• 제목/요약/키워드: Weld growth

검색결과 193건 처리시간 0.032초

Microstructure and CTOD (crack tip opening displacement) of Deposit Weld Metal in 30 mm Thick Plate

  • Lee Hae-Woo;Kim Hyok-Ju;Park Jeong-Ung;Kang Chang-Yong;Sung Jang-Hyun
    • 한국재료학회지
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    • 제14권9호
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    • pp.642-648
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    • 2004
  • The microstructure and crack tip opening displacement (CTOD) of deposit weld metal were investigated for a 30 mm- thick plate welded with flux cored arc welding (FCAW) and submerged arc welding (SAW) processes. The CTOD test was carried out both as welded condition and as stress-relieved specimen by local compression. The crack growth rates in FCAW were faster than those in a SAW, and the acicular ferrite content by the SAW process was increased relatively more than that by the FCAW process. The fatigue crack growth rate in a welded specimen was faster than that in locally compressed specimen. The CTOD value of locally compressed specimens was lower than that of as welded specimen. Furthermore, the CTOD value tested with the SAW process was higher than that tested with the FCAW process.

Variability of Fatigue Crack Initiation Life in Flux Cored Arc Welded API 2W Gr.50 Steel Joints

  • Sohn, Hye-Jeong;Kim, Seon-Jin
    • International Journal of Ocean System Engineering
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    • 제2권3호
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    • pp.160-169
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    • 2012
  • Flux Cored Arc Welding (FCAW) is a common practice to join thick plates such as the structural members of large scale offshore structures and very large container ships. The objective of this study was to investigate the mechanical properties and variability of the fatigue crack initiation life in the flux cored arc welded API 2W Gr.50 steel joints typically applied to offshore structures with a focus on the effect of the materials in fatigue crack growth life from the notch root of a compact tension specimen. Offshore structural steel (API 2W Gr.50) plates (60-mm thick) were used to fabricate multi-path flux core arc welded butt welded joints to clearly consider fatigue fractures at the weld zone from the notch. Fatigue tests were performed under a constant amplitude cyclic loading of R = 0.4. The mean fatigue crack initiation life of the HAZ specimen was the highest among the base metal (BM), weld metal (WM), and heat affected zone (HAZ). In addition, the coefficient of variation was the highest in the WMl specimen. The variability of the short fatigue crack growth rates from the notch tips in the WM and HAZ specimens was higher than in BM.

Fe-Cr-Ni강 용접금속부의 미세편석에 관한 해석 (Analysis of Microsegregation in Fe-Cr-Ni Weld Metal)

  • 박준민;박종민;안상곤;이창희;윤의박
    • Journal of Welding and Joining
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    • 제16권5호
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    • pp.56-66
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    • 1998
  • During solidification or welding of alloys, the solute redistribution brings out microsegregation. The microsegregation causes the formation of non-equilibrium second phases, shrinkage and porosity degrading mechanical/chemical properties Therefore, it has been required to predict microsegregation quantitatively. To predict the degree of microsegregation, more exact and appropriate computer simulation technique has been actively used during last two decades. To predict the degree of microsegregation in weld metal, an advanced two dimensional model was suggested. In the new model, both primary and secondary arm regions were defined for the analysis region. The growth in the primary arm regina was assumed to be a planar for effective calculation. Especially, for the growth of a secondary arm, a simple and effective mathematical function was established to show the growing pattern, the solute diffusion in the solid phase was calculated by finite difference method (FDM). The solid-liquid interface movement was considered to be in local equilibrium state. The experiments for welding of 310S stainless steel were carried out in order to examined the reasonability and feasibility of this model. The concentration profiles of the solute predicted by this model were compared with those obtained from experimental works.

