• Nuclear Engineering and Technology
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• 제48권1호
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• pp.259-267
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• 2016

Most manufacturing processes, including welding, create residual stresses. Residual stresses can reduce material strength and cause fractures. For estimating the reliability and aging of a welded structure, residual stresses should be evaluated as precisely as possible. Optical techniques such as holographic interferometry, electronic speckle pattern interferometry (ESPI), Moire interferometry, and shearography are noncontact means of measuring residual stresses. Among optical techniques, ESPI is typically used as a nondestructive measurement technique of in-plane displacement, such as stress and strain, and out-of-plane displacement, such as vibration and bending. In this study, ESPI was used to measure the residual stress on the welded part of butt-welded American Society for Testing and Materials (ASTM) A36 specimens with $CO_2$ welding. Four types of specimens, base metal specimen (BSP), tensile specimen including welded part (TSP), compression specimen including welded part (CSP), and annealed tensile specimen including welded part (ATSP), were tested. BSP was used to obtain the elastic modulus of a base metal. TSP and CSP were used to compare residual stresses under tensile and compressive loading conditions. ATSP was used to confirm the effect of heat treatment. Residual stresses on the welded parts of specimens were obtained from the phase map images obtained by ESPI. The results confirmed that residual stresses of welded parts can be measured by ESPI.

• 한국강구조학회 논문집
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• 제15권3호
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• pp.241-250
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• 2003

본 연구는 동종강재 및 이종강재 용접시 발생하는 잔류응력 특징을 파악하기 위해서 유한 요소법을 이용한 3차원 탄소성해석을 수행하였다. 결과에 의하면, 동종강재 맞대기용접시 용접부의 잔류응력은 고강도강재의 인장강도가 클수록(POSTEN60

• 대한기계학회논문집A
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• 제34권9호
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• pp.1137-1143
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• 2010

가스용접 구조물의 장 수명 피로설계기준(fatigue design criterion)을 결정하기 위해서는 정확한 응력해석과 체계적인 피로강도평가가 필요하다. 그러나 실 구조물로부터 피로설계기준을 결정하는 것은 대단히 어려우므로 구조물의 기계적 구조적 특성을 만족하는 간편 시편을 만들어서 $\Delta{\sigma}-N_f$ 관계를 도출하여 피로강도를 평가하고 있다. 그리고 가스용접에 의해 제작된 실 구조물의 피로설계를 위해서는 피로균열발생과 파단 기점이 되는 용접부의 용접잔류응력(welding residual stress)이 고려되어야 한다. 따라서, 본 연구에서는 플러그 및 링 가스용접 이음재에 대한 용접잔류응력을 고려하기 위해 용접 열 사이클(heat cycle)에 의한 비선형 열해석(non-linear thermal analysis)과 열 응력(thermal stress) 해석을 수행하고, 실험 치와 비교 분석하여 용접잔류응력을 고려한 응력 진폭-피로수명($(\sigma_a)_R-N_f$) 관계를 도출하여 자동적으로 피로설계기준을 제시할 수 있도록 하고자 하였다.

• Journal of Welding and Joining
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• 제21권6호
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• pp.64-70
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• 2003

Multipass welds of the 316L stainless steel have been widely employed in the pipes of Liquid Metal Reactor. Owing to localized heating and subsequent rapid cooling by the welding process, the residual stress arises in the weld of the pipe. In this study, the residual stresses in the 316L stainless steel pipe welds were calculated by the finite element method using ANSYS code. Also, the residual stresses both on the surface and in the interior of the thickness were measured by HRPD(High Resolution Powder Diffractometer) instrumented in HANARO Reactor. The experimental data and the calculated results were compared and the characteristics of the distribution of the residual stress discussed.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 1997년도 특별강연 및 춘계학술발표 개요집
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• pp.107-111
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• 1997

In this paper distribution of welding residual stress on the double fillet welded joint which exits and not exits root gap, i.e. full penetration and partial penetration is investigated by two dimensional cunduct and thermal elasto-plastic analysis. And stress distribution on notch-tip of the structure where welding residual stress regarded as initial stress and then external load is added is also investigated.

