Film thickness fluctuations in time-varying normal loading of rolling elastohydrodynamically lubricated contacts

Félix-Quiñonez, A; Morales-Espejel, Guillermo E.

doi:10.1243/09544062jmes1966

Cited by 12 publications

(11 citation statements)

References 21 publications

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“…The squeeze effect during the rapid decrease of the velocity (and the film thickness with it) results into a film larger than the steadystate predictions, by the formation of a lubricant entrapment, as proved experimentally and theoretically [40][41][42][43]. The current approach and results are supported by the results of the analytical/numerical investigation carried out in [32,33], which conclude that between the increase of speed due to rapid increase of contact dimensions and the squeeze effects the former is dominant.…”

Section: Comparison Of Experiments and Theorysupporting

confidence: 65%

“…Morales-Espejel [32], Felix-Quinonez and Morales-Espejel [33] proposed an improved semi-analytical method for evaluating the film thickness fluctuations in the normal-approach of EHD contacts. The method was based on squeeze film effects as well as the variation of lubricant entrainment speed caused by the oscillating load and change of the conditions in the inlet region of the EHD contact.…”

Section: Introductionmentioning

confidence: 99%

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Elastohydrodynamic Films Under Periodic Load Variation: An Experimental and Theoretical Approach

Glovnea

Zhang

2018

Tribol Lett

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The elastohydrodynamic lubrication regime occurs in systems where large elastic deformations, the hydrodynamic action of a converging wedge and eventually large variation of viscosity of the fluid combine to determine the formation of a continuous fluid film that separates the solid surfaces. Experimental and theoretical works, over the past few decades, have elucidated the role of various working and material parameters on the lubricant film thickness which plays a crucial role in protecting the solid surfaces from direct contact and ultimately from failure. These mechanisms are well understood for steady-state conditions; however, elastohydrodynamic contacts most often experience transient conditions, including variation of geometry, velocity of surfaces or load. In this case, the mechanisms of film formation are more complex involving film squeeze in addition to the mechanisms mentioned above. Experimental and theoretical modelling of transient phenomena in elastohydrodynamic lubrication include sudden variation of entrainment speed or load and changing geometry. No systematic experimental study on the effect of harmonic load vibration upon the elastohydrodynamic films has been published before. In order to cover this gap, this paper presents the results of an experimental study and of a simple theoretical approach on the behaviour of the elastohydrodynamic film thickness under harmonic variation of load.

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Section: Comparison Of Experiments and Theorysupporting

confidence: 65%

Section: Introductionmentioning

confidence: 99%

Elastohydrodynamic Films Under Periodic Load Variation: An Experimental and Theoretical Approach

Glovnea

Zhang

2018

Tribol Lett

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“…At Ω T/w = t T d 1 /t w ∼ 0.029, thermal transient effects become significant, lowering ∆h c m , ∆A h c and ∆C f m . Above Ω T/w ∼ 0.7 (or Ω h/w = t h /t w ∼ 0.029), hydrodynamic transient effects add up, progressively increasing the amplitude of the film thickness oscillations (Figure 14) as observed by Félix-Quiñonez and Morales-Espejel [40] in isothermal computations. Then, above Ω T/w ∼ 5.7 (Ω h/w ∼ 0.2), the latter completely overwhelms the former, inducing sharp modifications of the mean value of the central film thickness ∆h c m and of the friction coefficient ∆C f m (Figures 13 and 15).…”

Section: Resultsmentioning

confidence: 73%

Characteristic times in transient thermal elastohydrodynamic line contacts

Raisin

Fillot

Dureisseix

et al. 2015

Tribology International

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The paper presents a numerical and analytical analysis on transient effects in Thermal Elasto-Hydrodynamic (TEHD) contacts subjected to fluctuations of their operating conditions. Firstly, the system of equations, boundary conditions and numerical scheme used in the model are described. In addition, developments to solve transient TEHD problems are detailed, on the basis of a previous work [1] dedicated to the study of steady state cases. Then, the phenomena at the origin of transient effects in TEHD contacts are reviewed along with their characteristic time. In this context, a particular focus is placed on the thermal contribution. The complexity in finding a relevant thermal characteristic time is illustrated by the influence of the slide-to-roll ratio (SRR) on the contact performance (film thickness and friction). The dependency of the dominant heat transfer mode on the SRR is showed. A distinction between low sliding, pure sliding and high sliding conditions is made. Each configuration is thoroughly analyzed, leading to the formulation of new thermal characteristic times. Finally, time-dependent TEHD computations are performed in order to investigate the onset of transient effects. A direct relationship with the dominant thermal time is established and validated through a parametric study on the contact operating conditions and on the solid material properties. Numerical simulation of transient Thermal Elasto-Hydrodynamic (TEHD) systems has several interests: understanding local behavior to prevent failure of a designated system, working conditions, fluid properties, overall design, etc. For practical applications, taking into account the thermal effects is mandatory, and since time-dependent operating conditions often apply, the decision to use a quasisteady or a transient model is also required. In this article, we derive, a priori, characteristic time scales for a generic line contact TEHD problem, and discuss the discrepancies between the two models depending on the dynamical character of the problem. A decision criteria is proposed and tested on various conditions to assess its validity.

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“…The changing entrainment speed at the entrance of the contact due to the Hertzian width variation when the load fluctuates is in reality only one of the two important effects determining the film thickness variation in the EHD contact, as discussed in [24,25]. The other effect is the squeeze film influence introduced by the time-dependent Reynolds equation.…”

Section: Theoretical Analysis Based On Squeeze and Entrainmentmentioning

confidence: 99%

The Effect of Working Parameters upon Elastohydrodynamic Film Thickness Under Periodic Load Variation

et al. 2020

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There are a number of widely used machine components, such as rolling element bearings, gears and cams, which operate in the lubrication regime known as Elastohydrodynamics (EHD), where lubricant film thickness is governed by hydrodynamic action of convergent geometry, elastic deformation between non-conformal contacting surfaces, and the increase of lubricant viscosity with pressure. Variable loading conditions occur not only in all the machine components mentioned above, but also in natural joints such as hip or knee joints of humans or many vertebrates. Experimental studies of the behaviour of EHD films under variable loading are scarce and to authors' knowledge systematic studies of the evolution of lubricant film thickness in EHD contacts subjected to forced harmonic variation of load are even less common. The aim of the present study is to explore the effect of load amplitude on the EHD film behaviour. This is done in alternating cycles with the load varying about a fixed, preset value at various amplitudes. Experimental results are compared with a simple theoretical analysis based on the speed of change of contact's dimensions, a semi-analytical solution which includes both speed variation and squeeze effect, and finally with a full numerical solution. Keywords Elastohydrodynamic (EHD) • Film thickness • Vibrations • Amplitude • Harmonic force Abbreviations h c Central film thickness (m) h st Steady state film thickness under static load (m) h(t) Transient film thickness E Young's modulus E * Reduced modulus of elasticity U Entrainment velocity in x direction (m/s) u 0 Absolute velocity of the surfaces of the ball and disc (m/s

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Film thickness fluctuations in time-varying normal loading of rolling elastohydrodynamically lubricated contacts

Cited by 12 publications

References 21 publications

Elastohydrodynamic Films Under Periodic Load Variation: An Experimental and Theoretical Approach

Elastohydrodynamic Films Under Periodic Load Variation: An Experimental and Theoretical Approach

Characteristic times in transient thermal elastohydrodynamic line contacts

The Effect of Working Parameters upon Elastohydrodynamic Film Thickness Under Periodic Load Variation

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