• The Journal of Korean Academy of Prosthodontics
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• v.46 no.3
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• pp.298-306
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• 2008

STATEMENT OF PROBLEM: Effect of surface treatment of ceramic under loading does not appear to have been investigated. PURPOSE: The aim of this study was to investigate the effect of surface treatment of esthetic ceramic, which is performed to increase the bonding strength, on the fracture stress under controlled cyclic loading condition. MATERIAL AND METHODS: Sixty 1.0 mm-thick specimens were made from Mark II Vitablocs (Vita Zahnfabrik, Germany) and divided into 3 groups: polished (control), sandblasted, and etched. Specimens of each group were bonded to a dentin analog material base including micro-channels to facilitate the flow of water to the bonding interface. Bonded ceramics were cyclically loaded with a flat-end piston in the water (500,000 cycles, 15Hz). Following completion of cyclic loading, specimens were examined for subsurface crack formation and subsequent stress was determined and loaded to next specimen by the staircase method according to the crack existence. RESULTS: There were significant differences of mean fatigue limit in the sandblasted (222.86 ${\pm}$ 23.42 N) and etched group (222.86 ${\pm}$ 14.16 N) when compared to polished group (251.43 ${\pm}$ 10.6 N) (P<.05; Wald-type pair-wise comparison and post hoc Bonferroni test). Of cracked specimens, surface treated group showed longer crack propagation after 24 hours. All failures originated from the radial cracking without cone crack. Fracture resistance of this study was very low and comparable to failure load in the oral cavity. CONCLUSION: Well controlled cyclic loading could induce clinically relevant cracks and fracture resistance of Mark II ceramic was relatively low applicable only to anterior restorations. Surface treatment of inner surface of feldspathic porcelain in the matsicatory area could influence lifetime of restorations.

• Journal of the Korean Geosynthetics Society
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• v.16 no.4
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• pp.113-118
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• 2017

Numerical analysis was carried out using a finite element analysis program to analyze the behavior characteristics of enlarged cylinder type anchor. It was found that the ultimate resistance of enlarged cylinder type anchor increases with the enlargement angle from numerical analysis for various enlargement angle cases. In the case of $30-60^{\circ}$ of enlargement angle, the deformation and stress distribution characteristics in anchor are similar regardless of enlargement angle. However, when the same tensile force is applied, there is a difference in the degree of frictional resistance because of difference of displacement of top of grouting zone. Also, it was found that the maximum compressive force and tensile force were generated at the cone of the upper portion of the grouting zone, and tensile fracture of the upper grouting portion is likely to occur.

• Fire Science and Engineering
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• v.31 no.4
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• pp.12-19
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• 2017

The present paper is a study on the performance characteristics of organic-inorganic hybrid flame retardants. MDF plywood has been used, that are being used for the interior decoration of building structures, to make the samples for experiment according to the existing or non-existing treatment of organic-inorganic hybrid flame resistants. Later, the experiment on the measurement of flame retardant performance using a $45^{\circ}$ flammability tester and the experiment on the measurement of combustion characteristic using a cone calorimeter have been proceeded to confirm the performance characteristic of organic-inorganic hybrid flame retardants. From the result of experiments, it has been confirmed that both organic-inorganic hybrid flame retardants have merits of inorganic and organic substances, and that heat resistance, durability and adhesiveness have been largely improved. The performance on the flame retardant has also appeared with excellent effect such as the reduced generation of combustion gas and the decreased generation of smoke.

• Polymer(Korea)
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• v.32 no.2
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• pp.125-130
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• 2008

A commercial cyclic diphosphonate ester (TPMP) and melamine (MA) was combined and added to polyamide 6 (PA6) to prepare the fire retardant PA6. An increase of the oxygen index to 28.6 as well as an improvement of the UL-94 classification to V-0 rating was observed. Cone measurements explained the rate of heat release (RHR) decreased and TGA showed the early decomposition and high solid residue due to co-addition of TPMP and MA, suggesting the occurrence of synergistic effect of TPMP and MA on fire resistance of PA6. The morphology of the char developed during combust ion showed the appearance of thick, intumescent cells on the surface of retardant PA6, which protects the underlying material from the action of the heat flux or flame and limits the diffusion of combustible volatile products towards the flame and oxygen.

