• Transactions of Materials Processing
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• v.22 no.4
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• pp.216-222
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• 2013

Solid polymers exhibit rate-dependent deformation behavior such as nonlinear strain rate sensitivity and stress relaxation like metallic materials. Despite the different microstructures of polymeric and metallic materials, they have common properties with respect to inelastic deformation. Unlike most metallic materials, solid polymers and shape memory alloys (SMAs) exhibit highly nonlinear stress-strain behavior upon unloading. The present work employs the viscoplasticity theory [K. Ho, 2011, Trans. Mater. Process. 20, 350-356] developed for the pseudoelastic behavior of SMAs, which is based on unified state variable theory for the rate-dependent inelastic deformation behavior of typical metallic materials, to depict the curved unloading behavior of polyphenylene oxide (PPO). The constitutive equations are characterized by the evolution laws of two state variables that are related to the elastic modulus and the back stress. The simulation results are compared with the experimental data obtained by Krempl and Khan [2003, Int. J. Plasticity 19, 1069-1095].

• Journal of Korea Foundry Society
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• v.24 no.5
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• pp.281-289
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• 2004

The present study focused on the estimation of the interfacial heat transfer coefficient as a function of the surface temperature of the aluminum casting at the mold/casting interface to investigate the effects of superheat and coating layer. The casting experiments of aluminum into a cylindrical copper mold were systematically conducted to obtain the thermal history during solidification. The thermal history recorded by four thermocouples embedded both in the mold and the casting was used to solve the inverse heat conduction problem using Beck's method. The effects of superheat and coating on the interfacial heat transfer coefficient in the liquid state, during the solidification, and in the solid state were comparatively discussed. In the liquid state, the interfacial heat transfer coefficient is thought to be affected by the roughness of the mold, the wettability of the casting on the mold surface, and the thermophysical properties of the coating layer. When the solidification begins, the air gap forms between the casting and the mold, and the interfacial heat transfer coefficient becomes a function of the air gap as well as surface roughness and the superheat. In the solid phase, it depends only upon the thermal conductivity and the thickness of the air gap. The coating layer reduces seriously the interfacial heat transfer coefficient in the liquid state and during the solidification.

• Transactions of Materials Processing
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• v.21 no.8
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• pp.506-511
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• 2012

Aluminum brazing normally requires a careful control of temperature due to the small interval between brazing and melting temperatures for base materials. Unsuitable processing conditions, including brazing temperature outside admissible range, gap between brazed materials or inadequate flux feeding, can lead to joining defects. In this study, A357 was used as a filler metal for the brazing of pure aluminum base materials and brazed at temperatures in the semi-solid state. Interface microstructures with base materials were observed using optical metallography(OM) and scanning electron microcopy(SEM) with energy dispersive spectroscopy(EDS), and compared to conventional aluminum brazing.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.06a
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• pp.135-147
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• 1997

The production of light metal parts using aluminum is mainly performed by die casting and squeeze casting, which directly fabricate the required shape from the liquid state. However, die casting is subject to defects such as shrinkage porosity and air trapped when molten metal enters the cavity, whilst squeeze casting also has defects due to turbulent flow in the die cavity. Both diecasting and sqeeze casting have inhomogeneous mechanical property in terms of dendritic structure during solidification. Active research has been carried out on semi-solid processing, rather than on conventional process methods such as die casting, which involve various problems. Therefore in this paper, to introduce the fundamental technology for d e design, in die casting and forging process with semi-solid materials, relationship between stress and strain of semi-solid materials, and for producing parts die design has been proposed as parameters of globulization of the microstructure and gate shape. The prevention of various defects to produce sound parts are also introduced.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.221-225
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• 2009

A solar thermal collector is a solar collector specifically intended to collect heat: that is, to absorb sunlight to provide heat. A flat plate is the most common type of solar thermal collector, and is usually used as a solar hot water panel to generate solar hot water. A flat plate collector consists basically of an insulated metal box with a glass or a plastic cover and a dark-colored copper absorber plate. Solar radiation is absorbed by the copper absorber plate and transferred to water that circulates through the collector in copper tubes. Ultrasonic welding is an industrial technique whereby high-frequency ultrasonic acoustic vibrations are locally applied to work pieces being held together under pressure to create a solid-state weld. In this study, we developed solar collector ultrasonic welding machine with digital controlled power supply and tested various welding conditions such as welding pressure, welding amplitude, welding speed. Welding speed was considered in 2~12m/min. The width of ultrasonic welds was increased with welding amplitude by 2.2~2.5mm. The fracture load of ultrasonic welds showed 20% higher than domestic products.

