• Steel and Composite Structures
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• v.20 no.5
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• pp.999-1022
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• 2016

The use of Carbon Fiber Reinforced Polymer (CFRP) to strengthen steel structures has attracted the attention of researchers greatly. Previous studies demonstrated bonding of CFRP plates to the steel sections has been a successful method to increase the mechanical properties. However, the main limitation to popular use of steel/CFRP strengthening system is the concern on durability of bonding between steel and CFRP in various environmental conditions. The paper evaluates the performance of I-section steel beams strengthened with pultruded CFRP plate on the bottom flange after exposure to diverse conditions including natural tropical climate, wet/dry cycles, plain water, salt water and acidic solution. Four-point bending tests were performed at specific intervals and the mechanical properties were compared to the control beam. Besides, the ductility of the strengthened beams and distribution of shear stress in adhesive layer were investigated thoroughly. The study found the adhesive layer was the critical part and the performance of the system related directly to its behavior. The highest strength degradation was observed for the beams immersed in salt water around 18% after 8 months exposure. Besides, the ductility of all strengthened beams increased after exposure. A theoretical procedure was employed to model the degradation of epoxy adhesive.

• Journal of the Microelectronics and Packaging Society
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• v.11 no.2 s.31
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• pp.23-28
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• 2004

We utilized Ag capping layer for fluxless bonding. To investigate the effect of Ag capping layer, two sets of sample were used. One set was bare In and Sn solders. The other set was In and Sn solders with Ag capping layer. In ($10{\mu}m$) and Sn ($10{\mu}m$) solders were deposited on Cu/Ti/Si substrate using thermal-evaporation, and Ag ($0.1{\mu}m$) capping layers were deposited on In and Sn solders. Solder joints were made by joining two In and Sn deposited specimens at $130^{\circ}C$ for 30 s under 0.8, 1.6, 3.2 MPa using thermal compression bonder. The contact resistance was measured using four-point probe method. The shear strength of the solder joints was measured by the shear test of cross-bar sample in the direction. The microstructure of the solder joints was characterized with SEM and EDS. In and Sn solders without Ag capping layers were only bonded at $130^{\circ}C$ under high bonding pressure. Also the shear strength of the In-Sn solder joints under was lower than that of the Ag/In-Ag/Sn solder joints. The resistance of the solder joints was $2-4\;m{\Omega}$ The solder joints consisted of In-rich phase and Sn-rich phase and the intermixed compounds were found at the interface. As bonding pressure increased, the intermixed compounds formed more.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1996.05a
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• pp.220-223
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• 1996

Mechanical properties of Plasma-Enhanced Chemical Vapor Deposited (PECVD) silicon nitride thin film was studied to determine the feasibility of the film as a passivation layer over the aluminum bonding areas of integrated circuit chips. Ultimate strain of the films in thicknesses of about 5 k${\AA}$ was measured using four-point bending method. The ultimate strain of these films was constant at about 0.2% regardless of residual stress. Intrinsic and residual stresses of these films were measured and compared with thermal shock and cycling test results. Comparison of the results showed that more tensile films were more susceptible to crack- induced failure.

• Proceedings of the KSR Conference
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• 2009.05a
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• pp.574-580
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• 2009

This study is investigate the bending behavior of real size RC beams strengthened with carbon fiber sheets. For experimental study, 1 control beam and 8 strengthened beams of real size(4 NU-beams and 4 U-beams) are tested and compared. NU-beam has not a V-shaped band and V-beam has a V-shaped band. The variables of experiment are composed of the number of carbon fiber sheets, the existence of U-shaped band, and four point loading, etc. The experimental results showed that the strengthening system with U-shaped band controls the premature debonding and provides a more ductile failure mode than the strengthening system without V-shaped band. It can be found from the load-deflection curves that as the number of fiber sheets is increased, the maximum strength and the flexural rigidity is increased. For the strengthening method with carbon fiber sheets of the real size RC beams, it is required the finding a solution to the bonding problem.

• Restorative Dentistry and Endodontics
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• v.13 no.1
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• pp.103-111
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• 1988

The purpose of this study was to, examine the sealing ability of the denting bonding agent, when used with gutta percha cone, as a root canal sealer. Seventy two upper and lower extracted human teeth with single root were randomly selected and instrumented in a conventional method with K-file. After instrumentation and dry the canal with paper point, there were divided into three groups and twenty four teeth in each group were filled with the following material; In group I: Scotchbond in combination with gutta percha cone. In group II: AH 26 in combination with gutta percha cone. In group III: Tubli-Seal in combination with gutta percha cone. All specimens were immersed in Indian Ink, decalcified, and cleared. The depth of dye penetration into the canals were evaluated by caliper at the intervals of 1 day, 1 week, 2 weeks. The results were as follows; 1. Depth of dye penetration for all groups increased with time. 2. As to difference in mean dye penetration at time interval of 1 day and 14 days, Scotchbond group exhibited the smallest value as 0.53mm and Tubli-Seal group exhibited the largest value as 0.70mm. 3. There was the difference of dye penetration between each group, but its difference was not significant, statistically.

• Journal of the Korean Society of Visualization
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• v.18 no.3
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• pp.61-68
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• 2020

Thermographic phosphor (TP) thermometry is a noncontact optical measurement method and has been applied in many fields such as combustion and heat transfer. However, due to the limitation of bonding technology and measurement method, most TP thermometry studies were conducted only on the air environment with water-soluble binders. In this paper, a temperature measurement technology in water using TP is proposed by coatings of manganese activated magnesium fluorogermanate (Mg4FGeO6:Mn4+, MFG) with Polydimethylsiloxane (PDMS). Four MFG-PDMS coatings with different thicknesses were prepared. The lifetime of MFG was not affected by the thickness of the coating as a result of the experiment and analysis of phosphor intensity using a photomultiplier tube. To measure the surface temperature field of an immerged body in water, a cylinder-type cartridge heater was coated with MFG doped PDMS. Transient surface temperature field was successfully measured even the initial temperature is higher than the boiling point of water.

