• 대한기계학회논문집A
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• 제26권10호
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• pp.1971-1981
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• 2002

Two-dimensional solidification analysis during rheology forming process of semi-solid aluminum alloy has been studied. Two-phase flow model to investigate the velocity field and temperature distribution is proposed. The proposed mathematical model is applied to the die shape of the two types. To calculate the velocities and temperature fields during rheology forming process, the each governing equations correspondent to the liquid and solid region are adapted. Therefore, each numerical model considering the solid and liquid coexisting region within the semi-solid material have been developed to predict the defects of rheology forming parts. The Arbitrary Boundary Maker And Cell(ABMAC) method is employed to solve the two-Phase flow model of the Navier-Stokes equation. Theoretical model basis of the two-phase flow model is the mixture rule of solid and liquid phases. This approach is based on using the liquid and solid viscosity. The Liquid viscosity is pure liquid state value, however solid viscosity is considered as a function of the shear rate, solid fraction and power law curves.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집C
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• pp.604-609
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• 2001

In the sheet metal forming process, the drawbead is used to control the flow of material during the forming process. The drawbead provides proper restraining force to the material and prevents defects such as wrinkling or breakage. For these reasons, many studies for designing the effective drawbead have been conducted. For the analysis, the numerical method called the static-explicit finite element method was used. The finite element analysis code for this method has been developed and applied to the drawbead process problems. In result, convergence problem and computation time due to large non-linearity in the existing numerical analysis methods were no longer a critical problem. Futhermore, this approach could treat the contact friction problem easily by applying very small time intervals. It is expected that various results from the numerical analysis will give very useful information for the design of tools in sheet metal forming process.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2002년도 금형가공 심포지엄
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• pp.95-102
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• 2002

With recent trends leaning towards product miniaturization, the advent of new material and speedy delivery times, old style conventional trial-and-error methods have been only serving to weaken corporate competitiveness. Reliant on tiny increments of time-consuming experience, this antiquated approach begets a delayed delivery of product development, cost loss and quality depreciation. To solve such problems, the Dedicated Injection Molding CAPA (Computer Aided Plastics Application) performs a preliminary examination on problems rising from every stage of creation - from appropriate material selection and mold design to mass production - through a computer system. Thus, it determines the optimum design variables and process conditions while diagnosing and solving defective molds.

• 한국생산제조학회지
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• 제7권1호
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• pp.22-33
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• 1998

A continuum analysis of the evolution of plasticity and Bauschinger effect in a short fiber reinforced metal matrix composite, based on the FEM solution for a single fiber model has been performed to investigate the strengthening behavior. The evolution of matrix field quantities during one cycle of fully reversed loading have been examined in detail. The results indicate that the role of constrained matrix flow in generating different levels of matrix triaxiality during forward and reversed loading provides an important contribution to the developement of the Bauschinger effect in the metal matrix composite. Therefore, even when the plastic flow of the matrix material follows on isotropic hardening behavior, the Bauschinger effect is predicted for the composite material.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 하계학술대회 논문집 Vol.3 No.2
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• pp.1063-1066
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• 2002

An equivalent circuit for the superconductor flux flow transistor(SFFT) was combined with high temperature cooling device, based on the analogy between thermal and electrical variables using the high-temperature superconductor(HTS), is proposed. The device is composed of parallel weak links with a nearby magnetic control line. A model has been developed that is based on solving the equation of motion of Abrikosov vortices subject to Lorentz viscous and pinning forces as well as magnetic surface barriers. The use of thermal models the global performance of thermal cooling circuit and signal system to be checked by using electrical circuit analysis programs such as SPICE.

• 상하수도학회지
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• 제25권3호
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• pp.349-357
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• 2011

This study has an objective to estimate effect on water-quality enhancement by removal of contaminated river-bed material using a two-dimensional numerical modeling in the Seonakdong River, the Pyunggang River and the Maekdo River. RMA2 and RMA4 models were used for flow and contaminant transport simulation, respectively. After the analysis of the effects of flow restoration plan for the Seonakdong River system made by Lee et al (2008), simulation have been performed about scenarios which contains operations of the Daejeo Gate, the Noksan Gate, the Makdo Gate (on planning), and the Noksan Pumping Station. Because there is no option for elution from bed sediment in the RMA4 model, a simple technique has been used for initial condition modification for elution. The analyses revealed that the effect on water quality improvement due to dredging of bed sediment seemed to be less than 10 % of the total effect. The most efficient measure for the water quality improvement of the river system was the linked operation of water-gates and pumping station.

• 한국생산제조학회지
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• 제6권3호
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• pp.73-81
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• 1997

This study was to find the best adhesive condition comparing mechanical property in case of hot-melt adhesion using glue-gun, ultrasonic welding with adhesion and only ultrasonic welding in order to adhere thermoplastic resin of polyethylene (PE) in which reliable adhesion was resulted in case of ultrasonic welding with same materials of PE. The best welding condition were acquired at welding time 1 second, welding pressure 250kPa for PE-PE where welding time and welding pressure were increased in accordance with the increase of material strength. At the best ultrasonic welding conditions, bonding strength of PE-PE welding was about 21MPa of which material have tensile strength of 24MPa. Through the analysis of microscophic test for ultrasonic welding structure, it was distinguished between well welded structure with higher intermolecule flow and bad welded structure with lower flow, of which result is mostly correspond with the result of tensile strength test.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2001년도 춘계학술대회 논문집
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• pp.205-208
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• 2001

Localized shear band is investigated through the analysis of one-dimensional model for simple shearing deformation of thermally rate dependent material. Generally mesh size or interval of nodes play an important role in determining the overall flow behavior of the material. In order to observe these size effects we adapted non-local theory by including higher order strain gradients of the equivalent strain into the constitutive equation for the flow stress. for the ease of convergence and numerical stability the inplicit finite difference scheme is employed.

• 대한기계학회논문집
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• 제17권12호
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• pp.2970-2981
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• 1993

In hot closed-die forging the load increases rapidly near the final stage. Preforming operation is important to both the sound final forging and die-service life. In this study, the material flows during preforming and final forging are investigated. The physical modeling with Plasticine as a model material showed clear flow patterns. The forging process were numerically simulated by the finite element method with the isothermal and the non-isothermal models. The flow patten of the isothermal simulation showed good agreements with the experiments. Temperature changes and pressure distributions on the die surfaces during one cycle of the forging process were obtained from the non-isothermal simulation. High pressure and temperature were developed at certain areas of the die surfaces. It was concluded that those areas usually coincide with each other and should be distributed by the preforming operations to enhance the die life.

• 한국해양공학회지
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• 제14권2호
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• pp.70-75
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• 2000

In this paper a new constitutive model for ductile materials was proposed. This model can describe the material degradation due to the evolution of isotropic damage during elasto-platic deformation. The plastic flow rule was derived under the framework of thermodynamic approach of continuum damage mechanics(CDM) in which plastic strain hardening parameters and isotropic damage were taken as thermodynamic state variables. And the process to determine material constants for constitutive model using an experimental data was presented.