Papers by Author: Yong Mun Ryu

Abstract: It is difficult to control the pore size and distribution of Mg alloy foam by melt foaming method using titanium hydride as blowing agent and extraordinary coarse pore structures is often found in the Mg alloy foams. Using CaCO3 instead of titanium hydride as blowing agent, AZ31 Mg alloy foams with small well structure, porosity 35.0~72.0 % and average pore size 0.04~0.16 cm could successfully be fabricated In this study; AZ31 Mg alloy foam with the holding time of 30s had the best energy absorption. The energy absorption value of AZ31Mg foam was 5.52MJ/m³. After that, AZ31 foams sample was polished and rusted. The thickness cells were analyzed by use of Metallurgical Microscope and software. Then SEM micrograph of AZ31 Mg alloy foam and EDS analysis of the cell wall.

Abstract: In this study, finite element analysis was made to predict the tensile and compressive behaviors of aluminum foam material. The predicted tensile and compressive behaviors were compared with those determined from the tensile and compressive tests. X-ray imaging technique was used to determine internal structure of aluminum foam material. That is, X-ray computed tomography (CT) was used to model the porosities of the material. Three-dimensional finite element modeling was made by stacking two-dimensional tomography of aluminum foam material determined from CT images. The stackings of CT images were processed by three-dimensional modeling program. The results showed that the tensile stress-strain curve predicted from the finite element analysis was similar to that determined by the experiment. The simulated compressive stress-strain curve also showed similar tendency with that of experiment up to about 0.4 strain but exhibited a different behavior from the experimental one after 0.4 strain. The discrepancy of compressive stress-strain curves in a high strain range was associated with the contact of aluminum foam walls broken by the large deformation.

Abstract: The alpha-case formation mechanism was elucidated for the economic titanium casting. The α-case formation reaction between Ti and Al2O3 mold was examined in a plasma arc melting furnace. The reaction products were characterized by electron probe micro-analyzer and transmission electron microscopy. The α-case generation between Ti and Al2O3 mold was not able to be explained by the conventional α-case formation mechanism, which is known to be formed by the interstitials, especially oxygen dissolved from mold materials. However, from our experimental results and thermodynamic calculations and Calphad modeling (Thermo-calc®), it was confirmed that the α-case is formed not only by an interstitial element but also by substitutional metallic elements dissolved from mold materials. Our newly established α-case formation mechanism will surely lead to a variety of significant applications of the α-case controlled Ti casting.

Abstract: Recently the application of lever cam ass’y made of the high-functional polymer is increasing internationally to improve the productivity and weight reduction. But the application of injection molding of lever cam ass’y in our country is not reported yet because of the lack of the optimal selection technique of proper material and the optimal design of injection parameter. In order to solve the problem, the injection molding simulation is used. The modification of gate position and rib thickness was done and the parameters like injection time, injection temperature, packing pressure and cooling time were changed. As a result, the comparison between models was done and the optimal shape of lever cam ass’y was developed.

Abstract: Many researches of automotive companies have focused on reducing weight of vehicles in order to meet the needs for high fuel efficiency. Therefore, light metals such aluminum alloys have been applied on automotive body structures. Recently, roller hemming process has been introduced for hemming of aluminum automotive closing parts such as doors, roofs, and hoods. During Roller hemming, the flange of outer panels is bent and folded along the edge of inner panel by a roller attached robot. Since the stress caused by roller hemming can affect the quality of hemmed flanges, the research has focused on the stress analysis by simulation and experiment. Residual stress has been measured in the hemmed flanges and compared to the values of finite elemental analysis.

Abstract: A study on the tensile, compression and bending test of Aluminum foam Application for auto bumper and rod. We know a more efficiency to adhesive Aluminum foam out side of part in aspect to price, weight and capacity when make auto-component using aluminum foam. We secured basis properties of aluminum foam for applying auto-component by tensile, compressive and bending test. Aluminum foam was equipped to crash core with different shape. The results of maximum loads test are higher by full> cavity> bridge> half type relationship order. And, we could know that a difference of weight of full, cavity, and bridge type is not big.