다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

The Viscosity can be imagined as the force that should be applied to a layer of fluid belonging to the plane fixed to the velocity of the layer placed at a fixed distance. For example a fluid flowing in a tube at different speeds: the minimum speed is in the edge of the section (due to friction) and the maximum speed is at the center. The viscosity in this example is that pressure which is exerted on the wall allows a constant speed on the whole section.

Non-newtonian fluids.

Surface textures have been of great interest in the tribology community with nearly 1500 papers published on this topic in the past two decades. With pursuit of low emissions and environmental sustainability, the application of surface texturing to mechanical systems to lower friction and control wear is attracting increasing attention. There is no doubt that certain textured surface can have a beneficial effect on tribological performance but it is widely agreed that the optimization of textures should be carried out based on specific applications requirements. The purpose of this review article is to summarize the current state of the art in surface texturing applied to mechanical applications (cutting tools, piston-ring & cylinder liners, sealing and journal bearings) from the following aspects: application requirements, numerical/ experimental testing and validations, and tribological performance of textured surfaces (wear and friction), as well as limitations in texture designs according to certain applications. Patterns/grooves in micron-scale are the most typical shapes been studied, and benefits of partial texturing are applicable for most of these mechanical applications. Friction reduction of up to 34.5% in cutting tools, 82% in piston-ring & cylinder-liner, 65% in seals and 18% in journal bearings have been observed by experimental tests. Based on primary evidence from the literature, the last section provides general suggestions on current gaps in understanding and modelling and suggests future research directions.

https://iopscience.iop.org/article/10.1088/2051-672X/abb6d0/pdf

Tribological performance of surface texturing in mechanical applications—a review

The use of material for implant bearing has a vital role in minimizing failures that endanger implant recipients. Evaluation of contact pressure of bearing material can be the basis for material selection and have correlations with wear that contribute to the need of revision operations. The current paper aims to investigate three different metallic materials, namely cobalt chromium molybdenum (CoCrMo), stainless steel 316L (SS 316L), and titanium alloy (Ti6Al4V) for application in metal-on-metal bearing of total hip implant in terms of contact pressure. In silico model based on finite element simulation has been considered to predict contact pressure of metal-on-metal bearings under normal walking conditions. It is found that the use of Ti6Al-4V-on-Ti6Al4V is superior in its ability to reduce contact pressure by more than 35% compared to the other studied metal-on-metal couple bearings.

/pdf/in-silico-contact-pressure-of-metal-on-metal-total-hip-13e5d3vq.pdf

In Silico Contact Pressure of Metal-on-Metal Total Hip Implant with Different Materials Subjected to Gait Loading

A method for calculating thermohydrodynamic characteristics of complex-loaded sliding bearings is considered The non-Newtonian behavior of a fluid, as well as processes of heat transfer between a lubricating film and surrounding moving surfaces of the tribojoint, are allowed for Results of calculating hydromechanical characteristics of a connecting-rod bearing of an internal combustion engine are presented

Solving a thermohydrodynamic lubrication problem for complex-loaded sliding bearings with allowance for rheological behavior of lubricating fluid

One of the priority directions in the development of instrument diagnostics of car engines is test diagnostics. The main advantages of such testing are: significant coverage of the diagnosed engine systems; high informativeness and reliability of the diagnostic process with general simplification of the diagnostic process; reduction in the number of diagnostic parameters. In addition, one can achieve high automation of diagnostic process operations, adaptation of diagnostics interfaces and high intuitive level of functioning algorithms. The authors developed a diagnostic instrumental tool - a loader for gasoline engines (LGE-3), as well as a device for fixing the position of the throttle. The loader of the gasoline engine LGE-3 allows us to create any load and speed mode. Load on the cylinder is provided due to a complete shutdown of fuel in any cylinder and by disabling individual fuel cycles in the selected cylinder. The results of experimental studies on the example of electromagnetic injectors have shown a high efficiency of test diagnostics. The diagnostics modes at 25 and 70% degree of throttle valve opening are designed and recommended.

