• Title/Summary/Keyword: 잔류수명

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Establishment of An Optimal Process to Improve Structural Integrity by Investigating Effect of the Process Variables on Fatigue Lifetime of Steel-Sleeve Repair Welds in Buried Gas Pipeline (매설가스배관 강 슬리브 보수 용접부의 피로수명에 미치는 공정변수 영향 고찰을 통한 최적공정 수립)

  • Kim, Jong Sung;Lee, Cheol;Kim, Woo Sik;Kim, Ik Jung
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.41 no.11
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    • pp.1021-1033
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    • 2017
  • In this study, an optimum process to improve structural integrity was established by investigating effect of the process variables on fatigue lifetime of steel-sleeve repair welds in buried gas pipeline. Residual stresses in the repair welds were derived through sequentially-coupled temperature-stress analysis using ABAQUS, which is a commercial finite element analysis program. In addition, variations of operating stresses were derived by finite element linear elastic stress analysis. Fatigue lifetimes of the steel-sleeve repair welds were evaluated by substituting the derived weld residual stresses and operating stress variations into the structural stress/fracture mechanics approach as input. Parametric study using finite element analysis and fatigue assessment for various repair welding process variables were carried out to investigate the effects of the process variables on the fatigue lifetime. Finally, based on the effects of the process variables on the fatigue lifetime, an optimal process to minimize the welding time and economic costs and to improve the fatigue lifetimes was derived.

Residual fatigue life evaluation method for the cracked components under complex stress fields (복합응력장 하의 균열부재에 대한 잔류피로수명 평가방법)

  • Cho, Chang-Hee;Kim, sang-Tae;Kwon, Jae-Do
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.22 no.2
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    • pp.258-267
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    • 1998
  • This study reviews the influence function method(IFM) for calculating stress intensity factors (SIFs, K) and modifies it to apply for the estimating the residual fatigue life for the cracked components under complex stress fields. An IFM has been developed to analyze SIFs for surface cracks which are subjectedto nonuniformly distributed stresses. Through elastic superposition, the influence function method properly accounts for redistribution of stress as the crack grows through the component. This influence function is unique to the given geometry and independent of the loading. Some examples have been provided to show the effectiveness of the IFM including the distributions of K in a residual stress field. The significant effect of residual stress upon fatigue crack growth in a welded component has been demonstrated with the IFM.

Influence of residual stress due to shot peening on fatigue strength and life (피로강도 및 수명에 미치는 Shot Peening에 의한 잔류응력의 영향)

  • Lee, Jong-Gyu;Kim, Jeong-Gyu
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.21 no.9
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    • pp.1498-1506
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    • 1997
  • Procedures are presented for influence of shot peening on fatigue strength, fatigue life and effects of shot peening are discussed from experiments were taken between shot peened and unpeened SPS5, SM45C specimens. After the residual stress on shot peened specimens was measured by X-ray diffractometer, rotating bending fatigue tests were carried out. In addition, the compressive residual stress profile was obtained by the superposition method of three stresses which is based on Al-Obaid's equation. Predicted fatigue life considering residual stress profile which was obtained by the Al-Obaid's equation and another predicted fatigue life considering residual stress profile which was measured in test were compared. For the purpose of predicting fatigue life, Morrow's equation considering the residual stress and mean stress was used.

The Prediction of Fatigue Life According to the Determination of the Parameter in Residual Strength Degradation Model (잔류강도 저하모델의 파라미터결정법에 따른 피로수명예측)

  • 김도식;김정규
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.8
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    • pp.2053-2061
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    • 1994
  • The static and fatigue tensile tests have been conduted to predict the fatigue life of 8-harness satin woven and plain woven carbon/epoxy composite plates containing a circular hole. A fatigue residual strength degradation model, based on the assumption that the residual strength for unnotched specimen decreases monotonically, has been applied to predict statistically the fatigue life of materials used in this study. To determine the parameters(c, b and K) of the residual strength degradation model, the minimization technique and the maximum likelihood method are used. Agreement of the converted ultimate strength by using the minimization technique with the static ultimate strength is reasonably good. Therefore, the minimization technique is more adjustable in the determination of the parameter and the prediction of the fatigue life than the maximum likelihood method.

Fatigue Life Evaluation by ${\sigma}-N$ and ${\epsilon}-N$ Approaches Considering Residual Stresses (잔류응력을 고려한 국부변형률과 공칭응력 기준 피로수명 평가)

  • Goo, Byeong-Choon;Yang, Sung-Yong;Seo, Jung-Won;Jun, Hung-Chai
    • Proceedings of the KSME Conference
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    • 2004.11a
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    • pp.342-347
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    • 2004
  • To evaluate the fatigue lives of welded joints taking into residual stress relaxation, two approaches are applied. One is based on the conventional local strain analyses. The other is based on a model developed by the authors. In the first approach, the Ramberg-Osgood relation, Lawrence model and S.W.T. parameter are used. In the second approach, The S-N curve for a welded joint is deduced from that of the parent material. Residual stress relaxation obtained by finite element analysis is considered. Finally, we evaluate the fatigue lives for four weld details using the two approaches.

