• Restorative Dentistry and Endodontics
• /
• v.26 no.2
• /
• pp.180-187
• /
• 2001

The structure of current guides is largely illogical and without any rational use of color ordering. The shade guides are generally made of plastic (rather than the actual composite material) and do not accurately depict the true shade. translucency. or opacity of the composite resin after polymerization. To solve this problem, information based on evaluations of natural teeth and material that use the same method and experimental conditions is necessary. The present investigation measured the color of natural maxillary anterior teeth in vivo and compared the results with those of composite resins. 269 Korean subjects were selected for this study. Intact central incisor. lateral incisor. and canine were selected. The clinical crowns were free of caries or restorations. The middle site of the coronal portion on the labial surface of the tooth was measured by Chroma Meter. The five light activated. resin-based materials (Amelogen, Denfil, Elitefil, Spectrum, Z100) were used in this study. Resin composite was condensed into plastic mold with a diameter of 8mm and a thickness of 4mm. pressed between glass plates to flatten the surfaces. and polymerized using a Visilux II visible light activation unit. The surfaces were polished sequentially on wet sandpaper. Color measurements of each specimen were accomplished by Chroma Meter. A computer program that compares each tooth color with each composite resin color was written and the minimum CIELAB color difference ($\Delta$E$^*$) between tooth and each material was calculated. Under the conditions of this study: 1. Teeth tend to become darker with advancing age. 2. Canines were darker. more yellow. and less green than incisors. 3. The teeth from the women were lighter. more green. and less yellow than the male teeth. 4. In general. composite resins were lighter. more green. and less yellow than teeth. Deficiencies were noted in Hues in YR range. 5. Mean color differences between the five composite resin products and teeth were detectable to the naked eye($\Delta$E$^*$>1.0). 6. In comparing the mean $\Delta$E$^*$ values of materials. Spectrum showed the least followed by Z100, Elitefil, Amelogen, Denfil in increasing order.

• Restorative Dentistry and Endodontics
• /
• v.17 no.1
• /
• pp.69-82
• /
• 1992

An experimental investigation of the physical properties of light curing composite resin P-50 was performed, in which an argon ion laser beam was irradiated. The physical and mechanical properties of laser polymerized composite resin were determined by measuring the compressive strength, diametral tensile strength, curing depth and microhardness depending upon the experimental conditions such as the laser irradiation time(10sec, 20sec, 30sec) and laser power(300mW, 500mW, 1000mW). These observations were compared with a conventional visible light curing technique. In addition, to evaluate the marginal adaptation, Class V cavity was prepared on the buccal or lingual surface of the extracted premolar and filled with P-50 light curing resin. The test samples were irradiated with both light sources so that the interface between the restoration and the tooth structure were observed under scanning electron microscope. The most of physical and mechanical properties of the laser cured resin showed a remarkable improvement than those treated with the conventional light source, while the observations with the scanning electron microscope provided no significant difference for two polymerized sources. From the results in the experiment it appears that the potential of an argon ion laser is of important value of the use in the polymerization of composite resin.

• Restorative Dentistry and Endodontics
• /
• v.35 no.2
• /
• pp.65-68
• /
• 2010

Due to the improvement of the composite resin and esthetic desire of the patient, amalgam restoration has been replaced by composite resin. However, still there are many unsolved problems, for example, technique sensitivity, polymerization shrinkage stress and limited mechanical properties. These factors results in fracture of the restoration and secondary caries of the tooth. Also the use of the dental bonding system should be used for the retention of the restoration. In this paper, I want to talk about the present and the future of the remineralizing component released from dental composite resin to overcome the secondary caries and there possibility in the clinical use.

• Steel and Composite Structures
• /
• v.9 no.1
• /
• pp.39-58
• /
• 2009

Composite joints, considering the composite action of steel and concrete, exhibit, in general, high strength and high ductility. As a consequence, the use of this type of joint has been increasing in many countries, especially in those that are located in earthquake-prone regions. In this paper, a hysteretic model with pinching is presented that is able to reproduce the cyclic response of steel and composite joints. Secondly, the computer implementation and adaptation of the model in a spring element within the computer code Seismosoft is described. The model is subsequently calibrated using a series of experimental test results for composite joints subjected to cyclic loading. Finally, typical parameters for the various joint configurations are proposed.

