• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.10a
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• pp.208-208
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• 2003

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.3
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• pp.337-344
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• 1989

The upper bound elemental technique (UBET) is used to simulate the bulk flow characteristics in axisymmetric closed die forging process. Internal flow inside the cavity is predicted using a kinematically admissible velocity field that minimizes the rate of energy consumption. Application of the technique includes an assessment of the formation of flash and of degree of filling in rib-web type cavity using billets with various aspect rations. The technique considering bulging effect is performed in an incremental manner. The results of simulation show how it can be used for the prediction of forging load, metal flow, and free surface profile. The experiments are carried out with plasticine. There are good agreements in forging load and material flow in cavity between the simulation and experiment. The developed program using UBET can be effectively applied to the various forging problems.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.2
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• pp.102-112
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• 1997

This paper describes the method that can construct kinematically admissible velocity fields for forging of gear-like components which have tooth shape around the cylinder. The kinematically admissible velo- city fields for the various gear-like components, involute spur gear, trapezoidal spline, square spline, ser- ration and trochoidal gear, were constructed by pilling up the velocity components according to the shape of tooth and billet. The billets, of hollow and solid, were Al 2218 and 2024. To verify the method, the analyses and experiments were carried out and compared with each other. For analyses, the half pitches of com- ponents were divided into several deformation regions based on their tooth profile. A neutral surface was used to represent the inner flow of material during forging. Its location varied with the energy optimazation and its contour varied with the number of teeth. In experiment, the contour of material filling up the tooth zone is hyperbolic curve caused by the frictional drag on the interface of die-wall/workpiece but, in the analysis, it is an arc which retains the same contour during all forging operation.

• Transactions of Materials Processing
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• v.4 no.1
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• pp.59-69
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• 1995

A simple kinematically admissible velocity field is proposed to determine the final-stage extrusion load and the average extruded length in the square-die forward extrusion of regular polygonal-shaped bars from circular billets. From the proposed velocity field, the upper-bound extrusion load and the average extruded length are determined by minimizing the total power consumption with respect to four parameters. Experiments have been carried out with hard solder billets at room temperature. The theoretical predictions of the extrusion load are in good agreements with the experimental results and there is generally reason able agreement in average extruded length between theory and experiment.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1995.10a
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• pp.143-149
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• 1995

A simple kinematically admissible velocity field is proposed to drtermine the final-stage extrusion load and the average extruded length in the square-die forward extrusion of non-axisymmetric bars from circular billets. The proposed velocity field is applied to the square-die extrusion of trochoidal gear-shaped bars and rectangular-shaped bars, the profile function of a rectangular being approximated by using a Fourier series. Experiments have been carried out with hard solder billets at room temperature. The theoretical predictions of the extrusion load are in good agreements with the experimental results and there is generally reasonable agreements in average extruded length between theory and experiment.

• Transactions of Materials Processing
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• v.4 no.4
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• pp.390-397
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• 1995

A simple kinematically admissible velocity field is proposed to determine the final-stage extrusion load and the average extruded length in the square-die forward extrusion of non-axisymmetric bars from circular billets. The proposed velocity field is applied to the square-die extrusion of trochoidal gear-shaped bars and rectangular-shaped bars. The profile function of a rectangle is approximated by using a Fourier series. Experiments have been carried out with hard solder billets at room temperature. The theoretical predictions of the extrusion load are in good agreements with the experimental results and there is generally reasonable agreements in average extruded length between theory and experiment.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.134-138
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• 1996

A simple kinematically admissible velocity field for closed-die forging of clutch teeth is analysed which takes account of the profiled teeth chosen kinematically by approximating these as straight taper teeth. The upper bound load and the deformed configurations are predicted by the velocity field at varying punch movements considering differing frictional factors. Experiments were carried out using a model material of plasticine at room temperature where talcum powder was used as a lubricant. The theoretical predictions of the forging load and the relative pressures are found to be in reasonably good agreement with the experimental results.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.11
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• pp.91-97
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• 1995

In this study, a deformation model for the regular polygonal-shaped tubes from hollow-cylindrical billets is proposed and a kinematically admissible velocity field is obtained from this deformation model. The final stage upper-bound extrusion load and the average extruded length are determined by minimizing the total power consumption with respect to chosen parameters. Experiments have been carried out with hard solder billets at room temperature. The theoretical predictions of the extrusion load are in good agreements with the experimental results and there is generally reasonable agreement in average extruded height between theory and experiment.

• 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.

• Journal of the Korean Society of Safety
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• v.7 no.4
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• pp.85-94
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• 1992

This paper, discribes analysis of theree - dimensional extrusion with the use of dual stream functions, By this method admissible velocity fields for the extrusion of three- dimensional flow was newly derived kinematically. For square section the extrusion pressure was calculated by numerical solution program which was based on the upper bound analysis. The relationship between relative extrusion pressure and reduction of area, relative die length and constant friction factors were successfully calculated which was newly developed in this study. The results could be applied to design extrusion die.