## 3 Results and Discussion
### Residual Stress Measurement  
The influence of the production process on the fatigue behavior of structural components is very important, even if it is not always considered properly. This is one of the main issues in fatigue life estimations based on data resulting from standard fatigue tests of specimens obtained from the base material. Both possible strain hardening, due to local plastic deformation, and residual stresses are neglected in that case. This illustrates the importance of testing the finished components whenever possible. The section test approach certainly considers the effect of local plastic deformations and the finished state of the component surface. It is questionable, instead, to what extent possible residual stresses change during the preparation of the specimens. A stress release can be expected along the circumferential direction of the rim, where the cutting operation removes material constraints at the boundary of the sections. However, some doubts exist about the behavior along the rim axial direction, which is the principal stress direction during fatigue testing. To clarify this aspect, first, residual stress measurements were made on six points of a new rim in the same manufacturing conditions as the ones previously tested. Following that, the same points were measured again on rim section specimens obtained from that rim. A scheme representing the location of the measurement points on the complete rim is shown in Figure 19. The points are located approximately 120\({}^{\circ}\) from each other along the rim circumference, on both sides of the rim. The residual stresses were measured using X-ray diffraction. This is one of the most used non-destructive techniques [28; 29], which allows for repeating the measurement in the same point without affecting the local properties of the material. This was fundamental to verify the residual stresses of the specimens after the cutting operation of the original rim. The residual stresses were measured along two directions, as shown in Figure 20:  
* The rim axial direction, named as x;
* The rim circumferential direction, named as y.  
Figure 19: Location of residual stress measurement points along the rim circumference (**a**) and detail of the position on the rim profile section (**b**). Measurements were made at both sides of the rim. As already underlined, the rim axial direction (x) is the most important one. In fact, it is the principal direction of the stress acting in that specific rim radius both in service and fatigue testing conditions. This is proven by the crack development paths experienced in field use on similar components [14], which are perpendicular to that direction. The value of the residual stresses for the complete rim and for the rim section specimens are shown, respectively, in Tables 3 and 4. Analyzing the results of Table 3, it is interesting to notice how the residual stress along the axial direction is mainly compressive, with maximum values up to \(-96\) MPa in point 1B and \(-158\) MPa in point 2A. It is known that compressive residual stresses are usually beneficial to the fatigue life of the components, and, for that reason, they are sometimes induced on purpose [30]. Therefore, an overall state of compressive residual stress along the axial direction may lead to better fatigue life results of the rim in service, if compared to the fatigue data of the base material. However, point 3 shows a slight tensile stress along the same direction. This aspect needs further investigations into the production process,