• Journal of the Korean Society for Precision Engineering
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• v.23 no.9 s.186
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• pp.127-133
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• 2006

Cold expansion method is used to protect a fatigue fracture from fastener hole in the structure and aerospace industry. Cold expansion is that an oversized tapered mandrel goes through the hole and produces a compressive residual stress as well as plastic deformation around the hole. Here, mandrel shapes are one of the factors which are influenced on the residual stress distribution by cold expansion method. This paper, according to mandrel shapes (diameter of mandrel, length of mandrel and length of taper), we are performed a finite element analysis of residual stress distribution by cold expansion method. From this study, it has been found that diameter of mandrel and length of taper are an important factor which was generated a low compressive residual stress surround of fastener hole by cold expansion method.

• The Journal of the Acoustical Society of Korea
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• v.19 no.2
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• pp.3-7
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• 2000

This paper is on the sensitivity characteristics of a concentric composite mandrel type fiber optic acoustic sensor with inclusion of an air cavity With the finite element method, we have analyzed sensitivity variation of the sensor in relation to its geometrical factors such as thickness of the air cavity, thickness of the foaming layer, and the ratio of inner diameter/outer diameter of the mandrel. Results of the analysis suggest a thicker air cavity, a thinner foaming layer, and a smaller ratio of the inner diameter/outer diameter of the mandrel to be desirable for higher sensitivity. The sensor structure designed with the above rules provides the sensitivity of about 0.8dB higher than that of a normal concentric composite mandrel sensor without the inherent air cavity.

• Transactions of Materials Processing
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• v.27 no.5
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• pp.276-280
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• 2018

This paper has developed a forging process for conical shells for making aluminum cylindrical large shells. An incremental forging process was applied to reduce forging loads and die cost. The preform is designed based on the crosssectional area of the final forged shape. Inner diameter of the preform for mandrel forging is constant, and outer diameter is conical so that it matches the cross-sectional area of the product. However, simulation confirmed that the larger diameter is smaller than predicted and the length is larger than predicted because in the initial stage of forging, the large diameter portion first comes into contact with the anvil at the initial stage of forging and stretches in longitudinal direction. So, it has developed a rule to design the preform considering 3-D deformation instead of plane strain deformation at the beginning stage of mandrel forging. The developed mandrel forging process can be applied to more similar products and economic benefits may be obtained.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.430-434
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• 2004

Specifically designed mandrel is needed to expand tube of the heat exchanger with inner grooves. Configuration of the expanded tube depends upon the shape and feeding velocity of the mandrel. 3D simulation software LS-DYNA was used to obtain optimum design conditions of the mandrel. We show how configuration of the expanded tube varies with different design parameters such as the approaching angle, diameter , and the feeding velocity of the mandrel. Material property data for analysis were obtained through experiments with SHPB ( Split Hopkinson Pressure Bars ).

• Transactions of Materials Processing
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• v.19 no.6
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• pp.372-377
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• 2010

Elasto-plastic finite element analysis was performed for a burnishing process for the inner surface of a cylinder by mandrel. Three different configurations in roughness of the inner surface, two different thicknesses of the cylinder wall, and five different diameters of the mandrel were selected for the present investigation. Although the surface roughness was improved with the increase of the mandrel diameter, defects of folding occurred as the mandrel diameter exceeded certain limits. Improvements in the surface roughness, distributions of effective strain, effective stress and residual circumferential stress, and the variation of mandrel force were also investigated.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1630-1633
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• 2003

Hair pin bending machine is pipe forming machine consisting of heat exchanger product system. Hair pin produced by these machine is pathway of refrigerant and play a important role improving the performance and productivity of heat exchanger. The core technology of hair pin bending machine is forming the straight pipe into U-type without any defaults. Therefore, this paper study the relation between the pipe bending forming and the shape and position of mandrel using the elastic-plastic finite element analysis and provide a foundation technology for which developing the hair pin bending machine. The results are followed 1. Mandrel located in front of rotating center of bending die minimized the circular shape variation of copper pipe. 2. Diameter change of mandrel hardly effect the pipe shape.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.10a
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• pp.81-86
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• 1999

The installation of vertical drains by means of a mandrel causes significant remolding of the subsoil, especially in the immediate vicinity of the mandrel. Thus, a zone of smear will be developed with reduced permeability and increased compressibility. This paper is mainly concerned with a field study to investigate the effect of smear due to vertical drain installation. In the present study, a field smear test was conducted to assess the extent of the smear zone around the vertical drain. The extent of the smear zone around a vertical drain was evaluated from the CPT results. CPT test was carried out to some distance around the mandrel installation. The test results revealed that a smear zone was estimated to be 3.6~5.3 times of the mandrel diameter.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.148-151
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• 2003

The purpose of this study is to investigate the manufacturing technique on the U type Draw-Bending of inner groove tube. The U type tube requires the quality of product that satisfy sufficient conditions for a heat exchanger. The mandrel components act the important roles that prevent wrinkles and keep the shape of cross section of bended tube at bending process. We performed the FEM simulation using LS-DYNA software and the bending test of inner groove tube and then, compared bending simulation with bending test results about mandrel ball diameter, mandrel position and optimal clearance between mandrel and tube.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1705-1708
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• 2003

The purpose of this study is to investigate the manufacturing technique on the U type Draw-Bending of inner grooved tube. This bending process make the U shape tube by Hair Pin Bending machine. The U type tube requires the quality of product that satisfy sufficient conditions for a heat exchanger. The mandrel components act the important roles that prevent wrinkles and keep the shape of cross section of bended tube at bending process. We performed the FEM simulation using LS-DYNA software and the bending test of inner groove tube and then, compared bending simulation with bending test results about mandrel ball diameter, mandrel position and optimal clearance between mandrel and tube.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.1
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• pp.147-153
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• 2019

The prestressing steel wire, which is applied a tension to reinforce the structure, is applied flexure simultaneously by the duct and the deviator. In order to evaluate the deflected tensile performance of the prestressing steel wire subjected to both tensile and flexural stresses, the numerical analysis for 600 cases with variables of wire diameters, mandrel diameters, and friction coefficient between mandrel and steel wire was performed. As the result of analysis, the larger the diameter of the steel wire was, the lower the deflected tensile performance was, and the effect decreased with the increase of the wire elongation. The effect of mandrel diameter and friction coefficient between mandrel and wire on the deflected tensile performance of the wire was very small. But the deflected tensile performance and the friction coefficient between mandrel and strand showed a relatively high correlation. Therefore, it is necessary to make enough large elongation to secure the deflected tensile performance. If there is a restriction on the elongation, it is necessary to reduce the diameter of the steel wire to an appropriate value, and to increase the friction between steel wires by adjusting the surface condition of the steel wire.