• Tribology and Lubricants
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• 제15권4호
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• pp.343-353
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• 1999

The role of viscosity index improver's(Ⅶ) additives for modem engine lubrication is complex. Under the condition of atmosphere or low shear rate, the characteristics of Ⅶ added lubricant is verified and quoted frequently for mathematical model of lubricant behavior. However, recent research shows that added lubricant has the characteristics of shear thinning at high shear rate condition although it performs well enough over the whole range of working temperature. At high shear rate, they show significant decrease of apparent viscosity irrespective of temperature. Many experimental researches verify that Ⅶ added lubricant shows boundary film layer formation on the solid surface as well as shear thinning effect by its polymeric molecular characteristics. The intend of our research is to verify the effects of Ⅶ from the viewpoint of continuum mechanics, because conventional Reynolds'equation with only pressure-viscosity relation cannot fully predict the lubricant behavior under the Ⅶ added condition. In these aspects, Reynolds'equation of Newtonian fluid model lacks the reflection of real fluid behavior and there is no way to explain the non-linear characteristics of Ⅶ added lubricant. In this research, we mathematically modeled the Ⅶ added lubricant behaviors which are the characteristics of non-Newtonian fluid behavior at high shear rate and boundary film formation on the solid surface. The consideration of elastic deformation in the contact region is also included in our computation and finally the converged film pressure and the film thickness with elastic deformation are obtained. The results are compared with those of Newtonian fluid model.

• 소성∙가공
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• 제10권7호
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• pp.543-550
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• 2001

In order to find the effect of material property and lubricant viscosity on the frictional characteristics a sheet metal friction tester was designed and tensile test, surface roughness test, and friction test were performed with several kinds of drawing oils. Test results show that as the lubricant viscosity becomes lower, the friction coefficient is higher. When surface roughness is extremely low or high, friction coefficient is also high. Using these test results, the friction model considering lubricant viscosity and surface roughness is developed. The validity and accuracy of the friction model are shown by comparing the punch loads among FEM analysis results employing current friction model and conventional friction model respectively and experimental measurement.

• 소성∙가공
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• 제11권4호
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• pp.349-354
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• 2002

In order to find the effect of lubricant viscosity, sheet surface roughness, tool geometry, and forming speed on the frictional characteristics in sheet metal forming, a sheet metal friction tester was designed and manufactured and friction test of various sheet were performed. Friction test results showed that as the lubricant viscosity becomes lower, the friction coefficient is higher. When surface roughness is extremely low or high, the friction coefficient is relatively high. The result also show that as the punch radius and punch speed becomes bigger, the friction coefficient is smaller. Using experimental results, the mathematical expression between friction coefficient and lubricant viscosity, surface roughness, punch comer radius, or punch speed is also described.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2001년도 춘계학술대회 논문집
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• pp.24-27
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• 2001

Friction between the sheet and tools is one of the important factors affecting the sheet metal forming. Therefore, the clarification of the friction is essential to improve the formability of the sheet. In order to find the effect of material property and lubricant viscosity on the frictional characteristics, tensile test, surface roughness test and friction test are performed. The results showed that friction characteristics are mainly influenced by the surface roughness and lubricant viscosity. A mathematical model of the friction is developed for calculating friction coefficient in terms of surface roughness and lubricant viscosity. The validity and accuracy of the mathematical model of the friction are verified through the experiment and FEM analysis.

• 소성∙가공
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• 제13권6호
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• pp.528-534
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• 2004

In order to find the effect of lubricant viscosity, tool geometry, forming speed, and sheet material properties on the friction in the sheet metal forming, friction tests were performed. Friction test results show that as the lubricant viscosity becomes lower, the friction coefficient is higher. When surface roughness is extremely low or high, the friction coefficient is high. The bigger die corner radii and punch speed are, the smaller is the friction coefficient. From the experimental observation, the friction model which is the mathematical expression of friction coefficient in terms of lubricant viscosity, roughness and hardness of sheet surface, punch corner radius, and punch speed is constructed. By comparing the punch load found by FEM using the proposed friction model with that obtained from the experiment in 2-D stretch forming, the validity and accuracy of the friction model are demonstrated.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2003년도 학술대회지
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• pp.215-223
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• 2003

Viscosity index improver (VII) is one of the major additives to the modern multigrade lubricants for the viscosity stability against temperature rise. However, it causes shear thinning effects which make the film thickness lessened very delicately at high shear rate $(over\;10^5\;s^{-1})$ of general EHL contact regime. In order to exactly verify the VII's performance of viscosity stability at such high shear rate, it is necessary to make the measurement of EHL film thickness down to $\~100nm$ with fine resolution for the preliminary study of viscosity control. In this work, EHL film thickness of VII added lubricant is measured with the resolution of $\~5nm$, which will give very informative design tool for the synthesis of lubricants regarding the matter of load carrying capacity at high shear rate condition.

