Special track systems used to divert a train to other directions or other tracks are generally called
\'railway turnout\'. A traditional turnout system consists of steel rails, switches, crossings, steel plates, fasteners, screw spikes, timber bearers, ballast and formation. The wheel rail contact over the crossing transfer zone has a dip-like shape and can often cause detrimental impact loads on the railway track and its components. The large impact also emits disturbing noises (either impact or ground-borne noise) to railway neighbors. In a brown-field railway track where an existing aged infrastructure requires renewal or
maintenance, some physical constraints and construction complexities may dominate the choice of track forms or certain components. With the difficulty to seek for high-quality timbers with dimensional stability, a methodology to replace aged timber bearers in harsh dynamic environments is to adopt an alternative material that could mimic responses and characteristics of timber in both static and dynamic loading conditions. A critical review has suggested an application of an alternative material called fibre-reinforced foamed urethane (FFU). The full-scale capacity design makes use of its comparable engineering characteristics to timber, high-impact attenuation, high damping property, and a longer service life. A field trial to investigate in-situ behaviours of a turnout grillage system using an alternative material,
\'fibre-reinforced foamed urethane (FFU)\' bearers, has been carried out at a complex turnout junction under
heavy mixed traffics at Hornsby, New South Wales, Australia. The turnout junction was renewed using the
FFU bearers altogether with new special track components. Influences of the FFU bearers on track geometry (recorded by track inspection vehicle

http://www.techno-press.org/download.php?journal=smm&volume=1&num=1&ordernum=6

Monitoring in-service performance of fibre-reinforced foamed urethane sleepers/bearers in railway urban turnout systems

Railway switch and crossing (SC thereby helping ensure the rapid evolution of monitoring and fault detection in the railway industry at a time of the increased interest in condition based maintenance and the use of high-speed trains on the rail network.

/pdf/on-the-fault-detection-and-diagnosis-of-railway-switch-and-3uzw60oayo.pdf

On the Fault Detection and Diagnosis of Railway Switch and Crossing Systems: An Overview

A novel high-strength steel design is proposed, with a fine bainitic microstructure free from inter-lath carbides, for railway crossings applications. The design is based on the phase transformation theory and avoids microstructural constituents like martensite, cementite and large blocky retained austenite islands in the microstructure which are considered to be responsible for strain partitioning and damage initiation. The designed steel consists of fine bainitic ferrite, thin film austenite and a minor fraction of blocky austenite which contribute to its high strength, appreciable toughness and damage resistance. Atom probe tomography and dilatometry results are used to study the deviation of carbon partitioning in retained austenite and bainitic ferrite fractions from the T0/T0ʹ predictions. A high carbon concentration of 7.9 at.% (1.8 wt%) was measured in thin film austenite, which governs its mechanical stability. Various strengthening mechanisms such as effect of grain size, nano-sized cementite precipitation and Cottrell atmosphere at dislocations within bainitic ferrite are discussed. Mechanical properties of the designed steel are found to be superior to those of conventional steels used in railway crossings. The designed steel also offers controlled crack growth under the impact fatigue, which is the main cause of failure in crossings. In-situ testing using micro digital image correlation is carried out to study the micromechanical response of the designed microstructure. The results show uniform strain distribution with low standard deviation of 1.5% from the mean local strain value of 7.7% at 8% global strain.

Design of high-strength and damage-resistant carbide-free fine bainitic steels for railway crossing applications

A three-dimensional (3-D) explicit dynamic finite element (FE) model is developed to simulate the impact of the wheel on the crossing nose. The model consists of a wheel set moving over the turnout crossing. Realistic wheel, wing rail and crossing geometries have been used in the model. Using this model the dynamic responses of the system such as the contact forces between the wheel and the crossing, crossing nose displacements and accelerations, stresses in rail material as well as in sleepers and ballast can be obtained. Detailed analysis of the wheel set and crossing interaction using the local contact stress state in the rail is possible as well, which provides a good basis for prediction of the long-term behaviour of the crossing (fatigue analysis). In order to tune and validate the FE model field measurements conducted on several turnouts in the railway network in the Netherlands are used here. The parametric study including variations of the crossing nose geometries performed here demonstra...

https://tandfonline.com/doi/pdf/10.1080/00423114.2015.1136424

Numerical Analysis of the Dynamic Interaction between Wheel Set and Turnout Crossing Using the Explicit Finite Element Method

Switches and crossings (S&C) are critical elements on railway networks. Any failure of S&C usually leads to train delays and cancelations having a negative impact on the quality of service delivered, railway safety and also operating costs. S&C is a multi-component system and to enable proactive prevention of S&C unit faults, with their undesirable consequences, the ability to predict problems at component level is needed. This paper describes the derivation of lifetime distributions of individual S&C components based on field data collected. Maintenance was identified as a potential contributor towards increased frequency of reported S&C faults. The outcomes of the analysis and lifetime distributions for the elements of the switch units provide a means of predicting the expected number of maintenance activities, and associated costs for these units over any specified period of time. They provide an essential input to the optimisation of maintenance in developing an asset management strategy.

Fucheng Zhang

Papers

Numerical simulation of stress and deformation in a railway crossing