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In this study, finite element method (FEM) is applied to investigate the effect of material defect orientation on subsurface crack initiation in rolling bearings. First, the history of stress intensity factors (SIFs) of a subsurface cubic material defect is calculated. SIFs calculation is conducted when it is parallel to the rolling surface of a bearing ring ( φ = 0 ∘ ) under a ball rolling on the ring. Then, the effect of defect orientation, varying from φ = 0 ∘ to φ = 30 , 45 and 60 ∘ , on the history of SIFs is investigated. It is deduced that changing the defect orientation results in a threefold increase in the equivalent SIF range compared to parallel orientation. [ABSTRACT FROM AUTHOR]

In this study, finite element method (FEM) is applied to investigate the effect of material defect orientation on subsurface crack initiation in rolling bearings. First, the history of stress intensity factors (SIFs) of a subsurface cubic material defect is calculated. SIFs calculation is conducted when it is parallel to the rolling surface of a bearing ring ( φ = 0 ∘ ) under a ball rolling on the ring. Then, the effect of defect orientation, varying from φ = 0 ∘ to φ = 30 , 45 and 60 ∘ , on the history of SIFs is investigated. It is deduced that changing the defect orientation results in a threefold increase in the equivalent SIF range compared to parallel orientation. [ABSTRACT FROM AUTHOR]

To manufacture semi-finished hybrid workpieces with tailored properties, a finite element simulation assisted process chain design was investigated. This includes the process steps of cross wedge rolling, hot geometry inspection, induction hardening, and fatigue testing. The process chain allows the utilisation of material combinations such as high-strength steels with low-cost and easy to process steels. Here, plasma transferred arc welding is applied to supply the process chain with hybrid specimen featuring different steel grades. An overview of the numerical approaches to consider the various physical phenomena in each of the process steps is presented. The properties of the component behaviour were investigated via the finite element method (FEM) and theoretical approaches. At first, the manufacturing of a hybrid workpiece featuring a near net shape geometry with improved mechanical properties due to recrystallising the weld was computed, using the example of a cross wedge rolling process. The rolling process was designed by means of FEM to determine suitable process parameters and to reduce experimental testing. An optical multi-scale geometry inspection of the hot workpiece is meant to be carried out after each manufacturing step to detect potential undesired forming or cooling-induced deformations. Due to the heat transfer from the hot component to the ambient medium, an optical measurement is affected by the developing inhomogeneous refractive index field in air. To gain a basic understanding of the refractive index field and induced light deflection effects, computations were conducted using heat transfer and ray tracing simulations. According to the proposed process route, a subsequent local heat treatment of the hybrid component is required to adapt the mechanical properties by a spray cooling assisted induction hardening. The heat treatment step was computed via a 2D FEM calculation. After finishing by machining, the hybrid material shafts are examined in fatigue tests under load conditions. To predict the component's lifetime under rolling contact fatigue, a damage accumulation model was combined with an FE simulation. The resulting residual stress state after quenching and the geometry after the finishing process were used as input data for the fatigue life calculations. [ABSTRACT FROM AUTHOR]

Nowadays, micropitting is perceived as one of the prevalent wear mechanisms, which is responsible for the breakdown of high power density (power throughput/weight) machines. The current work demonstrates the evolution of surface damage and surface topography parameters during micropitting tests. The test surfaces are examined at different load stages utilizing 3D optical profiler, optical microscope, and scanning electron microscope. The effect of slide‐to‐roll ratio (SRR) on surface damage and topography parameters is also presented. It is observed that the severity of micropitting increases with an increase in the number of cycles. It is concluded that surface bearing index (Sbi), kurtosis (Sku), maximum valley height (Sv), and autocorrelation length (Sal) are positively correlated with surface damage, whereas mean summit curvature (Ssc) and skewness (Ssk) are negatively correlated with surface damage. Surface texture ratio (Str) and power spectral density (PSD) of test surfaces are used for analysing surface texture, and it is found that deterioration in surface texture occurs after 6 million cycles. It is also concluded that geometrical isotropy increases with an increase in SRR. [ABSTRACT FROM AUTHOR]

Rolling contact fatigue cracks and thermally induced defects are common problems in the railway industry especially as demands for increasing loads, speeds, and safety continue to rise. Often, the two types of defects are found together in the field, however, whether one causes the other to occur is not completely agreed upon. The effect of thermal damage, in the form of a martensite spot on pearlitic steel test bars, on the fatigue life in uniaxial low cycle fatigue experiments was investigated by the authors. However, the focus of the current work was to characterize the damage evolution from the low cycle fatigue (LCF) tests and correlate the crack initiation and propagation with the initial thermal damage. Residual stress measurements, digital image correlation, and X‐ray tomography were used to characterize the effects of the thermal damage before, during, and after fatigue testing, respectively. It was found that the thermal damage causes strain accumulation and crack initiation at the interface between the two materials. The strain evolution was visualized using digital image correlation (DIC), clearly showing the strain concentrations at the top and bottom of the white etching layers (WEL), where the residual stresses are also most tensile. X‐ray tomography confirmed the planar crack growth from the martensite spot. [ABSTRACT FROM AUTHOR]

Purpose: The efficient and economical use of natural resources is a big issue. Machine elements with a rolling contact are highly relevant because of their wide application in technical systems and a large production quantity. Innovative hard machining can reduce the friction and increase the fatigue strength of rolling element bearings. The purpose of this study is to focus on the surface properties of such parts. Design/methodology/approach: A new model to predict bearing fatigue life is presented which takes compressive residual stresses in the bearing subsurface area into consideration. The investigated bearings were machined by the processes of hard turning, hard turning with subsequent deep rolling and a combination of hard turning and deep rolling (turn-rolling) in one process step. Changes in the residual stress state during bearing fatigue tests were investigated and the influence of residual stresses on the bearings fatigue life was researched. Findings: Both combinations including the deep rolling process decrease the surface roughness and induce compressive residual stresses. As a result, the L10 fatigue life of roller bearings was increased by the factor of 2.5. Owing to the developed models, this effect can be considered within the design process. Originality/value: In the context of the research program "Resource efficient Machine Elements (SPP1551)," machining processes of bearings were investigated regarding the bearing fatigue life. By inducing beneficial residual stresses on the bearings' subsurface area, the fatigue life could be increased. Thus higher resource efficiency was achieved. To increase the productivity, a combination of hard turning and deep rolling was evaluated. [ABSTRACT FROM AUTHOR]

