Rail Specimens Research Articles

Effects of microstructure on the corrosion behavior of pearlitic rail steel under simulated salt fog conditions

In this paper, the corrosion resistance and mechanisms of rail specimens with different lamella spacings in a salt spray environment were evaluated and investigated. This investigation was achieved by controlling different cooling rates of pearlitic bodies through heat treatment to obtain various lamella spacings. The results indicated that the corrosion resistance of all the specimens decreased during the salt spray test. The specimens with slow cooling rates (resulting in large pearlitic sheet layer spacings) had poorer corrosion resistance than those with fast cooling rates. Specimens obtained with both fast and slow cooling rates (air cooling at a 0.01 °C/s cooling rate) displayed similar corrosion patterns. However, the corrosion stability of the specimen obtained at a cooling rate of 0.03 °C/s fluctuated considerably after 144 h of salt spray corrosion. This fluctuation was attributed to the transformations of corrosion products within the rust layer. The structural stability of the rust layer was related to the defects present in the material. Large defects increase the instability of the rust layer, thereby increasing the susceptibility to corrosion in a salt spray environment.

Wear study of additively manufactured repair material for R260 grade rails

Additive Manufacturing (AM) has been considered as a promising method for repairing rails and extending their service life. In this work, the wear rates of twin-disc specimens produced through laser additive manufacturing against ER7 material are studied applying creepages from 0.4 % to 2.6 %. The approved E11018-G electrode material is atomised and fully cladded into twin-disc rail specimens by Laser Powder Directed Energy Deposition. After the weight loss tests at 1400 MPa, experimental results are fitted with the theoretical adhesion curve modifying FASTSIM coefficients. This adhesion curve is employed to numerically calculate the slip contact area of each test. A non-linear correlation has been found and defined between wear and the slip area including the non-linear zone. This relationship is identified for tribochemical wear for low creepages and delaminative wear for middle and high creepages by surface and metallographic characterisation. The obtained results allow to predict the wear of the additively manufactured E11018-G repair material under wheel-rail contact conditions when the slip area is known.

Fatigue crack growth and microstructural analysis of rail steel specimens under periodic overloads

The present paper aims to study the effects of periodic overloads on the fatigue crack growth and microstructure of railway rail specimens. Numerical analysis and experimental tests were exploited to examine the crack path in specimens. A three-dimensional nonlinear boundary element model was used to predict the crack path in specimens. The effect of several parameters on the fatigue life of the rail steel specimens were evaluated using numerical model and experimental tests. The numerical and experimental test results revealed that the fatigue life curve had an optimal overload ratio at which the fatigue life was maximized. The number of fixed cycles was kept fixed between the overloads, measuring the effect of the overload ratio on the fatigue crack growth. Also, the fractographic analysis showed that by increasing the stretching speed of the rail steel specimens, the amount of plastic deformation is reduced and the brittleness of the material is increased.

Novel Coil Transducer Induced Thermoacoustic Detection of Rail Internal Defects Towards Intelligent Processing

A novel resonant tri-coil transducer is proposed to induce thermoacoustic (TA) signals for detecting rail internal defects. It consists of a ferrite plate-backed tri-coil and its associated circuits, a shielding layer, and a three-dimensional printed enclosure for supporting and securing. General TA detection theory is illustrated to understand how to detect rail internal defects. For achieving electromagnetic (EM) field shaping and focusing, the physical structure of the proposed transducer is optimized. It reduces backward EM fields and interference. Then, an equivalent circuit model between the proposed transducer and the rail is constructed to analyze optimal power transfer efficiency as a function of distance and frequency. To validate the design concept, the proposed transducer is fabricated for inducing TA signals, and experiments are performed. Several engineered rail specimens (UIC-60E) with different types of defects are prepared. The induced TA waves are found to be compressional. With selected features, a support vector machine algorithm-based multinomial classifier model is trained and employed for intelligent processing. Then, the proposed transducer is integrated into the self-designed automatic rail monitoring system. Experimental results show that the self-designed system can achieve an accuracy rate of 96.4%, successfully identifying defects in defect classification. The proposed transducer has low cost in fabrication and maintenance, focused magnetic fields with a large lift-off distance and enhanced acoustic wave intensity. Compared to earlier version of the system, the spacing between the transmitter and the rail has been further increased.

