• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.04a
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• pp.191-194
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• 2005

Impact properties of glass/Kevlar hybrid composites which have 3-D braided structures were studied. Results were compared to those of composites made of only glass fibers where the same epoxy resin were used as matrix. Absorbed impact energies evaluated through the combination of the data from the impact tester and high speed camera were compared to each other. In order to see the difference between the damaged area distribution CCD camera captures were performed.

• Macromolecular Research
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• v.10 no.4
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• pp.236-239
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• 2002

Centrifugation is a method to create functionally graded materials (FGM) with a thermosetting matrix. In this study the movement of short carbon fibers in an epoxy resin during the centrifugation process was modeled to determine the fiber distribution in the final product. For this purpose a form factor K was introduced to modify a set of equations that was previously shown to be valid for the motion of spheres. It was shown that the results of the simulation were in good agreement with the experimental data, when an empirical K factor of four was chosen.

• Composites Research
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• v.13 no.2
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• pp.72-80
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• 2000

Effect of graphite powder addition on the mechanical properties of carbon fiber reinforced carbon composites (C/C composites) was investigated. Greenbody (G/B) with 0~30wt.% graphite powder addition to phenol resin was prepared and carbonized at $1000^{\circ}C$ to make C/C composites. Flexural strengths of 20wt.% graphite powder additions showed maximum values in the both case of G/B and C/C composites. But, at the graphite addition over 20wt.%, there was negative effect due to the matrix inhomogeneity. Flexural strength of cured resin without graphite Powder was higher than that with graphite. However, flexural strength of carbonized resin with graphite increased three times as much as that of carbonized resin without graphite. Because the addition of graphite powder effects the restraint of shrinkage after carbonization and the deflection of crack path. In Mode II ENF test, energy release rates($G_{II}$) of G/B and C/C composites with the 20w1.% addition of graphite were both increased. But, the addition of graphite was more effective to the increase of $G_{II}$ in C/C composites than that in G/B.

• Journal of Dental Rehabilitation and Applied Science
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• v.21 no.1
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• pp.69-81
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• 2005

The objective of this study was to evaluate the toothbrush abrasion characteristics of class V restorations. Thirty extracted human premolars, which were collected from oral surgery clinics were used. We mounted five teeth in a metal ring mold of 50 mm in diameter and 15 mm in height using chemically cured acrylic resin. Class V cavities were prepared in lingual cervical root surfaces and restored using one of following restorative materials : Dentin Conditioner/Fuji II LC (Group FL), All Bond II/Z-250 (Group ZT), One-up Bond F/Palfigue Estelite (Group PE), F2000 Primer/Adhesive (Group FT), and Prime & Bond 2.1/Dyract AP (Group DR). They were stored under distilled water at $37^{\circ}C$ for seven days. The toothbrush abrasion test was conducted using a wear testing machine of pin-on disk type under a load of 1.5 N for 100,000 cycles. We have examined the bonded interfaces, the changes of surface roughness and color of abraded surfaces. From this experiment, the following results were obtained. 1. The change of surface roughness showed high degree: RMGIC>compomer>composite resin (p<0.05). 2. Because of the protrusion and missing of filler particles, SEM observation of abraded surfaces of RMGIC and compomers revealed the increase of surface roughness due to the selective removal of matrix resin. 3. The color change by toothbrush abrasion was affected in large part by the change of $L^*$ and $b^*$ of resin composites (p<0.05). 4. The color change by toothbrush abrasion was so small to detect by human eyes. 5. SEM observation of abraded surfaces revealed the interface bonding was the best in the FT group.