In the circumstances of high-speed railways, the wheel-rail vibration is significantly aggravated by polygonal wheel wear and rail corrugation, which subsequently leads to the wheel-rail interaction at higher frequencies and potential failure of the rail fastening. In this paper, a ω-type clip of the fastening in the CRH high-speed rail was used to investigate the failure mechanism. First, a dynamic wheel-rail coupling model and a finite element analysis of the rail clip were developed, from which the rail vibration frequency and modal frequencies of the clip with different installation torques were obtained. The experimental tests and modal simulation results were mutually verified. In addition, the real-time vibration measurement and the wheel-rail wear monitoring were carried out at a CRH high-speed railway site. It was found that the resonant frequencies of the ω-type clip in the installation condition coincided with the excitation frequencies of the wheel-rail interaction induced by wheel-rail wear. The high-frequency dynamic failure mechanism of a typical ω-type clip, W300-1, is put forward for the first time. Moreover, a high-frequency rail clip fatigue test system was designed and developed specifically for this study. The loading excitation frequency of the clip test used was set as 590 Hz, and the loading amplitude was 0.05 mm. After 125-minute operation of the test system, the clip was broken at the expected location predicted by the FEA model. The high-frequency fatigue test result further verified that the failure mechanism of the ω-type clip was due to the resonance of the clip with its excitation force from the wheel-rail interaction. Finally, the clip was then structurally improved taking into account the stiffness and mass, which led to its resonant frequencies shifting away from the high-frequency excitation range, hence avoiding resonance failure of the subject clip. [ABSTRACT FROM AUTHOR]

Additive manufacturing is steadily gaining acceptance in certain industry segments as a process for the manufacturing of dense metallic components. The Ni-based superalloys belonging to the Inconel family have for many years been in focus for AM research and AM produced components are now becoming commercially available. However, it is still unclear how the microstructural anisotropy, inherent to most AM materials, affects the material performance in a given application. The anisotropy may e.g. influence the mechanical properties and the performance in certain tribological situations, such as when subjected to rolling contact fatigue. Like most AM methods, the powder bed fusion – laser beam process gives the produced components a relatively rough surface. To perform well in demanding tribological situations, the components are commonly machined to a smooth finish. In this work, Inconel 625 produced using PBF-LB is evaluated in a rolling contact fatigue test. Test cylinders (Ø10 mm) have been produced using different build directions and scan strategies, resulting in varying microstructures and textures. In the rolling contact fatigue test, a cylindrical sample is mounted between two Ø 140 mm metal rollers, pulled together via a spring. After testing, the contact tracks are studied using SEM and EBSD to reveal cracks. Cracks were analysed with respect to the microstructure and anisotropies. It was found that the anisotropy influences both the nucleation and growth of cracks. The AM produced specimens were also found to be more prone to transgranular cracking than conventional Inconel 625, which predominantly displayed intergranular cracks. • AM IN625 tend to crack transgranularly, conventional IN625 intergranularly. • In AM rolling components, texture may dictate specific sites for crack nucleation. • In AM rolling components built with axis along build direction small damage dominate. • When built perpendicular to build direction the bottom part is most prone to fatigue. • AM rolling components built with contour will have fatigue crack along contour lines. [ABSTRACT FROM AUTHOR]

Pitting is frequently encountered in machine elements, such as bearings, cams and gears, containing parts in relative sliding-rolling motion. Most of investigations on rolling contact fatigue have been carried out by means of numerical/analytical models in the frame of LFEM, but the interpretation of the numerical results is still controversial. The SIFs history is highly non-proportional and the intensity of the peaks is not expected to cause propagation, since they do not exceed the fatigue threshold usually found for long cracks in steels and cast irons. To shed light on this issue, this work is intended to reproduce experimentally the SIF-cycles, estimated by our previous model of RCF crack, by using an alternative non-standard procedure. The novel experimental apparatus is based on the exploitation of a kinked edge crack subjected to a compressive load distributed through the thickness. Changing the load position and intensity permits to induce different values and ratios of SIFs. It has been found that lubricant is strictly necessary to trigger crack propagation, which can be in form either of coplanar extension followed by branching or of branching only. Coplanar extension occurs when mode II SIF range exceeds a certain threshold, well below the typical fatigue threshold. Empirical evidences are in accordance with the tendency of the RCF cracks to do coplanar extension and to branch into the bulk material and toward the surface. Coplanar extension is more pronounced in the interior of the sample, while branching occurs only at the edges. The results indicate that our previous modelling of RCF crack is likely to underestimate the effective SIFs. Thus this work would open the way to improve the actual understanding and modelling of RCF. [ABSTRACT FROM AUTHOR]

This study presents the wear and damage behaviours of U71Mn rail material with a friction pair of ER8 wheel material under different temperature conditions, which were explored using a rolling-sliding wear testing device. It turns out that, compared to those at 20 °C room temperature, the adhesion coefficient, wear rate and hardness all increase at low temperatures. Meanwhile, three types of damage mechanisms are proposed according to wear and rolling contact fatigue (RCF) behaviours under different temperature conditions: (a) room temperature (RT) damage mechanism, (b) ductile-brittle transition temperature (DBTT) damage mechanism, (c) below ductile-brittle transition temperature (BDBTT) damage mechanism. With the temperature decreasing from room to low temperature, the wear mechanism transforms from abrasive wear to adhesive wear and surface fatigue. Meanwhile, the rail material gradually becomes brittle and the subsurface damage at low temperature is more serious than that at room temperature. Furthermore, the subsurface damage at −15 °C is the worst. At low temperature, there is a wider size range of wear debris than that at room temperature. [ABSTRACT FROM AUTHOR]

