• 제목/요약/키워드: crack life

검색결과 951건 처리시간 0.021초

균열의 합체를 고려한 피로균열 진전수명의 확률분포 (The Probability Distribution of Fatigue Crack Propagation Life Considering Effect of Crack Coalescence)

  • 방홍인;윤한용
    • 대한기계학회논문집A
    • /
    • 제24권5호
    • /
    • pp.1281-1287
    • /
    • 2000
  • The studies of probability distribution of the fatigue crack growth life have been somewhat reported. But the study on the probability distribution of the fatigue crack growth life considering the crack coalescence for three dimensional surface fatigue crack has apparently not been reported to date. In this study, the computer program has been developed to predict the probability distribution of the fatigue crack growth life considering the crack coalescence. The effects of parameters for the distribution of the fatigue crack propagation life were evaluated by using the program.

피로균열전파 동안 하중감소에 의한 균열지연 (Crack Retardation byt Load Reduction During Fatigue Crack Propagation)

  • 김현수;남기우;안석환;도재윤
    • 대한기계학회논문집A
    • /
    • 제27권12호
    • /
    • pp.2004-2010
    • /
    • 2003
  • Fracture life and crack retardation behavior were examined experimentally using CT specimens of aluminum alloy 5083. Crack retardation life and fracture life were a wide difference. between 0.8 and 0.6 in proportion to ratio of load reduction. The wheeler model retardation parameter was used successfully to predict crack growth behavior. By using a crack propagation rule, prediction of fracture life can be evaluated quantitatively. A statistical approach based on Weibull distribution was applied to the test data to evaluate the dispersion in the retardation life and fracture life by the change of load reduction.

잔류응력에 의한 피로균열면 형상변화 및 수명예측 (Fatigue Crack shape Variations by a Residual Stress and Fatigue Life Predition)

  • 강용구;서창민;박원종
    • 한국해양공학회지
    • /
    • 제7권2호
    • /
    • pp.68-78
    • /
    • 1993
  • Fatigue crack shape variation by a residual stress during crack growth and life predition are studied. An analytical method is presented to predict the influence of a residual stress due to heattreatment on crack shape variations. Computer simulation results using this me thod are graphically shown that crack growth rate to surface direction are decreased due to compressive residual stress exisiting in surface area. These results are commpared with experimental results. The fatigue life is also predicted by computer simulation of crack aspect ratio variation which is based on the surface crack length increment per unit cycle calculated from a-N diagram. Predited life is about 12 percent lower than experimental life.

  • PDF

Crack growth life model for fatigue susceptible structural components in aging aircraft

  • Chou, Karen C.;Cox, Glenn C.;Lockwood, Allison M.
    • Structural Engineering and Mechanics
    • /
    • 제17권1호
    • /
    • pp.29-50
    • /
    • 2004
  • A total life model was developed to assess the service life of aging aircraft. The primary focus of this paper is the development of crack growth life projection using the response surface method. Crack growth life projection is a necessary component of the total life model. The study showed that the number of load cycles N needed for a crack to propagate to a specified size can be linearly related to the geometric parameter, material, and stress level of the component considered when all the variables are transformed to logarithmic values. By the Central Limit theorem, the ln N was approximated by Gaussian distribution. This Gaussian model compared well with the histograms of the number of load cycles generated from simulated crack growth curves. The outcome of this study will aid engineers in designing their crack growth experiments to develop the stochastic crack growth models for service life assessments.

티탄계 초소성합금 SP-700의 저사이클 피로수명곡선의 절곡현상에 대하여 (A Study on the Knee Point of Low-cycle Fatigue Life in High Formability Titanium Alloy SP-700)

  • 김민건;;지정근
    • 한국자동차공학회논문집
    • /
    • 제5권1호
    • /
    • pp.129-135
    • /
    • 1997
  • Previous studies has shown that the curve of low-cycle fatigue life was not expressed with the single line subjected to Manson-Coffin's law type and bent to short life in low ${\Delta}{\varepsilon}_p$ region. The main cause of this phenomenon has been considered that the localization of plastic strain in the crack initiation process fosters the crack initiation. In this study, the low-cycle fatigue life was investigated for each specimens omitted crack initiation process and it was found that fatigue life curve in log(${\Delta}{\varepsilon}_p$)-log($N_f$)was bent in low ${\Delta}{\varepsilon}_p$ region as ever. Therefore, the main cause of appearance of knee point in fatigue life curve is not found in the crack initiation process but in the crack propagation process. In the crack propagation process, the localization of the plastic strain in the vicinity of crack tip and the influence of test environment on the crack propagation rate were observed and these inclinations were more remarkable in low ${\Delta}{\varepsilon}_p$ region. Hence, it was concluded that these two phenomena in the crack propagation process were proved to the main cause which accelerates the crack propagation in low ${\Delta}{\varepsilon}_p$ region and bent the fatigue life curve in result.

