• 한국표면공학회지
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• 제46권6호
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• pp.264-270
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• 2013

Effects of preoxidation on high temperature wear of piercing plug tool steel sliding against SA210C steel used for production of seamless tube have been studied using a pin-on-disc CETR tribometer, under applied normal load of 20 N at $900^{\circ}C$ in air. It was found in the preoxidized pin specimens of piercing plug tool steel that the coefficient of friction decreased to about 0.4 at an initial stage followed by showing nearly constant value of about 0.4 during high temperature wear testing. On the other hand, it was also found in the pin specimens without preoxidation that the coefficient of friction increased and fluctuated, ranging from about 0.3 to 0.6 during the tests until the running period of about 800 sec. The compact and continuous Fe-oxide layer was formed on the contact surface of the preoxidized pin specimens after high temperature wear testing followed by penetrating along the grain boundaries of coarse ferrite in the decarburized region beneath the oxide layer due to the lower hardness of the region.

• Geomechanics and Engineering
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• 제12권6호
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• pp.1021-1046
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• 2017

The assessment of slope stability is an essential task in geotechnical engineering. In this paper, a three-dimensional (3D) finite element analysis (FEA) was employed to investigate the performance of different shear pin arrangements to increase the stability of a soil block resting on an inclined plane with a low-interface friction plane. In the numerical models, the soil block was modeled by volume elements with linear elastic perfectly plastic material in a drained condition, while the shear pins were modeled by volume elements with linear elastic material. Interface elements were used along the bedding plane (bedding interface element) and around the shear pins (shear pin interface element) to simulate the soil-structure interaction. Bedding interface elements were used to capture the shear sliding of the soil on the low-interface friction plane while shear pin interface elements were used to model the shear bonding of the soil around the pins. A failure analysis was performed by means of the gravity loading method. The results of the 3D FEA with the numerical models were compared to those with the physical models for all cases. The effects of the number of shear pins, the shear pin locations, the different shear pin arrangements, the thickness and the width of the soil block and the associated failure mechanisms were discussed.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2009년 추계학술발표대회
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• pp.239-242
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• 2009

Friction stir spot welding (FSSW), developed based on principle of friction stir welding, has been paid attention as a new solid-state spot welding process. Since FSSW can produce high-quality weld in Al alloys more easily than resistance spot welding, this process has been already used for construction of Al components in the automotive industries. Despite the large industrial interests in FSSW, fundamental knowledge on welding phenomena of this process has not been fully understood. In this study, FSSW phenomena, such as the consolidation mechanism, the microstructural evolution and the material flow, were examined in Al alloy 6061. This study clarified that the elliptical zone found in the vicinity of the pin hole on the cross section was characterized by the initially lapped surface of two sheets. Moreover, the following material flow was proposed; capture of the upper material with the threads on the pin surface, spiral flow along the tool rotation, and then release at the tip of the pin.

• 한국기계가공학회지
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• 제14권3호
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• pp.124-130
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• 2015

The purpose of this study is to investigate friction characteristics according to micro-dimple patterns. The surface texturing of micro-dimple patterns was tested to examine the friction of pin-on-disk using flat-on-flat contact geometry. The patterns of both dimple circle and groove pattern were adopted to carry out the effect of those ones. In the low loads, such as 13.8N and 27.7N, the friction coefficients of groove pattern were lower than those of dimple circle pattern. In many other comparisons of normal loads, the groove pattern had lower friction forces, which showed the effect of surface texturing. The relationship between sliding time and friction forces showed that the increase of friction forces of groove pattern were relatively lower than those of dimple pattern. In conclusion, the dimple patterns of dimple-circle pattern and groove pattern strongly contributed to reducing the friction between contacting materials.

• Tribology and Lubricants
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• 제25권4호
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• pp.231-235
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• 2009

In this study, the influence of contact pressure on the variation in coefficients of friction between porcine knee joint cartilage and Co-Cr alloy in a repeat pass sliding motion was investigated. Flat-ended cartilage pin specimens(9 mm diameter, 8 mm long) were prepared from porcine(6 months old) knee joints by a drill-type punch. Friction tests were conducted by using a pin-on-disk type friction tester for an hour in PBS lubricated condition under the contact pressures of 0.5, 1 and 2 MPa with 50 mm distance per a cycle at ambient condition. As a result, coefficients of friction increased as the test duration increased for all contact pressures. The maximum coefficients of friction were 0.082, 0.06 and 0.098 for 0.5, 1, and 2 MPa, respectively. It showed that coefficients of friction of porcine knee joint cartilage against Co-Cr alloy depended on the level of contact pressure and related to squeeze film lubrication mechanism.

