• Title/Summary/Keyword: Upper-bound Analysis

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Computation of Ultimate Bearing Capacity of Eccentrically Loaded Footing By Upper Bound of Limit Analysis Method (극한해석 상계법을 이용한 편심하중하의 기초 지지력 산정)

  • Kwon, Oh Kyun;Kim, Myoung Mo
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.12 no.1
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    • pp.187-196
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    • 1992
  • This paper estimates the bearing capacity of the eccentrically loaded footing by the upper bound of limit analysis method. Meyerhof method and Saran method used the limit equilibrium method in the estimation of bearing capacity. But, in this study the bearing capacity is estimated by the upper bound method. In applying the upper bound, the result depends on the failure mechanism. So this analysis uses the conventional failure mechanisms or the modified failure mechanisms. The comparisions are made between the results from this analysis and those obtained from the limit equilibrium method. Also, the influences of the parameters-eccentricity, internal friction angle, surcharge, G-value, and base friction of the footing on the bearing capacity factors have been examined.

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A Study on Material Characterization of Semi-Solid Materials (I) -Proposal of New Velocity Field for Upper Bound Analysis of Backward Extrusion- (반용융 재료의 물성치 평가에 관한 연구(I) -후방압출의 상계해석을 위한 동적 가용 속도장의 제안-)

  • 이주영;김낙수
    • Transactions of Materials Processing
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    • v.8 no.4
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    • pp.364-373
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    • 1999
  • For material characterization of semi-solid materials, backward extrusion process, which has been used in forming of hollow-sectioned products, was analyzed by the upper bound analysis in the current study. The existing kinematically admissible velocity field was applied to steady state at which there was no change in the assumed regions of velocity field. For unsteady state, new velocity field, as a function of dead zone angle, was proposed. Through the whole analysis, fiction between die and workpiece was also considered. It has been studied how the process variables, such as friction factor and punch velocity, and material parameters, such as strength coefficient, strain rate sensitivity could affect on analysis results. Finally, by the comparison with the finite element analysis, the reliability and efficiency of the proposed velocity field were discussed.

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Evaluation of Tunnel Face Stability with the Consideration of Seepage Forces (침투력을 고려한 토사터널 막장의 안정성 평가방법에 대한 고찰)

  • 남석우;이인모
    • Proceedings of the Korean Geotechical Society Conference
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    • 1999.10a
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    • pp.193-200
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    • 1999
  • Since Broms and Bennermark(1967) suggested the face stability criterion based on laboratory extrusion tests and field observations, the face stability of a tunnel driven in cohesive material has been studied by several authors. And recently, more general solution for the tunnel front is given by Leca and Panet(1988). They adopted a limit state design concept to evaluate the face stability of a shallow tunnel driven into cohesionless material and showed that the calculated upper bound solution represented the actual behavior reasonably well. In this study, two factors are simultaneously considered for assessing tunnel face stability: One is the effective stress acting on the tunnel front calculated by upper bound solution; and the other is the seepage force calculated by numerical analysis under the condition of steady state ground water flow. The model tests were performed to evaluate the seepage force acting on the tunnel front and these results were compared with results of numerical analysis. Consequently, the methodology to evaluate the stability of a tunnel face including limit analysis and seepage analysis is suggested under the condition of steady state ground water flow.

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A Study on the Drawing of Strip by Upper Bound Elemental Technique (상계요소법에 의한 판재 인발공정에 관한 연구)

  • Hur, K.D.;Choi, Y.;Choi, I.K.
    • Transactions of Materials Processing
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    • v.12 no.1
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    • pp.11-17
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    • 2003
  • For metal forming analysis, upper-bound solution is a practical method because the solution is overestimated. However it is not easy to determine the stresses on dies by using upper-bound solution. In this study, new scheme to calculate the stresses on dies based on upper bound solution is proposed. In the velocity fields, imaginary velocity is adapted to analyze the normal pressure on die surfaces. To verify the proposed scheme. plane strain drawing has been considered. The stresses on dies obtained by the proposed scheme are compared with the results of rigid plastic FEM and the experimental results. In the experiments, pressure film is used to measure the normal pressure on dies.

Upper and Lower Bound Solutions for Pile-Soil-Tunnel Interaction (한계해석법에 의한 파일-지반-터널 상호작용 해석)

  • Lee Yong-Joo;Shin Jong-Ho
    • 한국터널공학회:학술대회논문집
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    • 2005.04a
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    • pp.77-86
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    • 2005
  • In urban areas, new tunnel construction work is often taking place adjacent to existing piled foundations. In this case, careful assessment for the pile-soil-tunnel interaction is required. However, research on this topic has not been much reported, and currently only limited information is available. In this study, the complex pile-soil-tunnel interaction is investigated using the upper and lower bound methods based on kinematically possible failure mechanism and statically admissible stress field respectively. It is believed that the limit theorem is useful in understanding the complicated interaction behaviour mechanism and applicable to the pile-soil-tunnel interaction problem. The results are compared with numerical analysis. The material deformation patterns and strain data from the FE output are shown to compare well with the equivalent physical model tests. Admissible stress fields and the failure mechanisms are presented and used to develop upper and lower bound solutions to assess minimum support pressures within the tunnel.

