Rolling Contact Fatigue Strength Research Articles

GS22 ショットピーニングと自己き裂治癒の併用によるアルミナ炭化/ケイ素複合材の転動疲労強度向上

GS22 ショットピーニングと自己き裂治癒の併用によるアルミナ炭化/ケイ素複合材の転動疲労強度向上

The effect of slip ratio on the rolling contact fatigue property of railway wheel steel

Shelling is one of the typical rolling contact fatigue (RCF) failures of railway wheels. Creepage between wheels and rails due to rolling radius difference in curves is inevitable on railway tracks. Therefore, there are tangential stresses and slip phenomena on wheel treads. Eventually, initiation of RCF cracks being the origin of shelling is accelerated by creepage. The objective of the present paper is to evaluate RCF property of railway wheel steel. The effect of the slip ratio on the RCF strength of the railway wheel steel was evaluated. RCF tests were conducted using two cylindrical contact specimens under water lubrication at a slip ratio of 0.0–1.0%. The range of slip ratio is determined to assume a creepage between wheel and rail during curving. As a result, it was found that the traction coefficient increased with the increase in the slip ratio, and the fatigue strength decreased simultaneously. The results were evaluated by a shakedown map and Hirakawa’s RCF map. Experimental fatigue limits could be expressed more precisely by the criterion of Hirakawa’s RCF map than that expressed by the well-known shakedown map. Stress intensity factors (SIFs) of the cracks produced by the RCF test were calculated by finite element (FE) analysis where the effect of water pressure due to the penetration of water into the cracks is taken into account. Two peaks of the maximum tangential SIF occurred during one cycle of rolling contact. The direction of the crack propagation was estimated by the maximum tangential stress criteria. The results of the RCF test showed that the cracks were initiated at the surface, propagated obliquely in the depth direction and then branched into two directions. One was towards the surface and the other was towards the depth. These two crack directions were inspected experimentally, corresponding to the estimated crack directions from the two peaks of SIF by FE analysis. The effect of slip ratio on RCF crack propagation was discussed by using the SIFs of the RCF cracks where water penetration into the cracks was considered.

S042013 ショットピーニングと自己き裂治癒によるセラミックスの転動疲労強度向上([S04201]セラミックスおよびセラミックス系複合材料(1))

Ceramics are expected as high performance bearings. So investigation of the rolling contact fatigue strength is crucially important. To evaluate the effects of the shot peening and crack-healing on the rolling contact fatigue strength, rolling contact fatigue tests carried out on Si_3N_4/SiC composite. The residual stress, the apparent fracture toughness and Vickers hardness were investigated. The rolling contact fatigue strength was improved by compressive residual stress introduced by shot peening. The rolling contact fatigue strength decreased by pre-cracks. However, it was improved by conducting crack-healing and shot peening.

The Influence of Surface Texture on Rolling-Contact Fatigue of PEEK Bearings in Water

The effect of machining conditions on the rolling contact fatigue (RCF) strength of PEEK polymer bearings was investigated. RCF tests were carried out by using bearings machined by different conditions. The surface profile and roughness were observed before and after testing by laser confocal microscope. Pitting and cracking were associated with the different initial surface conditions. From the obtained results, we found that the RCF strength of machined surfaces decreases when the surface becomes rougher.

水素脆性型の転動疲労強度に及ぼすバナジウム添加の影響

In order to improve the rolling contact fatigue strength due to the hydrogen embrittlement, the effect of the vanadium addition was investigated. The rolling contact fatigue test was conducted using the specimen which hydrogen was charged cathodically. The vanadium addition was effective in improving the rolling contact fatigue strength due to hydrogen embrittlement. Also, the roller pitting life due to the hydrogen embrittlement increased with the vanadium addition. The hydrogen evolution rate profile by the thermal desorption analysis was measured. The hydrogen evolution rate above 100 ℃ increased with the vanadium addition. The incoherent vanadium carbide precipitates were observed by using FE-TEM and EDS. It was presumed that the incoherent vanadium carbide precipitates were the effective trapping sites of the diffusible hydrogen and improved the rolling contact fatigue strength due to hydrogen embrittlement.

Developmental studies on rolling contact fatigue test rig

To determine the rolling contact fatigue (RCF) strength of cryogenic treated gear and bearing steels, an experimental test rig based on nut-cracker mechanism is designed and developed in the laboratory. The test rig is designed for variable load, speed and lubrication condition. The failure monitoring is done using signals acquired from vibration and sound of the contacting rollers. The online monitoring and post processing of the signals is done in LabView and MatLab software, respectively. In the experimental studies, the effectiveness of the vibration and sound signals as a condition monitoring tool in predicting RCF failure is analyzed.

