Kris De Moerlooze

Farid Al-Bender

Experimental Investigation into the Tractive Prerolling Behavior of Balls in V-Grooved Tracks

A Model for the Transient Behavior of Tractive Rolling Contacts

The blends of bis(1,5-diaryl-2,4-dithiomalonamido)dioxomolybdenum(VI)
                   complexes in lithium-base grease are evaluated for their extreme pressure 
                   activity in a &#x201C;four-ball test&#x201D; using 12.7&#x2009;mm diameter alloy steel ball 
                   specimen. The additive, bis(1,5-di-p-methoxyphenyl-2,4-dithiomalonamido)dioxomolybdenum(VI)
                    and bis(1,5-di-p-chloro-phenyl-2,4-dithiomalonamido)dioxomolybdenum(VI) exhibited lower values 
                    of wear-scar diameter at higher load and higher values of weld load, flash temperature 
                    parameter, and pressure wear index as compared with lithium-base grease without additives. The
                     greases fortified with the developed additives prevent rusting and corrosion of bearings while
                      grease containing no additives did not pass these tests as per the standard tests. These greases 
                      have also better oxidation protection as compared to the grease that has no additive. The
                       topography and tribochemistry of the wear-scar surface are carried out by means of scanning
                        electron microscopy and Auger electron spectroscopy techniques, respectively.

Tarunendr Singh

Tribochemistry and EP Activity Assessment of  Mo-S Complexes in 
                        Lithium-Base Greases

In a rolling element system, the period of transition between motion commencement and the attainment of steady state, gross rolling, and termed prerolling is of common concern to many engineering applications. This region is marked by hysteresis friction behavior, with a characteristic friction-displacement curve, which is in particular relevant to motion characterization and control issues. In a previous paper, the authors carried out a theoretical analysis of tractive prerolling, leading to a model for simulating this phenomenon. The present paper is dedicated to the experimental investigation of tractive prerolling friction behavior, including validation of the theoretical model. Firstly, a kinematic analysis of the rolling motion in V-grooved tracks is carried out. Secondly, the influence of the normal load on the frictional behavior, in prerolling up to the attainment of gross rolling, is investigated on a dedicated test setup. Finally, the newly developed theoretical model is validated by comparison with the experimental results. Satisfactory agreement is obtained between theory and experiment.

The work presented in this paper aims to study the performance of a two-lobe hole-entry hybrid journal bearing system compensated by orifice restrictors. The Reynolds equation governing the flow of lubricant in the clearance space between the journal and bearing together with the equation of flow through an orifice restrictor has been solved using FEM and Galerkin&#x27;s method. The bearing performance characteristics results have been simulated for an orifice compensated nonrecessed two-lobe  hole-entry hybrid journal bearing symmetric configuration for the various values of offset factor 
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</svg>, restrictor design parameter 
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				<tspan style="font-size: 12.50px; " x="0" y="0">)</tspan>
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</svg>, and the value of external load 
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Further, a comparative study of the performance of a two-lobe hole-entry hybrid journal bearing system with a circular hole-entry symmetric hybrid journal bearing system has also been carried out so that a designer has a better flexibility in choosing a suitable bearing configuration. The simulated numerical results indicate that for the two-lobe symmetric hole-entry hybrid journal bearing system with an offset factor 
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</svg> greater than one provides 30 to 50 percent larger values of direct stiffness and  direct damping coefficients as compared to a circular symmetric hole-entry hybrid journal bearing system.

J. Sharana Basavaraja

Satish C. Sharma

S. C. Jain

Performance of an Orifice Compensated Two-Lobe  Hole-Entry Hybrid Journal Bearing

When an elastic body of revolution rolls tractively over another, 
the period from commencement of rolling until gross rolling ensues 
is termed the prerolling regime. The resultant tractions in this regime are 
characterized by rate-independent hysteresis behavior with nonlocal memory in 
function of the traversed displacement. This paper is dedicated to the theoretical 
characterization of traction during prerolling. Firstly, a theory is developed to calculate 
the traction field during prerolling in function of the instantaneous rolling displacement, 
the imposed longitudinal, lateral and spin creepages, and the elastic contact parameters. 
Secondly, the theory is implemented in a numerical scheme to calculate the resulting traction 
forces and moments on the tractive rolling of a ball. Thirdly, the basic hysteresis characteristics 
are systematically established by means of influence-parameters simulations using dimensionless 
forms of the problem parameters. The results obtained are consistent with the limiting cases available 
in literature and they confirm experimental prerolling hysteresis observations. Furthermore, in a second 
paper, this theory is validated experimentally for the case of V-grooved track.

A Model of the Transient Behavior of Tractive Rolling Contacts

The knowledge of the film thickness values is very important in lubricated contacts to verify the
lubrication conditions. Optical interferometry is one of the most used methodologies for film thickness
and shape determination of Elastohydrodynamic-lubricated contacts.
An image processing programme has been developed for the analysis of white light interferograms.
The programme, based on the analysis of the hue channel, has been developed in order to process big
amounts of images, as often generated under transient conditions. The measurement range is currently
limited to a maximum film thickness of 0.7&#x2009;<svg style="vertical-align:-2.29482pt;width:9.6374998px;" id="M1" height="9.6750002" version="1.1" viewBox="0 0 9.6374998 9.6750002" width="9.6374998"  xmlns="http://www.w3.org/2000/svg">
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			</text>

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</svg>m.
The programme has been used for analysing several images recorded in tests carried out with a ball
on disc contact under steady-state as well as transient conditions for different velocities and slide-to-roll
ratios. Under transient conditions, the entraining velocity is varied with a sinusoidal law for two
different frequencies.
The results obtained evidenced an asymmetric reduction of the film thickness when increasing the
percentage of sliding, both for stationary and transient conditions. Under transient conditions with
increasing test frequency, film thickness loops of increasing amplitude have been found that reduce
their amplitude more when the ball is running faster than the disc. Squeeze and thermal effects can
explain the results obtained.

E.  Ciulli

T.  Draexl

K.  Stadler

Film Thickness Analysis for EHL Contacts under Steady-State and Transient Conditions by Automatic Digital Image Processing

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<p><em>Advances in Tribology</em> publishes papers on the science of friction, wear, and lubrication. Topics covered include investigations into contact mechanics, wear and damage processes, surface and coating engineering, and lubrication technology.</p>


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title

Advances in Tribology publishes papers on the science of friction, wear, and lubrication. Topics covered include investigations into contact mechanics, wear and damage processes, surface and coating engineering, and lubrication technology.

Advances in Tribology