  • PDF

알루미늄 합금재의 피로크랙 전파거동에 미치는 미소원공결함 (The Influence of the Small Circular Hole Defect on the Fatigue Crack Propagation Behavior in Aluminum Alloys)

  • 김건호;이호연
    • Journal of Advanced Marine Engineering and Technology
    • /
    • 제32권6호
    • /
    • pp.834-840
    • /
    • 2008
  • We carried out fatigue testing with materials of aluminum alloyC7075-T6, 2024-T4) by rotary bending fatigue tester. We investigated fatigue limit, fatigue crack initiation, fatigue crack propagation behavior and possibility of fatigue life prediction to the different small circular hole defect. The summarized result are as follows; Fatigue limit of the smooth specimens were related tensile strength and yield strength. In case of more large applied stress and small circular hole crack defect, the fatigue crack was grown rapidly. The fatigue crack propagation behavior proceed at according to inclusion. Fatigue crack propagation ratio appeared instability and retardation phenomenon in the first half of fatigue life but appeared stability and replied in the latter half. On other hand, this experimental data of the materials are appeared fatigue life predictability.

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

  • 김원범;백점기;시도호
    • 대한조선학회논문집
    • /
    • 제44권4호
    • /
    • pp.417-424
    • /
    • 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.

구 접촉시 표면근처의 피로균열 시작수명에 관한 연구 (Study on the Near-Surface Fatigue Crack Initiation Life under Spherical Contact)

  • 설광조;김태완;조용주
    • 한국윤활학회:학술대회논문집
    • /
    • 한국윤활학회 2001년도 제34회 추계학술대회 개최
    • /
    • pp.172-178
    • /
    • 2001
  • Using dislocation pileup theory, the near surface crack initiation life was calculated. The crack initiation life calculted in the previous study is not a real life strictly and just for the cracking in substrate. In this study, two life equations which can be applied for each near-surface and substrate were used for a comparative study. The downward tendency of life at near surface and substrate was similar and the crack initiation life at near-surface was much shorter than the life in substrate. The improvement of the crack initiation life equations which were proposed by W. Cheng was discussed.

  • PDF

박판합금재료의 피로균열 전파특성에 대한 피로수명예측과 활용 (Prediction and Application of Fatigue Life on Characteristics of Fatigue Crack Propagation of Thin Sheet Alloy)

  • 이억섭;김승권
    • 한국정밀공학회지
    • /
    • 제24권2호
    • /
    • pp.103-109
    • /
    • 2007
  • In fatigue life prediction, it is important that fatigue life is affected by crack closure phenomenon in thin sheet Al alloy. In this research, we attempt to (1)analyze the characteristics of fatigue crack propagation in constant loading condition for thin sheet Al 2024-T3 alloy which is generally used in transportation structures, (2)identify the crack closure phenomenon in thin sheet comparing experimental results of thin and thick sheet specimen under same fatigue loading condition. In using the fatigue related material constants from these fatigue crack propagation analysis, we attempt to (3)operate the fatigue life estimating process with considering crack closure phenomenon and (4)analyze the experimental and prediction results of fatigue life in thin sheet Al alloy.

선체 용접부의 균열진전 및 피로수명 예측에 관한 연구(I) (A Study of Crack Propagation and Fatigue Life Prediction on Welded Joints of Ship Structure(I))

  • 김경수;;서용석;장범선;김범일;권영빈
    • 대한조선학회논문집
    • /
    • 제45권6호
    • /
    • pp.669-678
    • /
    • 2008
  • The fatigue life of ship structure under cyclic loading condition is made up of initiation and propagation stages. In this study, crack growth test is carried out on large scale structure test specimens and fracture mechanical analysis is performed. The fatigue lives measured from fatigue tests are compared with DNV, Matsuoka and BS 5400 S-N curve. And to predict the crack initiation life, S-N curve, corresponding to crack length 20mm at welded joint, is developed based on hot spot stress range. Also crack propagation life is calculated using crack growth equation. Consequently, computed crack propagation life is compared with experiment results.