Contact Fatigue Research Articles

Re‐recognition of deep spalling damage mechanism of rolling contact fatigue under heavy load

AbstractThis paper presents a detailed analysis of the nucleation and propagation of surface‐initiated crack in rolling contact fatigue (RCF) of bearing steel under heavy load. The cracks initiated from the junction of machining marks and trailing edge of dents formed by the plastic deformation. Crack propagation and spalling were mainly composed of three stages: (1) cracks initiating from surface defects propagate downward to form small spalling pits; (2) due to the surface stress and the maximum Hertz stress form a stress bridge, the cracks continue to expand towards the Hertz stress peak forming big spall; (3) the trailing edge of the spalling pit is used as the stress raiser to initiate next subsurface cracks and spalling expansion in successive. Different from previous understanding on the formation of subsurface‐initiated spalling, the results indicate that under heavy load the spalling at depth of the maximum shear stress zone in the subsurface can initiate from surface cracks.

A numerical study on tread wear and fatigue damage of railway wheels subjected to anti-slip control

Tread wear and rolling contact fatigue (RCF) damage propagated on railway wheels are the two extremely important focal points as they can tremendously deteriorate wheel/rail interactions and hunting stability and destroy wheel surface materials, and subsequently, cut down the lifetime of the wheels. The on-board anti-slip controllers are of essence aiming to hold back the striking slipping of the powered wheelsets under low-adhesion wheel/rail conditions. This paper intends to investigate the impact of anti-slip control on wheel tread wear and fatigue damage under diverse wheel/rail friction conditions. To this end, a prediction model for wheel wear and fatigue damage evolution on account of a comprehensive vehicle-track interaction model is extended, where the wheel/rail non-Hertzian contact algorithm is used. Furthermore, the effect of frictional wear on the fatigue damage at wheel surface is considered. The simulation results indicate that the wheel/rail contact is full-slip under the low-adhesion conditions with braking effort. The wear amount under the low-adhesion conditions is observably higher than that under the dry condition. It is further suggested that the wheel tread is prone to suffering more serious wear and fatigue damage issues with a higher anti-slip control threshold compared to that with a lower one.

Modeling and dynamic characteristic analysis of high speed angular contact ball bearing with variable clearance

In this paper, an analytical calculation model based on Jones raceway control hypothesis model was proposed for high-speed ball bearing, clearance, centrifugal displacement and thermal deformation are considered. The validity of the proposed model was verified by comparing with the Jones model, and the fatigue life model of bearing was established. The bearing dynamic characteristics under axial load and combined load are analyzed, and the change rule of each parameter is revealed. In addition, the influence of different clearances on high-speed bearing is studied, and the dynamic characteristics of bearing are further analyzed. The research show that the proposed model can break the limitation of Jones raceway control hypothesis model, and the bearing ball-raceway contact state and fatigue life are greatly affected by the change of working clearance. Therefore, the analytical calculation model in this paper not only meets the dynamic characteristics analysis of ball bearing under different operation conditions, but also has great significance for the design and use of bearing.

Wheel-rail contact and friction models: A review of recent advances

Rail transportation is regarded as a reliable, quick, and secure mode of transportation. The wheel-rail contact interaction is crucial to the railway operation since it is responsible for supporting, traction, braking, and steering of railway vehicles. Improper wheel-rail interactions may produce or exacerbate wheel-rail interface issues such as rolling contact fatigue (RCF) and wear, which can threaten the vehicle’s running safety and stability. A review of the evolution and recent literature on wheel-rail contact mechanics and tribology is presented here. Topics covered include the basics of wheel-rail contact problem and methodologies for modeling both the normal contact (Hertzian and non-Hertzian) and tangential contact (Kalker’s theories including CONTACT and FASTSIM algorithms, Polach’s theory, USETAB program, etc.). The paper also reviewed various effects of contaminants and environmental conditions (water, leaves, sand, temperature, humidity, etc.) in wheel-rail contact. Various wheel-rail empirical adhesion models like the Water-induced low adhesion creep force model (WILAC) model and adhesion models based on elastohydrodynamic lubrication (EHL) theory (Greenwood-Tripp [GT] and Greenwood-Williamson [GW] models) are also reviewed. Lastly, the paper discusses the need and challenges for developing and integrating the wheel-rail non-Hertz contact model and adhesion model, as well as open areas for further research.