• Polymer(Korea)
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• v.24 no.5
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• pp.721-727
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• 2000

The electrolytic plating of a metallic nickel on carbon fiber surfaces was carried out to improve mechanical interfacial properties of carbon fiber/epoxy resin composites. The surface characteristics of carbon fibers and the mechanical interfacial properties of final composites were characterized by X-ray photoelectron spectroscopy (XPS) and interlaminar shear strength (ILSS), respectively. It was found that the electrolytic Ni-plating conditions significantly affected the degree of adhesion at interfaces between carbon fibers and epoxy resin matrix in a composite system. Especially, the increase of O,$_{1s}$/$C_{1s}$ ratio, production of NiO groups, and formation of metallic nickel on the nickel-plated carbon fiber surfaces led to an increase of the ILSS of the composites. Also, the ILSS of the composites was greatly correlated with the $O_{1s}$/$C_{1s}$ ratio of the carbon fibers treated in this work.is work.

• Journal of the Korean Applied Science and Technology
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• v.33 no.1
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• pp.168-175
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• 2016

The surface of glass fiber bundle was modified with functionalized silanes and phenolic resin to improve the tensile strength as well as the adhesion of glass fiber to matrix phenolic resin. The surface modification of reinforcing glass fiber can play a significant role in controlling whole composite characteristics. We applied surface modification of glass fiber with two different functionalized silanes, such as glycidyltrimethoxysilane(G-silane) and aminopropyltriethoxysilane (A-silane), and phenol formaldehyde(PF) resin in one pot or separated process under different coating compositions and temperatures. Thermal treatment temperature is very important factor to improve the mechanical properties of modified glass fiber. Modified glass fiber bundle treated at $170^{\circ}C$ showed the highest tensile strength of $10.05g_f/D$. Surface analyses by scanning electron microscope(SEM) and FT-IR spectroscopy were used to characterize the surface coatings on glass fiber bundles. Mechanical property changes as functions of treatment conditions and coupling agent types were also explained.

• The Journal of Advanced Prosthodontics
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• v.4 no.4
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• pp.187-191
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• 2012

PURPOSE. The aim of the present study was to assess the effect of ascorbic acid, ethanol and acetone on microtensile bond strength between fiber posts pre-treated with hydrogen peroxide and composite resin cores. MATERIALS AND METHODS. Twenty four fiber posts were pre-treated with 24% hydrogen peroxide and divided into 4 groups as follows: G1: no treatment, as control group; G2: treatment with10% ascorbic acid solution for 5 minutes; G3: treatment with 70% ethanol solution for 5 minutes; and G4: treatment with 70% acetone solution for 5 minutes. Each fiber post was surrounded by a cylinder-shaped polyglass matrix which was subsequently filled with composite resin. Two sections from each sample were selected for microtensile test at a crosshead with speed of 0.5 mm/min. Statistical analyses were performed using one-way ANOVA and a post hoc Tukey HSD test. Fractured surfaces were observed under a stereomicroscope at ${\times}20$ magnification. The fractured surfaces of the specimens were observed and evaluated under a SEM. RESULTS. Means of microtensile bond strength values (MPa) and standard deviations in the groups were as follows: G1: $9.70{\pm}0.81$; G2: $12.62{\pm}1.80$; G3: $16.60{\pm}1.93$; and G4: $21.24{\pm}1.95$. G4 and G1 had the highest and the lowest bond strength values, respectively. A greater bond strength value was seen in G3 compared to G2. There were significant differences between all the groups (P<.001). All the failures were of the adhesive mode. CONCLUSION. Application of antioxidant agents may increase microtensile bond strength between fiber posts treated with hydrogen peroxide and composite cores. Acetone increased bond strength more than ascorbic acid and ethanol.

