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In order to study the rail corrugation phenomenon with the wavelength of 160-250mm in the steel spring floating slab track of a certain subway straight section, a rigid-flexible coupling dynamics model of the vehicle-steel spring floating slab track is established based on the finite element theory and the vehicle-track coupling dynamics theory. From the point of view of the vibration characteristics of track system and the contact characteristics of wheel and rail, the causes and mitigation measures of rail wave wear are studied by taking the rail wear power as the evaluation index. The generation of rail corrugation may be related to the transverse co-direction/reverse bending vibration modes of the rails on the left and right sides of the 8-15 order, the vertical bending mode of the track plate of the 8-9 order, and the torsional vibration mode of the track plate of the 6-8 order. Under the premise of not affecting driving safety, wear power at the rail wave wear frequency can be reduced by taking the vertical stiffness of the fastener 10~30 MN/ m, the vertical damping of the fastener more than 20 kN·s/m or the lateral damping of the fastener 30 kN·s/m, so as to slow down the development of rail wave wear. [ABSTRACT FROM AUTHOR]

• A ratcheting mechanism-based numerical model was applied to predict damage initiation in twin-disc tests of premium rail steels. • Wear- and RCF-dominated damages are distinguished by the depth of the ratcheting mechanism-based damage initiation locations. • A higher creepage results in a shallower damage initiation location and a shorter damage initiation life. • The initial wear rate increases with a higher creepage for wear-dominated damage. • HE2 rail steel presents the longest damage initiation life and the lowest initial wear rate compared to HE1 and LAHT. This work presents a ratcheting mechanism-based numerical model to study the initiation location and initiation life of rolling contact fatigue (RCF) or wear damage and the initial wear rate of premium rail steels under the laboratory twin-disc test conditions. Twin-disc tests are widely used in the studies of rail steels due to their ability to reproduce critical aspects of full-scale wheel-on-rail contact under controlled conditions and a relatively short test period compared to field tests. This study introduces a computational model to simulate the cyclic rolling contact for three premium rail steels (HE1, HE2, and LAHT) against wheel steel AAR Class-C under twin-disc test conditions. The cyclic rolling contact is achieved by repeatedly moving a non-Hertzian distribution of contact pressure and the calculated longitudinal surface traction upon a segment of the circumferential surface of the lower disc until a stabilized maximum ratcheting strain rate is reached. The RCF or wear damage initiation location is determined by the location showing the stabilized maximum ratcheting strain rate, and the damage initiation life is estimated by applying the ratcheting failure mechanism. Wear and RCF damages are distinguished by the depth of the damage initiation location. Wear damage is dominant when the location is near the surface. Otherwise, the damage will be RCF-dominated. The initial wear rate due to wear-dominated damage is estimated by identifying a critical profile and affected volume of worn material within the ratcheting strain rate field. The predicted initial wear rate is compared with the experimental result of the examined contact pair. This research can assist in a more profound understanding of the experiment results of a twin-disc test and provide a numerical basis for an experimental twin-disc test design. Furthermore, it may provide significant references for choosing rail steels. [ABSTRACT FROM AUTHOR]

Sliding wear tests were carried out with a pin-on-disc machine to study the tribological behavior of EN ER7 and AAR CLASS B wheel steels paired with cast iron and organic composite brake block materials. The contact stress was 0.61 MPa and the sliding speeds were 0.52 m/s and 0.62 m/s. The wear behavior was related to the friction coefficient recorded during the tests, the specific wear rate calculated at the end of the experiments and the microhardness profile obtained on the cross-section of the wheel pins. The worn surface and cross-section of the pins were analyzed by optical and scanning electron microscopy to investigate the main damage mechanisms. A stationary finite element model was proposed to estimate the contact temperature of the pin. The test results showed the same damage mechanisms for both steels, such as oxidative wear, delamination, abrasive wear and material transfer from the brake disc to the wheel pin, which led to adhesive wear. Overall, ER7 steel performed better when paired with the composite material as the pins showed lower specific wear rate; on the contrary, CLASS B pins had lower specific wear rate when the counterpart was cast iron. The tribological behavior of both steels was not influenced by the sliding speed. The simulations showed that the contact temperature was always higher when the disc in composite material was used, regardless of the pin material. Furthermore, ER7 steel demonstrated lower contact temperatures than CLASS B due to the lower friction coefficients in the experiments. • The wheel/brake tribology was investigated using a pin-on-disc setup. • ER7 and CLASS B steels were tested against cast iron and organic composite material. • The damage mechanisms of the wheel steels were identified. • A finite element model was proposed to estimate the steel pin contact temperature. • The contact temperature was always higher in the tests with the composite discs. [ABSTRACT FROM AUTHOR]

