• Restorative Dentistry and Endodontics
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• v.29 no.5
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• pp.454-461
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• 2004

The purpose of this study is to compare and to evaluate the effects of the degree of saturation on the progression of artificial root caries lesion. A total of 8 human premolars without any defects and cracks selected and the cementum were removed and the teeth were cleaned with ultrasonic device and pumice without fluoride. Each tooth was sectioned into 6 pieces and they were ground with #800 sandpaper until they had a thickness of 200pm. Specimens were applied with nail vanish except for the 2-3 mm window area after application of bonding agent. Under the constant pH, the specimens were divided into 6 groups (degree of saturation: 0.1415, 0.1503, 0.1597, 0.1676, 0.1771. 0.1977). Each group was immersed in acid buffer solution for 1. 2, 3, 5 days under controlled temperature ($25^{\circ}C$) and imbibed in water and examined using the polarizing microscope. The results were as follows 1. Although the degree of saturation of demineralization solution decreased, the depth of penetration in the dentin was constant. 2. Erosion was observed on the surface of all the teeth in the group I, II. In the group III, IV, V, surfaces were not changed. The teeth in the group VI showed the more mineralized surface but not the shape of the dentinal tubules distinctively. 3. In all groups, the lesion progressed rapidly at the first day of the experiment, but increased gradually as time elapsed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.38 no.3
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• pp.429-438
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• 2018

Cone and T-bar penetrometers have been frequently used to estimate the undrained shear strength of clay. For small-size model tests, miniature penetrometers should be used but their correlation factors have not been well published. In this study, a testing setup was developed to derive empirical factors of the miniature cone and T-bar penetrometers. A 350mm-diameter chamber and kaolin clay were utilized to prepare soil specimens consolidated under four different pre-consolidation pressures controlling undrained shear strength. Two miniature cones with two diameters of 10-mm and 16-mm and a T-bar penetrometer with 10-mm diameter were used to investigate boundary effect, penetration rate effect, and diameter and shape effect. Unconsolidated-undrained triaxial tests were carried out with samples taken from the specimens to measure undrained shear strength. Finally, empirical factors for the penetrometers were constructed to correlate tip resistance to undrained shear strength.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.2
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• pp.387-398
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• 2002

The impact response and damage of CLAS panel was investigated experimentally. The facesheet material used was RO4003 woven-glass hydrocarbon/ceramic and the core material was Nomex honeycomb with a cell size of 3.2mm and a density of 96 kg/㎥. The shield plane used was RO4003 and 2024-T3 aluminum. Static indentation and impact test was conducted to characterize the type and extent of the damage observed in two CLAS panels, and the performance of antenna used in a wireless LAN system. Correlation of peak contact force, residual indentation and the delamination area shows impact damage of the panel with an aluminum shield plane is larger than that of the panel with RO4003 shield plane, although the former is more penetration resistant. The damage was observed by naked eye, ultrasonic inspection and cross sectioning. The shape and size of delamination was estimated by ultrasonic inspection, and the area of delamination linearly increases as impact energy increases. The performance of impact damaged antenna was estimated by measuring return loss and radiation pattern. It was revealed that the performance of antenna was related to the impact damage and there was a threshold that the performance of antenna fell as impact energy level changed. The threshold was between the impact energies of 1.5J and 1.75J.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1507-1510
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• 2005

This study was carried out as a part of the research on the development of a maskless and electroless process for fabricating metal micro/nanostructures by using a nanoindenter and an electroless deposition technique. $2-\mu{m}-deep$ indentation tests on Ni and Cu samples were performed. The elastic recovery of the Ni and Cu was 9.30% and 9.53% of the maximum penetration depth, respectively. The hardness and the elastic modulus were 1.56 GPa and 120 GPa for Ni and 1.49 GPa and 100 GPa for Cu. The effect of single-point diamond machining conditions such as the Berkovich tip orientation (0, 45, and $90^{\circ}$) and the normal load (0.1, 0.3, 0.5, 1, 3, and 5 mN), on both the deformation behavior and the morphology of cutting traces (such as width and depth) was investigated by constant-load scratch tests. The tip orientation had a significant influence on the coefficient of friction, which varied from 0.52-0.66 for Ni and from 0.46-0.61 for Cu. The crisscross-pattern sample showed that the tip orientation strongly affects the surface quality of the machined area during scratching. A selective deposition of Cu at the pit-like defect on a p-type Si(111) surface was also investigated. Preferential deposition of the Cu occurred at the surface defect sites of silicon wafers, indicating that those defect sites act as active sites for the deposition reaction. The shape of the Cu-deposited area was almost the same as that of the residual stress field.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.20 no.5
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• pp.472-481
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• 2008

In this study hydraulic experiment was carried out to investigate the flow characteristics in the submerged outlet structure of Boryeong power plant and the efficiency of bubble reduction by installing horizontal porous plate in the outlet structure. The cross-sectional mean velocity in the submerged outlet structure was smaller than 1 m/s, the target value at the design stage to prevent bubble outflow to the open sea area. In addition, it was found that the maximum depth of bubble penetration is reduced 30 to 50% by installing the horizontal porous plate at the second falling location in the submerged outlet structure. It is expected that the total bubble amount entrained in the water will be most efficiently reduced by installing square-hole-shape porous plate of 20 cm hole size and making its central section as non-porous structure to dissipate the energy of falling water.