Local rolling contact fatigue (LRCF) has occasionally been observed on wheels of high-speed electrical multiple units (EMUs) in recent years in China. It typically propagates to 2.5–8.5 mm deep along shallow angles to the tread surface, leading to large material removal during lathe turning. To reveal the initiation and propagation mechanisms of LRCF, a thorough investigation has been conducted by means of field observations, statistical analyses, and numerical simulations. It is found that 69% of LRCF occurred on the leading axles of leading coaches, and its occurrence rate on the 380 km/h class EMU was 2.87 times that on the 250 km/h class. Records of a 380 km/h class EMU train have shown that LRCF initiated with an occurrence rate of 14.3% from indentations of 2.3–3.0 mm deep and 4 mm in diameter, and the crack depth increased by 0.011–0.031 mm every 1000 km. All these phenomena, among others, suggest that indentations are the main causes of LRCF. The cracks, according to 3D transient and 2D static simulations of wheel–rail rolling contact, probably initiate at the bottom of deep indentations with a characteristic dimension longer than 2–4 mm. Preventive measures against LRCF are recommended at the end. [ABSTRACT FROM AUTHOR]

Rolling contact fatigue (RCF) and wear are competing phenomena in railway wheels, but they are typically studied as independent events. In this work, preliminary tests are carried out with a twin-disc bench to explore the relationship between RCF and wear. First, the collected tests are reported on the shakedown maps to assess the cyclic response and calculate the fatigue index parameter used to predict the surface-initiated fatigue damage. Second, the fatigue index and material cyclic yield strength are related to the experimental wear rate. This work proposes maps to predict how the wear rate and cyclic response change by varying the contact conditions (clean or contaminated with water or sand), slip ratio and extraction position of specimens. Furthermore, the estimated wear rate is superimposed to the shakedown map to investigate a possible relationship between RCF and wear. The proposed approach allows to understand how a railway wheel steel behaves as a function of the working conditions and whether some working parameters can be changed without compromising the material performance. • Predictive maps for bi-disc tests are proposed. • Wear rate is superimposed to shakedown maps. • A higher fatigue index results in a higher wear rate. • Water contaminant drastically reduces the wear rate. • Reprofile operations increase the fatigue index and wear in clean contact. [ABSTRACT FROM AUTHOR]

• A Voronoi finite element model for crack initiation life of RCF is built. • The coupling damage model considers the microstructure of material. • The impact mechanism of grain characteristics and material defects is revealed. The material microstructure of plays an important role in crack initiation of rolling contact fatigue. To address crack initiation of tapered roller bearings, the inhomogeneous characteristic of material is considered. The random distribution of material grains is simulated with Voronoi graph, and a Voronoi finite element model of rolling contact fatigue is given. Numerical analysis of damage-life constitutive relation is carried out with finite element analysis. The effect of material microstructure inhomogeneity on initiation life of fatigue crack is studied. Researches show that the smaller the grain size, the more difficult the fatigue crack appearing. The larger the difference of elasticity modulus between non-metallic inclusions and matrix material, the greater the impact on fatigue life of crack initiation. The angular and sharp non-metallic inclusions reduce fatigue life more than rounded shape inclusions. Initiation life of fatigue crack has a minimum value on a critical depth of nonmetallic inclusion. The longer distance between two laterally arranged inclusions, the greater it affect the initiation life of fatigue crack. The effect of distance between two vertically arranged inclusions on fatigue crack initiate depends on the depth of inclusions. [ABSTRACT FROM AUTHOR]

Rolling contact fatigue and wear of rails are well-known problems. However, progress is not easy to predict because these problems interact with each other. Therefore, to reduce damage, the interactions between these two mechanisms must be clarified. In this study, the contact fatigue and wear of UIC 60 and KS 60 rail materials were investigated by twin-disc testing with various parameters. We found that ductility and fracture toughness are important factors on wear and contact fatigue. UIC 60 rail steel with higher ductility and fracture toughness than KS 60 rail steel has a higher resistance to contact fatigue but a lower resistance to wear. [ABSTRACT FROM AUTHOR]

Rolling contact experiments of (TiB + TiC)/Ti–6Al–4V composites reveal that inhomogeneous reinforcements reduce the materials’ rolling-contact fatigue (RCF) lives. The composite microstructures are examined and reconstructed based on the dual-beam focus ion beam scanning electron microscopy (FIB/SEM) technique. Integration of the microstructure-based stress analysis approach and Zaretsky’s RCF life prediction methodology leads to a new numerical RCF life modeling method. The newly developed mesh differential refinement scheme, together with the fast Fourier Transform techniques, is utilized to improve the efficiency and versatility of the proposed method. The RCF lives of the composites predicted by the new model are then compared with the experimental data, illustrating the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to analyze the influence of the load direction and the phenomenon of wear on rolling contact fatigue crack growth. For this purpose, a UIC60 rail with accurate geometry using FEM is studied. In this regard, a three-dimensional finite element model is provided. The maximum stress caused by wheel/rail contact for a new/worn wheel profiles was obtained using such model. Then, using Franc 3D software, during stress analysis for different situations of wheel, different values of stress intensity factors are obtained. The behavior of crack under fatigue loading was studied using a three-dimensional modeling. [ABSTRACT FROM AUTHOR]

Rolling contact wear is a complex phenomenon that might involve different wear mechanisms (adhesive, abrasive, fatigue and corrosive) and different stress concentration mechanisms (asperity, dent, debris, inclusions, etc.). The interactions among these mechanisms might accelerate or decelerate the overall wear progress. Therefore, it is complicated to model and monitor the fluctuations of wear progress. The current descriptive models are either describing individual physical phenomena within rolling contact wear or describing a specific stage of wear progress. Thus, the interactions among different wear mechanisms and the transition events among different stages of wear progress are not sufficiently addressed. Therefore, the purpose of this paper is to propose a descriptive model of the wear evolution process in rolling bearings over the whole lifetime. The descriptive model utilises a wide range of empirical findings in the literature to describe the wear interactions and evolution in the five-stage scenario: running-in, steady-state, defect initiation, defect propagation, and damage growth. The new descriptive model provides the most probable scenario of wear evolution in rolling bearings, which is useful for modelling and monitoring the wear progress. It illustrates the wear evolution stages, the involved wear mechanisms in each stage, the interaction among wear mechanisms in each stage, the surface topology changes and the influencing factors within each stage. For design, condition monitoring and prognosis purposes, these aspects are significantly important to understand, model, test and monitor the wear evolution process. [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]