There is an increased demand for railway services, which has resulted in an increase in speeds and axle loads. The increase in axle loads and speeds have resulted in an increase in severity of wheel and rail wear. The aim of this work was to investigate wear and rolling contact fatigue (RCF) performance of class B wheels against R350HT and R260 rail under different slip ratio using a twin-disc setup. The results showed that severity of wear was heavily dependent on slip ratio. It was found that class B wheels' wear rate was better against R260 rail than against R350HT rail. Three wear regimes were identified from plots of wear rate versus wear index (Tγ/A) being mild, severe and catastrophic. • Wear performance of class B wheel against R260 and R350HT rail steels was investigated across different slip ratios. • Slip ratio influences coefficient of friction, wear rate and depth of plastic deformation on both wheel and rail steels. • Three wear regimes were identified being mild, severe, and catastrophic [ABSTRACT FROM AUTHOR]

The effects of slippage on rolling contact of pearlitic wheel–rail steels (rail-U71Mnk/wheel-ER8 steels for China high-speed railway) have been investigated in the laboratory on a twin disc tester under different slippages (varying from 0.17%, 0.91%, 2.38%, 4.55%, to 9.43%). The morphology of the worn surface and the cross-sections have been detected by scanning electron microscopy (SEM), and the variation of chemical composition on worn surface and the phase structure of debris were detected by the electron energy dispersive spectrometer (EDS) and X-ray diffraction (XRD), respectively. The results indicate that, as the slippage increased, the friction coefficient raised up at steady state of the rolling contact friction as well as the wear volume. With the increasing slippage, the damage of wear zone was transformed from mild to severe, which presented the typical fatigue features: delamination and sub-cracks. The worn surface was covered with a thin tribo-film under a small slippage condition. With the increase of slippage, the oxidation wear behavior weakened and the size of the debris particles became larger. As the slippage increased, the mainly wear mechanism transformed from the oxidation wear to the fatigue wear (delamination mechanism) and then into the abrasive wear accompanying delamination. [ABSTRACT FROM AUTHOR]

Downsizing in mechanical systems requires effective lubrication strategies to ensure that increased contact stresses do not cause critical material failure during operation. Additionally, eco-toxicological considerations are becoming increasingly important. In this regard, the goal of this investigation is to transfer the running-in phase into the final step of the mechanical finishing process through the targeted pre-conditioning of novel, high toughness steel bearings without thermo-chemical treatments and compare these to conventional, case-hardened steels. Pre-conditioning involved implementation of the ecologically sustainable, bismuth-based additives to generate chemically reactive tribofilms on slip-rolling contacts by using a formulation with a high concentration of tribofilm forming additive. Generated tribofilms were analyzed by Raman spectroscopy to elucidate their molecular composition and, ultimately, determine the reaction mechanisms of bismuth-based tribofilm formation. Tribofilm-protected samples were subjected to slip-rolling endurance testing in a factory fill engine oil without pre-conditioning additives to determine the influence of pre-conditioned tribofilms on friction behavior and wear performance. It was observed that pre-conditioned tribofilms from the bismuth-based additives were able to yield lower coefficients of friction (COF) and profilometric wear coefficients than for steels without pre-conditioning. Moreover, COF values under mixed/boundary conditions approaching and even less than 0.04 were achieved, thereby rivaling DLC-coated alloy equivalents. [ABSTRACT FROM AUTHOR]

Systematic experimental investigations were conducted to study the damage behavior of rail steels with eutectoid and hypereutectoid microstructure under different axle load and curve radius conditions. The wear resistance and resulting failure mechanism, as well as subsurface crack development were evaluated by wheel/rail rolling contact test rig, which can realize a broad range of working conditions from mild condition to harsh condition. Results demonstrate that the wear resistance and rolling contact fatigue (RCF) damage depend on not only the working conditions employed, but also the microstructures. With the increase of axle load and reduction of curve radius, the wear rate increases for both rail steels. Damage mechanisms for the two rail materials are mainly surface fatigue cracks and delamination, which become much serious from the mild condition to harsh condition. The hypereutectoid rail possesses a better wear resistance than eutectoid rail in general. Wear regime map suggests that the hypereutectoid rail did not have a catastrophic wear region, but can be observed in eutectoid rail. The subsurface analysis shows that the working condition has a significant impact on surface crack development depending on specific microstructure types. The hypereutectoid rail is more suitable for harsh working conditions than eutectoid rail. • Wear and damage of two rail materials were investigated under harsh conditions. • High axle load and small curve radius play great effects on damage of rail materials. • Rail steel microstructure affects the fatigue cracks development. • Hypereutectoid rail did not have catastrophic wear region as observed in eutectoid rail. • Hypereutectoid rail is more suitable for harsh conditions than eutectoid rail. [ABSTRACT FROM AUTHOR]

