• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.11
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• pp.750-757
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• 2018

The mechanically stabilized earth wall abutment is an earth structure using a mechanically stabilized earth wall and it uses in-extensional steel reinforcements having excellent friction performance. In order to analyze the pullout behavior of in-extensional steel reinforcements usually applied on the mechanically stabilized earth wall abutment, effects of stiffness and particle-size distributions of backfills and also horizontal spacings were considered in this study. As a result of parametric analyses, the highest pulling force acted on the uppermost reinforcement, and the stiffness and the particle-size distributions of the backfill significantly affected the pulling resistance of the reinforced soils. The internal friction angle of backfills should be at least 25 degrees, the coefficient uniformity factor should be at least 4, and the horizontal spacing of the uppermost steel reinforcement should be less than 25cm. Therefore, in order to secure the pullout resistance of the reinforced soil, it is necessary a properly spacing of reinforcement and more strict quality control for the backfill.

• Korean Journal of Metals and Materials
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• v.46 no.6
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• pp.351-356
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• 2008

Thermally sprayed tungsten carbide-based powder coatings are being widely used for a variety of wear resistance applications. The coating deposited by high velocity processes such as high velocity oxy-fuel (HVOF) thermal spraying is known to provide improved wear resistant property. In this study, optimal coating process (OCP) is obtained by the study of coating properties such as surface hardness, porosity, surface roughness and microstructure of 9 coatings prepared by Taguchi program for 3 levels of four spray parameters. The Friction and wear behaviors of HVOF WC-CoCr coating prepared by OCP, electrolytic hard chrome (EHC) plating and Inconel718 (In718) are investigated by reciprocating sliding wear test at $25^{\circ}C$, $450^{\circ}C$. Friction coefficients (FC) of all of the 3 samples are decreased as increasing sliding surface temperature from $25^{\circ}C$ to $450^{\circ}C$. FC of WC-CoCr decreases as increasing the surface temperature from $0.33{\pm}0.02$ at $25^{\circ}C$ to $0.26{\pm}0.02$ at $450^{\circ}C$, showing the lowest FC among the 3 samples. Wear trace (WT) and wear depth (WD) of WC-CoCr are smaller than those of EHC and In718 both at $25^{\circ}C$ and $450^{\circ}C$. These show that WC-CoCr is highly recommendable for protective coating on In718 and other metal components.

• Journal of the Korean Geotechnical Society
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• v.23 no.5
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• pp.143-151
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• 2007

The factors affecting the geotechnical properties of cemented sands are known to be relative density, cementation level, stress level, and particle characteristics such as particle size, shape and surface conditions. It has been widely accepted that the friction angle of cemented sands is not affected by cementation while the cohesion of cemented sands was significantly influenced by cementation. The cementation that is a critical component of the strength of cemented sands will be broken with increasing confining pressure and great caution is required in evaluating the cohesion of cemented specimens due to their fragilities. In this study, a series of drained shear tests were performed with specimens at various cementation levels and confining stresses to evaluate the strength parameters of cemented sands. From the experiments, it was concluded that the cohesion intercept of cemented sand experiences three distinctive zone(cementation control zone, transition zone, and stress control zone), as the cementation level and the confining stress varies. In addition, for accurate evaluation of the strength parameters, the level of confining stress triggering the breakage of cementation bond should be determined. In this study, the relationship between the maximum confining stresses capable of maintaining the cementation bond intact and unconfined compression strength of the cemented sand was established.

• Journal of the Korean Geotechnical Society
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• v.24 no.2
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• pp.77-86
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• 2008

The disturbance zone and measured values are affected by the size of the penetrometer. The local value may be measured by the smaller penetrometer. An ultra small Micro-Cone penetrometer (5mm in outer diameter) is designed and manufactured to characterize soil properties with minimum disturbance during penetration tests. The tip resistance is measured by using stain gauges attached near the Micro-Cone. In addition, the friction sleeve is adopted to effectively remove the skin friction from the tip resistance. Design concern includes the installation of stain gauges, circuits, penetration systems, penetration rate, sampling rate, operating temperature, and calibration. Application tests show that the clay interface, and the soil layers consisting of clay and sand are clearly detected by the Micro-Cone. Furthermore, the cone tip resistances measured by the Micro-Cone and the miniature cone (16mm in outer diameter) are similar. Note the resolution is much higher in the Micro-Cone. This study shows that the Micro-Cone may effectively detect the soil interface with high resolution, and with minimum disturbance.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.32 no.1 s.55
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• pp.45-51
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• 2006

