Experimental and Numerical Investigations of the Stribeck Curves for Lubricated Counterformal Contacts

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
Tao He ◽  
Dong Zhu ◽  
Jiaxu Wang ◽  
Q. Jane Wang
Keyword(s):  
Shear Stress ◽  
Elastohydrodynamic Lubrication ◽  
Stribeck Curve ◽  
Boundary Lubrication Friction ◽  
Lubrication Regimes ◽  
Limiting Shear Stress ◽  
Wide Range ◽  
Basic Characteristics ◽  
Stribeck Curves ◽  
Film Lubrication

The Stribeck curve is an important means to demonstrate the frictional behavior of a lubricated interface during the entire transition from boundary and mixed to full-film lubrication. In the present study, a new test apparatus has been built that can operate under rolling–sliding conditions at a continuously variable speed in an extremely wide range, approximately from 0.00006 to 60 m/s, covering six orders of magnitude. Hence, a complete Stribeck curve can be measured to reveal its basic characteristics for lubricated counterformal contacts. The measured curves are compared with numerical simulation results obtained from an available unified mixed elastohydrodynamic lubrication (EHL) model that is also capable of handling cases during the entire transition. A modified empirical model for the limiting shear stress of lubricant is obtained, and a good agreement between the measured and calculated Stribeck curves is achieved for the tested base oils in all the three lubrication regimes, which thus well validates the simulation methods employed. Both the experimental and numerical results indicate that the Stribeck curves for counterformal contact interfaces behave differently from those for conformal contacts. When the rolling speed increases at a fixed slide-to-roll ratio, the friction continuously decreases even in the full-film lubrication regime due to the reduction of the lubricant limiting shear stress caused mainly by the rise of the surface flash temperature. In addition, the test results indicate that the boundary additives in a commodity lubricant may have considerable influence on the boundary lubrication friction but that on the friction in the mixed and full-film lubrication appears to be limited.

On the Stribeck Curves for Lubricated Counterformal Contacts of Rough Surfaces

2015 ◽  
Vol 137 (2) ◽  
Author(s):  
Dong Zhu ◽  
Jiaxu Wang ◽  
Q. Jane Wang
Keyword(s):  
Film Thickness ◽  
Numerical Solutions ◽  
Rough Surfaces ◽  
Elastohydrodynamic Lubrication ◽  
Real Data ◽  
Operating Conditions ◽  
Stribeck Curve ◽  
Flash Temperature ◽  
Wide Range ◽  
Stribeck Curves

The “Stribeck curve” is a well-known concept, describing the frictional behavior of a lubricated interface during the transition from boundary and mixed lubrication up to full-film hydrodynamic/elastohydrodynamic lubrication. It can be found in nearly every tribology textbook/handbook and many articles and technical papers. However, the majority of the published Stribeck curves are only conceptual without real data from either experiments or numerical solutions. The limited number of published ones with real data is often incomplete, covering only a portion of the entire transition. This is because generating a complete Stribeck curve requires experimental or numerical results in an extremely wide range of operating conditions, which has been a great challenge. Also, numerically calculating a Stribeck curve requires a unified model with robust algorithms that is capable of handling the entire spectrum of lubrication status. In the present study, numerical solutions in counterformal contacts of rough surfaces are obtained by using the unified deterministic mixed elastohydrodynamic lubrication (EHL) model recently developed. Stribeck curves are plotted in a wide range of speed and lubricant film thickness based on the simulation results with various types of contact geometry using machined rough surfaces of different orientations. Surface flash temperature is also analyzed during the friction calculation considering the mutual dependence between friction and interfacial temperature. Obtained results show that in lubricated concentrated contacts, friction continuously decreases as speed and film thickness increase even in the full-film regime until extremely high speeds are reached. This is mainly due to the reduction of lubricant limiting shear stress caused by flash temperature rise. The results also reveal that contact ellipticity and roughness orientation have limited influence on frictional behaviors, especially in the full-film and boundary lubrication regimes.

Extension of the Friction Mastercurve to Limiting Shear Stress Models

2003 ◽  
Vol 125 (4) ◽  
pp. 739-746 ◽  
Author(s):  
B. Jacod ◽  
C. H. Venner ◽  
P. M. Lugt
Keyword(s):  
Shear Stress ◽  
Friction Coefficient ◽  
Numerical Simulations ◽  
Coefficient Of Friction ◽  
Rheological Model ◽  
Operating Conditions ◽  
Limiting Shear Stress ◽  
Wide Range ◽  
Two Parameters ◽  
Stress Models

