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윤종헌,이정환 한국정밀공학회 2015 International Journal of Precision Engineering and Vol. No.
This paper mainly concerns a warm-forging with Mg-8Al-0.5Zn alloy for the differential case which covers differential gears in thetransmission assembly of the automobile. The optimum forging process has been proposed with numerical simulations, which has beenvalidated and compared with experiments conducted in the 1600-ton press shop. In order to validate the applicability of the Mgdifferential case into the automobile, its microstructure including texture evolution and mechanical properties in tension andcompression have been analyzed. It does not only show substantial light-weight design in the total weight of 50% compared withconventional ductile iron, but also demonstrate the net-shape in the outer surface as well as internal volume. However, insufficientmechanical properties and tension-compression asymmetry of the Mg-8Al-0.5Zn differential case are huge obstacles in adopting Mgalloys into the automobile parts, successfully
Calibration of hoop stress in ring tensile test with Zircaloy-4 tube
윤종헌,J. Kim,김형규,C. Won,송영남,박성혁 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.9
Since Zirconium (Zr) alloys have been widely used as cladding material in a nuclear fuel rod, material properties of Zr are essential in prediction of failure and undesirable deformation. This paper mainly concerns calibration procedure to obtain the hoop stress of Zircaloy-4 tube with a simple ring tensile (RTT) test linking with a Digital image correlation (DIC) technique since it is substantially difficult to obtain, directly, with specialized experiment such as burst test with internal pressure. The uniaxial tensile tests along the axial and RTT along the hoop directions were conducted with Zircaloy-4 tube in which anisotropic stains were analyzed with a DIC technique to validate appropriate deformation history. Anisotropic yield criterion based on the measured R-values ( R q = 1.88 and z R = 0.814) is able to capture the precise deformation mode in the ring tensile test. The flow curve along the hoop direction is calibrated by converting F, G, and H material parameters based on the R-values to the function of stress ratios.
Investigation of deformation and collapse mechanism for magnesium tube in axial crushing test
윤종헌,이영선,허훈 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.10
This paper demonstrates the quasi-static axial compression and high-speed axial compression tests of extruded magnesium alloy circular tubes for evaluating the crash and fracture behavior of mg parts. To capture the buckling and fracture behavior of Mg tube during the axial compression tests, FE simulation adopts different types of flow curves depending on the deformation mode such as tension and compression with LS-DYNA software. The Mg tube undergoes compressive plastic strain prior to buckling while according to the model based on Hill yield criterion only bulging along the radial direction is predicted. Due to the tension-compression asymmetry of Mg alloys,diameter of Mg tube expands largely at the initial plastic strain before having bulging or folding while only a bulging mode typical for materials with cubic crystal structure can be predicted. Simulation results such as punch load and deformation mode are compared with experimental results in the axial crushing test with AZ61 alloy.
인장 - 압축 비대칭성을 고려한 AZ31 판재의 항복함수 구성
윤종헌(J. H. Yoon),Oana Cazacu(O. Cazacu),이정환(J. H. Lee) 한국소성가공학회 2011 한국소성가공학회 학술대회 논문집 Vol.2011 No.10
In order to take into account strong anisotropy and tension-compression asymmetry of AZ31 sheet alloy simultaneously, Cazacu-Plunkett-Barlat (CPB06, Cazacu et al., 2006) yield criterion was adopted in material modeling. The variation of anisotropic coefficient which describe the yield surface evolution of AZ31 is optimized using an interpolation function based on the specific calibration results. It generates continuously yield surfaces, which makes it possible to describe different hardening rates in tension and compression as well as tension-compression asymmetry of magnesium alloys.