• Title, Summary, Keyword: Fatigue crack propagation behavior

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

  • Kim, G.H.;Lee, H.Y.
    • Journal of Advanced Marine Engineering and Technology
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    • v.32 no.6
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    • pp.834-840
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    • 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.

Fatigue Crack Propagation Behavior in STS304 under Mixed Mode Loading (혼합모드 하중에서의 STS304의 피로균열 전과거동)

  • Song, Sam-Hong;Lee, Jeong-Moo
    • Journal of the Korean Society for Precision Engineering
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    • v.18 no.9
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    • pp.131-139
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    • 2001
  • The use of fracture mechanics has traditionally concentrated on crack growth under an opening mechanism. However, many service failure occur from cracks subjected to mixed mode loadings. Hence, it is necessary to evaluate the fatigue behavior under mixed mode loading. Under mixed mode loading conditions, not only the fatigue crack propagation rate is of importance, but also the crack propagation direction. The mode I and II stress intensity factors of CTS specimen were calculated using elastic finite element method. The propagation behavior of the fatigue crack of the STS304 steeds under mixed mode loading condition was evacuated by using stress intensity factors $K_I$ and $K_II. The MTS criterion and effective stress intensity factor were applied to predict the crack propagation direction and the fatigue crack propagation rate.

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The Fatigue Behavior of Laser Weldment in Heterogeneous Materials (이종재료 레이저 용접부의 피로거동)

  • 권응관;오택열;곽대순;이종재
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • pp.759-764
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    • 1997
  • In this study, Fatigue behavior of laser weldment in heterogeneous materials was investigated. Fatigue strength test and fatigue crack propagation test were performed for specimens with laser weldment in heterogeneous materials, and hardness test was performed. From the fatigue strength test. it was observed that the difference of strength between heterogeneous materials had eflect on crack initiation position and fatigue limit. From the fatigue crack propagation test. it was observed that fatigue behavior of laser weldment in heterogeneous materials is different from that in same materials. The difference of strength between heterogeneous materials and laser weldment had effect on fatigue crack propagation rate.

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

  • Kim, S.G.
    • Journal of the Korean Society of Mechanical Technology
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    • v.13 no.2
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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.

Fatigue Crack Propagation Behavior in STS304 Under Mixed-Mode Loading

  • Lee, Jeong-Moo;Song, Sam-Hong
    • Journal of Mechanical Science and Technology
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    • v.17 no.6
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    • pp.796-804
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    • 2003
  • The use of fracture mechanics has traditionally concentrated on crack growth under an opening mechanism. However, many service failures occur from cracks subjected to mixed-mode loading. Hence, it is necessary to evaluate the fatigue behavior under mixed-mode loading. Under mixed-mode loading, not only the fatigue crack propagation rate is of importance, but also the crack propagation direction. In modified range 0.3$\leq$a/W$\leq$0.5, the stress intensity factors (SIFs) of mode I and mode II for the compact tension shear (CTS) specimen were calculated by using elastic finite element analysis. The propagation behavior of the fatigue cracks of cold rolled stainless steels (STS304) under mixed-mode conditions was evaluated by using K$\_$I/ and $_{4}$ (SIFs of mode I and mode II). The maximum tangential stress (MTS) criterion and stress intensity factor were applied to predict the crack propagation direction and the propagation behavior of fatigue cracks.

Prediction of Fatigue Crack Propagation Life under Constant Amplitude and Overloading Condition (일정진폭 및 과대하중 하에서의 피로 균열 성장 수명 예측)

  • 이억섭;김승권
    • Journal of the Korean Society for Precision Engineering
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    • v.15 no.10
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    • pp.113-119
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    • 1998
  • Ship structures and aircraft structures are consisted of thin sheet alloy, so it is very important to understand the characteristics of fatigue crack propagation of that material and to establish the data base. The data for fatigue crack propagation behavior scatter very much even under identical experimental conditions with constant loading. The behavior of fatigue crack propagation under regular and irregular cyclic loadings is known to be highly affected by complicated factors such as plastic zone developed at the vicinity of crack tip and reduction of cross sectional area. In this paper, the controlled stress amplitude and overload fatigue crack propagation tests have been conducted to investigate the effect of varying factors such as plastic zone size near the crack tip and area reduction factor (AF) on the fatigue crack propagation behavior A better simulation of fatigue crack propagation behavior is found to be obtainable by using Wheeler and Willenborg models with AF effect.

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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
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    • v.9 no.6
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    • pp.82-88
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    • 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.

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A Study on the Mechanical Properties and the Fatigue Crack Propagation Behavior of Ti Welding Material (Ti 용접재의 기계적 특성 및 피로크팩 진전거동에 관한 연구)

  • 최병기;장경천
    • Proceedings of the Korean Society of Machine Tool Engineers Conference
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    • pp.64-69
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    • 2002
  • The purpose of this paper was to investigate the welding characteristics and the fatigue crack propagation behavior of titanium commonly using power station, aircraft and ship. The experimented material was TIG welded in order to look over the characteristics according to the notch position and compare with other materials. We compared and reviewed the fatigue crack propagation behavior of nontch base metal and welded specimens having different notch position to evaluate the fatigue crack propagation behavior by welding condition.

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Effects by Applying Mode of Single Overload on Propagation Behavior of Fatigue Crack (단일과대하중의 작용모드가 피로균열의 전파거동에 미치는 영향)

  • 송삼홍;이정무
    • Journal of the Korean Society for Precision Engineering
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    • v.21 no.6
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    • pp.109-116
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    • 2004
  • In this study, when variable-amplitude load with various applying mode acts on the pre-crack tip, we examined how fatigue cracks behave. Hence aspects of the deformation caused by changing the applying mode of single overload and propagation behavior of fatigue crack were experimentally examined: What kinds of the deformation would be formed at pre-crack and its tip\ulcorner What aspects of the residual plastic deformation field would be formed in front of a crack\ulcorner How aspects of the plastic zone could be evaluated\ulcorner As applying mode of single overloading changes, the deformation caused by tensile and shear loading variously showed in each applying mode. The different aspects of deformation make influence on propagation behavior of cracks under constant-amplitude fatigue loading after overloading with various modes. We tried to examine the relationship between aspects of deformation and fatigue behavior by comparing the observed deformation at crack and crack propagation behavior obtained from fatigue tests.

The Influence of Grain Size on the Fatigue Crack Propagation Behavior in the Low Carbon Steel (SM26C) (저탄소강재(SM25C)의 피로크랙 전파거동에 미치는 결정립 크기의 영향)

  • 김건호
    • Journal of Advanced Marine Engineering and Technology
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    • v.26 no.1
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    • pp.76-82
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    • 2002
  • In this study, the rotary bending fatigue test was carried out with low carbon steel(SM25C). The specimens were heat-treated in order to change the grain size, and investigated items are fatigue limit, small crack initiation, fatigue crack propagation behavior and possibility of fatigue life prediction according to the different grain size. The summarized result are as follows ; Fatigue limit of the smooth specimen was dependent upon the grain size. The fatigue crack initiation of the small grain size specimen was delayed more than that of the large grain size specimen. And the small cracks of small grain size specimen were distributed in the narrow region of the main crack circumference contrary to the large grain size specimen. The main crack was grown along the grain boundary having co-alliance with small cracks. The experiment material has quantitatively disclosed the possibility of fatigue life prediction because the fatigue crack propagation behavior is dependent upon the grain size.