• Restorative Dentistry and Endodontics
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• v.34 no.2
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• pp.145-153
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• 2009

The purpose of this study was to evaluate the effect of instrument compliance on the polymerization shrinkage stress measurements of dental composites. The contraction strain and stress of composites during light curing were measured by a custom made stress-strain analyzer, which consisted of a displacement sensor, a cantilever load cell and a negative feedback mechanism. The instrument can measure the polymerization stress by two modes: with compliance mode in which the instrument compliance is allowed, or without compliance mode in which the instrument compliance is not allowed. A flowable (Filtek Flow: FF) and two universal hybrid (Z100: Z1 and Z250: Z2) composites were studied. A silane treated metal rod with a diameter of 3.0 mm was fixed at free end of the load cell, and other metal rod was fixed on the base plate. Composite of 1.0 mm thickness was placed between the two rods and light cured. The axial shrinkage strain and stress of the composite were recorded for 10 minutes during polymerization. and the tensile modulus of the materials was also determined with the instrument. The statistical analysis was conducted by ANOVA. paired t-test and Tukey's test (${\alpha}<0.05$). There were significant differences between the two measurement modes and among materials. With compliance mode, the contraction stress of FF was the highest: 3.11 (0.13). followed by Z1: 2.91 (0.10) and Z2: 1.94 (0.09) MPa. When the instrument compliance is not allowed, the contraction stress of Z1 was the highest: 17.08 (0.89), followed by FF: 10.11 (0.29) and Z2: 9.46 (1.63) MPa. The tensile modulus for Z1, Z2 and FF was 2.31 (0.18), 2.05 (0.20), 1.41 (0.11) GPa, respectively. With compliance mode. the measured stress correlated with the axial shrinkage strain of composite: while without compliance the elastic modulus of materials played a significant role in the stress measurement.

• Journal of the korean academy of Pediatric Dentistry
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• v.30 no.3
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• pp.530-539
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• 2003

The aim of this study was to evaluate the resistance to degradation of four commercial composite resins in an alkaline solution. The brands studied were Charisma, Filtek P 60, Palpique Estelite, and Spectrum. Preweighed discs of each brand were exposed to 0.1N NaOH solution at $60^{\circ}C$. After 2 weeks they were removed, neutralized with HCl, washed with water and dried. Resistance to degradation was evaluated on the basis of following parameters: (a) mass loss(%) - determined from pre-and post-exposed specimen weights; (b) Si loss(ppm) - obtained from ICP-AE analysis of solution exposed to specimens; and (c) degradation depth(${\mu}m$) - measured SEM and CLSM from polished circular sections of exposed specimens. The results were as follows: 1. The sequence of mass loss was in descending order by Palpique Estelite, Filtek P 60, Charisma, and Spectrum. 2. The sequence of the degree of degradation layer depth was in descending order by Filtek P 60, Charisma, Palpique Estelita, and Spectrum. 3. The sequence of the Si loss was in descending order by Chrisma, Spectrum, Palpique Estelite, and Filtek P 60. 4. The correlation coefficient between mass loss and degradation layer depth was relatively high(r=0.704, p<0.05). 5. When observed with SEM, destruction of bonding was observed between resin matrix and filler. 6. When observed with CLSM, degradation layer depth of composite resin surface was observed.

• Composites Research
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• v.18 no.2
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• pp.20-29
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• 2005

To evaluate the flexural deformation and strength of composite motor case above the glass transition temperature$(T_g),\;170^{\circ}C$, of resin material, a finite element analysis(FEA) model in which material non-linearity and progressive failure mode were considered was proposed. The laminated flexural specimens which have the same lay-up and thickness as the composite motor case were tested by 4-point bending test to verify the validity of FEA model. Also. mechanical properties in high temperature were evaluated to obtain the input values for FEA. Because the material properties related to resin material were highly deteriorated in the temperature range beyond $T_g$, the flexural stiffness and strength of laminated flexural specimen in $200^{\circ}C$ were degraded by also $70\%\;and\;80\%$ in comparison with normal temperature results. Above $T_g$, the failure mode was changed from progressive failure mode initiated by matrix cracking at $90^{\circ}$ ply in bottom side and terminated by delamination at the center line of specimen to fiber compressive breakage mode at top side. From stress analysis, the progressive failure mechanism was well verified and the predicted bending stiffness and strength showed a good agreement with the test results.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.4
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• pp.1483-1491
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• 2010

