• Journal of Dental Rehabilitation and Applied Science
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• v.18 no.4
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• pp.289-299
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• 2002

The bond strength is one of the most important factor in establishing long-term success of esthetic restorative dentistry. So, various restorative materials have been introduced to improve the esthetic and physical properties. Ormocer (organically modified ceramic) was developed as a result of such efforts. This study was performed to compare the shear bond strength of ormocer based adhesive with that of existing dentin adhesive. In this study $Admira^{(R)}$ and $Admira^{(R)}$ bond of the ormocer system are grouped together for ADM, Single $Bond^{(R)}$ which is an one-bottle adhesive and Z-250TM which is hybrid composite resin of BIS-GMA system for SIN, and $Definite^{(R)}$ of ormocer and Etch & $Prime^{(R)}$ 3.0 which is a self etching priming/ bonding agent for ETC. The results of this study were as follows. : (1) In the comparison of shear bond strength according to different adhesive system, shear bond strength was increased in the order of ETC group, SIN group, ADM group. There was no significant difference between ADM group and SIN group. However, there was a significant level of difference between ADM and ETC groups as well as SIN and ETC groups( p<0.05). (2) Examination by a scanning electron microscope showed a well established hybrid layer and resin tag in both ADM group and SIN group, while ETC group showed a minimal formation of the hybrid layer when compared with ADM and SIN groups. From the above results, it may be reasonable to start the clinical application of ormocer system, and it is recommended that ormocer system should be used along with an ormocer based adhesive because ormocer system showed the lower shear bond strength when it used with other existing self etching priming/bonding agent. The self etching priming/bonding agent showed relatively low shear bond strength, and it is considered that the further study should be needed.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.1
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• pp.171-178
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• 2019

Fiber-reinforced polymer (FRP) composites have proved to be reliable as strengthening materials. Most of existing studies used single types of FRP composites. Therefore, in this experimental study, carbon FRP sheet, aramid FRP sheet, and hybrid FRP plate including glass fibers were fabricated, and the effect of pre-stressed FRP composites on flexural strengthening of reinforced concrete (RC) beams was investigated. In total, eight RC beam specimens were fabricated, including one control beam (specimen N) without FRP composites and seven FRP-strengthened beams. The main parameters were type of FRP composite, the number of anchors used for pre-stressing, and thickness of FRP plates. As a result, the beam strengthened with pre-stressed FRP plate showed superior performance to the non-strengthened one in terms of initial strength, strength and stiffness at yielding, and ultimate strength. As the number of anchors and thickness of FRP plate (i.e., amount of FRP plates) increased, the strengthening effect increased as well. When hybrid FRP plates were pre-stressed, the strengthening effect was higher in comparison with pre-stressed single type FRP plate.

• Composites Research
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• v.34 no.2
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• pp.88-95
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• 2021

VARTM (Vacuum-assisted resin transfer molding) process is a low-cost process technology and affiliated with OoA (Out of Autoclave). Besides, it has been widely used in various fields. However, because of its lower quality than the autoclave process, it isn't easy to apply the VARTM process to the aerospace industry, which requires high reliability. The main problem of the VARTM process is the loss of mechanical properties due to the low fiber volume fraction and high void content in comparison to the autoclave. Therefore, many researchers have studied to reduce void and increase fiber volume fraction. This study examines whether the method of controlling atmospheric pressure could increase the fiber volume fraction and reduce void during the resin impregnation process. Reliability evaluation was confirmed by compressive strength test, fiber volume fraction analysis, and optical microscopy. As a result, it was confirmed that increasing the atmospheric pressure step by step in the VARTM process of impregnating the preform with resin effectively increases the fiber volume fraction and reduces void.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.4A
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• pp.281-290
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• 2009

In this study, an analysis technique of hybrid girder considering nonlinearity of steel-concrete contact surface is presented. Steel-concrete hybrid girder shows partial-interaction behavior due to the deformation of shear connectors, slip and detachment at the interface, and cracks under the applied loads. Therefore, the partial-interaction approach becomes more reasonable. Contact surface is modeled by interface element and analyzed nonlinearly because of cost of time and effort to detailed model and analysis. Steel and Concrete are modeled considering non-linearity of materials. Material property of contact surface is obtained from push-out test and input to interface element. For the constitutive models, Drucker-Prager and smeared cracking model are used for concrete in compression and tension, respectively, and a von-Mises model is used for steel. This analysis technique is verified by comparing it with test results. Using verified analysis technique, various analyses are performed with different parameters such as nonlinear material property of interface element and prestress. The results are compared with linear analysis result and analysis result with the assumption of full-interaction.

