• Title/Summary/Keyword: Fatigue crack

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Fatigue Crack Propagation Behavior in CTS Specimen Under Mixed-Mode Loading with Hole Defefects (원공 결함을 갖는 CTS 시험편의 혼합모드 하중 하에서의 피로균열 전파거동)

  • Song, Sam-Hong;Shin, Seung-Man;Lee, Jeong-Moo;Seo, Ki-Jeong
    • Proceedings of the KSME Conference
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    • 2003.04a
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    • pp.137-142
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    • 2003
  • In this study, the propagation behavior of fatigue crack effected hole defects was investigated under mixed-mode I+II loading. To create mixed-mode stress field at crack tip, the compact tension shear (CTS) specimen and loading device were used in this tests. The propagation experiments of fatigue crack were performed by changing of the loading application angle(${\phi}$) and the distance(L) estimated from pre-crack tip to hole center located side by side by side with a pre-crack. As L changes, the variation for propagation aspect of fatigue crack, fatigue life and crack propagation rate were examined under mixed-mode loading. Under mixed-mode loading, the propagation rate of fatigue crack increased while the propagation direction changed dramatically because of the interference of hole defects.

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A Study on Evaluation of Crack Opening Point in Al 2024-T3 Material (Al 2024-T3재의 Crack Opening Point의 평가에 관한 연구)

  • Choi, Byung-Ki;Jang, Kyeung-Cheun
    • Journal of the Korean Society of Safety
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    • v.19 no.2
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    • pp.16-20
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    • 2004
  • This paper aims to analyze fatigue fracture mechnisms with high strength aluminum alloys, which are widely used in vehicles or airplanes to prevent accidents. Usefulness of the crack opening point was proposed by using an effective stress intensity facor when evaluating the fatigue crack propagaion rate. Therefore an exact crack opening ratio can be measured for a more exact fatigue crack propagation rate. It is found that the fatigue crack propagation rate was valid within the range of experimentation as an effective stress intensity factor. Summarizing the results are as follows in this paper ; (1) It is found that the value of the crack opening ratio is constant at the rear of the specimen, U'=0.25 at the crack mouth and U'=0.45 at the crack tip, respectively regardless of the stress ratio. (2) The crack opening ratio is different according to measurement locations. The crack opening ratio value was measured at the crack mouth by a clip gage or measured behind the specimen by a strain gage. It is found that the crack opening ratio value is more accurate that any other measuring test for evaluating the crack propagation ratio test by effective stress intensity factor.

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

  • Huh, Yong-Hak;R. E. Edwards;M.W. Brown;E.R. de Ios Rios
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.27 no.7
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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.

Indentations near Crack Tip in Al-5086 and Characteristics of Fatigue crack Propagation (Al-5086의 균열선단에 가공한 압흔과 피로균열전파특성)

  • 송삼홍;김병석;최병호
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2000.11a
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    • pp.477-480
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    • 2000
  • It is useful way to make indentations near crack tip in order to increase fatigue life or repair a fatigue crack. In this study, bending fatigue tests were performed to investigate the optimal position of the indentations near crack tip. The results shows that fatigue life of the specimen is dramatically increased by indentation and the most effective location is the back of the crack tip.

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Effect of a Single Applied Overload on Fatigue Crack Growth Behavior in Laser-welded Sheet Metal

  • Kwak Dai-Soon;Kim Seog-Hwan;Oh Taek-Yul
    • International Journal of Precision Engineering and Manufacturing
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    • v.7 no.3
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    • pp.30-34
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    • 2006
  • We investigated fatigue crack growth behavior in laser-welded sheet metal caused by a single applied overload The fatigue specimens were made using butt jointed cold rolled sheet metal that was welded with a $CO_2$ laser, The effects of the specimen thickness and overload ratio were determined from fatigue crack propagation tests, These tests were performed in such a way that the fatigue loading was aligned parallel to the weld line while the crack propagated perpendicular to the weld line, Overload ratios of 1.0, 1.5, and 2. 0 were applied near the tip of the fatigue crack at points located 6, 4, and 2 mm from the weld line. The specimens were either 0.9 or 2.0 mm thick. The size of the plastic zone at the crack tip due to the single applied overload was also determined using finite element analysis.

