• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.1
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• pp.16-20
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• 2008

This paper presents the construction of micro tool clamping device using a Ni-Ti shape memory alloy(SMA) ring. Clamping force of the device is produced by elastic force of the SMA reverted to its original shape in normal temperature. Phase transformation of the SMA was realized by temperature control using a peltier element. Prototype of the SMA tool clamping device was fabricated and examined its clamping force and clamping/unclamping operation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.9
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• pp.770-781
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• 2008

In nuclear power plants, ferritic low alloy steel components were connected with austenitic stainless steel piping system through alloy 82/182 butt weld. There have been incidents recently where cracking has been observed in the dissimilar metal weld. Alloy 82/182 is susceptible to primary water stress corrosion cracking. Weld-induced residual stress is main factor for crack growth. Therefore exact estimation of residual stress is important for reliable operating. This paper presents residual stress computation performed by 6" safety & relief nozzle. Based on 2 dimensional and 3 dimensional finite element analyses, effect of welding variables on residual stress variation is estimated for sensitivity analysis.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.1
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• pp.152-159
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• 1998

Two angle-shaped extrusions have been studied in order to analyze the bending effect of the extruded product using the three-dimensional rigid-plastic finite element method. The velocity distribution at the outlet becomes the source for the construction of the bending configuration of the final product. in which an analytic scheme has been developed for the description of the bending. A systematic approach presented here appears to have sound agreement with the experimental result, and has been applied to a large extrusion of aluminum alloy.

• Journal of Welding and Joining
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• v.17 no.5
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• pp.89-96
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• 1999

The base metal and weld metal of alloy designed austenitic stainless steels were electrochemically tested in artificial sea water. Pitting resistance of 14 different stainless steels was evaluated by measuring pitting potential. The effect of alloy element to pitting potential was evaluated by changing chromium, nickel, sulfur content. The site of pitting initiation was observed by optical microscope. As a result of electrochemical test, pitting resistance of weld metal was higher than base metal, and rapidly cooled weld metal has higher pitting potential than slowly cooled weld metal. In case of primary δ-ferrite solidification, pitting potential was increased, but residual δ-ferrite was detrimental to pitting resistance. Chromium was more effective to pitting resistance than nickel, and sulfur was very detrimental element to pitting resistance.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.5
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• pp.661-669
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• 1986

In this study, the resistance spot welding process of an aluminum alloy was analyzed through the numerical simulation including the electric contact resistance and the heat generation in the electrode. The finite element model was used to solve the electro-thermal responses in weld cycles. The resistance of the contact area was represented as the contact element modeling, but the thermal resistance between the contact surfaces was neglected. Welding tests of Alclad 2024-T3 aluminum alloy were made not only to get the input data for the numerical simulation, but also to compare the numerical results. The contact resistance was determined initially by the contact resistance tests and assumed to decay exponentially up to the solidus temperature. The temperature distributions and dynamic resistance obtained numerically were in good agreement with the experimental results. Numerical results revealed that nugget growth depends mainly on the heat generated in the workpiece and its contact area. The heat generated in the electrode has, however, only a little effect on the nugget growth, and the heat generation in the electrode-workpiece interface is initially high but decrease repidly.

• Transactions of Materials Processing
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• v.17 no.2
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• pp.97-101
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• 2008

Unique constitutive behavior of magnesium alloys as one of hexagonal close packed(hcp) metals has been implemented into the commercial finite element program ABAQUS. The constitutive equations can represent asymmetry in tension-compression yield stresses and flow curves. For the verification purpose, the springback of AZ31B magnesium alloy sheet was measured using the unconstrained cylindrical bending test proposed in Numisheet'2002 benchmark committee. Besides the developed constitutive models, the isotropic models based on tensile and compressive properties were also considered for comparison purpose. The predicted results by the finite element analysis and corresponding experiments showed enhanced prediction capability in springback analysis.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.1
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• pp.86-91
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• 2006

Magnesium alloys have been widely used for many structural components of automobiles and aircraft because of high specific strength and good castability in spite of hexgonal closed-packed crystal structure of pure magnesium. In this paper, FE analysis was executed about the formability of AZ3l magnesium alloy on press forging process. For this, the variation of sheet temperature, distribution of punch force and the effect of heat transfer and friction between punch and sheet on the forming characteristics during press forging of AZ31 has been analyzed by finite element analysis. In order to obtain temperature dependence of material characteristics, uniaxial tension tests at elevated temperature were done under temperature of $100^{\circ}C\~ 500^{\circ}C$.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.10a
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• pp.230-233
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• 2007

Due to their low density, high specific strength and electromagnetic interference shielding, magnesium alloy sheets are used increasingly more often in automotive, aerospace, and electronics industries. However, magnesium ally sheets should be usually formed at elevated temperature because of their poor formability at room temperature. For the use of magnesium alloy sheets for an industrial, their mechanical properties at elevated temperature and appropriate forming process conditions have to be developed. In this study, the warm deep drawing process of AZ31 sheets is studied numerically by non-isothermal simulation. The difference between the isothermal simulation results and the non-isothermal simulation results and the progress of warm forming are discussed.

• Transactions of Materials Processing
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• v.12 no.4
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• pp.290-295
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• 2003

High temperature deformation behavior and prediction of final microstructure after forming of Ti-6Al-4V alloy were investigated in this study. Equiaxed and Widmanstatten microstructures of Ti-6Al-4V alloys were prepared as initial microstructures and compression tests were performed to obtain the flow curves at high temperatures (700∼110$0^{\circ}C$) and various strain rates (10$^{-4}$ ∼10$^2$/s). From the results of compression test, strain rate sensitivity (m) and activation energy (Q) were calculated and used to establish constitutive equation. To predict the final microstructure after farming, finite element analysis was performed considering the microstructural parameters such as grain size and volume fraction of second phase.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1130-1131
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• 2006

We found that the """interface reaction between Ni-based alloy bond, diamond, and steel core is very critical in bond strength of diamond tool. None element from metal bond diffuses into the steel core but the Fe element of steel core was easily diffused into the bond. This diffusion depth of Fe has a great effect on the bonding strength. The Cr in steel core accelerated the Fe diffusion and improved the bond strength, on the other hand, carbon decreased the strength. Ni-based alloy bond including Cr was chemically bonded with diamond by forming Cr carbide. However, the Cr and Fe in STS304 were largely interdiffused, the strength was very low. The Cr passivity layer formed at surface of STS304 made worse strength at commissure in brazing process.