• Journal of Welding and Joining
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• 제6권4호
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• pp.54-62
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• 1988

Major problems in welding Al-7020 include shrinkage, rpopositgy in welds and loss of strength in the heat affected zone. Thus it is important to examine the mechanical properties and reliability of welds. In this study, a series of experiments was carried out to determine the mechanical properties such as micro-hardness distribution, tensile strength, porosity and residual stress distribution of the Al-7020 weldment made by pulse-GMA welding. The resuts of the experiemnts are as folows. 1) The micro-hardness of weld metal and heat affected zone was lower than that of the base metal. 2) The tensile strength of the deposited metal was much lower than that of the base metal. 3) The porrosity in weld metal zone was negligible under the adopted conditsion of experiemnts. 4) The residual stress in the weld metal was lower than that of the heat affected zone, because the weld metal was softened. And the mciro-hardness distribution, the tensile strength and the residual stess distribution of the weldment in the as-welded condition were compared with those of the weldment after heat treatment.

• 한국생산제조학회지
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• 제5권3호
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• pp.31-39
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• 1996

The objective of this study is to investigate the influence of welding residual stresses on the fatigue crack growth behavior of cracks located transverse to the weld bead. For this purpose, G. T. A (Gas Tungsten Arc) welding was performed on hte Al alloy 1100-O plate and the same initial crack is made on HAZ(Heat Affected Zone), weld metal and base meta respectively. Specimens were used CT(Compact Tension) specimens. Initial welding residual stresses were measured by using strai gage sectioning method. All specimens were tested under constant amplitude load with stress ratio R=0.1, It is possible to predict fatigue crack growth behaviors and the fatigue life, using numerical analysis together with distribution of initial residual stress and the values of C and m obtained from $da/dN-{\Delta}K$

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.424-429
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• 2001

Residual stresses can be produced during manufacturing processes, eg. welding, machining and plastic working, and also in service. It can be superimposed with externally applied loads, so that unexpected deformations and failures of members will be occurred. Especially, the strength and the life of welded components are affected extensively by the residual stresses distributed around their weldments not only under static loads, but also fatigue loads. These residual stresses are not kept constant, but relaxed or redistributed during service. Under static loads the relaxation takes place when the residual stress superimposed with external stress exceeds locally the yield stress of material used. It is shown that under fatigue loads the residual stress is considerably relieved by the first or few cycle loading, and then gradually relaxed with increasing loading cycles. Although many investigations in this field have been carried out, the phenomenon and mechanism of the stress relaxation by mechanical means are still not clear, and there are few comprehensive models for predicting specific effects on the stress relaxation. In this study, the effects of applied static and fatigue loads on the residual stress relaxation were Investigated, and a model to predict quantitatively the residual stress relaxation was proposed.

• 한국공작기계학회논문집
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• 제17권3호
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• pp.115-121
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• 2008

A knowloedge of the residual stress distribution at circumferential welds can increase the prediction accuracy of a fracture assessment in pipe lines. In this study, in order to predict the residual stress distribution in the circumferential butt-welded pipes were measured, using the hole-drilling strain gauge method. Their practical applications were performed in to two kinds of pipes. As the results, the following characteristics were found. On the inner surface of pipes, the circumferential and axial residual stresses were both tensile near the center line of welding and both of them changed from tensile to compressive as the distance from the center line increased. On the outer surface, however, the circumferential residual stress was shown to be tensile wile the axial residual stress was compressive near the center line of welding, and later they were revered at the region far away from the centerline.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2004년도 추계학술발표대회 개요집
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• pp.150-152
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• 2004

This study was aimed at evaluation of residual stress of steel pipe structures. The production process of pipes was complex (at first bending was done by roll forming or press forming and welding was final process of making of steel pipes). So there could be effected high residual stresses in steel pipes. In order to evaluate the changes of residual stress the locations of measurement were selected carefully. Measurements of residual stress were done for various kinds of pipes (shapes in circular and square). For the evaluation of residual stress, hole-drilling method (ASTM E837 was applied. The results showed that along the weld Eine high tensile stress were measured as effected, and high tensile stresses were measured where large plastic deformation developed. Through these efforts, experimental results could be more effectively assisted by numerical method.