• 제목/요약/키워드: crack distribution

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An Evaluation of Residual Stress Redistribution in the Welding Residual Stress Field Caused by Fatigue Crack Propagation by Finite Element Method (용접잔류응력장에서 피로균열의 전파에 따른 잔류응력 재분포에 대한 해석적 평가)

  • Park, Eung-Joon;Kim, Eung-Joon
    • Journal of Welding and Joining
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    • v.26 no.6
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    • pp.92-96
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    • 2008
  • An investigation was performed to predict residual stress redistribution for the crack propagation initially through tensile residual stress field. The analytical method, which is based on Dugdale model by finite element analysis using elastic analysis method considering the superposition principle, was proposed to estimate the redistribution of residual stress caused by crack propagation. The various aspect of distribution of residual stress caused by crack propagation was examined based on the configuration change of specimen. The analysis results show that the aspect of redistribution of residual stress caused by crack propagation depends on the width of the specimen provided that the initial distribution of residual stress is identical.

Micro-Surface-Cracks Behavior of 304 Stainless Steel Under Creep-Fatigue Interaction at Elevated Temperature (고온하 304 스테인리스강의 크리프-피로상호작용하의 미소표면균열에 관한 파괴거동)

  • 서창민;이상돈;조일현
    • Journal of Ocean Engineering and Technology
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    • v.2 no.2
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    • pp.104-111
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    • 1988
  • This paper deals with the micro-surface-cracks behavior on the unnotched smooth specimens of Type 304 stainless steel at $593^{\circ}C$ in air under creep and creep-fatigue conditions that have 10 mim and 1 min load holding times respectively. The behaviors of the micro-surface-cracks have been visualized by means of surface replica method and optical micro-photography. The quantitative characteristics of initiation, growth and coalescence of micro-surface-cracks have been investigated by observing and measuring the crack growth behaviors. some of the important results are as follows: Main crack initiates at grain boundary in the early stage(10 to 20%)of its life time and grows through coalescence and finally leads to fracture. The distribution of micro-surface-crack length, 2a, can be plotted against the composite Weibull distribution. The growth rate of the main crack can be plotted against the stress intensity factor, crack tip opering displacement and J integral.

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Effect of Crack Orientation on Spatial Randomness of Fatigue Crack Growth Rate in FSWed 7075-T651 Aluminum Alloy Joints (마찰교반용접된 7075-T651 알루미늄 합금 용접부의 피로균열전파율의 공간적 변동성에 미치는 균열 방향의 영향)

  • Jeong, Yeui-Han;Kim, Seon-Jin
    • Journal of Power System Engineering
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    • v.18 no.1
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    • pp.91-98
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    • 2014
  • In this investigation, the effect of crack orientation on spatial randomness of fatigue crack growth rate (FCGR) in friction stir welded (FSWed) 7075-T651 aluminum alloy joints has been statistically analyzed by Weibull distribution. The fatigue crack growth tests are conducted under three different constant stress intensity factor range (SIFR) control at room temperature with R = 0.1 and frequency 10Hz on compact tension (CT) specimen machined at base metal (BM) and weld metal (WM). The experimental fatigue crack growth rate data were obtained for two types of specimens having LT and TL orientations. LT specimens both base metal and weld metal showed higher fatigue crack growth rate as compared to TL specimens. In the lower SIFR region, FCGR were found to be almost 3 times higher in higher SIFR region. The shape parameter of Weibull both LT and TL orientation for FCGR was increased with increasing SIFR, the scale parameter was also increased with increasing SIFR. The smallest value of the shape parameter was shown in weld metal specimens having LT orientation at lower SIFR region.

STOCHASTIC CHARACTERISTICS OF FATIGUE CRACK GROWTH RESISTANCE OF SM45C STEEL

  • Park, U.H.;Lee, H.W.;Kim, S.J.;Lee, C.R.;Kim, J.H.
    • International Journal of Automotive Technology
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    • v.8 no.5
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    • pp.623-628
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    • 2007
  • Reliability analysis based on fracture mechanics requires knowledge of the on statistical parameters m and C in the fatigue crack growth law $da/dN=C({\Delta}K)^m$. The purpose of the present study is to investigate if it is possible to explain the change of parameter m by the fluctuation of C only. In this study, we apply the Paris-Erdogan law treating the parameter C as random and the parameter m as constant. Fluctuations in crack growth rate are assumed to be dependent only on C. The material resistance to fatigue crack growth(Z=1/C) is treated as a spatially random process, that varies along the crack path. The theoretical crack growth rates at various stress intensity factors are discussed. Additionally, the results of constant ${\Delta}K$ fatigue crack growth tests are reported for the structural steel, SM45C. The experimental data have been analyzed to determine the probability distribution of fatigue crack growth resistanc.

The Fracture Distribution in ITO Coating with Compressive Bending Stress on Polymer Substrates

  • Lee, Sang-Keuk;Lee, Joon-Ung
    • Transactions on Electrical and Electronic Materials
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    • v.4 no.6
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    • pp.5-8
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    • 2003
  • In this paper, we investigated the fracture distribution in indium-tin-oxide (ITO) coating with compressive bending stress on polymer. Under compressive strain, the ITO island delaminates, buckles and cracks. As the mechanical compressive stress increases, the buckling width of ITO seems to be increased. These created cracks are related to well-defined distribution of mechanical stress in ITO island-arrays. We related. mechanical bending stress to crack distribution and derived theoretical equation of position-dependent bending stress. And, we verified the bending stress's magnitude to crack distribution observed from optical photographs.

