• Proceedings of the Korea Concrete Institute Conference
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• 1995.10a
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• pp.366-371
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• 1995

it is extremely difficult to perform the dynamic experiments with full-scale specimens. For this reason, small-scale structural models offer an attractive means to peform dynamic loading experiments. The purpose of this reserch is to estabilish the reliance for modeling techniques of small-scale specimens subjected to dynamic cyclic loading. This research focused on the similitude requirements for reinforced concrete frame structures subjected to dynamic cyclic loading. Length scale ratio of specimens were 1:2:4, and six specimens were tested at the frequencies of 0.0025Hz~2.0Hz. It was confirmed that modeling techniques based on the similitude requirements were useful method to evaluate the behavior of full-size R/C structures subjected to earthquake type loading.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1998.10a
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• pp.17-24
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• 1998

Plasma-sprayed coatings were obtained by spray-dried $Cr_2O_3$ powder with and without Mo addition. A reciprocal type tribo-tester was employed to examine friction and wear behavior of the specimens at room temperature. The composition and the worn surface of coated specimens were observed by XRD and SEM. The results showed that friction Coefficient of the Mo added specimens were lower than one of $Cr_2O_3$ specimen. But $Cr_2O_3$ specimen had a lower wear loss. Protecting layer were observed at the worn surface of coated specimens with Mo addition.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.315-320
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• 2003

Two different strength types of plain concrete plate specimens (200$\times$200$\times$60mm) were tested under different biaxial load combinations. The specimens were subjected to biaxial combinations covering the three regions of compression-compression, compression-tension, and tension-tension. The loading platens with Teflon pads were used to reduce a confining effect in boundary surface between the concrete specimen and the solid platen. The principal deformations in the specimens were recorded, and the failure modes along with each stress ratio were examined. Based on the strength data, the failure envelops were developed for each type of plain concrete. The biaxial stress-strain responses of concrete plate specimens for three biaxial loading regions were also plotted. The test data indicated that the strength of concrete under biaxial compression ($f_2 / f_1$$_1$=-1/-1) is about 17 percent larger than under uniaxial compression.

• Proceedings of the KACD Conference
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• 2001.11a
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• pp.578.2-578
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• 2001

The purpose of this study was to evaluate the color change of composite resin polymerized with three type of light curing units. Composite resin (Z100, shade A2) were condensed inside a 2 mm thick metal mold with 7 mm diameter and devided into three groups. Twenty specimens of each light curing units were made. Group 1 : the specimens were polymerized with Apollo 95E (AP) for 3 seconds ($1370{\;}㎽/\textrm{cm}^2$). Group 2: the specimens were polymerized with Spectrum 800 (SP) for 10 seconds ($250{\;}㎽/\textrm{cm}^2$) and 30seconds ($700{\;}㎽/\textrm{cm}^2$). Group 3: the specimens were polymerized with XL 3000 (XL) for 40 seconds ($480{\;}㎽/\textrm{cm}^2$).(omitted)

• Journal of Korea Foundry Society
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• v.27 no.1
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• pp.24-30
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• 2007

The effects of C, Si and RE additions on the tendency of chill formation of ductile cast iron obtained from metal mold casting were investigated. In case of metal mold cast, the ductile cast iron with 2.5%Si had pearlitic matrix, and specimens with 2.9%Si had bull's eye type regardless of C contents. As-cast specimen with a large amount of fine graphites could be obtained by adding 0.2% RE. Normalizing process was necessary to remove carbide and form a large amount of spheroidal graphites for the as-cast specimens. Good mechanical properties could be obtained by heat-treatment of as-cast specimens with pearlitic matrix. Normalizing the specimens with RE caused the reduction in mechanical properties.

• Computers and Concrete
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• v.2 no.5
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• pp.367-380
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• 2005

Recent earthquakes have shown that many of existing buildings in Iran sustain heavy damage due to defective seismic details. To assess vulnerability of one common type of buildings, which consists of low rise framed concrete structures, three defective and three standard columns have been tested under reversed cyclic load. The substandard specimens suffered in average 37% loss of strength and 45% loss of energy dissipation capacity relative to standard specimens, and this was mainly due to less lateral and longitudinal reinforcement and insufficient sectional dimensions. A relationship has been developed to introduce variation of plastic length under increasing displacement amplitude. At ultimate state, the length of plastic hinge is almost equal to full depth of section. Using calibrated hysteresis models, the response of different specimens under two earthquakes has been analyzed. The analysis indicated that the ratio between displacement demand and capacity of standard specimens is about unity and that of deficient ones is about 1.7.

• Journal of the Korea Concrete Institute
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• v.23 no.4
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• pp.405-411
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• 2011

Using combinations of carbon and glass fiber composites normally used for strengthening of concrete structures, the hybrid effect from strengthening concrete structures using the composite is studied. To produce the hybrid effects, the specimens were made with optimum proportions of carbon fibers with glass fibers. Then, direct tensile tests were conducted on the hybrid FRP (fiber reinforced polymer) specimens. Unlike the woven fiber sheet currently used in construction sites, the FRP specimens have to be directly combined with the fibers, which make the work very complicated. Therefore, direct tensile test specimens manufacturing method based on the combination of high-tension carbon fibers and E-type glass fibers was proposed and the effects of hybridization is studied through the direct tensile test. By comparing the ductility index, the modulus of elasticity, and the stress-strain curves of the specimens, the most optimum glass to carbon fiber combination ratio for the hybrid FRP was found to be 9 to 1 with ductile K-type epoxy. The study results are discussed in detail in the paper.

