• Journal of Advanced Marine Engineering and Technology
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• v.32 no.6
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• pp.931-937
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• 2008

The rail/wheel rolling contact affects the microstructure in the surface layer of rail. Recently. continuum damage mechanics allows us to describe the microprocesses involved during the straining of materials and structures at the macroscale. Elastic and plastic strains. the corresponding hardening effects are generally accepted to be represented by global continuum variables. The purpose of continuum damage mechanics is to introduce the possibility of describing the coupling effects between damage processes and the stress-strain behavior of materials. In this study. the continuum damage mechanics caused by elastic deformation was briefly introduced and applied to the fatigue damage of the rails under the condition of cyclic loading. The material parameter for damage analysis was first determined so that it could reproduce the life span under the compressive loading in the vicinity of fatigue limit. Some numerical studies have been conducted to show the validity of the present computational mechanics analysis.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.9 no.1
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• pp.25-34
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• 2010

Fretting damage reduces fatigue life of the material due to low amplitude cyclic sliding and changes in the contact surfaces of strongly connected machine and structures such as bolt, key, fixed rivet and connected shaft, which have relative slip of repeatedly very low frequency amplitude. In this study, the fretting fatigue behavior of 7050-T7451 aluminum alloys used mainly in aircraft and automobile industry were evaluated. The plain fatigue test and fretting fatigue test under cyclic bending load carried out commercial bending fatigue tester and specially devised equipments to cause fretting damage. From these experimental work, the following results obtained: (1) The plain fatigue limit for stress ratio R=-l was about 151MPa. (2) In case of fretting fatigue, fatigue limit for stress ratio R=-l about 72MPa, the fatigue limit for R=0 about 81MPa, and the fatigue limit for R=0.3 about 93MPa. (3) The fatigue limit reduction rates by the fretting damage were about 52%(R=-1), 46%(R=0) and 38%(R=0.3) respectively. (4) The fatigue limit reduction rate decreased with stress ratio increase. In fretting bending test, as stress ratio increased, occurrence of initial oblique crack by fretting decreased or phased out, so that fracture surfaces were formed by plain fatigue crack occurrence, and such tendency was notable as stress amplitude increased. (5) Tire tracks and rubbed scars were observed in the fracture surface and contacted surface.

• Proceedings of the KSR Conference
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• 2004.06a
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• pp.632-637
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• 2004

In the shrink or press fitted shaft such as railway axle, fretting can occur by cyclic stress and micro-slippage due to local movement between the shaft and the hub. When the fretting occurs in the press fitted shaft, the fatigue strength remarkably decreases compared with that of without fretting. In this paper, the analysis of contact stresses in a press fitted shaft in contact with a hub was conducted by finite element method and the micro-slip according to the bending load was analyzed. It is found that the largest stress concentration and maximum slip amplitude of shrink fitted shaft are found at the edge of the interface and the distribution of contact stresses at the contact edge has largely influenced and coefficient of friction.

• Journal of Surface Science and Engineering
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• v.45 no.6
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• pp.226-231
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• 2012

Characteristics of carburized surface layers in 0.18C-3.5Ni-1.5Cr-0.2Mo steels for main shaft bearings of wind turbines have been analyzed and evaluated before and after rolling contact fatigue tests. Mixed microstructure consisting of retained austenite and tempered martensite has been formed with compressive residual stresses in the surface hardened layers of the specimens showing uniform hardness distribution with value about Hv700 after vacuum carburizing and tempering. It has been found on the raceway of the layers of the specimens after rolling contact fatigue tests that the amount of retained austenite decreased and compressive residual stresses increased, resulting from cyclic contact stresses applied during the tests. It has been also revealed that higher durability of the bearings can be obtained through controlling the amount of the retained austenite in the surface of the bearing steels to be lower in this study.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.14 no.5
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• pp.199-203
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• 2004

Feasibility of 3Y-TZP for dental implant abutment was evaluated under the Hertzian cyclic fatigue by examining the extent of the indentation damage and strength degradation. Fatigue test was conducted at contact loads of 500 to 3000 N and up to $10^6$ cycles in exact in vitro environments. At 500 N, no strength degradation and crack generation was observed up to $5\times10^5$ contact cycles. As load rose, the dramatic reduction in strength was observed when the damage transition from ring to radial crack occurred. The. extent of strength degradation was more pronounced in vitro environment probably due to chemical corrosion of artificial saliva through cracks introduced during large numbers of contacts.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.957-965
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• 2011

