• Proceedings of the KSR Conference
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• 2002.05a
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• pp.289-294
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• 2002

Sand Compaction Pile (SCP) method, which uses sand material, is frequently used in Korea. However, the use of sand for SCP faces environmental and economical problems with the shortage of its resources. Therefore, it is necessary to substitute other materials for compaction piles. One of the alternatives is using gravel in lieu of sand. Granular Pile, constituted with sand and crushed-stone, is one of the methods to improve soft clay and loose sandy ground. In this study, modeled pile load tests are performed in test cell. The observations are made on the consolidation and the variation of water table of three different grounds, original, sand pile installed, and granular pile installed ground. In addition, engineering characteristics such as bearing capacity, settlement and drainage are investigated. The test results show that Gravel Compaction Pile (GCP) is more efficient for increasing bearing capacity and reducing settlement than SCP and had similar pore water pressure dissipation to sand. Therefore, the results show that GCP can be a good substitution for SCP.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.11
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• pp.233-243
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• 1998

The demand of high speed machining is increasing due to the high speed cutting and grinding provides high efficiency of process, short process time, improved metal removal capacity and better surface finish. Active magnetic bearings allow much high surface speed than conventional ball bearings and therefore greatly suitable for high speed cutting or grinding. This paper describes a design process of an active magnetic bearing system for a high speed grinding spindle with power 5.5kW and maximum speed 60,000rpm. Magnetic actuators are designed by the magnetic circuit theory considering static load condition, and examined with FEM analysis. Dynamic characteristics are also considered, such as bandwidth, stiffness, natural frequency and static deflection. System characteristics are simulated with a rigid rotor model.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.742-747
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• 2000

The optical storage device has recently experienced significant improvements, especially for the aspects of high capacity and fast transfer rate. However, it is the fact that the optical storage device has the lower access time for the randomly scattered data compared to the hard disk drives. It is, therefore, necessary to develop a new type of optical storage system. In this study, we investigate the air bearing characteristics for the optical disk drives which have the swing arm actuator similarly to the hard disk drives. Considering the requirements of the optical disk drives, we parametrize the shape of the air bearing surface and investigate its sensitivity to the flying characteristics for further optimized design outputs.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.18 no.6
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• pp.51-60
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• 2015

This study conducted shear strength test and plate bearing test to look into the characteristics of bearing capacity using geosynthetics case on forest road surface. The shear strength test showed that the internal friction angle at the time when geosynthetics was used was measured larger on average than that in the unreinforced case. Therefore, using geosynthetics case produced more bearing capacity reinforcement effect. The result from the comparison test of internal friction angle by geosynthetics type revealed that the internal friction angle at the time when geotextile case was used was measured larger. That was attributable to the difference between the area of the total cross section of geotextile made in type of non-woven fabric and its material. Plate bearing test showed that the settlement at the time when geosynthetics was used was measured smaller than that in the unreinforced case. Therefore, using geosynthetics produced more bearing power reinforcement effect. The result from the comparison test showed that geogrid case was measured smaller than geotextile case. Henceforth, It is seemed that it will be necessary to keep studying the reinforcement engineering and process of forest road surface which fits the characteristics and conditions of geosynthetics to prevent forest road demage.

• Journal of the Korean Geotechnical Society
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• v.18 no.4
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• pp.179-188
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• 2002

The scale effect should be considered to determine the bearing capacity and settlement of footings from plate-load test, because of the size difference between a footing and a loading plate. To analyze characteristics of bearing capacity and settlement according to the difference of loading plate sizes, model tests were performed with four different sizes of square plate, which are B=10, 15, 20, and 25cm respectively, on five different kinds of subsoils. Test results showed that the ultimate bearing capacity of a footing on the sand did not increase proportional to the traditional formula and the bearing capacity on the clay also increased a little with increasing the size of loading plate. The settlement of test plate on the sand did not increase as the traditional formula of Terzaghi and Peck (1967), and the settlement on the clay also did not increase proportional to the traditional formula.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.6
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• pp.562-569
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• 2011

In this study linear and nonlinear dynamic stability characteristics of a medium-size high-speed turbocharger, whose rotor is supported by two 3-lobe journal bearings, are analyzed to evaluate and identify the effects of its bearing design variables. The rotor has the rated speed of 40,500 rpm and maximum continuous speed of 45,000 rpm. At first, utilizing the linear stability analysis method, bearing designs of yielding stable or unstable LogDecs as small as possible are searched by manipulating with machined bearing clearances and preloads. As next, utilizing the nonlinear analysis method, limit cycles of the rotor responses at the rated and maximum continuous speeds are simulated to check their acceptances. Results have shown that for the turbocharger rotor-bearing system considered, the 3-lobe journal bearing design with a smaller machined clearance and a larger preload are preferred for the stable rotor responses. More importantly, since there exists a good correlation between the linear and nonlinear stability analysis results, it is concluded that firstly the linear stability analysis method may be applied to screen quickly the ranges of bearing designs for stable or least unstable solutions and then, lastly the nonlinear stability analysis method may be deployed to check an absolute motion stability in terms of the limit cycle.

