Rail Squats Research Articles

An unsupervised method based on convolutional variational auto-encoder and anomaly detection algorithms for light rail squat localization

As a typical short-wave rolling contact fatigue defect of rail surface, squats accelerate the degradation of the railway infrastructure. Early detection of rail squats contributes greatly to the maintenance of the railway system. This article proposes an automatic detection algorithm for light rail squat localization via the vehicle axle box acceleration signal. A convolutional variational auto-encoder, named CVAE, is tailored for feature extraction in an unsupervised manner. Then, two anomaly detection methods, namely elliptic envelope and one-class support vector machine (OCSVM) are employed as alternatives for rail squat detection. The validity and reliability of the proposed approach are verified by vehicle-track coupled dynamics simulation, where squats are considered as an irregularity excitation. And an in-lab experiment is conducted to further validate the effectiveness of the method. Comparative studies are conducted to investigate the influence of squat depth, feature extraction method, noise level and vehicle speed on the algorithm. The results demonstrate the elliptic envelope method is a better option for squat detection which can be explained by the consistency of the property of features extracted by CVAE and input data requirements of the elliptic envelope method. Furthermore, compared to the convolutional auto-encoder, CVAE is a better unsupervised feature extraction method because features extracted by CVAE are more sensitive to light squats. And it’s verified that the CVAE-elliptic envelope method is robust over signal noise and variability of vehicle speed.

Simulation for Propagation of Horizontal Fissures in Rail Squats

Simulation for Propagation of Horizontal Fissures in Rail Squats

Impact Responses of the Highspeed Railway Track Slabs

Impact loads pose a lot of hazards including causing severe damage to both railcars and rail track components, for example, cracking of slabs or sleepers. The impact loads can be as a result of several factors including flat spots on rail wheels attributed to the train braking, dipped rails, rail squats, corrugation, crossing transfers, etc. The impact loads are often over a short duration but of very high magnitude. For instance, the typical loading duration produced by wheel flats is about 1-10 milliseconds, while the force magnitude can be over 400 kN per rail seat. This paper highlights an investigation into the behaviour of a slab-track subjected to impact loading. A parametric study has been carried out using the finite element analysis software, Strand7, to investigate the behaviour of slab-track under the action of the impact loading conditions. This was done by analysing the ratio of maximum impact moment to maximum static force under varying slab support conditions. The outcome of this study will potentially lead to a better understanding and hence, the design of slab track systems in highspeed railway tracks subjected to the impact loading. Our study revealed that for a slab-track under the action of impact loading, the slab-track is more sensitive to changes in the support stiffness at midspan than at the rail seats and effects of increasing or reducing support stiffness are more significant at these locations.

Peridynamic Analysis of Rail Squats

Rail surface defects are a serious concern for railway infrastructure managers all around the world. They lead to poor ride quality due to excess vibration and noise; in rare cases, they can result in a broken rail and a train derailment. Defects are typically classified as ‘rail studs’ when they initiate from the white etching layer, and ‘rail squats’ when they initiate from rolling contact fatigue. This paper presents a novel investigation into rail squat initiation and growth simulations using peridynamic theory. To the best of the authors’ knowledge, no other comprehensive study of rail squats has been carried out using this approach. Peridynamics are well-suited for fracture problems, because, contrary to continuum mechanics, they do not use partial-differential equations. Instead, peridynamics use integral equations that are defined even when discontinuities (cracks, etc.) are present in the displacement field. In this study, a novel application of peridynamics to rail squats is verified against a finite element solution, and the obtained simulation results are compared with in situ rail squat measurements. Some new insights can be drawn from the results. The outcome exhibits that the simulated cracks initiate and grow unsymmetrically, as expected and reported in the field. Based on this new insight, it is apparent that peridynamic modelling is well-applicable to fatigue crack modeling in rails. Surprisingly, limitations to the peridynamic analysis code have also been discovered. Future work requires finding an adequate solution to the matter-interpenetration problem.

Investigation of the formation of corrugation-induced rail squats based on extensive field monitoring

Rail squats originate from a number of sources, such as corrugations, indentations and welds. A five-year continual field monitoring study was performed on squats induced by corrugations. This study indicated that a small black depression formed at the corrugation under wheel-rail dynamic forces, and then, a primary crack typically initiated on the gauge side edge of the depression. Subsequently, the crack began to propagate in the rail surface in a U shape toward the gauge side in both the traffic direction and the opposite-traffic direction and into the rail toward the field side at an angle of approximately 20°. Rail inclination could influence the crack initiation location and propagation path. The geometry of the black squat depression was initially elliptical, and then, its edge followed the U-shaped cracking path as it grew. The squats turned into a kidney-like shape, typically with a U-shaped crack. Tensile stress likely led to the squat crack initiation and propagation. This cracking phenomenon and mechanism are analogous to the ring/cone crack formation of brittle materials under sphere-sliding contact. As the squats grew further, a ridge formed in the middle part of the depression, and an I-shaped crack appeared at this ridge due to the impact of the wheels. This process eventually led to two-lung-shaped mature squats, typically with a Y-shaped crack. The findings of this paper provide insight into the formation of rail squats.

