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김회현(Hoi-Hyun Kim),김성수(Seong-Su Kim),백승세(Seung-Se Baek),권일현(Il-Hyun Kwon),양성모(Seong-Mo Yang),유효선(Hyo-Sun Yu) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.11
This research is conducted to investigate weldability characteristics with various welding conditions on the 4 lap spot welded joint of structural steel sheets in automobile. The relationship between the tensile-shear strength and the indentation depth has been investigated to evaluate the weldability and the optimum welding conditions. The welding current and the welding time have a greatly affect to the tensile-shear strength compared to the electrode force. It was found that the indentation depth has a relatively close relationship with the expulsion occurrence. The optimum welding conditions were proposed for the 4 lap spot welded joint.
자동차용 이종두께 점용접물의 압흔 깊이와 인장-전단강도 특성
김회현(Hoi-Hyun Kim),박정훈,Seung-Su Kim,백승세(Seung-Se Baek),권일현(Il-Hyun Kwon),양성모(Seong-Mo Yang),유효선(Hyo-Sun Yu) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.10
This research is to investigate welding characteristics based on the tensile shear strength with various welding conditions on the 3-lap spot welded joint. The indentation depth are used to propose the optimum welding conditions. The tensile-shear strength has affected by the welding current and the welding time for 3-lap spot welded joint constructed by a high strength steel sheet and galvanized steel sheet. Meanwhile it was found that the indentation depth has a relatively close relationship with the expulsion occurrence. The optimum welding conditions are proposed for the 3-lap spot weldment.
고장력 및 아연도금강판 점용접부의 피로 강도 및 수명 평가
김회현(Hoi Hyun Kim),박정훈(Jung Hun Park),백승세(Seung Se Baek),권일현(Il Hyun Kwon),양성모(Sung Mo Yang),유효선(Hyo Sun Yu) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.3
The fatigue life of the spot weldment has been only evaluated by the fatigue fracture life using a traveling microscope. In general, the fatigue life is classified of the initiation and the propagation life of fatigue crack. But it is very difficult to evaluate the fatigue initiation and propagation life for spot weldment by using a conventional technique such as traveling microscope and strain gauge method. In this study, the fatigue crack initiation and propagation life are evaluated on spot weldments made from high strength steel(HS40R) plate and galvanized steel(EZNCEN) plate by using DCPDM(DC potential drop method).
초초임계압 보일러 헤더용 P92 강 용접부의 크리프 특성 평가
백승세(Seung-Se Baek),김회현(Hoi-Hyun Kim),박정훈(Jung-Hun Park),권일현(Il-Hyun Kwon),유효선(Hyo-Sun Yu) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
P92 steel weldment scheduled to use for next generation ultra super critical (USC) boiler header is assessed on creep characteristics. The test method to assess local structure of weldment is small-punch creep (SP-Creep) test, which is a kind of micro test proved the availability on evaluation of mechanical property for local structure. The results are compared with that of tensile creep test for same material and SP-Creep test for X20CrMoV121 (X20) steel weldment. The creep properties of P92 steel weldment are clearly superior than that of X20 steel weldment. Overall, the creep resistance of coarse grain HAZ is inferior to the other structures while fine grain HAZ is most superior in the P92 steel weldment. The power law relationships can be obtained for each weldment structure of USC boiler header.
고온ㆍ고압용 보일러 헤더 고합금강 용접부의 크리프 특성 평가
백승세(Seung-Se Baek),권일현(Il-Hyun Kwon),김회현(Hoi-Hyun Kim),박정훈(Jung-Hun Park),이동환(Dong-Hwan Lee),유효선(Hyo-Sun Yu) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.10
The high temperature and pressure structural components show material degradation behavior due to long-term operation. Especially creep is well known as the major deterioration mechanism of the high temperature and pressure components. So, the creep properties evaluation of various microstructures of weldment, which are produced during welding process, is very important in securing the integrity and safety of power plant. This study applies SP-Creep test to evaluating creep properties according to aging. As a results, the SP-Creep curves of virgin and aged material show clearly three stage of creep behavior similar in tensile creep curve, and the power-law relationship of SP-Creep, that is dependency of SP-Creep rate on applied load, are definitely showed in both of virgin and aged materials. The SP-Creep rate are increase with increasing aging time as a whole. In the behavior of Larson-Miller parameter, decrease of LMP with increasing aging time is obvious in the lower load region that is closer in actual creep condition.
역해석과 소형펀치 시험에 의한 발전설비 용접부의 소성유동특성 평가
백승세(Seung-Se Baek),권일현(Il-Hyun Kwon),김회현(Hoi-Hyun Kim),이동환(Dong-Hwan Lee),양성모(Sung-Mo Yang),유효선(Hyo-Sun Yu) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.11
SP test has been confirmed the availability, however the application of SP test is hampered because the relation of stress-strain and load-displacement is not determined definitely. This study suggested an evaluation technique of plastic flow characteristic for X20CrMoV121 steel weldment through inverse analysis using SP test and finite element analysis(FEA). From the result, good agreement was found in load-displacement curves obtained from SP test and FEA. Also, The behavior of load-displacement curve from FEA show a rule that load is increase with increasing K(strength coefficient) and displacement is increase with increasing n(work hardening index). From the inverse analysis, true stress-strain curve could be obtained for each local structure of weldment. And the CGHAZ and WM, which showed lower load- displacement behavior, have smaller work hardening index, while FGHAZ have the largest index.
시효시간에 따른 USC내열강 용접부 미세조직의 크리프 특성 평가
박정훈(Jung-Hun Park),백승세(Seung-Se Baek),김회현(Hoi-Hyun Kim),박종진(Jong-Jin Park),양성모(Sung-Mo Yang),유효선(Hyo-Sun Yu) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.3
This Small Punch Creep Test is a Creep test method which uses comparatively smaller specimens than those required in conventional material creep tests. The size of the specimen is 10㎜×10㎜×0.5㎜. This method is used to evaluate the creep property of materials at high temperatures. In this study, the specimens used are made of aged P92 steel. The creep property of P92 steel specimens were evaluated using the SP Creep test at a high temperature at 650℃. The precipitation of the aged materials appears more than that of the virgin material in the 9Cr-1Mo steel. Decomposition of lath martensite phase, growth of carbides, and appearance of sub-gain boundary with increasing aging time was also observed in this study. The material degradation degrees of the aged materials at 730℃ for 500hrs is large. This is due to the brittle fracture behavior of the materials caused by the growth of carbides and migration towards grain boundary. However, for those materials aged at 730℃ for 3000hrs, ths degree of degradation was small This shows the recovery fo toughness by decreasing dislocation density and partial recrystallization with increasing of aging time.