• The Korean Journal of Ceramics
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• 제7권2호
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• pp.63-69
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• 2001

We investigated strength degradations from cyclic contact fatigue in self-toughened glass-ceramics. Hertzian indentation was used to induce cyclic contact load. Dynamic fatigue was also performed with changing stress rates from 0.01 to 10000 MPa/sec. After that, strength data and fracture origins were analysed. As the number of contact cycles increased or stressing rate decreased, severe strength degradation occurred by as much as 50% because of radial cracks developed from microcrack coalescence.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.142-143
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• 2006

Recently, automotive engines have changed to the silent chain system in order to reduce noise and to improve reliability. High contact fatigue strength is needed for the sprockets of silent chain system. As a result, a high-contact-fatigue-strength P/M material was developed using the technology of surface rolling, which densifies the surface layer of sintered parts. It was established that the contact fatigue strength of the developed material was a great improvement over that of the conventionally used sintered material.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1997년도 제25회 춘계학술대회
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• pp.74-79
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• 1997

Most of the results of recent research for the influence of indentation on rolling contact fatigue has been carried out with high strength material under the point contact. The plastic lug around the indent also has been known as a source of stress concentration. This study is undertaken to analyze the influence of indentation on rolling contact fatigue with low strength material under the line contact. The results in this study show that the plastic flow around indentation by rolling friction has a major influence, differed from the results of high strength material. And the change of residual stress and half-value breadth measured to the failure by X-ray diffraction can be identified to predict the rolling contact fatigue life of indented materials.

• 대한기계학회논문집A
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• 제31권2호
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• pp.197-204
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• 2007

Fretting is a contact damage process that occurs between two contact surfaces. Fretting fatigue reduces fatigue strength of the material due to low amplitude oscillatory sliding and changes in the contact surfaces of strongly connected machine and structure such as bolt, key, pin, fixed rivet and connected shaft, which have relative slip of repeatedly extreme low frequency amplitude. In this research, the fretting fatigue behavior of 2024-T3511 and 7050-T7451 aluminum alloys used mainly in aircraft and automobile industry were experimentally estimated. Based on this experimental wort the following results were obtained: (1) A significant decrease of fatigue lift was observed in the fretting fatigue compared to the plain fatigue. The fatigue limit of 2024-T3511 aluminum alloy decreased about 59% while 7050-T7451 aluminum alloy decreased about 75%. (2) In 7050-T7451 specimen using ATSI4030 contact pad, crack was initiated more early stage than using 2024-T3511 contact pad. (3) In all specimens, oblique cracks were initiated at contact edge. (4) Tire tracks and rubbed scars were observed in the oblique crack region of fracture surface.

• 한국기계가공학회지
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• 제20권5호
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• pp.128-134
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• 2021

A press-fitted shaft is an essential part used in industrial machines, and it is generally used to transmit large quantities of power. Very high contact pressure occurs at the end parts of the contact between the shaft and boss, which are press-fitted shaft components. Such contact pressure not only damages the contact surface of a press-fitted shaft but also reduces its fatigue strength. To improve a press-fitted shaft's fatigue strength, the contact pressure on the contact surface, which directly affects the fatigue strength, should be minimized. Thus, in this study, the design configuration optimization of the end part of the boss was based on the approximate optimization method and was aimed at minimizing the contact pressure at the end of a press-fitted shaft. Comparison of the contact pressure and the contact stress of a conventional press-fitted shaft with those of the optimized press-fitted shaft showed that the boss design of the optimized press-fitted shaft effectively improved the fatigue life.

• 한국결정성장학회지
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• 제14권5호
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• pp.199-203
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• 2004

유사구강 분위기인 인공타액 조건하에서 인공치아용 상부구조물 재료 중 하나인 3Y-TZP를 500~3000 N의 하중 조건으로 $10^6$ 횟수까지 헤르찌안 반복하중을 가하여 그 피로특성을 압입손상과 강도저하현상으로 관찰하였다. 500 N의 하중에서 $5\times10^5$ 반복 횟수까지 피로실험결과, 강도저하 및 균열현상은 관찰되지는 않았지만 반복하중 값이 증가함에 따라 링 균열에서 방사상 균열로 전이되었을 때 급격한 강도 저하현상이 관찰되었다. 또한 강도 저하 현상은 유사 구강분위기하에서 반복 하중 접촉시 발생한 균열을 통해 침투한 인공타액의 화학적 침식으로 가속화 되었다.

• Tribology and Lubricants
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• 제13권2호
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• pp.39-45
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• 1997

The shot peening treatment were conducted for improving the strength of rolling contact fatigue of machine element like a gear. This paper was undertaken to analyze the influence of shot peening treatment for inner race of ball bearing on the rolling contact fatigue. Shot peening treatment were applied to the full hardened and the carbonitrided bearing. And the rolling contact fatigue life test and X-ray diffraction test were carried out. The results of this study showed that the fatigue life of ball bearing in the clean and the contaminated oil could be improved by shot peening treatment. This effect was found to be more pronounced to the full hardened bearing. These facts might be due to the generation of compressive residual stress and the strain hardening of surface layer by shot peening treatment. The failure of the shot peened bearing were presumed to initiate at surface.

• 한국세라믹학회지
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• 제41권1호
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• pp.69-75
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• 2004

인공치아용 3Y-TZP와 (Y,Nb)-TZP/$Al_2O_3$ 복합체를 유사 구강분위기인 인공타액 하에서 500-3000N의 하중 조건으로 $10^6$ 횟수까지 헤르찌안 반복하중 피로특성을 조사하였다. 500N의 하중에서 $5{\times}10^5$까지 반복피로 실험결과, 강도 저하 및 균열 현상은 관찰되지 않았다. 피로특성은 SY-TZP가 (T,Nb)-TZP/$Al_2O_3$ 복합체보다 상전이에 의한 응역회복 때문에 우수하였다. 하중값이 증가함에 따라 링 균열에서 방사상 균열로 전이되었을 때 급격한 강도 저하 현상이 발생하였다. 강도 저하 현상은 유사 구강 분위기하에서 반복 하중 접촉 시 발생한 균열을 통해 침투한 인공타액의 화학적 침식으로 더욱 가속화 되었다.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1996년도 제24회 추계학술대회
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• pp.207-212
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• 1996

The shotpeening treatment were conducted for improving the strength of rolling contact fatigue of machine element like a gear. This paper was undertaken to analyze the influence of shotpeening treatment for inner race of ball bearing on the roiling contact fatigue. Shotpeening treatment were applied to the full hardened and the carbonitrided bearing. And the rolling contact fatigue life test and X-ray diffraction test were carried out. The results of this study showed that the fatigue life of ball bearing in the clean and the contaminated oil could be improved by shotpeening treatment. This effect was found to be more pronounced to the full hardened bearing.

• 한국세라믹학회지
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• 제40권7호
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• pp.662-666
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• 2003

인공치관용 알루미나-유리 복합체를 유사 구강분위기인 인공타액 하에서 200-1000 N의 하중 조건으로 $10^{6}$ 횟수까지 헤르찌안 반복하중 피로특성을 조사하였다. 200 N의 하중에서 $10^{6}$까지 반복피로 실험결과, 강도 저하 및 균열 현상은 관찰되지 않았다. 하중이 1000 N으로 증가함에 따라 링 균열에서 방사상 균열로 전이되었을 때 급격한 강도 저하 현상이 발생하였다. 강도 저하 현상은 유사 구강 분위기하에서 반복 하중 접촉 시 발생한 방사상 균열을 통해 침투한 인공타액과 유리상의 화학적 반응으로 더욱 가속화 되었다.