Rolling Contact Fatigue Tests Research Articles

Life and Flaking Failure of 13Cr-2Ni-2Mo and SUS440C Stainless Steel Bearings in Water

The rolling contact fatigue (RCF) tests of 13Cr-2Ni-2Mo and SUS440C stainless steels were carried out in water. Their groove surfaces and the flaking failures were observed. Some hair cracks, wear and high roughness area were found. While the flaking depth of SUS440C was shallower than that of 13Cr-2Ni-2Mo stainless steel, the RCF life of the latter was longer than the former one. The flaking depth did not influence the RCF life.

Rolling and Rolling-Sliding Contact Fatigue Failure Mechanisms in 32 CrMoV 13 Nitrided Steel—An Experimental Study

The aim of this work is to characterize the rolling and rolling-sliding contact fatigue failure mechanisms on the 32CrMoV13 nitrided steel. During rolling contact fatigue tests (RCF), two general features were observed: specimens presenting short lives and rough and sharpened spalling damage and specimens presenting long lives and only microspalling marks. It was possible to determine a contact fatigue limit of 3 GPa. During rolling-sliding contact fatigue tests (RSCF), a clearly different behaviour between the two specimens in contact has been observed: the driver shows circumferential and inclined cracks and only inclined cracks appear in the follower. This behaviour can be understood if the effect of the residual stress state in near-surface layers is considered. Before RCF tests, the residual stresses are compressive in all near-surface layers. After RCF tests, strong residual stress relaxation and even reversing behaviour was observed in the axial direction, which facilitates the surface crack initiation in the circumferential direction at rolling track borders.

Retained austenite stability on rolling contact fatigue performance of 8620 case‐carburized steel

AbstractVarying levels of retained austenite (RA) were achieved through varying undercooling severity in uniformly treated case carburized 8620 steel. Specimens were characterized via XRD and EBSD techniques to determine RA volume fraction and material characteristics prior to rolling contact fatigue (RCF). Higher RA volume fractions did not lead to improvement in RCF lives. XRD measurements after RCF testing indicated that little RA decomposition had occurred during RCF. A continuum damage mechanics (CDM) finite element model (FEM) was then developed to investigate the effects of RA stability on RCF. The results obtained from the CDM FEM captured similar behavior observed in the experimental results. Utilizing the CDM FEM, a parametric study was undertaken to examine the effects of RA quantity, RA stability, and applied pressure on RCF performance. The study demonstrates that the energy requirements to transform the RA phase are critical to RCF performance.

Development of white etching bands under accelerated rolling contact fatigue

Bearing steel under severe loading condition undergoes substantial subsurface microstructural alterations known as Dark etching regions and white etching bands. White etching bands (WEBs) develop after hundreds of millions of stress cycles in bearing components and have been reported for several decades but the formation mechanism of white bands is not fully elucidated. Current research presents a systematic rolling contact fatigue (RCF) testing in a rotary tribometer under accelerated conditions, where rolling cycles are simulated in a 4-ball test configuration. The post RCF investigations have been carried out to understand the formation mechanism of WEBs in a ball-on-ball point contact load. WEBs have been characterised with the help of nanoindentation and Energy-dispersive X-ray spectroscopy analysis. The quantitative analysis of WEBs growth with subsurface stress field has revealed that the unique orientations of white bands are governed by the plane of maximum relative normal stress along the contact track. Moreover, the accelerated growth and reversal of WEBs sequence at elevated temperature have revealed that the WEBs formation is dependent on temperature/load combination. The observed growth of lenticular carbides in current research is also compared with dislocation gliding model and the role of carbon diffusion within WEBs is highlighted.

