Rolling Contact Stresses Research Articles

The effect of highly elongated micro-contacts on rolling contact stress field

This study presents a boundary element model to analyze contact pressure distribution and the subsurface stress field in rough rolling elements. The methodology is demonstrated by the stress field of the backup roll and work roll in the cold/temper rolling process and characterized by a parallel orientation of roughness lay with rolling direction, resulting in a cluster of highly elongated elliptical micro-contacts. The numerical outcomes revealed that the amplitude of in-plane and out-of-plane shear stress components are strongly dependent on the ellipticity of the micro-contacts. Comparison with experimental results shows that the crack plane is oriented transversal to the rolling direction and the crack initiation location corresponds to the location where the shear stress components are maximum.

Laser cladding high-performance maraging-steel coatings on bainitic cross wing rails assisted with in-situ induction heating: Microstructure and performance

Railway crossing usually bears enormous impact force and rolling contact stress during service, resulting in various surface defects or even failure of the wing rail. Laser cladding (LC) maraging-steel coatings on the rail surface shows great potential for hardfacing or repairing the wing rail effectively. However, the performance of as-deposited coatings can hardly meet our expectations because the in-situ aging heat treatment (IAHT) effect during LC is too weak to trigger the precipitation effectively. In this paper, the LC technology assisted with in-situ induction heating (LC-IH) was proposed to prepare high-performance 18Ni300 coatings on the surface of bainitic wing rail, so as to make the precipitation much more sufficient. As a result, the bending strength and impact toughness of bainitic wing rail deposited with 18Ni300 coating by LC-IH are enhanced by 4.2% and 20.0%. Meanwhile, the wear resistance of the LC-IHed rail is enhanced to 3.3 times and 1.3 times as much as those of the untreated rail and LCed rail, respectively, while its plastic deformation and fatigue crack propagation depths are greatly decreased. The main mechanism is that the cumulative IAHT time during LC-IH process was prolonged by 15.8 times as much as that during LC process, making the nanoprecipitates precipitate much more effectively. Therefore, the LC-IH technology can prepare high-performance coatings in-situ without bulk heat treatment in the furnace, showing strong industrial potentials in the future.

Numerical study on ratcheting performance of heavy haul rail flash-butt welds in curved tracks

Ratcheting at the rail heads due to cyclic rolling contact stresses is often observed in heavy haul railways, especially when there are large steering forces developed in low-radius curves. Additionally, ratcheting behaviour can be exacerbated when associated with material strength loss in the heat affected zones of rail welds. However, the numerical evaluation of this failure mode requires a sophisticated representation of elastic–plastic contact pressures and traction distributions, which, to the best of the authors’ knowledge, cannot be directly measured by any existing tools. In this paper, in order to accurately evaluate the ratcheting performance at rail welds in curved tracks, attempts were conducted to modify the FaStrip algorithm to analytically estimate the traction distributions based on contact pressures and creepages obtained from static finite element analysis and multi-body dynamic simulations, respectively. Cyclic rolling contact was then simulated by repeatedly applying contact pressure and traction on the rail surface consisting of both the rail weld and the parent rail regions. The weld region was divided into 23 sub-zones in the rolling direction to represent the material inhomogeneity within the heat affected zones. Cases on a 2000 m radius curved track and a tangent track were studied for comparison. It was found that the ratcheting strain rate in curved tracks can be significantly elevated due to the higher magnitude of traction, and the location of the elements with the highest ratcheting strain rate was dependent on the traction distribution patterns. The proposed method provides a general tool for predicting rolling contact fatigue initiation life and location, which will benefit the maintenance efficiency of heavy haul rail welds in curved track.

Prediction of Work Hardening in Bearing Steels Undergoing Rolling Contact Loading with a Dislocation-Based Model

The work hardening behaviour of GCr15 bearing steel during rolling contact fatigue (RCF) is investigated. Ball-on-rod RCF tests and micro-indentation tests are performed to obtain various subsurface hardness profiles in rod specimens. It is found that orthogonal shear stress is responsible for work hardening under Hertzian contact and that the extent of hardness increase is positively associated with the stress level and number of cycles. A dislocation-based work hardening model is established by combining the Kocks–Mecking theory, the bearing steel plasticity equation and the Taylor relation. The proposed model is capable of predicting hardness changes with any given rolling contact stress state and number of cycles. The modelling results are compared against the experimental results, with good agreement obtained. This research also provides a methodology for studying the work hardening of different types of bearing steels undergoing RCF, from experiment to modelling.