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횡방향 TIG 용접된 Al6013-T4알루미늄 합금 용접부의 피로균열전파거동에 미치는 PWHT의 영향 (Influences of Post Weld Heat Treatment on Fatigue Crack Growth Behavior of Transverse TIG Welded Al6013-T4 Aluminum Alloy Joint)

  • 구나완;김선진
    • 동력기계공학회지
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    • 제16권4호
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    • pp.66-73
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    • 2012
  • 본 연구는 횡방향 TIG 용접된 Al6013-T4 알루미늄 합금 용접부의 피로균열전파거동에 미치는 용접후열처리(PWHT)의 영향을 조사하는 것이 주목적이다. 기초적으로 인장시험, 경도 및 미세조직이 조사되었으며, 피로균열전파거동을 고찰하기 위한 피로 시험은 모두 중앙균열인장(CCT) 시험편에 대하여 수행되었다. T82열처리에 있어서 시효시간은 피로균열전파율, 인장강도 및 경도에 대단히 민감함을 나타내었으며, 모재와 열영향부재의 경우가 용접재보다 기계적 성질이 우수하였다. 횡방향 TIG 용접한 Al6013-T4 시험재의 용접후열처리 조건에 따라서 피로균열전파 저항에는 차이가 나타났으며, 본 실험의 조건하에서 24시간 인공시효 PWHT-82 시험편이 피로균열전파 저항이 가장 우수한 결과를 나타내었다.

용접(鎔接)이음한 구조용강(構造用鋼)의 피노귀열진전거동(疲勞龜裂進展擧動) (The Propagation Behavior of the Fatigue Crack of the Welded Structural Steel)

  • 정영화;김익겸;이형근;정진석
    • 산업기술연구
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    • 제18권
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    • pp.117-124
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    • 1998
  • In recently, according to increase the construction rate of steel bridge, it is necessary to develop the high strength, high toughness steel. Thus, this study show to evaluate the fatigue characteristic of SWS 570 B first used within a country. With the weld-joined compact tension specimens compared with each other, that is, transverse and lengthwise about the crack propagation, high and low in the input heat level, the fatigue test were performed. The log-log curves between the fatigue crack propagation rate da/dN and the transition range of the stress intensity factor ${\Delta}K$ ahead the crack tip were drawed, with these data. By using this curve, we obtained C and m which is material constant from Paris-Erdogan power law. The obtained results from this study indicate that fatigue crack growth rate of SWS 570 B is not influenced by softening effect which occurs in the HAZ(heat-affected zone) when high and low heat input weld is carried out. Softening effects, which affect fatigue properties, are shown that it is not affected to the fatigue growth rates significantly.

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고온 보일러 헤더의 잔여수명평가 사례 연구 (A Case Study of Remaining Life Assessment for Boiler Header)

  • 백운봉;이해무;박종서;김동진;윤기봉
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2001년도 춘계학술대회논문집A
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    • pp.274-279
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    • 2001
  • Creep-fatigue crack growth behavior was experimentally measured particularly when a crack was located in the heat affected region of 1Cr-0.5Mo steel. Load hold times of the tests for trapezoidal fatigue waveshapes were varied among 0, 30, 300 and 3,600 seconds. Time-dependent crack growth rates were characterized by the $C_t$-parameter. It was found that the crack growth rates were the highest when the crack path was located along the fine-grained heat affected zone(FGHAZ). Cracks located in other heat affected regions had a tendency to change the crack path eventually to FGHAZ. Creep-fatigue crack growth law of the studied case is suggested in terms of $(da/dt)_{avg}$ vs. $(C_t)_{avg}$ for residual life assessment.

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과대하중에 의한 레이저 용접 판재의 피로균열 전파거동 (The Fatigue Crack Growth Behavior of Laser Welded Sheet Metal Due to Single Overload)

  • 조우강;오택열;곽대순
    • 한국정밀공학회:학술대회논문집
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    • 한국정밀공학회 2002년도 추계학술대회 논문집
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    • pp.854-858
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    • 2002
  • In this study, Fatigue crack growth behavior of the laser welded sheet metal due to a single overload was investigated. From Fatigue crack propagation test, it was observed that the retardation of fatigue crack growth has been more effective in the welded specimen than in the base metal. And if the distance between the welded part and the position of overload is too close the retardation of fatigue crack growth at the welded part has been decreased. From FEM analysis, it was observed the retardation has been more effective compressive residual stress than plastic zone.