The purpose of this study was to examine current status of the types of dental filling materials and preventive materials among Korean children in mixed dentition. Seven elementary schools were randomly selected from four metropolitan regions in South Korea. The total of 711 children aged 9-10 years old were examined with their parents’ informed consents. Oral examination was conducted by one trained dentist. The mean number of dfs was $7.9{\pm}8.0$ ($ds=1.3{\pm}2.5,\;fs=6.6{\pm}7.6$) and DMFS was $1.4{\pm}2.2$ ($DS=0.2{\pm}0.8,\;FS=1.1{\pm}2.1$). The average of filled surfaces using amalgam, composites, sealants, and others were $2.8{\pm}3.9,\;1.6{\pm}2.8,\;2.9{\pm}3.2$, and $4.5{\pm}7.0$, respectively. The use of dental filling material according to region, the amalgam was the highest in Daegu and the resin was the highest in Pusan. In permanent teeth, about 70% of total filling surfaces had sealant and about 20% was resin fillings, and the proportion of amalgam filling surfaces was less than 10%.

• Composites Research
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• v.29 no.4
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• pp.216-222
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• 2016

Ring-opening metathesis polymerization of p-dicyclopentadiene (DCPD) can be performed using the tungsten type catalyst. This reaction usually progresses in nitrogen condition, because the catalysts are extremely sensitive in air condition. To solve this problem, DCPD resin with tungsten (W) was cured using hot press after stirring of DCPD A and B liquid in air condition. Mechanical properties of DCPD were improved by reducing microvoid occurrence successfully by using hot press method. It might be because hot press could provide sufficient press on DCPD specimen. Addition of catalyst was not effective for the curing of resin in a short time. During polymerization, pressure and temperature had a great influence on the mechanical properties of DCPD.

• Composites Research
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• v.16 no.2
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• pp.54-61
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• 2003

In this study, manufacturing process for microcapsules with the self-healing agent was introduced and the characteristics of microcapsules manufactured by varying with various manufacturing process variables were evaluated through a particle size analyzer, an optical microscope, and a TGA. Urea-formaldehyde resin was used for the thin wall of microcapsules and DCPD (dicyclopentadiene) was used for the self-healing agent. The various manufacturing process variables, such as (1) 24hr, 40hr, 48hr, 60hr of the solution time of the EMA copolymer, (2) pH3.5, pH4.0, pH4.5 of the hydrogen ion concentration of the emulsified solution, (3) 400rpm, 500rpm, 600rpm, 1000rpm of the agitation speed of the emulsified solution, (4) $50^{\circ}$, $55^{\circ}$, $60^{\circ}$ of the reaction temperature of the emulsified solution, were considered. According to the results, the particle size distribution of microcapsules was affected on the agitation speed, and the thermal stability of microcapsules was influenced by the solution time of the EMA copolymer, the hydrogen ion concentration, and the reaction temperature of the emulsified solution. Therefore, suitable manufacturing process variables should be applied to obtain thermally stable microcapsules capable of containing the healing agent capable until the thin wall of microcapsules were to be burned.

• Restorative Dentistry and Endodontics
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• v.29 no.4
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• pp.386-398
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• 2004

