• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.12
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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.

• Geotechnical Engineering
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• v.4 no.4
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• pp.51-60
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• 1988

기초지반에 대한 응력·변형률관계를 규명하기 위하여 소성론에 기초를 둔 구성방정식이 폭넓게 이용되고 있다. 본문은 성토나 강성기초와 같은 지반구조물을 연약점토지반에 축조하였을 때에 발생하는 변형에 관해 연구코저 한 것이다. 본 연구를 위하여 2차원모형토조를 제작, 재하실험한 시료를 재하실험을통하여 침하, 융기, 측방변위등을 측정하고 이들을 여러구함식과 비교고찰하였다. 구성식으로서는 한계상태개념에 근거를 둔 Cam-clay, Modified Cam-clay그리고 시간의존성을 고려한 탄·정감성 model인 Sakiguchi model을 이용하고 이들을 수치해를 통해 고찰하였다. 본 모형실험에 의하면 변형을 예측하는데 있어서 ModifiedICam-clay model이 Original Cam-clay"model 보다 실측치에 가까웠으며 또한 시간의존성을 고려한 탄·점견성 model인 Sekiguchi model'는 본 실험에서처럼 단기간의 실험에서는 변형의 creep조건을 만족시키지 못하므로 현장조건에 따라 잘- 판단하여 적용하여 야할 것으로 판단 된다.

• Geotechnical Engineering
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• v.3 no.4
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• pp.7-20
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• 1987

This study was performed to investigate the effect of time-dependent creep on the deformation analysis of multi-dimensional consolidation using the finite element method for young Sedimentary clay. It was assumed that the creep in the clay had occured during consolidation. In the analysis, the Modified cam-clay theory originated from the critical state theory was used as the constitutive equation, in which a term equivalent to the creep was supplemnted. The results of the analysis were in good agreement with the observed values in the field.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1199-1203
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• 2008

It has been recognized that unsaturated soil behavior plays an importantrole in geomechanics. In the last decade several constitutive models have been proposed and used in the analysis. Many of them, however, are constructed in the frame work of rate independent model such as elasto-plastic one. Although rate dependency is an important characteristics of soil for both saturated and unsaturated soils, very few models have been developed taking account of rate dependency. In the present paper, we have developed an elasto-viscoplastic model considering an effect of suction based on the overstress-type viscoplasticity with soil structure degradation. In the model, we have adopted an averaged pore pressure composed of pore water pressure and air pressure to determine the effective stress.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2002.11a
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• pp.101-103
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• 2002

PDP등의 각종 전자부품에 사용되는 Ag paste 의 frit은 주로 PbO를 주성분으로 하는 물질이 사용되어왔다. 그러나 이러한 Pb계 재료는 환경유해한물질로 규제대상이 되고 있다. 이에 대비하여 본 연구에서는 Bi$_2$O$_3$을 주성분으로 하여 B$_2$O$_3$, SiO$_2$, A1$_2$O$_3$가 함유된 새로운 frit을 개발하였다. TMA등을 이용하여 열적 특성을 관찰하였으며, 전극용 Ag-Paste를 제조한 후 스크린프린팅하여 인쇄성과 미세구조를 관찰하였고, 전기저항 및 소성두께를 측정하였다. 또한 전이온도, 연화점, 열팽창계수등을 조사하여 기존의 Pb함유 frit과 물성을 비교하였으며 PDP용 Ag전극에 적용하는 새로운 frit으로의 가능성을 검토하였다.

• Journal of Chest Surgery
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• v.33 no.12
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• pp.982-987
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• 2000

미만성 악성 중피세포종은 예후가 불량한 드문 암종으로, 아직까지 적절한 병기 분류가 없고, 병리 조직학적인 진단이 쉽지 않다. 치료에 대해서 논쟁이 많지만 선택된 환자에서 늑막 폐절제술을 시행하고 보조적인항 화학요법과 방사선 요법이 생존 기간을 연장시킬 수 잇다. 저자들은 1992년 6월부터 7년간 미만성 악성 중피세포종 환자 4례에서 늑막 폐절제술을 시행하였으며 수술후 조기 사망은 없었다. 3례의 환자에서 수술후 보조요법을 시행할 수 있었다(보조 화학요법 2례, 보조 화학요법 및 방사선 치료 1례). 그러나 한 예에서는 수술후 발생한 심장염전에 의한 저산소성 뇌손상 및 농흉으로 인하여 보조용법을 시행할 수 없었다. 저자들은 저자들의 늑막 폐 절제술의 경험 및 미만성 악성 중피세포종에 대한 논란이 되는 점을 문헌고찰과 함께 보고하는 바이다.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.7
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• pp.129-138
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• 1998

The objective of this study is to demonstrate the ability of a computer simulation of microstructural evolution in hot forging of C-Mn steels. The development of microstructure is strongly dependent on process variables and metallurgical factors that affect time history of thermodynamical variables such as temperature, strain. and strain rate during deformation. Then finite element method is applied for the prediction of microstructural evolution, and it should be coupled with heat transfer analysis to consider the change of thermodynamical properties during forming process. In this study, Yada's recrystallization model and rigid-thermoviscoplastic finite element method are employed in order to analyze microstructural evolution during hot forging process. To show the validity and effectiveness of the proposed method, experiments are accomplished and the results of experiments are compared with those of simulations.

• Korean journal of food and cookery science
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• v.5 no.1
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• pp.9-13
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• 1989

The effect of acetic acid concentration on the qualities of mayonnaise was studied. The rheological properties, emulsifying stability and color of the mayonnaise were determined by rotary viscometer, rotary shaker and centrifuge, and color and color difference meter, respectively. The rheological behavior of mayonnaise showed plastic behavior with yield stress and that of shear thinning. The yield stress and consistency index increased as the acetic acid concentration increased. The emulsion stability was lowest at 4% acetic acid concentration and highest at 1% acetic acid concentration. With the increase of the acetic acid concentration, lightness increased and yellowness decreased.

• Journal of Powder Materials
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• v.30 no.1
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• pp.29-34
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• 2023

A fixed-point iteration is proposed to integrate the stress and state variables in the incremental analysis of plastic deformation. The Conventional Newton-Raphson method requires a second-order derivative of the yield function to generate a complicated code, and the convergence cannot be guaranteed beforehand. The proposed fixed-point iteration does not require a second-order derivative of the yield function, and convergence is ensured for a given strain increment. The fixed-point iteration is easier to implement, and the computational time is shortened compared with the Newton-Raphson method. The plane-stress condition is considered for the biaxial loading conditions to confirm the convergence of the fixed-point iteration. 3-dimensional tensile specimen is considered to compare the computational times in the ABAQUS/explicit finite element analysis.

• Journal of the Korean Society for Precision Engineering
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• v.10 no.2
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• pp.30-39
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• 1993

The study is concerned with the thermo-viscoplastic finite element analysis of nonisothermal hot container extrusion through conical dies. The problem is treated as a non-steady state incorporating the nonisothermal heat transfer analysis. The analysis of temperature distribution includes heat transfer though the boundary surface including conduction, convection and radiation. The analysis of heat transfer is decoupled with the analysis of deformation and the material interaction is considered through iteration procedure. The effect of important process parameters including die angle and extrusion ratio in the process is investigated. Due to the geometric feature for the container extrusion through conical dies, automatic remeshing is mandatory. Automatic remeshing is achieved by introducing the modular remeshing technique.