Welded Rail Research Articles

Nondestructive rail neutral temperature estimation based on low-frequency vibrations and machine learning

This paper describes the latest advancements of a non-invasive inspection/monitoring technique to estimate the rail neutral temperature (RNT), which is the temperature at which the net longitudinal force in continuous welded rails is zero. The technique is based on the measurement of the lowest modes of vibration of the rail of interest, and the application of machine learning (ML) to predict the RNT from the spectral densities of the vibrations’ frequencies. In the study presented in this article, the proposed technique was tested twice in the field. Vibrations were induced with an instrumented hammer on a 5° curved rail on concrete ties, and detected with a few wireless and wired accelerometers. The time-series were post-processed to extract the power spectral densities across the 0–700 Hz range. These densities constituted the input vector of a ML algorithm trained with experimental data and then tested with different experimental data. The RNT predicted by the algorithm were compared and showed very good agreement with the temperature estimated by an independent party and based on conventional strain-gage rosettes.

Study of the lateral resistance characteristics of ballast bed considering the sleeper group effect

By establishing the ballast track full scale model, this paper tested and compared the difference between the resistance of the sleeper group and the resistance of a single sleeper, and studied the effect of sleeper group on lateral resistance. The model of the ballast bed was established based on the discrete element method. We compared the lateral resistance of ballast bed composed of different number of sleepers and analyzed the particle movement and the contact characteristic. According to case calculations, we analyzed the lateral stability of continuous welded rail (CWR) considering the effect of sleeper group. The results show that the average resistance of five sleepers decreased by about 28% compared with that of a single sleeper. With the increase of sleeper’s number, the average resistance gradually becomes stable. The reduction of lateral resistance under the effect of sleeper group mainly occurs in the ballast side and sleeper end area and there is a common area of resistance at the side and end of sleepers. When the sleeper displacement reaches 2 mm, the contribution rate of crib resistance in the independent area and the common area is about 4.3:1:1, and the contribution rate of shoulder resistance is about 3.2:1:1. To ensure the safety of the CWR operation, it is suggested that at least three sleepers should be pushed at the same time when testing the lateral resistance and use the average lateral resistance as a reference value.

Influence of Guardrails on Track–Bridge Interaction with a Longitudinal Resistance Test of the Fastener

The guardrail is an indispensable part of ballasted track structures on bridges. In order to reveal its influence on the track–bridge interaction of continuous welded rail (CWR), the longitudinal resistance model of the guardrail fastener and its influential factors are established through tests. By taking a continuous girder bridge (CGB) for railways as an example, a stock rail-guardrail-sleeper-bridge-pier integrated simulation model is developed. The effects of the guardrails, installation torque of the guardrail fastener, and joint resistance of the guardrail under typical conditions are carefully examined. The research results indicate that the nominal longitudinal resistance of the guardrail fastener and the elastic longitudinal displacement of the rail prior to sliding approximately grow linearly with the growth of the installation torque. The presence of a guardrail can alleviate the track–bridge interaction in the range of the CGB, but exacerbate the interaction near the abutment with moveable bearings. This fact enables the abutment position to be considered as a new control point for the design of CWR on bridges. Considering the changing rules of the rail longitudinal force and rail gap, it is recommended that the installation torques of the guardrail fastener and guardrail joint are 40–60 N·m and 700–800 N·m, respectively. The recommended maximum longitudinal stiffness of piers for CGBs is evaluated. When the longitudinal stiffness of the pier for a CGB is lower than the recommended value, the influence of the guardrail can be neglected in the design of the CWR.

Integration of Traction Electricity Consumption Determinants with Route Geometry and Vehicle Characteristics

Traction electricity (TE) consumption in rail transportation (rail transport) is determined by factors (determinant) related to the characteristics of railway lines and vehicles. They have an impact on driving speeds, which, in turn, affect energy consumption. The scientific research presented here combined the results of expert, direct and indirect measurement methods, including brainstorming, mind mapping, system approach, heuristics, failure mode and effect analysis. The main objective was to demonstrate the influence of the determinants of TE consumption, depending on the route (road) geometry and characteristics of the traction of electric vehicles and whole trains (catenary-supplied electric vehicles, non-autonomous electric vehicles, and network traction vehicles, especially electric locomotives and electric multiple units, electric multiple-units (EMUs)). Using a new approach, the TE consumption equation, we applied values for the movement resistances of electric locomotives during braking for a jointed railway track Mres JRT braking and continuous welded rail tracks Mres CWRt braking. The values of the movement resistances of the electric locomotives during startup on the jointed railway track Mres JRT startup and continuous welded rail tracks Mres CWRt startup were also applied. They showed a strong correlation with the existing speeds of catenary-supplied electric vehicles. The implementation of the new innovative approach is an important contribution to the development of engineering and technical sciences, in particular, the disciplines of civil engineering, surveying/geodesy, and transport.