Experimental study on wheel-rail rolling contact fatigue damage starting from surface defects under various operational conditions

Surface defects in different railway lines experience different wheel-rail rolling contact actions owing to various railway line characteristics and vehicle operation parameters. This study focused on the evolution of defective wheel-rail rolling contact fatigue (RCF) behaviour under different operation conditions. Conical defects were created using an indentation apparatus. Wheel-rail RCF tests were performed using a twin-disc testing machine. Various operational conditions were simulated considering different slip ratios and wheel linear velocities on uphill and flat lines, as well as different vehicle axle loads and train configurations. The results indicate that surface damage, crack depths, and wear debris size increased only with decreasing wheel linear velocities, whereas the crack angles increased only with decreasing slip ratio. Meanwhile, both the wear rate and oxidation degree of wear debris were simultaneously affected by the slip ratio and wheel linear velocities. Under rolling conditions on flat lines, vehicle axle loads had a negligible influence on the wheel-rail RCF behaviour.

Prediction system of rolling contact fatigue on crossing nose based on support vector regression

It is essential to assess the rolling contact fatigue (RCF) of turnouts and maintain them in advance. It saves a lot of money while protecting the safety of railway operations. In Germany, the damage on rails, especially crossing noses, mainly depends on the subjective judgment of experts. There are no objective and comprehensive evaluation criteria. This paper presents the application of image processing and supervised machine learning algorithms to crossing nose fatigue judgment. The fatigue characteristics of the crossing nose rolling contact surface along the life cycle of the crossing nose are analyzed. The study used crack information from magnetic particle inspection (MPI) images of crossing nose surfaces. It uses basic image processing methods to collect physical information about features of fatigue cracks in images. Existing feature selection methods are used to exclude irrelevant features and retain valuable features. And we select the best feature selection method through the regression results. Statistically significant crack features and combinations that depict the surface fatigue state are found. In this paper, by comparing several usually machine learning regression algorithms, it is found that the supervised learning of support vector machine regression (SVR) has achieved the best results in the regression fitting of the crack feature data in this paper. The regression results form a simple system to evaluate the life cycle of crossing nose. The system finds the location of cracks that can create dangerous defects in the crossing nose surface. The research result consists of the early prediction of rail contact fatigue.

Fatigue-life and stress distribution of a glass-ceramic under different loading conditions

This study aimed to evaluate the effect of different loading conditions on the mechanical behavior and stress distribution of a leucite-reinforced glass-ceramic. Plate-shaped ceramic specimens were obtained from leucite-reinforced glass-ceramic (1.5 × 8.4 × 8.3 mm) and adhesively cemented to a dentin analog substrate. Monotonic and cyclic contact fatigue tests were performed to simulate sphere-to-flat contact, using a 6 mm diameter spherical piston; and flat-to-flat contact, using a 3 mm diameter flat piston. For the monotonic test (n=20), a gradual compressive load (0.5 mm/min) was applied to the specimen using a universal testing machine. Failure load data were analyzed with Weibull statistics. The cyclic contact fatigue test was performed using protocols (load and a number of cycles) defined by the boundary technique (n=30). Fatigue data were analyzed using an inverse power law relationship and Weibull-lifetime distribution. The stress distribution was investigated using Finite Element Analysis (FEA). The monotonic and the fatigue Weibull modulus were similar among the two contact conditions. In fatigue, the slow crack growth exponent was greater for sphere-to-flat contact, which indicates that the load level had a greater effect on the specimen's probability of failure. In conclusion, FEA showed different stress distribution for the tested loading conditions. The stress distribution and probability of fatigue failure of specimens tested in sphere-to-flat contact showed greater dependency to load level.