• Restorative Dentistry and Endodontics
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• v.42 no.2
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• pp.125-133
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• 2017

Objectives: This study compared the effect of hexamethyldisiloxane (HMDSO) and ammonia ($NH_3$) plasmas on the bond strength of resin cement to fiber posts with conventional treatments. Materials and Methods: Sixty-five fiber posts were divided into 5 groups: Control (no surface treatment); $H_2O_2$ (24% hydrogen peroxide for 1 min); Blasting (blasting with aluminum oxide for 30 sec); $NH_3$ ($NH_3$ plasma treatment for 3 min); HMDSO (HMDSO plasma treatment for 15 min). After the treatments, the Ambar adhesive (FGM Dental Products) was applied to the post surface (n = 10). The fiber post was inserted into a silicon matrix that was filled with the conventional resin cement Allcem Core (FGM). Afterwards, the post/cement specimens were cut into discs and subjected to a push-out bond strength (POBS) test. Additionally, 3 posts in each group were evaluated using scanning electron microscopy. The POBS data were analyzed by one-way analysis of variance and the Tukey's honest significant difference post hoc test (${\alpha}=0.05$). Results: The Blasting and $NH_3$ groups showed the highest POBS values. The HMDSO group showed intermediate POBS values, whereas the Control and $H_2O_2$ groups showed the lowest POBS values. Conclusion: Blasting and $NH_3$ plasma treatments were associated with stronger bonding of the conventional resin cement Allcem to fiber posts, in a procedure in which the Ambar adhesive was used.

• Tribology and Lubricants
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• v.35 no.2
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• pp.87-93
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• 2019

This work aims to develop a dry lubricant for oilless bush, especially a solid lubricant, thereby creating a coating method with improved properties of anti-friction and load-carrying capacity without oil lubrication. In this work, spherical-shaped powders of thermosetting resin such as polyimide (PI) are mixed with a binder matrix obtained by mixing a fluorocarbon compound resin such as Polytetrafluoroethylene (PTFE) or Ethylene tetra fluoro ethylene (ETFE) with itself or with a non-fluorocarbon thermoplastic resin such as Polyether ether ketone (PEEK). And these dry lubricant mixtures are thickly coated (200-300 mm in the thickness) on the inner surface of the bush by using a wet-typed air-spray deposition method. It was found that the load-carrying capacity of the solid lubricant for excavator bush (60 mm in diameter) that operates under a high load condition (at 40 MPa) is greatly improved owing to the spherical-shaped powders of thermosetting resin. In addition, the coefficient of friction at the sliding surface is also reduced less than 0.1. Thick coating also lowers the contact stress at the edge of a bush that results in better tribological performances. The result suggests that the lubrication performance and durability life of the bush can be remarkably improved even without lubrication (oil or grease).

• Nuclear Engineering and Technology
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• v.55 no.7
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• pp.2613-2620
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• 2023

Excellent thermal neutron absorption performance of boron expands the potential use of boron rich slag to prepare epoxy resin matrix nuclear shielding composites. However, shielding attenuation behaviors and mechanism of the composites against gamma rays are unclear. Based on the radiation protection theory, Phy-X/PSD, XCOM, and ⁶⁰Co gamma ray source were integrated to obtain the shielding parameters of boron rich slag/epoxy resin composites at 0.015-15 MeV, which include mass attenuation coefficient (µ_t), linear attenuation coefficient (µ), half value thickness layer (HVL), electron density (N_eff), effective atomic number (Z_eff), exposure buildup factor (EBF) and exposure absorption buildup factor (EABF).µ_t, µ, HVL, N_eff, Z_eff, EBF and EABF are 0.02-7 cm²/g, 0.04-17 cm^-1, 0.045-20 cm, 5-14, 3 × 10²³-8 × 10²³ electron/g, 0-2000, and 0-3500. Shielding performance is BS4, BS3, BS3, BS1 in descending order, but worse than ordinary concrete. µ and HVL of BS1-BS4 for ⁶⁰Co gamma ray is 0.095-0.110 cm^-1 and 6.3-7.2 cm. Shielding mechanism is main interactions for attenuation gamma ray by BS1-BS4 are elements with higher content or higher atomic number via Photoelectric Absorption at low energy range, and elements with higher content via Compton Scattering and Pair Production in Nuclear Field at middle and higher energy range.