Stress Evaluation in Rails Based on Vibration Data and Artificial Intelligence

An inspection technique for the estimation of longitudinal stress and rail neutral temperature (RNT) in continuous welded rails (CWR) is presented. The technique is based on the use of finite element analysis (FEA), vibration measurements, and machine learning (ML). The FEA is used to establish the dependency of the vibration characteristics (mode shapes and frequencies) of any given CWR to the conditions of the track and the longitudinal stress of the rail. The dependency is then used to train an ML algorithm that is tested using experimental data obtained with two accelerometers bonded to the rail of interest, during a field test conducted in Colorado, U.S. A commercial finite element (FE) software was used to model the rail track as a short segment repeated indefinitely and under varying boundary conditions and stress. Three ML models were developed using hyperparameter search optimization techniques and k-fold cross-validation to infer the stress or RNT from the frequencies of vibration extracted from the time waveforms recorded by the accelerometers. The results demonstrated that the success of the technique is highly dependent on the accuracy of the FE model. The results also demonstrated that ML was mostly able to learn from the experimental data and successfully predict the neutral temperature.

A review of non-destructive evaluation techniques for axial thermal stress and neutral temperature measurement in rail: Physical phenomena and performance assessment

Thermal buckling of continuous welded rail (CWR) has been a long-standing challenge for the railroad industry because of the high derailment rate and the associated social, economic, and environmental impacts it causes. Rail buckling is generally attributed to excessive thermally-induced axial compressive stress developed in the rail from high temperatures. Knowing the rail thermal stress or its rail neutral temperature (RNT) is critical for safe and efficient rail system operation. There has been great interest and much work on the development of nondestructive evaluation (NDE) techniques to estimate rail thermal stress and RNT in situ. This paper reviews the findings and conclusions from research about NDE approaches for estimating rail thermal stress or RNT, emphasizing the physical phenomena and performance interpretation related to each of the approaches. We identify the type of reference measurements each technique relies on and tabulate this information showing key assumptions, performance, and limitations for each technique.

Detection method of the neutral temperature in continuous welded rails based on nonlinear ultrasonic guided waves

ABSTRACT The continuous-welded rail (CWR) will generate longitudinal stress when the rail temperature deviates from the neutral temperature (NT). Although CWR has been widely used in modern rail transit systems, real-time monitoring of longitudinal stress in CWR, or equivalently NT, is still a technical challenge. In order to explore the possibility of nonlinear guided waves in NT detection, this paper identifies possible pairs of fundamental and second harmonic waves modes in the rail, and investigates the effects of stress and temperature on the nonlinear parameter of each mode pair that could produce cumulative second harmonics. Both of stress and temperature are found to have significant influence on the nonlinear parameter, thus how to decouple the influences of temperature and stress is the key to NT detection. It is also found that the variation pattern of the nonlinear parameter vs. temperature curve could be completely different for different mode pairs. Furthermore, when the temperature of CWR changes monotonically , the nonlinear parameters of almost all mode pairs increase or decrease monotonically, except one mode pair, the nonlinear parameter of which presents a clear local minimum at NT. Thus, this special mode pair can be used to detect NT without considering the coupling influence of temperature and stress.

Track Decay Rate (TDR) Measurement Method for Reactive Damping by Tuned Mass Damper (TMD)

TDR measures the rate of vibration decay along rail in dB/m. Higher TDR leads to lower noise radiation. However, new railways are often having low TDR due to the use of resilient fasteners (to provide vibration isolation between rail and supporting structure for ground borne noise concerns), which leads to high noise radiation. Rail damper is used to increase TDR (thus reduces railway noise), where TMD is an efficient damping mechanism dissipating the vibration energy of the rail. TMD provides reactive damping force, maximised after a few cycles of oscillations. TMD force is stronger with continuous excitation than impulse excitation. For convenient purposes in the industry, TDR measurements are primarily conducted by impulse method, which do not allow sufficient time to include reactive TMD force. Therefore, impulse excitation TDR is smaller than continuous excitation TDR. Continuous excitation TDR is considered to reflect more of the real case of wheel/rail interaction excitation during train running. Besides, TDR in terms of time decay in dB/s is an alternative approach for evaluating noise performance of the rail. This paper presents TDR measurement results under different conditions, e.g., impulse excitation against continuous excitation; freely supported short rail (~6m), short rail (~6m) with resilient fastener support as well as site measurements in continuous welded rails.

