## 3 Results and Discussion  
The first experimental series were carried out to determine the transmittable torque of the connection without the influence of impulse. The interference fit of all analyzed shaft-hub connections is approximately 21 \(\upmu\)m. A bolt is used to steadily increase the torque until it suddenly drops as the hub slips, which is shown in Figure 5. Two different hubs were tested. The maximum transmittable torque for the first hub (orange) is 170 Nm and, for the second hub (blue), 150 Nm. After the first slip, the hubs have been further loaded. The transmittable torque after the first slippage drops for both hubs to approximately 125 Nm. At the end of the experiment, the lever returns to the initial position and the torque drops to zero. It can be assumed that the reduction in the frictional force and accompanied slippage cause the damage to the contact surface between the shaft and the hub [20; 22] such as fretting, which can lead to a change in the coefficient of friction and the resulting transmittable torque. Figure 6 displays the results for the second experimental series. The preload torque varies between 110 Nm and 115 Nm, below the previously determined limit. The impact energy from the falling mass is 9 J. At the start of the experiment, the markers on the hub and the shaft lie on top of each other. The impulse forces the hub to slip, which, in turn, reduces the preloaded torque. This is reflected in the measured curve by the drop of the torque. Upon completion of the experiment, a discrepancy between the marker positions can be observed. In other studies, attempts are made to avoid this effect of unintentional \"self-unscrewing\" [31; 32]. Figure 4: Simulation setup for all degrees of freedom at the relevant points and all applied vectors for the simulation. Figure 5: Experimental results of the static torque test of different hubs (blue and orange lines). The connections initially transmit 170 Nm and 150 Nm, followed by a drop and a certain stabilization of the transmittable torque due to the local damage of the contact surface between the shaft and the hub. The diagram in Figure 7 illustrates a test in which the hub was preloaded once to 80 Nm and the same impulse (\(m=1.6\) kg, \(v=990\) mm/s) was initiated several times on the same position of the shaft. The measured curve shows that the highest reduction in the torque, about 20 Nm, is observed with the initial impulse. Further impulse initiation leads to a lower reduction in the torque due to the gradational reduction in the frictional force in the connection [25; 26; 27; 28]. A saturation of the minimum transmittable torque can be seen at 35 Nm. The modal analysis yields natural frequencies and their corresponding mode shapes, as illustrated in Figure 8. Two specific mode shapes have been identified with their respective natural frequencies. The initial form indicates a torsional mode occurring at a frequency of 5578 Hz, which can lead to an additional torque load experienced by the shaft-hub connection. In Figure 9a, the resulting radial stress as a function of the peripheral angle is shown. The accumulation with the preloaded torque on the connection may surpass the maximum limit, leading to a hub slippage. Figure 6: Experimental results on the impact behavior of the shaft–hub connection. The impact on the preloaded hub causes local slippage, which reduces the transmittable torque. The marker on hub is moving away from the marker of the shaft. Further impact leads again to the same phenomena. At the end of the experiment, the distance between the marker of the shaft and the marker of the hub is clearly visible. Figure 7: Experimental results of the impact behavior of the shaft–hub connection. The first impact on the preloaded hub results in the highest reduction in the torque. The relative torque reduction decreases with the number of impulses. The second mode indicates a bending shape at a natural frequency of 8155 Hz, resulting in a decrease in the localized contact pressure and, therefore, a lower transmittable torque.