• Advances in nano research
• /
• v.2 no.4
• /
• pp.199-210
• /
• 2014

Carbon nanotubes have exceptional mechanical, thermal and electrical properties, and are considered for high performance structural and multifunctional composites. In the present study, the natural frequencies of aligned single walled carbon nanotube (CNT) reinforced composite beams are obtained using shear deformable composite beam theories. The Ritz method with algebraic polynomial displacement functions is used to solve the free vibration problem of composite beams. The Mori-Tanaka method is applied to find the composite beam mechanical properties. The continuity conditions are satisfied among the layers by modifying the displacement field. Results are found for different CNT diameters, length to thickness ratio of the composite beam and different boundary conditions. It is found that the use of smaller CNT diameter in the reinforcement element gives higher fundamental frequency for the composite beam.

• Steel and Composite Structures
• /
• v.24 no.1
• /
• pp.79-91
• /
• 2017

Free vibrations of steel-concrete composite beams are analyzed by using the dynamic stiffness approach. The coupled equations of motion of the composite beams are derived with help of the Hamilton's principle. The effects of the shear deformation and rotary inertia of the two beams as well as the transverse and axial deformations of the stud connectors are included in the formulation. The dynamic stiffness matrix is developed on the basis of the exact general solutions of the homogeneous governing differential equations of the composite beams. The use of the dynamic stiffness method to determine the natural frequencies and mode shapes of a particular steel-concrete composite beam with various boundary conditions is demonstrated. The accuracy and effectiveness of the present model and formulation are validated by comparison of the present results with the available solutions in literature.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2004.10a
• /
• pp.220-223
• /
• 2004

The weight reduction of carbody structures is of great concern in developing high speed tilting train for the normal operation of tilting system. The use of composite materials for the carbody structures has many advantages due to their excellent material properties. In this paper, finite element analysis was conducted to analysis and design the composite structure of Tilting Train eXpress(TTX). According to JIS E 7105, static load tests were performed and the structural safety of the composite carbody structure was verified by conducting finite element analysis of the model to which reinforcing frame are added in the composite carbody structure. In addition, modal analysis was conducted to estimate the natural frequency of a train.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2005.11a
• /
• pp.243-246
• /
• 2005

The weight reduction of carbody stl1lctures is of great concern in developing high speed tilting train for the normal operation of tilting system. The use of composite materials for the carbody structures has many advantages due to their excellent material propel1ies. In this paper, finite element analysis was conducted to verify the safety of the composite structures of Tilting Train eXpress(TTX). A train prototype with carbon/epoxy composite carbody was manufactured to perform static loading tests according to JIS E 7105. The loading tests were simulated by FE analysis to compare with the test results. To obtain more accurate and detailed result of stress distribution in local region of carbody, the submodeling approach was used. The submodeling analysis results showed the high levels of stress concentration occured on window frame part of TTX as the loading test results did.

• Journal of the Korean Society for Advanced Composite Structures
• /
• v.1 no.4
• /
• pp.6-12
• /
• 2010

This study investigates how to apply composite material to the blast loading protection devices, mainly used for military purpose. Traditionally, earth-filled blast walls have been used for protecting important parts of military facilities and personnels. However these types of blast walls show difficulty in fabrication and portability because of their nature of heavy weight. Composite materials are known to have relatively higher specific stiffness and strength than any other metallic and earth-filled materials such as sand and gravels. Totally 4 times of TNT blast experiments were performed on the carbon/epoxy blast walls. After the end of each test, the improvement of blast wall was implemented to the structure. The test results show that the use of composite material in the blast protecting area is the one of very effective and reliable alternatives.

• Journal of the Korean Society for Precision Engineering
• /
• v.15 no.10
• /
• pp.203-208
• /
• 1998

Carbon fiber epoxy composite materials are widely used in the structures of aircrafts, robots and other machines because of their high specific strength, high specific stiffness and high damping. In order for the composite materials to be used in the aircraft structures or machine elements, accurate surfaces for bearing mounting or joints must be provided, which require precise machining. In this paper, the machinability characterisitcs of the drilling operation of the carbon fiber epoxy composite materials was experimentally investigated. The experimental results are as follows 1.The entrance of hole is very good manufacturing existing, but exit come to occur sever surface exfoliation. 2. The cutting force in drilling of the carbon fiber epoxy composite materials is decreased as the drilling speed increased. 3.The hole of the carbon fiber epoxy composite materials is not good manufacturing by use of the standard twist, therefore, the new drill designed in order to accurate hole.