Analysis of Soft-Elastohydrodynamic Lubrication Line Contacts on Finite Thickness

2018 ◽  
Vol 140 (4) ◽  
Author(s):  
Qie-Da Chen ◽  
Wang-Long Li
Keyword(s):  
Film Thickness ◽  
Finite Deformation ◽  
Contact Region ◽  
Finite Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Soft Materials ◽  
Systematic Analysis ◽  
Pressure Distributions ◽  
Green Strain ◽  
Line Contacts

Soft elastohydrodynamic lubrication (soft-EHL) is an important mechanism in biotribological systems. The soft-EHL has some distinct differences from the traditional hard-EHL, and a systematic analysis factoring in key features of the “softness” appears to be lacking. In this paper, a complete soft-EHL line-contact model is developed. In the model, the half-space approximation is replaced by the finite thickness analysis; the geometrical and material nonlinearity due to finite deformation is factored in; the surface velocities altered by the curvature effect are considered, and the load balance equation is formulated based on the deformed configuration. Solutions are obtained using a finite element method (FEM). The film thickness, pressure distributions, and material deformation are analyzed and discussed under various entraining velocities, elastic modulus, and material thickness of the soft layer. Comparisons are made between soft-EHL and hard-EHL modeling assumptions. The analyses show that the classical EHL modeling is not suitable for soft materials with high loads. The results show that the finite deformation (Green strain) should be considered in soft-EHL analysis. In the contact region, the hard EHL solver overestimates the pressure distribution and underestimates the film thickness and deformation.

Thermal Non-Newtonian Elastohydrodynamic Lubrication of Rolling Line Contacts

1991 ◽  
Vol 113 (3) ◽  
pp. 481-491 ◽  
Author(s):  
H. Salehizadeh ◽  
N. Saka
Keyword(s):  
Film Thickness ◽  
Contact Region ◽  
Elastohydrodynamic Lubrication ◽  
Pressure Profile ◽  
Shear Stresses ◽  
Hertz Contact ◽  
Minimum Film Thickness ◽  
Line Contacts ◽  
Pressure Spike ◽  
Heavy Loads

The two-dimensional thermal elastohydrodynamic equations were numerically solved for a Ree-Eyring type lubricant under pure rolling conditions. Profiles of lubricant pressure, film thickness, and temperature were obtained for medium to heavy loads and moderate to high rolling speeds. The pressure results generally show a small secondary peak near the outlet, but at the highest load considered no pressure spike is obtained and the pressure profile is almost Hertzian. The film thickness results show an increase in minimum film thickness with increasing rolling speeds, but at a lesser rate than those predicted for a Newtonian fluid under isothermal conditions. It is found that unless the lubricant becomes non-Newtonian in the inlet region, the reduction in minimum film thickness at high rolling speeds is completely due to thermal effect. The lubricant temperature profile and the amount of heat generated and dissipated in the contact region were also calculated. The lubricant temperature reaches a maximum just before the entrance to the Hertz contact region. Both shear and compression heating are found to be important in raising the lubricant temperature in the inlet. As the lubricant enters the Hertz contact zone, the temperature first drops rapidly, because of the rapid heat conduction to the rollers, and then remains almost constant for most of the Hertz contact. Near the exit where the pressure gradients are large, the lubricant temperature drops rapidly below the ambient because of lubricant expansion. The lubricant then heats up rapidly before leaving the contact area as a result of heat generated by shear stresses.

Rough Air-Soft Elastohydrodynamic Lubrication

2013 ◽  
Vol 420 ◽  
pp. 30-35
Author(s):  
Khanittha Wongseedakaew ◽  
Jesda Panichakorn
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Modulus Of Elasticity ◽  
Contact Region ◽  
Elastohydrodynamic Lubrication ◽  
Multilevel Methods ◽  
Inlet Temperature ◽  
Film Pressure ◽  
Air Inlet ◽  
Air Film

This paper presents the effects of rough surface air-soft elastohydrodynamic lubrication (EHL) of rollers for soft material under the effect of air molecular slip. The time independent modified Reynolds equation and elasticity equation were solved numerically using finite different method, Newton-Raphson method and multigrid multilevel methods were used to obtain the film pressure profiles and film thickness in the contact region. The effects of amplitude of surface roughness, modulus of elasticity and air inlet temperature are examined. The simulation results showed surface roughness has effect on film thickness but it little effect to air film pressure. When the amplitude of surface roughness and modulus of elasticity increased, the air film thickness decreased but air film pressure increased. However, the air inlet temperature increased when the air film thickness increased.

