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용접후열처리와 잔류응력이 SM490A의 피로수명에 미치는 영향
구병춘,서정원,이찬우,권석진 한국철도학회 2019 한국철도학회논문집 Vol.22 No.6
SM490A steels are widely used in various fields such as automobile, ship buildings, railway vehicles andwelded structures. Plastic deformation occurs in a welded structure during welding and residual stress remains in thepost-welded structure. Residual stress may lower the static strength and fatigue strength of the structure. In some cases,post-weld heat treatment may be used to remove the residual stress. In this study, the effects of heat treatment and residualstress on the fatigue strength of various specimens were experimentally investigated. Welding residual stress wasmeasured, and how residual stress relaxed when one cycle of external force was applied was also measured. Thechanges of microstructure due to heat treatment after welding were observed under a microscope. The microstructurechanged. It was found that postweld heat treatment had the effect of slightly increasing the fatigue strength of the parentmaterial by 15 MPa. Finally, specimens with residual stresses and without any changes in the structure were fabricated,and fatigue tests were conducted to show that the tensile residual stress lowers the fatigue strength by 33 MPa.
유한요소 해석에 의한 맞대기 용접 이음의 응력집중에 과한 연구
구병춘,최병일,김재훈 대한용접접합학회 2004 대한용접·접합학회지 Vol.22 No.4
The purpose of this study is to investigate the influence of weld bead profiles on stress concentration factors of double V groove butt-welded joints. The influence of three parameters such as toe radii, flank angles and bead heights on the stress concentration factors is studied by finite element analysis. It is shown that the three parameters have similar effects on the stress concentration factors. Finally a formula to estimate the stress concentration factors considering the three parameters and others is proposed and estimated results are compared with the results obtained by finite element analysis.
계장화 압입시험에 의한 용접부의 물성 측정 및 피로수명 예측
구병춘,이동형,권동일,최열,Goo, Byeong-Choon,Lee, Dong-Hyung,Kwon, Dong-Il,Choi, Yeol 한국철도학회 2004 한국철도학회논문집 Vol.7 No.2
When material properties depend much on positions in a material or it is difficult to make test specimens from a material or component, an instrumented indentation test described in ISO 14577-1, 14577-2 or KS B 0950 can be used to measure material properties and damage. In this study, first of all, the principals of the instrumented indentation test, KS B 0950 are introduced and yield strengths, tensile strengths and work hardening exponents of base materials, heat affected zones and weld materials are measured. In addition, the influence of post-weld heat treatment on the material properties is investigated. Finally the fatigue lift of butt welded specimens are evaluated by the local strain approach. To calculate local strains and stresses, elasto-plastic finite element analysis is conducted using the measured properties.
Al6061-T6 판재의 마찰교반용접 3D 유한요소 해석
구병춘,정현승,Goo, Byeong-Choon,Jung, Hyun-Seung 대한용접접합학회 2011 대한용접·접합학회지 Vol.29 No.4
Friction stir welding (FSW) is a solid state joining method patented in 1991 by The Welding Institute (TWI). It is widely used for joining light metals such as Al and Mg alloys. Foreign railway vehicle manufacturing companies have been applying FSW to car body welding, but domestic companies are in the beginning of feasibility study. Therefore, lots of experimental and analytical study is needed. In this study, three-dimensional finite element modeling of the friction stir welding of two Al6061-T6 plates was carried out. And temperature field and residual stresses were obtained and compared to experimental results in the literature. It is found the analytic thermal field is in a good agreement with the experimental results, but there are some differences between numerical and experimental residual stresses.
구병춘,김재훈,Goo, Byeong-Choon,Kim, Jai-Hoon 대한용접접합학회 2007 대한용접·접합학회지 Vol.25 No.1
A lot of fatigue tests on a material, JIS SM490A, with yielding strength of about 350 MPa and tensile strength of about 520 MPa were carried out. Various butt-welded specimens such as reinforcement removed, as-welded and weld toe ground, several types of fillet-welded specimens and full-size box type components were used. After having obtained S-N curves for the above- mentioned specimens, fatigue strengths were compared to those of foreign design codes, AWS, BS 7608 and ENV. It was found the fatigue strengths at low cycles are not in a good agreement with the foreign codes, but the fatigue limits are in a good agreement.
Characteristics of A356/SiC_p_ and A390/SiC_p_ composites
구병춘,김명호 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.7
Aluminum alloy matrix composites reinforced with SiC particles (AMC) are potential materials applicable to weight reduction of friction materials. We developed two AMC: A356/SiC and A390/SiC. 30 μm and 60 μm SiC particles with volume fraction of 20% were dispersed in the matrix of A356 and A390 alloys. When the temperature of the liquid alloy was higher than that of the melting point, SIC particles floated up to the surface because of the low viscosity, high surface tension and interfacial energy. To mix the ceramic particles,the aluminum alloy was in the mushy state near the solidus temperature, 610℃ for A356 and 645℃ for A390. Metallurgical, mechanical and tribological characteristics of the manufactured composites were evaluated.