• 대한기계학회논문집A
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• 제25권6호
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• pp.930-937
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• 2001

The friction and wear behavior of short carbon fiber reinforced polyetheretherketone was studied experimentally under dry sliding conditions against SCM440(AISI 4140) disks with different surface roughness and hardness at the low sliding speeds and the high pressures on a pin-on-disk apparatus. Under the low disk surface roughness value the earsplitting noise and stick-slip were occurred. The increased adhesion friction and wear factor with stick-slip made the friction and wear behavior worse. Under the high disk surface hardness the break and falling-off of carbon fibers were accelerated. The carbon fibers fallen off from the matrix were ground into powder between two wear surfaces and this phenomenon caused abrasive friction and wear factor to increase. So the friction and wear behavior became worse. With the transfer film made of wear particles formed on a disk, the carbon powder film formed on a pin lowered a friction coefficient.

• Tribology and Lubricants
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• 제34권6호
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• pp.318-324
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• 2018

This study aims to visualize the friction and wear behaviors of metal coatings in real time. The main mechanism of wear is identified by observing all the processes in which wear occurs. The friction coefficients of the moments are monitored to confirm the relationship between the friction and wear characteristics of the coating. Thin Ag coatings, which are several hundred nanometers in thickness, are prepared by depositing Ag atoms on silicon substrates through a sputtering method. A pin-on-disk-type tribo-tester is installed inside a scanning electron microscope (SEM) to evaluate the friction and wear characteristics of the Ag coating. A fine diamond pin is brought into contact with the Ag coating surface, and a load of 20 mN is applied. The contact pressure is calculated to be approximately 15 GPa. The moments of wear caused by the sliding motion are visualized, and the changes in the friction characteristics according to each step of wear generation are monitored. The Ag coating can be confirmed to exhibit a wear phenomenon by gradually peeling off the surface of the coating on observing the friction and wear characteristics of the coating in real time inside the SEM. This can be explained by a typical plowing-type wear mechanism.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1998년도 제28회 추계학술대회
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• pp.285-291
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• 1998

A hydraulic pin-on-disk type tribotester was developed and it's performance was investigated experimentally. The estimate of the performance was accomplished by comparing those of the pneumatic and the dead-weight loading method. The reliability to the performance was conformed. By hydraulic loading method more accra'ate friction coefficient could be got.

• Tribology and Lubricants
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• 제5권2호
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• pp.94-100
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• 1989

Friction and Wear behavior of continuous graphite fiber composites was studied for different fiber orientations against the sliding direction. The effect of fiber orientation on friction and wear of the composite and on the deformation of the counterface was investigated experimentally. Pin on disk type testing machine was built and employed to generate the friction and wear data. A graphite fiber composite plate was produced by the bleeder ply molding in an autoclave and machined into rectangular pin specimens with specific fiber orientations, i.e., normal, transverse, and longitudinal directions. Three different wear conditions were employed for two different periods of time, 24 and 48 hours. The wear track of the worn specimens and the metal counterface was examined with a scanning electron microscope (SEM) to observe the damaged fibers on the surface and wear film generation on the counterface. Wear mechanism of the composite during sliding wear is proposed based on the experimental results.

• 한국표면공학회지
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• 제44권6호
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• pp.233-238
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• 2011

The friction and wear characteristics of CrN and TiN coatings on SKD61 which is mold material using for extrusion of AZ80 magnesium alloy were investigated. The coatings were deposited by the arc ion-plating method, and the thickness were about $3.59{\mu}m$ and $3.28{\mu}m$, respectively. Reciprocating friction wear tests were conducted by varying pin load and temperature of counter substrate at un-lubricated condition. The pin loads were 11, 15 and 19 kgf, and the substrate temperatures were room temperature and $120^{\circ}C$. CrN coating which has a lower friction coefficient and a smaller adhesive wear with AZ80 magnesium alloy showed better wear resistance than TiN coating.