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• Local rolling contact fatigue (LRCF) is reproduced by scaled twin-disc tests. • Critical indentations over which LRCF initiates are found for test discs. • Influence of indenter geometry on plastic strain of indentations is analyzed. • Transferrable critical plastic strain for LRCF initiation is obtained. • Size-dependent critical depths are proposed for indentations in practice. Scaled twin-disc tests are conducted to study the initiation of local rolling contact fatigue (LRCF) from indentations on discs of U71MnG rail indented by sharp tap tips. Critical depths over which LRCF initiates are found for indentations of different geometries under oil lubrication. Simulating the indenting process with a static finite element modelling approach, a critical plastic strain of 170% corresponding to the critical depths is determined. Assuming this critical strain is transferrable, size-dependent critical depths are further derived for indentations on actual rails using the same modelling approach. After verification by LRCF damages in practice, a linearized relationship between the critical depth and the characteristic length is proposed for actual indentations, being 2.3–3.2 mm deep for ones with a characteristic length of 4.0–10.0 mm. [ABSTRACT FROM AUTHOR]

[Display omitted] • Common aerospace-quality bearing steels were studied under RCF and torsion fatigue. • An analytical model was developed and considered Fatemi-Socie failure criteria. • Good corroboration existed between simulation life and experimental results. • Calibrated analytical model offers 2/3rds time save compared to experiments. In this investigation common aerospace-quality bearing steels was evaluated in rolling contact fatigue both experimentally and analytically. Three aerospace-quality bearing steels was procured and evaluated. First, the bearing steels were evaluated using a 3 ball-on-rod rolling contact fatigue test rig. Next, the same bearing steels were evaluated using a torsion fatigue test rig in order to quantify these materials' performance against the damage causing stress in RCF – shear reversal. The torsion S-N data provided the foundation for the determination of material constants that were used in a continuum damage mechanics finite element model (CDM-FE model), which considered the Fatemi-Socie critical plane approach as the failure criteria. These material constants captured the material cleanliness effect between the various materials investigated. Additionally, the CDM-FE model utilized Voronoi tessellations to capture the material topological effect. RCF simulations were performed at the same operating conditions as in the 3 ball-on-rod test apparatus. Torsional fatigue results from this investigation indicated which material possessed the largest ultimate shear strength, and which material performed best in low cycle and high cycle fatigue. The three ball-on-rod results established experimentally which material performed superior in RCF. It was observed that good corroboration existed between the analytical simulation life predictions and the 3 ball-on-rod experimental results. [ABSTRACT FROM AUTHOR]

• Multiaxial cyclic features and ratcheting behavior of U75V rail steel. • Introducing a new isotropic hardening to capture the multiaxial cyclic features. • Introducing Tanaka's parameter to describe the multiaxial ratcheting behaviors. • Revealing the effect of non-proportionally additional hardening on the RCF. U75V rail steel exhibits cyclic softening and hardening under uniaxial and multiaxial strain-controlled cyclic loadings, respectively. The ratcheting behavior of U75V rail steel depends on the loading paths due to nonproportionally additional hardening. New evolution equations incorporating Tanaka's nonproportional parameter are introduced into the isotropic and kinematic hardening rules of the cyclic plastic constitutive model to describe the cyclic softening/hardening features and multiaxial ratcheting behavior. The simulated results agree with the corresponding experimental results. A finite element model of wheel-rail cyclic rolling contact is established to investigate the nonproportionally multiaxial effect on the rolling contact fatigue life. [ABSTRACT FROM AUTHOR]

[Display omitted] • High-performance Fe-based coatings were fabricated on the surface of U75V rails by a diode laser. • A rolling contact fatigue test was proposed based on the Hertz contact theory. • Evaluation of wheel-rail rolling contact dynamics based on 3D FEM. • The high-performance Fe-based coating significantly improved the RCF and wear resistance of U75V rails. The microstructures of the Fe-based alloy laser cladding layer were characterized by optical microscope, scanning electron microscope and X-ray diffractometer. The load-bearing performance was evaluated and compared with that of the U75V rail. 3D finite element modelling was performed using the ANSYS software. It is found that the phases of the coating are α-Fe, Fe-Cr, Ni-Cr-Fe and Fe 2 B, Fe 3 Si precipitates. The average microhardness of the coating can reach HV455.2, which is higher than that of the heat affected zone (HAZ) and the substrate. The coating can effectively reduce the wear and rolling contact fatigue of heavy-haul rail. [ABSTRACT FROM AUTHOR]

Abstract: In this investigation an elastic–plastic Voronoi finite element (EPVFE) model for rolling contact fatigue of Hertzian line contact was developed. The EPVFE model coupled with damage mechanics approach is used to investigate rolling contact fatigue (RCF) of tribo-components. Mises based plasticity model with kinematic hardening was employed to incorporate the effects of material plasticity. The model considers both; stress and accumulated plastic strain based damage laws in the constitutive damage modeling. The results indicate that once a fatigue crack initiates within the domain, the fatigue damage induced due to the accumulated plastic strains around the crack tip drives the majority of the crack propagation stage. The results from this investigation reveal that depending on the contact pressure the crack propagation stage can constitute 15–40% of the total life. The spall shape, fatigue lives and Weibull slopes obtained from the EPVFE model correlate well with the experimental results. The developed model was also used to investigate the effects of initial material imperfections such as inclusions and elastic modulus inhomogeneity on the fatigue lives. The results indicate that material flaws within the domain lead to a significant decrease in fatigue lives and increase in life scatter. [Copyright &y& Elsevier]

