• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.340-341
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• 2005

Three different composition 130um thickness PZT were fabricated by extrusion method and burned out at $550^{\circ}C$ and sintered at $1260^{\circ}C$/2.5hrs. Actuator was fabricated using glass and Si(100) wafer by MEMS process. From XRD data, in case of DECH, perovskite phase peak strength is higher than others. We were able to obtain the information of grain growth and porosity by SEM images. Also DECH PZT on glass membrane(100um thickness) have larger displacement than others.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.591-592
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• 2005

PTC Thermistors specimens were fabricated by added $MnO_2$ as donors, and $Nb_2O_5$ as acceptors and sintered $1250^{\circ}C$/2hrs. Average grain size decreased with increased in added $MnO_2$, and increased with added in $Nb_2O_5$. But, appeared liquid phase as $Bi_2O_3$ and $TiO_2$, affect to grain growth. XRD result, peak strength waslowed then crystallization not well, but, secondary phase were not showed all specimens. All specimens resistance were so high, about $40M\Omega$ over, couldn't measured to those resistance and doesn't appear PTCR effect.

• Journal of Korean Society of Steel Construction
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• v.26 no.1
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• pp.31-42
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• 2014

In this paper, concrete-filled steel tubular columns encased with precast reinforced concrete were studied. Four eccentrically loaded columns and a concentrically loaded column were tested to investigate the axial load-carrying capacity. The test parameters were the use of fiber reinforcement for cover concrete, eccentricity, column length, and lateral reinforcement. The maximum axial loads of the specimens agreed with the nominal strengths predicted by KBC 2009. However, in some specimens, the load carrying capacity quickly decreased after the peak strength due to spalling of the cover concrete.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.471-474
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• 2005

This study investigates the nano/microstructure, the aging response, and the mechanical/tribological properties of the eutectic regions in rheoformed A356 alloy-T5 parts using nano/micro-indentation and mechanical scratching, combined with optical microscopy and atomic force microscope (AFM). Most eutectic Si crystals in the A356 alloy showed a modified morphology as fine-fibers. The loading curve for the eutectic region was more irregular than that of the primary Al region due to the presence of various particles of varying strength. The aging responses of the eutectic regions in the rheoformed A356 alloys aged at $150^{\circ}C$ for different times (0, 2, 4, 8, 10, 16, 24, 36, and 72 h) were investigated. Both Victors hardness $(H_v)$ and indentation $(H_{IT})$ test results showed a similar trend of aging curves, and the peak was obtained at the same aging time of 10 h. A remarkable size-dependence of the tests was found.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.412-415
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• 2004

PTC Thermistors specimens were fabricated by added $MnO_2$ as donors, and $Nb_2O_5$ as accepters and sintered $1250^{\circ}C/2hrs$. Average grain size decreased with increased in added $MnO_2$, and increased with added in $Nb_2O_5$. But, appeared liquid phase as $BaTiO_3$ and $TiO_2$, affect to grain growth. XRD result, peak strength waslowed then crystallization not well, but, secondary phase were not showed all specimens. All specimens resistance were so high, about $40M{\Omega}$ over, couldn't measured to those resistance and doesn't appear PTCR effect.

• Bulletin of the Korean Chemical Society
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• v.17 no.5
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• pp.424-428
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• 1996

TlCl2(TCNQ)2.5 and Tl(TCNQ)3 were obtained from the reaction of LiTCNQ (TCNQ=tetracyanoquinodimethane) and TlX3 (X=Cl and NO3). These compounds were characterized by spectroscopic(IR, UV, EPR), electrochemical methods, and electrical conductivity measurements. Thermal analysis (TG, DSC) was also conducted. The room temperature electrical conductivities of these compounds are in the range of semiconductors. Spectroscopic studies indicate that Tl(TCNQ)3 has fully ionized TCNQ- ions in a form of simple salt, whereas TlCl2(TCNQ)2.5 is consisted of TCNQ- and TCNQ0 as a complex salt. EPR values of TCNQ- radical anion are 1.999 in both compounds and the signal attributable to metal ion is not observed, suggesting that any unpaired electrons are localized on TCNQ radicals, and metal atoms have diamagnetic state. Ligand decomposition and reduction process are simultaneously progressed in both compounds above at 200 ℃. The endothermic activation energy of TlCl2(TCNQ)2.5 is shown somewhat larger than that of Tl(TCNQ)3, it may be due to Tl-Cl bond strength. The mid-peak potentials of these compounds are very similar to those of TCNQ and the values of Epa and Epc are almost equal to 1. The wave of thallium ion is not detected in cyclic voltammogram, hence the redox processes of the complexes might be mainly localized to the TCNQ ligand rather than thallium ion.