Wear and damage behaviours of wheel and rail materials: Effects of friction modifier and environmental temperature

Low temperature conditions can aggravate the wear and fatigue damage of the wheel and the rail materials. Friction modifier (FM) is used to control the adhesion and alleviate the wear and damage. However, the wear and damage behaviours of wheel and rail with the application of FM under low temperature have not been revealed. Therefore, the present study aims to investigate the effect of FM on the wear and the rolling contact fatigue (RCF) damage of the wheel and the rail under low temperature conditions. Tests were conducted on a rolling-sliding wear testing apparatus with the samples enclosed in a temperature-controlled chamber. The results indicated that the effect of FM on the wear and the RCF damage of the wheel and the rail was influenced by the temperature significantly. Compared with the dry condition, the wear rate of the wheel decreased obviously at all temperature conditions when using FM. Meanwhile, the RCF damage of the wheel was relatively slight. Besides, there was no significant difference among the RCF damage of the wheel at different temperatures both under the dry and the FM conditions. At room temperature, the application of FM could alleviate the RCF damage of the rail. Under the low temperature condition, the performance of FM would fail, which would result in a severe oil wedge effect on the rail specimen. Therefore, the application of FM could induce a higher wear rate and severe RCF damages on rail material at the low temperature condition. The results of the present study could provide guidance for the development and design of FMs used in cold regions.

Running-in evaluation after a rail grinding process using a pin-on-disk tribometer

Rail grinding as a maintenance strategy plays an important role in controlling rail defects due to rolling contact fatigue, noise reduction, and train stability by reshaping the rail. However, the effect of roughness topography of the rail surface after a grinding process has not been extensively studied in terms of friction coefficient and running-in behaviour.In this work, rail disks specimens with different textures were characterized by different roughness parameters: Ra, Rq, Rt, Rp, Rv, Rz, Ssk, and Sku. All the textures were achieved by varying the amount of material removed and the work speed by using some emery stones with similar properties in rail grinders. The tests were performed by using a pin-on-disk tribometer in dry and grease-lubricated conditions. Pin specimens were manufactured from a wheel section with standard roughness.The results showed that in dry conditions, rail disk specimens with rougher surface patterns yield a higher friction coefficient and higher wear rate. On the other hand, under lubricated conditions, a rough surface does not give a low static friction coefficient in some cases. Additionally, microstructural analyses were carried out on the cross-section of rail specimens and some images were taken from the existing wear scars identifying the wear mechanisms and finding in some textures the presence of a white etching layer (WEL) and a brown etching layer (BEL).

PENGARUH PERLAKUAN MEDIA PENDINGIN NaCl TERHADAP PELAPISAN PERMUKAAN SURFACE TREATMENT PADA REL KERETA API UIC R54

This study aims to understand and determine how effective the addition of NaCl in the quenching surface treatment media for the UIC R54 railroad. This study applies a method that refers to the theory of surface treatment. First, the surface treatment process is carried out on the surface of the rail specimen. The cooling medium used in the surface treatment process is a mixture of NaCl of 200-800gr NaCl at intervals of 200gr with 1000ml of water. Furthermore, observations of the microstructure and measurement of the hardness value on the surface of the rail specimen were carried out. The average hardness value for raw material specimens is 283.52 BHN. The highest hardness value in specimens that have been surface treated is 346.36 BHN in the treatment of adding 60% NaCl to the quenching medium. In raw material specimens, the phase formed is dominated by ferrite and pearlite. Meanwhile, the phase formed after the surface treatment process is martensite. From these results it can be concluded that a mixture of 60% NaCl with water used as a cooling medium is effective in increasing the hardness value of the rail.