Thermal Non-Newtonian Elastohydrodynamic Lubrication of Line Contacts Under Simple Sliding Conditions

1992 ◽  
Vol 114 (2) ◽  
pp. 317-327 ◽  
Author(s):  
Shao Wang ◽  
T. F. Conry ◽  
C. Cusano
Keyword(s):  
Film Thickness ◽  
Surface Temperature ◽  
Thermal Effects ◽  
Elastohydrodynamic Lubrication ◽  
Reduction Factor ◽  
Simple Formulation ◽  
Maximum Surface ◽  
Line Contacts ◽  
Traction Coefficient ◽  
Maximum Surface Temperature

A computationally simple formulation for the stationary surface temperature is developed to examine the thermal non-Newtonian EHD problem for line contacts under simple sliding conditions. Numerical results obtained are used to develop a formula for a thermal and non-Newtonian (Ree-Eyring) film thickness reduction factor. Results for the maximum surface temperature and traction coefficient are also presented. The thermal effects on film thickness and traction are found to be more pronounced for simple sliding than for combined sliding and rolling conditions.

The Effects of Surface Irregularities on the Elastohydrodynamic Lubrication of Sliding Line Contacts. Part II—Wavy Surfaces

1984 ◽  
Vol 106 (1) ◽  
pp. 113-119 ◽  
Author(s):  
P. R. Goglia ◽  
C. Cusano ◽  
T. F. Conry
Keyword(s):  
Shear Stress ◽  
Film Thickness ◽  
Smooth Surface ◽  
Wave Amplitude ◽  
Elastohydrodynamic Lubrication ◽  
Wavy Surface ◽  
Line Contacts ◽  
Surface Irregularities ◽  
Wavy Surfaces ◽  
Octahedral Shear Stress

The micro-EHD effects caused by wavy surfaces have been analytically investigated. The investigation includes the effects of phase, wavelength, and wave amplitude on film thickness, pressure distribution and subsurface octahedral shear stress field. The presence of a wavy surface with a given wavelength produces pressure oscillations of the same wavelength. With increasing wave amplitude and decreasing wavelength, the micro-EHD action increases. This results in a maximum value of the octahedral shear stress which is greater in magnitude and closer to the surface than the corresponding smooth surface case. The slope of the wavy surface in the inlet region determines whether the average film thickness is smaller or larger than the smooth surface value.

Experimental Investigation of Lubricant Flow Properties Under Micro Oil Supply Condition

2012 ◽  
Vol 134 (4) ◽  
Author(s):  
Shanhua Qian ◽  
Dan Guo ◽  
Shuhai Liu ◽  
Xinchun Lu
Keyword(s):  
Film Thickness ◽  
Contact Region ◽  
Elastohydrodynamic Lubrication ◽  
Relative Length ◽  
Flow Properties ◽  
Oil Supply ◽  
Supply Condition ◽  
Lubricant Flow ◽  
Oil Pool ◽  
Disc Configuration

Lubricant flow properties of polyalphaolefin (PAO) oil have been experimentally investigated based on a ball-on-disc configuration under micro oil supply condition. The oil pool shape and central film thickness in the contact region were obtained using fluorescence microscopy and optical interferometry, respectively. It has been found that the relative length between the inlet meniscus and Hertzian center point in the oil pool to Hertzian radius was much larger than 1 in a smaller lubricant supply of 20 μl, and the corresponding contact region initially entered the elastohydrodynamic lubrication (EHL) region and then became starved with the increasing speed. The variations of the relative film thickness as a function of starvation degree and the ratio of relative length to Hertzian radius were proposed to explain the obtained results. Besides, the fluorescence technique was used to directly observe the inlet meniscus position of the oil pool and helped to gain more understanding of the lubricant flow properties under micro oil supply condition.

Occurrence of High Pressure Spike in Unidirectional Start–Stop–Start Point Contacts

2014 ◽  
Vol 136 (4) ◽  
Author(s):  
P. Sperka ◽  
J. Wang ◽  
I. Krupka ◽  
M. Hartl ◽  
M. Kaneta
Keyword(s):  
High Pressure ◽  
Film Thickness ◽  
Rolling Contact Fatigue ◽  
Contact Fatigue ◽  
Elastohydrodynamic Lubrication ◽  
Rolling Contact ◽  
Point Contacts ◽  
Pressure Distributions ◽  
Machine Element ◽  
Pressure Spike

The transient film thickness and pressure distributions in point elastohydrodynamic lubrication (EHL) contacts during start–stop–start motion are discussed based on experimental and numerical analyses. When the machine element starts to move after the stopping, where the oil is entrapped between two surfaces, the pressure at the exit area increases very much. The pressure increase depends markedly on the overall film thickness before the stopping of the motion, but is hardly controlled by the acceleration after the stopping. It can be considered that this phenomenon affects the rolling contact fatigue damage.

