• Title/Summary/Keyword: Kinematically Admissible

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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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Study on the Hydrofilm Extrusion through Conically Converging Dies (원추형 금형을 통한 박막식 정수압 압출 에 관한 연구)

  • 신동헌;조남선;양동열
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.7 no.2
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    • pp.168-174
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    • 1983
  • The study is concerned with an analysis on the hydrofilm extrusion through conical dies. The upper bound method is adopted for the analysis of metal deformation in connection with hydrodynamic lubrication theory for the lubricant in order to determine the extrusion pressure for some variables such as reduction of area, die cone angle. In the upper bound method, a kinematically admissible velocity field is found by assuming proper streamlines and applying the flow function concept to the region of plastic deformation. The effect of work hardening is incorporated approximately by calculating the strains at the exit of the die. The experiments are carried out with the commercially pure aluminium for some chosen variables at room temperature. It is shown that the theoretical predictions are in good agreement with the experimental observations.

A numerical method for the limit analysis of masonry structures

  • Degl'Innocenti, Silvia;Padovani, Cristina
    • Structural Engineering and Mechanics
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    • v.18 no.1
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    • pp.1-20
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    • 2004
  • The paper presents a numerical method for the limit analysis of structures made of a rigid no-tension material. Firstly, we formulate the constrained minimum problem resulting from the application of the kinematic theorem, which characterizes the collapse multiplier as the minimum of all kinematically admissible multipliers. Subsequently, by using the finite element method, we derive the corresponding discrete minimum problem in which the objective function is linear and the inequality constraints are linear as well as quadratic. The method is then applied to some examples for which the collapse multiplier and a collapse mechanism are explicitly known. Lastly, the solution to the minimum problem calculated via numerical codes for quadratic programming problems, is compared to the exact solution.

An Upper Bound Analysis for the Twisting Phenomenon of Extrusion (상계해법에 의한 압출가공의 비틀림 해석)

  • Kim, Han-Bong;Jin, In-Tai
    • Transactions of Materials Processing
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    • v.7 no.4
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    • pp.340-346
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    • 1998
  • A kinematically admissible velocity field is developed for the analysis of twisting of the extruded products with elliptical shapes from round billet. The twisting of extruded product is caused by the lin-early increased rotational velocity from the center on the cross-section of the workpiece at the die exit. In the analysis the rotational velocity in angular direction is assumed by the multiplication of radial distance and angular velocity. The angular velocity is zero at the die entrance. The increase rate of angular velocity is determined by the minimization of plastic work. The results of the analysis show that the angular velocity of the extruded product in creases with the die twisting angle, the aspect ratio of product the friction condition, the reduction of area, and decreases with the die length.

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A UBET Analysis on the Lateral Extrusion Process of a Spider (스파이더의 측방 압출 공정에 대한 UBET 해석)

  • 황범철;이희인;배원병
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2001.04a
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    • pp.1129-1133
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    • 2001
  • An upper bound elemental technique(UBET) has been carried out to predict the forming load, the deformation pattern and the extruded length of the lateral extrusion of a spider for the automotive universal joint. For the upper bound analysis, a kinematically admissible velocity field(KAVF) is proposed. From the proposed velocity field, the upper bound load, the deformation pattern and the average length of the extruded billets are determined by minimizing the total energy consumption rate which is a function of unknown velocities at each element. Experiments are carried out with antimony-lead billets at room temperature using the rectangular shaped punch. The theoretical prediction of the forming load, the deformation pattern and the extruded length are good in agreement with the experimental results.