Acoustic emission at the wheel-rail contact with micro-slip and stick-slip

The paper aims to analyse the occurrence of acoustic emission at the wheel-rail contact during micro-slip. The experimental model allows the contact pressure variation (MPa..GPa) and the sliding speed (0.01 to 0.5 mm/s) specific to the wheel-rail contact. It is determined experimentally and theoretically the appearance of the stick-slip phenomenon at the Hertzian contact of cylinder type (fixed-wheel specimen) - plane (mobile with very low speed - rail specimen). The experimental stand simultaneously measures the normal force, the friction force and the acoustic emission at different contact pressures, sliding speeds and rigidities of the wheel specimen fixing system. The specimens are made of UIC standard materials used in the driving wheels and rails. The stick-slip phenomenon occurs at low micro-slip speeds and normal bending stiffness. Experimentally, it is found that the jumps specific to the stick-slip phenomenon( friction coefficient-COF) are accompanied by the acoustic emission (AE) at the cylinder-plane interface. The energy emitted by AE (WAE) is correlated with the energy consumed by friction during the stick-slip period (WCOF). The theoretical model regarding the stick-slip phenomenon of the Hertzian contact with slip specific to the experimental stand allows the analysis of the stability of the stick-slip movement.

A Digital Lock‐in Amplifier Based on Adaptive Kalman Filter for Rail Defect Detection

In this paper, an eddy current testing system equipped with low‐performance processor is designed for rail defect detection. A digital lock‐in amplifier (DLIA) based on adaptive Kalman filter (AKF) is presented to detect the weak voltage induced in two differential coils. The proposed method can fast demodulate the amplitude of a signal with a randomized phase using one cycle of the sinusoidal signal, and simultaneously improve signal‐to‐noise ratio. This DLIA has made use of the sinusoidal orthogonality and concurrently utilized AKF to track on the amplitude variation of voltage, which is numerically simulated and analyzed in MATLAB. The simulated results indicate that increasing excitation frequency or sampling points in one cycle has an effective suppression in low‐frequency noise. Furthermore, the experiment is carried out to verify the performance of the system for rail defect detection. Finally, the experimental result shows that the proposed lock‐in amplifier has a root mean squared error of 1.3 mV and performs well in terms of memory consumption and precision. Moreover, the amplitude variation in differential coils is linearly tracked, and the surface defects on rail specimens can be detected.

Simulation and Experimental Study on Rolling Friction and Wear of Heavy Haul Wheel Tread

Rolling friction and wear testing of heavy haul wheel tread was performed. The results show that a new and dominant vibration was generated owing to the surface wear, resulting in the polygonalization wear of the wheel specimen. The slip between wheel and rail specimens accelerated the formation of polygonalization wear. The pearlite and proeutectoid ferrite in the outermost layer were completely fragmented to form a fine grain layer. There was an extreme state for the deformation of the microstructure in the outermost layer, and there was a corresponding extreme value for the hardness. The slip accelerated the surface microstructure to reach the plastic hardening limit, but it had little effect on the extreme value of hardness. The stress distribution of the wheel specimen surface was simulated. The results show that there were alternating principal tensile and compressive stresses at the contact surface of the wheel specimen and shear stresses with alternating directions in the subsurface of the contact patch. The depth of the maximum shear stress from the surface was mainly related to the normal load, while the slip has no significant effect on it. A coupling modeling method of finite-element method (FEM) and smoothed particle hydrodynamics (SPH) was used to simulate the microstructure evolution of CL70 wheel steel. The simulation results show that there was mutual mechanical interaction between ferrite and cementite in pearlite. Their deformation was inconsistent owing to their different mechanical properties, resulting in large tensile stress at the boundary between them, even in the compressive stress area below the contact patch.

