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Decarburization means carbon in rail material lost in the hot rolled process. It changes the microstructure of rail materials and will influence their rolling contact fatigue (RCF) characteristic. The objective of this study is to explore the effect of decarburized layer on rolling contact fatigue and propagation mechanism of crack under the wet condition using a rolling-sliding wear testing machine. The results show that the crack growth rate on the decarburized rail roller is over 4 times than that on the non-decarburized rail. Small pitting presents on the non-decarburized rail roller, which is dominated by transgranular crack. While, long mouth surface crack dominates on the decarburized rail roller and the cracks mainly grow along the ferrite line or the grain boundary. With the cycles increasing, the surface cracks of decarburized rail roller gradually break and forms spalling damage, eventually expands to bulk spalling. Meanwhile, the crack growth mechanism changes back to the transgranular propagation and propagates in depth with a large angle when the decarburization is worn off. [ABSTRACT FROM AUTHOR]

Decarburization can remain on the surfaces of rail head steels and affect their wear and damage processes. The current research explored the influence of a decarburized layer on wear resistance and damage behavior of rail materials using a rolling–sliding wear testing machine. A decarburized layer decreases the hardness and wear resistance of rail steels, and the wear rate of a decarburized rail is over twice that of the same steel without decarburization. Multi-layer peeling appears on rail rollers without decarburization, but a decarburized layer changes the damage mechanism of the rail steel. With an increase in the depth of decarburization, the damage of rail roller turns from major spalling to pitting and peeling. In addition, surface fatigue cracks become more serious as depth increases. By contrast, shallow decarburization has little effect on rolling contact fatigue (RCF) of the rail material. Only when the depth of the decarburization exceeds a certain thickness (i.e., about 0.5 mm based on the present results), RCF damage sharply worsens as decarburization depth increases. Furthermore, adhesive wear features are obvious on the rail roller only when a decarburized zone remains at the wear surface. [ABSTRACT FROM AUTHOR]

• The wear performance of the defected rail materials under various slip ratios and contact stresses was investigated. • The surface damage of the defected rail materials under various slip ratios and contact stresses was studied. • The effect of slip ratio and contact stress on crack propagation mechanisms near the dent was discussed. The defects on rail surface may have negative effects on the rolling contact fatigue (RCF) performance of the rail materials. This investigation researched on the RCF behaviors of the defected rail materials under various slip ratios and contact stresses. The results show that both the wear loss and the average crack length increase if the slip ratio or the contact stress increases. Moreover, the surface damage characteristics change from simple adhesion spots to significant fatigue crack grouping when slip ratio and contact stress rise. Finally, the experimental results also highlight that the slip ratio provides the deformation area for crack initiation whereas the contact stress accelerates the crack propagation by emphasizing the geometric effects. [ABSTRACT FROM AUTHOR]

Defects such as dents on the rail surface might induce severe rolling contact fatigue (RCF) and then threaten the running safety of railway vehicles. This study aims to explore the initiation and propagation of RCF cracks around dents with different sizes through observing both surfaces and cross-sections of the defective rail. The experiments are conducted on a wheel/rail twin-disc machine. Results indicate that the microstructure evolution process around the dent can be divided into three main stages, namely crack initiation, crack propagation and dent removal. Dents in different sizes act very similarly in each stage, including the position, the crack growth path and the final appearance after the dent has been fully worn off. However, dents in different sizes cause different lifetimes of crack initiation and different lasting times of dents at each stage. For the lager dent, cracks initiate later but propagate for a longer time period, so the dent size plays an important role in the RCF evolution process. • Dents with three different sharpness were made on the rail sample. • The evolution process of microstructure of defected rail material was studied. • Dent size plays a vital role in the wear and RCF damage of defected rail. • RCF cracks propagate in a "C" shape at the leading edge of dent. • Shaper dents initiate cracks later but need more time to be worn off. [ABSTRACT FROM AUTHOR]