Abstract: Quantifying the surface roughness evolution in contacts is a crucial step in the fatigue prediction process. Surfaces are initially conditioned by the running-in process and later altered by surface fatigue. The aim of this study is to understand and predict the evolution of the micro-geometry in the first few over-rolling cycles. Numerical predictions are validated by experiments. A major difficulty in understanding surface degradation is the measurement of the surface roughness evolution at the relevant scales. A twin disc micro-test rig, called μMag, was specially designed for this kind of analysis. The μMag allows the “in situ” observation of changes in the disc surface during interrupted tests, thus avoiding dismounting the specimens, which is a major cause of inaccuracy. The new method also maintains the relative position of the two discs. The precision of the measurements allows one to use the initial surface micro-geometry as input for the numerical contact calculation. Thus, the plastic deformation of the surfaces can be measured during the first cycles and compared to the numerical prediction. Results show a very good agreement between numerical predictions and experimental measurements. [Copyright &y& Elsevier]

Abstract: Crystallite size and dislocation density in RCF (rolling contact fatigue) affected layers have been identified using x-ray measurements for the serviced rails and rail disk sample. The evaluation of crystallite size and dislocation density was based on the modified Williamson-Hall and Warren–Averbach analyses. This evaluation enabled to provide a quantification of the microstructural evolution in the RCF layer with the increase of accumulated loading as well as an identification of the most deteriorated locations in the RCF layer. In summary, the surface layer experienced the highest deterioration in all evaluated cases. Furthermore, the accumulation of loading (in terms of MGT—Million Gross Tonnes) increased the depth of the surface RCF layer. A (111) texture formation was observed in the subsurface RCF layer after some accumulated operational loading. Further conclusions from the study are that it is essential to consider the surface roughness in the contact patch in addition to the microstructural variations such as the refinement, the plastic flow, etc., since it enhances the deterioration of surface RCF layer. In addition, the dislocations induced by the RCF were mostly stemmed from the screw dislocations in the surface RCF layer. In contrast, they were mostly derived from the edge dislocations in the subsurface RCF layer. This difference is likely owing to the characteristics of dislocations, the tangential load, the applied shear stress, localized stress concentration induced by the surface roughness contact, etc. [Copyright &y& Elsevier]

Abstract: This paper proposes the use of the weight function technique to calculate mode I and mode II stress intensity factors for a shallow surface crack typical of rolling contact fatigue, that experiences the detrimental effects of the pressurization of lubricating fluid. The weight function technique was able to easily take the pressurization into account just by adding the pressure term to the nominal stress component which is then integrated. The crack closure was also modeled by introducing an assumption for the distribution of the contact pressure on the crack face. The results were validated with the literature data and finite element analyses. Parametric simulations were performed showing that mode I and mode II stress intensity factors strongly depend on the crack angle with respect to the surface, and almost linearly on the size of the crack. In addition, the proposed algorithm was able to include any residual stress distribution. Compressive residual stress hinders pressurization and promotes the crack closure. This effect was parametrically investigated and it was found that cracks, and especially small ones, can even remain closed, with the opening effect of the pressurization completely suppressed. [Copyright &y& Elsevier]

Abstract: Rail squats remain a major rolling contact fatigue problem for mass transit authorities. Several studies have been conducted to supplement the standard characterization of rail squats. In particular an extensive tribological and metallurgical investigation was performed on samples of incipient squats from various areas. Surfaces and cross-sections of rail samples were observed by optical microscopy and scanning electron microscopy. These observations highlighted that the running band is composed of longitudinal contact strips with various surface and subsurface morphologies. This microstructure seems to be essential for the onset of squats. This new information makes it possible to account for the entire damage mechanism of a squat defect from initiation to propagation. [Copyright &y& Elsevier]

Abstract: Wear and rolling contact fatigue were investigated on unfilled PEEK and on three PEEK short fiber reinforced composites. For this aim, roller-shaped specimens were subjected to rolling contact tests at different contact pressure levels. Wear rate-pv product and contact pressure-life diagrams were obtained, depending on material hardness. Microscopic observations of rolling contact surfaces and sections of the rollers highlighted damages at two different scales, surface and bulk, leading independently to wear and rolling contact fatigue. These damages were also of different typology for unfilled PEEK and composites: micro-pitting and deep transversal cracks occurred on unfilled PEEK rollers, while delamination and spalling phenomena where found on composite rollers. [Copyright &y& Elsevier]

Abstract: Tools for the prediction of crack growth in rails are of vital importance for the railway industry. In this paper, numerical simulations of crack growth in rails are presented. More specifically, the focus is on short surface head check like cracks, often observed at the rail gauge corner. A fatigue crack propagation model expressed in terms of a crack driving force, derived from the concept of material forces, is presented. It is shown that only the component parallel to the crack tip of the crack driving force is a reliable quantity that can be used in numerical simulations of a Rolling Contact Fatigue (RCF) situation. In addition, it is shown that one term in the expression of the crack driving force is dependent on the computational mesh. The propagation model has been used for parametric studies of crack propagation to investigate key parameters such as loading and crack geometry. Results from these studies suggest that anisotropic effects from the highly deformed surface layer may need to be included in order to simulate head check growth in rails accurately. [Copyright &y& Elsevier]

A method is described which is an extension of rolling contact models with respect to plasticity. This new method, which is an extension of the STRIPES semi-Hertzian (SH) model, has been implemented in a multi-body-system (MBS) package and does not result in a longer execution time than the STRIPES SH model [J.B. Ayasse and H. Chollet, Determination of the wheel–rail contact patch in semi-Hertzian conditions, Veh. Syst. Dyn. 43(3) (2005), pp. 161–172]. High speed of computation is obtained by some hypotheses about the plastic law, the shape of stresses, the locus of the maximum stress and the slip. Plasticity does not change the vehicle behaviour but there is a need for an extension of rolling contact models with respect to plasticity as far as fatigue analysis of rail is concerned: rolling contact fatigue may be addressed via the finite element method (FEM) including material non-linearities, where loads are the contact stresses provided by the post-processing of MBS results [K. Dang Van, M.H. Maitournam, Z. Moumni, and F. Roger, A comprehensive approach for modeling fatigue and fracture of rails, Eng. Fract. Mech. 76 (2009), pp. 2626–2636]. In STRIPES, like in other MBS models, contact stresses may exceed the plastic yield criterion, leading to wrong results in the subsequent FEM analysis. With the proposed method, contact stresses are kept consistent with a perfect plastic law, avoiding these problems. The method is benchmarked versus non-linear FEM in Hertzian geometries. As a consequence of taking plasticity into account, contact patch area is bigger than the elastic one. In accordance with FEM results, a different ellipse aspect ratio than the one predicted by Hertz theory was also found and finally pressure does not exceed the threshold prescribed by the plastic law. The method also provides more exact results with non-Hertzian geometries. The new approach is finally compared with non-linear FEM in a tangent case with a unidirectional load and a complete slip: when plasticity is taken into account, and for large adhesion values, friction forces have an influence on the size of the contact patch. The proposed approach enables also to assess extensively the level of plasticity along a track through an indicator associated with a given yield stress. [ABSTRACT FROM AUTHOR]

