PSI - Issue 77

Job S. Silva et al. / Procedia Structural Integrity 77 (2026) 550–558 Author name / Structural Integrity Procedia 00 (2026) 000–000

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1. Introduction Freight wagons operating on railway networks are continuously subjected to random excitations caused by track irregularities, welds, joints, and switches. Such stochastic inputs excite structural vibrations that, if not adequately controlled, may accelerate fatigue damage in components such as wheel bearings (mounted within the axle boxes), bolsters, and frames (Lechner and Stephan, 2016). Beyond the structural implications, excessive vibration can compromise ride stability and reduce service life (Iwnicki et al., 2015). The Y25 bogie configuration, common in Europe and particularly in Portugal, is equipped with a primary suspension system based on coil springs and friction damping elements. This system isolates high-frequency shocks and controls the relative motion between the wheelsets and the bogie frame (Iwnicki et al., 2015). Traditionally, damping is achieved through dry friction, which is simple and robust but exhibits variability due to wear, surface contamination, and environmental effects (EVANS and ROGERS, 1998). Alternative damping systems - notably viscous and viscoelastic - have shown promising in transportation applications. These systems can provide improved stability and predictability, although their adoption in heavy freight wagons remains limited due to cost and maintenance constraints. A rigorous evaluation of such damping solutions requires reliable identification of modal parameters, namely natural frequencies, damping ratios, and mode shapes (Ewins, 2009). This paper presents an experimental–numerical methodology for modal identification of a scaled freight wagon. Using PSD and SSI methods, modal properties were extracted and compared with finite element (FE) simulations, providing a basis for future comparison of damping mechanisms. 2. Theoretical Background The dynamic behaviour of freight wagons depends on the interaction between suspension stiffness, damping mechanisms, and the flexibility of structural components. Understanding this relationship is essential to design and evaluate effective damping strategies. This section outlines the main damping configurations used in freight wagons and the modal identification methods adopted in this work. 2.1. Y25 Bogie and Dry Friction Damping The UIC Y25 bogie is the standard configuration for European freight wagons due to its robustness and adaptability (Iwnicki et al., 2015).It features a primary suspension connecting the axle boxes to the bogie frame. A schematic representation of the Y25 bogie suspension system is shown in Fig. 1.

Fig. 1. Y25 bogie suspension system.

The primary suspension often employs a Lenoir link friction damper — a mechanical system that provides load dependent damping through frictional contact (Ewins, 2009). Two inclined links convert vertical loads into horizontal forces acting on a plunger pressed against a friction plate (Melnik et al., 2024). As the load increases, the normal force at the friction interfaces rises, producing higher energy dissipation. Although the Lenoir link introduces strong nonlinearities and amplitude dependence due to stick–slip effects at the interfaces, these effects are here approximated as linear within the operating range considered (Crosbee and Wang, 2023). The Lenoir link arrangement is illustrated in Fig. 2.

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