Investigation of the Dynamical Behavior of High-Speed Turnouts

This thesis investigates the dynamic behavior, fatigue characteristics, and residual stress analysis of high-speed turnouts, which are essential components in high-speed rail networks. These turnouts face significant dynamic loads, leading to wear, fatigue, and performance degradation, making their study crucial for optimizing design and ensuring reliability.
The research is organized into three main components: a dynamic analysis using simulation, experimental fatigue assessment, and residual stress evaluation employing the contour method.
In the dynamic analysis, the focus is on the crossing panel of a swing-nose crossing, with particular attention to the effects of train speed and static axle load on the vertical deflections and longitudinal stresses within the turnout structure. The results demonstrate that the crossing nose (frog) exhibits a pronounced tendency for upward movement compared to the wing rails due to its mobility and differing support conditions. Maximum deflections are observed at the frog's tip, with tensile and compressive stresses peaking near this location; however, these stresses remain significantly below the material's endurance limit. Additionally, the study highlights the critical role of locking devices in mitigating intense dynamic responses, ensuring stability and reducing deflections during wheel passage.
The experimental fatigue analysis focuses on the high and very high cycle fatigue (HCF/VHCF) properties of pearlitic steel R350HT. Tests conducted under various surface conditions (fine-turned, electropolished, and mechanically polished) reveal that crack initiation predominantly occurs at the surface in the HCF regime, while interior failures are observed under specific conditions in the VHCF regime. Notably, the study finds that ferritic zones within the material serve as critical sites for interior crack initiation, identified through advanced microscopy techniques. The effect of different loading ratios (R = -1 and R = 0.1) further highlights the material's sensitivity to defects and its connection to mean stress and fatigue performance.
This research improves the process of selecting the optimal mesh size for residual stress analysis using Richardson Extrapolation and introduces two additional methods—Naïve Extrapolation and Intersection Plane Extrapolation (IPE)—to handle edge displacements effectively. These techniques prove valuable in improving residual stress calculations using finite element models, particularly in regions with significant edge effects and where computational efficiency is paramount.
In conclusion, this thesis provides comprehensive insights into the dynamic performance and material behavior of high-speed turnout components. By exploring how speed, axle load, and material properties interact, this work supports the development of more reliable and efficient high-speed rail systems. The findings pave the way for future research and engineering efforts aimed at enhancing the safety and longevity of railway infrastructure.