• 한국학교수학회논문집
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• 제4권1호
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• pp.103-114
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• 2001

The purpose of this study is to develop learning materials for functional concept on variable and to verify the effect of how well students could learn functional concept after they studied with those materials. To accomplish the purpose of this study, I developed learning materials and after teaching students with them. I have concluded the followings : First, there was little effect in teaching functional concept on variable between two experimental groups, whereas teaching functional concept had greater effect on forming functional concept in high level groups in those two experimental groups. Second, teaching functional concept on variable had little effect on students' understanding of functional concept and perfecting tables in Black box, graph, and mathematical problems, whereas there was much effect in students' understanding functional concept and solving relation formula, image, and range problems related to everyday life or general things. On the basis of the problems which appeared in the process of this study, the following can be suggested : First, we should develop learning materials fit for low level students so that they could understand functional concept. Second, we should continue to teach the basic problems like solving relation formula, image, and range, and understanding functional concept in graph until students are able to understand them exactly. Third, since the goals of Unit Function in a middle school textbook is to solve problems related to everyday life through functional thinking, there should be change in constructing systematic contents of Unit Function in a middle school textbook.

• 한국세라믹학회지
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• 제14권4호
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• pp.248-255
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• 1977

The effect of firing temperature, soaking time and batch composition upon the glass phase and pore formation as well as their distribution in slag foamed glass was investigated. Sulfur dioxide gas produced by the oxidation and reduction of metal sulfide in waterslag was attributed to foam forming agent. Slag foamed glass matrix was mainly composed of 35~60% glas phase and melilite crystalline phase. The increment of bentonite addition in batch lowered the foam forming temperature in studied system. The result showed also that the foam size distribution was broadened as th firing temperature wa inbereased.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1996년도 춘계학술대회논문
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• pp.62-72
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• 1996

A process model is formulated considering the effect of crystallographic testure developed in forming process. The deformation induced plastic anisotropy can be predicted by capturing the evolution of texture during large deformatin in the poly crystaline aggregate. The anisotropic stiffness matrix for the aggregate is derived and implemented in Dulerian finite element code. As an application , the evolution of texture in rolling, drawing and extrusion processes are simulated . The numerical results show good agreement with reported experimental textures.

• 한국세라믹학회지
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• 제29권5호
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• pp.391-395
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• 1992

In order to improve the compactness and uniformity in ceramic green body, we have developed dynamic CIP(Cold Isostatic Pressing) as a new forming method in which the CIP and the vibratory pressing were combined. In dynamic CIP, bulk density on alumina compacts was linearly increased with higher │Pmax-Pbias│and maximum pressure of dynamic-CIP was decreased over one-third of that of conventional CIP to obtain the same bulk density.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2010년도 춘계학술대회 논문집
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• pp.253-254
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• 2010

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 추계학술대회 논문집
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• pp.210-213
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• 1995

In this study,the effect of both process parameters (wheel velocity, friction coefficients between die and billet, etc) and die-shape (abutment height and shape, flash gap, etc.) on the surface defect on forming process is theoretically investigated. For this work, computer simulation was performed by using the DEFORM, a commercial FEM code. Through numerous simulations with different parameters and die shapes, We propose one optimal die shape for CONFORM process which can remove surface defect.

• 소성∙가공
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• 제5권4호
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• pp.297-304
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• 1996

A process model is formulated considering the effect of crystallographic texture developed in forming process. The deformation induced plastic anisotropy can be predicted by capturing the evolution of texture during large deformation in the polycrystalline aggregate. The anisotropic stiffness matrix for the aggregate is derived and implemented in Eulerian finite element code using a Consistent Penalty method. As an application the evolution of texture in rolling drawing and extrusion processes are simulated. The numerical results show good agreements with report-ed experimental textures.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 춘계학술대회 논문집
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• pp.463-466
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• 2005

The microstructure and mechanical properties of rheocast A356 aluminum alloy by electromagnetic stirring are studied. In the electromagnetic stirring, main parameters are stirring current and stirring time. Stirring current is ranged from 0 A to 60 A, and stirring time is 20, 40, and 60 sec. In the rheocasting, injection velocity and applied pressure are changed. In this paper, the effect of stirring current and stirring time on the morphology and mechanical properties are investigated and analyzed.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 추계학술대회 논문집
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• pp.285-288
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• 2009

The purpose of this study is to predict the forming limit diagram (FLD) of strain-rate sensitive materials on the basis of the Marciniak and Kuczynski (M-K) theory. The strain-rate effect is taken into consideration in such a way that the stress-strain curves for various strain-rates are inputted into the formulation as point data, not as curve-fitted models such as power function. Tensile tests and R-value tests were carried out at several levels of temperature and strain-rate from $25^{\circ}C$ to $300^{\circ}C$ and 0.16 to 0.00016/s, respectively to obtain the mechanical properties of AZ31B magnesium alloy sheet. The FLD of this material was experimentally obtained by limit dome height tests with the punch velocity of 0.1 and 1.0 mm/s at $250^{\circ}C$. The M-K theory-based FLD predicted using Yld2000-2d yield criterion was compared with the experimental results.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 춘계학술대회 논문집
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• pp.233-236
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• 2004

The major objective of this paper is to clarify the effect of constitutive laws on bulk forming design based on the ideal flow theory. The latter theory is in general applicable for perfectly/plastic materials. However, its kinematics equations constitute a closed-form system, which are valid for any incompressible materials, therefore enabling us to extend design solutions based on the perfectly/plastic constitutive law to more realistic laws with rate sensitive hardening behavior. In the present paper, several constitutive laws commonly accepted for the modeling of cold and hot metal forming processes are considered and the effect of these laws on one particular plane-strain design is demonstrated. The closed form solution obtained describes a non-trivial nonsteady ideal process. The design solutions based on the ideal flow theory are not unique. To achieve the uniqueness, the criterion that the plastic work required to deform the initial shape of a given class of shapes into a prescribed final shape attains its minimum is adopted. Comparison with a non-ideal process is also made.