Recently, railway industry has been developed not only functional parts such as acceleration and high performance of the railway but also emotional parts such as improved ride comfort and blocking noise. However, some important components of railway such as wheel and rail always had exposed too much operation time, cyclic load and rolling contact directly. The variations of load, vibration and chemical compositions were caused of wheel and rail having a lot of different types of contact fatigue damages. Therefore, It is necessary to improve inspection and maintenance technology in order to ensure safety and reliability of railway. Many researchers have already been reported the technology. Magnetic camera, one of the non-destructive testing technique can be used to inspect and evaluate the changes of magnetic field in ferromagnetic and paramagnetic materials with cracks. When an electromagnetic is applied to a specimen, a magnetic field will be distorted around a crack on the specimen. In present paper, the distribution of magnetic property in wheel with cracks using magnetic camera had investigated. The crack can be detected and evaluated by distribution analysis of magnetic field. The magnetic camera technique can be detected and evaluated the crack by rolling contact fatigue.

• Journal of the Korean Society for Railway
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• v.7 no.1
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• pp.14-19
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• 2004

The effect of surface damage on fatigue properties of catenary wires were investigated to estimate their service lift. As surface defects of the wires caused by surface corrosion increase, surface roughness gets worse, and as roughness increases, it is easy for moisture coming from rain and dew to be condensed around uneven parts of the surface. The condensed moisture causes a locally severe corrosion which leads to damage of the wires. Corrosion of catenaty wires can make their actual lifetime shorter than that originally designed. The amount of decrease was more prominent as environmental conditions became more corrosive. They are also vibrated with some amplitude everytime pantographs touch contact line. The frequent cyclic load on the wire may result in a fatigue fracture. Surface damage by corrosion can make formation of crack initiation at fatigue. In the present study, the fatigue life of the used wire was measured 35 to 50% compared with that of new one in average.

• Journal of the Korean Ceramic Society
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• v.40 no.7
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• pp.662-666
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• 2003

Hertzian cyclic fatigue properties of the alumina-glass dental ceramics were evaluated in exact in vitro environment at contact loads from 200 N to 1000 N and up to 10$\^$6/ cycles to investigate the indentation damage and strength degradation. At 200 N, no strength degradation and crack generation was observed up to 10$\^$6/ contact cycles. As load increased from 200 N to 1000 N, the drastic reduction in strength was found when the damage transition from ring to radial crack occurred. The extent of strength degradation was more pronounced in vitro environments probably due to chemical reaction of artificial saliva with glass phase through radial cracks introduced during large numbers of contacts.

• Journal of the Korean Ceramic Society
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• v.41 no.1
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• pp.69-75
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• 2004

The degree of the indentation damage and strength degradation for 3Y-TZP ceramics and (Y,Nb)-TZP/$Al_2O_3$ dental implant composites was investigated under the Hertzian cyclic fatigue. Fatigue tests were conducted at contact loads of 500 to 3000 N and up to $10^6$ cycles in exact in vitro environments. At 500 N, no strength degradation and crack generation was observed up to $5{\times}10^5$ contact cycles. Fatigue properties of 3Y-TZP ceramics was superior to (Y,Nb)-TZP/ㅍ composites due to stress relief caused by the phase transformation from tettagonal to monoclinic phase. As contact load increased, the drastic reduction in strength was found when the damage transition from ring to radial crack occurred. The extent of strength degradation was more pronounced in vitro environments probably due to chemical corrosion of artificial saliva through cracks introduced during large numbers of contacts.

• International Journal of Railway
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• v.5 no.2
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• pp.71-76
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• 2012

Recently, axle load, operating speed and traffic density on railroads have had a tendency to increase and thereby cause additional pressure applied on used track. These operating conditions frequently result in service failure due to wear caused by wheel-rail contact and fatigue damage under cyclic loading. Among rail defects, the transverse crack, which has been the most dangerous type of fatigue damages, is developed from the subsurface crack near the rail running face and grows perpendicular to the rail surface. Therefore, it is necessary to investigate systematically the growth behavior of transverse crack for rail steel under mixed mode. In this study, the fatigue crack growth behavior of the transverse crack in rail steel was experimentally investigated under mixed-mode variable amplitude loadings.