• Korean Chemical Engineering Research
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• v.58 no.1
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• pp.135-141
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• 2020

Although the graphene is regarded as a promising material for the electrode of the supercapacitor, its electrochemical performance is still less enough to satisfy the current demand raised in real applications. Here, using a home laser engraver, firstly we performed the prompt and selective reduction of the graphene oxide to produce multilayered and highly porous graphene maintaining high electrical conductivity. Subsequently, the resulting graphene was conformally deposited with pseudocapacitive thin VO_x using atomic layer deposition in order to enhance specific capacitance of graphene. We observed that various forms of VO_x exist in the VO_x/graphene hybrid through XPS analysis. The hybrid showed highly improved specific capacitance (~189 F/g) as compared to the graphene without VO_x. We expect that our approach is accepted as one of the alternatives to produce the graphene-based electrode for various energy storage devices.

• The Journal of the Korea Contents Association
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• v.19 no.4
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• pp.359-367
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• 2019

For this study, specimens were prepared using five types of composite resin and resin-reinforced glass ionomer Fuji II LC, and 29 days precipitation was done in four kinds of solution, which were soy sauce, gochujang, wine, and distilled water. Ten specimens for each coloring sample were divided into two groups, one those surfaces was polyester film and the other with 1200-grit abrasive paper, and 20 specimens per materials. Color change (${\Delta}{\ast}ab$) in the colored specimens is measured in 2days, 7days, 14days and 29days using spectrophotometer (CM-2600d, Konica, Minolta, Ramsey, NJ). All values were considered significant when P<0.05. 1. Each material is discolored over time under the influence of different storage solutions. 2. In soy source, among the specimens polished with polyester film, color change was observed in resin-modified glass ionomer Fuji II LC, prodigy and compomer F-2000 on day 2. Meanwhile, Fuji II LC showed noticeable color change in specimens prepared with 1200-grit sandpaper on day 2, which was followed by flowable resin on day 7. 3. On day 2, there was a color change with the specimens of flowable resin, resin-modified glass ionomer Fuji II LC and Prodigy among the hybrid specimen in the groups of polyester film in gochujang.

• The Journal of Korean Academy of Prosthodontics
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• v.38 no.2
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• pp.226-241
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• 2000

Recently a new generation of crown and bridge veneering resins containing submicron glass fillers was introduced. These ultrasmall particle hybrid composite materials distinguish themselves, compared with conventional microfill crown and bridge resins, through improved mechanical properties. It is claimed that these composites are suitable for metal free crowns and even bridges using fiber reinforcement. The purpose of this study was to evaluate the effect of thermal cycling on the tensile strength of the following veneering composites: Artglass(Heraeus Kulzer Co., Wehrheim, Germany), Estonia(Kuraray Co.. Japan), Sculpture(Jeneric Pentron Co., Wallingford, U.S.A.), and Targis(Ivoclar Co., Schaan Liechenstein). According to manufacturer's instructions, rectangular tensile test specimens measuring $1.5{\times}2.0{\times}4.5mm$ were made using a teflon mold. Whole specimens were divided into two groups. One group was dried in a desiccator at $25^{\circ}C$ for 10 days, and another group was subjected to thermal cycling($10,000{\times}$) in water($5/55^{\circ}C$). All test specimens were placed in a universal testing machine and loaded until fracture with a crosshead speed of 0.5mm/min. Weibull analysis and Tukey's test were used to analyze the data. The fracture surfaces of specimens were observed in SEM and the aliphatic C=C absorbance peak of Estenia and Targis resin was analyzed using Fourier transform infrared(FTIR) spectroscopy. Within the limitations imposed in this study, the following conclusions can be drawn: 1. Both in drying condition and thermal cycling condition, the highest tensile strength was observed in Estenia testing group(p<0.05). 2. The strength data were at to single-mode Weibull distribution, and the Weibull modulus of all veneering composite resin specimens increased after thermal cycling treatment. 3. After thermal cycling test, the highest tensile strength was observed in the Estenia group, and the lowest value was observed in the Targis group. The tensile strength values showed the significant differences between each group(p<0.05) 4. The aliphatic C=C absorbance peak of Estonia and Targis resin was decreased after light curing, and there was no distinct change after thermal cycling.

• Composites Research
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• v.32 no.1
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• pp.37-44
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• 2019

The reinforcement effect of micro-bolt for a bonded scarf joint was investigated. Three scarf ratios of 1/10, 1/20, and 1/30 were considered to examine the effect of scarf patch configuration on joint strength. To maintain the same density of micro-bolt, 16, 32, and 48 bolts were installed in the scarf joint specimens with scarf ratios of 1/10, 1/20, and 1/30, respectively. Tests were also carried out on the joints that are bonded with only adhesive and that are fastened with only micro-bolts to obtain reference values. The average failure loads of the adhesive joints with scarf ratios of 1/10, 1/20, and 1/30 were 29.7, 39.6, and 44.8 kN, respectively. In case of micro-bolt reinforcement, the failure loads at the same scarf ratios were 28.4, 37.2, and 40.1 kN, respectively, which corresponds to 96, 94, and 90% of the pure adhesive joint failure loads. In the case of using only micro-bolts, the failure loads were only 13-25% of the average failure loads of pure adhesive joints. Fatigue test was also conducted for the joints with scarf ratio of 1/10. The results show that the fatigue strength of hybrid joints using both adhesive and microbolts together slightly increased compared to the fatigue strength of adhesive joint, but the rate of increase was small to 2-3%. Through this study, it was confirmed that the reinforcement effect of micro-bolt is negligible in the scarf joints where shear stress is dominating the failure, unlike in the structure where peel stress is dominant.

