• 제목/요약/키워드: crack life

검색결과 951건 처리시간 0.029초

복수 표면균열의 확률적 특성을 고려한 용접부 피로수명 평가 (Fatigue Life Estimation of Welded Joints considering Statistical Characteristics of Multiple Surface Cracks)

  • 한정우;한승호
    • 대한기계학회논문집A
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    • 제29권11호
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    • pp.1472-1479
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    • 2005
  • Multiple surface crack distributed randomly along a weld toe influences strongly on the fatigue crack propagation life of welded joint. It is investigated by using statistical approaches based on series of systematic experiments. From the statistical results, initial crack numbers and its locations follow the normal distribution, and the probability of initial crack depths and lengths can be described well by tile Weibull distribution. These characteristics are used to calculate the fatigue crack propagation life, in which the mechanisms of mutual interaction and coalescence of the multiple cracks are considered as well as the Mk-factors obtained from a parametric study on the crack depths and lengths. The automatic calculation is achieved by the NESUSS, where the parameters such as the number, location and size of the cracks are all treated as random variables. The random variables are dealt through the Monte-Carlo simulation with sampling random numbers of 2,000. The simulation results show that the multiple cracks lead to much shorter crack propagation life compared with those in single crack situation. The sum of the simulation and tile fatigue crack initiation life derived by the notch strain approach agrees well with the experiments.

박판 Al 2024-T3 합금재료의 피로균열성장지연거동과 피로수명예측 (Retardation Behavior of Fatigue Crack Growth and Fatigue Life Prediction of Thin Sheet Al 2024-T3 Alloy)

  • 김승권
    • 한국기계기술학회지
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    • 제13권2호
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    • pp.31-37
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    • 2011
  • Sheet aluminum alloys have been used in manufacturing of machine structures. In fatigue crack propagation behavior of thin sheet aluminum alloys, it is important that fatigue crack growth rate is affected by crack closure phenomenon. In this work, we analyzed the characteristics of fatigue crack propagation behavior in experiment of constant stress condition for thin sheet Al 2024-T3 alloys, and identified the retardation behavior of crack growth by comparing experimental results of thin and thick plate specimen. We attempt to operate the fatigue life estimating process using the fatigue related material constants from referred fatigue crack propagation analysis. And we analyzed the experimental and prediction results of fatigue life of thin sheet aluminum alloy in order to identify the relation between retardation behavior of fatigue crack growth and crack closure phenomenon.

박판 Al 합금재료의 피로균열전파특성과 피로수명예측 (Characteristics of Fatigue Crack Propagation and Fatigue Life Prediction of Thin Sheet Al Alloy)

  • 김승권;이억섭;양형렬;여인철;박성완
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2008년도 추계학술대회A
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    • pp.356-361
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    • 2008
  • In characteristics of fatigue crack propagation, it is important that fatigue life is affected by crack closure phenomenon in thin sheet Al alloy. The purpose of this paper is to analyze the characteristics of fatigue crack propagation in constant loading condition for sheet Al 2024-T3 alloy of two sort of thickness and identify the difference of fatigue life in thin sheet specimen comparing experimental results of thin sheet specimen and relatively thick sheet specimen under same fatigue loading condition. In applying fatigue related material constants from fatigue crack propagation analysis, we attempt to operate the fatigue life estimating process of thin sheet specimen by modified Paris‘ law considering crack closure phenomenon and analyze the experimental and prediction results of fatigue life in thin sheet Al alloy.

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균열 검사 결과를 고려한 선체 잔류 피로 수명의 확률론적 예측 (Stochastic Remaining Fatigue Life Assessment Considering Crack Inspection Results)

  • 박명진;김유일
    • 대한조선학회논문집
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    • 제57권1호
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    • pp.1-7
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    • 2020
  • In general, an inspection schedule is established based on the long-term fatigue life during the design stage. However, in the design stage, it is difficult to clearly identify the uncertainty factors affecting long-term fatigue life. In this study, the probabilistic fatigue life assessment was conducted in accordance with the methodology of DNV-GL. Firstly, The initial crack distribution estimated through the initial crack propagation analysis was updated by reflecting the results of crack inspection. Secondly, the updated crack distribution was compared with the initial crack distribution, and the probability of failure was updated with the effect of crack inspection.

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

  • 김경수;심천식;권영빈;고희승;기혁근
    • 대한조선학회논문집
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    • 제45권6호
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    • pp.679-687
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    • 2008
  • The fatigue life of ship structure under cyclic loading condition is made up of crack initiation and propagation stages. For a welding member in ship structure, the fatigue crack propagation life is more important than the fatigue crack initiation life. To calculate precisely the fatigue crack propagation life at the critical welding location, the knowledge of the residual stress sensitivity on the fatigue strength is necessary. In this study, thermo elastic-plastic analysis was conducted in order to examine the effect of residual stress on the fatigue crack propagation life. Also the fatigue crack propagation lives considering residual stress were calculated using fatigue crack growth code, AFGROW, on the basis of fracture mechanics. AFGROW is widely used for fatigue crack growth predictions under constant and variable amplitude loading. The reliability of AFGROW on the fatigue of ship structure was confirmed by the comparison of the estimated results with the fatigue propagation test results.