A previous study of the behavior of friction in EHL contacts for the case of Eyring lubricant behavior resulted in a friction mastercurve. In this paper the same approach is applied to the case of limiting shear stress behavior. By means of numerical simulations the friction coefficient has been computed for a wide range of operating conditions and contact geometries. It is shown that the same two parameters that were found in the Eyring study, a characteristic shear stress, and a reduced coefficient of friction, also govern the behavior of the friction for the case of limiting shear stress models. When the calculated traction data is plotted as a function of these two parameters all results for different cases lie close to a single curve. Experimentally measured traction data is used to validate the observed behavior. Finally, the equations of the mastercurves for both types of rheological model are compared resulting in a relation between the Eyring stress τ0 and the limiting shear stress τL.

scholarly journals Mechanical Hybrid KERS Based on Toroidal Traction Drives: An Example of Smart Tribological Design to Improve Terrestrial Vehicle Performance

2013 ◽  
Vol 2013 ◽  
pp. 1-9 ◽  
Author(s):  
Francesco Bottiglione ◽  
Giuseppe Carbone ◽  
Leonardo De Novellis ◽  
Luigi Mangialardi ◽  
Giacomo Mantriota
Keyword(s):  
Energy Recovery ◽  
Elastohydrodynamic Lubrication ◽  
Mechanical Efficiency ◽  
Speed Ratio ◽  
Vehicle Performance ◽  
Lubrication Regimes ◽  
Recovery Potential ◽  
Wide Range ◽  
Unit Speed ◽  
Traction Drives

We analyse in terms of efficiency and traction capabilities a recently patented traction drive, referred to as the double roller full-toroidal variator (DFTV). We compare its performance with the single roller full-toroidal variator (SFTV) and the single roller half-toroidal variator (SHTV). Modeling of these variators involves challenging tribological issues; the traction and efficiency performances depend on tribological phenomena occurring at the interface between rollers and disks, where the lubricant undergoes very severe elastohydrodynamic lubrication regimes. Interestingly, the DFTV shows an improvement of the mechanical efficiency over a wide range of transmission ratios and in particular at the unit speed ratio as in such conditions in which the DFTV allows for zero-spin, thus strongly enhancing its traction capabilities. The very high mechanical efficiency and traction performances of the DFTV are exploited to investigate the performance of a flywheel-based Kinetic Energy Recovery System (KERS), where the efficiency of the variator plays an important role in determining the overall energy recovery performance. The energy boost capabilities and the round-trip efficiency are calculated for the three different variators considered in this study. The results suggest that the energy recovery potential of the mechanical KERS can be improved with a proper choice of the variator.

scholarly journals Tribological Studies on AISI 1040 with Raw and Modified Versions of Pongam and Jatropha Vegetable Oils as Lubricants

2012 ◽  
Vol 2012 ◽  
pp. 1-6 ◽  
Author(s):  
Y. M. Shashidhara ◽  
S. R. Jayaram
Keyword(s):  
Vegetable Oils ◽  
Friction And Wear ◽  
Mineral Oil ◽  
Significant Drop ◽  
Lubrication Regimes ◽  
Pin On Disc ◽  
Stribeck Curves ◽  
Sliding Distance ◽  
Friction And Wear Tests ◽  
Film Lubrication

The friction and wear tests on AISI 1040 are carried out under raw, modified versions of two nonedible vegetable oils Pongam (Pongamia pinnata) and Jatropha (Jatropha curcas) and also commercially available mineral oil using a pin-on-disc tribometer for various sliding distances and loads. A significant drop in friction and wear for AISI 1040 is observed under Pongam and Jatropha raw oil compared to mineral oil, for the complete tested sliding distance and load, increasing the potential of vegetable oil for tribological applications. Stribeck curves are also drawn to understand the regimes of lubrication. Both the vegetable oils showed a clear reduction in the boundary lubrication regimes, leading to an early start of full film lubrication.

A Parametric Study on Fatigue Life for Mixed Elastohydrodynamic Lubrication Point Contacts

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Xiao-Liang Yan ◽  
Xiao-Li Wang ◽  
Yu-Yan Zhang
Keyword(s):  
Shear Stress ◽  
Fatigue Life ◽  
Three Dimensional ◽  
Elastohydrodynamic Lubrication ◽  
Point Contacts ◽  
Newtonian Flow ◽  
Lubrication Regimes ◽  
Close Relationship ◽  
Lubrication Characteristics ◽  
Effect Of Surface

The lubrication characteristics and fatigue life are numerically analyzed under full film and mixed lubrication regimes, in which the three-dimensional sinusoidal surfaces with changeable wavelengths in x and y directions are used, the geometry changes of the contact areas are described by the various ellipticity, and the non-Newtonian flow of lubricant is described by the sinh-law rheology model. The results show that the influences of characteristic shear stress, wavelength ratio, and ellipticity on lubrication characteristics and fatigue life are remarkable. The effect of surface topography on lubrication characteristics has a close relationship with speed. Increasing the ellipticity and decreasing wavelength ratio and characteristic shear stress can prolong the fatigue life.