• Smart Structures and Systems
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• v.16 no.1
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• pp.67-79
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• 2015

Acoustic emission analysis is an effective technique for monitoring the evolution of damage in a structure. An experimental analysis on a set of reinforced concrete beams under flexural loading was carried out. A mixed AE analysis method which used both parameter-based and signal-based techniques was presented to characterize and identify different failure mechanisms of damage, where the signal-based analysis was performed by using the Hilbert-Huang transform. The maximum instantaneous energy of typical damage events and the corresponding frequency characteristics were established, which provided a quantitative assessment of reinforced concrete beam using AE technique. In the bending tests, a "pitch-catch" system was mounted on a steel bar to assess bonding state of the steel bar in concrete. To better understand the AE behavior of bond-slip damage between steel bar and concrete, a special bond-slip test called pullout test was also performed. The results provided the basis of quantitative AE to identify both failure mechanisms and level of damages of civil engineering structures.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.11
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• pp.86-93
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• 2020

The demand for maintenance in Korea infrastructure facilities constructed since the 1970s has increased significantly compared to the demand for new construction. Moreover, after the Gyeongju and Pohang earthquakes, seismic performance evaluation, repair, and retrofitting projects have been carried out. Therefore, in this study, a specimen was designed following the L-type GFRP Plate Externally Bonded Retrofit method, one among other retrofit methods. The L-type GFRP Plate was bonded to the specimen by epoxy and a washered steel nail. A four-point bending test was performed to confirm the strengthening effect of the Externally Bonded Retrofit method using an L-type GFRP Plate. The strengthening effect of the L-type GFRP plate was proven experimentally, and the behavior of the beam designed following the L-type GFRP Plate Externally Bonded Retrofit method was evaluated according to Korea's "Design Manual & Specification for Strengthening of RC Structures by Advanced Composites System". Furthermore, the effectiveness of the bonding method, a combination of epoxy and washered steel nail, was also checked. The results showed that the design, according to the guidelines mentioned above, predicted the strength of the member well, but the failure mode did not satisfy the design assumption because of unexpected damage to the GFRP plate due to the fixing method, washered steel nail.

• Computers and Concrete
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• v.29 no.6
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• pp.393-405
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• 2022

Lightweight concrete is a superior material due to its light weight and high strength. There however remain significant lacunae in engineering knowledge with regards to shear failure of lightweight fiber reinforced concrete beams. The main aim of the present study is to investigate the optimum usage of steel fibers in lightweight fiber reinforced concrete (LWFRC). Multi-scale finite element model calibrated with experimental results is developed to study the effect of steel fibers on the mechanical properties of LWFRC beams. To decrease the amount of steel fibers, it is preferred to reinforce only the middle section of the LWFRC beams, where the flexural stresses are higher. For numerical simulation, a multi-scale finite element model was developed. The cement matrix was modeled as homogeneous and uniform material and both steel fibers and lightweight coarse aggregates were randomly distributed within the matrix. Considering more realistic assumptions, the bonding between fibers and cement matrix was considered with the Cohesive Zone Model (CZM) and its parameters were determined using the model update method. Furthermore, conformity of Load-Crack Mouth Opening Displacement (CMOD) curves obtained from numerical modeling and experimental test results of notched beams under center-point loading tests were investigated. Validating the finite element model results with experimental tests, the effects of fibers' volume fraction, and the length of the reinforced middle section, on flexural and residual strengths of LWFRC, were studied. Results indicate that using steel fibers in a specified length of the concrete beam with high flexural stresses, and considerable savings can be achieved in using steel fibers. Reducing the length of the reinforced middle section from 50 to 30 cm in specimens containing 10 kg/m3 of steel fibers, resulting in a considerable decrease of the used steel fibers by four times, whereas only a 7% reduction in bearing capacity was observed. Therefore, determining an appropriate length of the reinforced middle section is an essential parameter in reducing fibers, usage leading to more affordable construction costs.

• Bulletin of the Korean Chemical Society
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• v.35 no.12
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• pp.3495-3501
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• 2014

A novel crystal, the mono-protonated metformin acetate (1), was obtained and characterized by elemental analysis, IR spectroscopy and X-ray crystallography. It was found that one of the imino group in the metformin cation was protonated along with the proton transfer from the secondary amino group to the other imino group. Its crystal structure was then compared with the previously reported diprotonated metformin oxalate (2). The difference between them is that the mono-protonated metformin cations can be linked by hydrogen bonding to form dimers while the diprotonated metformin cations cannot. Both of them are stabilized by intermolecular hydrogen bonds to assemble a 3-D supermolecular structure. The four potential tautomer of the mono-protonated metformin cation (tautomers 1a, 1b, 1c and 1d) were optimized and their single point energies were calculated by Density Functional Theory (DFT) B3LYP method based on the Polarized Continuum Model (PCM) in water, which shows that the most likely existed tautomer in human cells is the same in the crystal structure. Based on the optimized structure, their Wiberg bond orders, Natural Population Analysis (NPA) atomic charges, molecular electrostatic potential (MEP) maps were calculated to analyze their electronic structures, which were then compared with the corresponding values of the diprotonated metformin cation (cation 2) and the neutral metformin (compound 3). Finally, the possible tautomeric mechanism of the mono-protonated metformin cation was discussed based on the observed phenomena.