• Journal of the Korean Society of Manufacturing Process Engineers
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• v.8 no.4
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• pp.48-53
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• 2009

Inconel 718 alloy, widely used as material of aircraft engine, has a good mechanical property in high temperature, strong anti-oxidation characteristics in oxidated current over $900^{\circ}C$, and also is not easily digested in the air containing sulfur, therefore, its usage as mechanical component is expanding rapidly. Even though Inconel alloy 718 is difficult to machine, it requires highly precise processing/machining to sustain its component quality of high accuracy. In this paper, general turning operation conditions are tested to select the best cutting process condition by measuring surface roughness through implementing experiments with orthogonal array of cutting speed, feeding speed and cutting depth as processing parameters based on the Taguchi method. Optimal turning operation conditions are extracted from the proposed experimental models.

• Journal of the Korean Magnetics Society
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• v.8 no.3
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• pp.131-137
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• 1998

The thickness dependence of the microstructure and the giant magnetoresistance behavior of co-evaporated Co-Ag granular alloy films were investigated. The maximum magnetoresistance ratio of 24% was observed in the the as-deposited state of the 40 at. % Co alloy having 200 nm thickness. The surface scattering contributed about 20% to the total resistivity in the 20 nm thick films. The MR ratio dropped sharply when the film thickness was below 50 nm. The reduction in the Co particle size and the increase in solid solubility of Ag in fcc Co when the film thickness decreased were observed using a high resolution TEM. The aspect ratio of the Co particles was also affected by the film thickness. Those microstructural changes as well as the surface induced spin flipping play a significant role in the $\Delta$p change.

• Korean Journal of Metals and Materials
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• v.50 no.7
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• pp.511-516
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• 2012

Low temperature ${\delta}$-precipitation phenomenon below 2-step aging ($718^{\circ}C$, $8hr+621^{\circ}C$, 8 hr) temperature of cold drawn Inconel 718 alloy wire was investigated. The investigation was carried out on wires with a cold drawn ratio of 0, 20, 50 and 70% using OM, SEM, XRD, TEM, and DSC. In microstructures of 50 and 70% drawn wire, many precipitates were found along the grain boundaries and the twin boundaries in deformation band. From the results of the XRD and TEM analysis, the precipitates were identified as plate-like ${\delta}$-phase. From the results of the DSC analysis, it was also found that a temperature of ${\delta}$-precipitation decreases with an increase of the cold drawn ratio. We concluded that cold drawing of inconel 718 wire promotes the ${\delta}$-precipitation, and under the condition of a high drawing ratio, the ${\delta}$-phase could be precipitated at a temperature below the aging temperature ($718^{\circ}C$).

• Structural Engineering and Mechanics
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• v.9 no.3
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• pp.289-304
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• 2000

This study discusses on the experimental and analytical results of the global buckling tests, carried out on aluminum alloy double layer space grids composed of tubular members, ball joints and connecting bolts at the member ends, with the purpose of demonstrating the effectiveness of a simplified analysis method using an equivalent slenderness ratio for the members. Because very few experiments have been carried out on this type of aluminum space grids, the buckling behavior is investigated experimentally over the post buckling regions using several space grid specimen with various values for the member slenderness ratio. The observed behavior duping the experiments is compared with the analytically obtained results. The comparison is made based on two different schemes; one on the plastic hinge method considering a bending moment-axial force interaction for members and the other on a method using an equivalent slenderness ratio. It is confirmed that the equivalent slenderness method can be effectively applied, even in the post buckling regions, once the effects of the rotational rigidity at the ball joints are appropriately evaluated, because the rigidity controls the buckling behavior. The effectiveness of the equivalent slenderness method will be widely utilized for estimation of the ultimate strength, even in post buckling regions for large span aluminum space grids composed of an extreme large number of nodes and members.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.10a
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• pp.349-354
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• 2011

