• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09a
• /
• pp.559-560
• /
• 2006

Powder forging is used for heavy-loaded parts (rings of rolling-contact bearings, gears etc.) production. Rolling contact fatigue is material property values of which characterize possibility of practical utilization of such parts. Rolling contact fatigue of some steels obtained out of prealloyed powders Astaloy CrM, Atomet 4601, Atomet 4901 and powder blends iron-carbon-nickel by hot forging is studied in the present paper. Effect of various kinds of heat and thermomechanical treatment on rolling contact fatigue is determined. Thermomechanical treatment provides optimal values of rolling contact fatigue. In this case steel structure contains up to 40% of retained metastable austenite which is transformed to martensite on trials. Thus typically crack is generated on residual pores and non-metallic inclusions instead of martensite zones in wrought steels.

• Journal of the Korean Society of Safety
• /
• v.32 no.1
• /
• pp.15-20
• /
• 2017

A large amount of research has been performed on the rolling contact fatigue(RCF) life of bearings, since it directly affects the safety and reliability of mechanical systems. It is well known that rolling contact fatigue life is influenced by several parameters including contact pressure, oil contamination by water or metal particles, and the surface conditions of bearings. However, the detailed damage mechanisms involved in rolling contact fatigue have not been clearly identified yet. In this paper the effects of water contamination of the lubricant and surface roughness of bearing steel on the rolling contact fatigue life were investigated. Two types of specimens with different surface roughness values were prepared through turning and lapping operations. They were tested under two different lubrication conditions, i.e. oil lubricant with 100% of oil and the water contaminated condition with 80% of oil and 20% of water using the rolling contact fatigue testing machine. The surface damage induced by the rolling contact fatigue was observed by using atomic force microscope(AFM). Experimental results show that the rolling contact fatigue life, $L_{10}$ was reduced by 24 to 33% depending on the lubrication condition. The reduction of fatigue life in the range of 53 to 57% was also observed at different surface roughness conditions.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.16 no.3
• /
• pp.137-143
• /
• 2008

For most bearings, it is a common requirement to have long durability. Especially wheel bearing fatigue life is the most important in automotive quality. The contact fatigue life analysis of automotive wheel bearing considering real raceway rough surface is presented in this paper. Contact stresses are obtained by contact analysis of a semi-infinite solid based on the use of influence functions; the subsurface stress field is obtained using rectangular patch solutions. Mesoscopic multiaxial fatigue criterion which can yield satisfactory results for non-proportional loading is then applied to predict fatigue damage. Suitable counting method and damage rule were used to calculate the fatigue life of random loading caused by rough surface. The life analysis considering real rough surface of wheel bearing raceway is in good agreement with the experimental results.

• Journal of the Korean Society for Precision Engineering
• /
• v.27 no.3
• /
• pp.80-88
• /
• 2010

A simple computational model for modeling of subsurface crack growth under cyclic contact loading is presented. In this model, it is assumed that the initial fatigue crack will initiate in the region of the maximum equivalent stress at certain depth under the contacting surface. The position and magnitude of the maximum equivalent stress are determined by using the equivalent contact model, which is based on the Hertzian contact conditions with frictional forces. The virtual crack extension method is used for simulation of the fatigue crack growth from the initial crack up to the formation of the surface pit due to contact fatigue. The relationships between the stress intensity factor and crack length are then determined for various combinations of equivalent contact radii and loadings.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.29 no.10 s.241
• /
• pp.1384-1391
• /
• 2005

Damage often occurs on the surface of railway wheels due to wheel-rail contact fatigue. It should be removed before reaching wheel failure, because wheel failure can cause derailment with loss of life and property. The increase or decrease of the contact fatigue lift by the metal removal of the contact surface were investigated by many researchers, but they have not considered initial residual stress and traction force. The railway wheel has the initial residual stress formed during the manufacturing process, and the residual stress is changed by thermal stress induced by braking. The traction force and residual stress are operated on wheels of locomotive and electric motor vehicle. In this study, the effect of metal removal depth on the contact fatigue life for a railway wheel has been evaluated by applying lolling contact fatigue test. The effect of the traction force and metal removal on the contact fatigue life has been estimated by finite element analysis. It has been found that the initial residual stress determines the amount of metal removal depth if the traction coefficient is less than 0.15. If the traction coefficient is greater than 0.2, however, the amount of metal removal depth is independent on the intial residual stress.