In the field of makeup cosmetics, especially, powder-based foundations such as two-way cake, pact and face powder, the quality of which is known to be strongly influenced by the properties of powder, surface treatment technology is widely used as a method to improve the various characteristics of powder texture, wear properties, dispersion ability and so on. The two-way cake or pressed-powder foundation is one of the familiar makeup products in Asian market for deep covering and finishing purpose. In spite of the relent progress in surface modification method such as composition of powders with different characteristics and application of a diversity of coating ingredient (metal soap, amino acid, silicone and fluorine), this product possess a technical difficulty to enhance both of the adhesion power and spreadability on the skin in addition to potential claim of consumer about heavy or thick feeling. This article is covering the preparation and coating method of nano-vesicle that mimic the double-layered lipid lamellar structure existing between the corneocytes of the stratum corneum in the skin for the purpose of improving both of two important physical characteristic of two-way cake, spreadability and adhering force to skin, and obtining better affinity to skin. Nano-vesicle was prepared using the high-pressure emulsifying process of lecithin, pseudo ceramide, butylene glycol and tocopheryl acetate. This nano-sized emulsion was added to powder-dispersed aqueous phase together with bivalent metal salt solution and then the filtering and drying procedure was followed to yield the nano-vesicle coated powder. The amount of nano-vesicle coated on the powder was able to regulated by the concentration of metal salt and this novel powder showed the lower friction coefficient, more uniform condition of application and higher adhesive powder comparing with the alkyl silane treated powder from the test result of spreadability and wear properties using friction meter and air jet method. Two-wav cake containing newly developed coated powder with nano-vesicle showed the similar advantages in the frictional and adhesive characteristics.

• Korean Chemical Engineering Research
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• v.50 no.5
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• pp.783-788
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• 2012

Stern tube bearing is a shaft device playing important roles to reduce the friction of axial rotation and to support the weight of shaft. However, because there is no domestic producer of stern tube bering, imported stern tube bearings have many practical problems including prices, delivery and after services. This is why stern tube bearing should be localization. For the purpose of development of polyurethane resin for stern tube bearings, the effect of additives on the hardness, tensile strength and elongation of the polyurethane resin were systematically investigated. For the preliminary researches, depending on the type of curing agent, MOCA type and non-MOCA type polyurethanes were synthesized. Preliminary researches concluded that MOCA type polyurethane resin has more excellent mechanical properties than non-MPCA type for stern tube bearings that Tensile strength and Hardness of non-MOCA type investigated 23 D, 4.3 Mpa. Therefore, MOCA type polyurethane was adapted as base resin of this research. Silica, calcium carbonate and graphite were selected as additives for the enhancement of mechanical properties of polyurethane resin. Effect of the type and the dosage of these additives on the hardness, tensile strength, elongation of the polyurethane resin were experimentally examined. However, addition of calcium carbonate and graphite showed only minor effect on the hardness of the resin. Polyurethane resin with silica showed relatively excellent hardness, tensile strength and improved elongation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.5
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• pp.278-284
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• 2017

In this study, the heat input conditions suitable for the AZ61 magnesium alloy were derived by controlling the welding speed at a constant rotational speed. In addition, from an economic point of view, industry demands higher welding speeds. Therefore,the effects of the welding speed were studied. The rotational speed applied was 800rpm, and the welding speed was varied from 100 to 500mm/min to evaluate the behavior of the welded regions. Tensile and hardness tests were conducted to examine the mechanical properties. Optical microscopy was used to observe the microstructure and soundness of the welded regions. Defects were observed at the welded region when the welding speed was more than400mm/min. As the welding speed increased, the grain size of the stir zone decreased and the hardness tended to increase proportionally. When the rotational speed was 800 rpm and the welding speed was 200mm/min and 300mm/min, there wereno defects in the welded region and excellent mechanical properties were recorded. In addition, the joint efficiencies were 100.5% and 101.2%, respectively, and the ultimate tensile strength was similar to that of the base metal. Fracture of the tensile specimen occurred between the advancing side and stir zone, and the fracture location coincided with the region where the hardness decreased temporarily.