Study of transitional phenomena in rail vehicle dynamics in relation to the reliability and operational state of the continuous welded rail track in terms of rail joints

This paper presents the results of experimental and numerical studies on reliability and monitoring issues of railway infrastructure in terms of safety and operation. The state of knowledge concerning methods of assessing track condition, in particular rail joints used in continuous welded rail track of railway lines is described. Experimental results of rail joints used in track transition zones and the results of numerical studies/tests of the rail vehicle-track model are outlined. It is demonstrated, basing on the analyses of the experimental results, that not only should the rail joints used in continuous welded rail track be diagnosed during their acceptance, but also during their operation. It is proven that the currently used methodology for testing welded rail joints applied during acceptance testing of contact track is not fully correct and leads to misinterpretation of the measurement results. Moreover, the results of numerical simulation tests presented in this paper confirm the possibility of diagnosing the condition of rail joints by any vehicle passing over such a track equipped with a suitable system.

Rail Structure Interaction Analysis for Providing CWR on Un-Ballasted Multi-Span Open Web Steel Girder Bridge

Rail structure interaction (RSI) requires thorough study to understand the force transfer mechanism between the track and bridge components due to train vertical live loads, braking/traction loads and thermal loads accordingly. RSI analysis gives us an outline of the axial stress in rail, support reactions transferred to the bridge components and the relative displacement caused between the track and bridge. This paper investigates rail structure interaction analysis of unballasted multi-span steel through girder railway bridge carrying dedicated freight corridor (DFC) of 32.5t axle load. For this purpose, RSI analysis is performed as per the guidelines given in UIC774-3R [7] Code of Practice (International Union of Railways) for two different multi-span bridge with a span configuration of 7x63m and 6x48m respectively and the axial stress in rail, relative displacement between rail and bridge and support reactions transferred to the bridge components are calculated based on the span and stiffnesses of the bridges. From the analysis results, it shall be concluded whether to explore the possibility of providing a provision of continuous welded rail (CWR) on the bridge or to adopt switch expansion joints (SEJ) or other expansion devices accordingly.

Sensor system for determining the risk of track distortion in the continuous welded rail

The article considers the peculiarities of load formation in the continuous welded railroad tracks depending on temperature factors, geometric parameters and local curvature. The approach is proposed to determine the risk of distortion of the railway track depending on a combination of force and geometric factors on the ability of the ballast to keep the rail sleepers from moving laterally in relation to the direction of the track.

Numerical analysis of interface damage in ballastless track on simply supported bridge due to thermal and vehicle dynamic load

The stiffness, mass and damping matrix of 17 degree of freedom (DOF) vehicle model are derived on the basis of Lagrange equation. The bilinear discrete cohesive zone model (DCZM) is utilized to simulate the bonding performance of the interface between the track slab and the CA mortar layer. The ballastless track-bridge element model is proposed by the direct stiffness method, and the vehicle-ballastless track-simply supported bridge vertical-longitudinal coupled model with consideration of interface damage is established. In addition, based on the ballastless track-bridge element model, the ballastless track continuous welded rail (CWR) model on multi-span simply supported bridge is proposed. The ballastless track CWR model is employed to obtain the initial longitudinal relative displacement of track slab-CA mortar layer interface under bridge thermal load. The displacement response of ballastless track-bridge structure is taken as the initial displacement field of vehicle-track-bridge coupled dynamic model. The vehicle-track-bridge coupled model is adopted to obtain the interface damage of ballastless track under the action of bridge thermal load and vehicle dynamic load. Then, the effects of bridge temperature and longitudinal stiffness of the DCZM on the longitudinal relative displacement of ballastless track-bridge structure are investigated in detail. The mechanism and distribution law of interface damage of ballastless track under different running speeds, CA mortar layer gap length and DCZM parameters are discussed. The conclusions obtained in this paper could provide a technical guide for the formulation of maintenance standards for interface damage of ballastless track on simply supported bridge. Then, some parametric studies are presented based on the model in this paper. The analysis indicates that the longitudinal relative displacement of the track slab-CA mortar layer becomes large at both ends and small in the middle within the range of a simply supported bridge. When there is CA mortar layer void, the ballastless track interface is in the stress state of tension + shear mixed mode. The recommended threshold of void length of CA mortar layer is 0.65 m. More attention shall be paid to the construction quality of interface between the track slab and the CA mortar layer.