• Tribology and Lubricants
• /
• v.31 no.6
• /
• pp.272-280
• /
• 2015

Recently, Luu suggested fatigue life equation that uses every term of the Crossland equation with stress gradient effect. Luu’s model, however, has a limit of being unable to coverage small radii that are less than a specified length. Furthermore, rolling model has a very small contact area compared to the rolling element size, and fatigue failure occurs on the small radius such as surface asperity by cyclic loading. Therefore, it is necessary to modify fatigue life equation in order to enable fatigue analysis for a small radius. In this paper, the fatigue life considering a stress gradient effect in rolling contact was obtained using Luu’s modified equation. Fatigue analysis was performed to study the effect of stress gradient on the fatigue life using newly adopted equation and to compare the results with pervious models. In order to do this, a series of simulation such as surface stress analysis, subsurface stress analysis, and fatigue analysis are conducted for two rolling balls of same size that contact each other. Through such a series of processes, the fatigue life can be calculated and equation that is proposed in this paper evaluates the fatigue life in case the contact area is small.

• Tribology and Lubricants
• /
• v.22 no.6
• /
• pp.320-328
• /
• 2006

In this study, the simulation of rolling contact fatigue based on stress analysis is conducted under Elastohydrodynamic Lubrication state. To predict a crack initiation life accurately, it is necessary to calculate contact stress and subsurface stresses accurately. Contact stresses are obtained by contact analysis of a semi-infinile solid based on the use of influence functions and the subsurface stress field is obtained using rectangular patch solutions. And a numerical algorithm using Newton-Rapson method was constructed to calculate the Elastohydrodynamic lubrication pressure. Based on these stress values, several multiaxial high-cycle fatigue criteria are used and the critical loads corresponding to fatigue limits are calculated.

• Proceedings of the KSR Conference
• /
• 2002.10a
• /
• pp.733-738
• /
• 2002

In this study, contact fatigue in wheel-rail contact is simulated. It is necessary to calculate contact stress and subsurface stresses accurately to predict fatigue behavior. Contact stresses are obtained by contact analysis of semi-infinite solid based on influence function and subsurface stress field obtained by using rectangular patch solutions. Based on these stress values, several multiaxial high-cycle fatigue criteria are used and the critical loads corresponding to fatigue limits are calculated. The simulation results show that the critical load is decreasing rapidly and the site of crack initiation also moves rapidly to the surface from the subsurface when friction coefficient exceeds a specific value for all of three fatigue criteria.

• Tribology and Lubricants
• /
• v.21 no.3
• /
• pp.136-141
• /
• 2005

Analytical model to calculate the contact fatigue life of rough surface is presented in this paper. The effect of surface roughness can be calculated by this model. Computational method and the theoretical basis are also discussed. Contact stresses are obtained by contact analysis of a semi-infinite solid based on the use of influence functions; the subsurface stress field is obtained using rectangular patch solutions. Mesoscopic multiaxial fatigue criterion which can yield satisfactory results for non-proportional loading is then applied to predict fatigue damage. Suitable counting method and damage rule were used to calculate the fatigue life of random loading caused by rough surface. As a result of analysis the relationship between the life and the roughness as well as the most probable depth of the crack initiation is calculated.

• Journal of the Korean Society for Precision Engineering
• /
• v.27 no.8
• /
• pp.35-41
• /
• 2010

White Etching Layer(WEL) is a phenomenon that occurs on the surface of rail due to wheel/rail interactions such as excessive braking and acceleration. Rolling Contact Fatigue(RCF) cracks on the surface of rail have been found to be associated with WEL. In this study, we have investigated RCF damages of white etching layer using twin disc testing and fatigue analysis. These tests consist of wheel flat tests and rolling contact fatigue tests. WEL has been simulated by wheel flat test. It has been founded that the WEL with a bright featureless contrast is formed on the surface of specimen by etching. Rolling contact fatigue test was conducted by using flat specimens with the WEL generated by the wheel flat test. It has been observed that two types of cracks occur within the specimen. The contact fatigue test was simulated in 2D elastic-plastic FE simulations. Based on loading cycles obtained from the finite element analysis, the fatigue life analysis according to the thickness variation of WEL was carried out. The longest fatigue life was observed from the thickness of 20um.