Prediction of traction in elastohydrodynamic lubrication

1998 ◽  
Vol 212 (5) ◽  
pp. 321-332 ◽  
Author(s):  
A. V. Olver ◽  
H. A. Spikes
Keyword(s):  
Heat Transfer ◽  
Shear Stress ◽  
Iterative Scheme ◽  
Elastohydrodynamic Lubrication ◽  
Heat Transfer Analysis ◽  
Stress Model ◽  
Challenging Problem ◽  
Dimensionless Form ◽  
Limiting Shear Stress ◽  
Temperature And Pressure

The prediction of traction (friction) in lubricated rolling-sliding contacts remains a challenging problem despite the development of the realistic Maxwell-Eyring-limiting shear stress model by Johnson and co-workers in the 1980s. This is largely because there is a strong coupling between the elastohydrodynamic traction and the film temperature. An added complication is that the heat conducted into the rubbing surfaces, as well as influencing traction directly, also determines the temperature in the inlet to the contact and hence the thickness of the elastohydrodynamic film. In the present paper, the traction model of Johnson et al. is combined with a heat transfer analysis of the contacting bodies as well as the film thickness regression equation. In addition, the variations in the lubricant's rheological properties with temperature and pressure based upon the measurements of Muraki et al. have been included. The traction equation is expressed in dimensionless form and is solved using a simple iterative scheme, which in many cases allows estimation of the traction without the use of a computer. Closed-form equations for the friction are given for each of the traction regimes.

An Anomalous Elastohydrodynamic Lubrication Film: Inlet Dimple

2005 ◽  
Vol 127 (2) ◽  
pp. 425-434 ◽  
Author(s):  
F. Guo ◽  
P. L. Wong
Keyword(s):  
Shear Stress ◽  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Lubrication Film ◽  
Entrainment Velocity ◽  
Limiting Shear Stress ◽  
The Individual ◽  
Solid Liquid Interface ◽  
Solid Liquid ◽  
Wall Slippage

This paper presents a deliberately designed elastohydrodynamical lubrication (EHL) experiment for the study of the individual effect of the limiting shear stress and wall slippage. Very slow entrainment speeds were employed to avoid influential shear heating and oils of high viscosities were chosen to ensure that the conjunction was under typical EHL. An anomalous EHL film, characterized by a dimple at the inlet region, was obtained. Literature revealed that this inlet dimple was reported in some numerical studies taking into consideration the limiting-shear-stress characteristics of the lubricant and wall slippage. It was found that even under the same kinematic conditions, different types of film shape would be generated by simple disc sliding and simple ball sliding. Simple disc sliding produces an inlet dimple with a comparatively thick inlet film thickness, which droops rapidly toward the outlet region. For simple ball sliding, there is also an inlet dimple but the central film thickness is rather uniform. However, by prerunning the conjunction at a zero entrainment velocity (at the same linear speeds but in opposite directions) before the sliding experiment, the slope of the central film of simple disc sliding becomes smaller. It is probably due to the modification of solid-liquid interface, i.e., the slippage level, by the highly pressurized and stressed prerunning conditions. With a prescribed prerunning, which can produce very similar films at simple disc sliding and simple ball sliding, variation of film thickness was studied and it was found that the inlet dimple film has obvious dependence on entrainment speeds, but was not sensitive to loads. The present experimental results can be considered as direct evidence for those numerical findings of the inlet dimple. Tentatively, an effective viscosity wedge is proposed to account for the formation of the inlet dimple.

A Model of Mixed Lubrication Based on Non-Normalized Discretization and Its Application for Multilayered Materials

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Qingbing Dong ◽  
Zhanjiang Wang ◽  
Dong Zhu ◽  
Fanming Meng ◽  
Lixin Xu ◽  
...  
Keyword(s):  
Elastohydrodynamic Lubrication ◽  
Functional Materials ◽  
Computational Procedure ◽  
Pressure Balance ◽  
Engineering Structures ◽  
Lubrication Regimes ◽  
Lubrication Performance ◽  
Wide Range ◽  
Full Analysis ◽  
Multilayered Materials

This study presents a generalized model of mixed elastohydrodynamic lubrication, in which the dimensional Reynolds equation is discretized according to a modified differential scheme based on the full analysis of the pressure balance within the lubrication region. The model is capable of a wide range of lubrication regimes from fully hydrodynamic down to boundary lubrication, and both the steady-state and the time-dependent conditions can be considered. A simplified computational procedure is proposed for elliptical contacts without the ellipticity parameters specified. The evolution of lubrication behavior at startup and shutdown conditions is investigated and the transient effect of surface waviness is discussed. The model application is then extended to contacts of multilayered materials, and the effects of the layer stiffness and the fabrication methods on the stress fields and lubrication performance are analyzed. The conclusions may potentially provide some insightful information for the design and analysis of functional materials and their engineering structures.

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