• The Journal of Advanced Prosthodontics
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• v.12 no.5
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• pp.273-282
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• 2020

PURPOSE. To assess shear bond strengths (SBS) of resin composites on aged and non-aged prosthetic materials with various surface treatments. MATERIALS AND METHODS. Cerasmart (CE), Vita Enamic (VE), Vita Mark II (VM), and IPS e.max CAD (EC) blocks were sliced, and rectangular-shaped specimens (14 × 12 × 1.5 mm; N = 352) were obtained. Half of the specimens were aged (5000 thermal cycles) for each material. Non-aged and aged specimens were divided into 4 groups according to the surface treatments (control, air abrasion, etching, and laser irradiation; n = 11) and processed for scanning electron microscopy (SEM). The repair procedure was performed after the surface treatments. SBS values and failure types were determined. Obtained data were statistically analyzed (P≤.05). RESULTS. The material type, surface treatment type, and their interactions were found significant with regard to SBS (P<.001). Aging also had a significant effect on prosthetic material-resin composite bonding (P<.001). SBS values of non-aged specimens ranged from 12.16 to 17.91 MPa, while SBS values of aged specimens ranged from 9.46 to 15.61 MPa. Non-aged VM in combination with acid etching presented the highest score while the control group of aged CE showed the lowest. CONCLUSION. Etching was more effective in achieving durable SBS for VM and EC. Laser irradiation could be considered as an alternative surface treatment method to air abrasion for all tested materials. Aging had significant effect on SBS values generated between tested materials and resin composite.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.1
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• pp.183-192
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• 2008

Generally, application of steel pipe pile as deep foundation member needs special requirement for the connection method between steel pipe pile and concrete footing. Even though two types of connection method are suggested in the korea highway bridge code, type-B method is prevalent. In this study, vertical, lateral, and tension loading test are done for two types of type B connection to review stress concentration, formation and behavior of imaginary RC column in the footing. Welding type and hook type as the connection method are considered in this study. Test results show that welding type have the more reserve capacity than hook type and the specimens connected by the welding type behave as the imaginary RC column in the footing. However, the specimens connected by the hook type did not behave as the imaginary RC column in the footing but behave as the hinge.

• Journal of Periodontal and Implant Science
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• v.29 no.1
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• pp.209-231
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• 1999

Even though titanium(Ti) and its alloys are the most used dental implant materials, there are some problems that Ti wears easily and interferes normal osteogenesis due to the metal ions. Ti coated with bioactive ceramics such as hydroxyapatite has also such problems as the exfoliation or resorption of the coated layer, Recent studies on implant materials have been proceeding to improve physical properties of the implant substrate and biocompatibility of the implant surfaces. The purpose of the present study was to examine the physical property and bone tissue compatibility of bioinert nitrides ion plated Ti, Button type specimens(14mm in diameter, 2.32rrun in height) for the abrasion test and cytotoxicity test and thread type implants(3.75mm in diameter, 6mm in length) for the animal experiments were made from Ti(grade 2) and 316LVM stainless steel. Ti specimens were ion plated with TiN, ZrN by the low temperature arc vapor deposition, and the depth profile of the TiN/Ti, ZrN/Ti ion plated surface was examined by Auger Electron Spectroscopy. Three kind of button type specimens .of TiN/Ti, ZrN/Ti and Ti were used for abrasion test, and HEPAlClC7 cells and CCD cells were cultivated for 4 days with the specimens for cytotoxicity test. Thread type implants of TiN/Ti, ZrN/Ti, Ti, 316LVM were implanted on the femur of 6 adult dogs weighing 10kg-13kg. Two dogs were sacrified for histological examination after 45 days and 90 days, and four dogs were sacrified for the removal torque test of the implant') after 90 days. The removal torque force was measured by Autograph (Shimadzu Co., AGS-1000D series, Japan). Abrasion resistance of TiN/Ti was the highest, and that of ZrN/Ti and Ti were followed. The bioinert nitride ion plated Ti had much better abrasion resistance, compared with Ti, In the cytotoxicity test, the number of both cells were increased in all specimens, and there were no significant difference in cytotoxic reaction among all groups (p>0.1), In histological examination, 316LVM showed the soft tissue engagement in interface between the implant and bone, but the other materials after 45 days noted immature new bone formation in the medullary portion along the implant surface, and those after 90 days showed implant support by new bone formation in both the cortical and the medullary portion, The removal torque force of Tilv/Ti showed significantly higher than that of Ti(p(O,05). The difference in removal torque force between TiN/Ti and ZrN/Ti was not significant(p>0.05), and that of 316LVM was lowest among all groups(p<0.05). These results suggest that bioinert nitrides ion plated Ti can resolve the existing problems of Ti and bioactive ceramics, and it may be clinically applicable to human.