Coefficients of Friction: Static Versus Dynamic

Huang, Jack Youqin

doi:10.1115/jrc2020-8025

Cited by 3 publications

(3 citation statements)

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“…Note that wave length L=(2π)/ω. From analytical geometrics, radius of curvature for the cosine curve y can be expressed as R cos =| (1+ y' 2 ) 3/2 /y''| (14) Plugging in y' and y'', we have…”

Section: Determination Of the Curve Of Motion The Wheelsetmentioning

confidence: 99%

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Principles of Wheelset Hunting and Construction of Total Solution to Hunting

Huang¹

2021

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Wheelset hunting is a motion with two degrees of freedom. The second degree of freedom of hunting is investigated in this paper. Rolling radius difference is commonly understood as the root cause of wheelset hunting. Normally, hunting will begin as soon as the truck begins to move. Rolling radius difference will initiate the hunting and can only be used to determine the configuration of the first quarter of a hunting cycle. Then a mechanism will come into exist to determine the configuration of the second quarter of the hunting cycle, which is exactly the same as the one of first quarter but in the opposite direction. The second half of the hunting cycle is a mirror of the first half. The information from wheelset hunting is too large and too complicated for people to understand and analyze. However, the radius of curvature of wheelset circular motion can be calculated exactly, especially at some special configurations, even though the radius of curvature of wheelset circular motion keeps changing in both magnitude and direction. Furthermore, comparison of the radii of curvature between hunting curve and a cosine curve shows that the curve for the wheelset in hunting motion is sinusoidal. This is proven mathematically in the paper. The limits in Klingel's results were discussed. Due to the fact that Klingel's results are unable to provide a strong theoretical base for further understanding the complicated dynamic characteristics caused by hunting, misleading in hunting is overwhelmed. After understanding the principles of wheelset hunting, three critical speeds in hunting and dynamic loading for truck design in three directions were calculated; wheelset hunting curve while curving was generated; wheelset dynamic interaction was analyzed and the question "Why trains stay on tracks" was answered correctly, just to name a few. Thus, a total solution to the hunting problems can be expected and was discussed in the paper.

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Section: Determination Of the Curve Of Motion The Wheelsetmentioning

confidence: 99%

“…Wheelset hunting can be eliminated by a hunting eliminator [13]. 6) Coefficients of friction---static versus dynamic [14],…”

Section: Conclusion and Construction Of A Total Solution To Huntingmentioning

confidence: 99%

Principles of Wheelset Hunting and Construction of Total Solution to Hunting

Huang¹

2021

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“…Once a barrier is overcome, the distortions relax, whereby mechanical energy is dissipated (converted into other forms of energy). , The amount of dissipated energy for a given sliding distance results in the dynamic friction coefficient. The static friction coefficient is usually larger than the dynamic friction coefficient, − which allows us to draw conclusions on superlubricity based on the static friction coefficient. We thoroughly quantify the dependence of the static friction coefficient on the type of commensurability as well as static distortion waves by focusing on two exemplary organic/metal interfaces: Naphthalene on Cu(111) and tetrachloropyrazine (TCP) on Pt(111).…”

Section: Introductionmentioning

confidence: 99%

Impact of Static Distortion Waves on Superlubricity

Hörmann,

Cartus,

Hofmann

2023

ACS Omega

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Friction is a major source of energy loss in mechanical devices. This energy loss may be minimized by creating interfaces with extremely reduced friction, i.e., superlubricity. Conventional wisdom holds that incommensurate interface structures facilitate superlubricity. Accurately describing friction necessitates the precise modeling of the interface structure. This, in turn, requires the use of accurate first-principles electronic structure methods, especially when studying organic/metal interfaces, which are highly relevant due to their tunability and propensity to form incommensurate structures. However, the system size required to calculate incommensurate structures renders such calculations intractable. As a result, studies of incommensurate interfaces have been limited to very simple model systems or strongly simplified methodology. We overcome this limitation by developing a machine-learned interatomic potential that is able to determine energies and forces for structures containing thousands to tens of thousands of atoms with an accuracy comparable to conventional firstprinciples methods but at a fraction of the cost. Using this approach, we quantify the breakdown of superlubricity in incommensurate structures due to the formation of static distortion waves. Moreover, we extract design principles to engineer incommensurate interface systems where the formation of static distortion waves is suppressed, which facilitates low friction coefficients.

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Effect of Countersample Coatings on the Friction Behaviour of DC01 Steel Sheets in Bending-under-Tension Friction Tests

Trzepieciński,

Szwajka,

Szewczyk

et al. 2024

Materials

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The aim of this article is to provide an analysis of the influence of the type of hard anti-wear coatings on the friction behaviour of DC01 deep-drawing steel sheets. DC01 steel sheets exhibit high formability, and they are widely used in sheet metal forming operations. The tribological properties of the tool surface, especially the coating used, determine the friction conditions in sheet metal forming. In order to carry out the research, this study developed and manufactured a special bending-under-tension (BUT) friction tribometer that models the friction phenomenon on the rounded edges of tools in the deep-drawing process. The rationale for building the tribotester was that there are no commercial tribotesters available that can be used to model the phenomenon of friction on the rounded edges of tools in sheet forming processes. The influence of the type of coating and sheet deformation on the coefficient of friction (CoF) and the change in the topography of the sheet surface were analysed. Countersamples with surfaces prepared using titanium + nitrogen ion implantation, nitrogen ion implantation and electron beam remelting were tested. The tests were carried out in conditions of dry friction and lubrication with oils with different kinematic viscosities. Under dry friction conditions, a clear increase in the CoF value, with the elongation of the samples for all analysed types of countersamples, was observed. Under lubricated conditions, the uncoated countersample showed the most favourable friction conditions. Furthermore, oil with a lower viscosity provided more favourable conditions for reducing the coefficient of friction. Within the entire range of sample elongation, the most favourable conditions for reducing the CoF were provided by uncoated samples and lubrication with S100+ oil. During the friction process, the average roughness decreased as a result of flattening the phenomenon. Under dry friction conditions, the value of the Sa parameter during the BUT test decreased by 20.3–30.2%, depending on the type of countersample. As a result of the friction process, the kurtosis and skewness increased and decreased, respectively, compared to as-received sheet metal.

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Coefficients of Friction: Static Versus Dynamic

Cited by 3 publications

References 0 publications

Principles of Wheelset Hunting and Construction of Total Solution to Hunting

Principles of Wheelset Hunting and Construction of Total Solution to Hunting

Impact of Static Distortion Waves on Superlubricity

Effect of Countersample Coatings on the Friction Behaviour of DC01 Steel Sheets in Bending-under-Tension Friction Tests

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