• 한국재료학회지
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• 제13권8호
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• pp.491-496
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• 2003

Fe-Ni alloy nanoparticles were prepared by ERC (Evaporation and Rapid Condensation) method, and the crystal structure and the behavior of martensite for the nanosized alloy particles were investigated by X-ray diffraction analysis. The relation between the rate of martensite transformation and the internal strain of austenite was discussed. The lattice spaces of austenite and martensite for the nanoparticles agreed with those of the bulk materials. The rate of martensite transformation from austenite and the internal strain of austenite was reduced with decreasing the average size of Fe-Ni nanoparticles. It was thought that the residual austenite in the Ni content range of 11∼l5at% was caused by the internal strain, and the residual martensite in the Ni content range of 32∼36at% had its origin in the high surface energy of nanoparticles.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 추계학술대회논문집
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• pp.355-358
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• 2003

To estimate the residual stresses in the thin film and surface coatings, combined method based on nanoindentation and finite element (FE) analysis was developed. A simple equation for estimating the residual stress was composed of the hardness and the parameters which can be driven from the nanoindentation loading and unloading behaviors. FE analysis on the nanoindentation procedure under the various residual stress levels was performed to determine the parameters that included in the equation. The equation showed a good coincidence between the estimated residual stresses and those for the FE analysis. Thus the proposed method was considered as a useful method for estimating the residual stresses in the thin film without stress free specimen.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.652-656
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• 2002

The HDM(Hole Drilling Method) is a relatively simple and accurate method in measuring residual stress of welded metal. Various methods of evaluating residual stress are studied in welding field. The method of cutting holes on the plate much affects the accuracy of result. Especially for the hard material like stainless steel difficult to cut preciously is difficult to measure residual stress on welded metal. Because heat conduction of stainless steel is lower than other general steel, the magnitude of residual stress might be different as to changing of welding conditions. Therefore, The distribution of residual stress on the STS304 steel after welding using HDM is evaluated in this paper.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2000년도 특별강연 및 춘계학술발표대회 개요집
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• pp.251-255
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• 2000

Recently, the improvement of computer capacities and artificial intelligence ware caused to employ for prediction of residual stresses and strength evaluation. There are a lot of researches regarding the measurement and prediction of residual stresses for weldment using a neural network in the advanced countries, but in our country, a neural network as a technical part, has only been used on the possibilities of employment for welding area. Furthermore, the relationship between residual stress and process parameters using a neural network was wholly lacking. Therefore development of a new technical method for the optimized process parameters on the reduction of residual stress and applyment of real-time production line should be developed. The objectives of this paper is to measure the residual stress of butt welded specimen using strain gage sectioning method and to apply them to a neural network for prediction of residual stresses on a given process parameter. Also, the assessment of the developed system using a neural network was carried out

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2004년도 가을 학술발표회 논문집
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• pp.270-277
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• 2004

In this paper, path-independent values of the J-integral in the fininte element context for arbitrary two-dimensional and three-dimensional crack configurations in welds are presented. For the fracture mechanics analysis of cracks in welds, residual stress analysis and fracture analysis must be performed simultaneously. In the analysis of cracked bodies containing residual stress, the usual domain integral formulation results in path-dependent values of the J-integral. This paper discusses modifications of the conventional J-integral that yield path independence in the presence of residual stress generated by welding. The residual stress problem is treated as an initial strain problem and the J-integral modified for this class of problem is used. And a finite element program which can evaluate the J-integral for cracks in two-dimensional and three-dimensional residual stress bearing bodies is developed using the modified J-integral definition. The situation when residual stress only is present is examed as is the case when mechanical stresses are applied in conjunction with a residual stress field.

• Journal of Welding and Joining
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• 제19권6호
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• pp.664-670
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• 2001

The HDM(Hole Drilling Method) is a relatively simple and accurate methods in measuring residual stress of weldment. Various method of evaluating residual stress are studied in welding field. The method of cutting holes on the plate much affects the accuracy of result. Especially for the hard material like stainless which is difficult to cut preciously is difficult to measure residual stress of weldment. Because heat conduction of strainless steel is lower than other general steel, the magnitude of residual stress might be different as to changing of welding conditions. Therefore, the distribution of residual stress on the STS304 steel after welding using HDM is evaluated in this paper.

• 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.

• 한국자동차공학회논문집
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• 제9권6호
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• pp.201-206
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• 2001

The hole-drilling method makes a little hole through the metal surface that has residual stress and measures the relieved stress with a strain gage. It is used widely in measuring the residual stress of surfaces. In this method, the inclined hole is one of the source of error. This paper presents a finite element analysis of influence of the inclined hole for the uniaxial residual stress field. The stress differences between measured and applied residual stress increase proportionally to inclined angle of the hole. The correction equations which easily obtain the residual stress taking account of the inclined angle and direction are derived. The measurement error of stress due to the inclined hole can be reduced to around 1% through this study.

• 한국압력기기공학회 논문집
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• 제11권1호
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• pp.69-73
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• 2015

The study investigated effects of residual stresses and Charpy impact energy on brittle fractures of the butt weld between the valve and the piping, and of the valve body in nuclear power plants via a linear elastic fracture mechanics approach in the ASME B&PV Code, Sec.XI and finite element analysis. Weld residual stress in a butt weld between close check valve and piping, and residual stress in the valve due to casting process were assumed to be proportional to yield strength of base metal. Operating stresses in the butt weld and the valve body were calculated using approximate engineering formulae and finite element analysis, respectively. Applied stress intensity factors were calculated by assuming postulated cracks with specific sizes and then by substituting the residual stresses and the operating stresses into engineering formulae presented in the ASME B&PV Code, Sec.III. Plane strain fracture toughness was derived by using a correlation between Charpy V-notch impact energy and fracture toughness. Structural integrity of the weld and the body against brittle fracture was assessed by using the applied stress intensity factors, plane strain fracture toughness and the linear elastic fracture mechanics approach. As a result, it was identified that the structural integrity was maintained with decreasing the residual stress levels and increasing the Charpy V-notch impact energy.

• Steel and Composite Structures
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• 제44권2호
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• pp.199-210
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• 2022

This study build finite element analysis (FEA) models describing the bending events of coiled tubing (CT) at the wellhead and trips into the hole, accurately provide the state of stress and strain while the CT is in service. The bending moment and axial force history curves are used as loads and boundary conditions in the diametrical growth models to ensure consistency with the actual working conditions in field operations. The simulation diametrical growth results in this study are more accurate and reasonable. Analysis the factors influencing fatigue and diametrical growth shows that the internal pressure has a first-order influence on fatigue, followed by the radius of the guide arch, reel and the CT diameter. As the number of trip cycles increase, fatigue damage, residual stress and strain cumulatively increase, until CT failure occurs. Significant residual stresses remain in the CT cross-section, and the CT exhibits a residual curvature, the initial residual bending configuration of CT under wellbore constraints, after running into the hole, is sinusoidal. The residual stresses and residual bending configuration significantly decrease the buckling load, making the buckling and buckling release of CT in the downhole an elastic-plastic process, exacerbating the helical lockup. The conclusions drawn in this study will improve CT models and contribute to the operational and economic success of CT services.