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Treatment of Essential Boundary Conditions using Modified Weight Functions in Meshless Method (무요소법에서 가중함수를 수정한 필수경계조건 처리법)

  • 강명석;윤성기
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.11
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    • pp.2705-2712
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    • 2000
  • In meshless methods some techniques to impose essential boundary conditions have been developed since the approximations do not satisfy Kronecker delta properties at nodal points. In this study, new scheme for imposing essential boundary conditions is developed. Weight functions are modified by multiplying with auxiliary weight functions and the resulting shape functions satisfy Kronecker delta property on the bound ary nodes. In addition, the resulting shape functions possess and interpolation features on the boundary segments where essential boundary conditions are prescribed. Therefore the essential boundary conditions can be exactly satisfied with the new method. More importantly, the impositions of essential boundary conditions using the present method is relatively easy as in finite element method. Numerical examples show that the method also retains high convergence rate comparable to Lagrange multiplier method.

스퍼어 기거의 밀폐단조에 관한 상계해석

  • 최재찬;허관도;김창호;최종용
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1992.10a
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    • pp.52-56
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    • 1992
  • A kinematically admissible velocity field for closed-die forging of spur gear is proposed. The velocity field is divided into three regions of deformation. In the analysis, the involute curve is approximated to be straight line and the upper-bound method is used to calculate energy dissipation rate. A constant frictional factor has been assumed on the contacting surfaces. The effects of root diameter relative pressure is independent of root diameter for the same number of teeth, but increases with the number of teeth on a given root diameter. In the presence of friction, relative forging pressure increases with increasing root diameter at the start of forging, but decreases with increasing root diameter in the processing of forging.

An Analysis of Near-Net Forging of External Spline by an Upper Bound Elemental Technique (상계요소법에 의한 External Spline의 Near-Net 단조해석)

  • 양정호
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1996.04a
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    • pp.206-211
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    • 1996
  • Closed-die forging of external spine is analysed using an upper bound elemental technique. The kinematically admissible velocity field for three-dimensional deformation in forging of the external spine with trapezoidal teeth was obtained. The upper bound to the deforming load necessary and the the deformed configurations are predicted using integration of the formulation of energy expressions which were obtained from B(upset forging method) were considerd in the present analysis and the theoretical results compared with experimental ones Experiments were carried out on plasticine as model material at room temperature where talcum powder was used as a lubricant. The present investigation revealed that the analytical method B predicts a reducet forging load and improved configuration better than method A for the forged products.

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An Upper Bound Analysis for the Twisting Phenomenon of Extrusion of Elliptical Shapes from Round Billet (상계해법에 의한 원형빌렛으로부터 타원 단면을 가진제품의 압출가공의 비틀림 해석)

  • 김한봉;진인태
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 1998.03a
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    • pp.210-213
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    • 1998
  • A kinematically admissible velocity field is developed for the analysis of twisting of extruded products. The twisting of extruded product is caused by the linearly increased rotational velocity from the center on the cross-section of the workpiece at the die exit. In the analysis, the rotational velocity in angular direction is assumed by the multiplication of radial distance and angular velocity. The angular velocity is zero at the die entrance and is increased linearly by axial distance from die entrance. The increase rate of angular velocity is determined by the minimization of plastic work. The results of the analysis show that the angular velocity of the extruded product increase with the die twisting angle and the aspect ratio of product and friction condition and reduction area and show that angular velocity increases with the decreases in die length.

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An Upper Bound Analysis of the Shapes of the Dead Metal Zone and the Curving Velocity Distribution in Eccentric Plane Dies Extrusion (평다이를 사용한 편심압출가공에서의 비유동영역의 형상과 굽힘속도분포에 관한 상계해석)

  • 김진훈;진인태
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 1998.03a
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    • pp.250-253
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    • 1998
  • The kinematically admissible velocity field is developed for the shapes of dead metal zone and the curving velocity distribution in the eccentric plane dies extrusion. The shape of dead metal zone is defined as the boundary surface with the maximum friction constant between the deformable zone and the rigid zone. The curving phenomenon in the eccentric plane dies is caused by the eccentricity of plane dies. The axial velocity distribution in the plane dies is divided in to the uniform velocity and the deviated velocity. The deviated velocity is linearly changed with the distance from the center of cross-section of the workpiece. The results show that the curvature of products and the shapes of the dead metal zone are determined by the minimization of the plastic work and that the curvature of the extruded products increases with the eccentricity.

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