• Tribology and Lubricants
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• v.34 no.6
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• pp.270-278
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• 2018

STS 316L prepared by additive manufacturing (AM) exhibits deterioration of mechanical properties and wear resistance due to the presence of defects such as black-of-fusion defects, internal porosity, residual stress, and anisotropy. In addition, high surface roughness (integrity) of AM products remains an issue. This study aimed to apply ultrasonic nanocrystal surface modification (UNSM) technology to STS 316L prepared by AM to increase the surface hardness, to reduce the surface roughness, and to improve the friction and wear behavior to the level achieved by bulk material manufactured using traditional processes. Herein, the as-received and polished specimens were treated by UNSM technology and their resulting properties were compared and discussed. The results showed that UNSM technology increased the surface hardness and reduced the surface roughness of the as-received and polished specimens. These results can be attributed to grain size refinement and pore elimination from the surface. Moreover, the friction of the as-received and polished specimens after UNSM technology was lower compared to those of the as-received and polished specimens, but no significant differences in wear resistance were found.

• Tribology and Lubricants
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• v.36 no.6
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• pp.315-319
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• 2020

In various fields, several studies based on carbon nanotubes (CNTs) have been conducted. The results of previous studies, wherein CNT coatings have been incorporated as solid lubricants, demonstrate that the friction and wear characteristics of CNT coatings can be improved through the absorption/dispersion of the contact pressure by controlling the stiffness of the nanomesh structure comprising CNT strands. In this study, the friction and wear characteristics of the following are compared: CNT coating formed by spin coating of CNT solution, compressed CNT coating, and compressed/heated CNT coating (wherein CNT strands are squeezed through compression and/or heating). It is observed that the friction coefficient of the CNT coating having the largest number of voids between the CNT strands is significantly lower than those of the compressed CNT coating and the compressed/heated CNT coating. The wear tracks of the compressed CNT coating and the compressed/heated CNT coating indicate that some parts become torn or adhere into a lump. However, in the case of the CNT coating, a smooth wear surface is formed by rubbing. Furthermore, as the void space between the squeezed and adhered CNT strands decreases, the resistance to structural deformation increases, thereby resulting in an increased frictional force and a wear pattern that becomes torn or forms a lump. Hence, the results obtained from this study corroborate that the friction and wear characteristics of CNT coatings can be enhanced through the absorption/dispersion of the contact pressure by controlling the stiffness of the nanomesh structure of CNT coatings.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.7
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• pp.605-611
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• 2011

Shimmy is a self-excited vibration in lateral and torsional directions of a landing gear during either the take-off or landing. It is caused by a couple of conditions such as a low torsional stiffness of the strut, a free-play in the landing gear, a wheel imbalance, or worn parts, and it may make the aircraft unstable. This study was performed for an analysis of the shimmy stability on a small aircraft. A nose landing gear was modeled as a linear system and characterized by state-equations which were used to analyze the stability both in the frequency and time-domain for predicting whether the shimmy occurs and investigating a good design range of the important parameters. The root-locus method and the 4th Runge-Kutta method were used for each analysis. Because the present system has a simple mechanism using a friction to reinforce the stability, the friction, a non-linear factor, was linearized by a describing function and considered in the analysis and observed the result of the instability reduction.

• Journal of the Korean Geosynthetics Society
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• v.5 no.4
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• pp.27-33
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• 2006

Frictional properties between geostrip and sand paper interface were estimated considering soil particle size also the friction coefficients and angles were determined with normal stress. Three kinds of geostrips of design strength 50, 70, 100 KN/m were used and 5 sandpapers of P100, P220, P320, P400, P600 were used also. Shear strength between geostrip and sand paper interface with design strength showed big difference and this is due to the uniform surface pattern of each geostrip when contact to sandpaper without regard to design strength. Shear strength of geostrip was increased with design strength and geostrips/P100 sandpaper interface showed the biggest value. Finally, all of geostrips showed the decrease phenomena of post-peak strength and this is due to the abrasion of geostrip surface by shear test.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.237-237
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• 2010

