• Title/Summary/Keyword: crack life

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Evalustion and Prediction for the Fatigue crack Initiation and Growth Life by Reliability Approach (I) -Statistical Consideration for Fatigue Crack Growth Life- (신뢰성 공학적 피로 균열의 발생, 진전 수명 평가 및 예측에 관한 연구 ( I ) -피로 균열 진전 수명의 통계학적 분포 특성-)

  • 권재도;최선호;황재석;곽상국;전경옥;장재영
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.14 no.6
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    • pp.1583-1591
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    • 1990
  • Life prediction and residual life prediction of structures of machines are one of the most strongly world wide needed problems as requirement in the stage of slowly developing economy which comes after rapidly and highly developing stage. For the purpose of statistical life prediction, fatigue test was conducted under the 4 stress levels, and for each stress level, about 20 specimens are used. The statistical properties of crack growth parameter m and C in the fatigue crack growth law of da/dN=C(.DELTA.K)sup m/, and the relationship between m and C, and the statistical distribution pattern of fatigue crack growth rate can be obtained by experimental results.

A Study on the Fatigue Crack Propagation Behavior of Cr-Mo-V Alloy with Micro Defects at High Temperature. (미소 원공결함을 갖는 Cr-Mo-V강의 고온피로 크랙전파거동)

  • Song, Samhong;Kang, Myungsoo
    • Journal of the Korean Society for Precision Engineering
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    • v.13 no.12
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    • pp.70-77
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    • 1996
  • Fatigue tests were carried out at high temperature on a Cr-Mo-V steel in order to assess the fatigue life of components used in power plants. The characteristics of high temperature fatigue were divided in terms of cycle-dependent fatigue and time-dependent fatigue, each crack propagation rate was examined with respect to fatigue J-integral range, .DELTA. J$_{f}$and creep J-integral range, .DELTA. J$_{c}$. The fatigue life was evaluated by analysis of J-integral value at the crack tip with a dimensional finite element method. The results obtained from the present study are summarized as follows : The propagation characteristics of high temperature fatigue cracks are determined by .DELTA. J$_{f}$for the PP(tensile plasticity-compressive plasticity deformation) and PC(tensile plasticity - compressive creep deformation) stress waveform types, and by .DELTA. J$_{c}$for the CP(tensile creep- compressive plasticity deformation) stress waveform type. The crack propagation law of high temperature fatigue is obtained by analysis of J-integral value at the crack tip using the finite element method and applied to examine crack propagation behavior. The fatigue life is evaluated using the results of analysis by the finite element method. The predicted life and the actual life are close, within a factor of 2.f 2.f 2.

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Fatigue Life Prediction of $SIC_w$/Al Composites by Using the Monte-Carlo Simulation (몬테카르로 시뮬레이션에 의한 $SIC_w$/Al 복합재료의 피로수명에측)

  • Ahn, Jeong-Ju;Kwon, Jae-Do;Kim, Sang-Tae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.20 no.5
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    • pp.1552-1561
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    • 1996
  • It requires uch time and cost to obtain the fatigue crack growth life and fatigue crack growth path morphlogy from the fatigue crack growth tests. In this study, the Monte-Carlo simulation program was developed to predict the fatigue crack growth lofe and fatigue crack growth path morphology of metal matrix composites. Fatigue crack growth lives of 5%, 10%, 15%, 20%, 25% and 30% $SiC_w$/Al composites were predicted by usign the Monte-Carlo Simulation. And the fatigue crack growth lives of 25% $SiC_w$/Al and Almatrix from Monte-carlo simulation were compared with fatigue life from experiments in order to verify the accuracy of Monte-Carlo Simulation program.

Fatigue Crack Behavior of Triple Piece Spot by Crack Tip Opening Angle of Welded Specimen (3중 점용접재의 귤열단 열림각(CTOA)을 이용한 피로균열거동)

  • Song, Sam-Hong;Joo, Dong-Ho;Yang, Yun-Jin
    • Journal of the Korean Society for Precision Engineering
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    • v.18 no.5
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    • pp.74-83
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    • 2001
  • In this study, internal fatigue crack initiation and propagation behavior were investigated by triple piece spot welded specimen. To estimate fatigue life of the specimen varied with shape and thickness, Crack tip opening angle(CTOA) correlated with stress intensity factor was used as the stiffness parameter. The relation between fatigue life and CTOA can be arranged by the quantitative equation for each specimen by experiment. In addition, the variation of stress distribution was solved and the effect on fatigue crack behavior was examined by finite element method(FEM).

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A Case Study of Creep Crack Growth Remaining life Assessment for High Temperature Pressure Equipments (고온용 압력용기의 크리프 균열성장 잔여수명평가 사례 연구)

  • 백운봉;이해무;박종서;윤기봉
    • Journal of the Korean Society of Safety
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    • v.16 no.3
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    • pp.26-30
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    • 2001
  • Creep crack growth lift of high temperature pressure equipments was assessed for various crack locations and for various material properties. Surface cracks at the inner and outer surface of the vessel in the axial and circumferential directions were considered. The crack was located in the weld metal, in the parent metal or at the weld interface. Results shored that the crack at the weld interface was the most dangerous one. The crack located outside is weaker than that located inside. Safety factors of the case in which improper material properties were used the to unavailability of the correct material properties were discussed.