Abstract: The fracture behaviour of steel components with very hard material states under cyclic loading is mostly defined by non-metallic inclusions present in the material. The inclusion distribution is a result of specific conditions in steel making, casting and rolling processes. Standard methods (e.g. DIN EN 10247:2007) are commonly used for estimation of the distribution of non-metallic inclusions. These methods are based on random metallographic examination of longitudinal microsections and evaluation with standard pictures. For numerical evaluation of the endurance limit of very hard material states the knowledge of defect distribution of the material is necessary. However, the standard methods are not suitable to find the actual inclusion distribution. In a large investigation program on the fatigue strength of very hard material states, thin wall tubes made of a case hardening steel were tested. All fracture surfaces were investigated, size and coordinates of the fracture initiating defects were documented and analysed statistically. The defects appear as inclusion stringers stretched in rolling direction mainly containing Al-oxide. Several distribution functions for statistical analysis were investigated. Furthermore, transverse microsections with a total area of about 2000mm2 were investigated and the data of the maximum width of inclusion stringers were also analysed statistically. Comparison of the extreme value distribution of inclusions made by metallography and fractography, respectively, show that the metallographic method considerable underestimates the actual size of inclusions. Therefore micrographic methods are not suitable to generate input data for inclusion distribution based on fatigue design. [Copyright &y& Elsevier]

Abstract: The influence of asperity size, friction and residual surface stress on surface initiated rolling contact fatigue damage was investigated using the asperity point load mechanism. A parametric study was performed in two steps, first with a classic one-parameter-at-a-time approach, then as a 2-level full factorial design. The effect on fatigue initiation, damage size and spalling life for both early and developed spalling damage was examined for a gear application. Simplified response surfaces were derived as an engineering design tool for improved spalling resistance. The parametric investigation suggested that among the investigated parameters, reduced asperity height and local asperity friction will have the largest effect on the crack initiation risk. The simulations agreed with the engineering experiences that reduced surface roughness improves rolling contact fatigue resistance and that improved lubrication lengthens spalling lives and decreases fatigue risk. With compressive residual surface stresses the predictions suggested reduced fatigue risk and substantially decreased depth of individual spalls. Finally, predictions of experimentally observed effects of changing asperity size, friction and residual surface stress on spalling further motivates the asperity point load mechanism as the source behind surface initiated rolling contact fatigue. [Copyright &y& Elsevier]

The development of contact theories and numerical solutions for various applications is a field which expands rapidly. Although railway system is a transportation system with a long tradition, still a large number of unsolved problems exist. One of these problems is the assessment of the stress and strain status of the rail and the wheel under rolling contact conditions. The assessment requires the investigation of the mechanically originated damage of wheel and rail, as cracklike damage, prediction of wear and fatigue as well as change of material properties. Since the mechanical problem is of high complexity because of the contact condition and the material behavior, only a numerical approach seems to be appropriate. This paper presents a method which has the advantage that the structural analyst is allowed to solve both the contact problem and material nonlinearity using an unique simulation model [ABSTRACT FROM AUTHOR]

Since the accurate prediction of fatigue life has a significant value, many researchers have attempted to develop a reliable fatigue life model. Recently, rolling contact fatigue life models incorporating machining impact were developed. These models have contributed to a significant improvement in prediction accuracy as compared with earlier models, thus representing a major step forward in the modeling effort. This paper compares the prediction accuracy of these models with that of the prediction method in International Standards. When α is set to 0.25, the observed improvement of prediction accuracy as measured by variance of prediction errors due to these models over that due to prediction method in International Standards is statistically significant. Impact analyses of such improvement are conducted to illustrate its value. It is further noted that while difference was observed between the variance of prediction errors due to the crack initiation life model based on a dislocation model and that due to the crack initiation life model based on a local stress-life curve, the observed difference is not statistically significant. [ABSTRACT FROM AUTHOR]

Abstract: Rolling contact fatigue cracks in railway track called squats are studied in this paper. In the first part, the effects of an elastic foundation (sleepers and the ballast) on stress intensity factors obtained at a crack tip are studied. A simplified finite element model (FEM) and an extended finite element model (XFEM) were created to investigate these effects, the XFEM model being limited in geometrical size, but more able to model crack growth. Both FEM and XFEM confirmed that an elastic foundation leads to an additional bending stress which increases the crack growth rate significantly. Field results also authenticate that squat form cracks appear on timber sleepers more commonly than on concrete ones. These results indicate that considering these bending stresses in a FE model, is important to achieve a more realistic model of squat development. In the second part, a short crack of 250μm length is simulated to investigate how variations of traction ratio (TR), friction coefficient between the crack faces (FC) and the crack angle affect SIFs when the rail is mounted on an elastic foundation. Simulations show that a crack on a rail laid on elastic foundation (clips, sleepers and ballast) can lead to significantly higher SIFs in many conditions and consequently raises crack growth rate. This indicates that foundation stiffness is as important as water entrapment and friction coefficient between the crack faces. [Copyright &y& Elsevier]

