## 3 Results and Discussion
### Residual Stress Measurement
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Measurement Point**} & \multirow{2}{*}{**Stress Direction**} & **Stress [MPa]** & **Stress [MPa]** \\  & & **Valve Hole Side (A)** & **Opposite Side (B)** \\ \hline \multirow{2}{*}{Point 1} & Axial (x) & \(-8\pm 9\) & \(-6\pm 13\) \\  & Circumferential (y) & \(185\pm 13\) & \(157\pm 9\) \\ \hline \multirow{2}{*}{Point 2} & Axial (x) & \(23\pm 14\) & \(-1\pm 8\) \\  & Circumferential (y) & \(162\pm 19\) & \(103\pm 17\) \\ \hline \multirow{2}{*}{Point 3} & Axial (x) & \(40\pm 16\) & \(36\pm 5\) \\  & Circumferential (y) & \(158\pm 22\) & \(154\pm 23\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Residual stress measurements of the rim sections specimens. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Measurement Point**} & \multirow{2}{*}{**Stress Direction**} & **Stress [MPa]** & **Stress [MPa]** \\  & & **Valve Hole Side (A)** & **Opposite Side (B)** \\ \hline \multirow{2}{*}{Point 1} & Axial (x) & \(-38\pm 6\) & \(-96\pm 16\) \\  & Circumferential (y) & \(112\pm 11\) & \(87\pm 9\) \\ \hline \multirow{2}{*}{Point 2} & Axial (x) & \(-158\pm 12\) & \(-31\pm 10\) \\  & Circumferential (y) & \(15\pm 12\) & \(118\pm 12\) \\ \hline \multirow{2}{*}{Point 3} & Axial (x) & \(48\pm 12\) & \(34\pm 8\) \\  & Circumferential (y) & \(51\pm 8\) & \(95\pm 9\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Residual stress measurements of the complete rim. Figure 20: Residual stress measurement directions: axial (x) and circumferential (y). especially in relation to the rim rolling stage, to assess the uniformity and repeatability of its effect on the material properties. The residual stress state along the circumferential direction is mainly tensile. However, the stress induced on rims by standard loads in service is very low in that direction, if compared to the axial one, whose effect is predominant for the durability of the component. For example, in [14], the stress range, \(\Delta\varepsilon\), along the circumferential direction was three times lower than the axial one, with also compressive average values due to the effect of tyre pressure. That is the reason why, as a first step, this research focused on the stress along the rim axial direction. The measurements of the rim section specimens in Table 4, instead, show a complete relaxation of the compressive residual stress along the axial direction. Therefore, the section test approach seems not appropriate to consider that aspect, as regards this case study. However, the same approach could be used in experiments to assess the relaxation of residual stresses under different fatigue loads, which is a phenomenon that has been under investigation for many years [31; 32; 33; 34; 35; 36]. In fact, it has been proven that compressive residual stresses are present in rims after the production process, as suggested by the results of Table 3, and it would be interesting to verify whether, and to what extent, they relax in service conditions. However, planning a series of traditional dynamic radial fatigue tests would be very difficult and time-consuming for the industry standard. A more effective solution might be represented by the rim section fatigue testing, with different loads and duration applied to specimens with compressive residual stresses previously induced by proper process such as, for example, shot peening.