• Title/Summary/Keyword: Fatigue crack

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Fatigue Crack Propagation Characteristics in HAZ of A106 Gr B Steel Pipe Weldments (A106 Gr B강 배관용접부의 잔류응력해석 및 피로균열성장특성)

  • 김철한;배동호;김복기;조선영;홍정균;이범노
    • Proceedings of the KWS Conference
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    • 1999.05a
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    • pp.237-240
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    • 1999
  • In this study, residual stresses of the weldment were calculated by finite element analysis(FEA) and experiment. And, the crack closure behaviour and fatigue crack growth characteristics in field of residual stress of A106 Gr B steel pipe weldment were investigated under various stress ratio. Obtained results are as follows. I) $K_{op}$ was independent of $K_{max}$, and load ratio in fatigue crack growth. 2) In variation of load ratio, the scatter band of crack growth curve was reduced by half considering crack closure. and 3) Neglecting crack closure behaviour, actual fatigue crack growth rate can be underestimated' and Actual fatigue crack growth rate can be overestimated by $K_{res}$, in tensile residual stress field.

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A study on the Faigue Behavior and Mechanism of High Hardened Steel (고판도강재의 피로거동과 기구)

  • ;Song, Sam Hong
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.3 no.3
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    • pp.116-123
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    • 1979
  • On the basis of optical microscope and electro microscope observation for the fatigue fracture process of medium corbon martensitic structure produced by rapid heat treatment, mainly the abstracts of the studied results for the morphology of fatigue crack initiation process of high hardened steel are summarized as follows. Fatigue crack initiated from inclusion on the surface or subsurface. Above all the crack which initiated from inclusion exposed on the surface in as follows. (1) fatigue crack initiated from the boundary of the matrix and inclusion. (2) fatigue crack initiated at surrounding of small pit by drop out of inclusion.

Fatigue Crack Propagation Behaviors on Tensile and Compression Residual Stresses in Weld Zone (용접부의 인장 및 압축잔류응력에 관한 피로균열 전파거동)

  • 이하성;강동명
    • Journal of the Korean Society of Safety
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    • v.9 no.3
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    • pp.13-21
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    • 1994
  • Effects of tensile and compression residual stresses in the welded SS41 and A17075-76 on fatigue crack propagation behavior are investigated when a crack propagates from residual stresses region. We propose the fatigue crack growth equation on tensile and compression residual stresses in welded metal. The results obtained in this experimental study are summarized as follows . 1 ) A fatigue crack growth equation which applied fatigue fracture behavior of the welded metal is proposed. (equation omitted) where, $\alpha$, $\beta$, ${\gamma}$ and $\delta$ are constants, and R$_{eff}$ is effective stress ratio [R$_{eff}$=(Kmin+Kres)/(Kmax+Kres)], Kcf is critical fatigue stress intensity factor. The constants are obtained from nonlinear least square method. The relation between crack length and number of cycles obtained by integrating the fatigue crack growth rate equation is in agreement with the experimental data. 2) The experimental results confirmed that the cause of crack extension and retardation by residual stresses has relation to the phenomenon of crack closure. 3) The relaxing trend of residual stresses by the crack propagation was greater In case of compressive residual stress than that of tensile residual stress in the welded metal.tal.

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Study on the Characteristics of Corrosion Fatigue Crack for Gas Storage Tanks (가스저장탱크의 부식피로균열 특성에 관한 연구)

  • Lim, Uh-Joh;Shin, Jong-Dae
    • Journal of the Korean Society of Fisheries and Ocean Technology
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    • v.34 no.1
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    • pp.30-36
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    • 1998
  • Recently, with rapid increase of gas demand, there occurs much interest their security of safety in the gas storage tanks and pressure vessels etc. In order to solve the problems, the occurrence of corrosion fatigue crack and the propagation behavior must be investigated. Especially the occurrence of corrosion fatigue crack and the propagation behavior in the part which has concentrated stress or defects, must be studied more carefully. In this paper, the high-tensile steel of SPV 50 which is much used for building the LPG storage tanks was tested by the use of a plane bending corrosion fatigue tester under the various marine environments and in the air. These experiments were done to investigate the corrosion fatigue crack propagation behavior, the variation of aspect ratio for part through crack and electro-chemical characteristics of the metal. The main results obtained are as follows ; 1. Comparing the same surface crack length with the crack depth, the crack depth toward the thickness of specimen in air propagated faster than that in corrosion environment. 2. The aspect variation of the half elliptical crack can be estimated as following equation; b/a=i-jb/t where a : surface crack length, b : crack depth, t : specimen thickness, i,j : experimental constants but the slope j is decreased as specific resistance decreases. 3. As the specific resistance of corrosion environment decrease or the corrosion fatigue crack propagates, the corrosion potential become less noble.

