## 3 Results
### Full-Field DIC Study
#### 3.4.1 Tightening the Mounting Clamps  
Three measurement series were performed to analyze the influence of clamp tightening on the behavior of the magnet holder. Before each series, the magnet clamps were completely loosened to avoid the influence of the previously measured series. The reference images were made for non-tensioned bolts. In the first series, the bolts were tightened using the maximal torque equal to \(M_{c}\) = 6 Nm and with the increment \(M_{c,inc}\) = 2 Nm. In the remaining two series, the maximal torque and its increment were as follows: \(M_{c}\) = 8 Nm, \(M_{c,inc}\) = 4 Nm in the second series, and \(M_{c}\) = 4 Nm, \(M_{c,inc}\) = 1 Nm in the  
Figure 19: Speckle pattern on the surface of magnet holder.  
Figure 18: Displacement of magnet during positioning (realized by tensioning the screws with torque \(M_{r}\)).  
third series, respectively. The comparison of the performed measurements in all three series is presented in Figure 20. It is observed that at low \(M_{c}\) torque values (0-2 Nm), the relationship between the vertical displacement of the magnet and \(M_{c}\) torque is not linear, whereas above this range, the relationship is almost linear. The high repeatability of results was also obtained for all three series.  
The DIC studies performed confirmed the human-eye observations from previous measurements with dial gauges (Figure 15). First of all, the first tightened clamp causes a minimal displacement of the magnet towards clamps on the opposite side. This effect can be seen in Figure 21, in which the visible clamp on the left-hand side was tightened as the first one. This leads to magnet displacement to the right by about 0.1-0.2 mm (see points LC, CC, and RC in Figure 21). This displacement of the magnet can be reduced by tightening the screws with smaller torque increments. Tightening of the clamps also leads to deformation of the inner and outer frames. The inner frame \"opens\" as the result of tensioning the clamps, which leads to the gap increasing between the inner frame and the magnet. This effect is visible at points IFL and IFR, in which horizontal translations are similar in absolute value but they have different signs. Similar behavior is also observed in the outer frame (points OFLU and OFRU). The repeatability and accuracy of DIC analysis are verified by displacement observations at the support points (points OFLD and OFRD). In both observed points, the fluctuations of the results were at a low and acceptable level.  
Further analysis was performed in that way, in that clamps were loosened before each measurement. Similarly, the bolts were tightened with small increments of torque. Six experiments with different maximal \(M_{c}\) torque values were compared and summarized in the diagram in Figure 22. Here, the vertical displacements \(u_{y}\) of the points LC, CC, and  
Figure 21: Horizontal deformation of magnet grip caused by tightening of clamps: (**a**) series 3—\(M_{c}=2\) Nm; (**b**) series 3—\(M_{c}=4\) Nm.  
Figure 20: Influence of clamp-tightening torque \(M_{c}\) on magnet displacement.  
RC of the magnet and the horizontal displacements \(u_{x}\) of the points IFL and IFR of the inner frame are presented (location of points is given in Figure 21). Summing up the results given in Figures 20 and 21, it can be concluded that tightening the clamp screws causes the magnet to rise relative to the holder. Therefore, the clamp screws should be tightened to the same level and with small increments of torques. Inaccuracies in bolt tensioning can lead to an inclined position of the magnet, which can be difficult to correct during the alignment process. The performed experiments also show the repeatability of the magnet holder behavior.