• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.273-276
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• 2008

Thermoplastic resin takes place stress relaxation and creep according to temperature and time. In room temperature, time dependent deformation (TDD) of polymer was carried out at previous study. In this study, it evaluates time dependent deformation to relate temperature. Nanoscale indents can be used as cells for molecular electronics and drug delivery, slots for integration into nanodevices, and defects for tailoring the structure and properties. Therefore, it is important to control pattern depth for change of indent depth by creep when using Nanoindenter. For evaluating TDD at high temperature, it is occurred thermal-nanoindentation test by changing hold time at maximum load. Temperature is putted at $90^{\circ}C$, hold time at maximum loads are putted at 1, 10, 50, 100, 200, 300 and 500s.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.326-329
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• 2005

As a flexible method to fabricate sub-micrometer patterns, Focused Ion Beam (FIB) instrument and Self-Assembled Monolayer (SAM) resist are introduced in this work. FIB instrument is known to be a very precise processing machine that is able to fabricate micro-scale structures or patterns, and SAM is known as a good etch resistance resist material. If SAM is applied as a resist in FIB processing fur fabricating nano-scale patterns, there will be much benefit. For instance, low energy ion beam is only needed for machining SAM material selectively, since ultra thin SAM is very sensitive to $Ga^+$ ion beam irradiation. Also, minimized beam spot radius (sub-tens nanometer) can be applied to FIB processing. With the ultimate goal of optimizing nano-scale pattern fabrication process, interaction between SAM coated specimen and $Ga^+$ ion dose during FIB processing was observed. From the experimental results, adequate ion dose for machining SAM material was identified.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.11
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• pp.186-194
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• 2004

In this research, microfabrication technique using localized electrochemical deposition (LECD) with ultra short pulses is presented. Electric field is localized near the tool tip end region by applying a few hundreds of nano second pulses. Pt-Ir tip is used as a counter electrode and copper is deposited on the copper substrate in 0.5 M CuSO$_4$ and 0.5 M H$_2$SO$_4$ electrolyte. The effectiveness of this technique is verified by comparison with LECD using DC voltage. The deposition characteristics such as size, shape, surface, and structural density according to applied voltage and pulse duration are investigated. The proper condition is selected from the results of the experiments. Micro columns less than 10 $\mu$m in diameter are fabricated using this technique. The real 3D micro structures such as micro pattern and micro spring can be fabricated by this method. It is suggested that presented method can be used as an easy and inexpensive method for fabrication of microstructure with complex shape.

• Journal of Ocean Engineering and Technology
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• v.27 no.6
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• pp.95-99
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• 2013

Lead zirconate titanate (PZT) thick films with a thickness of $10-20{\mu}m$ were fabricated on silicone substrates using an aerosol deposition method. The starting powder, which had diameters of $1-2{\mu}m$, was observed using SEM. The average diameter ($d_{50}$) was $1.1{\mu}m$. An XRD analysis showed a typical perovskite structure, a mixture of the tetragonal phase and rhombohedral phase. The as-deposited film with nano-sized grains had a fairly dense microstructure without any cracks. The deposited film showed a mixture of an amorphous phase and a very fine crystalline phase by diffraction pattern analysis using TEM. The as-deposited films on silicon were annealed at a temperature of $700^{\circ}C$. A 20-${\mu}m$ thick PZT film was torn out as a result of the high compressive stress between the PZT film and substrate.

• Journal of Welding and Joining
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• v.34 no.4
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• pp.23-27
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• 2016

A 3D printed metal part and thermal plastic polymer part were joined by direct laser irradiation. The 3D metal part was fabricated by using DED(Direct Energy Deposition) with STS316 material. The experiment was carried out through no patterned metal surface, 3D metal printed surface and micro laser patterned surface. The most secure joining quality was obtained at the laser micro patterned surface specimen and the counterparts of polymers were PLA and PE based thermo plastics. The applied laser power was 350Watt and the distance of patterns was maintained at $150{\mu}m$. The laser line width was optimized at $450{\mu}m$ and the laser micro pattern depth was $180{\mu}m$ for the best joining quality. Based on the result analysis, the possibility of laser material joining for metal to polymer was proposed and multi-material joining will be possible in 3D laser direct material fabrication.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.12
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• pp.2217-2226
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• 2007

