• 한국산학기술학회논문지
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• 제7권6호
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• pp.1012-1020
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• 2006

철도차량의 차륜에서 발생하는 크랙은 표면으로부터 개시하는 표면크랙, 내부에서 개시하는 내부크랙으로 나눌 수 있고, 이들 크랙은 철도의 안전운행에 위험요소가 된다. 그러므로 이들 크랙의 성장수명 판단은 매우 중요하다. 본 연구에서는 철도차륜의 표면크랙 및 내부크랙의 응력분포상태, 변위 및 성장수명을 연구하였다. 특히 내부 및 표면크랙에 대해 유한요소해석을 실시하여 크랙선단의 응력상태, 변위, 응력확대계수를 찾아내었고, 이를 바탕으로 Paris 공식을 사용하여 성장수명을 예측하였다.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.461-462
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• 2002

Rolling element bearing fatigue life can be significantly reduced by debris particles in lubricants. The debris particles cause raceway surface dents that initiate early fatigue damage. Optical interferometry has been found to be the best method for characterizing bearing raceway debris dent damage. This technique is used to determine the important features, sizes and density of dents. The resulting data file is then used to determine bearing fatigue life. Tests show that bearings manufactured by different processes and material types are affected differently by debris damage and that these differences must be considered by life prediction methodologies. Bearings made by a specific enhanced process can significantly resist the deleterious effects of debris damage and outperform bearings made by other means.

• 대한기계학회논문집A
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• 제21권7호
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• pp.1149-1155
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• 1997

J-integral for a subsurface horizontal crack in a circular plate with an inner hole under rolling line contact is evaluated according to loading positions with various load conditions, crack length and crack location. Two-dimensional crack is modeled, and the relation between Tresca stress for uncracked model and J-integral is discussed. The loading location which gives the maximum J-integral depends on load condition and crack location, and the presence of friction force increases Tresca stress and J-integral near the surface. Regardless of friction force, crack location that gives maximum J-integral is the same as that of maximum Tresca stress in an uncracked model, and the value of J-integral is propotional to crack length. It is also showed that the variation of an inner radius of a disk does not effect J-integral value.

• International Journal of Precision Engineering and Manufacturing
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• 제2권1호
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• pp.87-93
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• 2001

A reliable analytic model that determines the exit cross sectional shape a workpiece(material) in round-oval (oroval-round) pass sequence has been developed. The exit cross sectional shape of an outgoing workpiece is predicted by using the linear interpolation of the radius of curvature of an incoming workpiece and that of roll groovw to the roll axis direction. The requirements placed on the choice of the weighting function were to ensure boundary conditions specified. The validity of the analytic model has been examined by not rod rolling experiment with the roll gap and specimen size changed. The exit cross sectional shape and area of the workpiece predicted by the proposed analytic model were good agreement with those obtained experimentally. We found that the analytic model has not only simplicity and accuracy for practical usage but also save a large amount of computational time compared with finite element method.

• Journal of Advanced Marine Engineering and Technology
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• 제32권6호
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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.

• 한국정밀공학회지
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• 제17권9호
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• pp.174-180
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• 2000

A reliable analytic model that determines the cross sectional shape of a workpiece(material) in round-oval(or oval-round) pass sequence has been developed. the cross sectional shape of an outgoing workpiece is predicted by using the linear interpolation of the radius of curvature of an incoming workpiece and that of roll groove to the roll axis direction. The requirements we placed on the choice of the weighting function were to ensure boundary conditions specified. The validity of the analytic model has been examined by hot rod rolling experiment with the roll gap and specimen size changed. The cross sectional shape and area of a workpiece predicted by the proposed analytic model were good agreement with those obtained experimentally. It was found that the analytic model has not only simplicity and accuracy for practical usage but also save a large amount of computational time compared with finite element method.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 춘계학술대회 논문집
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• pp.220-226
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• 1995

A study on the spalling causes of work roll for cold rolling was performed in the cold rolling mill. Performance of work roll is dependent to a great extent on spalling sothat both roll manufactures and users show great interest in spalling. So this paper shows that spalling origin on the roll surface. As being well known, spalling mostlyoccurred due to developing fatigue fracture originated a crack on a roll. But such spalling can be prevented by proper roll maintenance, The spalling accidents have sharply decreased since 1981 because of the use of ultrasonic test to detect cracks on a roll.

• 대한조선학회지
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• 제11권2호
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• pp.7-14
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• 1974

Hydrodynamic moments produced by the rolling oscillation on the free surface and the associated swaying force were exactly calculated by Ursell-Tasai method for the cylinders with Kim's chine form sections($a_1,\;a_7$). The coefficient of the added moment of inertia $K_{\varphi^{\tau}}$, the progressive wave height ratio $\bar{A}$, the coefficient of swaying forces $K_{RS}$, ${\alpha}_{RS}$ of rolling oscillations are shown in the several figures. The results of the computation were compared with those of lewis form sections. It is concluded that the effect of the section form on the added moment of inertia is significant for the cylinder with the section of same beam-draft ratio and sectional area coefficient, on the other hand, a little effect appears on the wave damping.

• 한국재료학회지
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• 제7권3호
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• pp.224-228
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• 1997

2종류의 질화규소에 대하여 Ring형시험편을 이용하여 접촉피로시험을 하였다. 질화규소는 금속재료에서와 같은 형태의 피로현상을 나타냈고, 파면해석 및 관찰결과 접촉피로에 있어서 균열의 발생은 고탄소크롬강의 경우와 같이 표면하의 반복전단응력에 의한 것으로 밝혀졌다. 그리고 시험펴 파단면에서 표면하의 Heltz전단응력의 변동이 최대로 되는 깊이의 위치에 다수의 균열이 관찰되었다.

• 한국산학기술학회논문지
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• 제12권3호
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• pp.1058-1062
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• 2011

티타늄합금 안경테 홈선을 제작하기 위한 냉간 압연 롤러를 설계하고 제작 후 그에 대한 성능 평가를 실시하였다. 롤러의 표면 거칠기 값은 $Ra=0.05-0.15{\mu}m$이고 $Rz=0.23-0.67{\mu}m$였다. 이 값은 티타늄안경테 PVD(Physical Vapor Deposition)도금을 위한 바렐 연마 후 측정한 표면 거칠기 값 $Ra=0.04{\mu}m$, $Rz=0.3{\mu}m$과 비교할 때 만족할만한 결과였다. Ti-3Al-2.5V(Half titanium)와이어를 냉간 압연한 결과 경도가 221Hv, 247Hv(1st), 270Hv(2nd)등으로 증가하므로 적절한 열처리와 다단압연공정이 필요함을 알 수 있었다.