Rail Hardness Research Articles

A rapid in-situ hardness detection method for steel rails based on LIBS and machine learning

The railway, as a public transportation system, has played a significant role in global economic development. However, the pursuit of high speed and heavy load in trains has brought significant bending and shear stresses on the rails, making the performance of steel rails a notable focal point. The properties of steel rails are crucial factors determining the operational safety of high-speed trains, while the surface hardness is regarded as a key mechanical characteristic. This study is to develop a new rapid in-situ method to measure the hardness of steel rails, by employing Laser-Induced Breakdown Spectroscopy (LIBS) and specified analysis technology. Three distinct methods, including spectral line intensity ratios, plasma excitation temperature and machine learning, have been compared and analysed. Particularly, a multivariate model is established and optimized using the machine learning methods for U71Mn steel rail hardness analysis. In the machine learning algorithms, variance normalization is utilized, resulted in a significant improvement for the information retention during the data dimensionality reduction process. Subsequently, twelve algorithm combinations were explored, revealing that the Particle Swarm Optimization employed in Support Vector Regression (PSO-SVR) yielded the lowest mean squared error (MSE). Further refinement of the PSO-SVR was achieved through the incorporation of adaptive stochastic weights, resulting in an elevated coefficient of determination (R2) to 0.9876. Finally, the performance of the model on the new five samples was validated with an R2 of 0.9864. Otherwise, its potential applicability may be extended to broader domains, providing robust support for enhancing the precision and reliability of LIBS technology in surface hardness quantitative analysis.

Optimal ratio of hardnesses of wheel and rail steels, providing minimal wear of the wheel-rail friction pair

The determination of the optimal range of hardness of the hardened layer of the wheel rim and the tread surface of the rail head is considered in order to increase the wear resistance of the wheel-rail friction pair. Laboratory tests were carried out to establish the optimal ratio of wheel and rail hardness, which are tested under operating conditions. Keywords: hardness, wheel, rail, plasma hardening, crack resistance, fracture pattern, structure, martensite, troostite, sorbite. aliya-981@mail.ru

Effect of Rail Hardness on Wheel-rail Rolling Wear and Damage under the Moderate Sandstorm Environment

Effect of Rail Hardness on Wheel-rail Rolling Wear and Damage under the Moderate Sandstorm Environment

Study on wear and rolling contact damage mechanism between quenched U75V rail and wheels with different microstructures

Most existing wheel/rail hardness matching studies have been carried out using pearlite steels with different hardnesses; no relevant wheel–rail hardness matching research has been carried out for other microstructure types such as bainite and other tempered materials. In this paper, a CL60 wheel (pearlite) was quenched and tempered to obtain wheel materials with a certain hardness gradient, and matching tests between different wheel materials and a quenched U75V rail were carried out to explore the influence of wheel microstructures on wheel–rail damage. The results showed that with increasing tempering temperature, the wheel microstructure changes from tempered troostite to tempered sorbite, with ferrite changing from a needle shape to a multilateral shape; additionally, the cementite particles grow obviously larger, resulting in a gradual decrease in wheel hardness. With the increase in the wheel/rail hardness ratio, the wear rate of the wheel and wheel–rail system first increases and then decreases; the wear rate of tempered sorbite is the highest. Wear surface analyses indicate that typical peeling appears on the wear surfaces of the CL60 wheel as well as the coupled rail. Tempered sorbite shows slight peeling; however, severe peeling and delimitation occur on the wear surface of its coupled rail. Moreover, severe peeling and serious material delamination are present on the wear surface of tempered troostite, and typical peeling appears on its coupled rail surfaces. The fatigue crack initiation and propagation behaviors of wheel and rail materials are closely related to their microstructures. The cracks in pearlite always initiate on the surface and propagate along the ferrite line. Short and shallow fatigue cracks appear on the tempered sorbite with a high wear rate, and the cracks in the tempered troostite easily expand into the centre of the samples, indicating poor rolling contact fatigue (RCF) resistance. Therefore, the pearlite structure shows better comprehensive mechanical properties for wheel service; moreover, more attention should be given to wheel microstructure when conducting research on wheel–rail matching.

Experimental study on wear properties of wheel and rail materials with different hardness values

This paper aimed to investigate the wear properties of different wheel-rail material pairs with various hardness values. Twin-disc wear experiments were carried out via cross-matching five types of wheel material (ER7, ER8, CL60, C-class and D-class) and four types of rail material (U71Mn, U75V, PG4 and PG5). The effects of bulk hardness, post-test hardness, hardening ratio, and rail/wheel hardness ratio (HR/HW) on the wear rate of wheel and rail materials were analyzed.The results indicated that the wheel wear rates decreased with wheel bulk hardness and slightly increased with the rail bulk hardness. However, the rail wear rates decreased with the increasing wheel bulk hardness under 1% creepage and 1500 MPa contact pressure. In addition, both the wheel and rail wear rates showed increasing trends with the increase in wheel hardening ratio and the pre-test HR/HW. The surface damage of the harder C-class and D-class wheels, and the high-hardness PG4 and PG5 rail materials were relatively slight. The premium PG4 and PG5 rails possessed significantly shorter cracks than the base material pair (ER8-U71Mn), whereas, the fatigue cracks in U75V rail steel were relatively longer. The results will not only help optimize wheel and rail hardness matching, but also improve the prediction of wear and crack growth reliant on wheel and rail material properties.

