• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
• /
• 2001.06a
• /
• pp.354-359
• /
• 2001

CNTs were added to Ultra-high molecular weight polyethylene (UHMWPE) to improve the tribological properties of UHMWPE. CNTs which have a diameter of about 10-50nm, while their length is about 3-5nm were produced by the catalytic decomposition of tile C$_2$H$_2$ using a tube furnace. UHMWPE/CNTs composites were fabricated by hot pressing method. It is shown that friction coefficient was increased and wear resistance was improved as CNTs were added to UHMWPE because of excellent mechanical properties of CNTs located on UHMWPE surface.

• Tribology and Lubricants
• /
• v.30 no.4
• /
• pp.234-239
• /
• 2014

Magneto-rheological elastomer (MR elastomer) is a smart material, because it has mechanical properties that change under a magnetic field. An MR elastomer changes its stiffness characteristics when the inner particles (iron particles) align along the direction of a magnetic field. There has been much research to make use of this characteristic to control vibration issues in various mechanical systems, such as for mounting systems in the automotive field, home appliances, etc. Furthermore, the friction and wear properties of MR elastomer have been studied, as these relate to the durability of the material needed to meet engineering requirements. Rolling friction (or rolling resistance) is one of these friction properties, but has not yet been studied in the context of MR elastomers. In this study, an MR elastomer is fabricated in the shape of a hollow cylinder to evaluate the rolling friction characteristic under a magnetic field. The test apparatus is setup and a strain gauge is used to calculate the rolling resistance under test conditions. Permanent magnets are used to supply the magnetic field during tests. The load and rolling speed conditions are also considered for the tests. The test results show that rolling friction characteristic has a different trend under different magnetic field, load, and rolling speed conditions. It is assumed that the stiffness change of an MR elastomer under a magnetic field has an effect on the rolling friction characteristic of the MR elastomer. For the future work, the rolling friction characteristics of MR elastomers will be controlled by adjusting the strength of the magnetic field using electromagnets.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
• /
• 2004.11a
• /
• pp.47-52
• /
• 2004

The purpose of this study is to investigate the friction characteristics of brake pads according to different ratios of $BaSO_4/CaCO_3$. Four brake pads with different ratios of $BaSO_4/CaCO_3$ were manufactured. The friction characteristics of brake pads were tested using 1/5 reduced scale tester. With increasing of the amount of $BaSO_4$ density and shear strength of brake pads were increased and hardness of brake pads were decreased. In effectiveness, the friction coefficient of brake pad was higher and the stability of friction coefficient was better as the ratio of $BaSO_4$ increased. In fade test, friction coefficient of B3 sample used only $CaCO_3$ was decreased rapidly. B1 sample showed a good noise performance without noise generation. The wear resistance of samples were decreased with increasing of the ratio of $CaCO_3$.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.3 no.4
• /
• pp.151-157
• /
• 1979

An experomental study on drg reduction in the rough tubes is presunted using the drrective drag reducing proymer solutions. The friction factors of the rough tubes follow the maximum drag reduction asymptote for the lower Reynolds numbers in the turbulent flow. However, as the Reynols number is increased the rougher tube results deviate from the maximum drag rduction asymptote sooner than the less rough tube results. There appears a systematic deviation from the maximum drag reduction asymptote depending on the relative roughness just as friction factors for the Newtonian hluid inthe rough tubes exhibit in the turbulent region. The minor loss results inthe various fittings such as elbows, tees, and gate valves are presunted The fittings show higher values of the loss coefficient in the drag reducing polymer solutions than in the Newtonian fluid, which is quite contrary to the drag reduction phenomenon in the straight tubes. The eqivalent length of the fittings for the drag reducing polymer solutions is many times longer than that for Newtonian fluids due to the increase of the loss coefficient and the decrease of the friction factor. It is speculated that the solid-like behavior of the polymer solutions in the abruptly changing folw passage plays a significant role in increasing the loss coefficient.

• Journal of the Korean Society for Precision Engineering
• /
• v.28 no.8
• /
• pp.915-928
• /
• 2011

Titanium for dental implant application has the superior properties of biocompatibility, specific strength, and corrosion resistance. However, it is extremely difficult to find a suitable surface treatment method for sufficient osseointegration with biological tissue/bone cell and implant surface. Surface treatment technology using laser has been researched as the way to increase surface area of implant. In this study, to develop the surface treatment process with improved adhesion between implant and bone cell at the same time for superior biocompatibility, pulsed laser beam was overlapped continuously for scribed surface morphology and determination of friction coefficient. As the results, surface area and friction coefficient was increased over 2 times by the comparison with sand blasting, which is used for the conventional method. In this time, the optimal condition for laser beam power and beam irradiation speed was 13 watt and 50 mm/sec, respectively.