Effects of Metallic Parameters for Distribution of Fatigue Crack Growth Rate - Dependence of Grain Size -; (피로크랙진전속도의 분포에 대한 금속학적 인자의 영향 - 결정입자 의존성 -)

  • Yoon, Han-Yong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.20 no.7
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    • pp.2141-2147
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    • 1996
  • The strength of material is scattered owing to the inhomogenity of microstructure, in spite of the same material. Therefore, in order to design the mechanical structure with the reliability engineering, it is important to grasp the statistical nature of material strength. In this paper, effects of grain sezes for the statistical nature of the fatigue crack growth was discussed. And the statistical nature of mechanical properties was compared with the statistical nature of the fatigue crack growth rate.

The Stress Distribution of Indium-tin-oxide (ITO) film on flexible Display Substrate by Bending (Flexible Display 기판 위의 Bending에 따른 ITO 필름의 Stress 분포)

  • 박준백;황정연;서대식;박성규;문대규;한정인
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.16 no.12
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    • pp.1115-1120
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    • 2003
  • In this paper, we investigated the position dependent stress distribution of indium-tin-oxide (ITO) film on Polycarbonate (PC) substrate by external bending force. It was found that there are the maximum crack density at the center position and decreasing crack density as goes to the edge, In accordance with crack distribution, it was observed that the change of electrical resistivity of ITO islands is maximum at the center and decrease as goes to the edge. From the result that crack density is increasing at same island position as face plate distance (L) decreases, it is evident that the more stress is imposed on same island position as L decreases.

Probabilistic Remaining Life Assessment Program for Creep Crack Growth (크리프 균열성장 모델에 대한 확률론적 수명예측 프로그램)

  • Kim, Kun-Young;Shoji, Tetsuo;Kang, Myung-Soo
    • Journal of the Korean Society for Precision Engineering
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    • v.16 no.6
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    • pp.100-107
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    • 1999
  • This paper describes a probabilistic remaining life assessment program for the creep crack growth. The probabilistic life assessment program is developed to increase the reliability of life assessment. The probabilistic life assessment involves some uncertainties, such as, initial crack size, material properties, and loading condition, and a triangle distribution function is used for random variable generation. The resulting information provides the engineer with an assessment of the probability of structural failure as a function of operating time given the uncertainties in the input data. This study forms basis of the probabilistic life assessment technique and will be extended to other damage mechanisms.

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Study of Materials and Stress Ratios on Fatigue Crack Propagation Rate Using Parameter ΔA (.DELTA.A를 파라미터로 이용한 피로크랙전파속도에 미치는 재료 및 응력비의 영향에 대한 연구)

  • 박영철;오세욱;김광영;허정원;강정호
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.16 no.7
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    • pp.1373-1380
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    • 1992
  • The local cyclic strain distribution near the crack tip has been investigated by the fine Dot Grid Strain Measurement Method, which had been suggested strain measurement method to resolve experimental difficulties by authors. It has been found that the magnitude of the local cyclic strain distribution(.DELTA..epsilon.$_{eq}$ )near a crack tip has been varied by the applied cyclic load level and material, but the shape of the local cyclic strain distribution near the crack tip has been experimentally scrarcely altered : that is .DELTA..epsilon.$_{eq}$ = .DELTA.A.f(.theta.). $r^{-1}$ . Consequently, the local cyclic strain field near the crack tip could be favorably characterized by a single parameter fatigue strain intensity factor .DELTA.A. In addition, with the viewpoint that .DELTA.A depends on material and load level, .DELTA.A has been applied to evaluate the fatigue crack propagation rate and usefulness of the result has been considered. As a result, it has been ascertained that .DELTA.A has been a useful parameter to evaluate the fatigue crack propagation rate.

Crack-Healing Behavior of $Al_2O_3$ Ceramics for Textile Machinery (섬유기기용 $Al_2O_3$계 세라믹스의 균열치유거동)

  • An, B.G.;Kim, M.K.;Ahn, S.H.;Kim, J.W.;Park, I.D.;Nam, K.W.
    • Journal of Power System Engineering
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    • v.10 no.1
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    • pp.60-64
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    • 2006
  • Alumina ceramic for textile machinery was sintered and subjected to three-point bending. A semicircular surface crack was made on each sample. Crack-healing behavior was systematically studied, as a function of crack-healing temperature and crack size. The bending strength and fracture toughness of the crack-healed sample from $1200^{\circ}C\;to\;1400^{\circ}C$ were investigated. A statistical approach based on Weibull distribution was applied to the test data to evaluate the dispersion in the fracture toughness. Alumina ceramic for textile machinery have the ability to heal after cracking, from over $1300^{\circ}C$. The material can completely heal a $65{\mu}m$ diameter semielliptical crack. The fracture toughness could be explained by 2-parameter Weibull distribution.

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