• Transactions of Materials Processing
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• v.3 no.1
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• pp.3-17
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• 1994

The semi-solid metal forming for vigorously agitated semi-solid alloys has been widely studied over the last decade. Metal forming processes are now being developed using alloys in the semi-solid state, among them are rolling, forging, extrusion, and die casting. Some of these are now employed commercially to produce a components and are also used to fabricate metal matrix composites. The semi-solid materials can be processed either directly during solidification and for this purpose mechanical stirring was demonstrated to produce a highly solidification. This paper is concerned with the influence of processing parameters on limitations of semi-solid forming.

• Journal of Mechanical Science and Technology
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• v.15 no.12
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• pp.1876-1881
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• 2001

We present the numerical analysis of the growth of a silicon (Si) single crystal. In the MCZ (Magnetic-field-applied Czochralski) method, two magnetic fields that stand opposite to each other generate a cusp magnetic field. In this work, the three cusp magnetic fields used for the analysis are an extern magnetic field, a surface magnetic field and an internal magnetic field. Each case was evaluated mainly as to the degree of stirring, shaft symmetry and the stability of the flow. As a result, the cusp magnetic field that yielded to best conditions was the internal magneic field.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.227-230
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• 2005

Many rheocasting processes had been proposed because of the difficulty of recycling, the limit of material, and the high cost of raw material in thixocasting. But, these rheocasting processes also had disadvantages such as the high initial Investment cost and the lower mechanical properties than thixocasting. In this study, a continuous fabrication of rheological material with pressure rotation equipment was newly devised to overcome the disadvantages of rheocasting process. In order to investigate the thixoformability, reheating experiments were carried out with the material fabricated by the newly devised equipment. Morphological characteristics between mechanical stirring and reheating were compared.

• Journal of the Korean Ceramic Society
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• v.52 no.2
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• pp.137-139
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• 2015

In this study, we examined the influence of molten $KNO_3$ flow on mechanical properties and their deviation when a chemical toughening process was applied to soda lime silicate glass ($Na_2O-CaO-SiO_2$). $KNO_3$ melt flow was controlled using three methods: (1) glass tray rotation, (2) impeller stirring, and (3) natural convection. DOL and hardness were found to be enhanced by tray rotation because this rotation was able to maintain the concentration around the glass surface, in contrast to other methods. However, there did not appear to be a statistically significant difference in the 3-point bending strength for the three flow conditions due to the ground edge condition.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.10
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• pp.1033-1041
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• 2012

Performance evaluation of a direct carbon fuel cell (DCFC) was conducted according to coals and a graphite particle. Several fuel properties such as thermal reactivity, textural structure, gas adsorption characteristic, and functional groups on the surface of fuels were investigated and their effects on electrochemistry were discussed. The strong carbon structure inside of fuels led the rapid potential decreasing in high current density region, because it caused small surface area and low pore volume. The functional groups on the surface were related to the low current density region. The maximum current density and power density of fuels were affected by the total carbon content in fuels. The effect of operating conditions such as stirring rate and operating temperature was investigated in this study.

• Journal of Welding and Joining
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• v.20 no.3
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• pp.67-73
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• 2002

In an attempt to evaluate the feasibility of friction stir welding(FSW) for joining carbon steels, microstructures and mechanical properties of friction stir welded carbon steels with different grain structures were investigated. In comparison of O-type stir zone(SZ) appeared in various aluminium alloys, configuration of SZ in friction stir welded carbon steels displayed U-type. Plastically deformed pearlite band structure was identified to surround the SZ, indicating the existence of so-called thermo-mechanically affected zone(TMAZ). However, the TMAZ of carbon steels was much narrower than that of Al alloys. The microstructures of both stir zone and TMAZ revealed bainite matrix in a conventional carbon steel for shipbuilding, while, in the same region, ferrite matrix microstructures were formed in a low carbon fine grained steel. The conventional carbon steel showed superior stirring workability to that of the fine grained carbon steel. The yield and tensile strength of the friction stir welded joints were comparable to those of the base metals, and the elongation in welded joints demonstrated excellent ductility. Absorbed energy in SZ of the fine grained carbon steel was ten times higher than that obtained from conventional submerged arc weld metal of the same steel. Based on these results, the application FSW to carbon steels was found to be feasible.

• Journal of the Korean Society for Heat Treatment
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• v.32 no.3
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• pp.124-130
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• 2019

Friction stir welding is one of the interesting welding methods for titanium and its alloy which proceeds with plastic flow due to thermo-mechanical stirring and friction heat. Solid-state welding can solve severe problems such as high-temperature oxidation, interstitial oxygen diffusion and grain coarsening by liquid-state welding. Dynamic recrystallization and grain refinement can vary significantly with the plunging load and rotational speed of tool during friction stir welding, and suitable process conditions must be optimized to obtain microstructure and better mechanical characteristics. Suitable FSW conditions were 1000 kg of plunging load and 200 rpm of rotational speed and it showed YS 270 MPa, UTS 332.1 MPa, and El 17.3%, which were very similar to those of wrought titanium sheet.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.27 no.6
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• pp.289-294
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• 2017

Films fabricated using atomic layer 2-dimensional nanosheets exhibit various physical properties depending on the size of the nanosheet. This is because the physical properties of the film depend on the interfacial properties between the sheets. Therefore, the synthesis of large-sized nanosheets is very important because it can reduce the dependency of the film on the interfacial properties. In this study, we succeeded in fabricating $TiO_x$ nanosheets with atomic layer thickness over micrometer size by using single-crystallized starting material and its chemical exfoliation. In addition, it was revealed that the mechanical agitation speed (the stirring speed of a magnetic bar) during the exfoliation step using the organic material is closely related to the nanosheet size and the colloidal concentration of the nanosheets.

• Journal of the Korean institute of surface engineering
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• v.45 no.5
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• pp.181-187
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• 2012

The Friction Stir Welding (FSW) has mainly been used for making butt joints in Al alloys. The development of Friction Stir Lap Welding (FSLW) would expand the number of applications. In this study, microstructures and mechanical properties of FSLW in A5052 alloy were investigated under varying rotating speed and probe length. Investigating the characteristics as FSLWed conditions were as below ; Failure Maximum load by shear fracture was increased proportional to the width of joint area, which was increased by input heat, stirring intensity in the case of 2.3 mm probe length. Tensile fracture occurred, and maximum load was determined due to side worm hole of joint area and softening of microstructure in the case of 3.0 mm probe length. In the case of 3.7 mm probe length, material hook and bottom worm hole were appeared at the end interface of joint area. The most sound FSLW condition with no defects was 3.0 mm probe length and 1500 rpm-100 mm/min. No defects were showed in 1500 rpm-100 mm/min and 1800 rpm-100 mm/min, but Vickers microhardness distribution in TMAZ/HAZ which was fracture zone was lower in 1800 rpm-100 mm/min than in 1500 rpm-100 mm/min. In this condition highest tensile strength, 215 MPa (allowable rate 78% of joint efficient) was obtained.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3045-3049
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• 2007

This paper presents a numerical study to enhance the mixing of polyurethane resin in a container. In general, the properties of polyurethane resin vary with the production environment, such as temperature. However in this study we assumed that the dynamic viscosity of the polyurethane is kept constant at 15 [Pa s]. We computed the flow solution and visualized the mixing pattern for different shapes of mixers by using commercial code, ANSYS CFX. In order to quantify mixing, we employed the concept of mixing index by volume integration.