Surface Observation of Induction-Heated 13Cr-2Ni-2Mo Stainless Steel after Interrupted Fatigue Testing under Rolling Contact Stress in Water

In order to investigate the wear behavior of induction-heated 13Cr-2Ni-2Mo stainless steel, we performed the rolling contact fatigue (RCF) tests in water. We interrupted the RCF test at each 1.0×105 cycles and measure the wear loss and observed the contact surface. After the RCF tests, we found the oxygen concentration area in the contact area.

Finite element study of cyclic plasticity near a subsurface inclusion under rolling contact and macro-residual stresses

This work investigates plastic deformation around non-metallic inclusions in rolling contact fatigue applications. Subsurface stresses from Hertzian theory are applied in form of far-field loading on an elasto-plastic micro-mechanical model of an isolated inclusion. Initial and cyclic micro-scale plasticity are quantified, assuming linear kinematic hardening for the steel matrix and elastic or elastic perfectly plastic behavior for the inclusion. The accumulated plastic strain and cyclic plasticity are evaluated in the matrix. The effect of the yield strength on the elasto-plastic behavior of the matrix around the inclusions is investigated along with the effect of superimposed macro-residual stresses.

Combined effect of rolling contact fatigue and corrosion on structural performance of rails

ABSTRACT An accurate structural assessment of rails under combined effect of fatigue and corrosion prevents a phenomenal disaster, also saves millions of dollars and people’s lives. Recent studies which are proposed to simulate a precise model fail to take into account the different underlying mechanism for rail corrosion. The current study presents a numerical procedure to investigate crack initiation under combined effect of fatigue and corrosion. A three-dimensional (3D) finite element model (FEM) which accounts for rolling contact stresses due to wheel-rail contact loads is developed. Then, stress distribution is used in a MATLAB code to estimate the fatigue crack initiation life. The advantage of the proposed model is considering the combined effect of rolling contact fatigue and corrosion on structural integrity of rails. This model is applied to a case study of rail assessment in Melbourne, Australia. The cracks orientations and locations which were based on the FEM results were in good agreement with the field observations.

Contact Yield Initiation and Its Influence on Rolling Contact Fatigue of Case-Hardened Steels

AbstractStress distributions and plastic deformation zones are factors directly influencing the fatigue life of components under cyclic contact. An effective approach to improving the resistance of a steel to contact fatigue failure is surface hardening, which builds gradient yield strength from the surface of the steel to the bulk. When using the distortion energy theory as the criterion to identify failure initiation for a case-hardened steel, contact yield starts in the subsurface wherever the von Mises stress reaches the local material strength, rather than at the point of the maximum von Mises stress in the subsurface. If the yield strength changes from the surface to the bulk following a straight line, the location of yield initiation should occur at the tangency of the strength line and the von Mises stress curve. Analyses on circular, rectangular, and elliptical contacts are presented to reveal the locations of contact yield initiation for such case-hardened steels subjected to rolling contact stresses, for which the influence of friction can be ignored. A group of formulas relating contact yield initiation, in terms of the critical pressure, location of the first yield, and plasticity index (transition to plasticity) to case-hardening parameters, such as the case slope, the minimum case depth, and surface and bulk strengths, are derived to facilitate contact element designs using case-hardened materials. The results are applied to examine the rolling contact behaviors of several case-hardened steels, and the data correlation suggests that their rolling contact fatigue lives are related to a nondimensional case-hardening slope besides external loading.

2D and 3D characterization of rolling contact fatigue cracks in manganese steel wing rails from a crossing

Rail wheel contact at switches and crossings (S&Cs) induces impact stresses along with rolling contact stresses, resulting in plastic deformation and eventually crack formation. Damaged and deformed wing rails of a manganese steel crossing are studied and the microstructure, hardness and 3D crack network within the steel are characterized. It is found that the surface of the rail receives the maximum deformation resulting in a hardened top layer. The deformation is manifested by a high density of twins and dislocation boundaries in the microstructure. A complex crack network is revealed in high resolution by X-ray tomography.

