• Journal of the Korean GEO-environmental Society
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• v.14 no.10
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• pp.17-27
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• 2013

This paper explores stress release induced by unloading in dry sand. A series of model tests were carried out to measure stresses developed in testing sand during loading and those released during unloading for different boundary conditions. It was found that stress in the sand increased linearly with applied load. At the onset of unloading, almost no stress release was observed. Significant stress release took place when the shear stress in the sand induced by unloading exceeded the frictional resistance and caused movement of sand particles. The initiation and the magnitude of stress release depend on the stress condition prior to unloading, the decrease of external load, and also the frictional resistance in sand. A new conceptual stress-release model was next developed based on the model test results by considering the fundamental frictional behavior of granular materials.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.415-416
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• 2002

Experiments have been conducted to investigate scuffing mechanism in oil lubricated piston-ring /cylinder sliding contacts. Samples were extracted from actual components to simulate the real contact geometry and other influencing conditions. A standard test machine. with some modifications, has been used for the investigation of the effects of surface temperature load and sliding velocity. preliminary tests were carried out to find the critical temperature of scuffing using gradient temperature under a constant load, reciprocating frequency and stroke. The experimental and analytical results show that a transition from lubricated contact to adhesion, accompanied by the phenomena such as material transfer between the two sliding surfaces, local contact welding and temperature rise, and sharp increase in friction coefficient, appears to contribute to the final failure of scuffing.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.3
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• pp.600-611
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• 1994

The purpose of this research is to propose a model for the prediction of residual strength. For this purpose, two-paremeter model based on Caprino's is developed and formulated by the ratio of indentation due to impact and normalized residual strength. The damage zone is considered only as an indentation. Impact tests are carried out on laminated composites by steel balls. Test material is carbon/epoxy laminate. The specimens are composed of $[{\pm}45^{\circ}/0^{\circ}/90^{\circ}]_2$ and $[\pm}45^{\circ}]_4$ stacking sequence and have $0.75^T{\times}0.26^W{\times}100^L(mm) dimension. A proposed model shows a good correlation with the experimental results And failure mechanism due to high impact velocity is discussed on CFRP laminates to examine the initiation and development of damage by fractography and ultrasonic image ststem. The effect of the unidirectional ply position on the residual strength is considered here.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.3
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• pp.218-226
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• 2002

This study was carried out to develop continuously variable-speed transmission(CVT) fur an agricultural tractor. The full-toroidal variator mechanism with flour discs and six rollers was utilized as a device fur changing speed ratio continuously. In system layout design, the sizes of the roller cylinders and the end-load cylinder, which were critical factors for controlling the variator, were designed. The planetary gear unit and six pairs of the gear assemblies were designed to establish the maximum speed of the vehicle at 30 ㎞/hr. In addition, the hydraulic clutch, the silent chain, the hydraulic manifold and the electronic controller were designed. Based on the design, a prototype CVT was developed and tested. Test results show that the CVT developed in this study could successfully provide variable speed of the tractor.

• Environmental Mutagens and Carcinogens
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• v.16 no.2
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• pp.117-123
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• 1996

This study was carried out to examine the mechanism of Arsenic cytotoxicity through several in vitro test systems. Dose-dependent decrease of cell survival by Arsenic was observed by colony forming assay. Arsenic was weak mutagenic in inducing HGPRT point mutation in CHO cells. The frequency of chromosomal aberrations increased in a dose-dependent manner and the most frequent type of chromosomal aberrations induced by Arsenic were chromatid type deletions. U!trafiltrates of culture media from CHO cells treated with Arsenic induced sister chromatid exchanges(SCE) in CHO cells and Arsenic was able to induce lipid peroxidation in CHO cells. The results suggested that the ultrafiltrates of media from CHO cells treated with Arsenic contain clastogenic factor(CF) and Iipid peroxidation might be involved in the formation of CF.

• Tribology and Lubricants
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• v.12 no.3
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• pp.6-11
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• 1996

There has been a growing concern for the use of mineral oil based lubricants because of the worldwide interest in environmental issues. This has prompted the use of vegetable oils as more environmentally acceptable base fluids. In view of this, four-ball wear test was carried out to investigate the tribological behavior of selected vegetable oils blended with ZDDP, TCP and DBP under high speed and temperate conditions. Of the additive evaluated, the new additive, DBP has provided antiwear performance superior to the two other additives more commonly used. This superior performance by DBP is probably caused by different wear mechanism. This wear mechanism has been evidenced by the surface analysis of worn balls conducted using optical microscope and EDAX.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05a
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• pp.338-341
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• 2006

In recent years, carbon fiber reinforced polymer(CFRP) has been widely used for reinforcement of damaged concrete structures. However, the fundamental mechanisms of load transfer and load-resistance for reinforced concrete beams retrofitted by CFRP are not fully understood. Acoustic emission(AE) technique was used to evaluate the characteristics of damage progress and the failure mechanism of reinforced concrete beams retrofitted by CFRP. In this study, three-paint-bending test has been carried out to investigate the AE characteristics of four specimens. The results show that the AE technique is a valuable tool to study the failure mechanism of reinforced concrete beams retrofitted by CFRP.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1589-1592
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• 2003

Automatic grease lubricator of gear type was developed by mechanical design, analysis and test with products manufactured by rapid prototyping machine. The mechanism of gear driving was designed in similar to the watch mechanism and lubrication could be controlled by PCB circuit. The body of the lubricator was analyzed by stress analysis with different constructed angle. Digital mockup was analyzed and RP products were combined with PCB circuit and grease. RP products and injection moulding products were tested and compared for roughness and roundness, Finally the grease was drained out for testing the time.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.6
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• pp.56-62
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• 2008

An Allium-odorum is difficult material to handle because it is soft and weak mechanically. For bundling work of allium-odorum, we must grip in the bundle shape of unit weight. However it is difficult to grip allium-odorum by hand because the bundle bulk is very big. Especially, in packing work, the bundle shape of allium-odorum package is more important than other vegetables because the sale price depend on the bundle shape. In this paper, we propose bundling mechanism for a rectangular shape, and semi-auto bundling mechanism by a eccentric roller and a triangular link. We carry out mechanical model and analysis respectively using the CATIA V5 and SimDesigner. We have manufactured the prototype of the semi-automatic bundling machine, and got satisfied result through field test. This machine is in the process of commercialization.

• Proceedings of the KSR Conference
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• 2007.05a
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• pp.162-168
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• 2007

The critical speed above which the vehicle become unstable should be fundamentally verified in the development of new train. In case of high speed tilting train, which require both higher critical speed and higher curving speed, the critical speed should be more carefully treated because the both requirements are conflicting each other in the conventional train design. This research has been performed to estimate the linear and non-linear critical speed of 200km/h Korean Tilting Train which has been developing. The newly developed self-steering mechanism was attached to the tilting train to secure critical speed under the lower yaw stiffness which was inevitable to secure higher curving performance. The simulation to predict critical speed was done by commercial vehicle dynamic S/W. Full scale roller rig test was carried out for the validation of numerical results and effectiveness of self-steering mechanism.