• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.595-596
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• 2006

The flexible organic thin film transistor (OTFT) array to use as a switching device for an organic light emitting diode (OLED) was designed and fabricated in the microcontact printing and low-temperature processes. The gate, source, and drain electrode patterns of OTFT were fabricated by microcontact printing which is high-resolution lithography technology using polydimethylsiloxane(PDMS) stamp. The OTFT array with dielectric layer and organic active semiconductor layers formed at room temperature or at a temperature tower than $40^{\circ}C$. The microcontact printing process using SAM(self-assembled monolayer) and PDMS stamp made it possible to fabricate OTFT arrays with channel lengths down to even nano size, and reduced the procedure by 10 steps compared with photolithography. Since the process was done in low temperature, there was no pattern transformation and bending problem appeared. It was possible to increase close packing of molecules by SAM, to improve electric field mobility, to decrease contact resistance, and to reduce threshold voltage by using a big dielecric.

• Bulletin of the Society of Naval Architects of Korea
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• v.7 no.1
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• pp.37-44
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• 1970

The plate under shear loading umformly distributed on the end portions of its side boundary was considered. Infinite hyperbolic serieses and Fourier serieses were combined as a stress function and from which exact solutions for the 15 cases for the parameters of b/L=0.25, 0.5, 1.0 and l/L=0.2, 0.4, 0.6, 0.8, 1.0 are obtained. In each cases the first 5 terms of the infinite series at the 36 points as shown in Fig. 3. The results are presented in Fig. 4-1, 4-2, and 4-3. The conclusions are as follows: 1) The stresses ${\sigma}_x$ increase very slightly as $\chi$ increases in the range of 0<x<L-l 2) When the parameters satisfy the conditions b/L<0.25 and l/L<0.2, the stresses in the region of 0<x<L-l can be obtained by replacing the uniform shear loading by the equivalent uniform shear loading by the equivalent uniform tensile force and pure bending moment at x=l. 3) The stress ${\sigma}_y$ is negligible throughout the region. 4) When the parameter b/L varies, the stresses ${\sigma}_x$ and u vary as L/b, while strain $\upsilon$ varies as $(L/b)^2$.

• Steel and Composite Structures
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• v.18 no.5
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• pp.1291-1303
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• 2015

Damage caused by low velocity impact is so dangerous in composites because although in most cases it is not visible to the eye, it can greatly reduce the strength of the composite material. In this paper, damage development in U-section glass/polyester pultruded beams subjected to low velocity impact was considered. Different failure criteria such as Maximum stress, Maximum strain, Hou, Hashin and the combination of Maximum strain criteria for fiber failure and Hou criteria for matrix failure were programmed and implemented in ABAQUS software via a user subroutine VUMAT. A suitable degradation model was also considered for reducing material constants due to damage. Experimental tests, which performed to validate numerical results, showed that Hashin and Hou failure criteria have better accuracy in predicting force-time history than the other three criteria. However, maximum stress and Hashin failure criteria had the best prediction for damage area, in comparison with the other three criteria. Finally in order to compare numerical model with the experimental results in terms of extent of damage, bending test was performed after impact and the behavior of the beam was considered.

• Proceedings of the KSME Conference
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• 2000.04a
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• pp.831-836
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• 2000

During machining, since more than 50% compliance of the cutting point in machine tool structures comes from headstocks, with the remainder coming from beds, slides and structural joints, the structural analysis of the headstock is very important to improve the static and dynamic performances. Especially, in case of machining hard and brittle materials such as glasses and ceramics with the grinding machine, the reinforced headstock with the high damping material is demanded. Since the fiber reinforced composite materials have excellent properties for structures, owing to its high specific modulus, high damping and low thermal expansion, it is expected that the dynamic and thermal characteristics of the headstock will be improved if they are employed as the materials fur headstock. In this paper, the design and the manufacturing methods as well as the static and dynamic characteristics of a steel-composite hybrid headstock were investigated analytically and experimentally to improve the performance of the grinding machine system.

• Proceedings of the KIEE Conference
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• 1999.07g
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• pp.3325-3327
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• 1999

A microgripper driven by E-T (electro-thermal) actuators has been designed and fabricated by surface micromachining. This microgripper consists of two E-T actuators. Each actuator has two arms with different widths joined at the end to form a 'U' shape. The wider 'cold' arm has a narrow flexure at the end (anchor or electrode side) for easy bending, This actuator can be fabricated with only two masks - one for the sacrificial layer and the other for the poly-Si structure layer. An E-T actuator bends its arm due to unequal thermal expansion between the 'cold' arm and the 'hot' arm, This actuator tip moves laterally in an arcing motion towards the cold arm side when the structure is unevenly heated by the applied current. Therefore each microgripper is actuated inwards and can hold a micro object. The fabricated E-T actuator was operated in the range of $2{\sim}12V$ and $1{\sim}5mA$. and maximum tip displacement was $13.6{\mu}m$. This device may become useful in many applications because an E-T actuator can be designed and fabricated easily, and obtain large displacement.