• Journal of Welding and Joining
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• v.16 no.5
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• pp.134-141
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• 1998

In this study, a fillet size for bending fatigue strength of one side fillet welded T-joint, used in box type girder and other welding structure, was investigated by bending fatigue test with or without edge preparation and burn through, with variation of joint shape. As a result, the following conclusions were obtained. (1) In one side fillet welded T-joint, the larger the leg length, the greater the bending fatigue strength. The increase in bending fatigue strength. (2) One side filet welded T-joint with edge preparation showed higher bending fatigue strength than that with twofold-large leg length and without edge preparation. (3) In one side fillet welded T-joint without edge preparation, both manual welding and automatic welding were carried out with same condition. In this case, automatic welding shoed deeper penetration and more increased horizontal leg length than manual welding, so that automatic welding offers grater bending fatigue strength. (4) For one side fillet welded T-joint without edge preparation, the ratio(h/t) of the leg length (h) and the main plate thickness (t) in which toe crack can occur was 1.2 over. (5) In one side fillet welded T-joint with edge preparation, the burn through led to reduced bending fatigue strength. However, this bending fatigue strength was higher than that of one side fillet welded T-joint without edge preparation and with a larger leg length.

• Journal of Welding and Joining
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• v.33 no.6
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• pp.27-35
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• 2015

Laser welding sector in the automotive industry has been widely recognized as one of the most important bonding processes, such as parts welding. Efforts to improve productivity and weld quality have been progressing steadily. In addition, laser welding is suitable for welding process that can produce high-quality welds suitable for flexible production and small quantity batch productions. In order to ensure the rigidity of the material, high strength material are applied to more than 1 GPa class body parts and automotive bumper beams. However, not only the situation is that the trend of domestic research, but also development is based on product molding considering freedom of shape where reinforcement is applied to meet the safety regulations and high-speed crash performance, despite the use of high strength materials. The tendency for heat-affected zone (HAZ) softening phenomenon common in areas of laser welded high tensile steel welding confirmed the occurrence of weld softening effect according to the process parameters. Based on this, range of process parameters could be selected for ensuring weld quality.

• KIEAE Journal
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• v.13 no.5
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• pp.59-66
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• 2013

Current Architectural Facade Designs have been trending to increased glass areas resulting in increasing impact on interior lighting and daylighting. In regards to indoor environmental quality, the increase in window space has a large impact on the daylighting received which ultimately impacts the liveability of a space. Especially when considering seasons, in the summer, excessive daylighting can result in glare as well as put an increased load in conditioning the air space further reducing energy efficiency. As a result, in order to improve the sustainability performance of a building, it is important to limit the natural lighting exposure to properly meet the needs and conditions of the building occupants. One of the most representative features to limit excessive sunlight exposure, is to incorporate operable blind systems. To this end, this research has been based on simulations performance through the Radiance Program. Radiance is capable of analyzing performance of daylight and impact of sunlight. Through analysis of different slat angles and blind shapes, impact and minimization of energy usage was evaluated. Furthermore, seasonal analysis was performed in order to understand the effects of seasonal climate factors. Ultimately this research provides an analysis of operable blinds optimization and effects of blind shape, control factors and angle of shading.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.1
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• pp.17-23
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• 2020

In this study, the behaviors of a vessel and the ground during the vessel impacting an underwater slope that is part of an artificial protective island are analyzed using the coupled Eulerian-Lagrangian scheme. To consider the large deformation including the shear failure of soil, the Eulerian domain is used to model the ground and water, while the impacting objects are modeled as the Lagrangian domain. For efficiency, the mass scaling scheme is applied to the modeling of the impacting objects, and the ground is modeled by setting the Eulerian volume fraction values. To verify the applicability of the constructed model, a dynamic penetration anchor problem is analyzed. The impacting vessel is modeled using solid elements following the external shape of a container ship, and an analysis of a collision on the slope is performed. As a result, collision behaviors such as displacement, velocity, and dissipation energy are estimated, and the necessity of a parametric study as further research is established.

• Journal of Welding and Joining
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• v.23 no.3
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• pp.76-82
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• 2005

Recently the application of laser welding technology has been considered to shipbuilding structure. However, when this technology is applied to primer coated steel, good quality weld beads are not easily obtained. Because the primer-coated layer caused the spatter, humping bead and porosity which are main part of the welding defect attributed to the powerful vaporizing pressure of zinc. So we performed experiment with objectives of understanding spatter and porosity formation mechanism and producing sound weld beads in 6mmt primer coated steels by a $CO_2$ CW laser. The effects of welding parameters; defocused distance, welding speed, coated thickness and coated position; were investigated in the bead shape and penetration depth on bead and lap welding. Alternative idea was suggested to suspend the welding defect by giving a reasonable gap clearance for primer coated thickness. The zinc of primer has a boiling point that is lower than melting point of steel. Zinc vapor builds up at the interface between the two sheets and this tends to deteriorate the quality of the weld by ejecting weld material from lap position or leaving porosity. Significant effects of primer coated position was lap side rather than surface. Therefore introducing a small gap clearance in the lap position, the zinc vapor could escape through it and sound weld beads can be acquired. In conclusion, formation and suspension mechanism of the welding defects was suggested by controling the factors.