Uniform Equations in the Inlet and Exit Zones of Heavily Loaded Point and Line Elastohydrodynamically Lubricated Contacts Involved in Various Steady Motions

2015 ◽  
Vol 137 (2) ◽  
Author(s):  
Ilya I. Kudish
Keyword(s):  
Film Thickness ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Point Contacts ◽  
Lubrication Film ◽  
Lubricated Contacts ◽  
Asymptotic Equations ◽  
Line Contacts ◽  
Steady Motions ◽  
Numerical Approaches

Heavily loaded point elastohydrodynamically lubricated (EHL) contacts involved in steady purely transitional, skewed transitional, and transitional with spinning motions are considered. It is shown that in the central parts of the inlet and exit zones of such heavily loaded point EHL contacts the asymptotic equations governing the EHL problem along the lubricant flow streamlines for the above types of contact motions can be reduced to two sets of asymptotic equations: one in the inlet and one in the exit zones. The latter sets of equations are identical to the asymptotic equations describing lubrication process in the inlet and exit zones of the corresponding heavily loaded line EHL contact (Kudish, I. I., 2013, Elastohydrodynamic Lubrication for Line and Point Contacts: Asymptotic and Numerical Approaches, Chapman and Hall/CRC). For each specific motion of a point contact, a separate set of formulas for the lubrication film thickness is obtained. For different types of contact motions, these film thickness formulas differ significantly (Kudish, I. I., 2013, Elastohydrodynamic Lubrication for Line and Point Contacts: Asymptotic and Numerical Approaches, Chapman and Hall/CRC). For heavily loaded contacts, the discovered relationship between point and line EHL problems allows to apply to point contacts most of the results obtained for line contacts (Kudish, I. I., 2013, Elastohydrodynamic Lubrication for Line and Point Contacts: Asymptotic and Numerical Approaches, Chapman and Hall/CRC; Kudish, I. I., and Covitch, M. J., 2010, Modeling and Analytical Methods in Tribology, Chapman and Hall/CRC).

Analysis of EHL Circular Contact Start Up: Part I—Mixed Contact Model With Pressure and Film Thickness Results

2000 ◽  
Vol 123 (1) ◽  
pp. 67-74 ◽  
Author(s):  
Jiaxin Zhao ◽  
Farshid Sadeghi ◽  
Michael H. Hoeprich
Keyword(s):  
Film Thickness ◽  
Contact Region ◽  
Elastohydrodynamic Lubrication ◽  
Contact Problems ◽  
Iteration Scheme ◽  
Mixed Lubrication ◽  
Contact Forces ◽  
Solid Contact ◽  
Start Up ◽  
Lubricated Contact

In this paper a model is presented to investigate the start up condition in elastohydrodynamic lubrication. During start up the lubrication condition falls into the mixed lubrication regime. The transition from solid contact to lubricated contact is of importance when investigating the start up process and its effects on bearing performance. The model presented uses the multigrid multilevel method to solve the lubricated region of the contact and a minimization of complementary energy approach to solve the solid contact region. The FFT method is incorporated to speed up the film thickness calculation. An iteration scheme between the lubrication and the solid contact problems is used to achieve the solution of the mixed lubrication contact problem. The results of start up with smooth surfaces are provided for the case when speed increases from zero to desired speed in one step and the case when speed is linearly increased to desired speed. The details of the transition from full solid contact to full lubricated contact in EHL start up are presented. The change of pressure and film thickness as well as contact forces and contact areas are discussed.

Soft-Elastohydrodynamic Lubrication Line Contact Analysis on a Strip of Bio-Materials

2019 ◽  
Vol 141 (11) ◽  
Author(s):  
Qie-Da Chen ◽  
Wang-Long Li
Keyword(s):  
Relative Motion ◽  
Finite Deformation ◽  
Soft Tissues ◽  
Finite Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Transversely Isotropic ◽  
Von Mises Stress ◽  
Equivalent Model ◽  
Line Contact ◽  
Curvature Effects

Abstract The characteristics of anisotropic material, finite deformation, and lubrication in biological system diminish the friction and wear between soft tissues with relative motion. In this research, the lubrication between pleura surfaces in relative motion is analyzed by soft elastohydrodynamic lubrication (soft-EHL) line contact with an equivalent model. The model is a soft, transversely isotropic (TI) elastic strip with finite thickness sliding under a rigid sinusoidal surface, which is used to simulate the surface irregularities, with lubricant in between. The material nonlinearity and the curvature effects due to finite deformation, which are significant in soft-EHL, are considered in the present study. The pressure distribution, film thickness, von Mises stress, and material deformation are analyzed and discussed under various combinations of elastic moduli and Poisson's ratios for the transversely isotropic models. The simulation results reveal that the soft-EHL modeling fit actual result better than the traditional EHL (t-EHL) modeling. The Poisson's ratio νp = 0.1 and νpz = 0.49 situation will have more gentle stress distribution. The present soft-EHL solver can be used to realize some desired stress distributions and to identify the mechanical properties bio-materials under the aids of experiments.

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