• 제목/요약/키워드: fatigue crack initiation

검색결과 337건 처리시간 0.029초

해수환경중 부식피로균열 발생수명 평가에 관한 연구 (Research for the Evaluation of Corrosion Fatigue Crack Initiation Life)

  • 김원범;백점기;시도호
    • 대한조선학회논문집
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    • 제44권4호
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    • pp.417-424
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    • 2007
  • With regard to corrosion fatigue crack initiation life (Nc), it has been treated ambiguously for the member which doesn't have stress concentration area. In this research, in order to clarify the corrosion fatigue crack initiation life (Nc), corrosion fatigue tests were carried out. Reasonable and universal corrosion fatigue crack initiation life (Nc) was defined and corrosion fatigue crack initiation/propagation model was suggested also. As the fatigue crack which emanates from the pit is usually small, accordingly it is treated as a small crack. In addition, the observation of the corrosion fatigue fracture surfaces using SEM was conducted. And the fracture mechanics analysis using an intrinsic crack model was conducted for the treatment of the small crack. Finally, the followings were obtained. When there is no clear stress concentration point which seems to fall into a corrosion fatigue crack initiation life, the significance of the definition and suggestion of the moment of the reasonable and universal corrosion fatigue crack initiation life (Nc), at which the fatigue crack propagation rate becomes faster than the corrosion pit growth rate so that the fatigue crack initiates from the pit and propagates in earnest, has been clarified.

프레팅 피로 균열의 발생 위치 및 방향 예측 (Prediction of Initiation Location and Direction of Fretting Fatigue Crack)

  • 허용학
    • 대한기계학회논문집A
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    • 제27권7호
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    • pp.1185-1192
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    • 2003
  • Governing parameters for determination of the location of crack initiation and direction of crack initiation were investigated by performing fretting fatigue tests and analysis on Al 2024-T351. Fatigue tests were carried out using biaxial fatigue machine. It was shown that the dominant fatigue crack tended to initiate at the outer edge of one of the four bridge pads, growing at an angle beneath a pad, before turning perpendicular to the orientation of the axial load. Distribution of stresses generated during fretting fatigue loading along the interface was calculated by elastic FE simulation. It can be known that the location of crack initiation can be predicted by using the maximum tangential stress range. Futhermore, the crack initiation direction can also be predicted by a maximum tangential stress range.

해양 구조물용 고장력강의 부식피로특성 (Characteristic of Corrosion Fatigue of High Strength Steel for Marine Structures)

  • 최성대;;;정선환;이종형
    • 한국정밀공학회:학술대회논문집
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    • 한국정밀공학회 2003년도 춘계학술대회 논문집
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    • pp.409-412
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    • 2003
  • Fatigue strength. especially crack initiation behavior of high strength steel under marine water environment was investigated. Marine structures were usually constructed by lot of weld joints and were designed by basis of the fatigue strength of weld joints. This study was carried out to mini. The fatigue initiation behavior is more important rather than crack propagation behavior under the design of marine structures, because it is very difficult to find out the crack propagation phenomena and repair the damaged part of welded joints in sea water Then, the new configuration specimen for fatigue crack initiation tests was proposed. Using this new specimen, it is easy to carry out the crack initiation tests with relatively low cycling loading and clearly find out a crack initiation fatigue life.

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노치 에서의 피로 균열 발생 과 전파 에 관한 연구 (Fatigue Crack Initiation and Propagation at Notches)

  • 이강용;이택성
    • 대한기계학회논문집
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    • 제8권2호
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    • pp.141-144
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    • 1984
  • 본 연구에서는 완전 역 피로응력(completely reversed fatgue stress)를 받는 타원 노치에서 균열 발생과 전파에 대한 이론 임계 피로 한도를 응력 세기 계수 개념 을 도입하여 임의의 재질과 임으의 타원 노치 형상에 대해서 적용할 수 있도록 유도하 며 그 결과는 기존 이론보다 Frost의 실험치에 더 잘 일치함을 보이고자 한다.

국부 변형률 근사를 이용한 원통형 노치시편의 피로균열 발생수명의 예측 (The Prediction of Fatigue Crack Initiation Life of Cylindrical Notch Specimens Using Local Strain Approximation)

  • 임재용;홍성구;이순복
    • 대한기계학회논문집A
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    • 제28권6호
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    • pp.791-798
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    • 2004
  • Fatigue crack initiation lives of round cylindrical notch specimen were investigated. Firstly, local strain approximation methods, such as the modified incremental Neuber's rule and the modified incremental Glinka's equivalent strain energy density(ESED) rule, were used to get multiaxial stress and strain state components at the notch tip. Based on the history of local stress and strain, multiaxial fatigue models were used to obtain fatigue crack initiation lives. Because the solution of Neuber's rule and Glinka's ESED rule make the upper and lower bound of local strain approximations, fatigue crack initiation lives are expected to place between life predictions by two local strain approximations. Experimental data were compared with the fatigue crack initiation life prediction results.