Combining welding-induced residual stress with thermal and mechanical stress in continuous welded rail

Continuously welded rail (CWR) with flash-butt welded joints has become standard practice for railway construction around the world. The welding process during rail installation or repair forms a residual stress field in the weldment altering locally the distribution and amplitude of the total stress that develops when the rail is in service. This paper presents a computer simulation approach to study the combined residual, thermal, and mechanical stress caused by the fastener system that develops in rail during the in-track welding and installation. The proposed approach simulates within a Finite Element Analysis framework the rail welding and installation sequence using detailed thermal and mechanical models of the weldment formation, and in-track installation. The model is validated with experimental measurements reported in the literature. It is implemented in a study that demonstrates the combined effects of such stresses with stress that develops in the rail during a daily solar-induced thermal cycle. A non-trivial stress gradient is observed where the mean tensile stress in the weldment is elevated relative to the rail at large. The higher mean stress warrants further investigations in view of fatigue performance under wheel loading. The proposed computer simulation approach is a tool that will enable future investigations focusing on more detailed examinations of weldment behavior, particularly concerning fatigue failures and track configurations, as well as in optimizing welding parameters to control the development of residual stresses.

Review of factors affecting stress-free temperature in the continuous welded rail track

Railways have a significant role to play in sustainable transportation. Rail travel is currently the only mode of rapid, large-scale, long-distance transport for both freight and passengers that offers zero carbon dioxide emissions at the point of use. However, our railway infrastructure needs to be more robust and resilient to the combined effects of climate change, traffic growth and increases in vehicle loads and speed. Rail buckling is of increasing concern as environmental temperatures rise and traffic loads, speed and intensity of use increase. A key indicator and control of the propensity for track buckling is the stress-free temperature of the rails. However, determining the actual stress-free temperature of a given section of track is challenging. Knowledge of the factors affecting stress-free temperature will help in the identification of vulnerable sections of track and the development of an appropriate maintenance regime. This paper reviews and discusses the factors affecting stress-free temperature in ballasted railway track with continuous welded rails (CWR).

Vibration-Based Approach to Measure Rail Stress: Modeling and First Field Test.

This paper describes a non-invasive inspection technique for the estimation of longitudinal stress in continuous welded rails (CWR) to infer the rail neutral temperature (RNT), i.e., the temperature at which the net longitudinal force in the rail is zero. The technique is based on the use of finite element method (FEM), vibration measurements, and machine learning (ML). FEM is used to model the relationship between the boundary conditions and the longitudinal stress of any given CWR to the vibration characteristics (mode shapes and frequencies) of the rail. The results of the numerical analysis are used to train a ML algorithm that is then tested using field data obtained by an array of accelerometers polled on the track of interest. In the study presented in this article, the proposed technique was proven in the field during an experimental campaign conducted in Colorado. A commercial FEM software was used to model the rail track as a short rail segment repeated indefinitely and under varying boundary conditions and stress. Three datasets were prepared and fed to ML models developed using hyperparameter search optimization techniques and k-fold cross validation to infer the stress or the RNT. The frequencies of vibration were extracted from the time waveforms obtained from two accelerometers temporarily attached to the rail. The results of the experiments demonstrated that the success of the technique is dependent on the accuracy of the model and the ability to properly identify the modeshapes. The results also proved that the ML was also able to predict successfully the neutral temperature of the tested rail by using only a limited number of experimental data for the training.

Neutral Temperature Estimation of Continuous Welded Rails using Group Velocity of Ultrasonic Waves

This study proposes a neutral temperature estimation technique of continuous welded rails using group velocity of ultrasonic waves. In case of boundary-confined metallic structures, especially civil infrastructures exposed to harsh environmental conditions such as continuous welded rail, thermal stress is one of the critical control factors to avoid structural breakage and buckling. It has been known that the ultrasonic wave propagation is sensitive to target structure’s stress variation, so that the neutral temperature can be determined based on the propagation characteristics of stress-dependent ultrasonic wave. To numerically investigate the stress-dependent ultrasonic wave behavior, a 3D rail model with 1 mm mesh size was constructed using actual material property and dimensions of KR60 rail. Here, the two boundary conditions, i.e., Fix-Free and Fix-Fix boundary conditions, applied to the 3D model so that neutral temperature is extracted. The simulation results showed that the group velocity of ultrasonic waves was consistently decreased on the Fix-Free boundary condition according to temperature increase. Similarly, the group velocity on the Fix-Fix boundary condition was also decreased, but the decrement of group velocity was less than the Fix-Free boundary one due to thermal stress. Based on the observation, the stress-dependent group velocity trends can be estimated using the difference between the Fix-Free and Fix-Fix boundary resultants. Finally, the neutral temperature can be estimated by picking up the cross point of two group velocity trend graphs.