Study on fatigue wear competition mechanism and microstructure evolution on the surface of a bainitic steel rail

The wear and fatigue competition mechanism of a bainitic rail steel was studied through rolling contact fatigue test. Results showed that the damage process could be divided into initial (before 2.0 × 105 cycles), middle (around 2.0 × 105 cycles) and late (after 2.0 × 105 cycles) stages, with the dominant damage mechanisms of wear, wear and fatigue, and fatigue in each respectively. With increasing rolling cycles, the retained austenite transformation played an important role in achieving dynamic equilibrium between wear and fatigue. Moreover, the untransformed retained austenite could release crack tip stress and effectively control the excessive propagation of fatigue cracks.

Wear and Rolling Contact Fatigue Analysis of AISI 52100 Bearing Steel in Presence of Additivated Lubricants

Tribological properties of lithium potassium titanate (PT), molybdenum disulphide, and tungsten disulphide-dispersed mineral oil (MO) were investigated. The sample containing 2 wt.% WS2 exhibited the lowest coefficient of friction. However, the wear scar diameters of the additivated samples were very narrow. Extreme pressure properties of mineral oil were enhanced with the addition of additives. The rolling contact fatigue results exhibited better fatigue life of the balls in MoS2 and PT-dispersed MO. Surface characterization of the balls indicated more pitting on the balls of the MO and WS2-dispersed MO as compared to MoS2 and PT, indicating a stable film in the case of MoS2 and PT, which was confirmed by the presence of additives on ball surfaces by Raman spectrograph. The results of extended rolling contact fatigue tests proved that PT-added mineral oil provided the highest life cycles of the tested balls, followed by MoS2 and WS2-added mineral oil; thus, indicating PT as a plausible alternative to MoS2 and WS2.

Observation of Crack Originating from Non-Metallic Inclusions in Furnace-Induction Heated SUJ2 Steel under One-Point Rolling Contact Fatigue at High Contact Pressure

It is important to reveal the mechanism of crack growth from non-metallic inclusions because it commonly causes the origin of flaking fracture. In order to observe the cracks initiated from non-metallic inclusions under contact pressure, we performed one-point rolling contact fatigue tests using furnace-induction heated SUJ2 steel. We measured the hardness distribution of the furnace-induction heated (FIH) specimen and observed cracks with the inclusions at cross-sections.

Rolling contact fatigue study of chilled and quenched/tempered ductile iron compared with AISI 1080 steel

Both ductile iron and steel are widely used to build rolling elements. As ductile irons generally cost less than steels, this study was conducted to evaluate its rolling contact fatigue (RCF) performance by comparing with that of the AISI 1080 steel.The RCF resistance of two ductile iron variants, chilled ductile iron (CDI) and quenched and tempered ductile iron (Q&T DI), was evaluated. RCF testing was performed using a 3-ball and rod rig. The CDI and Q&T DI results were compared to those of Q&T 1080 steel. The three groups of specimens were processed to ensure a consistent surface hardness of 60 HRC prior to testing. Q&T DI exhibits a much lower RCF loading capacity (2.1 GPa) compared with CDI (3.6 GPa). Under the same loading condition, CDI demonstrated a significantly lower RCF resistance compared with Q&T 1080 steel. Failures in CDI was found to be independent of graphite, which explains CDI’s improved RCF life compared to Q&T DI. This improvement is attributed to higher micro-hardness and less variation throughout the material. The microstructure of tested CDI was analyzed with electron backscatter diffraction (EBSD) from the specimen surface to the core. These observations on carbide volume fraction and growth preference correlated to cooling rate differences between the material groups. This study paves the way for mechanistically based process design of ductile iron variants to achieve comparable RCF life of steels.

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.

Rolling contact fatigue deformation mechanisms of nickel-rich nickel-titanium-hafnium alloys

The deformation mechanisms that dictate the tribological performances of heat treated Ni55Ti45, Ni54Ti45Hf1 and Ni56Ti36Hf8 alloys are revealed through rolling contact fatigue (RCF) testing and transmission electron microscopy (TEM) analyses. Analysis of worn samples that passed a 5×108 cycle RCF runout condition shows that damage is primarily confined to deformation bands that propagate several hundred nanometers – to – several microns beneath the surface. These bands nucleate via localization of dislocation slip within the B2 austenite phase of the alloys. For the Ni55Ti45 and Ni54Ti45Hf1 samples, further damage and eventual spall failures occur by shearing and dissolution of the strengthening Ni4Ti3 nanoprecipitates within the deformation bands, followed by nanocrystallization that sometimes includes stress-induced nucleation of B19′ nanocrystals. Eventually, complete amorphization occurs prior to fracture. The relative 15 – 25% increase in RCF contact stress performance of the Ni56Ti36Hf8 alloy correlates with a more limited depth of damaged material beneath the wear surface; heavily damaged material beneath spall failure sites only extends 1.5 µm into the sample, compared to > 6 µm for Ni55Ti45 and Ni54Ti45Hf1 alloys. This superior RCF damage resistance of the Ni56Ti36Hf8 alloy results from a lower fraction of B2 matrix phase (≤ 13 %) that is highly confined by both cubic Ni-rich NiTiHf and H-phase nanoprecipitates. Specifically, this microstructure limits the widths of deformation bands within the B2 austenite phase to less than the size of the strengthening nanoprecipitates, which in turn inhibits precipitate shearing and dissolution processes that precede nanocrystallization and amorphization.

Monitoring the Damage Evolution in Rolling Contact Fatigue Tests Using Machine Learning and Vibrations

This study shows the application of a system to monitor the state of damage of railway wheel steel specimens during rolling contact fatigue tests. This system can make continuous measurements with an evaluation of damage without stopping the tests and without destructive measurements. Four tests were carried out to train the system by recording torque and vibration data. Both statistical and spectral features were extracted from the sensors signals. A Principal Component Analysis (PCA) was performed to reduce the volume of the initial dataset; then, the data were classified with the k-means algorithm. The results were then converted into probabilities curves. Metallurgical investigations (optical micrographs, wear curves) and hardness tests were carried out to assess the trends of machine learning analysis. The training tests were used to train the proposed algorithm. Three validation tests were performed by using the real-time results of the k-means algorithm as a stop condition. Metallurgical analysis was performed also in this case. The validation tests follow the results of the training test and metallurgical analysis confirms the damage found with the machine learning analysis: when the membership probability of the cluster corresponding to the damage state reaches a value higher than 0.5, the metallurgical analysis clearly shows the cracks on the surface of the specimen due to the rolling contact fatigue (RCF) damage mechanism. These preliminary results are positive, even if reproduced on a limited set of specimens. This approach could be integrated in rolling contact fatigue tests to provide additional information on damage progression.

Friction Coefficient and Wear of PEEK-PTFE Hybrid Radial Ball Bearings under Dry Conditions

In this paper, in order to investigate friction coefficient and wear of PEEK-PTFE hybrid radial bearings, rolling contact fatigue tests were performed under radial loads ranging from 93N to 387N at 600rpm in dry conditions. It was found that friction coefficients were 0.013 to 0.032 throughout the tests. Operation temperature followed the change in the friction coefficient, and PEEK-PTFE radial ball bearings exhibited stable performance even though the temperature locally approached 100 °C due to frictional heat. Moreover, wear loss of bearing components excluding alumina balls increased exponentially with increase of load.

Observation of Surface and Subsurface Crack Propagation in PPS Thrust Bearings under Rolling Contact Fatigue in Water

In this study, crack propagation in PPS thrust bearings under rolling contact fatigue (RCF) in water was observed in order to investigate the relation between cracks and flakings. RCF tests in water under loads of 700 N and 900 N were performed. The semi-circular cracks propagated in a direction perpendicular to the rolling direction were observed under a load of 700 N. The line cracks propagated in a direction parallel to the rolling direction at periphery of contact area and the semi-circular cracks were observed under a load of 900 N. To study the subsurface cracks, full section of rolling contact area was observed. It is concluded that the flaking mechanism in PPS thrust bearing has three features as follows: Initiation and propagation of surface cracks depend on the load; When load is 700N, the semi-circular cracks growing from the surface and the cracks branching from the main subsurface cracks join to form the flaking; When load is 900N the line cracks and the semi-circular cracks growing from the surface join to form the flaking.

Contact Temperature Calibration of PPS Thrust Bearings under Dry Condition

In the present study, Rolling Contact Fatigue (RCF) tests of Poly-phenylene-sulfide (PPS) thrust bearings under dry condition were carried out and the relationship between fatigue life of bearings and temperature was studied. Furthermore, in order to investigate maximum temperature of PPS thrust bearings in service, in order to obtain the calibration data, the temperatures of rolling contact element and Infrared (IR) temperature on the side of top race were measured and correlated. It is concluded that the contact temperature of failure PPS bearing was higher than the glass transition point but lower than a melting point of PPS.

Effect of Surface Ultrasonic Rolling Treatment on Rolling Contact Fatigue Life of D2 Wheel Steel.

A GPM-30 fatigue machine was used to investigate the influence of surface ultrasonic rolling (SURT) on the rolling contact fatigue (RCF) life of D2 wheel steel. The experimental results present that the RCF life of the grinding processing sample is 4.1 × 105 cycles. During the RCF process, the flaking of the fine grain layer and high surface roughness of the grinding processing sample cause the production of RCF cracks. When the samples are treated by SURT with 0.2 MPa and 0.4 MPa, the RCF life is 9.2 × 105 cycles and 9.6 × 105 cycles, respectively. After SURT, the surface roughness of the samples is reduced, and a certain thickness of gradient-plastic-deformation layer and a residual-compressive-stress layer are produced. These factors lead to the improvement of the RCF property. However, when the static pressure increases to 0.6 MPa during SURT, the RCF life of the sample is reduced during RCF testing. The micro-cracks, which are formed during SURT, become the crack source and cause the formation of RCF cracks, decreasing of the RCF life.

Influence of a Nonuniform Microstructure on the Rolling Contact Fatigue Properties of ER8 Steel Wheel

To mitigate the damage caused by rolling contact fatigue (RCF) on wheels, RCF tests are conducted to obtain the RCF limit of the surface area of an ER8 wheel tread that comprised a nonuniform microstructure. The microstructure topography of the RCF area is observed with optical microscopy, a scanning electron microscopy, and a transmission electron microscopy. The hardness, elasticity, and plasticity of different areas of the nonuniform microstructure are analyzed with a nanoindentation instrument. The results show that, besides pearlite and proeutectoid ferrite (matrix), a large amount of upper bainite is present. This component, therefore, interrupts the continuity of the wheel steel matrix, leading to a nonuniform microstructure and an RCF limit of 1074 MPa, which is lower than that of a wheel worn to the limit area and that comprised a normal microstructure. Furthermore, cracks mainly initiate and propagate at the boundary of the upper bainite and matrix. Although the hardness and the elasticity of the upper bainite are higher than those of the matrix, the plasticity is lower. Furthermore, under the effect of the contact stress, the difference between their deformations leads to stress concentration at the boundary, facilitating the initiation and propagation of cracks in steel wheels and accelerating the damage due to RCF.

Influence of laminar plasma quenching on rolling contact fatigue behaviour of high-speed railway wheel steel