Evaluation of the coefficient of friction of rail in the field and laboratory using several devices

ABSTRACTAccurate friction measurement is vital to apply appropriate friction management techniques to the wheel/rail interface. This work analyses different friction measurement techniques under a variety of conditions in the laboratory and the field. Tests have been carried out using a pendulum tester, hand-push tribometer, twin-disc machine and full-scale rig in the UK and Colombia for a variety of interfacial conditions and rail hardness. The pendulum has been found to be more sensitive to different conditions than the hand-push tribometer. This is due to the area that the pendulum sweeps being smaller, and so it can be more carefully controlled and therefore measure the surface condition being tested. This is in contrast to the push tribometer which needs a long section of rail to take a measurement. Twin-disc and full-scale rig creep curves show good agreement between each other.

Investigation of the influence of rail hardness on the wear of rail and wheel materials under dry conditions (ICRI wear mapping project)

Some railway managers and practitioners fear that introducing premium rail materials will have a detrimental effect on the wheels of trains that use the line. A review of relevant investigations across all scales in the laboratory, and in the field has been carried out. This showed that, as rail hardness increases, its wear, and overall system wear reduces. Wheel wear does increase with increasing rail hardness, but only for wheels running on rails that are softer than them. Similar trends were observed in all studies, so it seems that the fears were unfounded.While the wear trends appear well characterised some issues have been identified. One relates to the varying work hardening capability of wheel and rail materials. Often only bulk hardness is quoted, but work hardening can increase material surface hardness by up to 2.5 times and make materials that were initially softer, harder than the opposing material. Another related issue is test length. It is essential that enough cycles are applied such that the materials reach steady state wear, i.e., the point at which work hardening has reached its limit. In previous work it is not always clear that steady state wear has been reached. Some gaps have been identified in the current knowledge base, the largest of which is the failure to determine which mechanisms lead to the wear trends seen.Analysis of recent work on different clad layers on rail discs and premium rail materials allowed some of these gaps to be addressed. Results indicated that opposing wheel material hardened to the same level independent of rail hardness. Wheel wear is therefore stress driven under the conditions used, and dictated by the wheel material properties only. At higher slip levels relationships become less clear, but here temperature and therefore hot hardness is most influential and is as yet uncharacterised.

EFFECT OF LASER QUENCHING ON MICROSTRUCTURE AND PROPERTIES OF THE SURFACE OF TRACK MATERIALS

With the rapid development of rail transit, the wear problem of track has become a serious challenge. Laser quenching is a new surface modification process, and it is expected to improve the service life of the track. Laser quenching was carried on the surface of rails by using 6[Formula: see text]kW fiber laser. The microstructure, hardness, wear resistance, and contact fatigue resistance (CFR) of the phase transformation hardening layer were studied by optical microscope (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), microhardness tester, and wear tester. The results show that the microstructure of the hardened layer is composed of fine martensite and a small fraction of retained austenite. The microstructure of substrate is pearlite and ferrite. The hardness of rails quenched by the laser increased nearly two times than that of the un-treated track materials. When the laser power is 1000[Formula: see text]W, the depth of hardened layer reaches 0.8[Formula: see text]mm, and the wear resistance of hardened layer increases 167% than that of the substrate. The number, length, and depth of fatigue cracks decreased on the cross-section of worn rails after laser quenching, which indicates that laser quenching can improve the CFR of rails.

A novel laser surface compositing by selective laser quenching to enhance railway service life

With the rapid development of high-speed and heavy-haul trains, it is challenging to improve the service life of rails. In order to ensure toughness and contact fatigue resistance (CFR) of rails, the present technical standards restrict the hardness of rails to be beneath HB400 and forbid the martensite structure in rails. In this study, a novel laser surface compositing (LSC) based on selective laser quenching is proposed to strengthen the rails. By designing the hardening area sizes and proportions rationally, the wear resistance of the rails is enhanced by 2.2–3.5 times without noticeably deteriorating their contact fatigue resistance (CFR). Furthermore, the wear and contact fatigue behaviours of the LSC rails were investigated systematically.