Influence of Crowning on Rolling Contact Fatigue Strength and Failure Mode of Steel Roller

The rolling contact fatigue of crowned rollers made of bearing steel SUJ2 was investigated with a two-roller test machine under a sliding-rolling contact condition with oil lubricant. The nominal crowning radii of the rollers were 110 mm, 90 mm and 60 mm. The roller was mated with a non-crowned roller or a roller with a concave crowning radius of 110 mm. The contact pressure and subsurface stress were analyzed with three dimensional FEM. Within the applied load in this experiment no edge loading or minor edge loading occurred in the crowned rollers mated with the non-crowned roller and major edge loading occurred in the crowned rollers mated with the concave crowned roller. In case that no edge loading or minor edge loading occurred, the failure mode of the rollers were pitting caused by surface cracking and the rolling contact fatigue strength evaluated with the normal load increased with increasing crowning radius. In case that the edge loading was great, the failure mode of the rollers tended to be spalling caused by subsurface cracking and the influence of the crowning radius on the rolling contact fatigue strength was little.

Rolling Contact Fatigue Property of Sintered and Carburized Compacts Made of Molybdenum Hybrid-Alloyed Steel Powder

A new molybdenum hybrid-alloyed steel powder has been developed. The powder is based on a molybdenum prealloyed steel powder to which molybdenum powder particles have been diffusion bonded. The sintered compact made of the developed powder has a finer pore structure than that of the conventional molybdenum prealloyed steel powder, because the ferritic iron phase (α-phase) with a high diffusion coefficient is formed in the sintering necks where molybdenum is concentrated resulting in enhanced sintering. The rolling contact fatigue strength of the sintered and carburized compacts made of this powder improved by a factor of 3.6 compared with that of the conventional molybdenum prealloyed steel powder. The improvement in the rolling contact fatigue strength should result from the fine pore structure without coarse pores acting as stress concentration points.

Evaluation of Rolling Contact Fatigue Properties of White Layer in Railway Wheel Steel

Spalling is one of the typical rolling contact fatigue (RCF) failure of railway wheels, initiating at white layers, as the result of unexpected wheel slides. As for spalling, evaluation methods of fatigue strength have not been tried and tested. The purpose of this study is to propose a prediction method of RCF strength for crack initiation at white layers. In this study, 1) RCF tests in order to evaluate spalling behavior of wheel steels, 2) axial fatigue tests to obtain fatigue strength of white layer itself, and 3) elastic-plastic FEM analyses simulating the RCF tests to calculate stress distribution in/around white layers were conducted. As the results, the following facts were clarified. 1) In RCF tests, cracks were initiated at the leading edge of white layers particularly under slip condition. 2) Fatigue strength of the white layer can be evaluated accurately using the endurance limit diagram estimated by a straight line passing the true fracture strength and fully reversed fatigue strength. 3) According to FEM analysis results, the maximum stress at the leading edge of white layer is larger than at the trailing edge, and the maximum stress of the white layer increases by taking into consideration of small surface profile change during RCF test. Moreover, Dang Van model, which is one of the multiaxial fatigue strength evaluation methods, was applied to predict the white layer's fatigue strength in RCF tests. It can be concluded that the present prediction method is reasonably acceptable for crack initiation assessment of spalling and that in case of the existence of relatively apparent surface profile change, stress evaluation has to be done by taking it into consideration.

Influence of coating thickness on rolling contact fatigue of alumina ceramics thermally sprayed on steel roller

The influence of the sprayed layer thickness on rolling contact fatigue of a thermally sprayed alumina ceramics with a nominal composition of Al 2O 3–2.3 mass% TiO 2 was investigated using a two-roller test machine under pure rolling contact condition with oil lubricant. The influence of undercoating of sprayed nickel-based alloy on rolling contact fatigue was also investigated. Thicknesses of the ceramics-sprayed layer of tested rollers were 0.2, 0.5 and 1.0 mm. The failure mode of sprayed rollers was spalling caused by subsurface cracking. In the case of sprayed rollers without undercoating, rolling contact fatigue strength of rollers with 0.2 mm thickness sprayed layer was the smallest. Rolling contact fatigue strength of sprayed roller with 0.2 mm thickness sprayed layer was improved by undercoating. In case the failure depth was small as compared with the thickness of sprayed layer, effect of undercoating on the rolling contact fatigue strength was little. The depths where the maximum values of subsurface shear stresses occurred, almost corresponded to the observed depth of spalling cracks.

2206 トラクション油潤滑下における鋼ローラの転がり疲れ(OS1-7 強度(2))

A rolling contact fatigue test was carried out under a traction oil lubricating condition and the test result was compared with that under a turbine oil lubricating condition. The minimum film thicknesses under both lubricating conditions were almost equal. The failure mode of both lubricating conditions was pitting caused by surface cracking. The rolling contact fatigue strength under the traction oil lubricating condition was greater than that under the turbine oil lubricating condition. The cracks observed on the roller surfaces tested under the traction oil lubricating condition were the longer along the axial direction of the rollers.