Tuned mass damper is widely used in many applications of industry. The main advantage of tuned mass damper is that it can increase the damping ratio of system and reduce the vibration amplitude. Meanwhile, the natural frequency of system will be divided by two peaks, and the peak speeds are closely related to the mass and the stiffness of auxiliary mass system added. In addition, the damping ratio will also affect the peak frequency of the dynamic response. In the present research, the nonlinear mechanical characteristics of rubber is investigated and put into use, since it is usually manufactured as the spring element of tuned mass damper. By the sense of the nonlinear stiffness as well as the damping ratio which can be changed by preload applied on, the shape memory alloy is proposed to control the auxiliary mass system by self-optimizing. Supported by the experiment data of rubber, the 1 DOF theoretical model and finite element model based on computer simulation are implemented to perform the feasibility of the proposed semi-active tuned mass damper working on the drive shaft.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.7
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• pp.1047-1054
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• 2001

Atomic Force Microscope (AFM) was used to study cross sectional profiles and dimensions of fatigue striations in 2017-T351 aluminum alloy. Their widths(SW) and heights (SH, SH(sub)h, SH(sub)ι) were measured from the cross sectional profiles of three-dimension AFM images. The following results that will be helpful to understand the fatigue crack growth mechanism were obtained. (1) The relation of SH=$\alpha$(SW)(sup)1.2 was obtained. (2) The ratio of the striation height to its width SH/SW, SH(sub)h/SW and SH(sub)ι/SW did not depend on the stress intensity factor range ΔK and the stress ratio R( =P(sub)min/P(sub)max = K(sub)min/K(sub)max). (3) Effect of precipitate on the morphology of striation was changed by the relative dimensional difference between the striation width SW and the precipitates. From these results, the applicability of the AFM to nano-fractography is discussed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.4 s.175
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• pp.955-962
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• 2000

Scanning Probe Microscope (SPM) such as Scanning Tunneling Microscope (STM) and Atomic Force Microscope (AFM) was shown to be the powerful tool for nano-scale characterization of a fracture surface . AFM was used to study cross sectional profiles and dimensions of fatigue striations in 2017-T351 aluminum alloy. Their widths (SW) and heights (SH) were measured from the cross sectional profiles of three-dimension AFM images. The following results that will be helpful to understand the fatigue crack growth mechanism were obtained. (1) Coincidence of the crack growth rate with the striation width was found down to the growth rate of 10-5 mm/cycle. (2) The relation of SH=0.085(SW)1.2 was obtained. (3) The ratio of the striation height to its width SH/SW did not depend on the stress intensity factor range K and the stress ratio R. (4) Not only the SW but also the SH changed linearly with the crack tip opening displacement (CTOD) when plotted in log-log scale. From these results, the applicability of the AFM to nano-fractography is discussed.

• Journal of Powder Materials
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• v.20 no.4
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• pp.308-312
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• 2013

In this paper, we describe experiment results using a vibration assisted hybrid femtosecond laser (${\lambda}$:795 nm) ultra-precision machining system. The hybrid system we have developed is possible that optical focal point of the femtosecond laser constantly and frequently within the range of PZT(piezoactuator) vibrator working distance. Using the hybrid system, We have experimented on brass and studied about differences of result of hole aspect ratio compare to general experiment setup of femtosecond laser system. Aspect ratio of a micro hole on brass is increased as 54% with 100 Hz vibration frequency and surface roughness of the side wall also improved compare to non-vibration.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.369-372
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• 2005

A study on the microstructure, the texture and the formability of the samples after ECAPed and subsequent heat-treated AA 1050 aluminum alloy sheet have been carried out. The specimens after the ECAP showed a very fine grain size, a decrease of <100> // ND. The <110>// ND textures appears in the specimens after the ECAP and subsequent heat-treatment at $400^{\circ}C$ for 1 hour. One of the most important properties in sheet metals is formability. The r-value or plastic strain ratio has was as a parameter that expressed the formability of sheet metals. The change of the plastic Strain ratios after the ECAP and subsequent heat-treatment conditions were investigated and it was found that they were two times higher than those of the initial Al sheets. This could be attributed to the formation above texture components through the ECAP and subsequent heat-treatment of AA 1050 Aluminum alloy sheet.

• Analytical Science and Technology
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• v.6 no.2
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• pp.181-195
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• 1993

The purpose of this research is to improve the density and the hardness of the SUS alloys for wear resistant materials. The dependence of the density, shrinkage ratio and hardness of various alloys on the sintering temperature and composition were examined. Alloys added with 3% Ti shows the most proper sintering properties of shrinkage ratio and the hardness which is enough to substitute for existing high price materials.