• Journal of Biomedical Engineering Research
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• v.20 no.1
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• pp.99-106
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• 1999

Ultra-high molecular weight polyethylene (UHMWPE) was crosslinked in the melt state to enhance wear resistance, Dicumyl peroxide (DCP) and triallyl cyanurate (TAC) was used as a crosslinking agent and a promoter, respectively. With increasing amount of DCP and TAC used, gel content of crosslinked UHMWPE (XUMPE) increased, while the melting temperature, crystallizaiton temperature, crystallinity, and tensile properties decreased. The results of pin-on-disk wear test and ball-on-disk test with small applied load showed reduced wear volumes of XUMPE from that of the unmodified UHMWPE. As the wear mechanism effected in the experimental condition of this study was thought to be deformation rather than adhesion or fatigue, a new parameter, the ratio of maximum contact stress to yield stress, was proposed to correlate well with observed wear resistance. In ball-on-disk wear test with larger applied load, XUMPE showed higher wear volumes than that of the unmodified UHMWPE which were accompanied with increased friction coefficients and surface roughness of the wear tracks. When contact stress was well above yield stress, the failure of XUMPE, as well as deformation, was thought to be much accelerated.

• The Korean Journal of Ceramics
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• v.4 no.3
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• pp.193-198
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• 1998

This paper presents the effects of an initial braking velocity, a braking pressure, and the number of braking stop on the tribological behaviors for the three different C-C composites using an inertia dynamic-friction tester. The C-C composites were prepared through the processes of several cycles of pitch impregnation/carbonization with different friction surface texture such as continuous 8-harness satin fabric (ADD-1), chopped fiber (ADD-2) and chopped fiber (ADD-3) having higher fiber volume fraction on friction than ADD-2 by about 10%. ADD-1 exhibited a higher fraction coefficient (0.41~0.33) than those of ADD-2 and ADD-3 (0.32~0.26) under the various initial braking velocities and braking pressures. The fraction coefficients decreased with increasing the initial velocity and the braking pressures. Wear rate by the thickness change after every 25 stop indicated that ADD-2 and ADD-3 having 1.7~2.7 $\mu\textrm{m}$/stop/pair were much lower than that of ADD-1 showing 5.0~6.5 $\mu\textrm{m}$/stop/pair. All specimens showed a little bit lower wear rate during the middle stage than the initial and latter stages among 100 braking stops. ADD-1 showed higher friction coefficient and wear rate due to the active pull-out of the fibers, evidenced by thicker were film and wear debrises.

• Tribology and Lubricants
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• v.30 no.4
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• pp.240-245
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• 2014

Low alloy heat resistant brake disk and sintered brake pad are applied to mechanical brake system for the speed-up of urban rapid transit. In this research, we analyzed how the frictional characteristics between brake disk and pad are influenced by the disk mass. At a high disk mass, the friction stability was the lower value as a result of the lack of tribofilm formation at the disk surface. Wear rates of friction materials showed the higher value at a low disk mass and wear rates of 10 mm and 15 mm showed the similar level. Average friction coefficient was the lower value at the 10 mm disk thickness and range of variation of average friction coefficient was also the smaller value at the 10 mm disk thickness. However, there were no significant changes in the friction coefficients under any of test conditions. Surface roughness of a disk showed the highest value at the 5 mm disk and surface roughnesses of 10 mm and 15 mm showed the similar level. As a result, friction characteristics of disk mass influenced the friction stability, as well as the wear rate of friction pad and disk, but not the friction coefficient.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.41 no.1
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• pp.110-117
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• 2018

Machines and facilities are physically or chemically degenerated by continuous usage. One of the results of this degeneration is the process mean shift. By the result of degeneration, non-conforming products and malfunction of machine occur. Therefore a periodic preventive resetting the process is necessary. This type of preventive action is called 'preventive maintenance policy.' Preventive maintenance presupposes that the preventive (resetting the process) cost is smaller than the cost of failure caused by the malfunction of machine. The process mean shift problem is a field of preventive maintenance. This field deals the interrelationship between the quality cost and the process resetting cost before machine breaks down. Quality cost is the sum of the non-conforming item cost and quality loss cost. Quality loss cost is due to the deviation between the quality characteristics from the target value. Under the process mean shift, the quality cost is increasing continuously whereas the process resetting cost is constant value. The objective function is total costs per unit wear, the decision variables are the wear limit (resetting period) and the initial process mean. Comparing the previous studies, we set the process variance as an increasing concave function and set the quality loss function as Cpm+ simultaneously. In the Cpm+, loss function has different cost coefficients according to the direction of the quality characteristics from target value. A numerical example is presented.