Improved rolling contact fatigue performance of selective electron beam melted Ti6Al4V with the as-built surface using induction-heating assisted ultrasonic surface rolling process

In this paper, the effects of induction-heating assisted surface ultrasonic rolling processing (IH-USRP) on the rolling contact fatigue (RCF) performance of selective electron beam melting (SEBM) built Ti6Al4V was evaluated with respect to surface integrity, chemical composition, and microstructure were investigated. At the room temperature (RT), the surface roughness and line roughness (Ra and Rz) of the USRP treated sample are reduced by 92 % and 95 %, 78 %, and 66 % compared to the untreated sample, respectively, and the surface hardness is also increased by 17 %. The surface quality and hardness are further improved when samples treated by IH-USRP, and the oxide mixture could be found on the sample surface. The surface roughness and line roughness (Ra and Rz) of the IH-USRP treated sample at 650 °C were reduced by 96 % and 98 %, 85 %, and 83 %, respectively, while the surface hardness was 33 % higher than that of the untreated one. The surface quality improvement reduces the stress concentration, and the increased surface hardness means higher critical shear stress, which promotes the average RCF life by 196 %.

Dry rolling-sliding wear behavior of ER9 wheel and R260 rail couple under different operating conditions

This work aimed to evaluate the effects of contact stress and slip ratio on wear and rolling contact fatigue of ER9 wheel steel and R260 rail steel couple under unlubricated conditions using a dual disk test. It was demonstrated that as either contact stress or slip ratio increased, so did the wear rate and surface damage of both ER9 wheels and R260 rail rollers. The wear rate of the ER9 wheel steel containing proeutectoid ferrite and the smaller structure size of pearlite increased significantly when compared to the rail steel containing fully pearlite in each pair. After testing according to the conditions used in this work, the surface hardness of the pearlitic rail steel was higher than that of the ferrite-pearlite wheel steel. The average hardening ratio of ER9 wheel steel and R260 rail steel was 0.7 and 1.28, respectively. This was consistent with the subsurface deformation angle. With full pearlite in the microstructure of rail steel, the main wear mechanism was predominantly caused by fatigue cracking and peeling, with some adhesive wear. Whereas the most prominent mechanism of the ferrite-pearlite wheel steel was adhesive wear, which was followed by spalling and small fatigue cracks.

Research on the Effect of Pearlite Lamellar Spacing on Rolling Contact Wear Behavior of U75V Rail Steel

The damage mode of U75V rail steel in application is determined by its rolling wear behavior. In this paper, the pearlite microstructure of U75V steel is characterized to investigate the relationship between wear and fatigue behavior. The results show that, with decreasing of pearlite lamellar spacing, the wear resistance of the steel increases and the contact fatigue resistance decreases. The spacing decreasing causes the change of the wear mechanism from abrasive wear to adhesive wear, as well as the damage mode from wear damage to fatigue damage. The smaller the pearlite lamellar spacing is, the stronger the deformation of the cementite lamellar is. The thin cementite lamellar is hardly broken in the rolling friction to pile up a large number of dislocations in the ferrite matrix and the work hardening degree was improved. So, the plastic deformation layer is difficult to remove, and fatigue cracks are easy to initiate and extend to the interior of the material.

Numerical modelling of rolling contact fatigue damage initiation from non-metallic inclusions in bearing steel

Bearing failure is a cause of concern in a variety of machinery such as turbines, transmissions, drills, engines, etc. It is often associated with rolling contact fatigue (RCF) triggered from damage initiation at non-metallic inclusions (NMI’s). Experimental evidence shows that damage initiation lifetime is highly sensitive to the NMI characteristics and its bonding with the steel matrix. This study numerically investigates the role of NMI features and its bonding with the steel matrix on damage initiation lifetime. NMI characteristics modelled in this study are derived from an experimental investigation of a failed bearing. Simulation results highlight a near to instantaneous debonding at the matrix-inclusion interface followed by accelerated crack initiation. The critical depth for damage initiation shifts towards the surface with the increase in friction coefficient between roller and raceway. The simulations also reveal that larger inclusions show earlier damage initiation, indicating a size effect. The damage hotspots from the simulation results were compared with experimental findings and a hypothesis for crack initiation from a NMI is put forward.