Abstract: The purpose was to develop a fracture mechanics based method for determining the life of surface initiated rolling contact fatigue or spalling. The life simulations were based on the asperity point load mechanism, a mode I crack growth assumption and LEFM. The life prediction was verified against the spalling life in some gear teeth, which had been measured for the simulation data. The computational tool required an equivalent mixed-mode life parameter. Such are suggested in the literature and some of these were evaluated. Also, the work required material properties for crack growth at stress cycles with highly compressive minimum loads. An experimental series was performed for crack growth at R <0. Negative crack closure limits K I,cl were suggested by the compliance but not the crack growth rate. Simulations with small negative closure limits predicted the spalling life in the gears. It was however noted that the life predictions depended more on K I,cl than the equivalent mixed-mode life parameter. [Copyright &y& Elsevier]

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: This paper discusses the relationship between ACFM signal and RCF defects in railway rails and wheels using an FEM model developed with COMSOL Multiphysics that has been verified for single and multiple RCF type cracks. The response to semi-elliptical defects of surface length 2mm to 40mm, and elliptical ratio 1:1 to 1.75:1, has been simulated and it is shown that the ACFM signal is most sensitive to, and therefore able to accurately size, RCF defects <20mm surface length (classified by Network Rail on rails as light-moderate). The sensitivity to sensor lift off and sensor angle relative to crack angle, which is of importance for high-speed and fixed sensor systems, is presented for a semi-elliptical crack. For a complex defect extending into the rail beyond the surface breaking component (a morphology that can be seen for moderate, heavy or severe RCF cracks in rail), the effect of using a sizing algorithm based on semi-elliptical shapes is quantified; it is shown that the defect would be undersized by 34.4% using this approach. Finally, the ACFM response to clusters of 4 semi-elliptical defects with inter-crack spacings of between 1mm and 19mm is presented. It is shown that closely spaced cracks give a large signal that could be interpreted as one large defect; this effect is quantified. [Copyright &y& Elsevier]

Abstract: This paper addresses rolling contact fatigue (RCF) testing in ultra high vacuum (UHV) under high speed conditions. A ball–rod RCF test platform has been adapted for testing in UHV conditions that allows rapid accumulation of stress cycles, over 10 million cycles within 5h of testing at 130Hz rotation. The UHV environment and solid lubrication enables good vibration detection for the onset of spall. In this paper, approximately 0.2μm of silver is applied to the balls and provides sufficient lubrication for up to 25h of testing, or 50 million stress cycles in high vacuum at 130Hz. Seventy-nine RCF tests using thin-film silver lubrication have been completed covering two ball sizes, and two rod and ball materials. 9.53mm diameter Rex 20 steel and silicon-nitride (Si3N4) rods were tested against 7.94mm diameter Rex 20 and 12.7mm diameter M50 steel balls. It was found that ball size and material hardness did not affect the stress cycle life over a Hertzian contact stress range of 2.1–4.2GPa and Rockwell C hardness range of 62–77. Rather, the key limiter to test length is lubrication depletion based on 79 tests and an average silver thickness of 0.2μm. One of the two failure modes were observed for all tests: (i) early life spall of the silver coating, and (ii) depletion of silver lubrication followed by spall failure of both the ball and rod surfaces. A third-body storage model along with the Control Volume Fraction Coverage (CVFC) assumption and analysis was used to predict lubrication availability between asperities on the third body. There is good agreement between calculated and measured post-test lubrication thickness using the third-body storage model. [Copyright &y& Elsevier]

Abstract: A computational model for determination of static capacity and fatigue lifetime of large slewing bearings is presented. In the proposed model, contact load distribution along the bearing raceways is calculated on the basis of the static equilibrium between contact loads acting on the raceways, and external loads acting on the bearing. On the basis of the maximum contact force and some typical and experimentally determined material parameters, the static capacity of a bearing is calculated and a comparison of different approaches for a calculation of the fatigue lifetime of a bearing is presented. The following calculation methods are compared: ISO standardised calculation approach, a stress-life approach and a strain-life approach. The presented vector based calculation approach for a calculation of the contact load distribution seems to be an appropriate approach for a fast evaluation of the influence of the bearing clearance and the deformation of bearing rings on the contact load distribution. The comparison of fatigue lifetimes calculated with different calculation methods shows that the choice of method for the calculation of an equivalent mean stress significantly effects the calculated lifetimes. Furthermore, the comparison of lifetimes also shows that, by assuming that ISO standardised calculation approach gives relevant results and provided that material parameters are properly defined, the stress-life approach is, to some degree, a proper method for calculation of the rolling bearing fatigue lifetime. [Copyright &y& Elsevier]

Abstract: The crack path of surface initiated rolling contact fatigue was investigated numerically based on the asperity point load mechanism. Data for the simulation was captured from a gear contact with surface initiated rolling contact fatigue. The evolvement of contact parameters was derived from an FE contact model where the gear contact had been transferred to an equivalent contact of a cylinder against a plane with an asperity. Five crack propagation criteria were evaluated with practically identical crack path predictions. It was noted that the trajectory of largest principal stress in the uncracked material could be used for the path prediction. Different load types were investigated. The simplified versions added some understanding but the full description with cylinder and asperity pressures was required for accurate results. The mode I fracture mechanism was applicable to the investigated rolling contact fatigue cracks. The simulated path agreed with the spall profile both in the entry details as in the overall shape, which suggested that the point load mechanism was valid not only for initiation but also for rolling contact fatigue crack growth. [Copyright &y& Elsevier]

Abstract: The effect of shot peening on rolling contact fatigue (RCF) and lubricant film thickness within non-conformal rolling/sliding contacts operated under mixed lubrication conditions was observed in this study. Rolling contact fatigue tests and film thickness measurements were carried out using specimens with modified surface topography by shot peening process using glass beads having diameter between 0.07 and 0.11mm. It has been shown that the effect of shot peening on RCF has no positive effect even if shot peened surface of the roller exhibited somewhat higher hardness in contrast to the grounded surface. The reduction of RCF may be caused due to asperities interactions because after shot peening the surface roughness of the roller was increased. Film thickness measurements confirmed that the contact is realized actually only between asperity peaks of shot peened ball and smooth disc. Conversely, no negative effect on RCF was observed when the shot peened surface of the roller was polished. The polish of asperity peaks causes the creation of lands and micro-cavities, which may be employed as lubricant micro-reservoirs. From film thickness measurements it has been observed that lubricant emitted by shallow micro-cavities can provide the local increase in lubrication film thickness, which thereby reduces asperities interactions. Similar results were obtained for start-up conditions where the squeeze lubricant enlarges film thickness and reduces surface interactions. From the obtained results, it can be suggested that properly designed surface topography modification could help to increase the efficiency of lubrication films leading to the enhancement of contact fatigue life of non-conformal mixed lubricated rolling/sliding contacts. [Copyright &y& Elsevier]

