• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.753-756
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• 2008

HPFRCC (High-Performance Fiber Reinforced Cementitious Composites), which is relatively more ductile and has the characteristic of high toughness with high fiber volume fractions, can be used in structures subjected to extreme loads and exposed to durability problems. In the case of using PVA(polyvinyl alcohol) fibers, it is noted by former studies that around 2% fiber volume fractions contributes to the most effective performance at HPFRCC. In this study, therefore, compressive and flexural tests were implemented to evaluate the compressive and flexural capacities of HPFRCC while the total fiber volume fractions was fixed at 2% and two different PVA fibers were used with variable fiber volume fractions to control the micro-crack and macro-crack with short and long fibers, respectively. Moreover, specimens reinforced with steel and PVA fiber simultaneously were also tested to estimate their behavior and finally find out the optimized mixture. In the result of these experiments, the specimen consists of 1.6% short fibers (REC 15) and 0.4% long fiber (RF4000) outperformed other specimens. When a little steel fibers added to the mixture with 2% PVA fibers, the flexural capacity was increased, however, when high steel fiber volume fractions applied, the flexural capacity was decreased.

• The Journal of Advanced Prosthodontics
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• v.10 no.2
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• pp.101-112
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• 2018

PURPOSE. The purpose of this study was to investigate the effect of various surface treatments (ST) on the shear bond strength of resin composite to three bilayer dental ceramics made by CAD/CAM and two veneering ceramics. MATERIALS AND METHODS. Three different bilayer dental ceramics and two different veneering ceramics were used (Group A: IPS e.max CAD+IPS e.max Ceram; Group B: IPS e.max ZirCAD+IPS e.max Ceram, Group C: Vita Suprinity+Vita VM11; Group D: IPS e.max Ceram; Group E: Vita VM11). All groups were divided into eight subgroups according to the ST. Then, all test specimens were repaired with a nano hybrid resin composite. Half of the test specimens were subjected to thermocycling procedure and the other half was stored in distilled water at $37^{\circ}C$. Shear bond strength tests for all test specimens were carried out with a universal testing machine. RESULTS. There were statistically significant differences among the tested surface treatments within the all tested fracture types (P<.005). HF etching showed higher bond strength values in Groups A, C, D, and E than the other tested ST. However, bonding durability of all the surface-treated groups were similar after thermocycling (P>.00125). CONCLUSION. This study revealed that HF etching for glass ceramics and sandblasting for zirconia ceramics were adequate for repair of all ceramic restorations. The effect of ceramic type exposed on the fracture area was not significant on the repair bond strength of resin composites to different ceramic types.

• Composites Research
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• v.24 no.1
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• pp.37-44
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• 2011

In this paper, Particle Swarm Optimization(PSO) is applied to the design of the Frequency Selective Surface(FSS) and residual stresses of hybrid radome is predicted. An equivalent circuit model with Square Loops arrays was derived and then PSO was applied for acquiring the optimized geometrical parameters with proper resonant frequency. Residual stresses occur in the FSS embedded composite structures after cocuring and have a great influence on the strength of the FSS embedded composite structures. They also effect transmission quality because of delamination. Therefore, the thermal residual stresses of FSS embedded composite structures were analyzed using finite element analysis with considering the effects of FSS pattern, and composite stacking sequence.

• Composites Research
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• v.23 no.3
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• pp.13-18
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• 2010

One of the biggest challenges in the nano-field is how to effectively disperse nano-scale particles, especially CNTs, which are strongly agglomerated by intermolecular van der Waals forces. This study suggests a new method, discharge flocking, in order to disperse nano-scale particles effectively, which combines corona discharge phenomenon and a traditional electrostatic flocking process. In order to evaluate the discharge flocking process, composite specimens were fabricated by the process and RFI(resin film infusion) process, and then the mechanical and electrical properties of the specimens were measured and compared. Moreover, the evaluation of gas discharge effect on the CNTs and epoxy was performed to compare the mechanical and electrical properties of the composite specimens including the plasma treated CNTs. The experimental results showed that the electrical and mechanical properties of the specimens fabricated by the discharge flocking process were similar to those of the RFI process. In addition, plasma treated CNTs were not affected by gas discharge during the discharge flocking process.

• Applied Chemistry for Engineering
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• v.23 no.3
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• pp.271-278
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• 2012

In this work, we have prepared the nanocomposite by the reaction of mica and zinc oxide, and investigated the application of nanocomposite to UV protecting creams. Mica treated with 3-aminopropyltrimethoxysilane (APTMS) reacted with 1,4-phenylenediisothiocyanate (PDC) to give -N=C=S functionalized surface, which was further reacted with zinc oxides coated with APTMS to give mica-zinc oxide nanocomposites. The composites were characterized by EA, EDS, TGA, SEM, zeta potential measurement, powder XRD, and DRS UV/Vis analyses. Finally, we measured transmittances of ultraviolet protection creams manufactured by using mica composite covered with zinc oxides in the range of 280~400 nm. The nanocomposites developed in this work might be applicable as inorganic hybrid materials for UV protecting creams.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.11a
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• pp.4-4
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• 2012