Influence of Sprayed Layer Thickness on Rolling Contact Fatigue of Ceramics Sprayed Roller

The influence of the sprayed layer thickness on the rolling contact fatigue of a thermally sprayed alumina ceramics with a nominal composition of Al2O3-2.3 mass%TiO2 was investigated using a two-roller test machine under pure rolling contact condition with oil lubricant. The influence of undercoating of sprayed nickel based alloy on the rolling contact fatigue was also investigated. The thicknesses of the ceramics sprayed layer of the test rollers were O.2, 0.5 and l.O mm. The failure mode of the sprayed rollers was spalling caused by subsurface cracking. In case of the sprayed rollers without undercoating, the rolling contact fatigue strength of the rollers with O.2 mm thickness sprayed layer was the smallest. The rolling contact fatigue strength of the sprayed roller with 0.2mm thickness alumina sprayed layer was improved by undercoating. In case that the failure depth was small as compared with the thickness of the sprayed layer, the effect of undercoating on the rolling contact fatigue strength was little. The depths, where the maximum values of subsurface shear stresses occurred, almost corresponded to the observed depths of spalling cracks.

911 新軸受鋼製スラスト軸受の転がり疲れ強さ(機素潤滑設計II)

911 新軸受鋼製スラスト軸受の転がり疲れ強さ(機素潤滑設計II)

Physical metallurgy aspects of rolling contact fatigue of rail steels

The relation between rolling contact fatigue (RCF) strength and contamination of a rail steel (with oxides, size, and shape of carbides etc.), the laminated nature of the initial structure, content of carbon, austenitic grain size, structural heterogeneity, thermomechanical damages (TMD) and the scale factor has been studied. It has been shown, how the alumina fraction, alumina inclusion size, grain size, degree of structural heterogeneity, intensity of thermomechanical damages and the carbide volume fraction exert the most influence on RCF strength. On the basis of these studies a new RCF strength index – shelling index (SI) is presented.

SUJ2製ローラの転がり疲れに及ぼすクラウニングの影響(O.S.02-4 歯車の強度(4))

This paper describes about influence of crowning on rolling contact fatigue of steel roller. The edge load at the contact edge and subsurface shear stresses were calculated with FEM. In case that no edge load or minor edge load, the rolling contact fatigue strength of rollers evaluated with the normal load increased with increasing the crowning radius. The stressed volume varied widely with the crowning radius. The rolling contact fatigue strength should be evaluated from the point of view of the stressed volume.

浸炭歯車材の転がり疲労強度評価における表面形状変化の影響(材料力学(転がり・摩擦・摩耗))

浸炭歯車材の転がり疲労強度評価における表面形状変化の影響(材料力学(転がり・摩擦・摩耗))

131 Si_3N_4 の転がり疲れに関する研究 : 第 2 報潤滑状態の影響

To investigate the influence of lubrication on the rolling contact fatigue strength of Si_3N_4 ceramics, the fatigue life was tested under four type of oil lubricants. The thinner oil film thickness is, the weaker the rolling contact fatigue strength becomes under the hydrodynamic lubrication, but it is nearly equal under the mixed and boundary lubrication.

The Influence of Heat Generation In the Contact Zone on Bearing Fatigue Behavior

The material behavior of the standard bearing steel SAE 52100 and the heat resistant bearing steels M50, M50 NiL, and Cronidur 30 as a function of the operational temperature has been investigated. The reduction in rolling contact fatigue strength due to a temperature rise was found to be significantly higher than the reduction of hardness. The mechanism of heat generation due to the bearing operation induces a temperature distribution, which makes it necessary to distinguish between the temperature ruling the subsurface fatigue processes and a higher temperature dominating the surface originated damage initiation.

Rolling Contact Fatigue and Scuffing of Surface Modified Rollers. In Case of Electroless Ni-P Alloy Plated Rollers and Sulfurized Rollers.

The influence of the surface modification treatment on the rolling contact fatigue and the scuffing capacity of rollers was examined by two cylinder test under oil lubrication. The surfaces of test rollers were modified by the electroless Ni-P alloy plating and the sulfurizing. The rolling contact fatigue strength and the scuffing capacity of the surface modified rollers were larger than those of the non-coated rollers. In the fatigue test the failure mode of both the surface modified rollers and the non-coated rollers was the spalling caused by subsurface cracking. The friction coefficient of the Ni-P plated rollers was smaller than that of the non-coated rollers, and the surface roughnesses of the modified rollers were decreased with increasing wear of modified layers. The small friction coefficient and the small roughness contribute to the improvement of the scuffing capacity, and moreover they might reduce the surface contact stresses and the rolling contact fatigue strength might be improved.

Effect of Crowning Radius on Rolling Contact Fatigue Strength of Case-Hardened Steel Roller.

This paper deals with the effect of crowning radius on the rolling contact fatigue strength of case-hardened steel roller. Three types of the rollers, which had crowning radii of 30 mm, 15 mm and 7.5 mm, were fatigue-tested under a sliding rolling contact condition. The rolling contact fatigue strength of the roller became higher as the crowning radius became smaller. The failure modes of the rollers with crowning radii of 15 mm and 7.5 mm were pitting and wear, while the failure mode of the roller with a radius of 30 mm was only pitting. The pitted depth of all rollers depended almost on the depth of the maximum amplitude of the ratio of principal shear stress to Vickers hardness. The rolling contact fatigue life of the rollers could be expressed using non-dimensional value pmax/(Λ·Hυ) independent of the crowning radius, where, pmax, and Λ and Hυ are the maximum Hertzian stress, specific film thickness and Vickers hardness, respectively.