• The korean journal of orthodontics
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• v.44 no.1
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• pp.44-49
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• 2014

Objective: To evaluate the effects of ultrasonic instrumentation with different scaler-tip angulations on the shear bond strength (SBS) and bond failure mode of metallic orthodontic brackets. Methods: Adhesive pre-coated metallic brackets were bonded to 72 extracted human premolars embedded in autopolymerizing acrylic resin. The teeth were randomly divided into 3 groups (n = 24 each) to undergo no treatment (control group) or ultrasonic instrumentation with a scaler-tip angulation of $45^{\circ}$ ($45^{\circ}$-angulation group) or $0^{\circ}$ ($0^{\circ}$-angulation group). SBS was tested in a universal testing machine, and adhesive remnant index (ARI) scores were recorded. The Kruskal-Wallis test and Mann-Whitney U-test were used for statistical analysis. Results: The control group had a significantly higher mean SBS value than the treated groups, which showed no significant differences in their mean SBS values. The ARI scores were not significantly different among the groups. Conclusions: Ultrasonic instrumentation around the bracket base reduces the SBS of metallic orthodontic brackets, emphasizing the need for caution during professional oral hygiene procedures in orthodontic patients. The scaler-tip angulation does not influence the SBS reduction and bond failure mode of such brackets.

• Proceedings of the KWS Conference
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• 1995.10a
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• pp.123-125
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• 1995

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.65-68
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• 1995

A slicing method by thin diamond blade is widely usd slicing of hard and brittle materials such as ceramics,glass and ferrite etc.. In this study, a new slicing system which realizes highly efficient and mirror surface slicing was developed by applying ELID-grinding with metallic bond diamond blades and its performance was evaluated. Hard and brittle materials such as ceramics,glass and ferrite were used as workpiece. Metallic bond diamond blades with grit sizes #325 and #2000 were used. Experimental results show that highly efficient slicing and good mirror surface can be successfully obtained using the developed slicing system with ELID features.

• Korean Journal of Metals and Materials
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• v.49 no.6
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• pp.425-439
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• 2011

A review of the development history of interatomic potential models for ionic materials was carried out paying attention to the way of future development of an interatomic potential model that can cover ionic, covalent and metallic bonding materials simultaneously. Earlier pair potential models based on fixed point charges with and without considering the electronic polarization effect were found to satisfactorily describe the fundamental physical properties of crystalline oxides (Ti oxides, $SiO_2$, for example) and their polymorphs, However, pair potential models are limited in dealing with pure elements such as Ti or Si. Another limitation of the fixed point charge model is that it cannot describe the charge variation on individual atoms depending on the local atomic environment. Those limitations lead to the development of many-body potential models(EAM or Tersoff), a charge equilibration (Qeq) model, and a combination of a many-body potential model and the Qeq model. EAM+Qeq can be applied to metal oxides, while Tersoff+Qeq can be applied to Si oxides. As a means to describe reactions between Si oxides and metallic elements, the combination of 2NN MEAM that can describe both covalent and metallic elements and the Qeq model is proposed.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.5
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• pp.713-723
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• 1986

The purpose of this research was to study the heat transfer characteristics of heat pipe which used non-metallic(SiO$_{2}$), circumferential wick and meshed slab wick as ADI method and experimental results. Compared wick experimental data and results by ADI method showed the good agreement and ADI method was utilized in pridicting the performance of heat pipe. Also, ADI method was applied to predict heat pipe performance according to the various volume ratios of metallic bond. The heat transfer characteristics of heat pipe could be predicted by heat flux and superheat term below the maximum heat flux limit. According to the addition ratio of metallic bond, heat transfer ratio could be improved as 2-3 times and when heat conductivity ratio(K$_{b}$/K$_{a}$) was increased at 4-12 ratio, heat transfer was in creased as 1.7-2.4 times, and the prediction of heat transfer could be show as exponential type. In producting non-metallic wick used to low heat pipe, metallic bond which is the conductivity of good quality and enduring for high temperature will be improved as in important problem.

• Journal of Welding and Joining
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• v.8 no.3
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• pp.31-38
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• 1990

The bonding mechanism and bond strength were investigated for the cold pressure welding of Al to Al, Cu to Cu and Al to Cu by upsetting. A phenomenon of bonding betweenthe metallic components has been observed by a scanning electron microscope and metallurgical microscope. A modified equation for bond strength with respect to the reduction of height shows reasonably a good agreement with the experimental data. When the values of the hardening factor and threshold deformation for the given materials could be determined, the theoretical bond strength can be calculated.

• Korean Journal of Metals and Materials
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• v.47 no.1
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• pp.13-20
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• 2009

This work presents functionally graded coatings (FGC) of hydroxyapatite (HA) and metallic powders on Ti-6Al-4V implants using plasma spray coating method. HA has been the most frequently used coating material due to its excellent compatibility with human bones. However, because of the abrupt changes in thermomechanical properties between HA and the metallic implant across an interface, and residual stress induced on cooling from coating temperture to room temperature, debonding at the interface occurs in use sometimes. In this work, FGC of HA and Ti or Ti-alloy powders is made to mitigate the abrupt property changes at the interface and the effect of FGC on residual stress release is investigated by evaluating the mechanical bond strength between the implant and the HA coating layers. Thermal annealing is done after coating in order to crystallize the HA coating layer which tends to have amorphous structure during thermal spray coating. The effects of types and compositional ratio of metallic powders in FGC and annealing conditions on the bond strength are also evaluated by strength tests and the microstructure analysis of coating layers and interfaces. Finally, biocompatibility of the coating layers are tested under ISO 10993-5.

• Journal of Applied Reliability
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• v.15 no.3
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• pp.197-206
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• 2015

Failure analysis of pre-insulated pipe (SPPS 380, 400A) transporting high temperature water ($95{\sim}110^{\circ}C$) for a plant was carried out. The damaged area (${\Phi}5mm$) of pre-insulated pipe was found only on welds. The chemical composition of damaged pipe meets specification of carbon steel pipes for pressure service (KS D 3562). As results of microstructure analysis, crack propagated from outer to inside after pitting corrosion occurred on the outside surface. The non-metallic inclusion existed on the end of crack. And the non-metallic inclusion continuously and linearly formed along with the bond line of welds. Based on SEM-EDS analysis, the nonmetallic inclusions have higher Manganese (Mn) and Oxygen (O) content but sulfur (S) was not detected. As results of water quality analysis, hydrogen ion concentration and minerals like Fe, Mg, Si were in low level. But the content of dissolved oxygen (11.2 ppm) was slightly higher than that of standard. It seems that the cause of damaged pipe is grooving corrosion due to MnO inclusion formed on bond line and corrosion took place nearby welds.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.12
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• pp.3028-3044
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• 1993

A metallic bond of great strength for the same or dissimilar metals can be produced by the explosive welding. The formation of a metallic jet at the interface between the two impacting plates has been simulated using the numerical hydrocode DYNA2D. The mechanism of explosive welding for the wave formation is also analyzed by the computer simulation technique. The microscopic with the experimentally observed behaviour of the explosive welding. The computer simulations of the explosive welding process have proven especially useful for analyzing the mechanism of metallic bones.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.05b
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• pp.207-213
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• 1997

The computational scheme on a irradiation temperature of U-10Zr fuel was established considering porosity formation, bond sodium infiltration and constituent redistribution. Thermotransport theory was adapted to model the redistribution phenomenon. As a results, the bond sodium seems to be logged in the outer region of fuel slug. The main driving force for constituent redistribution appears to be the Zr solubility change along to radial position of the fuel. It is evident that the heat of transport also has some contribution to the redistribution.