Surface dents on railroad rails may be caused, for example, by the drop of freight goods or the impact of ballast rocks and may have a deep effect on the rail service life. To better understand this problem, this investigation aims at exploring the rolling contact fatigue behavior of the rail materials (as, for example, PD3 steel) after being impacted by two kinds of hard bodies: a simple spherical steel ball and a more realistic ballast rock. The results show that the residual tensile stress, which is distributed on the shoulders of the dent, decreases the rolling contact fatigue (RCF) resistance of the material around the dent. Moreover, the unbalanced wear behavior between the two shoulders of the dent makes the situation even worse on the side of the dent where the tangential force acts firstly. Finally, due to the higher martensite hardness with respect to the matrix material, the crack propagates faster around the dent in presence of white etching layer on the bottom of the dent itself. • The residual tensile stress on the shoulders of rail dents was modelled through FE models. • The unbalanced wear on the shoulders of the rail dent leads to a sever fatigue damage on one side of the dent. • The crack growth mechanism on two typical dents was studied in detail. [ABSTRACT FROM AUTHOR]

The objective of this study is to explore the rolling contact fatigue (RCF) behaviors of wheel materials with a flat under different braking conditions using a JD-1 wheel/rail simulation apparatus. The results indicates that the microstructure of wheel flat zone is composed of white etching layer (WEL), transition layer (TL), plastic deformation layer (PDL). The martensite caused by thermal effect is clarified in the WEL of wheel flat zone. There are three kinds of damage forms including the material accumulation, plowing and peeling in the front, the middle and the back of wheel flat zone, respectively. Fatigue cracks caused by impact only initiate and propagate in the back of wheel flat zone. Meanwhile, with the braking speed or braking time increasing, the fatigue damage of wheel flat zone worsen and the thickness of WEL increases, which brings an increase of fatigue crack length and propagation angle. [ABSTRACT FROM AUTHOR]

The surface crack of wheel/rail is a significant problem affecting the safety and maintenance of railway. This study presents the experimental results to explore the formation and damage mechanism of rolling contact fatigue (RCF) surface cracks of wheel/rail materials under dry condition. The results indicate that the surface cracks mouths on the rail roller are perpendicular to the resultant direction of shear force. Fatigue cracks grow along a larger angle to depth on the rail rollers than on the wheel rollers due to the difference of materials. Meanwhile, there are visible subsurface and secondary cracks as well as lamellar structure cracks. The vertical force changed in the later 1.5×10 5 cycles leads to a significant difference in the cracks propagation. [ABSTRACT FROM AUTHOR]

The objective of this study is to evaluate the effect of slip ratio on the wear and rolling contact fatigue (RCF) of wheel/rail materials using a rolling–sliding wear testing apparatus. The results indicate that two wear types are presented in terms of wear rate: type I (mild wear) and type II (severe wear). In type I wear, cracks propagate parallel to the surface. While in type II, the peeling is aggravated and spalling can be observed. With the slip ratio increasing, the wear mechanism of rollers transforms from slight oxidation wear and peeling to severe fatigue wear and spalling. Due to the mild wear and light plastic deformation in type I, the angle and depth of cracks show no obvious differences between the wheel and rail rollers. The crack depth and angle increase in type II wear owing to severe plastic deformation, while the depth is smaller on the wheel rollers. The size of flake wear debris presents an increasing trend and the main composition is Fe 2 O 3 and metallic iron, and the content of iron diminishes with increasing oxidation. [ABSTRACT FROM AUTHOR]

One of the issues in the railway field is the damage caused by wear and RCF which deeply affects wheel and rail. These phenomena are closely connected and directly impact both on vehicle dynamics (comfort, stability, safety, etc.) and on the costs (line management, maintenance, etc.), decreasing the useful life of wheel and rail. To face these problems and detect abnormal operating conditions, this work aims at developing a modelling approach for railway and tramway applications that effectively combines wear and RCF models. The former has been validated by means of on-field experimental data whereas the latter through specific laboratory tests carried out on a dedicated test-rig. The proposed approach is capable of simultaneously predicting both the profiles shape evolution due to wear and the total RCF damage along the wheel and rail profiles, reaching a good compromise between accuracy and efficiency. Thanks to the high numerical efficiency, the wear-RCF model can be easily implemented into complex multibody models of railway and tramway vehicles to perform large-scale simulations. • The new modelling approach allows the simultaneous calculation of wear and RCF on wheel and rail. • The model can be implemented into complex multibody models of railway vehicles. • The new RCF model evaluates the crack dimensions and the position of the crack along profiles. • The RCF law is experimentally developed through a specific test campaign on test rigs. [ABSTRACT FROM AUTHOR]