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우완측,김동규,안규백,Woo, Wanchuck,Kim, Dong-Kyu,An, Gyu-Baek 대한용접접합학회 2015 대한용접·접합학회지 Vol.33 No.1
Residual stresses are inherently introduced into the engineering components during manufacturing including rolling, forging, bending and welding processes. Excessive residual stresses are known to be detrimental to the proper integrity and performance of components. Neutron diffraction has become a well-established technique for the determination of residual stresses in welds. The deep penetration capability of neutrons into most metallic materials makes neutron diffraction a powerful tool for the residual stress measurements through the thickness of the weld specimen. Furthermore, the unique volume-averaged bulk characteristic of the scattering beam and mapping capability in three dimensions is suitable for the engineering purpose. In this presentation, the neutron diffraction measurements of the residual stresses will be introduced and measurement results will highlighted in thick weld plates.
굴곡측정법을 이용한 극후판 용접부 잔류응력분포 정량분석
김동규,우완측,강윤희,Kim, Dong-Kyu,Woo, Wanchuck,Kang, Youn-Hee 대한용접접합학회 2015 대한용접·접합학회지 Vol.33 No.1
Residual stresses arising from the materials processing such as welding and joining affect significantly the structural integrity depending on the external loading condition. The quantitative measurement of the residual stresses is of great importance in order to characterize the effects of the residual stresses on the structural safety. In this paper, we introduce a newly devised destructive technique, the contour method (CM), which is applied for the measurements of the residual stress distributions through the thickness of a 80 mm thick steel weld. Residual stresses are evaluated from the contour, which is the normal displacement on a cut surface produced by the relaxation of residual stresses, using a finite element model. The CM provides a two-dimensional map of the residual stresses normal to the cut surface. The CM developed in the present study was validated in comparison with the residual stress distribution determined by a well-established neutron-diffraction residual stress instrument (RSI) instrumented in HANARO neutron research reactor.
고융점 금속 3D프린팅 소재의 중성자회절 잔류응력 측정
김동규,우완측 대한용접접합학회 2018 대한용접·접합학회지 Vol.36 No.6
Recently metal 3D printing technology has been considered as one of the most innovative manufacturing technology due to its various advantages. In particular, there have been urgent needs for technology using high melting point metal (HMPM) for the extreme environmental applications such as defense weapon, aerospace rocket, power plant. In this study, we conducted feasibility test for fabrication of Mo and W alloys using direct energy deposition (DED), which is one of the major additive manufacturing (AM) technologies. It is of great concern that the as-processed HMPMs are expected to have significant residual stress due to the use of high laser power in the 3D printing process. So we measured the residual stress and microstructure of Mo and W alloys processed by DED using non-destructive neutron diffraction method. The result demonstrated that the residual stress in the as-processed HMPMs is not significant raging form -100 to 200 MPa regardless of the high applied heat input due to the low thermal expansion and stress relief caused by intergranular micro-cracking.
서석호,우완측,이수열,Seo, Sukho,Huang, E-Wen,Woo, Wanchuck,Lee, Soo Yeol 한국재료학회 2018 한국재료학회지 Vol.28 No.7
Fatigue crack growth retardation of 304 L stainless steel is studied using a neutron diffraction method. Three orthogonal strain components(crack growth, crack opening, and through-thickness direction) are measured in the vicinity of the crack tip along the crack propagation direction. The residual strain profiles (1) at the mid-thickness and (2) at the 1.5 mm away from the mid-thickness of the compact tension(CT) specimen are compared. Residual lattice strains at the 1.5 mm location are slightly higher than at the mid-thickness. The CT specimen is deformed in situ under applied loads, thereby providing evolution of the internal stress fields around the crack tip. A tensile overload results in an increased magnitude of the compressive residual stress field. In the crack growth retardation, it is found that the stresses are dispersed in the crack-wake region, where the highest compressive residual stresses are measured. Our neutron diffraction mapping results reveal that the dominant mechanism is by interrupting the transfer of stress concentration at the crack tip.