scholarly journals SILICONE MAGNETIC NANOFLUIDS ADAPTED FOR THE CONDITIONS OF BOUNDARY FRICTION

2020 ◽  
pp. 546-556
Author(s):  
Александр Николаевич Болотов ◽  
Ольга Олеговна Новикова ◽  
Владислав Викторович Новиков
Keyword(s):  
Elevated Temperatures ◽  
Experimental Studies ◽  
Boundary Friction ◽  
Space Technology ◽  
Antioxidant Additive ◽  
Friction Mode ◽  
Antifriction Properties ◽  
Magnetic Nanofluids ◽  
Antiwear Properties ◽  
Plastic Lubricants

Известные в настоящее время магнитные смазочные наножидкости имеют недостаточно хорошие триботехнические характеристики при эксплуатации в режиме граничного трения. Предложен способ адаптации для граничного трения магнитных силоксановых наножидкостей, путем модификации их состава химически активными антифрикционными, противоизносными и противозадирными присадками. Создан ряд смазочных композиций магнитных наножидкости на основе полиэтилсилоксана ПЭС-5. Поведенные экспериментальные исследования показали, что наиболее значительное улучшение антифрикционных и противоизносных свойств наножидкостей достигается при введении в их структуру хлорсодержащих присадок Совол и 3Н2ТЭ. Добавление в наножидкость антиокислительной присадки ДФ-11, фторсодержащей присадки ЭО-1, металлоплакирующего соединения МКФ-18 не привело к значимому улучшению антифрикционных свойств. Установлено, что магнитные наножидкости с модифицирующими присадками, по трибосвойствам сопоставимы с традиционными немагнитными жидкими смазочными материалами и превосходят пластичные смазки на основе полиэтилсилоксана. Разработанные композиции на основе силоксановых наножидкостей, будут востребованы для смазывания подшипников качения и скольжения, зубчатых передач, контактных уплотнений, которые функционируют при низких и повышенных температурах в газовой среде или в условиях вакуума. Наиболее успешно они могут применяться в вакуумной и космической технике, для магнитных трибоузлов, где возможна только однократная заправка ограниченным объемом смазочного материала. Currently known magnetic lubricant nanofluids have insufficiently good tribological characteristics when operating in the boundary friction mode. An adaptation method is proposed for the boundary friction of magnetic siloxane nanofluids by modifying their composition with chemically active antifriction, antiwear and extreme pressure additives. A number of lubricating compositions of magnetic nanofluids based on polyethylsiloxane PES-5 have been created. Conducted experimental studies have shown that the most significant improvement in the antifriction and antiwear properties of nanofluids is achieved with the introduction of Sovol and 3N2TE chlorine additives into their structure. Adding to the nanofluid the antioxidant additive DF-11, the fluorine-containing additive EO-1, the metal-plating compound MKF-18 did not lead to a significant improvement in the antifriction properties. It has been established that magnetic nanofluids with modifying additives are comparable in tribological properties with traditional non-magnetic liquid lubricants and are superior to plastic lubricants based on polyethylsiloxane. The developed compositions based on siloxane nanofluids will be in demand for lubrication of rolling and sliding bearings, gears, contact seals, which operate at low and elevated temperatures in a gas environment or in a vacuum. Most successfully, they can be used in vacuum and space technology, for magnetic frictional units, where only one refueling with a limited amount of lubricant is possible.

scholarly journals Experimental study on the thermal behaviour of fire exposed slim-floor beams

2018 ◽  
Author(s):  
Vicente Albero ◽  
Ana Espinós ◽  
Enrique Serra ◽  
Manuel L. Romero ◽  
Antonio Hospitaler
Keyword(s):  
Cross Section ◽  
Thermal Behaviour ◽  
Thermal Model ◽  
Elevated Temperatures ◽  
Experimental Studies ◽  
Composite Beams ◽  
Technical Equipment ◽  
Design Code ◽  
Special Configuration ◽  
The Cross

