• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.4
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• pp.839-849
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• 1990

본 연구에서는 위와 같은 열 점소성 해석의 여러 수치해석 기법을 첫째, 변형 과 온도 해석을 연계 방식과 비연계 방식으로 계산한 후 결과를 검토하고, 둘째, 온도 해석을 유한 요소법과 유한 차분법으로 계산한 후 각각의 장단점과 효율적 방법을 검 토하는데 목적이 있다.또한 이 결과로 계속적인 3차원 열 점소성 해석 연구수행의 기초를 마련하고자 한다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.1
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• pp.190-200
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• 1991

Certain structural components are exposed to high temperatures. At high temperature, under thermal and mechanical loading, metal components exhibit both creep and plastic behavior. The unified constitutive theory is to model both the time-dependent behavior(creep) and the time-independent behavior(plasticity) in one set of equations. Microscopically both creep and plasticity are controlled by the motion of dislocations. A finite element method is presented encorporating a unified constitutive model for the transient analysis of viscoplastic behavior of structures exposed to high temperature.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.5
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• pp.1166-1180
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• 1990

The study is concerned with the two-dimensional thermo-viscoplastic finite element analysis for radial forging as an incremental forging process. The deformation and temperature distribution of the workpiece during radial forging are studied. The analysis of deformation and the analysis of heat transfer are carried out for simple upsetting of cylinder by decoupling the above two analyses. A method of treatment for heat transfer through the contact region between the die and the workpiece is suggested, in which remeshing of the die elements is not necessary. Radial forging of a mild steel cylinder at the elevated temperature is subjected to the decoupled finite element analysis as well as to the experiment. The computed results in deformation, load and temperature distribution are found to be in good agreement with the experimental observations. As an example of viscoplastic decoupled analysis of hot radial forging, forging of a square section into a circular section is treated. The stresses, strains, strain rates and temperature distribution are computed by superposing material properties as the workpiece is rotated and forged incrementally. It was been thus shown that proposed method of analysis can be effectively applied to the hot radial forging processes.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.05a
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• pp.151-155
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• 2006

Elastic-viscoplastic structural analysis is performed for regenerative cooling chamber of liquid rocket thrust chamber using Bodner-Partom visco-plastic model. Strain rate test was also conducted for a copper alloy at various temperatures in order to get material constants of visco-plastic model used in the structural analysis. Material constants of visco-plastic model were obtained from strain rate test results and visco-plsstic model was incorporated into finite element program, Marc, by means of user subroutine. The structural analysis results indicate that the deformation of cooling channel is mostly caused by thermal loading rather than pressure loading and confirmed structural stability of the cooling channel under operating condition.

• Journal of the Korean Society of Propulsion Engineers
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• v.10 no.4
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• pp.69-76
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• 2006

Elastic-viscoplastic structural analysis has been performed for regenerative cooling chamber of liquid rocket thrust chamber using Bodner-Partom visco-plastic model. Strain rate test was conducted for a copper alloy at various temperatures in order to get material constants of visco-plastic model used in the structural analysis. Material constants of visco-plastic model were obtained from strain rate test results and visco-plastic model was incorporated into finite element program, Marc, by means of a user subroutine. The structural analysis results indicated that the deformation of cooling channel is mostly caused by thermal loading rather than pressure loading and confirmed structural stability of the cooling channel under the operating condition.

• Transactions of Materials Processing
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• v.1 no.2
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• pp.32-39
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• 1992

대형 강괴의 자유단조 공정 중에서 코깅(cogging)작업은 강괴 단조의 초기에 단면을 줄이면서 길이 방향으로 늘리는 작업이다. 코깅 작업의 역활은 주조시 발생하는 강괴 내부의 기공을 압착시켜 제거하며 주조 조직을 파괴하여 물성치를 균질화하고 향상시키는 것이다. 그러나 대형강괴의 작업에는 제약조건이 많이 있고 작업공정에서 공정변수도 여러가지 이다. 따라서 본 논문에서는 변형해석과 온도해석을 할 수 있는 3차원 열-점소성 유한요소해석 프로그램을 개발하고, 코깅공정에서 다이의 형상과 다이폭, 다이 겹침과 엇갈리기, 강괴의 온도 구배, 압하 깊이와 패스 설계등의 여러 공정 변수의 영향을 해석하여, 단조 효과를 최대화하는 최적의 단조 공정을 예측하여 공정개선에 적용하는 것이 목적이다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.901-904
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• 2002

The cutting thickness of ultra-precision machining is generally very small, only a few micrometer or even down to the order of a flew manometer. In such case, a basic understanding of the mechanism on the micro-machining process is necessary to produce a high quality surface. When machining at very small depths of cut, metal flow near a rounded tool edge become important. In this paper a finite element analysis is presented to calculate the stagnation point on the tool edge or critical depth of cut below which no cutting occurs. From the simulation, the effects of the cutting speed on the critical depths of cut were calculated and discussed. Also the transition of the stagnation point according to the increase of the depths of cut was observed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1992.03a
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• pp.103-114
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• 1992

Cogging is generally the initial and primary step in the manufacture of practically all large open-die forgings, and consists of forging and ingot by reducing the cross-section and simultaneously enlarging the body. A three-dimensional thermo-viscoplastic finite element model is used to study the distribution of internal stresses and strains of workpiece and temperature of workpiece and die during cogging process. Simulations are carried out on an circular ingot, using v-die and flat die, to study the effects of die configuration, die width, penetration depth, temperature gradient, die overlapping and pass design.

• 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.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.1
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• pp.1-15
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• 1998

In this paper, thermo-viscoplastic finite element analysis of the effect of tool edge radius on cutting process are performed. The thermo-viscoplastic cutting model is capable of dealing with free chip geometry and chip-tool contact length. The coupling with thermal effects is also considered. Orthogonal cutting experiments are performed for 0.2% carbon steel with tools having 3 different edge radii and the tool forces are measured. The experimental results are discussed in comparison with the results of the FEM analysis. From the study, we confirm that this cutting model can well be applied to the cutting process considered the tool edge radius and that a major causes of the "size effect" is the tool edge radius. With numerical analysis, the effects of the tool edge radius on the stress distributions in workpiece, the temperature distributions in workpiece and tool, and the chip shape are investigated.estigated.