• Investigative Magnetic Resonance Imaging
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• v.11 no.1
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• pp.10-19
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• 2007

Conventional MRI methods using T1-, T2-, diffusion-, perfusion-weighting, and functional imaging rely on characterizing the physical and functional properties of the tissue. In this review, we introduce an imaging modality based on measured the mechanical properties of soft tissue, namely magnetic resonance elastography (MRE). The use of palpation to identify the stiffness of tissue remains a fundamental diagnostic tool. MRE can quantify the stiffness of the tissue thereby providing a objective means to measure the mechanical properties. To accomplish a successful clinical setting using MRE, hardware and software techniques in the area of transducer, pulse sequence, and imaging processing algorithm need to be developed. Transducer, a mechanical vibrator, is the core of MRE application to make wave propagate invivo. For this reason, considerations of the frame of human body, pressure and friction of the interface, and high magnetic field of a MRI system needs to be taken into account when designing a transducer. Given that the wave propagates through human body effectively, developing an appropriate pulse sequence is another important issue in obtaining an optimal image. In this review paper, we introduce the technical aspects needed for MRE experiments and introduce several applications of this new field.

• The Journal of Engineering Geology
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• v.30 no.2
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• pp.161-173
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• 2020

This study is to examine the engineering characteristics of colunmar joints in Mudeugsan National Park, a global geopark. For these purposes, physical and mechanical properties of Mudeungsan Tuff, evaluation for the weathering degree of columnar joints, and crack behavior monitoring in columnar joints were conducted. The physical properties of Mudeungsan tuff were 1.02% for the average porosity, 0.38% for the average absorption, 2.69 g/㎤ for the average specific gravity, and 4,948 m/s for the average elastic wave velocity. Its mechanical properties were 337 MPa for the average uniaxial compressive strength, 68 GPa for the average elastic modulus, 0.29 for the average Poisson's ratio, 41.3 MPa for the average cohesion strength, and 62.8° for the average friction angle. the average rebound Q-value of the silver Schmidt hammer for the three columnar joint blocks at the Ipseok-dae was shown as 49.3. when this value is converted into uniaxial compressive strength, it becomes 70.5 MPa, which is about 21% of the uniaxial compression strength of Mudeungsan tuff. In addition, according to the results of crack monitoring measurements for the three columnar joint blocks at the Ipseok-dae, the crack behavior is less than 1 mm, so it is believed that its behavior in Ipseak-dae columnar joints has hardly occured to date.

• Korean Journal of Soil Science and Fertilizer
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• v.17 no.2
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• pp.90-95
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• 1984

To improve the physico-mechanical characteristics of heavy clayey paddy soils(Hwadong series) on Diluvial terrace after application of fine sand and briquette ashes, barley and rice were cultivated for 2 years. The influences of sand and briquette ashes on soil properties and on the crops were summarized as follows: 1. Application of the adding materials could not affect the yield of rice but barley yields were increased significantly about 18-19% in the plots of sand 100t/10a(clay 15% adjusted) and in the plots of briquette ashes. 2. The porosity and the content of water stable aggregates were decreased in the plots of sand and briquette ash adding. The chemical properties were slightly decreased in the plots of sands while the contents of av. $SiO_2$: and extr K were increased in the plots of briquette ashes. 3. Soil mechanical properties such as cone penetration resistance, shearing resistance and plastic index etc. were decreased while the friction resistance increased in the plots of sand and briquette ash treatments. Consequently, the adaptability to mechanization was increased. 4. The content of rice roots in subsoils (10-20cm) were increased in the plots of sand and briquette ash treatments.