Research on Residual Stress of Cr12 Surface Layer after Rolling Processing

In normal temperature, the effect of rolling motion and extrusion stress will lead to the occurrence of subgrain size refinement, changes of the dislocations and phase transition caused by plasticity, which will change the mechanical properties of the workpiece’s material on the surface layer and directly affect the fatigue strength and service life of the workpiece. In this paper, the residual stress of Cr12 after rolling processing by different rolling pass and contact stress are studied through experiments. Through the analysis of the test results, it is shown that: with the increase of rolling pass, the residual stress on the workpiece surface layer increase continuously, after rolling 3 passes, the residual stress will no longer continue to increase and remain stable. When the contact stress is less than 717 MPa, the residual stress increase obviously, and when it reaches 717 MPa, the residual stress keep relatively stable state with the increase of contact stress. In the depth direction, the residual stress decreases with the depth, and the maximum residual stress may appear at a certain depth from the surface.

Tribological Study on Tailored-Formed Axial Bearing Washers

To enhance tribological contacts under cyclic load, high performance materials are required. Utilizing the same high-strength material for the whole machine element is not resource-efficient. In order to manufacture machine elements with extended functionality and specific properties, a combination of different materials can be used in a single component for a more efficient material utilization. By combining different joining techniques with subsequent forming, multi-material or tailored components can be manufactured. To reduce material costs and energy consumption during the component service life, a less expensive lightweight material should be used for regions remote from the highly stressed zones. The scope is not only to obtain the desired shape and dimensions for the finishing process, but also to improve properties like the bond strength between different materials and the microscopic structure of the material. The multi-material approach can be applied to all components requiring different properties in separate component regions such as shafts, bearings or bushes. The current study exemplarily presents the process route for the production of an axial bearing washer by means of tailored forming technology. The bearing washers were chosen to fit axial roller bearings (type 81212). The manufacturing process starts with the laser wire cladding of a hard facing made of martensitic chromium silicon steel (1.4718) on a base substrate of S235 (1.0038) steel. Subsequently, the bearing washers are forged. After finishing, the surfaces of the bearing washers were tested in thrust bearings on an FE-8 test rig. The operational test of the bearings consists in a run-in phase at 250 rpm. A bearing failure is determined by a condition monitoring system. Before and after this, the bearings were inspected by optical and ultrasonic microscopy in order to examine whether the bond of the coat is resistant against rolling contact fatigue. The feasibility of the approach could be proven by endurance test. The joining zone was able to withstand the rolling contact stresses and the bearing failed due to material-induced fatigue with high cycle stability.

Thermomechanical capacity of wheel treads at stop braking: A parametric study

During tread braking, the treads of railway wheels are subjected to a complex loading due to combined rolling contact and thermally induced stresses. In revenue traffic the running mode of the train varies and the operational parameters will influence the life of the wheels. To prevent excessive damage, it is therefore important to understand at which operational conditions wheel damage becomes unacceptable. The current study aims to find limits for tread braking with respect to the influence of thermal stresses on rolling contact fatigue (RCF) of the wheel tread when subjected to repeated stop braking. A parametric study, using 3D FE simulations and involving operational parameters such as axle load, maximum vehicle speed, deceleration, brake block material and initial wheel temperature, is carried out for a new wheel with an S-shaped web. Additional analyses investigate impact from wheel geometry by studying a wheel with a straight web and a wheel with a thin (worn) rim. The effects of simultaneous thermal loading from wheel–block frictional contact during braking and mechanical loading, due to the traversing wheel–rail rolling contact, are studied in an uncoupled thermomechanical analysis. In the wheel–rail contact simulations, frictional rolling contact stress distributions induced by braking are accounted for. Interfacial shear stresses and partial slip are also included in the model. A temperature-dependent elastoplastic model is utilised to characterise changes in material behaviour during braking. In the vicinity of the wheel tread, damage evolutions for the studied brake load cases are evaluated. The results show that high tread temperatures, in particular temperatures above 450 °C, have a strong detrimental influence on the RCF formation and, hence, also on the thermomechanical capacity of the wheel. On the other hand, it is found that for braking temperatures between 300 °C and 375 °C, the fatigue resistance is increased due to strain hardening effects. In addition, the parametric study points towards actual braking load cases that can give such temperatures in terms of initial speeds, axle loads, etcetera. Specifically, the study shows that the train axle load, that controls the normal wheel–rail contact force, has a substantial impact on the life of the wheel treads. Wheels having straight webs and S-shaped wheel web exhibit the same fatigue life of their treads, whereas a reduction in wheel rim thickness promotes ratchetting due to increased flexural stresses from the mechanical wheel–rail contact loading.