• Transactions of Materials Processing
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• v.6 no.3
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• pp.239-249
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• 1997

The behaviour of alloys in the semi-solid state strongly depends on the imposed stress state and on the morphology of the phase which can vary from dendritic to globular. To optimal net shape forging of semi-solid materials, it is important to investigate for filling phenomena in forging process of arbitrarily shaped dies. To produce a automotive part which has good mechanical property, the filling pattern according to die velocity and solid fraction distribution has to be estimated for arbitrarily shaped dies. Therefore, the estimation of filling characteristic in the forging simulation with arbitrarily shaped dies of semi-solid materials are calculated by finite element method with proposed algorithm. The proposed theoretical model and a various boundary conditions for arbitrarily shaped dies is investigated with the coupling calculation between the liquid phase flow and the solid phase deformation. The simulation process with arbitrarily shaped dies is performed to the isothermal conditions of two dimensional problems. To analysis of forging process by using semi-solid materials, a new stress-strain relationship is described, and forging analysis is performed by viscoelastic model for the solid phase and the Darcy's law for the liquid flow. The calculated results for forging force and filling limitations will be compared to experimental data. The filling simulation of simple products performed with the uniform billet temperature(584$^{\circ}C$) from the induction heating by the commercial package MAGMAsoft. The initial step of computation is the touching of semi-solid material with the end of die gate and the initial concept of proposed system just fit with the capability of MAGMAsoft.

• Bulletin of the Korean Chemical Society
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• v.20 no.8
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• pp.875-878
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• 1999

A new concept ？？soft solution processing？？ has been introduced to fabricate advanced solid state materials in an economical, environmentally friendly, and energy and material efficient way. The prepared films show the desired and prospective properties despite of low temperature synthesis and no post-synthesis annealing. Successful examples demonstrate that soft solution processing is capable of preparing advanced materials with planned properties through the easy control of reaction conditions in a suitable aqueous solution in a single synthetic step without huge energy consumption and without any sophisticated equipment.

• Transactions on Electrical and Electronic Materials
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• v.13 no.5
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• pp.225-228
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• 2012

In order to synthesize LED phosphor materials, we have applied three novel synthesis techniques, "melt synthesis", "fluidized bed synthesis" and "vapor-solid hybrid synthesis", in contrast with the conventional solid state reaction technique. These synthesis techniques are also a general and powerful tool for rapid screening and improvements of new phosphor materials.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.47 no.5
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• pp.41-47
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• 2010

This paper has proposed parallel BCH, one of error correction coding methods which has been used to NAND flash memory for SSD(solid state disk). To alter error correction capability, the proposed design improved reliability on data block has higher error rate as used frequency increasingly. Decoding parallel process bit width is as two times as encoding parallel process bit width, that could reduce decoding processing time, accordingly resulting in one half reduction over conventional ECC.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.220-223
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• 2005

We studied the effect of composition, processing, and sintering temperature on the microwave properties of $Mg_{3-x}Co_x(VO_4)_2$ system which is applicable to LTCC. When $Mg_{3-x}Co_x(VO_4)_2$ was fabricated by solid-state reaction process and sintered at the temperature range of $800\sim910^{\circ}C$, it was found that the optimum composition of x was 2 at which microwave properties of 910$^{\circ}C$-sintered one were as follows: $Q\times f_0\sim55,200GHz$ and $\varepsilon_r\sim10$. When $(MgCo_2)(VO_4)_2$ was fabricated by sol-gel process and sintered at 800$^{\circ}C$, $Q\timesf_0$was 34,400GHz which is much high compared to those fabricated by solid-state reaction process at the same sintering temperature.