Steel-concrete composite beams embedded in floors (slim-floors) offer various advantages such as the floor thickness reduction or the ease of installation of under-floor technical equipment. However, this typology presents important differences in terms of thermal behaviour, as compared to other composite beams, when exposed to elevated temperatures. These differences are due to their special configuration, being totally contained within the concrete floor depth. Moreover, the current European fire design code for composite steel-concrete structures (EN 1994-1-2) does not provide any simplified thermal model to evaluate the temperature evolution of each slim-floor part during a fire. Additionally, only a few experimental studies can be found which may help understand the thermal behaviour of these composite beams. This paper presents an experimental investigation on the thermal behaviour of slim-floor beams. Electrical radiative panels were used in the test setup to produce the thermal heating. The thermal gap between the lower flange of the steel profile and the bottom steel plate was studied, being found to be one of the most influential elements over the cross-section temperature gradient. The experimental campaign was developed by varying the cross-section configuration in order to evaluate the influence of this parameter over the slim-floor thermal behavior. Finally, the experiments carried out were used to develop and calibrate a finite element thermal model which may help in further research on the thermal behaviour of slim-floor composite beams.

scholarly journals A research on magnetic properties of magnetic nanodispersed lubricants

2019 ◽  
Vol 298 ◽  
pp. 00015 ◽  
Author(s):  
Alexander Bolotov ◽  
Vladislav Novikov ◽  
Olga Novikova
Keyword(s):  
Magnetic Properties ◽  
Experimental Studies ◽  
Operating Conditions ◽  
Oil Composition ◽  
Initial State ◽  
Optimal Operating ◽  
Composition And Structure ◽  
Friction Mode ◽  
Hall Sensors ◽  
Lubricating Properties

The paper presents the results of theoretical and experimental studies of the magnetic properties of magnetic lubricating oils. It shows oil magnetization curves in the initial state and after tests in the boundary friction mode. Oil properties were measured by an original magnetometer with Hall sensors. It has been established that triboeffects change oil composition and structure and decrease its magnetization. The results will help determine the optimal operating conditions of magnetic oils while maintaining their magnetic and lubricating properties.

Modification of μm Thick Surface Layers Using keV Ion Energies

1983 ◽  
Vol 27 ◽  
Author(s):  
L. E. Rehn ◽  
N. Q. Lam ◽  
H. Wiedersich
Keyword(s):  
Elevated Temperature ◽  
Elevated Temperatures ◽  
Diffusion Processes ◽  
Experimental Studies ◽  
Surface Layers ◽  
Enhanced Diffusion ◽  
Radiation Enhanced Diffusion ◽  
Ni Alloy ◽  
Ion Energies ◽  
Radiation Induced

ABSTRACTRoot-mean-square diffusion distances for both vacancy and interstitial defects in metals can be very large at elevated temperatures, e.g. several μm's in one second at 500°C. Consequently, defects that escape the implanted region at elevated temperature can produce compositional and microstructural changes to depths which are much larger than the ion range. Because of the high defect mobilities, and of the fact that diffusion processes must compete with the rate of surface recession, the effects of defect production (ballistic mixing), radiation-enhanced diffusion and radiation- induced segregation become spatially separated during ion bombardment at elevated temperature. Results of such experimental studies in a Cu-Ni alloy are presented, discussed and compared with predictions of a phenomenological model. Contributions to the subsurface compositional changes from radiation-enhanced diffusion and radiation- induced segregation are clearly identified.

scholarly journals Direct atomistic simulation of brittle-to-ductile transition in silicon single crystals

2010 ◽  
Vol 1272 ◽  
Author(s):  
Dipanjan Sen ◽  
Alan Cohen ◽  
Aidan P. Thompson ◽  
Adri Van Duin ◽  
William A. Goddard III ◽  
...  
Keyword(s):  
Single Crystals ◽  
Atomistic Simulation ◽  
Large Scale ◽  
Elevated Temperatures ◽  
Experimental Studies ◽  
Crack Tip ◽  
Threshold Value ◽  
Atomic Scale ◽  
Brittle To Ductile Transition ◽  
First Time