Objectives: The purpose of this study was to observe the reaction kinetics and the degree of polymerization of composite resins when cured by different light sources and to evaluate the effectiveness of the blue Light Emitting Diode Light Curing Units (LED LCUs) compared with conventional halogen LCUs. Materials and Methods: First, thermal analysis was performed by a differential scanning calorimeter (DSC). The LED LCU (Elipar Freelight, $320{\;}mW/\textrm{cm}^2$) and the conventional halogen LCU (XL3000, $400{\;}mV/\textrm{cm}^2$) were used in this study for curing three composite resins (SureFil, Z-250 and AEliteFLO). Second. the degree of conversion was obtained in the composite resins cured according to the above curing mode with a FTIR. Third, the measurements of depth of cure were carried out in accordance with ISO 4049 standards. Statistical analysis was performed by two-way ANOVA test at 95% levels of confidence and Duncan's procedure for multiple comparisons. Results: The heat of cure was not statistically different among the LCUs (p > 0.05). The composites cured by the LED (Exp) LCUs were statistically more slowly polymerized than by the halogen LCU and the LED (Std) LCU (p < 0.05). The composite resin groups cured by the LED (Exp) LCUs had significantly greater degree of conversion value than by the halogen LCU and the LED (Std) LCU (p =0.0002). The composite resin groups cured by the LED (Std) LCUs showed significantly greater depth of cure value than by the halogen LCU and the LED (Exp) LCU (p < 0.05).

• Journal of Energy Engineering
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• v.26 no.4
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• pp.84-91
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• 2017

Fiber reinforced plastic (FRP) is a typical plastic composite which is fabricated using fiber reinforcement with resin to represent the high strength properties. The mechanical properties of FRP should be determined by a fibrous material, and the studies about the role of fiber as a reinforcement has been an interested subject, whereas a study along the effect of filler is not so big. However, the filler effect must be considered on the properties of the composite, because the filler influence on the plastic or resin compound which reacts as a matrix material of the composite. Thus, in this work, we studied the filler effect with size and content using $3-6{\mu}m$ of ground calcium carbonate. The specimen was prepared by sheet molding compound (SMC) method, and the mechanical properties were compared with bending strength and tensile strength. As a result, it was confirmed that the size and contents of calcium carbonate affected the strength of composites, and the condition of $2.8{\mu}m$ which was the smallest size condition showed the highest strength.

• Composites Research
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• v.24 no.6
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• pp.56-63
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• 2011

The objective of this study is to investigate appropriate bonding methods of solar cells in order to apply solar cells, which have been receiving particular attention as a renewable energy due to fossil energy depletion and environment issues, to composite structures. Back-contact solar cells with approximately 24.2% energy conversion efficiency were used in this study. Since silicon-based solar cells are mechanically fragile, the secondary-bonding methods using adhesive were examined in this study. The experiment was conducted with three kinds of bonding materials such as EVA film, Resin film and elastic adhesive. The performance of solar cells for three types of adhesives under mechanical loading on test specimens is conducted. In addition, the measuring equipment was designed to evaluate the performance of the solar cells under mechanical loading in real time and the fracture characteristics depending on bonding materials were evaluated. The reason decreasing solar cells efficiency were analyzed and considered by Fractography. The results show that the solar cell performance is largely affected by bonding techniques. Moreover, the bonding method using elastic adhesive shows best solar cell efficiency.

• Composites Research
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• v.28 no.4
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• pp.168-175
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• 2015

Recently, the applications of carbon fiber reinforced plastics (CFRPs) have become broader than ever when it comes to such industries as automotive, ships, aerospace and military because of their lightweight-ness and high mechanical properties. Thermosetting plastics like epoxy are frequently used as the binding matrix in CFRPs due to their high hardness, wetting characteristics and low viscosity. However, they cannot melted and remolded. For this reason, thermosetting plastic wastes have caused serious environmental problems with the production of fiber reinforced plastics. Thus, many studies have focused on the carbon fiber reinforced thermoplastics (CFRTPs) and recycling carbon fiber. In this study, recycled carbon fiber (RCF) was prepared from CFRPs using a pyrolysis method, which was employed to separate resin and carbon fiber. The degree of decomposition for epoxy resin was confirmed from thermal gravimetric analysis (TGA) and scanning electron microscope (SEM). The RCF was cut and ground to prepare a carbon fiber composite sheet (CFCS). CFCS was manufactured by applying recycled carbon fibers and various thermoplastic fibers. Various characterizations were performed, including morphological analyses of surface and cross-section, mechanical properties, and crystallization enthalpy of CFCS at different cooling conditions.