• Journal of Surface Science and Engineering
• /
• v.43 no.3
• /
• pp.132-141
• /
• 2010

NiTi alloy has been used for orthodontic wire due to good mechanical properties, such as elastic strength and frictional resistance, combined with a high resistance to corrosion. Recently, these wire were coated by polymer and ceramic materials for aesthetics. The purpose of this study was to investigate surface characteristics of polymer coated NiTi alloy wire for orthodontics using various instruments. Wires (round type and rectangular type) were used, respectively, for experiment. Polymer coating was carried out for wire. Specimen was investigated with field emission scanning electron microscopy(FE-SEM), energy dispersive x-ray spectroscopy(EDS) and atomic force microscopy(AFM). The phase transformation of non-coated NiTi wire from martensite to austenite occurred at the range of $14{\sim}15^{\circ}C$, in the case of coated wire, it occurred at the range of $16{\sim}18^{\circ}C$. Polymer coating on NiTi wire surface decreased the surface defects such as scratch which was formed at severe machined surface. From the AFM results, the average surface roughness of non-coated and coated NiTi wire was 13.1 nm, and 224.5 nm, respectively. From convetional surface roughness test, the average surface roughness of non-coated and coated NiTi wire was $0.046{\mu}m$, and $0.718{\mu}m$, respectively.

• Tribology and Lubricants
• /
• v.38 no.1
• /
• pp.8-14
• /
• 2022

Amorphous carbon (a-C) has excellent wear resistance and, therefore is used as a coating to protect numerous mechanical components to prolong their lifetimes. Among the a-C coatings, diamond-like carbon (DLC) and DLC-containing silicon (Si-DLC) receive extensive attention owing to their enhanced wear resistance and low frictional characteristics. In this study, the friction and wear characteristics of DLC and Si-DLC coatings are analyzed. For comparative analysis, DLC-coated and Si-DLC-coated vanes are utilized with the counterpart of a roller for the friction tests. Since the lubricated mechanical components are generally vulnerable to wear when a lubricant film does not form properly, friction tests are conducted under boundary lubrication conditions to promote wear. A cylinder-on-cylinder type tribometer is used to perform the friction tests with various normal load conditions. After the friction test, a 3D laser confocal microscope is used for quantifying the wear volume to calculate the wear rate of each specimen. Consequently, the DLC-coated specimen shows a lower coefficient of friction (COF) and wear rate than the specimen without the coating, while the Si-DLC coating shows a higher COF than the bare specimen. The results of this study are expected to contribute to improving the efficiency and reliability of compressors.

• Journal of the Korean Geotechnical Society
• /
• v.35 no.12
• /
• pp.7-13
• /
• 2019

In the case of the drilled shaft, one of the methods for calculating unit skin friction stress of rock socket parts is to measure the roughness of the excavated face. This method is to estimate the unit skin frictional resistance using a device which measures the roughness shape of the excavated face in the excavation step. In this study, the roughness shapes of the face of the rock socket part in the drilled shaft were measured directly in the perforated hole and the results are used to identify the characteristics of the unit skin friction of the bedrock. In addition, the static load test and the load transfer test were performed on the same pile to verify the result of the roughness test.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.15 no.1
• /
• pp.163-168
• /
• 1991

During Compression molding of polymeric composite materials, the flow characteristics should be obtained. Understanding the flow states may be useful for determination of optimum molding conditions, charge pattern etc. So far, for obtaining the flow analysis, no-slip boundary condition was applied on the mold surface. However, The study under consideration of the slip was conducted by Barone and Caulk. They have introduced the nondimensional parameter which is the ratio of viscous to friction resistance and governs the frictional condition. But the method for determining the parameter could not be proposed. In our work, the parameter which explains the interfacial friction is measured under a variety of molding conditions. Two-dimensional rectangular part and circular hollow disk are simulated with the measured parameter using the finite element method. Effects of the parameter on shapes of flow fronts are also presented.

• Journal of Power System Engineering
• /
• v.8 no.3
• /
• pp.30-35
• /
• 2004

In the steel making industries, the continuous casting process has been applied to the number of company because of its economical benefit. Casting rolls are utilized for frictional drive and transport of solidifying slap. Dimensional tolerances, mechanical stability and surface condition of the cast roll can affect both the surface and internal quality of the product being cast. To overcome these problems, the industry is accelerating on the rate of technology improvements. Samples were overlaid on the S45C steel by submerged arc welding process. And the hardness, wear, electrochemical corrosion and oxidation tests were carried out. Test results were that all these materials were satisfying basic requirements of caster rolls. By these results, the addition of 0.1%Nb and 0.15%V increase mechanical properties and tempering resistance by its superior carbide forming characteristics in low carbon $12{\sim}13%Cr$ martensitic stainless steels.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.18 no.3
• /
• pp.270-278
• /
• 2009

Friction stir welding is a relatively new solid state joining process. A6061-T6 and A5052-H32 aluminium alloy has gathered wide acceptance in the fabrication of light weight structures requiring a high strength to weight ratio and good corrosion resistance. This friction stir process uses a non-consumable tool to generate frictional heat in the abutting surfaces. The welding parameters such as tool rotational speed, welding speed, etc., and tool pin profile play a major role in deciding FSP zone formation in A6061-T6 and A5052-H32 aluminium alloy. Three different tool pin profiles have been used to fabricate the dissimilar butt joints. The formation of friction stir processed zone has been analysed macroscopically. Tensile properties of the joints have been evaluated and correlated with the friction stir processed zone formation.