A novel laser-based duffing oscillator system to identify weak ultrasonic guided wave signals related to rail defects

Laser-generated Rayleigh wave is a promising candidate for noncontact and remote inspection of railway as it can inspect in line-to-line fashion. Attribute to the recent advancement of optical design, wavelength of the laser generated-Rayleigh wave can be controlled at desired frequency band. By adjusting the wavelength of the Rayleigh wave, detection of defect occurred at different depths in rail become possible. Internal and subsurface defects that occur beneath the surface of railhead usually only reflect very small portion of wave energy hence accurate determination of their presences becomes challenging. Besides, such reflected-defect signal is usually contaminated with strong random noise which further hinder identification of weak reflected-defect signal. This study presents a novel method for detection of surface, subsurface and internal defects in railhead using laser-generated Rayleigh wave and chaotic oscillator. The use of laser-generated Rayleigh wave provides a fast mean to assess the health condition of railhead without the need to physically mounting sensor on the specimen. The use of chaotic oscillator can accurately reveal wave signal that is related to defect occurred in railhead. The effectiveness of the proposed method has been verified using numerical simulation model. Three rail specimens were machined with internal, subsurface and surface-breaking defects, respectively. Experimental results revealed that the proposed method can accurately and reliably reveal the presence of reflected-defect signal under strong random noise conditions. The present study also shows that the proposed system is promising in revealing hazardous defects occurred on rai

Reliability verification of stress data from extracted specimens using LCR wave stress data from full-section rail specimens

Non-destructive stress measurement using ultrasonic techniques is based on calculation of the acoustoelastic coefficient obtained from the relationship between material stress and sound wave velocity. Longitudinal critically refracted (LCR) waves are the most suitable for ultrasonic stress measurement testing. This is because these waves exhibit a relatively large change in flight time in relation to a change in stress. In general, to calculate the acoustoelastic coefficient, tensile tests are performed with specimens extracted from the test objects to be inspected, and the difference in the speed of ultrasonic waves is measured in relation to the stress applied. However, train rails are usually subjected to compressive loads and no research has been conducted to confirm whether the results obtained using this method match the coefficients obtained from test objects in full cross-section. Therefore, results from compression tests on full cross-section specimens are needed as reference data to determine the reliability of the results obtained using extracted specimens. In this study, experiments were conducted to compare the result from applying compressive loads to full cross-section specimens to the experimental result obtained from specimens extracted from each rail section. For this purpose, ultrasonic probes capable of generating LCR waves were designed and manufactured to apply the technique to measure the applied stress. Based on the results obtained using this probe, the acoustoelastic coefficient values obtained from each specimen were compared. Then, the feasibility of calculating the internal stresses in railway rails using the acoustoelastic constants obtained from the extracted specimens was determined, and the reliability of the method was verified. It was concluded that there was no significant difference in the acoustoelastic coefficients calculated using the data from extracted specimens and those using full cross-section specimens.

Research on rail crack detection technology based on magneto-optical imaging principle

The detection of rail top crack is of great significance in ensuring the safe operation of railway. Based on the principle of magnetic flux leakage detection and Faraday magneto-optical effect, a high-resolution and non-destructive magneto-optical imaging detection method is proposed in this paper. This paper analyses the principle of magneto-optical imaging, establishes a rail magnetic flux leakage detection experimental system based on magneto-optical effect, and detects the rail specimen with crack through experiment. The experimental results show that the change of crack width and depth will affect the magneto-optical imaging results, and the minimum crack size that can be detected by this experimental system is 0.4mm wide and 0.5mm deep. This paper realizes the detection of rail crack defects by using magneto-optical imaging method, and provides the basis for building an efficient, portable and high-resolution rail non-destructive testing equipment.

Experimental study on the mechanism of wheel-rail steels crack initiation and wear growth under rolling contact fatigue

A twin-roller fatigue test rig was used to reproduce the process of the coexistence of fatigue crack initiation and wear growth in the specimens from rail specimens. Based on the test rig situation, a prediction model was established according to the prediction method for coexistence of crack initiation and wear growth in rail. Both the results, including wear, crack initiation position and crack length in the specimens by the test and simulation were analyzed for verifying prediction model. The results show that there are many states such as micro-pores and micro-cracks on the contact surface at the same time. The crack initiation position is about 0.031mm from the worn contact surface, which is basically consistent with the experimental observation results. The surface crack length distribution is basically the same, distribution in 0.10~0.35mm. The predicted method of the coexistence of the crack initiation and wear growth is feasible.

