Stribeck Curve for Starved Line Contacts

2006 ◽  
Vol 129 (1) ◽  
pp. 181-187 ◽  
Author(s):  
I. C. Faraon ◽  
D. J. Schipper
Keyword(s):  
Film Thickness ◽  
Layer Thickness ◽  
Boundary Lubrication ◽  
Numerical Data ◽  
Contact Model ◽  
Stribeck Curve ◽  
Lubrication Regime ◽  
Straight Line ◽  
Line Contacts ