Rolling Contact Fatigue Strength Research Articles

Effect of boron addition on the rolling contact fatigue strength of Fe-Ni-Mo-B-C sintered alloys

Effect of boron addition on the rolling contact fatigue strength of Fe-Ni-Mo-B-C sintered alloys

Influence of steel cleanliness and heat treatment conditions on rolling contact fatigue of 100Cr6

The aim of this work is to determine the rolling contact fatigue (RCF) strength of steel AISI 52100 (DIN 100Cr6) as a common bearing steel in different heat treated conditions. In order to study and evaluate the steel cleanliness and its influence on the fatigue behavior the results are compared to AISI L3 (DIN 102Cr6) as a cold-working tool steel containing higher amounts of non-metallic inclusions as a consequence of a different metallurgical processing. In this work experimental results obtained from both materials with martensitic and bainitic microstructures are presented. In addition, the inclusion content in each material was analyzed using extreme value statistics, and the endurance limits are predicted based on the maximum expected inclusion in the maximum loaded volume as a critical crack initiating defect. The predicted RCF values are in good agreement with the experimental results. Irrespective of the microstructure, the hardness after heat treating dominates the endurable Hertzian pressure. The second important parameter, which determines the endurance limit, is the cleanliness of the steel. Furthermore, the crack pattern in the surface and microstructure of the RCF specimens were analyzed by optical microscopy. The results show no microstructural modifications such as dark etching regions or white etching bands. However, the formation of butterflies was detected around non-metallic inclusions in both steels.

Micro-scale frictional behavior of a bearing steel (JIS SUJ2) in cyclic sliding motion

Application of fracture mechanics has recently been emphasized to establish the mechanics-based evaluation of the rolling contact fatigue strength for designing mechanical elements such as bearing, rail/wheel, gear, etc. Flaking that is a typical rolling contact failure mode is intimately related to the shear-mode (modes II and III) fatigue crack growth, which is significantly affected by the interaction of opposing crack faces. Understanding the tribological properties on the crack faces being in the reciprocating sliding contact is therefore essential for the material design as well as the mechanical design of many components associated with rolling contact fatigue. The present study carried out a ring-on-ring test by making use of a combined axial-torsional fatigue testing machine to investigate the micro-scale frictional phenomena under the non-lubricated condition. The material investigated was a heat-treated high-carbon-chromium bearing steel (JIS SUJ2) with a Vickers hardness of 753. The tests were conducted up to 104 cycles under the various conditions of mean contact pressures of 10-100 MPa, relative displacement amplitudes of about 10-100 μm, sinusoidal frequencies of 0.1-10Hz, and initial surface roughness values, Ra, of 0.2-1.7. The time variations of the tangential force, contact load and the relative displacement between contact surfaces were periodically monitored at a predetermined number of cycles during testing.

Quantitative evaluation of the flaking strength of rolling bearings with small defects as a crack problem

Rolling contact fatigue (RCF) tests were conducted on rolling bearings with drilled holes at the mid-point of the raceway. Flaking limit was determined by the shear-mode threshold of a crack that emanated at the edge of drilled hole. To quantify the RCF strength according to fracture mechanics principles, Mode II stress intensity factor (SIF) range of the crack was derived. Taking a small crack effect on the shear-mode fatigue crack into account, RCF strength was successfully evaluated as a crack problem, irrespective of the diameters and depths of the hole. The values of the threshold SIF range obtained by RCF tests were in good agreement with those obtained in the torsional fatigue tests under static compression.

Bearings Downsizing by Strength Enhancement and Service Life Extension.

Slim bearings are used widely in aircrafts, robots, wind turbines, and industrial machineries, where their size and weight are very important for the performance of a system. The common materials of slim bearings for robots and industrial machineries are based on SAE52110 bearing steel, and special heat treatment and a super polishing process are used and adapted to improve the rolling contact fatigue (RCF) strength of bearings. The improvement in RCF strength, depending on contact stress, surface hardness, and the friction behavior before and after ultrasonic nanocrystalline surface modification (UNSM) treatment was validated. Simple analysis shows that these improvements can reduce the size and weight of slim bearings down to about 3.40–21.25% and 14.3–26.05%, respectively. Hence, this UNSM technology is an opportunity to implement cost-saving and energy consuming super-polishing, a heat treatment process, and to reduce the size and weight of slim bearings.

Simulation of rolling contact fatigue strength for traction drive elements (comparison with fatigue test)

Simulation of rolling contact fatigue strength for traction drive elements (comparison with fatigue test)

SIMULATION OF ROLLING CONTACT FATIGUE STRENGTH FOR TRACTION DRIVE ELEMENTS

The simulations of the rolling contact fatigue strength for traction drive elements was carried out, and the estimation accuracy of it was verified by comparing with the experimental result. The experiment was carried out by following the 14 S-N testing method. The material of test rollers was carburized JIS SCM420H. The calculated rolling contact fatigue strength in failure rate of 50% at 107 cycles was 750 MPa with a standard deviation of 35.4 MPa. The rolling contact fatigue strength of 1120 MPa with a standard deviation of 50.8 MPa was obtained as a result of experiment. The calculated standard deviation was about equal to the experimental result. Though there was 370 MPa difference between calculated and experimental fatigue strength. Including of the hardening of roller and the influence of compressive residual stress in the simulation and the determination of the depth of failure initiation will decrease above error.

Effect of Laser Power on Delamination Initiation Behaviour of CrAlN Coating on Steel Substrate Laser-Quenched after Coating Process under Rolling Contact Fatigue

In order to investigate the effects of new surface modification method “Laser quenching after coating” on the rolling contact fatigue strength of ceramic coated steel, CrAlN coated specimens were processed by this method under various laser power conditions, and the thrust type rolling contact fatigue tests were carried out for these specimens. The delamination initiation life of CrAlN coated specimen increased with the laser power, however the excessive laser power decreased the delamination initiation life. The adhesive strength of CrAlN coated specimen showed similar variation for the increase of the laser power. The film hardness was almost constant for the increase of the laser power, however the excessive laser power also decreased the film hardness. From these results, it was considered that the increase of the delamination initiation life of CrAlN coated specimen was caused by the increase of the adhesive strength, and the decrease of the delamination initiation life at high laser power was affected by the decrease of the adhesive strength and/or the film hardness.

Influence of solid solution strengthening on spalling behavior of railway wheel steel

The object of this paper is to investigate the influence of solid solution strengthening on the spalling behavior of railway wheel steel. White etching layer (WEL) was reproduced by twin-disc test and analyzed by phase transformation kinetic. Spalling of WEL was then evaluated by rolling contact fatigue (RCF) test and finite element analysis. The results show that solid solution strengthening improves the resistance to WEL formation for wheel steel through increasing the austenitization temperature. WEL remarkably reduces the RCF life of wheel steel. Whether containing WEL or not, solid solution strengthened steel exhibits a better rolling contact fatigue strength than the traditional wheel steel.

Effect of Repeated Quenching on Rolling Contact Fatigue Properties of JIS SUJ2 Bearing Steel

One important method to improve the material properties is refinement of the prior austenite grain size. Repeated quenching is used as a grain refinement method. In the present work, samples of SUJ2 steel were furnace quenched once and thrice in order to investigate the effect of repeated quenching on rolling contact fatigue (RCF) strength. After the RCF tests, maicrostructure observations, Vickers hardness and retained austenite measurements, RCF life evaluation using the Weibull distribution were carried out. It was found that the dispersion of the life population was reduced by repeatedly quenching.

Effect of elevated temperature on shelling property of railway wheel steel

A type of tread damage called thermal mechanical shelling (TMS) is one of the main causes for heavy haul wheel removals in North America. Wheels are considered to have a shorter service life for TMS than other causes of removals as rolling contact fatigue (RCF) strength decreases because of elevated temperature from tread brakes. In this study, to evaluate the relationship between RCF life and elevated temperature, RCF tests and FE analyses were conducted. Twin disc type RCF tests with induction heating were applied to evaluate RCF life under thermal cycling simulating tread brakes. Test results show that RCF life was shorter with the higher maximum temperature and the longer holding time at elevated temperature. Softening of the material because of microstructure change was observed for the test specimens tested at the maximum 500°C. Then, crack tip opening behaviour was evaluated by elasto-plastic FE analysis. FE analysis results showed that crack tip opening displacement (CTOD) was larger with the higher temperature and the longer holding time at elevated temperature. Moreover, CTOD increased with a decrease of the material strength. These results indicate that wheel life of TMS decreases by acceleration of fatigue crack propagation with elevated temperature.

G0300902 レーザ熱処理によるセラミックス被覆鋼の転がり疲労はく離発生寿命の向上化に関する研究

In order to investigate the effects of new surface modification method "Laser quenching after coating" on the rolling contact fatigue strength of ceramic coated steels, CrAIN coated steel specimens and TiAIN coated steel specimens were processed by this method and the thrust type rolling contact fatigue tests were carried out for these specimens. In the process of the laser quenching after coating, laser irradiation was carried out under various laser power conditions. The delamination initiation life of CrAIN coated specimen increased with the heat input, however the excessive heat input decreased the delamination initiation life. The adhesive strength of CrAIN coated specimen showed similar variation for the increase of the heat input, and a good correlation was recognized between the delamination initiation life and the adhesive strength. It was considered that the delamination initiation life of CrAIN coated specimen was strongly affected by the adhesive strength. For TiAIN coated specimen, the delamination initiation life once increased and then decreased with increasing the heat input, although the adhesive strength increased monotonously. The hardness of TiAlN film decreased from the heat input at which the delamination initiation life began to decrease. By laser irradiation, the film hardness of TiAIN decreased more easily than that of CrAIN, because the oxidation temperature of TiAIN was lower than CrAIN. The decrease of the delamination initiation life of TiAIN coated specimen laser-irradiated under the high heat input condition could be explained by the decrease of the film hardness. The delamination initiation life of TiAIN coated specimen was strongly affected by the decrease of the film hardness caused by laser irradiation.

Delamination initiation life and growth behaviour of ceramic coated steels quenched after coating process under rolling contact loading condition

In order to investigate the effects of a new surface modification method, ‘the substrate quenching after coating’ on the rolling contact fatigue strength, TiN coated steel specimens and CrAlN coated steel specimens were processed by this method and the thrust type rolling contact fatigue tests were carried out for these specimens. In the process of the substrate quenching after coating, two types of quenching methods, furnace quenching and laser quenching, were used.For the furnace quenched specimens, the delamination initiation life of CrAlN coated specimen was longer than that of TiN coated specimen. This reason could be explained by the difference of the oxidisation of CrAlN and TiN in their furnace quenching process. For CrAlN coated specimens, the delamination initiation life of the laser quenched specimens was longer than that of the furnace quenched specimens. After the initiation, the delamination of the furnace quenched specimen grew much faster than that of laser quenched specimen. These reasons could be explained by the difference of the process time of the furnace quenching and the laser quenching. The process time, in which the ceramic coating of the specimen was exposed to an elevated temperature, of the furnace quenching was much longer than that of laser quenching.It is considered that substrate laser quenching after coating could be an effective way to improve the delamination initiation life and to reduce the delamination growth rate under rolling contact fatigue.

Mechanical Properties and Kinetics of Borided AISI M50 Bearing Steel

The present study reports on mechanical properties and kinetics of borided AISI M50 steel. AISI M50 steel is widely used for critical aircraft engine bearings operating at elevated temperatures with its combination of good hot hardness and excellent rolling contact fatigue strength. AISI M50 is also intermediate high-speed steel which make it suitable for using as woodworking tools and hacksaw blades. Despite its wide range of use, there is almost no published research on the boronizing of AISI M50 steel in the literatures. Boronizing thermochemical treatment was carried out in a solid medium consisting of EKabor-I powders at 850, 950, and 1,050 °C for 2, 4, 6, and 8 h, respectively. The presence of borides FeB and Fe2B on the steel substrate was confirmed via X-ray diffraction analyses and energy-dispersive X-ray spectroscopy. The results of this study indicated that the boride layer has a smooth and compact morphology, and its hardness was found to be in the range of 1,630–2,040 HV. Depending on process time and temperature, the thickness of boride layer ranged from 6 to 216μm. Layer-growth kinetics were analyzed by measuring the extent of penetration of the FeB and Fe2B sublayers as a function of boronizing time and temperature. The fracture toughness of borides ranged from 3.89 to 3.51 MPa m1/2. Moreover, an attempt was made to investigate the possibility of predicting the iso-thickness of boride layer variation and to establish an empirical relationship between process parameters and boride layer thickness.

Effect of crowning radius on rolling contact fatigue strength for traction drive elements (Evaluation by simulation)

A simulation of the rolling contact fatigue strength of a traction drive element was developed. This simulation accounts for both the distribution of sizes of inclusions in the element material and the influence of traction forces at the element surface. The shear strength of the matrix structure surrounding an inclusion was estimated with an equation. The hardness distribution and the Weibull distribution of inclusion dimensions, which are necessary parameters to calculate the rolling contact fatigue strength, were determined by observation of an actual test specimen. The purpose of this report is simulations to evaluate the effect of the crowning radius on the rolling contact fatigue strength and the torque capacity. The simulations were carried out by varying the crowning radius of the virtual roller. To consider the effect of the crowning radius, a simulated two-dimensional virtual roller, which has actual material properties, was modified to a roller multilayered toward the axial direction. The simulation assuming the actual roller led to a difference of 1.0% from the experimental rolling contact fatigue strength. This difference was 2.4 points smaller than the result for the two-dimensional virtual roller. The rolling contact fatigue strength decreased with increasing crowning radius for two reasons. One was the increase in the number of inclusions under the high stress due to the increasing crowning radius. The other was the expansion of the portion of the roller subject to high stresses down to a depth having small hardness. However, the torque capacity calculated from the contact force resulting in failure increased with the increasing crowning radius.

Effect of Size and Depth of Small Defect on the Rolling Contact Fatigue Strength of Bearing Steel JIS-SUJ2

To quantitatively estimate rolling contact fatigue strength as a crack problem, rolling contact fatigue tests were performed on JIS-SUJ2 bearing steel using specimen plates into which small holes of various diameters and depths had been drilled. In all the tests, fatigue cracks initiated at the edge near the bottom of the hole, and then propagated by the shear-mode. Even in the specimens that did not fail after being tested up to N = 2×108 cycles, short fatigue cracks were found at the edge. The fatigue life Nf plotted against the maximum contact pressure qmax varied greatly on the basis of the diameter and depth of the hole. The effect of the depth of crack initiation on Nf was uniquely characterized by using the nominal shear stress amplitude τa, instead of qmax Further, by considering the rolling contact fatigue strength as a small shear-mode crack problem, the fatigue life data was plotted using the novel parameter, τa/(√area)−1/6, where the area is a projected area of the hole. Consequently, all the fatigue life data was successfully fitted to a unified line irrespective of the diameter and depth of the hole, i.e., a defect size dependence on the rolling contact fatigue strength was manifested in a small crack regime.

Simulation of Rolling Contact Fatigue Strength for Traction Drive Elements

A simulation of the rolling contact fatigue strength of a traction drive element was proposed. The simulation can account for both the distribution of sizes of inclusions in the element material and the influence of traction forces at the element surface. The shear strength of the matrix structure surrounding an inclusion was estimated with an equation. The hardness distribution and the Weibull distribution of inclusion dimensions, which were necessary parameters to calculate the rolling contact fatigue strength, were determined by observation of an actual test specimen. And the rolling contact fatigue strength was compared with the distribution of shear stresses in a roller affected by traction forces. A simulation assuming the same traction coefficient as that in the experiment predicted a rolling contact fatigue strength of 810 MPa with a standard deviation of 39.2 MPa, which differed from the experimental value by only 2.5%. Simulations of the rolling contact fatigue strength were then carried out while varying the traction coefficient. The contact force resulting in failure was observed to fall as the traction coefficient increased and the torque capacity increased. Thus, the torque capacity increases with the traction coefficient, regardless of changes in the rolling contact fatigue strength.

1.5Cr – 0.2Mo 焼結合金鋼ローラの面圧疲労強度

The rolling contact fatigue tests were carried out using case-carburized rollers made of 1.5Cr – 0.2Mo alloyed sintered steel and SCM415 wrought steel. Two kinds of P/M rollers having the initial density of 7.25 × 103 kg/m3 and 7.60 × 103 kg/m3 were prepared. The effects of the case-hardening depth on the rolling contact fatigue strength were mainly investigated. The failure mode of all P/M rollers was spalling caused by the cracking under the contacting surface. When the effective case-hardening depth was set to 1.2 mm or more, the contact fatigue strength after 2 × 107 cycles of surface rolled P/M rollers reached 2 GPa and the maximum surface damage depth remarkably decreased of about 0.2～0.3 mm, which is almost equivalent to the depth that maximum shear stress becomes the peak. The finite element analysis of contact stress shows that the maximum shear stress distribution descends suddenly at the position that is slightly deeper than the effective case-hardening layer, which is corresponding to the location of the maximum failure depth of spalling when the effective case-hardening depth of P/M rollers was less than 1 mm.

Effect of Size and Depth of Small Defect on the Rolling Contact Fatigue Strength of a Bearing Steel SUJ2

Effect of Size and Depth of Small Defect on the Rolling Contact Fatigue Strength of a Bearing Steel SUJ2

Improvement of Rolling Contact Fatigue Strength of Silicon Nitride by Shot-Peening

Improvement of Rolling Contact Fatigue Strength of Silicon Nitride by Shot-Peening