살물선의 피로균열 전파해석과 피로강도 평가에 대한 연구 (A Study on Fatigue Crack Propagation Analysis and Fatigue Strength Evaluation for Bulk Carrier)

  • 엄동석;김충희
    • Journal of Welding and Joining
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    • 제11권4호
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    • pp.112-124
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    • 1993
  • It has been reported that fatigue damage sometimes occurred at the stress concentrated and dynamic loaded structural members of bulk carrier. In this paper, studies on fatigue strength of hull structures are reviewed, and the program for evaluating fatigue strength is developed. And the fatigue crack initiation and propagation on the end part of cargo hold frame of bulk carrier were calculated by FEM stress analysis and the fatigue strength evaluation program. These method can be applied not only to the crack initiation life but also to crack propagation life for the hull structural members at the hull design stage and be effective as the guideline to prevent the crack initiation or to estimate the fatigue strength for repairing of the fatigue damaged structures of real ships.

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임계평면법을 이용한 거친 표면의 구름접촉시 피로균열 시작수명 (The Fatigue Crack Initiation Life under the Rolling Contact of Rough Surfaces using Critical Plane Approach)

  • 설광조;김태완;조용주
    • Tribology and Lubricants
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    • 제19권1호
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    • pp.26-30
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    • 2003
  • The stresses of surface and substrate under the rough surface contact are irregular. Using rainflow counting method for irregular stresses, the fatigue surface crack initiation lift was calculated. With the surface generated by computer, this paper figures out the random load generated by contacting to the rough surface, analyzes the stress of its subsurface, and calculates the fatigue crack initiation life of the rough surface fatigue theory.

SNCM강의 피로균열의 발생 및 전파속도에 미치는 질화처리의 영향 (Effect of Nitriding on Fatigue Crack Initiation and Growth Rate in Ni-Cr-Mo Steel)

  • 김민건;임복규
    • 열처리공학회지
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    • 제16권6호
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    • pp.315-319
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    • 2003
  • Effect of nitriding on fatigue crack initiation and growth rate has been studied in Ni-Cr-Mo steel. Specimens were nitrided at $860^{\circ}C$ for 15 hr. The fatigue limit of nitrided specimens were superior to those ofannea1ed($860^{\circ}C$, 15 hr) specimens. Based on detailed observations of slip band and micro crack initiation, it is concluded that the excellent fatigue limit of nitrided specimens is attributed to improved slip initiation resistance by nitriding. The characteristic of fatigue crack growth rate of nitrided specimens was investigated by comparing with those of annealed specimens. It was found that the crack growth rate was markedly decreased and the threshold stress intensity factor range was improved by nitriding. It is concluded that the excellent fatigue limit of nitrided specimens is also attributed to improved fatigue crack growth rate and threshold stress intensity factor range by nitriding.

SNCM강의 피로균열의 발생 및 전파속도에 미치는 질화처리의 영향 (Effect of Nitriding on Fatigue Crack Initiation and Growth Rate in SNCM)

  • 김민건;이상호
    • 산업기술연구
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    • 제23권A호
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    • pp.3-7
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    • 2003
  • Effect of nitriding on fatigue crack initiation and growth rate has been studied on SNCM. Specimens were nitrided for 15 hr at $860^{\circ}C$. The fatigue limit of nitrided specimens was superior to that of annealed($860^{\circ}C$, 15 hr) specimens. Based on detailed observations of slip band and micro crack initiation, it is concluded that the excellent fatigue limit of nitrided specimens is attributed to improved slip initiation resistance by nitriding. The characteristic of fatigue crack growth rate of nitrided specimens was investigated and compared with those of annealed specimens. It was found that by nitriding the crack growth rate was markedly decreased and the threshold stress intensity factor range was improved. It is concluded that the excellent fatigue limit of nitrided specimens is also attributed to improved fatigue crack growth rate and threshold stress intensity factor range by nitriding.

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두개의 미소원공결함에서의 피로크랙발생과 전파에 관한 연구 (Fatigue Crack Initiation and Propagation From Two Micro Hole Defects)

  • 송삼홍;배준수
    • 대한기계학회논문집A
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    • 제21권5호
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    • pp.842-849
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    • 1997
  • The aim of this study is an investigation of the interaction of two micro hole defects affecting fatigue crack initation life and propagation behavior. The locatio of two micro hole defects was considered as an angle of alignment and the distance between the centers of two micro hole defects. The fatigue cracking behavior is experimented under bending. When micro defects are located close to each other, the fatigue crack initiation lives are varied with their relative locations. In the experiments, the area of local plastic strain strongly played a role in the fatigue crack initiation lives. Therefore we introduce a parameter which contains the plastic deformation area at stress concentrations and propose a fatigue crack initiation life prediction curve. In addition, the directions and propagation rates of fatigue cracks initiated at two micro hole defects are studied experimentally.