Proteins enable biology to be viable through molecular interactions (such as in antigen-antibody, ligand-receptor, and drug-target) with

• Journal of Korea Foundry Society
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• v.19 no.6
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• pp.493-500
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• 1999

Squeeze casting was used for fabricating a light metal base composite having high strength and wearresistance. Reactive sintering was used to prepare the preform of Squeeze casting. To utilize Fe-Al intermetallic compounds and SiC particle as a reinforcement, there needs to prepare Fe-Al mixed powder at 50, 60, 70at.%Al, and add SiC powder to the above mixture at 4, 7, 16, 24wt.%. The prepared mixture with SiC was reactive sintered in a tube furnace at $660^{\circ}C$ to get a porous hybrid preform of intermetallic compound and SiC. The preform prepared above was placed in a metal mold, preheated at $660^{\circ}C$ AC4C matrix was injected into the mold with the temperature of the melt at $610^{\circ}C$ After these processes, 66MPa was applied to the mold for 5 minute to finish the whole procedure. The maximum reaction temperature was increased with the increased Al amount, but decreased with the increased SiC amount. The density of the preform was decreased with SiC amount increase in the compacts due to swelling of the preform. An optical microscope was applied to observe the micro structure and the dispersion of the reinforcements. To analyze phases, We utilized XRD, EDS. Hardness test were chosen to get the information of mechanical properties. There were no significant changes in micro structure between the composite and preform. However, it was shown that uniform dispersion of the reinforcers and complete infiltration of the melt into the preform were achieved through the procedure of the squeeze casting. It was observed that the hardness of the composite is decreased with increased SiC amount, resulting from the volumetric expansion of the preform.

• The Journal of Korean Academy of Prosthodontics
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• v.38 no.4
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• pp.438-445
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• 2000

The ideal restorative material should mimic the properties of the tissues it replaces. Dental composite resins have been used widely as restorative materials due to its advantages such as excellent esthetics and ease of manipulation. But inadequate wear resistance has been a major factor limiting the use of composite restorative materials. Improved manufacturing techniques have allowed the development of hybrid composites, with a greater percentage volume filler loading, which have improved physical and mechanical properties. However they are lacking in the study of wear resistance. The purpose of this study was to evaluate the wear of human enamel against ceromer by the use of a pin-on-disk type wear testers. Discs of ceromer(Targis ; lvoclar Vivadent, Amherst. NY) and discs of type III gold alloy as a control were used f9r test specimens. Intact cusp of premolar and molar were used for enamel specimens. The wear of enamel was determined by weigh-ing the cusp before and after each test, and the weight converted to volumes by average densi-ty of enamel. Surface profilometer was used to quantify wear of the ceromer and gold specimens. Vicker's hardness tester was used to evaluate the surface hardness of test specimens. The SEM was used to evaluate the wear surfaces The results were as follows; 1. Ceromer produced less enamel wear than gold(p<0.05) 2. The wear volume of ceromer was greater than that of gold(p<0.01) 3. The hardess of ceromer was lower than that of gold, but there was no correlation between the hardness and wear of the ceromer and gold. 4. SEM analysis revealed that there were many voids and microcracks in the wear tract of ceromer In gold group, many minute V-shaped grooves were examined.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.177-180
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• 2008

SHCC shows the high energy tolerance capacity due to the interfacial bonding of the fibers to the cement matrix. For effective material design and application of SHCC, it is needed to investigate the damage process and micro-fracture mechanism of cement matrix reinforced with different types of fibers. The objective of this paper is to investigate the direct tensile response of cement composites reinforced with single and hybrid fibers using acoustic emission(AE) technique. In this study, the correlations between AE signal and result of the direct tensile response of SHCC. For these purposes, three kinds of fibers were used: PET1.5%, PET1.0+PE0.5%, PET1.0%+PVA0.5%. The result of the direct tensile response of SHCC, for the same volume fraction of fibers, ultimate strength of PET-PE specimen was 2.7 times higher than specimens with PET fibers. And from AE signal value, AE event numbers and cumulative energy were different according to kind of fiber because of the different material properties of reinforced fiber.

• Magazine of the Korea Concrete Institute
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• v.8 no.6
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• pp.235-243
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• 1996

The mechanical behavior ot concrete is strongly influenced by various scenarios of crack initiation and crack propagation. Recently. the study of the interface fracture and cracking in interfacial regions is emerged as an important field, in the context of the developement of high performance concrete composites. The crack path criterion for elastically homogeneous materials is not valid when the crack advances at an interface because. in this case, the consideration of the relative magnitudes of the fracture toughnesses between the constituent materials and the interface are involved. In this paper, a numerical method is presented to obtain the values of two interfacial fracture parameters such as the energy release rate and the phase angle at the tip of an existing interface crack. Criteria based on energy release rate concepts are suggested for the prediction of crack growth at the interfaces and an hybrid experimental-numerical study is presented on the two-phase beam composite models containing interface cracks to investigate the cracking scenarios in interfacial regions. In general, good agreement between the experimental results and the prediction from the criteria is obtained.