• Tribology and Lubricants
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• 제36권6호
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• pp.365-370
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• 2020

Recently, additive manufacturing (AM) technology has been applied to various industries such as automotive, aviation, medical, and electronics. Most prior studies are limited to the mechanical properties of printed materials, and few studies are being conducted on their tribological characteristics. However, the friction and wear characteristics of the material should be studied in order to utilize the components manufactured using AM technology as mechanical parts. In this study, the friction and wear characteristics of acrylonitrile-butadiene-styrene (ABS)-like resin printed with stereo lithography apparatus (SLA) 3D printing are evaluated according to the viscosity of silicon oil lubricant using a ball-on-disk experiment. Lubricants with a viscosity of 500, 1000, and 2000 cSt are prepared for the experiment. If silicon oil lubricants are used during the ball-on-disk test, the coefficient of friction (COF) and wear rates are significantly reduced, and the higher the viscosity of the lubricant, the lower will be the COF and wear rates. It is also verified that the temperature of the specimen owing to friction also decreases according to the viscosity of the lubricant. This is because of the silicon oil film thickness, and the higher the viscosity of the lubricant, the thicker will be the oil film. More studies on the tribological characteristics of 3D printing materials and suitable lubricants will be required to use 3D printed parts as mechanical elements.

• Journal of Advanced Marine Engineering and Technology
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• 제15권1호
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• pp.59-70
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• 1991

Rupture of lubricant film, thermal characteristics, and variation of viscosity are very important factors to evaluate the performance of journal bearing. Variation of external conditions, load or rotational speed, largely influence these facters. For example, if rotational speed increases lubricant bulk temperature increases and viscosity drops. In this paper the effect of rotational speed variation on the characteristics of lubricant film in a journal bearing is investigated by experiment and theoretical analysis. It has been measured number of lubricant film rupture and lubricant bulk temperature form journal bearing which have been established at the various operating speed of shaft. The range of speed variation is from 900rpm to 2100rpm. Theoretical analysis has been carried out for rupture of lubricant film and thermal characteristics, and these results are compared with experimental results.

• Tribology and Lubricants
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• 제11권2호
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• pp.1-7
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• 1995

Viscosity index is an arbitray number used to characterize the variation of lubricant viscosity with respect to temperature. It is well recognized in the oil industry that as refining severity increases, lubricant VI increases. Consequently, VI is often perceived as a measure of lubricant quality. Futhermore, a 95 VI minimum specification is commonly imposed in marketing base stocks. These factors provide the incentitive for this study to carefully analyze VI definition and two component viscosity blending techniques to investigate how they affect VI change, and finally to examine possible avenues to produce 95+VI base stocks by blending sub-95 VI base stocks.

• Korea-Australia Rheology Journal
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• 제15권3호
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• pp.117-124
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• 2003

Elastohydrodynamic lubrication (EHL) film is measured under the condition of viscosity index improver added to base oil. In-situ optical contact method using the interference principle make the measuring resolution of ~5 nm possible and enables the measuring range all over the contact area of up to ~300 $\mu\textrm{m}$ diameter. What is more important to the developed method by the author is that the measurement of EHL film thickness is possible in the range from 100 nm to 2 $\mu\textrm{m}$, which is the regime of worst contact failures in precision machinery. Viscosity index improver (VII) is one of the major additives to the modem multigrade lubricants for the viscosity stability against temperature rise. However, it causes shear thinning effects which make the film thickness lessened very delicately at high shear rate (over $10^5 s^{-1}$) of general EHL contact regime. In order to exactly verify the VIIs performance of viscosity stability at such high shear rate, it is necessary to make the measurement of EHL film thickness down to ~100 nm with fine resolution for the preliminary study of viscosity control. In this work, EHL film thickness of VII added lubricant is measured with the resolution of ~5 nm, which will give very informative design tool for the synthesis of lubricants regarding the matter of load carrying capacity at high shear rate condition.