Transverse Crack Detection of Rail Base Considering Wedge-Like Structure and Using a Bulk-Wave Electromagnetic Acoustic Transducer

In this article, the contributions are to further study and verify a bulk-wave electromagnetic acoustic transducer (EMAT) for the transverse crack detection of rail base and to propose an auxiliary method for achieving efficient detection. There is no verification for rail treated as a plate in the previous publication. For the verification, the wedge-like rail base is reasonably simplified into the front view and the side view to replace the 3-D finite-element model (FEM) simulation. In addition, the experiment to detect an artificial transverse crack of the standard rail specimen is carried out to verify the treatment of the wedge-like rail base. Both simulation and experimental results demonstrate that the wedge-like rail base can be inspected as a steel plate using a spiral-coil EMAT, but the only time of flight is hard to detect the transverse crack of the wedge-like rail base due to low SNR. For solving the problem of low SNR, this article proposes an auxiliary method of watching for the disturbances of the back-wall echo. Also, the limit condition of the auxiliary method is analyzed for practical applications.

A machine learning framework for guided wave-based damage detection of rail head using surface-bonded piezo-electric wafer transducers

Due to repeated heavy loads, environmental conditions and non-frequent monitoring, the rail is subjected to heavy damage resulting in sudden failure. Hence, a frequent, faster, and efficient monitoring strategy is required. This paper attempts to investigate the application of guided wave (GW) generated through surface-bonded piezo-electric wafer transducer (PWT) to detect damages in rail at high frequencies. Firstly, a combined experimental and simulation study is presented in an effort to understand the dispersion characteristics of guided wave and its interaction with head damages in a relatively small rail specimen. The numerical simulation results are validated with those obtained from the experiments showing a good agreement between them. Secondly, a framework based on the machine learning algorithm is proposed to efficiently detect damage in rail head. Numerous inseparable guided wave modes are observed at higher frequencies implying the inability to detect damage through specific mode. Therefore, a machine learning framework is trained using time, frequency, and time–frequency domain features of the signal. Total 672 numerical simulations of different types of damage with different severity and location in the rail head are carried out to train and validate the model. It is found that GW generated through surface bonded PWTs is able to detect minimum defect size of 5% of head area with 1 mm thickness. Finally, the proposed framework is tested using simulation and experiment results of arbitrary damage in the rail head. The error in estimating severity was found to be in the range from 2.00% to 16.67%.

Experimental Measurement of Residual Stress Distribution in Rail Specimens Using Ultrasonic LCR Waves

Longitudinal critically refracted (LCR) waves are considered bulk longitudinal waves and penetrate into an effective depth beneath the surface parallel to the material surface. Such LCR waves can be employed to measure residual stresses because the acoustoelastic effect is the basis for ultrasonic residual stress measurements. This effect is described by the relationship between change of wave travel time and stress applied when such waves propagate in a stressed medium. In this paper, stresses applied in a rail were evaluated by using a developed LCR probe. With this transducer, it was verified how the difference in the arrival times of the LCR waves showed a trend as the tensile stresses increased. The acoustoelastic coefficients were calculated using the relationship between the stresses and the travel times, and the residual stresses of the used rails were measured using these coefficients. In addition, the difference in residual stress distribution according to the characteristics of the wheel-rail contact surface was analyzed from the obtained residual stress value. It was concluded that this non-destructive evaluation technique using LCR waves could be employed for accurate stress measurement of rails because differences in stress applied to the rail can be detected.

