• Title/Summary/Keyword: Fatigue crack

Search Result 1,961, Processing Time 0.027 seconds

Fatigue Crack Growth Behavior for Welded Joint of X80 Pipeline Steel

  • Kim, Young-Pyo;Kim, Cheol-Man;Kim, Woo-Sik;Shin, Kwang-Seon
    • Journal of the Korean Society for Nondestructive Testing
    • /
    • v.29 no.1
    • /
    • pp.43-48
    • /
    • 2009
  • The fatigue crack growth behavior of high strength X80 pipeline steel was investigated with compact tension specimens that crack growth directions were aligned either parallel or normal to the rolling direction of the pipeline. Also, the fatigue crack growth rates for welded joint of X80 pipeline steel were investigated with compact tension specimens that crack growth directions were aligned either parallel or normal to the welding line. The experimental results indicated the fatigue crack growth behavior was markedly different in three zones, weld metal, heat affected zone and base metal of welded joints. There was a trend toward increment in the fatigue life of weld metal and heat affected zone as compared with the X80 pipeline steel.

Effect of Width and Thickness Ratio on the Fatigue Crack Arrest Behavior of SA-508 Pressure Vessel Steel Variable Thickness Plates (SA-508 압력용기용강 변후재의 피로균열 Arrest 거동에 대한 변후 형상비의 영향)

  • 이환우;이갑래;최용식
    • Journal of the Korean Society of Safety
    • /
    • v.6 no.4
    • /
    • pp.45-52
    • /
    • 1991
  • The purpose of a fatigue crack arrest desing is to prvent a fatigue fracture of machine and structure resulted from unstable crack growth. In all cases of load transfer to second elements such as stringers, doublers or flangers, crack arrest is possible; arrest occuring when the fatigue crack reaches the second element. In the present work, the possibility of crack arrest and the design criterion of fatigue crack arrest in the variable thickness plates are examined numericaiiy by using fatigue crack arrest thresthod $\Delta$K$_{th}$of SA-508 reactor vessel steel and stress intensity factor which was obtained in the previous work as a result of 3-dimensional finite element analysis for CT type variable thickness plates having discontinuous interface.e.

  • PDF

Effect of Specimen Thickness to Corrosion Fatigue Crack Propagation Behavior of Structure Rolled Steel (일반구조용 압연강재의 부식피로균열전파거동에 미치는 시험편 두께의 영향)

  • 조약래
    • Journal of the Korean Society of Fisheries and Ocean Technology
    • /
    • v.28 no.3
    • /
    • pp.286-294
    • /
    • 1992
  • In this paper, the corrosion fatigue crack propagation behavior of structure rolled steel (SWS 41C) was investigated by changing the thickness, and this experiment was done by the three point bending corrosion fatigue tester. The main results obtained are as follows: 1) As the thickness of specimen becomes thicker, the corrosion sensitivity to initial stage crack becomes some sensitive, and that the fatigue life becomes more sensitive. 2) The crack growth rate to initial stage crack (da/dN) was retarded as the thickness of specimen becomes thicker. But after initial stage crack, as the thickness of specimen is more thicker, da/dN is more rapid. 3) As the corrosion fatigue crack length grows, the accelerative factor of thick specimen (t=12mm) is more higher than that of thin specimen (t=6mm). 4) As the corrosion fatigue crack length grows, the corroson potential of both thick specimen and thin specimen becomes more less noble potential, however thick specimen (t=12mm) tends to more less noble potential than that of thin specimen(t=6mm).

  • PDF

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

  • Lim, Jae-Yong;Hong, Seong-Gu;Lee, Soon-Bok
    • Transactions of the Korean Society of Mechanical Engineers A
    • /
    • v.28 no.6
    • /
    • pp.791-798
    • /
    • 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.

Effect of Specimen Thickness on Probability Distribution of Fatigue Crack Propagation Behavior in Magnesium Alloy AZ31 (AZ31 마그네슘합금 시편의 두께가 피로균열진전거동의 확률분포에 미치는 영향)

  • Choi, Seon-Soon
    • Journal of the Korean Society of Manufacturing Technology Engineers
    • /
    • v.18 no.4
    • /
    • pp.395-400
    • /
    • 2009
  • As the variables affecting the fatigue behavior have uncertainty, the fatigue crack propagation is stochastic in nature. Therefore, the fatigue life prediction is critical for the design and the maintenance of many structural components. In this study, fatigue experiments are conducted on the specimens of magnesium alloy under the different thicknesses of specimen. The effects of specimen thickness on the probability distribution of the fatigue crack propagation life and the crack size are estimated experimentally. The probability distribution of the crack size and the fatigue life for different specimen thicknesses are investigated by Anderson-Darling test and the best fit for those probability distributions are also presented.

  • PDF

Evaluation of Fatigue Strain Intensity Factor on Fatigue Crack Propagation Rate (da/dN) (금속 재료의 피로 균열 전파 속도(da/dN) 평가를 위한 변형율 확대 계수의 유효성 검토)

  • 유재환;최재강;손종동
    • Journal of the Korean Society of Safety
    • /
    • v.11 no.2
    • /
    • pp.3-8
    • /
    • 1996
  • Fatigue fracture is the cyclic fracture phenomena at a very small local area near a crack tip. Therefore, the detailed quantitative experimental analysis about local cyclic strain distribution near a crack tip is prerequisite In order to make an effective parameter able to account for fatigue fracture problems. However, there are few reports on detailed quantitative experimental analysis of a local cyclic strain distribution near a crack tip, because of experimental difficulties. In this study, the distribution of local fatigue strains near a fatigue crack tip was in detail studied using by fine dot grid strain measurement method. From these results, a single parameter, which characterizes local fatigue strain field, was proposed. In addition, this parameter was applied to evaluate the fatigue crack propagation rate.

