• Proceedings of the Korean Society of Precision Engineering Conference
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• 2011.06a
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• pp.1539-1540
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• 2011

• Tribology and Lubricants
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• v.24 no.5
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• pp.228-233
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• 2008

In this study, the methodology for determination of shoulder height in the internal shape design of ball bearing using 3D contact analysis is proposed. The static analysis of a ball bearing was performed to calculate the distribution of applied contact load and angles among the rolling elements. From each rolling element loads and the contact geometry between ball and inner/outer raceway, 3D contact analyses using influence function are conducted. These methodology is applied to HDD ball bearing. A critical axial load and a critical shoulder height which are not affected by edge are calculated. The proposed methodology may be applied to other rolling element bearing for the purpose of reducing the material cost and improving the efficiency of the bearing design process.

• Tribology and Lubricants
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• v.28 no.1
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• pp.19-26
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• 2012

Rolling contact fatigue of an urban railway wheel was analysed during its rolling. A FEM analysis was performed using a 3D modelling of rail and wheel, considering the slope of the rail and nonlinear isotropic and kinematic hardening behavior of the rail and the wheel. The maximum von-Mises stress and contact pressure between the rail and wheel were 656.9 MPa and 1111.4 MPa, respectively, under axial load of 85 kN with friction coefficient of 0. The fatigue initiation life prediction relationships by strain-lifetime (${\varepsilon}$-N) and Smith-Watson-Topper method were drawn for the wheel steel as follows: $N_i=7.35{\times}10^6{\times}SWT^{-3.56}$ and $N_i=5.41{\times}10^{-9}{\times}(\frac{{\Delta}{\varepsilon}}{2})^{-5.77}$. The fatigue lifetimes of the wheel due to rolling contact were determined to be infinite by ${\varepsilon}$-N and SWT methods.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.12
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• pp.2019-2027
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• 2003

Pitting wear is a dominant from of polyethylene surface damage in total knee replacements, and may originate from surface cracks that propagate under repeated tribological contact. In this study, stress intensity factors, K$\_$I/and $_{4}$, were calculated for a surface crack in a polyethylene-CoCr-bone system under the rolling and/or sliding contact pressures. Crack length and load location were considered in determination of probable crack propagation mechanisms and fracture modes. Positive K$\_$I/ values were obtained for shorter cracks in rolling contact and for all crack lengths when the sliding load was apart from the crack. $_{4}$ was the greatest when the load was directly adjacent to the crack (g/a=${\pm}$1). Sliding friction caused a substantial increase of both K$\_$I/$\^$max/ and $_{4}$$\^$max/. The effective Mode I stress intensity factors, K$\_$eff/, were the greatest at g/a=${\pm}$1, showing the significance of high shear stresses generated by loads adjacent to surface cracks. Such behavior of K$\_$eff/ suggests mechanisms for surface pitting by which surface cracks may propagate along their original plane under repeated rolling or sliding contact.

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

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1222-1227
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• 2003

Pitting wear is a dominant form of polyethylene surface damage in total knee replacements, and may originate from surface cracks that propagate under repeated tribological contact. In this study, stress intensity factors, $K_{I}$ and $K_{II}$, were calculated for a surface crack in a polyethylene - CoCr - bone system under the rolling and/or sliding contact pressures. Crack length and load location were considered in determination of probable crack propagation mechanisms and fracture modes. Positive $K_{I}$ values were obtained for shorter cracks in rolling contact and for all crack lengths when the sliding load was apart from the crack. $K_{II}$, was the greatest when the load was directly adjacent to the crack $(g/a={\pm}1)$. Sliding friction caused a substantial increase of both $K_{I}^{max}$ and $K_{II}^{max}$. The effective Mode I stress intensity factors, $K_{eff}$, were the greatest at $g/a={\pm}1$, showing the significance of high shear stresses generated by loads adjacent to surface cracks. Such behavior of $K_{eff}$ suggests mechanisms for surface pitting by which surface cracks may propagate along their original plane under repeated rolling or sliding contact.

• Journal of the Korean Society for Heat Treatment
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• v.21 no.1
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• pp.10-19
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• 2008

To investigate the effect of ultrasonic nano-crystalline surface modification (UNSM) treatment on rolling contact fatigue and residual stress properties of bearing steels, this paper carried out a rolling contact fatigue test, measured residual stress and retained austenite, performed a wear test, observed microstructure, measured micro hardness, and analyzed surface topology. After the UNSM treatment, it was found that the surface became minute by over $100{\mu}m$. The micro surface hardness was changed from Hv730~740 of base material to Hv850~880 with about 20% improvement, and hardening depth was about 1.3 mm. The compressive residual stress was measured as high as -700~-900 MPa, and the quantity of retained austenite was reduced to 27% from 34%. The polymet RCF-6 ball type rolling contact fatigue test showed over 4 times longer fatigue lifetime after the UNSM treatment under 551 kgf load and 8,000 rpm. In addition, this paper observed the samples, which went through the rolling contact fatigue test, with OM and SEM, and it was found that the samples had a spalling phenomenon (the race way is decentralized) after the UNSM treatment. However, before the treatment, the samples had excessive spalling and complete exploration. Comparison of the test samples before and after the UNSM treatment showed a big difference in the fatigue lifetime, which seems to result from the complicated effects of micro particles, compressive residual stress, retained austenite, and surface topology.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1997.04a
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• pp.101-110
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• 1997

An experimental study was performed to discover the tribological behaviors of pure silver coated 52100 bearing steel. Pure silver coatings ranging from 80 nm to several micrometers were produced by a thermal evaporation coating method. Experiments using a thrust ball bearing-typed rolling test-rig were performed for the investigations of the influence of coating thickness on the tribological rolling behavior. The existence of optimum film thickness which revealed minimum rolling resistance was discovered. A careful analysis on the contact surfaces for the optimum film thickness has been performed. The contact patches produced by the transferred silver films played an important role for the rolling resistance to keep low.

• Tribology and Lubricants
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• v.13 no.3
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• pp.85-92
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• 1997

An experimental study was performed to discover the tribological behaviors of pure silver coated 52100 bearing steel. Pure silver coatings ranging from 80 nm to several micrometers were produced by a thermal evaporation coating method. Experiments using a thrust ball bearing-typed rolling test-rig were performed for the investigations of the influence of coating thickness on the tribological rolling behavior. The existence of optimum film thickness which revealed minimum rolling resistance was discovered. A careful analysis on the contact surfaces for the optimum film thickness has been performed. The contact patches produced by the transferred silver films played an important role for the rolling resistance to keep low.

• Nuclear Engineering and Technology
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• v.55 no.3
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• pp.989-998
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• 2023

Under nuclear reactor severe accidents, the resuspension of radioactive aerosol may occur in the containment due to the disturbing airflow generated by hydrogen combustion, hydrogen explosion and containment depressurization resulting in the increase of radioactive source term in the containment. In this paper, for containment conditions, by considering the contact between particle and rough deposition surface, the distribution of the distance between two contact points of particle and deposition surface, rolling and lifting separation mechanism, resuspension model based on random contact with rough surface (RRCR) is established. Subsequently, the detailed torque and force analysis is carried out, which indicates that particles are more easily resuspended by rolling under low disturbing airflow velocity. The simulation result is compared with the experimental result and the prediction of different simulation methods, the RRCR model shows equivalent and better predictive ability, which can be applicable for simulation of aerosol resuspension in containment during severe accident.