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440 MPa급 도금강판의 저항 점 용접 시 AC 및 MFDC전원에 따른 가용전류구간 비교 연구 (A Comparative Study of Weldable Current Range on AC and MFDC Resistance Spot Welding for 440 MPa Grade Steel Sheet)

  • 지창욱;박찬수;김치호;조용준;오동진;김명현;김양도;박영도
    • Journal of Welding and Joining
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    • 제35권1호
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    • pp.34-42
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    • 2017
  • This paper presents a comparative study of the AC and MFDC resistance spot welding process with consideration of sheet thickness. The previous studies have confirmed that there is difference in the optimum welding current and expulsion current with AC and MFDC. The aim of this study was revealing the effect of sheet thickness on weldable current range and expulsion behavior for AC and MFDC welding processes. The optimum welding current of AC was lower (1.6 kA) than MFDC welding process in 0.8 mm sheet thickness. Early nugget growth being caused by the peak current of AC developed weld interface deformation, which resulted in suppressing the growth of corona bond and occurrence of low current expulsion. The resistance spot welding for thicker sheet (1.4 mm) required lower current of 0.6 kA for the expulsion on the MFDC welding process. The growth of contact diameter (size of corona bond) and button diameter was linear up to the expulsion current with MFDC welding process. Therefore, more attention is required when the AC and MFDC resistance spot welding process is applied for different thickness of steel sheet combination for automotive application.

확장 유한 요소법(XFEM) J-적분을 이용한 노후 순시선의 균열 성장 수명 예측 (Prediction of Crack Growth Lives of an Aged Korean Coast Guard Patrol Ship based on Extended Finite Element Method(XFEM) J-Integral)

  • 김창식;리춘보;김영훈;정준모
    • 대한조선학회논문집
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    • 제54권4호
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    • pp.335-343
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    • 2017
  • The Newman-Raju formula and contour integral-based finite element analyses(FEAs) have been widely used to assess crack growth rates and residual lives at crack locations in ships or offshore structures, but the Newman-Raju formula is known to be less accurate for the complicated weld details and the conventional FEA-based contour integral approach needs concentrated efforts to construct FEA models. Recently, an extended finite element method(XFEM) has been proposed to reduce those modeling efforts with reliable accuracy. Stress intensity factors(SIFs) from the approaches such as the Newman-Raju formula, conventional FEA-based J-integral, and XFEM-based J-integral were compared for an infinitely long plate with a propagating elliptic crack. It was concluded that the XFEM approach was far reliable in terms of prediction ability of SIFs. Assuming a 25 year-aged coast guard patrol ship had the prescribed cracks at the bracket toes attached to longitudinal stiffeners in way of deck and bottom, SIFs were derived based on the three approaches. To obtain axial tension loads acting on the longitudinal stiffeners, long term hull girder bending moments were assumed to obey Weibull distribution of which two parameters were decided from a reference (DNV, 2014). For the complicated weld details, it was concluded that the XFEM approach could cost-effectively and accurately estimate the crack growth rates and residual lives of ship structures.

잔류응력을 고려한 IB형 spot 용접이음재의 피로강도 평가 (Fatigue Strength Evaluation of IB-Type Spot Welded Lap Joint considered Residual Stress)

  • 손일선
    • 한국공작기계학회:학술대회논문집
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    • 한국공작기계학회 1997년도 추계학술대회 논문집
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    • pp.127-131
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    • 1997
  • In systematic and orderly estimation of fatigue strength of the spot welded lap joints, because the influence of residual stress of fatigue crach initiation and growth is not negligible, there need to estimate fatigue strength considered residual stress at near spot weld part of the lap joints. Therefore, in this thesis, peformed stress distribution and residual stress analysis at near the spot weld part by F.E.M and X-ray diffraction method, and obtained the maximum principal stress considered residual stress at nugget edge by superposing residual stress at nugget edge by superposing their results. From the results obtained above, we could find that fatigue strength of the IB-type spot welded lap joints was rearranged by the maximum principal stress considered residual stress at nugget edge and was entirely low about 13 percents compare with that neglected residual stress.

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