/pdf/test-diagnostics-of-engine-systems-in-passenger-cars-3x9zve364h.pdf

Test diagnostics of engine systems in passenger cars

Motor oil of the internal combustion engine is a means to deliver particles of friction geo-modifiers to the friction surfaces. In this case, the influence of friction geo-modifiers such an important parameter as engine oil HTHS viscosity is of practical interest. The purpose of this article is to determine the HTHS viscosity multigrade engine oils of SAE class 5W-40 with different concentrations of friction geo-modifiers on the basis of pure serpentine. The tapered bearing simulator TBS 2100E TANNAS was used to measure the viscosity of oils at shear rates 106 s−1. A lubricating composition was prepared using two samples of multigrade engine oils viscosity grade SAE 5W-40. The mass concentration of the friction geo-modifiers was 0.1, 0.3, and 0.5% in each sample. The friction geo-modifiers lead to insignificant decrease in HTHS viscosity multigrade engine oil of viscosity grade SAE 5W-40. The viscosity decreased on 3.5–6.5% for the analyzed samples of motor oils. Therefore, the working conditions of the bearings of the crankshaft are changed insignificantly at the introduction of the friction geo-modifiers in motor oil.

Influence of Friction Geo-modifiers on HTHS Viscosity of Motor Oils

The article describes the influence of the geo-modifiers of friction on the antiwear properties of lubricants. Geo-modifiers of friction are the fine powders of mineral materials. This work is directed on the investigation the influence of the geo-modifiers of friction in the form of the hard lubricant compositions, which based on a mineral serpentine, on the antiwear properties of greases and gear oils. This composition is the fine powder serpentine with the addition of components such as chalk, borax, kaolin and talc. We compared the antiwear properties of the greases without geo-modifiers of friction and the antiwear properties of greases containing the geo-modifiers of friction from 0.5 % to 3 %. The Litol-24 and transmission oil TAD-17 was used for testihg. The four-ball machine of friction was used for tests accordance with GOST 9490-75. As geomodifiers the serpentine was used, the fraction of which has a size from 0.87 microns to 2.2 microns. Such parameter as the wear scar diameter was used for evaluation of the antiwear properties of lubricants. As a result of tests it was established that the antiwear greases properties improved on 26-50 % depending on the concentration of the geo-modifiers of friction based on the pure serpentine. © 2017 Published by Faculty of Engineering Corresponding author: Igor Levanov Department of Motor Transport, South Ural State University, Chelyabinsk, Russia. E-mail: levanovig@susu.ru

/pdf/investigation-antiwear-properties-of-lubricants-with-the-geo-200w4jhuyh.pdf

Investigation Antiwear Properties of Lubricants with the Geo-Modifiers of Friction

Failures of friction bearings of the crank mechanism comprise from 5 to 25 % of engine failures. The analysis of the main reasons for failures shows that the dominant reasons are the following: excess of loading conditions; severe operating conditions; non-observance of the periodic maintenance of the lubrication system; violation of the procedure and conditions of maintenance (contamination, oil residues, etc.); use of poorquality oils and filters, etc. It is possible to prevent the growth of failures of friction bearings by a continuous monitoring of their complex technical state. For that purpose, we have supposed that the technical state of the crankshaft main bearings of the crank mechanism can be determined by measuring the pressures in the central oil line and calculating their difference in the cycles with the maximum load and without it at different engine crankshaft rotation frequency. As a result of the experimental work, we developed a method for in-place diagnostics of the state of friction bearings of the internal combustion engine, as well as an instrument that provides loading conditions for the bearings of the crank mechanism. We obtained an experimental dependence for determining the wear degree of the crankshaft main journal by the difference in the minimum pressure amplitudes of two adjacent cycles during the operation of the diagnosed cylinder in various modes. © 2018 Published by Faculty of Engineering Corresponding author: Vladimir Shepelev Department of Automobile Transport, Automobile and Tractor Faculty, South Ural State University, 76 Lenin Avenue, Chelyabinsk 454080,Russia E-mail: shepelevvd@susu.ru

/pdf/diagnostics-of-friction-bearings-by-oil-pressure-parameters-220hwxfbdi.pdf

E. Zadorozhnaya

Papers

Solving a thermohydrodynamic lubrication problem for complex-loaded sliding bearings with allowance for rheological behavior of lubricating fluid

Test diagnostics of engine systems in passenger cars

Influence of Friction Geo-modifiers on HTHS Viscosity of Motor Oils

Investigation Antiwear Properties of Lubricants with the Geo-Modifiers of Friction

Diagnostics of Friction Bearings by Oil Pressure Parameters During Cycle-By-Cycle Loading