• Korean Journal of Materials Research
• /
• v.16 no.12
• /
• pp.766-770
• /
• 2006

The frictional behavior of oxide films on top of the plasma nitrocarburized compound layers was investigated in terms of post-oxidation treatment temperatures. The post-oxidation treatment at both temperatures($400^{\circ}C,\;500^{\circ}C$) produced magnetite($Fe_3O_4$) films which led to a significant enhancement in corrosion resistance. However, this process did not result in any improvement in frictional behavior of the nitrocarburized surface. The wear mechanisms were governed predominantly by the abrasive action of the slider on the surface irrespective of the counterface material(SiC and Bearing steel). When the specimen was sliding against a SiC counterface, the oxide films were destroyed during the early stage of the sliding process and the wear debris of the oxide film at the sliding track had a great influence on the friction coefficient. On the other hand, when sliding against a bearing steel counterface, the slider was mainly worn out due to the much higher hardness of the surface hardened layer. The fluctuation of the friction coefficient of $400^{\circ}C$-oxidized/ nitrocarburized specimen is much severer than that of $500^{\circ}C$ specimen, due to the less amount of wear debris.

• Tribology and Lubricants
• /
• v.22 no.3
• /
• pp.127-130
• /
• 2006

DLC (Diamond Like Carbon) films show very desirable surface interactions with high hardness, low friction coefficient, and good wear-resistance properties. The friction behavior of hydrogenated DLC film is dependent on tribological environment, especially surrounding temperature. In this work, the tribological behaviors of DLC (Diamond-like carbon) films, prepared by the radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) method, were studied in elevated temperatures. The ball-on-disk tests with DLC films on steel specimens were conducted at a sliding speed of 60 rpm, a load of 10N, and surrounding various temperatures of $25^{\circ}C,\;40^{\circ}C,\;55^{\circ}C\;and\;75^{\circ}C$. The results show considerable dependency of DLC tribological parameters on temperature. The friction coefficient decreased as the surrounding temperature increased. After tests the wear tracks of hydrogenated DLC film were analyzed by optical microscope, scanning electron spectroscopy (SEM) and Raman spectroscopy. The surface roughness and 3-D images of wear track were also obtained by an atomic force microscope (AFM).

• The korean journal of orthodontics
• /
• v.23 no.4 s.43
• /
• pp.671-691
• /
• 1993

To estimate the possibility in the application of TiN ion-plating to the orthodontic appliance, this study investigated frictional force and frictional coefficient between non-ionplated and TiN ion-plated to the orthodontic appliance. The obtained results were as follows : 1. For each group, the frictional force between metal bracket and arch wire in the wet condition was exhibited lower than that in the dry condition. 2. In the dry condition, the frictional force was lowest with fourth group, and it increased in the order of the 3rd, 1st, and 2nd group. Same situation happened in the wet condition. 3. Experimental results using ceramic & plastic bracket showed that group B was lower than group A, and group D was similar to group C. 4. The surface texture after experiment showed that the scratch due to a friction with bracket was observed in an arch wire of dry contition. Also the surface of bracket was rougher than before. 5. We observed that a specimen surface processed with the TiN ion plating was smoother than that of without the TiN ion plating. 6. The surface texture of a metal bracket and an arch wire in the wet condition was observed smoother than that in the dry condition. 7. In the dry condition, the friction coefficient of each specimen was very similar to each other, but in the wet condition, the friction coefficient of specimen processed with the TiN ion plating showed lower values.

• KSTLE International Journal
• /
• v.4 no.2
• /
• pp.56-59
• /
• 2003

Boron carbide thin coatings were deposited on silicon wafers by DC magnetron sputtering using a ${B}_4$C target with Ar as processing gas. Various amounts of methane gas (${CH}_4$) were added in the deposition process to better understand their influence on tribological properties of the coatings. Reciprocating wear tests employing an oscillating friction wear tester were performed to investigate the tribological behaviors of the coatings in ambient environment. The chemical characteristics of the coatings and worn surfaces were studied using X-ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES). It revealed that ${CH}_4$addition to Ar processing gas strongly affected the tribologcal properties of sputtered boron carbide coating. The coefficient of friction was reduced approximately from 0.4 to 0.1, and wear resistance was improved considerably by increasing the ratio of ${CH}_4$gas component from 0 to 1.2 vol %. By adding a sufficient amount of ${CH}_4$(1.2 %) in the deposition process, the boron carbide coating exhibited lowest friction and highest wear resistance.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
• /
• 2003.11a
• /
• pp.78-84
• /
• 2003

Boron carbide thin coatings were deposited on silicon wafers by DC magnetron sputtering using a $B_4C$ target with As as processing gas. Various amounts of methane gas $(CH_4)$ were added in the deposition process to better understand their influence on tribological properties of the coatings. Reciprocating wear tests employing an oscillating friction wear tester were performed to investigate the tribological behaviors of the coatings in ambient environment. The chemical characteristics of the coatings and worn surfaces were studied using X-ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES). It revealed that $CH_4$ addition to As processing gas strongly affected the tribologcal properties of sputtered boron carbide coating. The coefficient of friction was reduced approximately from 0.4 to 0.1, and wear resistance was improved considerably by increasing the ratio of $CH_4$, gas component from 0 to $1.2\;vol\;\%$. By adding a sufficient amount of $CH_4\;(1.2\%)$ in the deposition process, the boron carbide coating exhibited lowest friction and highest wear resistance.