  • PDF

Crack propagation in flexural fatigue of concrete using rheological-dynamical theory

  • Pancic, Aleksandar;Milasinovic, Dragan D.;Goles, Danica
    • Computers and Concrete
    • /
    • v.27 no.1
    • /
    • pp.55-62
    • /
    • 2021
  • The concrete fatigue analysis can be performed with the use of fracture mechanics. The fracture mechanics defines the fatigue crack propagation as the relationship of crack growth rate and stress intensity factor. In contrast to metal, the application of fracture mechanics to concrete is more complicated and therefore many authors have introduced empirical expressions using Paris law. The topic of this paper is development of a new prediction of fatigue crack propagation for concrete using rheological-dynamical analogy (RDA) and finite element method (FEM) in the frame of linear elastic fracture mechanics (LEFM). The static and cyclic fatigue three-point bending tests on notched beams are considered. Verification of the proposed approach was performed on the test results taken from the literature. The comparison between the theoretical model and experimental results indicates that the model proposed in this paper is valid to predict the crack propagation in flexural fatigue of concrete.

Life Prediction by Retardation Behavior of Fatigue Crack and its Nondestructive Evaluation (피로균열의 지연거동에 따른 수명예측 및 비파괴평가)

  • Nam, Ki-Woo;Kim, Seon-Jin
    • Journal of Ocean Engineering and Technology
    • /
    • v.13 no.3 s.33
    • /
    • pp.36-48
    • /
    • 1999
  • Fatigue life and crack retardation behavior after penetration were experimentally examined using surface pre-cracked specimens of aluminium alloy 5083. The Wheeler model retardation parameter was used successfully to predict crack growth behavior after penetration. By using a crack propagation rule, the change in crack shape after penetration can be evaluated quantitatively. Advanced, waveform-based acoustic emission (AE) techniques have been successfully used to evaluate signal characteristics obtained form fatigue crack propagation and penetratin behavior in 6061 aluminum plate with surface crack under fatigue stress. Surface defects in the structural members are apt to be origins of fatigue crack growth, which may cause serious failure of the whole structure. The nondestructive analysis on the crack growth and penetration from these defects may, therefore, be one of the most important subjects on the reliability of the leak before break (LBB) design. The goal of the present study is to determine if different sources of the AE could be identified by characteristics of the waveforms produced from the crack growth and penetration. AE signals detected in four stages were found to have different signal per stage. With analysis of waveform and power spectrum in 6061 aluminum alloys with a surface crack, it is found to be capabilities on real-time monitoring for the crack propagation and penetration behavior of various damages and defects in structural members.

  • PDF

Fatigue Crack Growth Characteristics of the Pressure Vessel Steel SA 508 Cl. 3 in Various Environments

  • Lee, S. G.;Kim, I. S.;Park, Y. S.;Kim, J. W.;Park, C. Y.
    • Nuclear Engineering and Technology
    • /
    • v.33 no.5
    • /
    • pp.526-538
    • /
    • 2001
  • Fatigue tests in air and in room temperature water were performed to obtain comparable data and stable crack measuring conditions. In air environment, fatigue crack growth rate was increased with increasing temperature due to an increase in crack tip oxidation rate. In room temperature water, the fatigue crack growth rate was faster than in air and crack path varied on loading conditions. In simulated light water reactor (LWR) conditions, there was little environmental effect on the fatigue crack growth rate (FCGR) at low dissolved oxygen or at high loading frequency conditions. While the FCGR was enhanced at high oxygen condition, and the enhancement of crack growth rate increased as loading frequency decreased to a critical value. In fractography, environmentally assisted cracks, such as semi-cleavage and secondary intergranular crack, were found near sulfide inclusions only at high dissolved oxygen and low loading frequency condition. The high crack growth rate was related to environmentally assisted crack. These results indicated that environmentally assisted crack could be formed by the Electrochemical effect in specific loading condition.

  • PDF

The effect of the excessive loading and welding anisotropy on the fatigue crack propagation behavior of TMCP steel for offshore structure (해양구조물용 TMCP강의 피로균열진전거동에 미치는 용접이방성 및 과대하중의 영향)

  • ;;三澤啓志
    • Journal of the Korean Society of Manufacturing Technology Engineers
    • /
    • v.9 no.6
    • /
    • pp.82-88
    • /
    • 2000
  • The effect of the welding for the offshore structure in the TMCP steel on the fatigue crack propagation rate and crack opening-and-closure behavior was examined. The welding anisotropy of the TMCP steel and crack propagation characteristics of the excessive loading were reviewed. (1) It seemed that a heat which was generated by the welding made a compressive residual stress over the base metal, so fatigue crack propagation rate was placed lower than in case of the base metal. (20 In the base metal, an effect of the anisotropy which has an effect of fatigue crack propagation rate of the excessive load and the constant amplitude laos was not found but in the welding material case, fatigue crack propagation rate of the excessive load in the specimen of the width direction was located in the retard side as compared with a specimen rolling direction. (3) A crack opening ratio of the used TMCP stel in this study was not changed after excessive loading but a retard phenomenon of crack propagation was observed. Consequently, it was thought that all of the retard phenomenon of crack propagation did not only a cause of the crack opening-and-closure phenomenon.

  • PDF