This study aims at determining the influence of laminar plasma quenching (LPQ) on the rolling contact fatigue (RCF) behaviour under water condition of high-speed railway wheel steel. The wheel and rail test rollers were treated by LPQ with different scanning speeds (700, 900, 1100, 1300 mm/min), which generated different depth of heat affected zones (HAZs) and residual compressive stresses in the surface layer. To obtain an insight of the microstructures and their corresponding thermal treatment applied, the temperature evolution was simulated during the LPQ by Finite Element Modelling and the micro-structures of cross-sections below the roller surfaces were characterized. The results showed martensite, retained austenite and undissolved cementite in the HAZ as a consequence of the ultrafast heating and cooling rates. The produced residual compressive stresses resulted in an increase of ~30% of the RCF life indicating that LPQ could effectively improve the RCF resistance. Further investigations showed that the high density dislocation martensitic structure of the HAZ of reduced the plastic deformation, which could delay the RCF crack initiation and decrease the depth of RCF crack growth. During the RCF test, some retained austenite of the LPQ treated wheel roller transformed into twin martensite under the effect of strain induced martensitic transformation. The plastic deformation in the untreated wheel roller resulted in a refined microstructure showing lots of sub-grains generated in both pearlite and ferrite regions. Furthermore, we have observed that the lattice structures of the martensite in the LPQ treated sample and sub-grains of the plastically deformed untreated sample were similar to the BCC structure of the ferrite at the substrate in the high-speed railway wheel steel. We conclude from the obtained results that the LPQ processing enhances the RCF life and that this improvement is influenced by the obtained microstructure in the HAZ.

Research on Key Control Technology of Intelligent Rolling Contact Fatigue Test Facility

An intelligent rolling contact fatigue test equipment is developed, and the control methods are presented. For obtaining the slip accurately, the control method based on master-slave synchronization is proposed. For controlling the loads in high precision, the control method took into consideration the influence by two factors, displacement and the load. The nonlinear interference and excess torque in load control are effectively suppressed. Based on the SIMOTION D425 which is the Siemens integrated motion control system, the control system architecture of the intelligent rolling contact fatigue test equipment is constructed. The solutions of slip ratio and the experimental load controlled by these methods are satisfactory with the requirement of design precision. In the validation experiment, the load control accuracy is ±3%, the average error of load control is 1.77%, and the average error of slip control is 0.26%. The experiment results show the proposed control methods are feasible and effective.

Re-investigation of dark etching regions and white etching bands in SAE 52100 bearing steel due to rolling contact fatigue

Microstructural alterations such as dark etching regions (DERs) and white etching bands (WEBs) have been known to manifest in the subsurface of steel bearings due to rolling contact fatigue (RCF) under medium-high stress cycles. Even though such manifestations have been reported substantially in literature for decades, their formation and their evolution mechanisms are not fully understood. As part of the re-investigation of DERs and WEBs, this paper presents the results from characterization of DER and WEBs, including both low angle bands (LABs) and high angle bands (HABs), formed in SAE 52100 bearings at different stages of bearing life. Angular contact ball bearings (ACBBs), subjected to RCF testing under different contact pressure, stress cycles and steel cleanliness, have been examined to reveal new information related to the microstructural alteration processes, e.g. the 3-D structure of the WEBs and their growth pattern. Contrary to some of the literature results, the experimental results have shown that the mean depths and density of WEBs (LABs and HABs), as opposed to DER, are correlated with the position and distribution of the principle shear stress. The results also show that HABs form as a consequence of LABs especially in densed LAB areas in the ACBBs studied here.

Tribochemical degradation of vacuum‐stable lubricants: A comparative study between multialkylated cyclopentane and perfluoropolyether in a vacuum ball‐on‐disc and full‐bearing tests

AbstractIn this study, the decomposition of a multialkylated cyclopentane (MAC) and a perfluoro‐poly‐ether (PFPE) lubricant was investigated in a ball‐on‐disc sliding test under vacuum and in a rolling contact fatigue (RCF) test on full bearings. In situ mass spectrometry was conducted to study the tribochemical formation of hydrogen in a steel‐on‐steel ball‐on‐disc sliding contact. Further investigations on lubricant degradation in rolling‐sliding contact indicated fragmentation and oxidation reaction of the MAC oil by interaction with the oxide layer and the nascent bearing steel.Finite element method (FEM) analysis was carried out to model the contact in the ball‐on‐disc experiments and to extract contact surface temperature fields.Post‐RCF hydrogen analysis of bearing components indicated increased hydrogen content in the samples lubricated with the MAC fluid. The RCF tests with PFPE did not indicate any signs of surface damage.