A ratcheting mechanism-based numerical model to predict damage initiation in twin-disc tests of premium rail steels

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

Mechanistic study of dark etching regions in bearing steels due to rolling contact fatigue

Dark etching region (DER) formation is the first stage of a series of subsurface microstructural alterations induced by cyclic stresses during rolling contact fatigue in bearing steels followed by the formation of low angle bands (LAB) and high angle bands (HAB). A unified formation mechanism for LAB and HAB development in bearing steels has been proposed as a series of energy build-up and release in a recent study. This paper presents the development of DER through the analysis of two different steel, 100Cr6 and 50CrMo4, at various stages in the lifetime of bearings using SEM, EBSD and nanoindentation. It is found that early stages of DER consist of patches of multiple dark etching bands orientated at three distinct orientations relative to the rolling direction. As the dark etching bands grow in density, they contribute to the refinement of the parent microstructure through fragmentation of martensite laths. The fragmentation as well as intersections of dark etching bands lead to the creation of stress points within the region that become nucleation sites for the formation of equiaxed ferrite grains through recrystallization, which has been found to be the initiation stage of LAB. Hence this study establishes a link between DER and LAB/HAB development in rolling bearings.

Rolling-sliding contact fatigue failure and associated evolutions of microstructure, crystallographic orientation and residual stress of AISI 9310 gear steel

In the present study, rolling-sliding contact fatigue (RSCF) failures of AISI 9310 gear steel were analyzed systematically, in terms of characterizing the fatigue life, evolution of microstructure and crystallographic orientation, and variation of microhardness and residual stress distributions. The RSCF experiments were conducted using a twin rollers fatigue test rig. The RSCF life of AISI 9310 steel roller decreased continuously with increasing the maximum Hertzian contact pressure, however, it could be effectively improved by additional shot peening process owing to the enhanced microhardness and compressive residual stress near the roller surface. The main fatigue damage characteristics near the roller surface were consisted of inclined cracks, micropitting, spallation and plastic deformation. Although the compressive residual stress was reduced by RSCF, there was an obvious increase in the microhardness which should be attributed to the refined microstructure, increased dislocation density as well as phase transformation from retained austenite to martensite. In addition, the accumulated plastic strain during RSCF resulted into development of several preferred crystallographic orientations corresponding to ideal shear texture components of body-centered cubic (BCC) materials that has been seldom reported.

Investigation on 3D fatigue crack propagation in pitch bearing raceway of offshore wind turbines

In complex marine environments, pitch bearings are more prone to crack initiation, propagation, and evolution, which leads to contact fatigue problems. Accurately identifying and predicting the evolution of early crack extensions in pitch bearings can effectively prevent major economic losses caused by failure. The two limitations of the current research on pitch bearing cracking are the low efficiency of the simulation and the fact that the contact fatigue models are mostly simplified to two-dimensional models. These models do not accurately reflect the influence of the raceway geometry parameters on the real situation. This study combined Bladed and MATLAB for an integrated life cycle simulation using Python and a cloud platform to reduce the simulation duration. A three-dimensional modelling method was proposed to calculate the crack propagation in pitch bearings throughout the full life cycle. The effects of different operating conditions, crack depths, and initial crack angles were investigated and analyzed. The results suggested that the maximum Hertz contact stress was 2961.4 MP. When the initial crack angle was greater than 0°, the crack generally propagated towards the core area. When the crack angle was less than 30°, the crack propagated gradually in depth and towards the surface. The fatigue life at an initial crack angle of 60° was 1.5 times that of an initial crack angle of 30°.