Abstract: Fretting wear proceeds through particle detachment from the contacting surfaces which, while trapped in the contact zone, can affect the frictional and wear response. Ball-on-flat fretting experiments were carried out between steel specimens under gross slip regime. A transition in the coefficient of friction was linked to a critical contact pressure. The microstructure and chemical composition of the third body evolve with the applied pressure. The evolution of the friction coefficient is strongly dependent on the third body properties. The wear is controlled by the applied load and thus the real contact area within the wear track. [Copyright &y& Elsevier]

Abstract: Four-ball testers are widely used for determining the rolling contact fatigue life of bearing components. The tester simulates the rolling conditions in the bearing where the upper ball and the cup simulate the inner and outer rings, respectively, and the planetary balls represent the rolling elements in the bearing. However, in many studies the upper ball is utilized as the ball whose rolling contact fatigue (RCF) life is investigated, mainly to speed up the fatigue process. In this paper, a four-ball tester is used to study the effect of ball configuration, i.e. upper ball versus the planetary ball, on the RCF life. It was observed that the 52100-steel upper ball''s L 10 life is 7.4 times shorter than that of 52100-steel lower planetary balls. For M50 tool steel, the L 10 life of the upper ball was 5.9 times shorter than that of the lower planetary ball. The lesser number of stress cycles per revolution of tester''s spindle and the skid of lower balls resulting in rolling on multiple rolling tracks are the contributing factors to the longer RCF life of planetary balls. [Copyright &y& Elsevier]

Abstract: Driven by a requirement for increased performance and cost-effectiveness, the basic pearlitic microstructures of rail steels are being progressively refined and novel microstructures are being developed. With such progress, increased attention must be paid to potential ‘weak spots’ in the microstructure such as non-metallic inclusions. For the past few decades, rail steels have become progressively cleaner with regard to harmful brittle inclusions, however the effect of rolling–sliding contact forces on nominally benign, ductile inclusions requires further consideration. This work examines the characteristics of ductile, Mn-based inclusions in used rail and rail test discs. Where the structure near-surface has been subject to a high component of transverse creepage, ductile, axially aligned inclusion ‘stringers’ become strain-flattened to form planes of weakness along which micro-cracks initiate and propagate, thus facilitating wear and rolling contact fatigue (RCF) cracking. The progression of shape change of these ductile inclusions approaching the contact surface has been examined by optical and electron microscopy including focussed ion beam (FIB) analysis. As-manufactured ductile inclusions shapes and distributions have also been surveyed with respect to the (geographical) source of the rail steel. Comparative data for these different steel sources are given. [ABSTRACT FROM AUTHOR]

Plasma selective quenching is a technology which can significantly improve the wear resistance of rail material. However, there are few studies on damage characteristics of rail materials with plasma selective quenching (PSQ). In this study, the influence of PSQ on wheel-rail wear and damage characteristics was studied. The research results show that PSQ has a great influence on damage characteristics of rail materials; PSQ can significantly reduce rail wear; The damage characters of quenched specimens could be divided into three stages: quenched zone wear, quenched zone wear and spall pits, substrate wear. •The influence of the plasma selective quenching on wheel-rail wear and RCF damage was studied. •An electron microscope was used to observe the damage of the wheel/rail surface. •Plasma selective quenching has a great influence on RCF damage of wheel and rail. •An excessive proportion of the quenched area of rail leads to increased wheel wear. [ABSTRACT FROM AUTHOR]

A multi-step FE modeling strategy has been proposed to predict the temperature evolution, thermo-mechanical response, surface fatigue life and wear behaviors in railway rail for multi wheel passages. Equivalent contact pressure and heat source were coupled and moved simultaneously on rail surface to achieve a balanced advantage of low computational cost and high accuracy. Wheel configuration at locomotive plays a significant role on rail temperature. The highest temperature of 776.05 °C was developed with a slip ratio of 9.43% after 9 wheel passages. Rolling contact fatigue life of rail material decreased quickly with slip ratio due to significant thermal softening effect. Transition from mild to severe wear was found at slip ratio of 2.38% according to the corresponding rail flash temperatures. • A modelfor multi wheel passages of train locomotives considering both contact pressure and thermal effects was proposed. • Practical scenario of two locomotives was introduced to study the temperature evolution on rail surface. • Relation between slip ratio and rolling contact fatigue life of rail material was predicted. • Wear of rail was mild when slip ratio was ≤2.38% but transited into severe wear when slip ratio was higher. [ABSTRACT FROM AUTHOR]