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The Fatigue Crack Initiation Life under the Rolling Contact of Rough Surfaces using Critical Plane Approach (임계평면법을 이용한 거친 표면의 구름접촉시 피로균열 시작수명)

  • 설광조;김태완;조용주
    • Tribology and Lubricants
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    • v.19 no.1
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    • pp.26-30
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    • 2003
  • The stresses of surface and substrate under the rough surface contact are irregular. Using rainflow counting method for irregular stresses, the fatigue surface crack initiation lift was calculated. With the surface generated by computer, this paper figures out the random load generated by contacting to the rough surface, analyzes the stress of its subsurface, and calculates the fatigue crack initiation life of the rough surface fatigue theory.

A Study on the Effect of a Single Overload on Fatigue Crack Retardation (단일과대하중이 피로균열성장에 미치는 영향에 관한 연구)

  • Kim, Kyung-Su;Kim, Sung-Cahn;Shin, Chun-Sik;Park, Jin-Young;Lee, Chang-Hwan
    • Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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    • 2002.10a
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    • pp.73-78
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    • 2002
  • Ships and ocean structures are generally under random loading. Various type of variable-amplitude loading affects fatigue crack growth and fatigue life. However interaction effects due to irregularity of loading including random loading have not explained exactly and it is difficult to examined fatigue crack growth behaviour and fatigue life for this reason. Therefore in this paper crack growth tests with constant-amplitude loading including a single overload were conducted to measure plastic zone size near crack tip of DENT specimen. And the observed plastic zone sized were discussed in terms of crack growth rate. As a result of this the effect the plastic rue size due to the overload is examined on the effect on crack growth rate and, consequently, fatigue life.

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Fatigue Life Evaluation of Spot Weldment Using DCPDM (직류전위차법을 이용한 점용접부의 피로수명 평가)

  • 유효선;이송인;권일현;안병국
    • Journal of Welding and Joining
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    • v.19 no.1
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    • pp.58-64
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    • 2001
  • The initiation and propagation lives of fatigue crack were studied for spot weldments composed of cold rolled steel plates(SPC$\times$SPC) and galvanized steel plates(GA$\times$GA) using DC potential drop method(DCPDM). Through the various test results, it was known that the fatigue crack initiation and propagation behaviors in all specimens could be definitely detected by DCPDM. The fatigue crack initiation life( $N_{i}$) detected by DCPDM in SPC$\times$SPC and GA$\times$GA spot weldments increased as the welding current and the nugget diameter( $N_{d}$) increased. The fatigue crack propagation life($\Delta$ $N_{f-i}$) declined as the difference of $N_{i}$ and the fatigue fracture life( $N_{f}$) also increased according to the decrease of fatigue load, $\Delta$P and the increase of nugget diameter. In the same spot weldments, the increase of nugget diameter came to increase fatigue crack propagation life owing to a decrease of stress concentration in front of nugget, especially the increasing extent for GA$\times$GA spot weldment was very high. In the welding current 6kA, $N_{f}$ for GA$\times$GA spot weldment decreased more than that of SPC$\times$SPC specimen due to zinc layer coated in steel plate and undersized nugget diameter. On the other hand, in 8kA and 10kA, the GA$\times$GA spot weldment showed higher $N_{f}$ in spite of lower $N_{i}$, than that of SPC$\times$SPC specimen except 3,000N fatigue load.ue load. load.d.

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Fatigue Life Prediction of Tire Belt Edge (타이어 벨트 끝단의 피로수명 예측)

  • 김재연;양영수;김기운
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2004.10a
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    • pp.954-957
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    • 2004
  • Tire belt durability is characterized by the initiation of a crack at the belt edge region, and the propagation of the crack until the ply is separated. Experimental methods have been used to analysis of the belt durability in the cord-reinforced rubber composite tires, but it takes much cost and time to make experiments. In this paper, a finite element method to analyze the fatigue life of a crack at the belt edge of tires is presented. The fatigue life is analyzed by using a three-dimensional Finite Element Modeling. This method includes a global-local finite element analysis to provide the detail necessary to model explicitly an internal crack and use of the J-integral for energy release rate evaluation.

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Fatigue Growth Life Prediction for Collinear Multiple Surface Cracks (동일평면상에 존재하는 복수표면균열의 피로성장수명예측)

  • Lee, J.H.;Choy, Y.S.;Kim, Y.J.
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.7 s.94
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    • pp.1668-1677
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    • 1993
  • The objective of this paper is to develop a computational model for predicting the fatigue propagation of collinear multiple surface cracks under constant amplitude and variable amplitude loadings. After examining fatigue crack growth behavior for CT specimens and single surface crack specimens, empirical equations of(11) and(12) are proposed for the prediction of fatigue life in a multiple surface crack geometry. The accuracy of the proposed model is verified using a life prediction computer program. Several case studies were performed to check the accuracy of the proposed model and to verify the usefulness of the developed program. Good agreement is observed between the numerical results based on the proposed model and the published experimental data.