## 3 Results
### Mechanical Characterization  
As it can be expected, the results from the single lap shear tests show a strong dependency on the pin type and pin-orientation as well as the fiber orientation in relation to the load direction. For all pin types and pin orientations, it can be seen that a significant \begin{table}
\begin{tabular}{c|c c c c c} \hline _Pin Type_ & _Cylindrical_ & _Elliptical 0\({}^{\circ}\)_ & _Elliptical 90\({}^{\circ}\)_ & _Polygonal Sharp_ & _Polygonal Blunt_ \\ \hline _Pin-height h_ [mm] & 1.80 \(\pm\) 0.01 & 1.78 \(\pm\) 0.02 & 1.82 \(\pm\) 0.01 & 1.79 \(\pm\) 0.02 & 1.81 \(\pm\) 0.01 \\ _Punch penetration depth s_ [mm] & 0.87 \(\pm\) 0.00 & 0.90 \(\pm\) 0.00 & 0.93 \(\pm\) 0.00 & 0.87 \(\pm\) 0.01 & 0.87 \(\pm\) 0.00 \\ _Sheet thickness_ [mm] & 1.50 \(\pm\) 0.00 & 1.50 \(\pm\) 0.00 & 1.49 \(\pm\) 0.01 & 1.50 \(\pm\) 0.00 & 1.50 \(\pm\) 0.00 \\ _Rel. punch penetration depth_ [\%] & 57.91 \(\pm\) 0.15 & 59.58 \(\pm\) 0.20 & 62.58 \(\pm\) 0.31 & 58.11 \(\pm\) 0.39 & 58.10 \(\pm\) 0.18 \\ _Residual sheet thickness_ [mm] & 0.63 \(\pm\) 0.00 & 0.61 \(\pm\) 0.00 & 0.56 \(\pm\) 0.01 & 0.63 \(\pm\) 0.01 & 0.63 \(\pm\) 0.00 \\ \hline \end{tabular}
\end{table} 
Table 4: Pin height h, punch penetration depth s, sheet thickness, relative punch penetration depth in relation to initial sheet thickness and residual sheet thickness for the investigated and extruded pin geometries (n = 4). increase in the maximum force comes with a fiber orientation of 90\({}^{\circ}\). Table 5 and Figure 6 give a summary of the measured maximum forces in the single lap shear test. Therefore, the increase in force between fibers in 0\({}^{\circ}\) and 90\({}^{\circ}\) lies between 33.3% for the cylindrical pins and 55.4% for elliptical pins with an orientation of 0\({}^{\circ}\) in relation to the load direction. It is noticeable that the non-rotational symmetric pins lead to increased maximum forces in comparison to cylindrical pins independently on the pin- and fiber orientation. However, the increase in maximum force for an elliptical pin 0\({}^{\circ}\)/0\({}^{\circ}\) and the polygonal sharp/0\({}^{\circ}\) pin compared to a cylindrical 0\({}^{\circ}\) pin is relatively low with only 4.6% and 3.3%, respectively, in comparison to the corresponding cylindrical pins tested with the same fiber orientation. When comparing elliptical pins with different orientation, it shows that a 90\({}^{\circ}\) pin orientation leads to an increase in maximum force of 70.5% (0\({}^{\circ}\) fiber orientation) and 73.6% (90\({}^{\circ}\) fiber orientation), which leads to the conclusion that for elliptical pins in CFRT/metal joining, an orientation of the pin in 0\({}^{\circ}\) to the load direction is strongly inferior in comparison to a pin orientation of 90\({}^{\circ}\). When comparing this result with [PERSON] et al. [15], where a material combination of a DP600 and aluminum EN AW-6014 was investigated, this finding is contrary. [PERSON] et al. found an increased joint strength under shear load, when the pin was oriented in 0\({}^{\circ}\) of 878 \(\pm\) 7 N in comparison to 811 \(\pm\) 9 N with a pin oriented in 90\({}^{\circ}\) while in both cases the failure occurred due to a broken-off pin structure. This is explained with a higher area moment of resistance of the pin of 0.39 mm\({}^{3}\) in 0\({}^{\circ}\) in comparison to 0.2 mm\({}^{3}\) in 90\({}^{\circ}\), which leads to pin failure at higher loads when the pin is oriented in 0\({}^{\circ}\). In the present study, however, the joint did not fail due to pin breakage and consequently other mechanisms were found (compare Section 3.3). For polygonal pins, it shows that a \"blunt\" orientation in relation to the load direction is superior in means of maximum transmitted force with an increase of 25.2% (0\({}^{\circ}\) fiber orientation) and 23.1% (90\({}^{\circ}\) fiber orientation) in comparison to the \"sharp\" orientation. Figure 6: Maximum force in single lap shear tests.