The sleeper group influences on lateral resistance and stability of ballast bed

ABSTRACT The sleeper group, composed of a certain number of rail sleepers, influences the characterization of lateral resistance and the stability of continuous welded rail (CWR). According to full-scale model tests and discrete element model simulation tests of ballast bed, we established a new lateral stability analysis model of CWR considering the effect of sleeper group and resistance sharing characteristics, and compared it with the traditional model. The case analysis shows that the lateral stability analysis result of CWR is safer when considering the effect of sleeper group. When the curve radius is 300 m, the safety margin of the sleeper group model is about 20.8% larger than that of the traditional model. For CWR with potential large lateral displacement in special sections (such as small-radius and large temperature difference), it is advisable to consider the effect of sleeper group for the lateral stability analysis.

Sensitivity of Geometric Parameters in the Sustainability Development of Continuous Welded Rail

Continuous Welded Rails (CWR) are a key infrastructure element in the safety and efficiency of rail transportation. Their correct exploitation (operational) requires surveying and diagnostic monitoring based not only on the results of rail displacement measurements, but also on the geometric parameters of the track in the horizontal (H) and vertical (V) planes. Many researchers have proposed different approaches for surveying and diagnostic monitoring of CWR. However, they do not refer to the determination of railway track defectiveness (parametric defects, track defectiveness) respectively on straight and curvilinear segments. Research topics involving CWR constitute a continuous openness to research with particular application of synergy effects in the optimization of monitoring of CWR geometry shaped by exploitation processes. In this study, based on real measurement data of six geometric parameters (H: track gauge, gradient of track gauge, horizontal irregularities and V: cant, twist, vertical irregularities), the most sensitive parameters in sustainable development CWR are defined. The research answered that the most sensitive parameters in the sustainability development of CWR belong in the range of the plane H: gradient of track gauge and horizontal irregularities, and in the plane V: vertical irregularities. These escalate especially on curvilinear sections, requiring more significant maintenance capacity. Due to the growing importance of rail transportation as a sustainable, environmentally friendly, and mass transit mode, the research results provide a basis for life cycle management of CWR.

Numerical Analysis of Guided Wave Transmission Through a Long Defect in a Rail Track

Abstract Guided wave ultrasound has been used to continuously monitor welded rail track by transmitting guided wave ultrasound between alternate transmit and receive stations along the rail. A section of rail was encountered where transmission was not reliably achieved. It was found that there was considerable flank wear on the head of the rail, which varied in a sinusoidal pattern over approximately 10 m. The scattering due to the wear is investigated in this paper using numerical modeling. A 3D finite element (FE) model of the section of rail containing the wear defect was coupled to two semi-analytical finite element models of the incoming and outgoing waveguides. In the case of a 10 m long defect, which is over 100 wavelengths long, the 3D FE matrices were excessively large, and the global matrices could not be assembled nor solved. An approach of successively assembling layers of the mesh and reducing out internal degrees-of-freedom in the dynamic stiffness matrix was successfully adopted. The influence of the length of wear on the transmission loss was computed. It was found that short wear lengths generally cause more transmission loss although the relationship is not monotonic. It was found that the long-wear seen in the field does not cause transmission loss. In this case, where the change in cross section is gradual the incoming mode converted to a single mode in the smallest cross section and this mode converted back to the incoming mode in the second half of the wear section.

PROCESSES OF WELDED JOINT STRUCTURE FORMATION DURING ELECTRIC RESISTANCE WELDING OF RAILWAY RAILS

During operation of a continuous welded rail track, most of the fractures occur in welded joints. Welded joints failures take place due to various reasons including the presence of the hardened areas in the welded joint and increased local wear of the rolling surface. The paper presents the dilatometry results and the obtained continuous cooling transformation diagram of the supercooled austenite decomposition for R350LHT rail steel, which make it possible to define the critical cooling rate. It was determined that during welding in hard modes the welded joint cooling rate is lower than the critical one which leads to the martensite formation in the welded seam. The positions of critical points and phase equilibrium areas for the given rail steel were also modeled. It is proposed to use a new method for welding railroad rails based on the knowledge of dependences of the structural components dispersity and, first of all, pearlite and carbide particles formed in the process of obtaining welded joints of rails on the composition of steel and the conditions of their cooling.