z}\) was 3.88 \(\rm\upmu\)m--Figure 4.