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Fatigue Life Evaluation Model of Welded Joints With Residual Stress (잔류응력을 고려한 용접 이음부의 피로수명 평가 모델)

  • Goo, Byeong-Choon;Yang, Sung-Yong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.28 no.9
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    • pp.1328-1336
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    • 2004
  • According to our fatigue tests carried out at 20 Hz, R=0.1 on transversely butt-welded joints, fatigue strengths of as-welded specimens, that is, specimens having residual stress are higher than those of annealed specimens in short life range, but vice verse in long life range. This behavior seems to be concerned mainly with residual stress relaxation by applied loading. After analyzing the welding process, we conducted finite element analysis to quantify the degree of residual stress relaxation. By taking into account residual stress relaxation, modified Goodman diagram, and nominal stress, we evaluated the fatigue life of the welded joint from the S-N curve for the parent material. The estimated results are in a good agreement with the experimental results.

A Proposal of parameter Determination Method in the Residual Strength Degradation Model for the Prediction of Fatigue Life(II) (피로수명예측을 위한 잔류강도 저하모델의 파라미터 결정법 제안(II))

  • Kim, Sang-Tae;Jang, Seong-Su
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.25 no.9
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    • pp.1452-1460
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    • 2001
  • A new method of parameter determination in the fatigue residual strength degradation model is proposed. The new method and minimization technique is compared experimentally to account for the effect of tension-compression fatigue loading of spheroidal graphite cast iron and graphite/epoxy laminate. It is shown that the correlation between the experimental results and the theoretical prediction on the fatigue life and residual strength distribution using the proposed method is very reasonable. Therefore, the proposed method is more adjustable in the determination of the parameter than minimization technique for the prediction of the fatigue characteristics.

Fatigue Life Evaluation of Welded Joints With Residual Stress (잔류응력을 고려한 용접 이음부의 피로수명 평가 모델)

  • Goo, B.C.;Yang, S.Y.
    • Proceedings of the KSME Conference
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    • 2004.04a
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    • pp.108-113
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    • 2004
  • According to our fatigue tests carried out at 20 Hz, R=0.1 on transversely butt~welded joints, fatigue strengths of as-welded specimens, that is, specimens having residual stress are higher than those of annealed specimens in short life range, but vice verse in long life range. This behavior seems to be concerned mainly with residual stress relaxation by applied loading. After analyzing the welding process, we conducted finite element analysis to quantify the degree of residual stress relaxation. By taking into account residual stress relaxation, modified Goodman diagram, and nominal stress, we evaluated the fatigue life of the welded joint from the S-N curve for the parent material. The estimated results are in a good agreement with the experimental results.

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Fatigue Life Analysis of Butt-welded specimen by Local Strain Approach (국부변형률방법을 이용한 용접시험편의 피로수명 해석)

  • Lee Dong-Hyong;Seo Jung-Won;Goo Byeong-choon;Seok Chang-Sung
    • Proceedings of the KSR Conference
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    • 2003.10c
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    • pp.73-78
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    • 2003
  • The residual stresses and. distortions of structures by welding exert negative effect on the safety of railroad structures. This investigation performs a thermal elasto-plastic analysis using finite element techniques to evaluate residual stresses in butted-welded joint. Considering this initial residual stresses, local stress and strain at the critical location (weld toe) during the loading were analyzed by elastic plastic finite element analysis. Fatigue crack initiation life and fatigue crack propagation life of butt-welded specimen were predicted by local strain approach and Neuber's role and Paris law. It is demonstrated that fatigue life estimates by local strain approach closely approximate the experimental results.

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Effect of Indentation Residual Stresses on the Fatigue Crack Initiation Life (피로균열 발생수명에 대한 압입 잔류응력의 영향)

  • 이환우;강태일
    • Journal of the Korean Society for Precision Engineering
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    • v.21 no.5
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    • pp.158-165
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    • 2004
  • Up to now, many crack repair techniques have been developed for inhibiting crack growth in structural components. However, the simplest way for inhibiting crack growth is to apply a indentation at the crack tip or at some distance ahead of the expected crack growth path so as to produce residual compressive stresses that can reduce the effective stresses around the crack tip. In spite of its importance to the aerospace industry, little attention has been devoted to evaluation of the indentation residual stress effect on the fatigue crack initiation life quantitatively. Therefore, in the present work, the magnitude and distribution of the indentation residual stresses were investigated in order to estimate the beneficial effect on fatigue crack initiation by using finite element method. Furthermore, to examine the validity of finite element analysis results, residual stress distribution in the indented specimen was measured by using X-ray diffraction technique, and fatigue crack behavior at fastener hole in aluminum alloy 7075-T6 before and after indentation processes was investigated.