• Corrosion Science and Technology
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• v.9 no.4
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• pp.147-152
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• 2010

Conventional paints for conversion coating applications in steel production derived mainly from water-based polymer dispersions containing several additives actually show good general performance, but suffer from poor scratch and abrasion resistance during use. The reason for this is because the relatively soft organic binder matrix dominates the mechanical surface properties. In order to maintain the high quality and decorative function of coated steel sheets, the mechanical performance of the surface needs to be improved significantly. In fact the wear resistance should be enhanced without affecting the optical appearance of the coatings by using appropriate nanoparticulate additives. In this direction, nanocomposite coating compositions (Nanomer$^{(R)}$) have been derived from water-based polymer dispersions with an increasing amount of surface-modified nanoparticles in aqueous dispersion in order to monitor the effect of degree of filling with rigid nanoparticles. The surface of nanoparticles has been modified for optimum compatibility with the polymer matrix in order to achieve homogeneous nanoparticle dispersion over the matrix. This approach has been extended in such a way that a more expanded hybrid network has been condensed on the nanoparticle surface by a hydrolytic condensation reaction in addition to the quasi-monolayer type small molecular surface modification. It was expected that this additional modification will lead to more intensive cross-linking in coating systems resulting in further improved scratch-resistance compared to simple addition of nanoparticles with quasi-monolayer surface modification. The resulting compositions have been coated on zinc-galvanized steel and cured. The wear resistance and the corrosion protection of the modified coating systems have been tested in dependence on the compositional change, the type of surface modification as well as the mixing conditions with different shear forces. It has been found out that for loading levels up to 50 wt.-% nanoparticles, the mechanical wear resistance remains almost unaffected compared to the unmodified resin. In addition, the corrosion resistance remained unaffected even after $180^{\circ}$ bending test showing that the flexibility of coating was not decreased by nanoparticle addition. Electron microscopy showed that the inorganic nanoparticles do not penetrate into the organic resin droplets during the mixing process but rather formed agglomerates outside the polymer droplet phase resulting in quite moderate cross linking while curing, because of viscosity. The proposed mechanisms of composite formation and cross linking could explain the poor effect regarding improvement of mechanical wear resistance and help to set up new synthesis strategies for improved nanocomposite morphologies, which should provide increased wear resistance.

• Restorative Dentistry and Endodontics
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• v.25 no.1
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• pp.123-132
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• 2000

To overcome problems of conventional glass ionomers, resin components have been added to glass ionomers. On a continuum between glass ionomers and composites are a variety of blends, employing different proportions of acid-base and free radical reactions to bring about cure. Popular groups defined between the ends are resin-modified glass-ionomers(RMGIs), polyacid-modified composite resins(Compomers) and ionomer modified resins. These groups show different clinical properties, and in selecting these materials for a restoration, one should sufficiently understand these different setting properties. In this study, some difference in the setting characteristics of different groups of hybrid ionomers were examined. Two RMGIs (Fuji2 LC,GC / Vitremer, 3M), three Compomers (Dyract AP, Dentsply / F2000, 3M / Elan, Kerr) were involved in this study. The identification of the setting characteristics of different groups was achieved by a two-stage study. First, thermal analysis was performed by a differential scanning calorimeter, and then the hardness of each group at different depth and time were measured by a micro-hardness tester. Thermal analysis was performed to identify the inorganic filler content and to record the heat change during setting process. The setting process was progressed for each material by chemical set mode and light-cured mode. In the hardness test, samples of materials were prepared with a 6mm-diameter metal ring, and the hardness was measured at the top, and 1mm, 2.5mm, 4mm below at just after a 40 second-cure, and after 10 minutes, 24 hours, and 7 days. Statistical analysis was performed by Mann-Whitney rank sum test to assess significant differences between set modes and types of materials, and by ANOVA and T-test to evaluate the statistical meanings of data at different times and depths of each materials. Followings are findings and conclusions derived from this study. Thermal analysis; 1. Compomers show no evidence of chemical setting while RMGIs exhibit heat output during the process of chemical setting. 2. Heat of cure of RMGIs exceed Compomers. 3. The net heat output of RMGIs through light-cured mode is higher than through chemically set mode. Hardness test; 1. Initial hardness of RMGIs immediately after light cure is relatively low, but the hardness increases as time goes by. On the contrary, Comomers do not show evident increase of the hardness following time. 2. Compomers show a marked decrease of setting degree as the depth of the material increases. In RMGIs, the setting degree at different depths does not significantly differ.