Railway vehicle dynamics is strongly affected by track irregularities, which can influence the safety and the running behaviour of the vehicle. The EN 13848-5:2017 standard provides the limits of track irregularities for standard track but does not states specific restrictions for switches and crossings. Furthermore, since turnouts have a limited length, their track geometric irregularities cannot be accurately described by stochastic functions usually adopted for railway vehicle dynamics simulations. Nevertheless, irregularities in railway turnouts, related to the non-uniform stiffness of the track support and to the variation of the rail profiles along the longitudinal direction should be considered in dynamic simulations, as they can generate large dynamic loads, strongly affecting the vehicle dynamics and running stability. The aim of the paper is to expand the Switches and Crossing benchmark exercise analysing the effect of several kinds of irregularity with different wavelengths and amplitudes on a complete turnout on the main quantities related to the vehicle dynamics. The influence of each defect on each quantity is estimated through a post-processing sensitivity analysis based on power spectral density calculation. This sensitivity analysis is hence used to combine different types of defects in order to detect irregularity combinations that could compromise running safety.

Tram manufacturers have different ways of approaching the design of low-floor trams with compact and reliable running gears, and therefore several tram architectures can still be found. A complete standardization of trams is nearly impossible, and technical innovations can be more easily introduced if compared to conventional railway vehicles, but the trend towards large-scale standardization based on vehicle “platforms” can be seen in recent years. However, the current “standard” tram architecture, which includes only non-pivoting bogies, is not able to solve some typical problems of tram operations, such as high wheel and rail wear and high-pitched tonal noise (squeal) in sharp curves, which are described in the present paper. This research analyses the tram market with the aim of describing the state of the art of currently available products and comparing their main technical parameters. The analysis is based on information available from the literatures (journals, web) where data about the vehicles can be found, while a new designation code (tram architecture designation, TAD for short) is specifically introduced for easier identification of the different tram architectures. Even if the complete low floor is still one of the main requested features, several solutions combining pivoting and non-pivoting bogies are commercially available, showing a tendency to give more relevance to running quality performance with respect to the recent past.

This paper describes a methodology developed to systematically pre-process rail profile data from switches and crossings for railway vehicle dynamics simulation. The methodology accepts two data sources, unworn geometries from CAD drawings or worn geometries from digitised track measurements. The method addresses key challenges with the relative positioning and quality improvement of the input data and explains the necessary steps to ensure compatibility with the interpolation schemes used to represent the rail profile in certain multibody software. The case studies presented show how small misalignments in the processed digitised measurements affect simulation results and how simulations can help understand the qualitative evolution of switches and crossings rail profiles in a used track. This paper concludes that one of the most challenging tasks remains the automation of rail pre-processing for measured data because it is difficult to correct vertical and lateral misalignments of the profile cross-sections without a reference system.

Purpose: The braking system used on a recently upgraded metro vehicle showed very high low-frequency noise and vibrations levels in service affecting passengers’ comfort and leading to both brake calliper lever failures and to premature wear of brake pads. The characteristics of the phenomenon were such that it was classified as a groan noise type. As brake pads with different characteristics were tested trying to attenuate the issue without success, the paper describes the approach adopted by the authors to tackle the issue. Methods: The dynamic behaviour of all the components involved during the braking phase (wheelset, callipers, brake discs and part of the bogie frame) was analysed by numerical simulations and tests during service, finding a coincidence of the natural frequencies of the wheelset and the brake support. As this resonance was believed to be the root cause of the problem, a number of structural modifications were proposed. Results and Conclusions: After a careful selection process that included robustness and sensitivity analyses, the accepted modification proved to be effective in solving the issue and was applied with satisfaction to the whole fleet.

Tread braking is still extensively used on freight wagons due to lower purchasing and maintenance costs compared to disk braking. Cast iron brake blocks were replaced by composite materials (organic or sintered) that result in a lower wheel roughness, reducing rolling noise. Unfortunately, composite brake blocks have a lower thermal conductivity, negatively affecting the wheel mechanical behavior as the braking energy is almost entirely dissipated by the wheels, which are therefore subjected to higher temperatures. Mechanical properties of the wheel material, such as yield stress and Rolling Contact Fatigue (RCF) behavior, markedly decrease with temperature, resulting in higher wear rates and wheel tread damage. Contacted to analyze defects not clearly defined in the current regulations used for maintenance and inspections, the authors surveyed the literature and the technical documentation about tread-braked wheels. The paper provides an updated view about the state-of-the-art of the research on thermomechanical behavior of railway wheels and discusses the implication of the increased thermal stresses generated by composite brake blocks.