• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.8
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• pp.1269-1276
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• 2001

In case of contact fatigue, the accurate calculation of surface tractions and subsurface stress is essential to the predication of crack initiation life. Surface tractions influencing shear stress amplitude have been obtained by contact analysis based on influence function. Subsurface stress has been obtained by using rectangular patch solutions. In this study, to simulate asperity contact under sliding condition, the tip of asperity was simulated by sphere and to calculate crack initiation life in the substrate, dislocation pileup theory was used.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.1
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• pp.292-300
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• 1995

According to the number of cold-rolled coils, the amount of roll wear and thermal expansion, and roll gap profile were calculated, by using the actual data from the finishing mill. Also, based on those data, the calculations of the deflection, the flattening, and the contact pressure of vwork rolls and backup rolls were made respectively. Specially, in the calculation of contact pressure, the numerical results were obtained not only during the normal rolling, but also during the abnormal rolling, by modeling mathematically the dynamic impact force which occurs when the head section of the strip is threading through rolls. With those results the growth of the fatigue region and the fatigue damage of rolls were predicted. Also the optimum roll-grinding depth was determined to maximize the roll life.

• Journal of the Korean Society of Safety
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• v.26 no.3
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• pp.1-7
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• 2011

Fatigue damage on the train wheel surface was estimated by considering the effect of friction coefficient of rolling on the contact surface between the wheel and rail during operation. From FEM analys, the maximum Tresca stress was 550.7 MPa at a depth of 2.07 mm under the maximum contact pressure ($P_{max}$ = 894.3 MPa) between wheel and rail. The maximum stress continued to increase along with the increase in the frictional coefficient. The fatigue initiation lifetime of the wheel by the rolling contact was predicted using the Smith-Watson-Topper (SWT) equation and the maximum principal strain equation (${\varepsilon}$-N).

• Tribology and Lubricants
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• v.13 no.3
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• pp.48-55
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• 1997

The ball bearing with thin-section raceways which is much lighter than other conventional bearings used in most modem passenger cars and small tracks. The important design parameters of this bearing is the groove radius of raceways, the diametral clearance, the free contact angle and so on. The optimal value of these parameters were determined by considering the dynamic load capacity, the contact angle and the calculated fatigue life. The contact angle between a ball and raceways was calculated by considering the local contact deformation and the structural deformation of thin-section raceways which was estimated by FEM. The raceways were made by means of the press-forming process. The fatigue life tester was designed and manufactured. The fatigue life test was executed and the reliability of this bearing was confirmed.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2000.11a
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• pp.44-49
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• 2000

Recently, PM-high speed steel(PM-HSS) has reportedly been a good alternative material for rolling mill because of its superior peformance to conventional HSS. This paper has been aimed to investigate the possibility for application to rolling contact element for PM-HSS by X-ray diffraction technique. The X-ray elastic constant for PM-HSS has been found by X-ray diffraction during the four-point bending test. Residual stress and half-value breadth on the contact surface during rolling contact fatigue process by X-ray diffraction have also been measured. The result of this study shows that the application of X-ray diffraction technique to PM-HSS could be as possible alternative material as conventional HSS. Half-value breadth on rolling contact surface by X-ray diffraction is not changed during rolling contact fatigue process. On the other hand, the residual stress is changed. This suggests that dislocation reaction has been hardly occurred in rolling contact, depending on supersaturated carbon in PM-HSS.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.3
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• pp.149-156
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• 2003

The estimation of fatigue limit for the component with complicated shape is difficult than of standard fatigue specimen, due to complex test equipment. So, we substitute maximum principle stress from FEM results for fatigue limit diagram made by standard fatigue specimen. Then we can estimate endurance safety of component with high trust. The static stress analysis, the nonlinear contact stress analysis and the model analysis for turbine blade is performed by ANSYS ver. 5.6. the comparison of maximum static stress around hole with maximum contact stress between pun and hole can make the cause of fracture for turbine blade clear. The difference of fatigue limit between fatigue test by standard specimen and in-service mechanical components is due to surface roughness and machining condition etc. In in-service mechanical components, Goodman diagram has to consider surface roughness for failure analysis. To find fracture mechanism of torison-mounted blade in nuclear plant. This study performs the static stress, the nonlinear contact stress and the modal analysis on torison-mounted blade with finite element method and makes the estimation for safety of turbine blade.

• Tribology and Lubricants
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• v.16 no.6
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• pp.477-483
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• 2000

Rolling contact fatigue (RCF) tests were performed for two kinds of commercial silicon nitride balls using 4-Ball rolling contact fatigue life tester under EHL condition (Λ=8.9) and boundary lubrication condition (Λ=0.2). All the test balls were finished up to the dimensional accuracy of Grade 5 defined in KS B 2001 (Steel Balls for Ball Bearings) with a size of 8.731 mm. RCF tests were then conducted under the initial theoretical maximum contact stress 6.63 GPa and the spindle speed 10,000 rpm. All the test balls were not failed until 3.75 $\times$ 107 contact cycles and wear tracks of test balls were not conspicuous under EHL condition (Λ= 8.9). In the operations of low lambda regime (Λ= 0.2), all the test balls were surface damaged and high rolling wear resistance was achievable in fully densified using MgO 1 wt% and HIPed balls. Rolling wear of silicon nitride balls under boundary lubrication condition depend mainly on grain size and intergranular phase content of silicon nitride balls.

• International Journal of Railway
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• v.5 no.3
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• pp.129-134
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• 2012

Contact fatigue damages on the rail surface, such as head checks and squats are a growing problem. The fatigue cracks forming on the contact surface grow according to load and lubricating conditions and may end up breaking the rail. Rail fracture can be avoided by preventing the cracks from reaching the critical length. Therefore, the crack growth rate needs to be estimated precisely according to the conditions of the track and load to develop a maintenance plan against rail damages. Therefore, it is important to understand the mechanism of cracks initiation and growth on a rail due to repetitive rolling contact. In this study, we have investigated the crack growth behavior on the rail surface by using the twin-disc tests and the finite element analysis.

• Proceedings of the KSR Conference
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• 2002.05a
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• pp.590-596
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• 2002

Contact wires are made by metallic materials and exposured at atmosphere. We have investigated mechanical properties and the present condition of air pollution as to the messenger wires and ACSR wires of these contact wires. Mechanical properties between new contact wires and used, the used one's tensile strength and elongations was decreased by effect from corrosion. We observed a fatigue properties which was investigated by fatigue test because contact wires were affected with amplitude vibration everytime the train passed through the railways. In the evaluation of fatigue test, it was also shown that fatigue life of the used wires was decreased 50 ∼ 60% compared with that of new ones in average by effect from corrosion.

• Korean Journal of Materials Research
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• v.7 no.3
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• pp.224-228
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• 1997

Rolling contact fatigue tests were performed for two types silicon nitrides using disk- type specimens. Materials showed a fatigue behaviour similar to that typically found in metallic materials From the fractographic and metallographic observations, it has been found that the crack initation in the silicon nitrides subjected to rolling contact fatigue is to be induced by cyclic subsurface shear stress, as is known in steel bearing. On the mid-sections of the specimens, many subsurface cracks which lay parallel to the contact surface can be found at a depth where fluctuation of the Herzian shear stress was the maximum.