Reply to Giannakos, K. Comment on: Toughness of Railroad Concrete Crossties with Holes and Web Openings. Infrastructures 2017, 2, 3

This paper responds to the discussion [1] by Dr. K. Giannakos over our technical note [2].[...]

In Situ Monitoring of Rail Squats in Three Dimensions Using Ultrasonic Technique

Rail squats and studs are typically classified as the growth of any cracks that have grown longitudinally through the subsurface of rails. This study highlights in situ monitoring of squat/stud distribution and its growth in the field. Squat/stud growth has been determined and plotted using the ultrasonic measurement device and the crack depths at each reference grid node form a three-dimensional contour of rail squat crack. In this study, the crack propagation of squats/studs is roughly estimated to be almost linear to repeated train loads called as accumulated passing tonnages up to a certain degree of propagated crack length. This in situ monitoring is of significance to railway authorities in order to effectively and efficiently prioritize maintenance functions, which will improve safety and reliability of the rail network.

Dynamic Wheel–Rail Interaction Over Rail Squat Defects

Dynamic interaction between wheel and rail generates vibration and acoustic radiations transmitted through other media such as structural track systems, air, and rolling stock. Noteworthy, both wheel and rail irregularities often induce additional impact vibration and noise along the rail corridor. Rail squats and studs are typically classified as the development of any cracks that have grown longitudinally and laterally through the subsurface and become a laminated crack resulting in a depression of the rail surface. The rail defects are commonly referred to as ‘squats’ when they are initiated from rolling contact fatigue cracks, and as ‘studs’ when they are associated with a white etching layer due to wheel slips or excessive tractive effort. Interestingly, recent research shows that rail squats can be found almost everywhere, and every type of track structures, gradients and geometries in either light passenger or heavy freight traffics and for low, medium or high speed trains all over the world. A more pronounced issue appears when the crack grows and finally flakes off the rail. This paper highlights the monitoring of wheel–rail interaction over rail squat defects. Using the axle box acceleration data obtained from the calibrated track recording vehicle, the frequency spectra can be analysed. The results demonstrate an apparent influence of squats on the wheel–rail interaction over the defective sections and increased acoustic radiation at the high frequency range. The practical understanding will also enhance the development of acoustic- and vibration-based monitoring systems of rail surface defects.

Field statistical and finite element analysis of rail squats

In this paper, squats on 262km of Australian railway track have been statistically investigated. Data from more than 4900 squat occurrences has been collected. At each point, rail type, rail, sleeper type, the curve radius and rail direction are recorded as fixed parameters. A linear mixed model has been used to statistically identify the parameters and parameter combinations that are more likely to lead to the occurrence of squats and results are compared with those from a 3D finite element model. Results show that squats are more likely to occur in sharper radius curves due to higher lateral traction and at locations with a softer foundation due to the elastic foundation effect.

NDI of Rail Squats and Estimating Defect Size and Location Using Lock-In Thermography

Rail squats are a form of near surface rolling contact fatigue damage found in rail heads. Currently, the most popular method to detect the rail squats is utilizing ultrasonic techniques to determine their presence and measure their depths. This technique needs to be direct contact between the probe and the rail head, with a coupling fluid in at the interface. Other weaknesses of these ultrasonic techniques include false detections as well as missed detections. Infrared thermography is a relatively new non-destructive inspection technique used for a wide range of applications but is not used for rail squat detection. Lock-in thermography is a non-destructive inspection technique that can be used for the detection of near surface defects. It utilizes an infrared camera to detect the thermal waves and then produces a thermal image, which displays the local thermal wave variation in phase or amplitude. In inhomogeneous materials, the amplitude and phase of the thermal wave carries information related to both the local thermal properties and the nature of the structure being inspected. This comparison is then used to determine the phase angle difference (Δf) between the input and the thermal response of the object. The aim of this paper is to determine whether lock-in thermography can be used to firstly locate squats in rails, and secondly measure their depths. It has demonstrated the feasibility for using such a technique in generating thermal responses that could be adequately utilized for the purpose of defect characterization.

Tribological characterization of rail squat defects

Rail squats remain a major rolling contact fatigue problem for mass transit authorities. Several studies have been conducted to supplement the standard characterization of rail squats. In particular an extensive tribological and metallurgical investigation was performed on samples of incipient squats from various areas. Surfaces and cross-sections of rail samples were observed by optical microscopy and scanning electron microscopy. These observations highlighted that the running band is composed of longitudinal contact strips with various surface and subsurface morphologies. This microstructure seems to be essential for the onset of squats. This new information makes it possible to account for the entire damage mechanism of a squat defect from initiation to propagation.

1210 レール白層周辺傷のパーライト部への影響(接触問題とトライボロジ,OS9 接触問題とトライボロジ)

It is confirmed the stiffening layer that is called a white etching layer or white layer is generated on the rail. Moreover, it is reported that the generation of a similar stiffening layer occurs on the bearing and the brake disc. A micro crack that occurs on the rail white layer is a starting point of the crack that progresses on the rail and it grows up to the rail squats. A concrete finding has not been obtained yet though, the generation of a rail white layer is known conceptual. In this paper, we report the relation between the rail white layer and the micro crack that occurs on the laid rails.