균열 형상비 변화에 따른 단일표면파로균열의 성장특성과 수명예측 (Growth Characteristics and Life Prediction of Single Surface Fatigue Crack with the Variation of crack Configuration Ratios)

  • 서창민;서덕영;정정수
    • 한국해양공학회지
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    • 제7권2호
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    • pp.173-181
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    • 1993
  • This work has been investigated the ralationship between single surface crack length and crack depth have influence on the fatigue life. The simulation based on experimental results of 2.25 Cr-1Mo steel at various crack configuration ratios has enabled successful prediction of fatigue life at room temperature. The effect of crack depth should be considered for predicting fatigue crack growth rates as well as that of surface crack length. It is also shwn that the crack growth mechanisms are in good agreement with expreimental data according to the interaction of crack length and crack depth.

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굽힘피로 하중을 받는 배관의 피로균열 발생수명 예측 (Crack Initiation Life Analysis in Notched Pipe Under Cyclic Bending Loads)

  • 곽상록;이준성;김영진;박윤원
    • 대한기계학회논문집A
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    • 제25권10호
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    • pp.1528-1534
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    • 2001
  • In order to improve Leak-Be(ore-Break methodology, more precisely the crack growth evaluation, a round robin analysis was proposed by the CEA Saclay. The aim of this analysis was to evaluate the crack initiation life, penetration life and shape of through wall crack under cyclic bending loads. The proposed round robin analysis is composed of three main topic; fatigue crack initiation, crack propagation and crack penetration. This paper deals with the first topic, crack initiation in a notched pipe under four point bending. Both elastic-plastic finite element analysis and Neuber's rule were used to estimate the crack initiation life and the finite element models were verified by mesh-refinement, stress distribution and global deflection. In elastic-plastic finite element analysis, crack initiation life was determined by strain amplitude at the notch tip and strain-life curve of the material. In the analytical method, Neuber's rule with the consideration of load history and mean stress effect, was used for the life estimation. The effect of notch tip radius, strain range, cyclic hardening rule were examined in this study. When these results were compared with the experimental ones, the global deformation was a good agreement but the crack initiation cycle was higher than the experimental result.

Prediction of fatigue crack initiation life in SA312 Type 304LN austenitic stainless steel straight pipes with notch

  • Murthy, A. Ramachandra;Vishnuvardhan, S.;Anjusha, K.V.;Gandhi, P.;Singh, P.K.
    • Nuclear Engineering and Technology
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    • 제54권5호
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    • pp.1588-1596
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    • 2022
  • In the nuclear power plants, stainless steel is widely used for fabrication of various components such as piping and pipe fittings. These piping components are subjected to cyclic loading due to start up and shut down of the nuclear power plants. The application of cyclic loading may lead to initiation of crack at stress raiser locations such as nozzle to piping connection, crown of piping bends etc. of the piping system. Crack initiation can also take place from the flaws which have gone unnoticed during manufacturing. Therefore, prediction of crack initiation life would help in decision making with respect to plant operational life. The primary objective of the present study is to compile various analytical models to predict the crack initiation life of the pipes with notch. Here notch simulates the stress raisers in the piping system. As a part of the study, Coffin-Manson equations have been benchmarked to predict the crack initiation life of pipe with notch. Analytical models proposed by Zheng et al. [1], Singh et al. [2], Yang Dong et al. [25], Masayuki et al. [33] and Liu et al. [3] were compiled to predict the crack initiation life of SA312 Type 304LN stainless steel pipe with notch under fatigue loading. Tensile and low cycle fatigue properties were evaluated for the same lot of SA312 Type 304LN stainless steel as that of pipe test. The predicted crack initiation lives by different models were compared with the experimental results of three pipes under different frequencies and loading conditions. It was observed that the predicted crack initiation life is in very good agreement with experimental results with maximum difference of ±10.0%.

크랙 사이의 간섭에 의한 피로크랙 전파거동의 변화 (The Variation of Fatigue Crack Propagation Behavior by Crack-crack Interaction)

  • 송삼홍;배준수;최병호
    • 한국정밀공학회:학술대회논문집
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    • 한국정밀공학회 1994년도 추계학술대회 논문집
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    • pp.820-825
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    • 1994
  • It is improtant to examine life or crack propagation behavior of structures because of its safety evaluation. The purpose of this study is to investigate the effect of crack-crack interaction to evaluate fatigue life and crack behavior. In this study, the behavior of the interaction of two cracks is studied by experiment. The vertical distance of two cracks is varied to make different interaction stress field. In addition, the effect of plastic zone is considered to examine crack propagation path and propagation rate.

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잔류응력장을 전파하는 용접 토우부 균열의 전파해석 (Analysis on the Fatigue Crack Propagation of Weld Toe Crack through Residual Stress Field)

  • 김유일;전유철;강중규;한종만;한민구
    • Journal of Welding and Joining
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    • 제18권5호
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    • pp.33-40
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    • 2000
  • Fatigue crack propagation life of weld toe crack through residual stress field was estimated with Elber's crack concept. Propagation of weld toe crack is heavily influenced by residual stress caused by welding process, so it is essential to take into account the effect of residual stress on the propagation life of weld toe crack. Fatigue crack at transverse and longitudinal weld toe was studied respectively, which represent typical weld joint in ship structure. Numerical and experimental studies are performed for both cases. Residual stress near weldment was estimated through nonlinear thermo-elasto-plastic finite element method, and residual stress intensity factor with Glinka's weight function method. Effective stress intensity factor was calculated with Newman-Forman-de Koning-Henriksen equation which is based on Dugdale strip yield model in estimating crack closure level U at different stress ratio. Calculated crack propagation life coincided well with experimental results.

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