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현주식(Joosik Hyun),문만빈(Manbeen Moon),오현운(Hyunwoon Oh) 한국자동차공학회 2009 한국자동차공학회 학술대회 및 전시회 Vol.2009 No.11
HS440, HS590 as an automotive steel sheet, which are used for a structural part in an auto-body, are occasionally exposed in the various temperature environments(about -50℃ ~ 150℃). Therefore, It is required to evaluate the mechanical characteristics(tensile strength, yield strength, elongation, work-hardening exponent etc.) under the low to high temperature environment. In this study, in order to identify the mechanical characteristics of HS440 and HS590, the uniaxial tensile tests are performed with the variation of temperature range from -60℃ to 200℃. Tensile tests carried out using universal testing machine(ZWICK Z250) with installed temperature chamber and acquired stress-strain relation, tensile strength, yield strength, elongation, work hardening exponent at the various temperature conditions. The test results showed that the mechanical properties(strength, elongation etc.) increased in the low temperature(0℃ ~ -60℃) and decreased in the high temperature(50℃ ~ 200℃). Accordingly, It is necessary to evaluate the accurate material properties and has to consider the change of mechanical properties with the variation of temperature for the safety design of an auto-body.
Gihak Yim(임기학),Jiyoung Kim(김지영),Byeoungkeuk Jin(진병극),Joosik Hyun(현주식) 한국자동차공학회 2021 한국자동차공학회 부문종합 학술대회 Vol.2021 No.6
The application of galvanized steel sheets is increasing as the quantity of outer panel applied to global automotive makers is increasing, and for this reason, predicting the formability of galvanized steel sheets is becoming more important for steel manufacturers to cope with quality issues when forming automotive parts. Since galvanized steel sheets and galvannealed steel sheet have different microstructures and properties, they have different forming characteristics and quality problems in forming process. when forming the outer panel, the main forming mode is deep drawing. At this time, the friction characteristic is one of the dominant factors that influence the part formability. However, in the case of galvanized steel sheets, the fluctuation of friction characteristics according to forming speed and load is different than that of galvannealed or non-coated cold rolled steel sheet. Therefore, in order to enhance the formability prediction of galvanized sheet, evaluation of friction variation by forming condition is important. However, not much research has been done to evaluate the friction variation of galvanized coated sheet by different forming condition or its application in forming analysis. In this study, friction variation of mild grade steel with different coating was derived for different speed and loading conditions, considering actual forming process. In addition, the effect of post treatment on friction was evaluated, and the application of friction variation in forming analysis was studied. To summarize, the aim of this paper is to evaluate the effect of coating, post treatment and forming condition on friction characteristics in steel sheets for outer panels, and to review methods to apply friction variation in forming analysis for formability prediction improvement.