• Journal of the Korean GEO-environmental Society
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• v.2 no.3
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• pp.89-99
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• 2001

In this study, the numerical analysis of piezocone penetration and dissipation tests has been conducted using the Modified Cam-Clay model, which is generally used in soil mechanics. The Modified Cam-Clay model and related mathematical equations in finite element derivation have been formulated in the Updated Lagrangian reference frame to take the large displacement and finite strain nature of piezocone penetration into consideration. The cone tip resistance, the pore water pressure, and the dissipation curve obtained from the finite element analysis have been compared and investigated with the experimental results from piezocone penetration test performed in Yangsan site. The numerical results showed good agreement with the experimental results; however, the better numerical simulation of the continuous and deep penetration needs further research.

• Journal of the Korean Geotechnical Society
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• v.16 no.4
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• pp.191-199
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• 2000

In this research, the finite element analysis of piezocone penetration and dissipation tests has been conducted using the anisotropic elastoplastic-viscoplastic bounding surface model, virtual work equation, and theory of mixtures formulated in the Up[dated Lagrangian reference frame for the large deformation and finite strain nature of piezocone penetration. The formulated equations have been implemented into a finite element program. The cone resistance, excess pore water pressure, and dissipation of excess pore water pressure from the finite element analysis have been compared and investigated. An effective simulation could be performed with the use of the anisotropic and viscous soil model. The finite element formulations and the results are described in part 'I' and part 'II' respectively.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.1528-1537
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• 2005

The purpose of this study is investigated the method for estimation of the liquefaction on the reclaimed land, located in Incheon and assessed the ability of liquefaction under the condition of criteria, which is the magnitude '6.5' of seismic on the basis of the domestic seismic characteristics. Performed not only field test but the experiment as well to study how the fine content would affect into the dreging and reclaimed land and also estimated the safety factor through the empirical method and anticipated detail method based on the results. Within the reclaimed land, there are many sized soils which are almost extended from well-graded silty sand(SM) to poor-graded fine grained sand, and which have the condition, so called, the liquefaction which is easily to bring into under the circumstances within the ground. However, partly, now that the soil is mixed with silt and silty clay which include the content of fine grained dust quite a bit, the difficulties and inconveniences has been expected while trying to find the ratio of cyclic resistance, but finally Seed and Idriss method showed the most way when we estimate the safety factor on the liquefaction.

• Composites Research
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• v.13 no.4
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• pp.75-82
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• 2000

A small diameter steel-ball impact experiment was performed to study the impact resistance of the surface of glass plates bonded with glass fabric/epoxy lamina. Five kinds of materials were used in this study: soda-lime glass plates, glass/epoxy lamina(one layer)-bonded and unbonded glass plates, glass/epoxy lamina(three layers)-bonded and unbonded glass plates. The range of impact velocity was 40 120m/s. The maximum stress and absorbed fracture energy were measured on the back surface of glass plates. With increasing impact velocity, various types of surface cracks such as ring, cone, radial and lateral cracks took place in the interior near the impacted site of glass plates. The cracks drastically decreased with glass/epoxy lamina coating. The surface fracture behavior could be evaluated using the maximum stress and the absorbed fracture energy.

• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.2
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• pp.68-77
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• 2019

C/SiC composites were developed by a liquid silicon infiltration(LSI) method for use as heat-resistant parts of solid and liquid rocket propulsion engines. The heat resistance characteristics according to the composition ratio (carbon / silicon / silicon carbide) were evaluated by specimen test through arc plasma, supersonic torch test. An ablation equation for oxidation reactions was presented. Through the combustion test it was verified that various parts such as nozzle insert, exit cone and combustion chamber heat resistant parts for rocket propulsion can be manufactured and proved high ablation performance and thermal structure performance.

• Journal of the Korean Geotechnical Society
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• v.24 no.4
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• pp.89-100
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• 2008

Applying graph and correlation developed in other countries to the domestic field has limits. Therefore, it is necessary that Piezocone factor should be determined by including ground characteristics obtained from various test results in the domestic site for better application. In this study, laboratory tests and field tests were performed to find the characteristics of soft ground which was widely distributed around Siwha lake. A comparative analysis of these tests with Piezocone penetration test was performed and the Piezocone factor was estimated by correlationship analysis of undrained shear strength and cone resistance. Also, an appropriate Piezocone factor in the study site was reestimated by utilizing statistical analysis method for deriving reliable result.