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Thermo-Mechanical Fatigue Crack Propagation Behaviors of 1.5Cr-0.67Mo-0.33V Alloy (1.5Cr-0.67Mo-0.33V강의 열피로 크랙전파 거동)

  • 송삼홍;강명수
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.9
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    • pp.2133-2141
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    • 1995
  • The thermo-mechanical fatigue tests were performed on the specimens extracted from 1.5Cr-0. 67Mo-0.33V alloy. The characteristics of thermo-mechanical fatigue crack propagation were examined and reviewed in view of fracture mechanics. The results obtained from the present study are summarized as follows : (1) The propagation characteristics of isothermal low-cycle fatigue crack are dominated by .DELTA.J$_{f}$ in case of PP waveform, and .DELTA.J$_{c}$ in case of CP waveform. (II)The propagation characteristics of thermo-mechanical fatigue crack are dominated by .DELTA.J$_{c}$ for in-phase case, and by .DELTA.J$_{c}$ for out-of-phase. The present results were in good agreement with the equation of propagation law for isothermal low-cycle fatigue crack in case of thermo-mechanical fatigue.tigue.e.

Evaluation of Fatigue Crack Growth Rate on the Surface of Steel Members Using COD(Crack Opening Displacement) Measurement (COD(Crack Opening Displacement) 측정에 의한 강재표면의 피로균열진전속도 평가)

  • Kim, Kwang Jin;Kim, In Tae
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.15 no.2
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    • pp.179-188
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    • 2011
  • Steel structures have been allowed to have fatigue damage tolerance in fact. If it would be assessed whether fatigue crack is growing or not and How fast fatigue crack is propagating, we should make a rational decision on methods and a period of reinforcement in the maintenance. In this study, fatigue crack growth tests on two kinds of through-thickness cracked steel plates and a out-of-plane gusset welded joint were conducted to evaluate fatigue crack growth rate using the COD(Crack Opening Displacement), and COD measurement using strain gauges was examined to offer a practical method. As a result, we proposed a reasonable assessing method for fatigue crack growth rate using the COD and it was experimentally proved practical to estimate the COD through measuring strains.

A Study of Fatigue Crack Threshold Characteristics in Pressure Vessel Steel at Low Temperature (압력용기용 강의 저온 피로크랙 하한계 특성에 관한 연구(II))

  • 박경동;김정호;정찬기;하경준
    • Journal of Ocean Engineering and Technology
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    • v.14 no.3
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    • pp.78-83
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    • 2000
  • In this study, CT specimens were prepared from AST SA516 Gr. 70 which was used for pressure vessel plates for room and low temperature service. And we got the following characteristics from fatigue crack growth test carried out in the environment of room and low temperature at 25$^{\circ}C $, -60$^{\circ}C $, -80$^{\circ}C $ and -100$^{\circ}C $ and in the range of stress ratio of 0.05, 0.3 by means of opening mode displacement. At the constant stress ratio, the threshold stress intensity factor range ${\delta} K_{th}$ in the early stage of fatigue crack growth (Region I) and stress intensity factor range $\delta $K in the stable of fatigue crack growth (Region II) were increased in proportion to descending temperature. It was assumed that the fatigue resistance characteristics and fracture strength at low temperature is considerable higher than that of room temperature in the early stage and stable of fatigue crack growth region. The straight line slope relation of logarithm da/dN -$\delta $K in Region II, that is, the fatigue crack growth exponent m increased with descending temperature at the constant stress ratio. It was assumed that the fatigue crack growth rate da/dN is rapid in proportion to descending temperature in Region II and the cryogenic-brittleness greatly affect a material with decreasing temperature.

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Statistical Distribution of Fatigue Crack Growth Rate for Friction Stir Welded Joints of Al7075-T651 (Al7075-T651의 마찰교반용접된 접합부의 피로균열전파율의 통계적 분포)

  • Ahn, Seok-Hwan;Kim, Seon-Jin
    • Journal of Power System Engineering
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    • v.17 no.4
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    • pp.86-93
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    • 2013
  • This paper deals with the effects of driving force and material properties on statistical distribution of fatigue crack growth rate (FCGR) for the friction stir welded joints of Al 7075-T651 aluminum plate. In this work, the statistical probability distribution of fatigue crack growth rate was analyzed by using our previous constant stress intensity factor range controlled fatigue crack growth test data. As far as this study are concerned, the statistical probability distribution of fatigue crack growth rate for the friction stir welded (FSWed) joints was found to evaluate the variability of fatigue crack growth rate for base metal (BM), heat affected zone (HAZ) and weld metal (WM) specimens. The probability distribution of fatigue crack growth rate for FSWed joints was found to follow well log-normal distribution. The shape parameter of BM and HAZ was decreased with increasing the driving force, however, the shape parameter of WM was decreased and increased with increasing the driving force. The scale parameter of BM, HAZ and WM was increased with the driving force.

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.

Fatigue crack propagation of buried pipe steel under mixed model loading (혼합모드하중을 받는 매석배관강의 피로균열전파 거동)

  • 이억섭;최용길
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2000.11a
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    • pp.473-476
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    • 2000
  • Recently, many studies focus on mixed-mode fatigue-fracture characteristics of characteristics of materials. In order to reveal crack initiation and propagation mechanisms in combined -mode fatigue. This paper investigates the initiation and propagation behavior of the fatigue crack of the STS304 specimens under mixed mode loading conditions. moreover crack arrest and branch phenomena were analyzed with respect to the change do the angle of inclined loading. The relationship between the angle of inclined loading and the angle of branched crack was studied. A greate number of cycles are necessary to initiate a new crack from the initial crack. The direction of the new crack propagation is determined by MTS theory.

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