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Jo, Y J,Kim, Y H,Jo, Y H,Seong, J G,Chang, S Y,Van Tyne, C J,Lee, W H American Scientific Publishers 2014 Journal of Nanoscience and Nanotechnology Vol.14 No.11
<P>A single pulse of 1.5 kJ/0.7 g of atomized spherical Ti powder from 300 μF capacitor was applied to produce the porous-surfaced Ti implant compact by electro-discharge-sintering (EDS). A solid core surrounded by porous layer was self-consolidated by a discharge in the middle of the compact in 122 μsec. Average pore size, porosity, and compressive yield strength of EDS Ti compact were estimated to be about 68.2 μm, 25.5%, and 266.4 MPa, respectively. Coatings with hydroxyapatite (HAp) on the Ti compact were conducted by electrostatic-spray-deposition (ESD) method. As-deposited HAp coating was in the form of porous structure and consisted of HAp particles which were uniformly distributed on the Ti porous structure. By heat-treatment at 700 degrees C, HAp particles were agglomerated each other and melted to form a highly smooth and homogeneous HAp thin film consisted of equiaxed nano-scaled grains. Porous-surfaced Ti implant compacts coated with highly crystalline apatite phase were successfully obtained by using the EDS and ESD techniques.</P>
C. H. JEON,S. W. HAN,B. D. Joo,C. J. Van Tyne,문영훈 대한금속·재료학회 2013 METALS AND MATERIALS International Vol.19 No.5
The deformation characteristics of Al-Cu double layered sheet during rolling with various process parameters were studied by both a physical modeling technique and the finite element method. Physical modeling and the finite element method are complementary, due to their different advantages and limitations. Physical modeling simulates metal forming operations by using a model workpiece under conditions similar to those in actual production. The deformation characteristics of double layered sheet during rolling were also simulated using a commercial finite element code, FORGE TM. The effects of process parameters, such as total reduction ratio, initial thickness ratio and differential speed ratio on the rolling characteristics were the primary focus of the investigation. In addition, an analytical model for double layered sheet rolling is also proposed with the use of a force-thickness diagram. From the results, the effect of the process parameters on the rolling of the Al-Cu double layered sheet has been determined.
Yoon, S.,Van Tyne, C.J.,Lee, H. Elsevier 2014 Current Applied Physics Vol.14 No.7
The electrical properties of 9 mol% MgO-ZrO<SUB>2</SUB> (Mg-PSZ) with 1 mol% Al<SUB>2</SUB>O<SUB>3</SUB> and the mechanisms for electrical degradation were investigated using structural, morphological, and electrochemical analyses. The addition of Al<SUB>2</SUB>O<SUB>3</SUB> caused an increase in both the monoclinic and the Mg-rich phases at the grain boundaries in the Mg-PSZ. Coarse grains larger than 20 μm and an intergranular layer composed of the Mg-rich phase were identified in a specimen sintered at 1600 <SUP>o</SUP>C. This specimen exhibited a minimum of ionic conductivity (4.98 x 10<SUP>-4</SUP> S cm<SUP>-1</SUP> at 700 <SUP>o</SUP>C) due to the grain boundary resistance (245 Ω cm<SUP>2</SUP>), which dominated the overall resistance. A similar trend was observed over the entire temperature range (600-1500 <SUP>o</SUP>C). An intergranular siliceous impurity (SiO<SUB>2</SUB>) was present in conjunction with the Mg-rich phase. This impurity and the Mg-rich phase acted as a barrier layer for oxygen ion diffusion. The presence of the intergranular phases (i.e. the monoclinic and Mg-rich phases) contributed to the degradation of the ionic conductivity in Mg-PSZ with an Al<SUB>2</SUB>O<SUB>3</SUB> addition.
The die turning injection (DTI) process for the fabrication of hollow parts
Lee, H.J.,Joo, B.D.,Moon, Y.B.,Van Tyne, C.J.,Moon, Y.H. Elsevier 2012 Journal of materials processing technology Vol.212 No.4
<P><B>Abstract</B></P><P>The die turning injection (DTI) process, which can fabricate hollow plastic parts with a complex geometry, is proposed in this study. DTI is a new technology, which is accomplished in three steps: (1) the primary injection step, (2) the die turns, and (3) the secondary injection step. Two separate halves of the part are injection molded during the primary injection. The die rotates to align the two halves for the secondary injection. The secondary injection along the aligned surfaces joins the two halves into the final hollow part. The proposed DTI technology provides several advantages. It has the ability to form hollow parts with high dimensional accuracy, the equipment requires a small working space and the machine control is fairly simple. To verify the feasibility of DTI process, industrial trials were performed to manufacture a hollow nozzle part for a washing machine. To optimize the process, a finite element (FE) analysis was performed using the commercial code, Autodesk Moldflow Insight. To design the hot runner system for the primary injection step, two types of hot runner systems, a V-shaped and a T-shaped runner, were investigated. The critical parameter that was measured in these two runner designs was the amount of warpage. An FE analysis for the secondary injection step was also performed to analyze the flow characteristic at the aligned surfaces of the two separate hollow halves. The cooling channel was also designed to cool the mold and control the uniformity of injection temperature. With appropriate control of the injection conditions, a hollow nozzle part having excellent dimensional accuracy was successfully manufactured using the proposed DTI process.</P>
Kim, B.J.,Van Tyne, C.J.,Lee, M.Y.,Moon, Y.H. Elsevier 2007 Journal of materials processing technology Vol.187 No.-
<P><B>Abstract</B></P><P>The hydroformability of an extruded aluminum alloy at elevated temperatures was investigated in this study. To properly analyze the process, it is necessary to account for the variation in the mechanical properties of the aluminum that depend on the forming temperature and the heat conduction during warm hydroforming. Simulations coupling the plastic deformation and temperature distribution in the warm hydroforming process were performed and compared with experimental data. The multi-purpose finite element code DEFORM-2D can handle the calculations, but requires significant computation time if contact heat transfer between the die, the tube, and the pressure medium occurs. Experiments were conducted with a high temperature tribometer (pin-on-disk) allowing the measurement of the friction coefficient for the aluminum alloys at several temperatures. These friction results are applied to the coupled simulation. From the simulations, the optimal process parameters, such as internal pressure and preset temperature on hydroformability, can be found. The comparison of the finite element analysis with the experimental results shows that the hydroformability trends (given by bulge height) and the temperature distribution of the tube specimen agree well with one another. The finite element results also showed that the temperature distribution did not strongly affect the hydroformability of the aluminum tubes.</P>