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A Study on Arbitrary Cross Section Shaped Three-Dimensional Extruion with Upper Bound Method-Finite Element Method Couple (임의 단면 형상의 3차원 압출에 대한 상계해법-유한요소법 Couple에 관한 연구)

  • 이병섭;홍성인
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 1996.03b
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    • pp.145-155
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    • 1996
  • The extrusion velocity of billet through a die and the shapes of the die are the important factors in the metal forming process of the extrusion of billet. in recent years, the life cycle of products is goingfaster. Although the former finite element method was capable of yielding a detailed analysis, it requires lots of time and extensive coding effort. Then, some simple devices were developed and based on upper bound method. For this purpose , a kinematically admiasible velocity field is formulated for extrusion of cylinders with arbitrary cross section and die profile on their outer surfaces by using a modified upper bound approach, which configures simulataneous extruding speeds in three directions . Also, In order to display mesh of the cold forward extrusion process using the approach , the automatic three-dimentional mesh generation produced by the approach coupled finite element method with upper bound method.

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A Study on the Process of Tube End Spining by the Upper bound Method and Finite Element Method (상계해법과 유한요소법을 이용한 스피닝공정 해석에 관한 연구)

  • 김진형;홍성인;이영선
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 1996.03b
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    • pp.23-30
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    • 1996
  • The purpose of this study was to investigate changes in thewall thickness of tube sinking and working forces by the upper bound method and ABAQUS code. The independent variables were : Workpiece material, original wall thickness of tube, die angle, friction, and diameter reduction. The results indicated that of these five variables were a factor in wall-thickness increase and working forces. Three variables, a inner tube wall angle and two angles of the velocity discontinuous surfaces, are optimized in this proposed velocity field by the upper bound method. In this method, we can estimate the working forces and final tube thicknesses whcih are similar to acturla forming process. Optimized process variables which are obtained by upper bound method are used in ABAQUS pre-model . In ABAQUS analysis, the stress and the strain contours which are considered to be heat generation occured by the friction during forming process are observed.

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A Study of the Twisting and Extrusion Process of the Product with Involute Helical Fin from the Round Billet by the Upper Bound Analysis (상계해법에 의한 원형빌렛으로부터 인볼루트 헬리컬핀을 가진 제품의 비틀림 압출가공법에 관한 연구)

  • 박대윤;진인태
    • Transactions of Materials Processing
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    • v.10 no.4
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    • pp.302-310
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    • 2001
  • The twisting and extrusion process of the product with involute helical fin from the round billet is developed by the upper bound analysis. The twisting of extruded product is caused by the twisted inclined die surface connecting the die enterance section and the die exit section linearly. In the analysis, the internal shear surface is defined as the curved twisted plane from the twisting of die surface and the shear work is calculated by the consumption of shear energy. The increase rate of angular velocity is determined by the minimization of plastic work. The angular velocity of die exit can be controlled by the land length and the length of inclined die. The alular velocity assums to be increased linearly by the axial distance from the die enterance to the die exit. The results of the analysis show that the angular velocity of the extruded product increases with the die twisting angle, the reduction of area, and decreases with the die length, the friction constant.

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Analysis of the Corner Cavity of Axisymmetric Backward Extrusion by the Upper Bound Approach (상계해석을 이용한 축대칭 후방압출 공정의 Corner Cavity 해석)

  • 박재훈;변홍석;김영호
    • Journal of the Korean Society for Precision Engineering
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    • v.17 no.2
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    • pp.144-150
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    • 2000
  • In this paper, the formation of a corner cavity in the final stage of axisymmetric backward extrusion process is studied by means of upper bound analysis using kinematically admissible velocity. The quantitative relationships between corner cavity formation and process parameters are studied. And analytical results are compared with those of experiment to which plasticine is used. It is found that the analytical results agree well with experimental one. In addition, to restrict the formation of a corner cavity, driven container is applied to backward extrusion and the results are compared with those of FEM. The critical thickness of the bottom of the billet decreases with increase in reduction of area, and increases with decrease in friction. To prevent the formation of corner cavity, the concept of moving container was applied. Throughout this process, the occurrence of a corner cavity is delayed and forming limit area is enlarged.

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Yield and Compression Behavior of Semi-Solid Material by Upper Bound Method (상계법에 의한 반융용 재료의 항복과 압축거동)

  • 최재찬;박형진;박준홍
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1995.10a
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    • pp.195-198
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    • 1995
  • In Semi-Solid Forging, it is necessary to control the forming variables accurately in order to make near-net-shape products. Generally, the defects of products may occur due to liquid segregation which can be caused by the degree of deformation and condition of friction in Semi-Solid Forging, where the segregation is to be predicted by flow analysis. This paper presents the feasibility of theoretical analysis model using the new yield function which is proposed by Doraivelu et al. to the flow analysis of the semi-solid dendritic Sn-15%Pb alloys instead of adopting the yield criterion of Shima & Oyane which is used by Charreyron and usefulness of the adopted yield function. The distribution of the liquid fraction at various strains in radial direction and the influence of friction are estimated by Upper Bound Method.

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