에너지소비와 엔진 부품의 마모문제를 해결하기 위해, soft-phase를 doping한 hard상의 coating에 대한 실험이 최근 중요한 연구 테마로서 진행 중이다. 특히 MoN-Cu coating은 미국 Argon 연구소의 Erdemer박사 등에 의해, 고온 및 상온 윤활성이 우수한 코팅층으로 보고된 이후 많은 연구가 진행되고 있다. 그러나 기존 연구는 Mo와 Cu의 원소타겟을 이용한 연구가 주력이 되었다. 높은 경도와 저온 고온에서의 낮은 나노 혼합물 코팅 종류는 일반적으로 Mo와 Cu와 같은 원소 합금을 이용한 다수 타겟을 이용한 공정에 의해 진행되어왔다. 이러한 복수의 타겟에 의해 증착 동안에는, 정확한 조성, 큰 크기의 시편들의 균일 증착을 조절하기가 쉽지 않다. 또한, 코팅층에 3번째 성분을 추가하기가 어렵다는 문제점이 있다. 본 연구에서는, 최상의 마찰계수와 표면경도를 보이는 MoN-Cu층을 형성시키기 위하여 합금으로 단일 타겟을 제조하였다. 이를 위한 최적 조성을 결정하기 위하여 Mo, Cu 단일 타겟을 이용한 Unbalanced Magnetron sputtering 법으로 다양한 Cu 함량의 MoN+Cu 합금을 제조하였으며, 이에 대한 경도 및 마찰계수 측정을 통해 최적의 Cu 함량을 결정하였다. 이러한 최적 조성의 Cu 타겟제조를 기계적 합금화와 Spark plasma sintering 기술을 이용하여 제작하였으며, 복수의 합금 타겟과 단일 합금 타겟으로 제조된 코팅층의 물성 비교를 통해 합금 타겟의 우수성 여부를 확인하고자 하였다. 증착된 두 조건의 물성을 비교 단일 타겟은 두가지 타겟으로 증착한 것보다 비슷한 조성에서 경도가 높았으며 경도가 비슷한 조성에서는 마찰계수가 낮았다. 또 입자는 10 at.% Cu 조성에 대해 단일타겟이 50nm 결정립을 갖는 반해 단일타겟은 측정이 불가능할 정도의 미세한 결정립을 가졌다. Erdemir의 연구 결과에 의하면, Cu 함량이 증가함에 따라 columnar 형태의 코팅층구조가 나노 구조로 변한다고 하였는데, 본 연구에서 복수의 원소 타겟에서는 확인이 안되었으며, 단일 합금 타겟에서 완벽한 featurless 형태의 코팅층 구조와 우수한 조도의 박막층을 얻을 수 있었다. 이렇게 제조된 다양한 코팅층에 대한 마찰계수 측정이 진행중이다.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.14 no.2
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• pp.69-78
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• 1978

It is well known that the aluminizing steel is excellent in corrosion resistance and heat resistance. Therefore it has been used as boiler parts, heat exchanger parts and guide rails which are used under comparatively simple conditions. Recently, it has been noticed that aluminizing steel has high resistance to various atmosphere, high temperature oxidation and seawater resistance. So its usage has been extended widely to the production of parts such as intake and exhaust valve of internal combustion engine, turbine blade and pipelines On ships which required such properties. It is considered that aluminium coated steel is excellent in wear resistance because of high hardness on main ingredient FezAIs of Fe-AI alloy layer existed in diffusion coating layer. And it will beused as a new material taking wear resitance with seawater resistance in marine field. However it is difficult to findout any report concering the wear behaviors or properties of alum in izing steel. In this study the experiment was carried out under the condition of rolling-sliding contact using an Amsler-type wear testing machine at 0.80, 0.91, 1. 10, 1. 25% of slip ratio and 55.43, 78.38, 110.85 kg/mm^2 of Hertz's contact stress in run-in period for the purpose of service-ability test of aluminizing steel as a wear resisting material and obtaining the available design data. The followings are the obtained results from the experimen tal study; 1) The 2nd diffusion material has most excellent wear resistance. This material has brought out about 18% decrease of wear weight in a lower friction load level and 40~G decrease in a higher level comparing to the raw material. 2) Satisfactory effect of wear resistivity cannot be much expected in 2nd diffusion specimens. This is considered due to the formation of fine void in the alloy layer near the boundary to the aluminium layer. 3) Fracture on friction surface of aluminizing steel by the rolling-sliding contact is spalling, and spalling crack occurres initially beneath the specimen surface near the boundary in diffusion coating layer.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.2
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• pp.57-62
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• 2007