In this paper, we propose a microstrip antenna with sufficient impedance bandwidths and gains for the 2.65GHz antenna which can be used in the satellite digital multimedia broadcasting. The prposed 2.65GHz satellite DMB bandwidth microstrip antenna is implemented on a substrate, which is small enough to be installed in practical mobile phones, and described simulation feature using by CST MicroWave Studio program. And also, we measured the antenna performance between the proposed antenna and the commercial antenna. From the analysis, it was found that the radiation pattern of proposed antenna is superior to the commercial antenna and an acceptable frequency band is more wider than the existing products.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.5
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• pp.8-15
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• 2018

Films with special properties (e.g., water-repellent films, optical films, anti-reflection films, and flexible films) are referred to as functional films. Recently, there has been interest in fine patterning methods for film fabrication. In particular there have been many studies that use a UV nanoimprint process involving a UV curing method. In this paper, a polymer film was fabricated by the UV nanoimprint process with a micro-pattern, and its durability was evaluated by a wear test and a nano-indentation test. The film mechanical properties (such as coefficient of friction, hardness, and modulus of elasticity) were measured. Moreover, the choice of PUA type resin used in the UV nanoimprint process was confirmed to impact the durability of the thin film. Despite making the polymer film samples using the same method and PUA type resin, different coefficient of friction, hardness, and modulus of elasticity values were obtained. PUA 4 resin had the most favorable coefficient of friction, hardness, and modulus of elasticity. This material is predicted to produce a high durability functional film.

• Structural Engineering and Mechanics
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• v.69 no.2
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• pp.231-241
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• 2019

In this paper, a new higher order shear deformation model is developed for static and free vibration analysis of functionally graded beams with considering porosities that may possibly occur inside the functionally graded materials (FGMs) during their fabrication. Different patterns of porosity distributions (including even and uneven distribution patterns, and the logarithmic-uneven pattern) are considered. In addition, the effect of different micromechanical models on the bending and free vibration response of these beams is studied. Various micromechanical models are used to evaluate the mechanical characteristics of the FG beams whose properties vary continuously across the thickness according to a simple power law. Based on the present higher-order shear deformation model, the equations of motion are derived from Hamilton's principle. Navier type solution method was used to obtain displacement, stresses and frequencies, and the numerical results are compared with those available in the literature. A comprehensive parametric study is carried out to assess the effects of volume fraction index, porosity fraction index, micromechanical models, mode numbers, and geometry on the bending and natural frequencies of imperfect FG beams.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.2
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• pp.86-92
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• 2021

Usually, the die-cast components used in small mobile devices require finishing processes, such as computer numerically controlled coating. In such cases, porosity is the most important defect. The shape of the molten aluminum that passes through the runner and gate in a mold is the one of the factors that influences gas porosity. To define the spurt index, which numerically indicates the shape of molten aluminum after the gate, Reynolds number and Ohnesorge number are used. Before die fabrication, computer-aided engineering analysis is performed to optimize the filling pattern. Finally, X-ray and surface inspection are performed after casting and machining to evaluate how the spurt index affects porosity and other product parameters. Based on the results obtained herein, a new gating system design process is suggested.

• Tribology and Lubricants
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• v.37 no.1
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• pp.1-6
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• 2021

This paper presents the experimental results of hydrophobic surfaces developed using a stereolithography-based additive-manufacturing technique. The additive manufacturing technique can be used to manufacture objects with complex geometries from computer-aided design data. Several additive manufacturing methods, such as selective laser sintering, fused deposition modeling, stereolithography apparatus (SLA), and inkjet-based system, have been developed. The SLA is a form of three-dimensional printing technology used to create prototypes, patterns, and production parts in successive layers through photochemical processes. Light causes chemical monomers and oligomers to cross-link together to form objects composed of polymers. Moreover, this method is economical for fabricating surfaces with high output resolution and quality. Here, we fabricate various surfaces using different shapes using an SLA. The surfaces with micro-patterns are fabricated for 10 cases, including the biomimetic surface. The fabricated surfaces with various micro-patterns are evaluated for hydrophobicity performance based on the static contact angle. The contact angle is measured three times for each case, and the averaged value is used. The results indicate that the arrangements in a staggered structure have a larger contact angle than those in a line when the same micro-pattern is applied. Moreover, the mimetic surfaces exhibit more hydrophobic characteristics than those of artificial micro-patterns.