• Journal of the Korean Society of Safety
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• v.18 no.3
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• pp.14-21
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• 2003

This study deals with the influence of ceramic coating on characteristics of friction and abrasion of aluminum allot(7075 T6) used in mechanical casting. In this research, frictional wear characteristic of ceramic coating materials such as $A1_2O_3$, $Si_3N_4$, SiC was investigated using aluminum alloy(7075 T6) and stainless 403 cast iron under room temperature and normal air pressure. The coating layer was observed using SEM. The conclusions are as follows: 1) Friction coefficients of $A1_2O_3$, SiC and $Si_3N_4$ are obtained 0.63 0.56 and 0.54 respectively. 2) Abrasion resistance of stainless 403 cast iron with $Si_3N_4$ is the best among the ceramic coating materials. 3) Abrasion mechanism of aluminum alloy(7075 T6) coaled with ceramic material and stainless 403 cast iron is caused by brittle fracture. 4) Coating the ceramic material on the aluminum alloy(7075 T6) can effectively increase the antiwear, impact properties, and corrosion resistance.

• International Journal of Ocean System Engineering
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• v.3 no.3
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• pp.147-151
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• 2013

This study was to correctly estimate the friction and wear behavior of carbon fiber and PEEK sheet composites, and the validity of using them as alternatives to the metal-based materials used for artificial hip joints. Moreover, this work evaluated the friction coefficient according to the fiber ply orientation, along with the fractured surfaces of the carbon/PEEK composites. The unidirectional composites had higher friction coefficients than those multidirectional composites. This was caused by the debonding between the carbon fiber and the PEEK sheet, which was proportional to the contact area between the sliding surface and the carbon fiber. The friction test results showed that there was no significant differences in relation to the fiber ply orientation. However, in a case where the speed was 2.5 m/s, the friction coefficient was relatively large for configuration I. The friction surface of the specimen was analyzed using an electron microscope. In all cases, the debonding of the fiber and PEEK could be confirmed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.250-253
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• 2009

In this study, the friction test was performed to find friction characteristics of advanced high strength steel (AHSS) sheets and the multiple regression method was employed to obtain friction models. The friction coefficients associated with the lubricant viscosity, drawing speed, and blank holding pressure are measured. Differently from GA steel sheets, the effects of the lubricant viscosity and pulling speed are a little, which are explained by a theory of adhesion and wear as well as a deformation of friction surface. In addition, the effects of friction parameters are numerically represented by friction regression models.

• Journal of the Korean Ceramic Society
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• v.34 no.4
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• pp.380-386
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• 1997

The tribological properties of ceramics are very important in the application to engineering ceramic parts such as seal rings, pump parts, thread guides, and so on. In this study, the effects of graphite addition on the mechanical and tribological properties of alumina/graphite composites were investigated. The composites were prepared by the adding of graphite powder to the mixture of Al2O3, talc and calcium carbonate. Bending strength, water absorption, friction coefficient, the amount of worn out material at a certain time, and maximum surface roughness(Rmax) of the prepared composites were measured. Crystalline phases and microstructure were examined with XRD and SEM. The melt of Al2O3-CaO-MgO-SiO2 system was shown over 10 vol% graphite composition. As the amount of the graphite is increased, needle like crystals of mullite were formed and grown. We obtained the good properties of friction coefficients and wear resistance at the powder composition containing 15 vol% of graphite.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.1
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• pp.48-55
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• 2003

Hidden Markov Model(HMM) has a doubly embedded stochastic process with an underlying stochastic process that can be observed through another set of stochastic processes. This structure of HMM is useful for modeling vector sequence that doesn't look like a stochastic process but has a hidden stochastic process. So, HMM approach has become popular in various areas in last decade. The increasing popularity of HMM is based on two facts : rich mathematical structure and proven accuracy on critical application. In this paper, we applied continuous HMM (CHMM) approach with AR coefficient to detect and predict the chatter of lathe bite and to diagnose the wear of oil Journal bearing using rotor shaft displacement. Our examples show that CHMM approach is very efficient method for machine health monitoring and prediction.

• Korean Journal of Materials Research
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• v.1 no.1
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• pp.9-17
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• 1991

TiC coating formed on $Si_3N_4-TiC$ composite ceramic by chemical vapor deposition (CVD) has an improved microstructures, better thermal shock resistance and interfacial bonding than TiN coating does. TiN coating formed by CVD, however, has lower friction coefficients against steels and better chemical stability. The experimental results indicate that the coated insert is superior to the uncoated one in flank and crater wear resistance. And the multilayer coating shows an improved wear resistance than the monolayer coating.