Abstract: Shelling is one of the typical rolling contact fatigue (RCF) failures of railway wheels. Creepage between wheels and rails due to rolling radius difference in curves is inevitable on railway tracks. Therefore, there are tangential stresses and slip phenomena on wheel treads. Eventually, initiation of RCF cracks being the origin of shelling is accelerated by creepage. The objective of the present paper is to evaluate RCF property of railway wheel steel. The effect of the slip ratio on the RCF strength of the railway wheel steel was evaluated. RCF tests were conducted using two cylindrical contact specimens under water lubrication at a slip ratio of 0.0–1.0%. The range of slip ratio is determined to assume a creepage between wheel and rail during curving. As a result, it was found that the traction coefficient increased with the increase in the slip ratio, and the fatigue strength decreased simultaneously. The results were evaluated by a shakedown map and Hirakawa’s RCF map. Experimental fatigue limits could be expressed more precisely by the criterion of Hirakawa’s RCF map than that expressed by the well-known shakedown map. Stress intensity factors (SIFs) of the cracks produced by the RCF test were calculated by finite element (FE) analysis where the effect of water pressure due to the penetration of water into the cracks is taken into account. Two peaks of the maximum tangential SIF occurred during one cycle of rolling contact. The direction of the crack propagation was estimated by the maximum tangential stress criteria. The results of the RCF test showed that the cracks were initiated at the surface, propagated obliquely in the depth direction and then branched into two directions. One was towards the surface and the other was towards the depth. These two crack directions were inspected experimentally, corresponding to the estimated crack directions from the two peaks of SIF by FE analysis. The effect of slip ratio on RCF crack propagation was discussed by using the SIFs of the RCF cracks where water penetration into the cracks was considered. [Copyright &y& Elsevier]

Abstract: Crack nucleation, first spall generation and spall growth in rolling contact fatigue (RCF) are known to be highly sensitive to the heterogeneity of the microstructure. Yet the current state-of-the-art in the design of high performance bearing materials and microstructures is highly empirical requiring substantial lengthy experimental testing to validate the reliability and performance of these new materials and processes. We have laid the groundwork necessary to determine the influence of microstructure in RCF and related very high cycle fatigue problems. Crystal plasticity material models provide more realistic accumulations of localized plastic strains with cycling compare to homogenized J2 plasticity. With J2 plasticity, the bearing must be overloaded to capture significant plasticity near inclusions; with crystal plasticity, realistic bench test loads can be applied with plastic strain accumulation observed near inclusions in cases where RCF failure is anticipated. [Copyright &y& Elsevier]

Abstract: The risk for initiation of fatigue cracks in the rail head and web in the weld zone of a rail is studied. The interaction between the welding residual stress field and the stress field caused by service loads is simulated in a nonlinear finite element (FE) analysis where the welding residual stress distribution (shape) and magnitude, the service load magnitude and the material parameters used in the fatigue life estimation are varied. The initiation of fatigue cracks is assessed using the shear-stress-based multiaxial fatigue criterion proposed by Dang Van, and the propagation of fatigue cracks in the rail web is carried out using a Paris-type crack growth law. A discussion is presented of the interpretation of using the Dang Van criterion to assess crack initiation for stress–response load cycles with low shear stress amplitudes and high hydrostatic stress levels. In addition, the accuracy in the fatigue life assessment is evaluated by statistical uncertainty analysis where the variances according to the Gauss approximation formula are studied. The risk for fatigue crack initiation and propagation in the rail head and rail web, respectively, is enhanced due to the welding residual stress, and the uncertainty in load level dominates the uncertainty in the fatigue assessments. [Copyright &y& Elsevier]

• The state of residual stresses of on-line heat-treated rails was studied. • Rail manufacturing influences the stress state of rails after repeated wheel loads. • FP max differs with residual stresses applied or not. • The relationship between FP max and residual stresses is complicated. Rolling contact fatigue cracks shorten rail service life, and increase costs of rail maintenance and replacement significantly. The aim of the present study is to investigate the effect of residual stresses induced by manufacturing and repeated wheel-rail contact on fatigue crack initiation in rails. To this end, three-dimensional finite element models of rail on-line heat treatment, rail straightening, and wheel-rail contact were established to study the state of residual stresses of on-line heat-treated rails. The effect of residual stresses induced by rail manufacturing and repeated wheel-rail contact on fatigue crack initiation was analyzed based on a fatigue parameter FP max by Jiang–Sehitoglu low cycle fatigue criterion. Rail fatigue crack initiation mechanism under the combined action of wheel load and residual stresses was studied. The results show that residual stresses induced by rail manufacturing affect the stress state of on-line heat-treated rails after repeated wheel loads. The influence of residual stresses induced by rail manufacturing and repeated wheel-rail contact on the FP max of rails is significant. However, there is no positive or negative correlation between residual stresses and FP max of rails under different wheel loads and friction coefficients. [ABSTRACT FROM AUTHOR]