Abstract: Friction coefficient plays an important role in determining the contact tractions and consequently the stresses that drive damage mechanisms in components subjected to fretting fatigue. Friction coefficient evolves to different magnitudes at different points in the contact interface. Effect of this spatial variation in friction coefficient on the shear distribution for contacts involving similar isotropic materials has been presented in this paper. Full sliding tests have been conducted to obtain friction coefficient as a function of sliding distance. Well characterized set of experiments to determine the average friction coefficient in fretted specimens is briefly discussed. Existing analysis for obtaining the shear traction for arbitrary smooth profiles has been modified to take the variation of friction coefficient from one point to another into account. Using this analysis, spatial variation of friction coefficient in fretted specimens has been obtained. It has been found that using a constant friction coefficient (equal to the slip zone friction coefficient) throughout the contact zone is a good enough approximation in most of the cases. However, in some cases, when the slip zones extend into regions where the friction coefficient has not reached the asymptotic value, actual distribution of friction coefficient gives a different shear stress distribution as compared to a constant slip zone friction coefficient. [Copyright &y& Elsevier]

Abstract: Alternating current field measurement (ACFM) sensors can be used to detect surface breaking defects in metal components. In rails rolling contact fatigue (RCF) cracks form due to the wheel–rail contact stresses. These cracks are surface breaking and can have complex shapes. A COMSOL model has been developed for a commercial ACFM system and RCF cracks in rails. In this paper model results are compared to experimental measurements using an ACFM pencil probe for calibration defects machined into a rail and real RCF defects (light and moderate categories; <20mm surface length) in a rail removed from service. X-ray tomography has been used to determine the size and morphology of the real RCF cracks for input into the model. It has been shown that the model can be used to determine the change in normalised Bx signal due to the presence of calibration defects machined into a new rail. The model has also been used to compare the experimental data for the real RCF cracks to the reconstructed model cracks and a semi-elliptical approximation to their shape. [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: The continual demand for higher load-bearing capacity and improved performance and reliability of gears and other components increases the role of high endurable Hertz pressures and low friction. Coatings prepared by high velocity oxy-fuel spraying (HVOF), one of the most important thermal spray processes, have the potential to serve as a technical solution for highly loaded components such as gears. In this work the rolling contact fatigue (RCF) behaviour of HVOF-sprayed WC–17%Co coatings was investigated on roller specimens with coating thicknesses of 600μm and 100μm deposited on 16 MnCr 5 steel substrates in the unhardened, quenched and tempered, and case-hardened states with hardness values of 190 HB, 400 HB and 58–62 HRc, respectively. The endurable Hertz pressures of the coated specimens were benchmarked against uncoated case-hardened 16 MnCr 5 steel. The failed coatings and coating damages before failure were thoroughly studied by optical and SEM microscopy. The highest durability was realised for a coating thickness of 600μm through the use of the quenched and tempered substrate (about 130% of the benchmark). Coatings on these substrates showed a minimal amount of micropits and no other damage such as large cracks after testing. It can be assumed that differences in specimen preparation by grit blasting prior to spraying and different substrate strengths were responsible for the different results for the coated unhardened, quenched and tempered, and case-hardened substrates. The durability for a coating thickness of 600μm was higher than for a coating thickness of 100μm when unhardened and case-hardened substrates were used. Further improvements in the rolling contact fatigue behaviour could be achieved by optimisation of the combination of coating thickness and substrate strength and by use of other WC-based coatings. [Copyright &y& Elsevier]

The rolling contact fatigue (RCF) behaviour of the plasma-sprayed CrC-NiCr cermet coatings under different tribological conditions of contact stress was investigated. Four sets of fatigue life data of coatings were characterized by Weibull distributions. The failure modes of the coatings were classified on the basis of worn surface observations of the failed coatings. Results showed that the failure mode of the coating was related to the magnitude of contact stress. The RCF life data of the coatings tested at high contact stresses exhibited high scattering, because the bimodal distribution of the fatigue life data was seen in the Weibull plot. Generally, when the contact stress was relatively low, the coatings were prone to fail in spalling and cohesive delamination. However, at high contact stress, the coatings often failed due to interfacial delamination. At different contact stress levels, the maximum shear stress amplitude was the main reason for the generation of spall and delamination. [ABSTRACT FROM AUTHOR]

Abstract: Subsurface initiated rolling contact fatigue cracks initiate in the vicinity of material defects. As these exist randomly in the material, fatigue will appear randomly under otherwise constant conditions. By combining statistical methods with a contact mechanics and fatigue analysis, probabilities of fatigue initiation are evaluated. The developed model takes as input contact geometry, contact load and the statistical properties of the material defects. It is shown that under some well-defined presumptions the probability of rolling contact fatigue initiation in a rolling wheel can be expressed by a simple formula. Based on this, the parametric influence is assessed and it is found that the mean material defect size has a large influence. The benefit of material cleanliness testing procedures and the influence of the allowed defect size on the risk of subsurface initiated rolling contact fatigue in railway wheels are then quantified with the aid of numerical simulations. [Copyright &y& Elsevier]

Abstract: Continuing from research reported at CM2006, we report further investigation of the interaction of rail with friction modifiers (FM) related to wear and RCF generation. This work examines the relative effects of FM on standard (R260) and premium (R350HT) rail using a test rig. Under dry conditions, the premium rail shows clearly reduced wear and RCF generation compared to the standard rail. Application of FM reduces wear and RCF propensity for both standard and premium rail, with the best result achieved by a combination of R350HT and FM. Results on plastic flow were similar and consistent with the wear and RCF pattern. Longer term testing with FM application was terminated after four times the normal test cycle length without any RCF formation. Application of FM to pre-existing RCF cracks did not lead to acceleration of crack growth (e.g. by hydropressurization) under the experimental conditions used. Field results were reviewed for both premium rail and FM effects on RCF, and are found to be generally consistent with test rig results. [Copyright &y& Elsevier]