Numerical Study of Rayleigh Wave Interaction with Rolling Contact Fatigue Type of Defects

ABSTRACT Rolling Contact Fatigue or Damage (RCF/RCD) presents significant maintenance challenges to railroads across the globe. Quantifying RCF/RCD crack depths and density in rails is important for all railroads to manage their grinding programs effectively and efficiently and being able to conduct ultrasonic testing (UT) of rails for reliable detection of internal fatigue damage. This work focuses on the modeling of Rayleigh waves UT approach to detect and characterize RCF type of defects which can form as: vertical, oblique or branched shaped surface breaking defects in the rail head. Specifically, the transmission coefficient (Tc) of Rayleigh waves was studied using finite element analysis (FEA). The effect of crack tip geometry on Tc values is discussed. The results suggest that for oblique, and branch cracks, characterization based purely on the Tc can be challenging due to symmetric sinusoidal fluctuations in the Tc. A real crack using a micrograph image was also modeled to validate the Tc results for oblique and branched cracks. This points to the need for additional parameters to be identified for efficient and reliable characterization of RCF/RCD type of defects in rails.

AN ADDITIVE MANUFACTURING AND LATTICE STRUCTURES PERSPECTIVE FOCUSED ON BIOMIMETIC KNEE IMPLANT DESIGN

There are different types of knee implants, each seeking to restore the natural behavior of a healthy knee. Factors such as contact stress, wear and fatigue have been extensively analyzed for their design.

Investigation of Quantitative Evaluation of Rolling Contact Fatigue Cracks in Rail Steel by X-Ray Diffraction Line Profile Analysis

Investigation of Quantitative Evaluation of Rolling Contact Fatigue Cracks in Rail Steel by X-Ray Diffraction Line Profile Analysis

Condition monitoring of pitting evolution using multiple sensing

Pitting on surfaces is a type of rolling contact fatigue (RCF) occurs in rolling-sliding contacts operating under mixed or boundary lubrication conditions. The early detection of pitting is of great importance due to its potential detrimental effects on the performance and reliability of machinery components, such as rolling element bearings and gears. This research aims to investigate the responses of multiple sensors to the progression of pitting and achieve early detection of pitting initiation. Experiments were conducted on a TE74 twin-disc tribometer to investigate the behaviour of bearing steel discs. Mild wear and pitting fatigue were obtained with specimens of different roughness combinations. During testing, vibration, acoustic emission (AE) and electrostatic (ES) data were recorded, and post-test signal analysis was conducted in both the time domain and frequency domain. After testing, the worn surfaces were examined to determine the mechanisms responsible for specific features seen in the sensor data. The presence of pitting in the near-surface region was observed, and its development was effectively monitored using the employed sensing techniques. The stages of running-in, pitting initiation, and pitting formation were identified through the analysis of time-domain parameters and frequency spectrums. Vibration signal analysis exhibited a more prominent indication of pitting formation, whereas AE and ES methods demonstrated an ability to detect the onset of pitting at an earlier stage.

Guidelines for rail quality selection to increase service life based on wear and fatigue behavior of various wheel and rail materials

The Austrian rail network is very diverse: The lines in the alpine areas have very tight radii while the lines in the flat areas (east and north of Austria) are mainly straight high-speed lines. This leads to different levels of wheel and rail wear. Accordingly, the objective of this study was to experimentally model a laboratory-scale cyclic wheel-rail contact to investigate wear behavior and rolling contact fatigue at different radii (RCF).A novel test system was set up at AC2T research GmbH to reproduce unidirectional loading on a real track. Tribotests were performed with rail (grades R260, R350HT & R400HT) and wheel (grades ER7 & ER9) parts from the field. This newly designed principle is an effective method to characterize the wheel-rail contact. Wear characterization was done after defined testing cycles to detect (i) area loss and (ii) change in surface topography.