Analysis and Propagation Behavior of Dissimilar Friction Welded Materials for Fatigue Crack in around Interface (이종마찰압접 계면근방에서의 피로균열의 전파거동 및 해석)

  • 오환섭
    • Proceedings of the Korean Society of Machine Tool Engineers Conference
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    • 1998.10a
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    • pp.140-145
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    • 1998
  • In this study, analysis for fatigue crack propagation behavior of interface and aroud interface under rotary bending stress. Though K values are nearly the same in around interface by BEM 2-D, fatigue crack propagated H.A.Z. Around Interface crack propagation speed is m=0.678 in H.A.Z by Paris' law. In this case(friction welded materials: STS304, SM15C), fatigue crack growth is considered SM15C metal microstructure and elastic flow from this result. Result is more metal microstructute dependence than stress dependence by analysis (BEM 3-D, BEM 2-D) and fatigue crack propagation

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Fatigue Crack Growth Rates and Directions in STS304 under Mode I and Mixed Mode (단일 및 혼합모드하에서 304스테인리스강의 피로균열 진전속도와 방향특성)

  • 권종완;양현태
    • Transactions of the Korean Society of Machine Tool Engineers
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    • v.11 no.3
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    • pp.102-109
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    • 2002
  • The fatigue crack growth under mixed mode condition has been discussed within the scope of linear fracture mechanics such as maximum tangential stress, maximum tangential principal stress and minimum strain energy density. The purpose of this study is to investigate the characteristics of fatigue test crack growth in 304 stainless steel under mixed node. The fatigue test results carried out by using inclined pre-crack specimens was compared to both of the theoretical predictions of the criteria, maximum tangential stress and stain energy density. As difference from theoretical analysis, the transition region from mixed mode to mode I appeared in the fatigue test. There is deep relationship between the angle of slanted pre-crack and transition. Therefore, as applying the different stress intensity factor to each node I+II and mode I, the directions and rates of fatigue crack growth are evaluated more accurately under mixed mode.

Effect of Specimen Thickness on the Statistical Properties of Fatigue Crack Growth Resistance in BS4360 Steel

  • Kim, Seon-Jin;Itagaki, Hiroshi;Ishizuka, Tetsuo
    • Journal of Mechanical Science and Technology
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    • v.14 no.10
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    • pp.1041-1050
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    • 2000
  • In this paper the effect of specimen thickness on fatigue crack growth with the spatial distribution of material properties is presented. Basically, the material resistance to fatigue crack growth is treated as a spatial stochastic process, which varies randomly on the crack surface. The theoretical autocorrelation functions of fatigue crack growth resistance with specimen thickness are discussed for several correlation lengths. Constant ${\Delta}K$ fatigue crack growth tests were also performed on CT type specimens with three different thicknesses of BS 4360 steel. Applying the proposed stochastic model and statistical analysis procedure, the experimental data were analyzed for different specimen thicknesses for determining the autocorrelation functions and probability distributions of the fatigue crack growth resistance.

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A Study On the Factors that Affect Fatigue Crack Growth Rate in Steels - Specimen Thickness Effect - (강재의 피로균열전파율에 미치는 영향인자에 관한 연구)

  • Kim, Seon-Jin;Nam, Ki-Woo;Hong, Jin-Pyo
    • Journal of Ocean Engineering and Technology
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    • v.13 no.2 s.32
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    • pp.58-65
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    • 1999
  • The effect of specimen thickness on fatigue crack growth rate was studied. The objective of the present study is to investigate the effect of specimen thickness on the fatigue crack growth behavior at various stress intensity factor ranges and also the variation of material restance to fatigue crack growth. The fatigue crack growth resistance was treated as a spatial stochastic process, which varies randomly on the crack path, Compact tension specimens with a LT orientation for structural steel were used. All testing was done at a constant stress intensity level. The experimental data were analyzed for the size effect to determine the Weibull distributions of the material resistance.

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Elastic-Plastic Fatigue Crack Growth and J Integral (彈塑性 疲勞균열進展과 J積分)

  • 송지호;김일현;박영조
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.8 no.1
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    • pp.26-33
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    • 1984
  • Constant-load-amplitude fatigue crack growth tests were carried out on 5083-0 aluminum alloy under elastic and elastic-plastic conditions. Crack length, crack closure and monotonic fatigue deformation were measured by Kikukawa's unloading elastic compliance monitoring technique and elastic-plastic fatigue crack growth rates were analysed in terms of J integral. Elastic-plastic fatigue crack growth rates can be well expressed by effective cyclic J integral until general yielding occurs. Beyond general yielding, monotonic fatigue deformation becomes significant and growth rates cannot be characterized by a single parameter of effective cyclic J integral alone. However, introducing one more parameter, maximum J integral J$_{max}$ to account for the effect of monotonic fatigue deformation, can explain fatigue crack growth behavior beyond general yielding.