Abstract: This paper reports on metallurgical characterisation of small cracks in pearlitic steels, using observations from both twin disc tests and rails removed from service, plus methods to determine three-dimensional (3D) aspects of such cracks. Tests to varying fractions of rolling contact fatigue (RCF) life have been assessed, based on twin disc tests where “average 100% RCF life” has been defined by eddy current detection of cracks between 200 and 800μm in depth. Contact surface features and microstructural alterations have been mapped against near-surface strain and compared with worn rail examinations. Initial crack growth along favourably aligned and strained, prior-austenite (PA) grain boundaries, particularly if the boundary contains pro-eutectoid (PE) ferrite, was found to be restricted or halted at the PA grain limit or where the boundary altered to be less-favourably aligned. For samples with up to 55% RCF life, initial crack propagation length was still less than the average PA grain size. 3D aspects of this early growth and the deformed PA grain shapes were found to be linked to ratcheting flakes and flake cracks on test disc and rail contact surfaces. The results have shown how initial RCF crack propagation is very microstructurally influenced. [Copyright &y& Elsevier]

Abstract: Spalling is rolling contact fatigue (RCF) damages of railway wheels, as a result of unexpected wheel slides on a rail. The major characteristic in spalling is that fatigue cracks initiate from white layers. In this study, in order to evaluate the influence of the white layer geometries on spalling properties, RCF tests and elasto-plastic FEM analyses were carried out. Moreover, the Dang Van model, which is the multiaxial fatigue strength evaluation methods, was applied to predict the crack initiations in RCF tests. There are three main results from this study. Firstly, RCF tests yielded that the crack initiations were less in the smaller white layers than in the larger ones. In addition, the crack initiations of the matrices were less than those of the white layers. Secondly, FEM analysis results showed that the maximum stresses were lower in the smaller white layers than in the larger ones. This result corresponded to the crack initiation behaviours of RCF tests. Finally, the fatigue strength prediction results by the Dang Van model were reasonably equivalent to the RCF test results. Therefore, it was concluded that the crack initiations in spalling could be reduced by the smaller white layer. [Copyright &y& Elsevier]

Abstract: Within the framework of materials fracture mechanics the computational model for investigation of fracture processes and prediction of rolling bodies residual lifetime under their cyclic contact has been formulated. The step-by-step calculation of crack propagation paths using solutions of the singular integral equations of two-dimensional contact problems for solids with curvilinear cracks and also local fracture criteria under complex stress–strain state are the basis of the model; calculation takes into account the fatigue crack growth resistance characteristics of materials and tribojoints performance parameters. The algorithms of cracks propagation paths construction in the contact zone take into account a change of the stress–strain state, that is caused both by the cracks extension and a counterbody movement (load change) in a contact cycle. They also take into consideration the possible change of fracture mechanism in the cracks propagation process and friction between cracks faces. Taking into account the published experimental data on crack initiation and propagation under cyclic contact of solids, two criteria of material local fracture have been included in the calculation model: the criterion of generalized normal opening (σ θ -criterion) and the criterion of generalized transverse shear. Conditions for evaluation of pitting particles sizes in dependence on the service parameters and characteristics of fatigue crack growth resistance have been formulated. Realization of the model is given for a wheel–rail pair under boundary lubrication in contact. Using the fatigue crack growth resistance characteristics of RSB 12 and 75KhGST (75ХГСТ) rail steels, their residual lifetime has been evaluated by pitting development. The corresponding curves of contact fatigue have been constructed. [Copyright &y& Elsevier]

Abstract: A railway switch (turnout) is a very important element of the railway infrastructure. Due to the discontinuity in the rail geometry high dynamic amplification of the wheel loads occurs in the crossing nose. These dynamic forces can severely damage the turnout structure. Especially the high-frequency impact loads (the so-called P 1 forces) are responsible for RCF damage on the crossing nose. In the present study the relationship between the elastic properties of the turnout supporting structure (such as the rail pads, under sleeper pads and ballast mats) and the occurrence of RCF damage on the crossing point has been investigated. The RCF damage can be reduced by decreasing the high-frequency dynamic forces in the crossing nose. The dynamic interaction between the railway vehicle and track structure has been analysed numerically using DARTS_NL software (TU Delft). The performance of the turnout has been assessed using numerical simulations in which a railway vehicle (the ICE locomotive) was running through the turnout at 140km/h. In this simulation only the vertical dynamic forces in the crossing point have been considered: lateral behaviour was disregarded. The results of the parameter analysis have demonstrated that by varying the elastic properties of the supporting track structure the forces on the crossing point can be significantly reduced. It was also shown that by varying substructure elasticity the dynamic forces on other track components such as sleepers and ballast can be reduced as well. [Copyright &y& Elsevier]

Abstract: The influences of train speed and rail roughness level on rolling noise and subsurface initiated rolling contact fatigue (RCF) impact are studied. In particular, the consequences of short-pitch rail corrugation on tangent track with wavelengths in the interval 3–8cm are simulated using models of dynamic vehicle–track interaction. Based on the calculated results, a criterion in terms of a limit for maximum levels of rail roughness with respect to the current traffic conditions can be determined. Such a criterion may be useful for planning of rail grinding intervals if used together with a system for regular monitoring of rail roughness levels. It is concluded that the importance of controlling rail roughness increases with increasing train speed. Increasing axle loads on freight vehicles from 22.5 tonnes to 30 tonnes leads to a significant increase in RCF impact. In operational practice, this is usually compensated for by introducing more conformal wheel–rail profile combinations. Calculated vertical wheel–rail contact forces and rolling noise levels show good agreement with field measurements. [Copyright &y& Elsevier]

Abstract: A previous simplification of the Dang Van equivalent stress measure for assessment of subsurface initiated rolling contact fatigue (RCF) related to wheel–rail contact is modified. The new criterion is intended for real-time assessment of subsurface RCF from measured wheel–rail contact forces. The only needed parameters in the new expression for the equivalent stress are the vertical force and the wheel and rail radii. Comparisons between the new and the original criterion are carried out and show good agreement for the studied cases of tangent track operations. By employing principles of vehicle dynamics the criterion is further extended to the case of operations in curves. Reasonable consistency was found for curve radii down to approximately 2000m. [Copyright &y& Elsevier]