• Steel and Composite Structures
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• v.23 no.4
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• pp.483-491
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• 2017

This paper presents an experimental study on the behavior of concrete-encased composite columns with multiseparate steel sections subjected to axial and eccentric loads. Six 1/4-scaled concrete-encased composite columns were tested under static loads. The specimens were identical in geometric dimensions and configurations, and the parameter of this experiment was the eccentricity ratio of the applied load. Each two of the specimens were loaded with 0, 10%, and 15% eccentricity ratios. The capacity, deformation pattern, and failure mode of the specimens were carefully examined. Test results indicate that full composite action between the concrete and the steel sections can be realized even though the steel sections do not connect with one another. The concrete-encased composite columns can develop stable behavior and sufficient deformation capacity by providing enough transverse reinforcing bars. Capacities of the specimens were evaluated based on both the Plain Section Assumption (PSA) method and the superimposition method. Results show that U.S. and Chinese codes can be accurate and safe in terms of bending capacities. Test results also indicate that the ACI 318 and Mirza methods give the best predictions on the flexural stiffness of this kind of composite columns.

• Wind and Structures
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• v.31 no.6
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• pp.575-591
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• 2020

Wind load is typically considered as one of the governing design loads acting on a structure. Understanding its nature is essential in evaluation of its action on the structure. Many codes and standards are founded on state of the art knowledge and include step by step procedures to calculate wind loads for various types of structures. One of the most accepted means for calculating wind load is using Gust Load Factor or base bending Moment Gust Load Factor (MGLF), where codes are adjusted based on local data available. Although local data may differ, the general procedure is the same. In this paper, ASCE 7-16 (2017), which is used as the main reference in the U.S., and Korean Building Code (KBC 2016) are compared in evaluation of wind loads. The primary purpose of this paper is to provide insight on each code from a structural engineering perspective. Herein, discussion focuses on where the two codes are compatible and differ. In evaluating the action of wind loads on a building, knowledge of the dynamic properties of the structure is critical. For this study, the design of four figurative high-rise buildings with dual systems was analyzed.

• Journal of the Korean institute of surface engineering
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• v.57 no.3
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• pp.192-200
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• 2024

Cu as a heat exchanger tube is an important component in thermal fluid transfer. However, Cu tubes are exposed to stress in certain environments, leading to stress corrosion cracking (SCC). In this study, the effect of Sn addition on microstructure and corrosion characteristics was examined. The microstructural examination revealed the presence of columnar crystal and a grain refinement due to the addition of Sn. Electrochemical measurements showed that the 5 wt.% NH₃ environment was the most vulnerable environment to Cu corrosion, and the corrosion current density increased as stress increased. The immersion test exhibited the formation of Cu2O and Cu(OH)₂ corrosion product in 3.5 wt.% NaCl and 5 wt.% NH₃ environments, respectively. Results indicated that Sn addition to Cu was an important factor in improving the mechanical strength.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.6
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• pp.581-586
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• 2018

Cast iron manhole lids cause environmental pollution during the manufacturing process, and the work environment is very poor. In addition, if the height of the manhole cover does not match the height of the road surface, it causes considerable inconvenience and safety problems. This study proposes a height - adjustable steel manhole cover that can replace cast iron manhole covers and easily match the road surface with the upper surface of the manhole cover. Structural analysis was performed to grasp the design variable of the structure of the manhole cover, satisfying the required quality performance. To fabricate a manhole cover that satisfies the required load capacity, the optimal design for the U-shaped reinforcement structure was made. The cylindrical shape of the height adjustment part and the low frame were formed by bending the steel sheet into a circular shape and then welding. Reinforcing bars were also made by bending a steel plate. The height adjustment groove was machined by a CNC milling machine. Four prototypes were fabricated and a load bearing test was carried out, and new manhole cover was made reflecting results of the test. In the load bearing test, there was no breakage of the welded part, and deformation occurred mainly at the contact area between the groove and gusset plate. Deformation of 1 to 2.7mm occurred due to a load of 450kN. On the other hand, after removing the load, there was almost no residual deformation, and the load bearing evaluation was judged to be satisfactory because the manhole cover could be disassembled and reassembled.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.11a
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• pp.36.2-36.2
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• 2009

Low dielectric materials have been great attention in the semiconductor industry to develop high performance interlayer dielectrics with low k for Cu interconnect technology. In our study, the dielectric properties of SiOC /SiO2 thin film derived from polyphenylcarbosilane were investigated as a potential interlayer dielectrics for Cu interconnect technology. Polyphenylcarbosilane was synthesized from thermal rearrangement of polymethylphenylsilane around $350^{\circ}C{\sim}430^{\circ}C$. Characterization of synthesized polyphenylcarbosilane was performed with 29Si, 13C, 1H NMR, FT-IR, TG, XRD, GPC and GC analysis. From FT-IR data, the band at 1035 cm-1 is very strong and assigned to CH2 bending vibration in Si-CH2-Si group, indicating the formation of the polyphenylcarbosilane. Number average of molecular weight (Mn) of the polyphenylcarbosilane synthesized at $400^{\circ}C$ for 6hwas 2, 500 and is easily soluble in organic solvent. SiOC/SiO2 thin film was fabricated on ton-type silicon wafer by spin coating using 30wt % polyphenylcarbosilane incyclohexane. Curing of the film was performed in the air up to $400^{\circ}C$ for 2h. The thickness of the film is ranged from $1{\mu}m$ to $1.7{\mu}m$. The dielectric constant was determined from the capacitance data obtained from metal/polyphenylcarbosilane/conductive Si MIM capacitors and show a dielectric constant as low as 2.5 without added porosity. The SiOC /SiO2 thin film derived from polyphenylcarbosilane shows promising application as an interlayer dielectrics for Cu interconnect technology.