• Tribology and Lubricants
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• v.37 no.1
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• pp.7-13
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• 2021

Ball bearing is a device that supports and transmits a load acting on a rotating shaft, and it is a type of rolling bearings that uses the rolling friction of the balls by inserting balls between the inner ring and the outer ring. Grease, which is prepared by mixing a thickener with a base oil, is a lubricant commonly used in bearings and has the advantage of a simple structure and easy handling. Bearings are increasingly being used in high value-added products such as semiconductors, aviation, and robots in the era of the 4th industrial revolution. Accordingly, there is an increasing demand for bearing grease. The selection of grease is an important factor in the bearing design. Therefore, a study must be conducted on the grease life evaluation to select an appropriate grease according to operating conditions such as a high temperature, high rotational speed, and high load. In this study, we evaluate the life of ball-bearing grease according to various operating conditions, namely, temperature, speed, and load changes. For this, we develop and theoretically verify a grease life test machine for ball bearings. We conduct a life test of grease according to various operating conditions of bearings and predict the grease life with a 10% and 50% failure probability using the Weibull analysis. In addition, we analyze the oxide characteristics of the grease over time using the Fourier transform infrared spectroscopy and the deterioration characteristics of the grease using the carbonyl index.

• Journal of the Korean Geotechnical Society
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• v.23 no.5
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• pp.89-100
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• 2007

In this study, various field and laboratory tests were performed to investigate the characteristics of shear strength and bearing behavior to be considered in the estimation of stability and trafficability in early stage of stabilization process in marine clay dredged deposit. Site characterization was carried out to grasp the basic properties of the deposit. Field vane test, unconfined compression test and direct shear test were conducted to evaluate the shear strength distribution for varied depths, and the characteristics of shear strength and stress-strain behavior of the crust layer. Plate load tests were also performed to estimate the bearing capacity and to assess load-settlement behavior and failure pattern of the deposit. The bearing capacity was also estimated using previously proposed methods for double-layered clay deposit. The estimated bearing capacity was compared with the results of the plate load tests and then, the applicability of the estimation method was discussed.

• Korean Journal of Materials Research
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• v.33 no.12
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• pp.558-564
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• 2023

In this study, we designed and manufactured a large angular contact ball bearing (LACBB) with low deformation using JIS-SUJ2 steel and analyzed changes in its structural characteristics and chemical composition upon heat treatment. The bearing was produced by hot forging and heat treatment including a quenching and tempering (Q/T) process, and its properties were analyzed using 4 mm thick specimens. A difference in the size distribution of the carbide in the outer and inner parts of the bearing was observed and it was confirmed that large and non-uniform carbide was distributed in the inner part of the bearing. After heat treatment, the hardness value of the outer part increased from 13.4 HRC to 61 HRC and the inner part increased from 8.0 HRC to 59.7 HRC. As a result of X-ray diffraction (XRD) measurements, the volume fraction of the retained austenite contained in the outer part was calculated to be 3.5~4.8 % and the inner part was calculated to be 3.6~5.0 %. The surface chemical composition and the content of chemical bonds were quantified through X-ray photoelectron spectroscopy (XPS), and a decrease in C=C bonds and an increase in Fe-C bonds were confirmed.

• Journal of the Korean GEO-environmental Society
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• v.14 no.3
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• pp.41-49
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• 2013

The rotate penetration pile is a type of displacement pile: the surrounding soil is displaced when installing the pile, and the pile can exert a large bearing power and pullout force. In addition, it uses displaced soil method that does not generate slime, and its applications are increasing in foreign countries owing to the environmentally friendly characteristics such as small noise and vibration. However, mostly driven piles-which are directly driven to the ground, and bored pile- pre-fabricated piles are buried to prebored underground, are used; however, rotate penetration piles still have limited use. Most of the laboratory tests have been carried out until now to identify the support behavior after installation of piles and ground construction, the evaluating the support behavior is lacking due to the rotation intrusive process of the rotate penetration piles. Therefore, this study used indoor experiments simulating rotation intrusive process in weathered soil, to evaluate the bearing power behavior for the weathered soil, varying the diameter of the helical bearing plates, helical bearing plate spacing, number of the helical bearing plates, and helical bearing plate specifications. As the outcome of this study, the helical pile bearing power evaluation results, change in bearing power in accordance with main specifications, and review on the comparative analysis with the existing theories were provided.