• Advances in concrete construction
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• v.8 no.2
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• pp.77-90
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• 2019

This paper aims to investigate vibration frequency decrease (vibration period elongation) of reinforced concrete (RC) structure with unreinforced infill wall and reinforced infill wall exposed to progressively increased artificial earthquake load on shaking table. For this purpose, two shaking table experiments were selected as a case study. Shaking table experiments were carried on 1:1 scaled prototype one bay one storey RC structure with infill walls. The purpose of this shaking table experiment sequence is to assess local behavior and progressive collapse mechanism. Frequency decrease and eigen-vector evolution are directly related to in-plane and out-of-plane bearing capacities of infill wall enclosure with reinforced concrete frame. Firstly, frequency decrease-damage relationship was evaluated on the base of experiment results. Then, frequency decrease and stiffness degradation were evaluated with applied Peak Ground Acceleration (PGA) by considering strength deterioration. Lastly, eigenvector evolution-local damage and eigenvector evolution-frequency decrease relationship was investigated. Five modes were considered while evaluating damage and frequency decrease of the tested specimens. The relationship between frequency decrease, stiffness degradation and damage level were presented while comparing with Unreinforced Brick Infill (URB) and Reinforced Infill wall with Bed Joint Reinforcement (BJR) on the base of natural vibration frequency.

• Computers and Concrete
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• v.17 no.6
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• pp.723-737
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• 2016

In this paper an approach was described for determination of direction of sliding block in rock slopes containing planar non-persistent open joints. For this study, several gypsum blocks containing planar non-persistent open joints with dimensions of $15{\times}15{\times}15cm$ were build. The rock bridges occupy 45, 90 and $135cm^2$ of total shear surface ($225cm^2$), and their configuration in shear plane were different. From each model, two similar blocks were prepared and were subjected to shearing under normal stresses of 3.33 and $7.77kg/cm^{-2}$. Based on the change in the configuration of rock-bridges, a factor called the Effective Joint Coefficient (EJC) was formulated, that is the ratio of the effective joint surface that is in front of the rock-bridge and the total shear surface. In general, the failure pattern is influenced by the EJC while shear strength is closely related to the failure pattern. It is observed that the propagation of wing tensile cracks or shear cracks depends on the EJC and the coalescence of wing cracks or shear cracks dominates the eventual failure pattern and determines the peak shear load of the rock specimens. So the EJC is a key factor to determine the sliding direction in rock slopes containing planar non-persistent open joints.

• Geomechanics and Engineering
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• v.17 no.4
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• pp.323-331
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• 2019

The presence of defects in nature changes the physical parameters of the rock. In this paper, by studying the rock-like specimens with conjugated fractures, the horizontal angle and length are changed, and the physical parameters and failure modes of the specimens under uniaxial compression test are analyzed and compared with the results of simulation analysis. The experimental results show that the peak strength and failure mode of the rock-like specimens are closely related to the horizontal angle. When the horizontal angle is $45^{\circ}$, the maximum value is reached and the tensile failure mode is obtained. The fracture length affects the germination and propagation path of the cracks. It is of great significance to study the failure modes and mechanical properties of conjugated fracture rock-like specimens to guide the support of fractured rock on site.

• Steel and Composite Structures
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• v.30 no.6
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• pp.591-601
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• 2019

This research study investigates experimentally and analytically the axial compressive behaviour of Concrete Filled Fiber Reinforced Polymer Tube (CFFT) columns with and without Fiber Reinforced Polymer (FRP) bars. The experimental program comprises five circular columns of 204-206 mm outer diameter and 800-812 mm height. All columns were tested under concentric axial compressive loads. It was found that CFFT columns with and without FRP bars achieved higher peak axial compressive loads and corresponding axial deformations than conventional steel reinforced concrete (RC) column. The contribution of FRP bars was about 12.1% of the axial compressive loads carried by CFFT columns reinforced with FRP bars. Axial load-axial deformation ($P-{\delta}$) curves of CFFT columns were analytically constructed, which mapped well with the experimental $P-{\delta}$ curves. Also, an equation was proposed to predict the axial compressive load capacity of CFFT columns with and without FRP bars, which adequately considers the contributions of the circumferential confinement provided by FRP tubes and lower ultimate strength of FRP bars in compression than in tension.