Study of constitutive relation of rail decarburized layer

Rail decarburized layer has significant impact on the wear and rolling contact fatigue in the wheel-rail interaction. Due to the lack of constitutive relation of rail decarburized layer, it is impossible to analyse accurately the influence of rail decarburized layer on wheel-rail contact. To obtain the constitutive relation of this layer of decarburized non-uniform material, nano-indentation experiments were carried out at different vertical positions in the decarburization layer on a rail specimen with decarburization thickness of 0.55 mm. Young’s modulus and hardness were determined using Oliver and Pharr method. Axisymmetric two-dimensional finite element models were established in ABAQUS to simulate the nano-indentation loading process and the power law elastic–plastic stress–strain relationships were obtained for material at different vertical positions in the rail decarburized layer. A set of dimensionless functions were proposed for Young’s modulus, hardness, yield stress and strain hardening exponent at arbitrary depth in a rail decarburized layer or in a decarburized layer treated by rail pre-grinding. The results show that the Young’s modulus and hardness decrease from the rail bulk to the surface of the decarburized layer. The Young’s modulus and hardness near the surface are 11% and 35% lower than those in the rail bulk, respectively. However, the yield stress exhibits an increasing trend from rail bulk to the decarburized surface, where yield stress is 20% higher than the rail bulk. Analysis shows that the main reason that causes the reduction of hardness at the decarburized layer surface is the reduction of Young’s modulus but not the yield stress.

Development of multi-band tuned rail damper for rail vibration control

The intense interaction force between the wheel-rail causes the vibration of wheel and rail, and generates rolling noise. Increasing the rail damper is an effective way to suppress rail vibration. In this paper, a shear-type multi-band tuned rail damper (MTRD) consist of internal mass bars and external resilient layer to reduce rail vibration is proposed. Mass bars are wrapped inside resilient layer and placed along the length of rail. Resilient layer between two adjacent mass bars can enforce them perform shearing motion corresponding to the layer along the main vibration direction of rail. Different oscillation frequencies corresponding to different mass bars can be tuned by adjusting the structure of MTRD. It achieves an increase in the operating frequency band and a widening of the operating frequency range of MTRD. The influence of parameters of MTRD on its performance is investigated by the finite element method (FEM). One of three designed MTRD models is selected for prototype production after comparative analysis. Laboratory measurements are conducted on a rail specimen and 12 m track platform. Results show the main operating frequency band of designed MTRD is in the range of 200 Hz–800 Hz, achieves the goal of the desired frequency band. Frequency response function tests of rail on 12 m platform show the MTRD could suppress rail vibration in the range of 100–2000 Hz. To estimate the practical reduction effects of MTRD on vibration, a small radius curve of metro line is selected for field measurements. The measured track decay rate (DR) shows MTRD could increase DR at frequencies above 80 Hz with a max increment of 5 dB/m and 9.3 dB/m in vertical and lateral direction respectively. Reduction of rail vibration and rolling noise when trains pass is also measured. The overall vibration level of rail achieves a max reduction of 10.9 dB and 6.3 dB in vertical and lateral directions respectively. The overall sound pressure level is reduced by 5.9 dB(A) at the speed of 60 km/h.

Interrogating the health condition of rails using the narrowband Rayleigh waves emitted by an innovative design of non-contact laser transduction system

The article reports an innovative optical system that is designed to interrogate the health condition of macroscopically intact rail specimens by measuring its inherent nonlinearity using the narrowband Rayleigh waves. A line-arrayed pattern is developed through the optical system that generates narrowband Rayleigh waves with high power on the surface of the rail. As a result of lattice-anharmonicity, a second harmonic is produced in the wave that is sensed by a scanning laser Doppler vibrometer. The spectral amplitudes of the first and generated second harmonics are used to calculate the inherent nonlinearity using an amplitude-based nonlinearity equation. These measurements are carried out on the head, web, and foot of the rail. The performance of the non-contact experiment is also compared with that of a contact experiment carried out using wedge transducers. The experimentally evaluated nonlinearity of the rail steel is further compared with that obtained using a physics-based nonlinearity equation that relies on the higher-order elastic constants. Agreement of the results shows that the new optical system is effective in generating Rayleigh waves in rails and thereby measuring the inherent nonlinearity of the rail track. The estimation of inherent nonlinearity may help in diagnosing the health status of the macroscopically intact rail specimens in terms of their microstructural consistency and level of dissolved impurities before fixing them on a track.