AbstractSilicon is an important material not only for semiconductor applications, but also for the development of novel bioinspired and biomimicking materials and structures or drug delivery systems in the context of nanomedicine. For these applications, a thorough understanding of the fracture behavior of the material is critical. In this paper we address this issue by investigating a fundamental issue of the mechanical properties of silicon, its behavior under extreme mechanical loading. Earlier experimental work has shown that at low temperatures, silicon is a brittle material that fractures catastrophically like glass once the applied load exceeds a threshold value. At elevated temperatures, however, the behavior of silicon is ductile. This brittle-to-ductile transition (BDT) has been observed in many experimental studies of single crystals of silicon. However, the mechanisms that lead to this change in behavior remain questionable, and the atomic-scale phenomena are unknown. Here we report for the first time the direct atomistic simulation of the nucleation of dislocations from a crack tip in silicon only due to an increase of the temperature, using large-scale atomistic simulation with the first principles based ReaxFF force field. By raising the temperature in a computational experiment with otherwise identical boundary conditions, we show that the material response changes from brittle cracking to emission of a dislocation at the crack tip, representing evidence for a potential mechanisms of dislocation mediated ductility in silicon.

scholarly journals Effect of silica fume and lateral confinement on fire endurance of high strength concrete columns

2006 ◽  
Vol 33 (1) ◽  
pp. 93-102 ◽  
Author(s):  
V K.R Kodur ◽  
R McGrath
Keyword(s):  
Silica Fume ◽  
Fire Resistance ◽  
High Strength Concrete ◽  
Elevated Temperatures ◽  
Experimental Studies ◽  
High Strength ◽  
Concrete Columns ◽  
Main Concern ◽  
Strength Concrete ◽  
Fire Endurance

Fire represents one of the most severe environmental conditions, and therefore should be properly accounted for in the design of structural members. The increased use of high strength concrete (HSC) in buildings has raised concerns regarding the behaviour of such concrete in fire. In particular, spalling at elevated temperatures, as identified in studies by a number of laboratories, is a main concern. In this paper, results from experimental studies on the fire resistance of HSC columns are presented. A comparison is made of the fire resistance performance of HSC columns with and without silica fume and with different confinement configurations. The effect of silica fume and the effect of confinement on the fire performance of HSC columns will be discussed. The results show that the fire endurance of HSC columns with higher silica fume content is lower and the reduced tie spacing and the provision of cross-ties are beneficial in minimizing the spalling in HSC.Key words: fire resistance, high strength concrete, reinforced concrete columns, spalling.

Residual Strength of Super High Strength Concrete Used Stone-Chip after Exposure to High Temperatures

2011 ◽  
Vol 374-377 ◽  
pp. 2456-2460
Author(s):  
Guo Can Chen ◽  
Zhi Sheng Xu ◽  
Wei Hong Tang
Keyword(s):  
High Temperatures ◽  
High Strength Concrete ◽  
Elevated Temperatures ◽  
Experimental Studies ◽  
High Strength ◽  
Normal Strength Concrete ◽  
Strength Concrete ◽  
Fine Aggregates ◽  
Normal Strength ◽  
Peak Value

This paper presents the results of experimental studies on the residual compressive strength of concrete produced with stone-chip as fine aggregates with the compressive strengths of unheated specimen ranging from 45.8 to 129.5MPa after exposure to high temperatures and the experimental parameters being the temperature, admixtures, and PP fiber. Specimens were heated in an electric furnace for 4h to high temperatures ranging from 150 to 960°C. Experimental results showed that the compressive strengths of super high strength concrete used stone-chip (abbreviated to SHSCUS) and normal strength concrete used stone-chip (abbreviated to NSCUS) after exposure to elevated temperatures changed in the manners different from that of normal strength concrete, which reached their peak at about 400°C, and the presence of pp fibers in SHSCUS concrete could reduce the risk of spalling at the high temperatures and the peak value after fire.

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