• Tribology and Lubricants
• /
• v.23 no.4
• /
• pp.170-174
• /
• 2007

Wear and scuffing tests were conducted using friction and wear measurement of piston rings and cylinder blocks in low friction diesel engine. The frictional forces, wear amounts and cycles to scuffing in boundary lubricated sliding condition were measured using the reciprocating wear tester. The cylinder blocks were used as reciprocating specimens, and the piston rings with several coatings were used as fixed pin. Several coatings were used such as DLC, TiN, Cr-ceramic and TiAlN in order to improve the tribological characteristics. From the tests wear volume of piston ring surfaces applied various coatings were compared. During the tests coefficients of friction were monitored. Test results showed that DLC coatings showed good tribological properties. TiN and Cr-ceramic coated rings showed good wear resistance properties but produced high friction.

• Advances in materials Research
• /
• v.4 no.3
• /
• pp.165-178
• /
• 2015

Friction coefficient of epoxy metal matrix composites were investigated. The main objective was to increase the friction coefficient through rubber sole sliding against the epoxy floor coating providing appropriate level of resistance. This was to avoid the excessive movement and slip accidents. Epoxy metal matrix composites were reinforced by different copper wire diameters. The epoxy metal matrix composites were experimentally conducted at different conditions namely dry, water and detergent wetted sliding, were the friction coefficient increased as the number of wires increased. When the wires were closer to the sliding surface, the friction coefficient was found to increase. The friction coefficient was found to increase with the increase of the copper wire diameter in epoxy metal matrix composites. This behavior was attributed to the fact that as the diameter and the number of wires increased, the intensity of the electric field, generated from electric static charge increased causing an adhesion increase between the two sliding surfaces. At water wetted sliding conditions, the effect of changing number of wires on friction coefficient was less than the effect of wire diameter. The presence of water and detergent on the sliding surfaces decreased friction coefficient compared to the dry sliding. When the surfaces were detergent wetted, the friction coefficient values were found to be lower than that observed when sliding in water or dry condition.

• Geomechanics and Engineering
• /
• v.8 no.1
• /
• pp.53-66
• /
• 2015

Plastic wastes, particularly polyethylene terephthalate (PET) generated from used bottled water constitute a worldwide environmental issue. Reusing the PET waste for geotechnical applications not only reduces environmental burdens of handling the waste, but also improves inherent engineering properties of soil. This paper investigated factors affecting shear strength improvement of PET-mixed residual soil. Four variables were considered: (i) plastic content; (ii) plastic slenderness ratio; (iii) plastic size; and (iv) soil particle size. A series of unconfined compression tests were performed to determine the optimum configurations for promoting the shear strength improvement. The results showed that the optimum slenderness ratio and PET content for shear strength improvement were 1:3 and 1.5%, respectively. Large PET pieces (i.e., $1.0cm^2$) were favorable for fine-grained residual soil, while small PET pieces (i.e., $0.5cm^2$) were favorable for coarse-grained residual soil. Higher shear strength improvement was obtained for PET-mixed coarse-grained residual soil (148%) than fine-grained residual soils (117%). The orientation of plastic pieces in soil and frictional resistance developed between soil particles and PET surface are two important factors affecting the shear strength performance of PET-mixed soil.

• Tribology and Lubricants
• /
• v.23 no.1
• /
• pp.14-18
• /
• 2007

SCM415 alloy was implanted with nitrogen ions using plasma source ion implantation (PSII), at a dose range of $1{\times}10^{17}\;to\;6{\times}10^{17}N^{+}cm^{-2}$. Auger electron spectrometry (AES) was used to investigate the depth profile of the implanted layer. Friction and wear tests were carried out on a block-on-ring wear tester. Scanning electron microscopy (SEM) was used to observe the micro-morphology of the worn surface. The results revealed that after being implanted with nitrogen ions, the frictional coefficient of the surface layer decreased, and the wear resistance increased with the nitrogen dose. The tribological mechanism was mainly adhesive, and the adhesive wear tended to become weaker oxidative wear with the increase in the nitrogen dose. The effects were mainly attributed to the formation of a hard nitride precipitate and a supersaturated solid solution of nitrogen in the surface layer.