Soft novel form of white-etching matter and ductile failure of carbide-free bainitic steels under rolling contact stresses

There has been a great deal of work on the formation of hard white-etching regions in conventional bearing steels such as 1C-1.5Cr wt% when subjected repeatedly to rolling contact stresses. The regions are a consequence of localised mechanical attrition across microcrack faces and mixing, which refine the local structure and force cementite to dissolve. This white-etching matter is often associated with brittle phenomena because the hardness can exceed 1100 HV. In contrast, carbide-free mixtures of bainitic ferrite and retained austenite when subjected to the same loading have been unexpectedly found not to develop the characteristic patches of hard material and to show instead signs of ductility in the attrited regions. The work presented here shows that the white-etching areas that develop in carbide-free bainite are softer than their surroundings, whether they are in hard nanostructured bainite destined for bearing applications or when the steel is designed for the manufacture of rails. Advanced characterisation tools were used for the first time to understand carbon redistribution during its formation. The deep interest about soft white-etching matter originates from the idea that it could lead to the reduction in premature failure of wind turbine gearbox bearings and white-etching layer grinding of rails.

Modeling wear and rolling contact fatigue: Parametric study and experimental results

A recently developed simulation model is used to study wear and rolling contact fatigue crack initiation. The model is capable of predicting the damage pattern observed in a full-scale test-rig experiment with respect to crack initiation and wear under conformal contact conditions. The crack initiation model assesses the propensity for rolling contact fatigue crack initiation at the surface of rails based on the combined assessment of the rolling contact stresses and the plastic shear strain distribution in a near-surface layer. Crack initiation is not necessarily linked to low wear rates. If favorable microstructural crack paths away from the surface exist, crack initiation can also take place in parts of the rail where high wear rates are observed. The parametric study shows that an increasing angle of attack of the wheel and an increasing coefficient of friction lead to an increase in the profile height change at the gauge corner of the rail. Likewise, the effective stress for crack initiation at the gauge corner of the rail increases with both an increasing angle of attack and an increasing coefficient of friction, but it is insensitive with respect to small changes in the rail inclination under test rig conditions.

Study on the Steel Rail Rolling Contact Stress with Consideration of Initial Residual Stress

Based on ANSYS/LS-DYNA explicit analysis software, this paper established the three-dimensional finite element model of wheel/rail rolling contact in curve negotiation with consideration of the residual stress impact after rail straightening process. It used the dynain file method to apply the initial resid- ual stress to the rails, and conducted numerical simulation to the process of dynamic wheel/rail rolling contact under the operation condition which is corresponding to the setting of taking velocity and axle load as the varia- bles. The simulation results can show that with the increase of velocity, the equivalent stress on the outer rail railhead and at the rail web will increase accordingly; the equivalent stress on the inner rail railhead and at the rail web will decrease accordingly; and the equivalent stress on the rail flange will be basically the same. With the increase of axle load, all the equivalent stress on the railheads and rail web of the inner rail and the outer rail will increase accordingly while the equivalent stress on the rail flange will be basically the same.

