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〈학술논문〉 ASTM compliance offset 균열열림하중 결정법 정확도 향상에 관한 연구
정연일(Younil Chung),송지호(Jiho Song) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11
A There are two serious drawbacks to the ASTM offset method for determination of crack opening load, discontinuity and inconsistency problems. The former is the lack of opening load value in the lower 5% load range due to the procedure that the compliance offset is plotted against the mean load of the segment span of 10% of the cyclic load range. The latter is that the ASTM method underestimates, estimates accurately, or overestimates the opening load, depending on the maximum compliance offset value and the stress ratio. To overcome the two drawbacks, the so-called normalized-extended ASTM method is proposed and evaluated quantitatively in detail using the data of 7475-T7351 and 2024-T351aluminum alloys. The normalizedextended ASTM method improves the standard ASTM method significantly and provides very good correlation of crack growth rate stress ratio effects. The normalized-extended ASTM method is strongly recommended for crack opening load determination.
자동차용 샤시부품의 용접부 피로수명 향상 방안에 관한 연구
정연일(Younil Chung),권혁선(Hyuksun Kwon) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10
The automotive chassis components are structural assemblies that support the engine, suspension, and steering components of vehicles. For the development of AHSS chassis components, the weld parts’durability of them is very important. In this paper, the effect of torch angle, push angle, weld voltage, weld speed and gas is precisely analyzed. Maintaining the same heat input level, the difference of fatigue life is investigated according to changing torch and push angle. The more torch and push angle are large, the more the fatigue life is long. In this study, Hot Spot Stress, HSS, is also measured precisely by using strain gages attached on the fatigue weld specimens. Toe angle is a main factor to control HSS of weld specimen. To enhance weld fatigue life of automotive components, it is necessary to make toe angle large.
뜨임처리 온도에 따른 고장력강의 피로 및 기계적 물성평가
정연일(Younil Chung),권혁선(Hyuksun Kwon) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
In this study, after hot press forming and quenching process, the mechanical and fatigue properties of HPF steel produced by POSCO is evaluated precisely according to tempering temperature. Tensile, hardness and fatigue tests were performed at room temperature. As tempering temperature is increasing, the tensile strength and Vickers hardness values are decreasing, while the total elongation value is increasing. The increase rate of elongation between 200℃ and 350℃ tempering temperature is higher than other tempering ranges though the tensile strength decreases similarly. In this study, the HPF steel tempered at 250℃ shows the best result in the low cycle fatigue test.
고장력강 MAG 용접부 피로파손에 영향을 미치는 인자에 관한 연구
정연일(Younil Chung),권혁선(Hyuksun Kwon) 한국자동차공학회 2011 한국자동차공학회 부문종합 학술대회 Vol.2011 No.5
The automotive chassis components are structural assemblies that support the engine, suspension, and steering components of vehicles. For the development of AHSS chassis components, the weld parts’ durability of them is very important. In this paper, the effect of torch angle, push angle, weld voltage, weld speed and gas is precisely analyzed. Fist of all, through the tensile tests of weld specimens, torch angle, push angle and weld speed are main factors to decide tensile strength. Because the relation between tensile strength and fatigue strength is proportional, it is assumed that torch angle, push angle, weld speed are the main factors to control fatigue life. Next, maintaining the same heat input level, the difference of fatigue life is investigated according to changing torch and push angle. The more torch and push angle are large, the more the fatigue life is long.
이민성(Lee Minsung),정연일(Chung Younil),정기석(Chung Gisuk),한성수 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11
In this study, light weight wheel rim, one of the automotive chassis part, was developed using TWIP(Twinning Induced Plasticity) steel. TWIP steel has advantage to achieve complex cross section due to the excellent formability. An optimal design of wheel rim was suggested from the parametric study of design variables : distance of mounting groove, bead radius, position and the number of beads. The beads were added in the circumference direction of a rim surface to enhance the stiffness. The structure and durability analysis were performed with FEA in order to verify its performance. Adding beads around a wheel rim could be a dominant factor to reduce maximum stress and improve fatigue life under radial load. The hydroforming process for manufacturing a wheel rim with enhanced stiffness and reduced weight is proposed.
임지호(Jiho Lim),정연일(Younil Chung) 한국자동차공학회 2009 한국자동차공학회 학술대회 및 전시회 Vol.2009 No.11
A crash box of an automotive body should has characteristics of low impact force and high energy absorption in order to reduce the repairing cost and to achieve light-weight design. But, conventional crash box with collapse type have high impact force by buckling and low energy absorption due to local deformation by bending, so it is necessary to develop a crash box with new concept. Although an energy absorber with tube expansion type used in a train meets both requirements, this is not proper to adopt an automobile due to high weight. In this paper, novel crash box is developed to absorb the energy by double walled collapse of an expanded and a fixed tubes after the tube expansion of an expanded tube. This crash box should be satisfied not to have the buckling of both tubes before completion of the expansion. In order to adopt new developed crash absorber with tube expansion type to a crash box of an automotive body, the interrelation between of design parameters of a crash absorber and the absorbed energy is studied. And, tube expansion type is compared with conventional collapse type in a viewpoint of the impact force and the crash energy absorption. Finally, values of design parameters which are the thickness, the radius, the length, the expansion angle, the expansion ratio and the friction coefficient are determined from the parameter study.