The lubricational characteristics about friction wear has an effect on the material quality of surface. In this paper, we studied the lubricational characteristics through the surface modification experiment by spray coating the surface with $MoS_{2}$ and PTFE solid lubricants. In the case of $MoS_{2}$ and PTFE coating, the friction coefficient of Journal is lower than that for noncoating so the friction characteristics is excellent. In particular, the beginning characteristics of $MoS_{2}$ coating is excellent, and in the case of PTFE coating, seizure dose not appear seizure. $MoS_{2}$ and PTFE coating are excellent in the extreme pressure at high load. The wear characteristics is excellent in the following order; PTFE < $MoS_{2}$ < Non Coating. For Non coating, seizure appears at the beginning due to the heat, but in the case of $MoS_{2}$ and PTFE coating, it will have the excellent heat stability even at high temperature.

• Tribology and Lubricants
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• v.30 no.5
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• pp.291-294
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• 2014

Multiple additives can help improve the performance of generally used lubricants. These additives include MoS2, cadmium, chloride, indium, sulfide, and phosphide, which are harmful to both humans and the environment. Thus, researchers in this industry have been trying to reduce the use of these additives by finding alternatives. Nanodiamonds are one of these candidates. Nanodiamond particles are very hard, chemically stable, and highly heat-conductive. This research involved uniformly dispersing nanodiamond particles in marine engine oils via a matrix synthesis method at various concentrations (0, 0.1, 0.3, 0.5, and 1.0 wt). Friction and wear tests involved constant loads on ball-on-disk specimens, where the ball was AISI 51200 steel, the disk was AISI 1020 steel, and the sliding speed was 0.217 m/s. The lowest wear occurred at a suitable concentration of nanodiamonds (0.3 wt). However, excessive amounts of nanodiamonds caused them to act as abrasive debris because of their hardness, which increased the wear amount. The friction coefficient decreased as the nanodiamond concentration increased because their octagonal, almost spherical shape caused them to act as rolling contact elements between two surfaces.

• Tribology and Lubricants
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• v.35 no.5
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• pp.317-322
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• 2019

In spite of progress in tribological research, machine component failure due to friction and wear has been reported frequently. This failure may lead to secondary damage that can cause huge expense for maintenance and repair. To prevent economic loss, it is important to detect and predict the initial failure point. In this sense, various researchers have been tried to develop Condition Monitoring (CM) method using Acoustic Emission (AE) generated while the materials undergo failure. In this study, effect of particles on friction and wear was investigated using the pin-on-plate friction test and AE signal was recorded with a band-width type AE sensor. The experiments were performed in dry and lubricant conditions using steel and glass as specimens. After the experiment, 3D laser microscope image was captured to evaluate the wear behavior quantitatively. The AE signal was analyzed in time-domain and frequency-domain. The amplitude was compared with the frictional results. The results of this study showed that particle generation accelerate wear, generate high magnitude AE signal and change the frequency characteristics of the signal. Also, lubricant condition test results showed low coefficient of friction, low wear rate, and low magnitude of AE signal compared to the dry condition. It is expected that the results of this study will aid in better assessment of wear in CM technology

• Tribology and Lubricants
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• v.38 no.6
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• pp.227-234
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• 2022

Recently, the demand for improving energy efficiency has rapidly increased because of the growing concerns over environmental issues. In this work, the tribo-test and simulation for the initial wear and lubrication performance were performed for the piston pin in the small end system of the connecting rod of a marine engine, to obtain useful data for improving the efficiency of marine engine systems. In addition, a diamond-like carbon (DLC) coating was applied to the piston pin to explore feasibility of eliminating the bush used in the system. The initial wear and lubrication characteristics between the uncoated piston pin and bush were compared with that between the DLC-coated piston pin and connecting rod in the tribo-test. The simulation for the wear and lubrication performance according to the wear progression was conducted based on the data obtained from the test. The wear characteristics were quantitatively assessed by the wear depth and wear volume, and the lubrication performance was characterized with the change of pressure and minimum oil film thickness with respect to the crank angle. It was found that the DLC-coated piston pin may provide better initial wear characteristics and lubrication performance. The results of this work may provide fundamental information for marine engines with improved efficiency.