Study on spatial curve meshing and its application for logarithmic spiral bevel gears

The goal of the paper is to develop the theory of curving meshing and apply it in high performance gear transmission. With this aim, this study investigates the gear geometry and kinematics of space curve meshing in gear design field. Here, definition of conjugate curves and the method of obtaining them are described. What's more, an extended method to get tooth surfaces from a space curve and its conjugate curve is proposed and the meshing characteristics of these tooth surfaces are argued. Then, based on arguments for conjugate curve theorem, this paper proposes the mathematical model of conical-helix bevel gears from the idea of logarithmic spiral bevel gears. To validate this model and investigate the tooth contact characteristics of conical-helix bevel gears, the numerical example of a pair of these gears with specific profiles is represented by applying the general computer program, ANSYS 14.0. Results show that the main characteristics of these gears include loads in the same direction, pure rolling contact and low bending stresses. The results also agree with the theoretical derivations for conjugate curves and conical-helix bevel gears.

Hertz Contact Problem between Wheel and Rail

Rail-wheel contact problems have been analyzed by the use of the three-dimensional finite element models. Based on these models, the paper presents a study regarding the applicability of the Hertz contact to rail-wheel contact problems. Beside a standard rail, the study also considers a crane rail and a switching component. The bodies of the contact problem are the standard rail UIC60 and the standard wheel UICORE. The maximum contact pressure which the material can support in the elastic range in steady state conditions is known as the shakedown limit. With an operating contact pressure below the shakedown limit the rail would be expected to remain elastic a long period of its lifecycle. However, examination of rail cross-sections shows severe plastic deformation in a sub-surface layer of a few tens of microns thickness; the contact patch size is in tens of millimeters. Three-dimensional elastic-plastic rolling contact stress analysis was conducted incorporating elastic and plastic shakedown concepts. The Hertzian distribution was assumed for the normal surface contact load over a circular contact area. The tangential forces in both the rolling and lateral directions were considered and were assumed to be proportional to the Hertzian pressure. The elastic and plastic shakedown limits obtained for the three-dimensional contact problem revealed the role of both longitudinal and lateral shear traction on the shakedown results. An advanced cyclic plasticity model was implemented into a finite element code via the material subroutine. Finite element simulations were conducted in order to study the influences of the tangential surface forces in the two shear directions on residual stresses and residual strains. The Hertz theory is restricted to frictionless surfaces and perfectly elastic solids, but it is the best method for determining deformations and stress from pitch of contact. Form change due to wear and plastic deformation of a rail can reduce the service life of a track. The purpose of this investigation was to study the development of these damage mechanisms on new and three years old rails in a commuter track over a period of two years.

The effect of material property grading on the rolling contact stress field

This paper investigates the subsurface stress field induced by a rigid cylinder rolling over a functionally graded coating-substrate system. The Fourier transform is employed to extract the stress components within the graded coating and the homogeneous substrate. The distributions of the stresses are given through the depth and along the coating–substrate interface. The contour plots of normalized Von Mises stresses are provided as well. The results indicate that continuous variation of the shear modulus substantially reduces the difference between the in-plane stresses along the interface. Also, the softening coating leads to the minimum value of the stress concentration near the contact surface.

Transient CFD Analysis of Multi-Lobe Bearings at 60000RPM for A Gas Turbine

Transient CFD Analysis of Multi-Lobe Bearings at 60000RPM for A Gas Turbine

Three-dimensional elastic–plastic stress analysis of wheel–rail rolling contact

Abstract A finite element model with the implementation of an advanced cyclic plasticity theory was used to study the three-dimensional elastic–plastic rolling contact stresses of wheel and rail. Three-dimensional rolling contact was simulated by multiple translations of the normal pressure and tangential tractions across the rail surface. The contact area, normal contact pressure and tangential tractions were calculated by the Kalker's program CONTACT. The finite element simulations were conducted to investigate the influence of partial slip condition and varying contact load on the rolling contact stresses and deformations. The results show that the partial slip condition or the creepage has a greater effect on the residual strains than on the residual stresses. While the residual strains and surface displacements increase at a reduced rate with increasing rolling passes, the residual stresses stabilize after a limited number of rolling passes. The present simulation results also indicate that a varying normal contact force results in a plastic deformation induced wavy rolling contact surface profile. Such a wavy surface profile evolves with rolling history and tends to stabilize due to the decaying ratchetting rate. The residual stresses and strains near the wave trough of the residual wavy deformation are higher than those near the wave crest of the residual wavy deformation. The wave depth of the residual wavy deformation increases with an increase of creepage.