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오승택(Seung Taik Oh),이두환(Doo Hwan Lee),한도석(Do Suck Han),장용민(Yong Min Jang),김대용(Daeyong Kim) 한국소성·가공학회 2008 소성가공 : 한국소성가공학회지 Vol.17 No.8
As one way of cost innovation and weight saving of the automobile, the one-piece typed lower control arm was developed for the purpose of replacing the box typed lower control arm. In order to overcome less buckling strength of the one-piece typed lower control arm, the design parameters such as the high strength steel grade, the thickness and the shape of main panel were optimized based on Taguchi method.
Nb 및 Mo 첨가 페라이트계 스테인리스강의 등온 저주기 및 열기계적 피로에 따른 변형거동
정재규 ( Jae Gyu Jung ),오승택 ( Seung Taik Oh ),최원두 ( Won Doo Choi ),이두환 ( Doo Hwan Lee ),임종대 ( Jong Dae Lim ),오용준 ( Yong Jun Oh ) 대한금속·재료학회 2009 대한금속·재료학회지 Vol.47 No.11
This paper deals with cyclic stress and strain responses during isothermal low cycle fatigue (LCF) and thermo-mechanical fatigue (TMF) loadings on Nb and Mo containing 15Cr stainless steel, which is used for exhaust manifolds in automobiles. The test temperatures (Ti) of the isothermal LCF were 600 and 800℃. The minimum temperature of the TMF test was 100℃ and the maximum temperaures (Tp) were varied between 500 and 800℃. In both loading conditions, weak cyclic softening is observed at Ti=Tp=800℃, but the transition to strong cyclic hardening is completed with the temperature decrease below Ti=600~700℃ for LCF and Tp=500~600℃ for TMF. The stress-strain hysteresis loops in the TMF loading show a significant stress relaxation during compressive (heating) half cycle at Tp>500℃, which develops tensile mean stress during cycling. Due to the stress relaxation, the TMF test sample reveals much lower dislocation density than the isothermally fatigued sample at the same temperature with Tp. A detailed correlation between fatigue microstructure and cycling deformation behavior is discussed.
고장력강판 적용 샤시부품의 용접부 내구수명 향상기술 개발
이광복(Kwang Bok Lee),오승택(Seung Taik Oh) 대한용접·접합학회 2015 대한용접·접합학회지 Vol.33 No.4
In general, discontinuity of metallurgical and structural points of weld zone could decline the fatigue strength. For the lightweight trend, the AHSS application in automotive chassis is in-progress. However, there are few research reports on AHSS welds fatigue strength in especially automotive chassis parts. Therefore, in this study, we evaluated the effects of the factors affecting the AHSS welding fatigue strength. As the result, the stress concentration of weld bead is the most important factor for welding fatigue strength. For the enhancement of welding fatigue strength, we focused on reducing the stress concentration of the welding beads. So, we applied and proved the plasma welding process and GTAW (Gas Tungsten Arc Welding) dressing method. It was verified by uniaxial fatigue specimen, fatigue performance increased from 40 to 60% by applying TIG dressing method compared to the conventional GMAW (Gas Metal Arc Welding). These results could be recommended the enhancement of fatigue performance of AHSS.
강인찬,오승택,강동명,백승호 대한금속재료학회(대한금속학회) 1991 대한금속·재료학회지 Vol.29 No.4
One aspect of the properties of austempered ductile iron (ADI) which should be exploited further in promoting engineering applications is their fracture toughness. In this study ductile irons with various Si content were austempered and the relationship among austempering temperatures, quantity of retained austenite and fracture characteristics was investigated. As Si content increases from 2.28% to 3.0%, the precipitation of carbide during bainite transformation is suppressed, and the fracture toughness and the amount of the retained austenite is increased. The high Si content limits the formation of martensite in the structure and minimizes segregation of other elements at cell boundaries. But in the excessive Si content (3.3%) showed the formation of islands of free ferrite in the bainitic structures and it decreased the fracture characteristics.