Extreme Pressure Environments

The aim of the paper is to investigate the effect of size of multiwalled carbon nanotubes (MWCNTs) as additives for dispersion in gear oil to improve the tribological properties. Since long pristine MWCNTs tend to form clusters compromising dispersion stability, they are mildly processed in a ball mill to shorten the length and stabilized with a surfactant before dispersing in lubricant. Investigations are made to assess the effect of ball milling on the size and structure of MWCNTs using electron microscopy and Raman spectroscopy. The long and shortened MWCNTs are dispersed in EP 140 gear oil in 0.5% weight. The stability of the dispersed multiwalled carbon nanotubes is evaluated using light scattering techniques. The antiwear, antifriction, and extreme pressure properties of test oils are evaluated on a four-ball wear tester. It is found that ball milling of MWCNTs has a strong effect on the stability and tribological properties of the lubricant. From Raman spectroscopy, it is found that ball milling time of up to 10 hours did not produce any defects on the surface of MWCNTs. The stability of the lubricant and the antiwear, antifriction, and extreme pressure properties have improved significantly with dispersion shortened MWCNTs. Ball milling for longer periods produces defects on the surface of MWCNTs reducing their advantage as oil additives.

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A New Model For Hydrogen-Induced Crack (HIC) Growth in Metal Alloy Pipelines Under Extreme Pressure

Procedia Structural Integrity ◽

10.1016/j.prostr.2020.11.056 ◽

2020 ◽

Vol 28 ◽

pp. 873-885

Author(s):

Alla V. Balueva ◽

Ilia N. Dashevskiy ◽

Jerry Magana

Keyword(s):

Metal Alloy ◽

Extreme Pressure ◽

New Model

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Probability Characteristics, Area Reduction, and Wind Directionality Effects of Extreme Pressure Coefficients of High-Rise Buildings

Applied Sciences ◽

10.3390/app11157121 ◽

2021 ◽

Vol 11 (15) ◽

pp. 7121

Author(s):

Shouke Li ◽

Feipeng Xiao ◽

Yunfeng Zou ◽

Shouying Li ◽

Shucheng Yang ◽

...

Keyword(s):

Probability Distribution ◽

Pressure Coefficient ◽

Wind Pressure ◽

Extreme Pressure ◽

Distribution Law ◽

Distribution Fitting ◽

Pressure Coefficients ◽

High Rise ◽

Area Reduction ◽

The Mean

Wind tunnel tests are carried out for the Commonwealth Advisory Aeronautical Research Council (CAARC) high-rise building with a scale of 1:400 in exposure categories D. The distribution law of extreme pressure coefficients under different conditions is studied. Probability distribution fitting is performed on the measured area-averaged extreme pressure coefficients. The general extreme value (GEV) distribution is preferred for probability distribution fitting of extreme pressure coefficients. From the comparison between the area-averaged coefficients and the value from GB50009-2012, it is indicated that the wind load coefficients from GB50009-2012 may be non-conservative for the CAARC building. The area reduction effect on the extreme wind pressure is smaller than that on the mean wind pressure from the code. The recommended formula of the area reduction factor for the extreme pressure coefficient is proposed in this study. It is found that the mean and the coefficient of variation (COV) for the directionality factors are 0.85 and 0.04, respectively, when the orientation of the building is given. If the uniform distribution is given for the building’s orientation, the mean value of the directionality factors is 0.88, which is close to the directionality factor of 0.90 given in the Chinese specifications.

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Sonication-Assisted Solvothermal Synthesis of Noncovalent Fluorographene/Ceria Nanocomposite with Excellent Extreme-Pressure and Anti-Wear Properties

Tribology International ◽

10.1016/j.triboint.2021.106991 ◽

2021 ◽

pp. 106991

Author(s):

Limin Ma ◽

Zhangpeng Li ◽

Kaiming Hou ◽

Weihong Jia ◽

Jinqing Wang ◽

...

Keyword(s):

Solvothermal Synthesis ◽

Extreme Pressure ◽

Wear Properties

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On the Fictitious Grease Lubrication Performance in a Four-Ball Tester

Lubricants ◽

10.3390/lubricants9030033 ◽

2021 ◽

Vol 9 (3) ◽

pp. 33

Author(s):

Sravan K. Joysula ◽

Anshuman Dube ◽

Debdutt Patro ◽

Deepak Halenahally Veeregowda

Keyword(s):

Critical Factor ◽

Maximum Load ◽

Test Method ◽

Extreme Pressure ◽

Motor Speed ◽

Low Friction ◽

Grease Lubrication ◽

Additive Package ◽

Variable Frequency Drive ◽

Lubrication Performance

The extreme pressure (EP) behavior of grease is related to its additives that can prevent seizure. However, in this study following ASTM D2596 four-ball test method, the EP behavior of greases was modified without any changes to its additive package. A four-ball tester with position encoders and variable frequency drive system was used to control the speed ramp up time or delay in motor speed to demonstrate higher grease weld load and lower grease friction that were fictitious. A tenth of a second delay in speed ramp up time had showed an increase in the weld load from 7848 N to 9810 N for grease X and 6082 N to 9810 N for grease Y. Further increase in the speed ramp up time to 0.95 s showed that the greases passed the maximum load of 9810 N that was possible in the four-ball tester without seizure. The mechanism can be related to the delay in rise of local temperature to reach the melting point of steel required for full seizure or welding, that was theoretically attributed to an increase in heat loss as the speed ramp-up time was increased. Furthermore, the speed ramp up time increased the corrected load for grease X and Y. This resulted in lower friction for grease X and Y. This fictitious low friction can be attributed to decrease in surface roughness at higher extreme pressure or higher corrected load. This study suggests that speed ramp up time is a critical factor that should be further investigated by ASTM and grease manufacturers, to prevent the use of grease with fictitious EP behavior.

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Comparison Between the Action of Nano-Oxides and Conventional EP Additives in Boundary Lubrication

Lubricants ◽

10.3390/lubricants8050054 ◽

2020 ◽

Vol 8 (5) ◽

pp. 54

Author(s):

Valdicleide Silva Mello ◽

Marinalva Ferreira Trajano ◽

Ana Emilia Diniz Silva Guedes ◽

Salete Martins Alves

Keyword(s):

Friction Coefficient ◽

Boundary Lubrication ◽

Friction And Wear ◽

Film Formation ◽

Environmental Issues ◽

Protective Film ◽

Extreme Pressure ◽

Extreme Pressure Additives ◽

Environmental Requirements ◽

Lubrication Conditions

Additives are essential in lubricant development, improving their performance by the formation of a protective film, thus reducing friction and wear. Some such additives are extreme pressure additives. However, due to environmental issues, their use has been questioned because their composition includes sulfur, chlorine, and phosphorus. Nanoparticles have been demonstrated to be a suitable substitute for those additives. This paper aims to make a comparison of the tribological performance of conventional EP additives and oxides nanoparticles (copper and zinc) under boundary lubrication conditions. The additives (nanoparticles, ZDDP, and sulfur) were added to mineral and synthetic oils. The lubricant tribological properties were analyzed in the tribometer HFRR (high frequency reciprocating rig), and during the test, the friction coefficient and percentual of film formation were measured. The wear was analyzed by scanning electron microscopy. The results showed that the conventional EP additives have a good performance owing to their anti-wear and small friction coefficient in both lubricant bases. The oxides nanoparticles, when used as additives, can reduce the friction more effectively than conventional additives, and displayed similar behavior to the extreme pressure additives. Thus, the oxide nanoparticles are more environmentally suitable, and they can replace EP additives adapting the lubricant to current environmental requirements.

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