Effects of Rail Hardness on Rail Wear and Head Check Initiation

In China, rail head check on heavy-haul railways is the main type of rolling contact fatigue defect, especially since the advent of rail with good wear resistance and high hardness. The influence of hardness on rail wear and head check was explored by use of a method to predict rail head check initiation by considering wear. The proposed method combined a profile wear model based on the Archard wear model and a prediction model for head check initiation life based on the critical plane theory, which used the worn profile iterations and the accumulation of fatigue damage as determined by the amount of wear. An analysis of the head check initiation characteristics of the as-rolled rail, U78CrV/U76CrRE, and the heat-treated rails, U71Mn, U75V, and U78CrV, was performed by considering wear. Results indicated that, when wear is taken into consideration, head check in all four kinds of rails started at the subsurface of the rail, at a depth of 1 to 2.5 mm (measured from the top of the rail) and at a lateral distance of 15 to 18 mm from the rail center; these results were more similar to field observations than results without consideration of wear. When all other conditions were identical, the rail with the highest hardness had a lower wear growth rate and a longer period before head check initiation. Therefore, it was determined that the rail with the highest hardness, U78CrV heat-treated rail, was more resistant to wear and head check initiation than were the other three rail grades.

Field and laboratory investigation of the relationship between rail head check and wear in a heavy-haul railway

Head checks (HCs) are widespread in railway tracks. They can cause rail fracture. In theory, and under some laboratory conditions, a proper amount of natural wear exists which is just enough to suppress HC initiation and growth and is called magic wear rate. It will minimize the costs of rail maintenance. In practice, such magic wear rate still seems elusive. This paper is an attempt to investigate the feasibility of magic wear rate under operational conditions. To such an end, the growth of and competition between HCs and wear in the high rail of a curve of a heavy-haul railway is analyzed. The length and depth of the HCs were measured by laboratory examination and image recognition from rail specimens sampled at different traffic gross tonnages. Rail wear was calculated from the measured rail profile. Three phases of HCs and wear evolution and competition were identified. It was found that the wear rate was almost constant for a broad range of traffic tonnages, even though the rail hardness varied significantly. With such a wear rate the initially severe HCs were reduced in size, indicating the feasibility of engineering magic wear rate to avoid HCs by the proper design or selection of the materials and profiles of the rails.

Experimental simulation and prediction of wear of wheel flange and rail gauge corner

Abstract The experimental research on the wears of wheel and rail has been carried out using a large rolling-sliding contact test machine with the actual profiles of wheel and rail. Primarily, the effects of axle load, the angle of attack, rail hardness and lubrication on wear behaviors of wheel flange and rail gauge corner have been particularly focused in research. Based on those experimental results, the Archard wear coefficients of Japanese track were calculated under various conditions. A wear prediction model of rail profile taking into consideration contact stress, slip ratio at contact patch and material hardness was established based on the experimental results and the wheel–rail contact analyses. The prediction results were compared with the measured values of the actual rail and the effectiveness of wear prediction methodology was verified for the actual railway system.

Characterization of hypervelocity gouge craters in rail conductors

Gouging is a frequently encountered rail damage phenomenon and has been observed in several large-bore guns. In this study the size and number of gouges have been determined as a function of position and velocity. Detailed analysis was performed on rails recovered from single shot experiments. Rail hardness and surface and microstructural characteristics of gouges have been determined and analyzed to relate materials properties to gouge formation. We observed hardening and plastic flow of copper beneath a gouge crater. Transmission electron microscope studies showed twinning in copper. We find that gouge sizes are closely related to armature contact size. The gouge is generally shorter than the contact length and no wider than the contact. Our study shows that rail hardness is affected in the vicinity of a gouge. After gouges are formed on a rail, the hardness is no longer uniform and performance of the rail conductor is affected.

A comparison of the wear behaviors of six elemental wire conductors

The goal of this work is to relate properties of armature materials to observed armature performance. In simple railgun electromagnetic launchers, the wear behavior of the widely-used aluminum alloys as sliding electrical contacts on copper rail conductors leads to a progressive change on the rail conductor surface as debris from the armature/rail interaction adheres to the rail. Here, the authors compare the behavior of wires of silver, copper, aluminum, nickel, molybdenum, and tantalum as armature conductors on ETP copper rail conductors. Some of these wires were also tested on molybdenum rail conductors to assess the effects of rail hardness. The emphasis is on the effect of current/contact under current densities greater than 1 kA/mm/sup 2/ on the wear behavior and eventual failure of the armature wire conductors. Characteristics of material transfer and a descriptive model are presented. The value of temperature-dependent properties such as hardness and surface tension are related to materials transfer of the wire conductors as the contact surface deforms and flows in response to specific driving current profiles. >

Wear of Steel in Combined Rolling and Sliding

An experimental laboratory investigation of the wear of railroad rail and car wheel materials has shown that increasing the hardness of rails will reduce rail wear but will increase wheel wear. Similarly, harder wheels will reduce wheel wear, but at the expense of increased rail wear. Decreasing relative humidity will substantially increase wear of both materials and will accentuate differential hardness effects. A theory is developed which explains the humidity effects on wear in terms of cyclic plasticity. The increased friction at low humidity brings the subsurface plastic zone to the surface. Presented as an American Society of Lubrication Engineers paper at the ASME/ASLE Lubrication Conference in San Francisco, California, August 18–21, 1980.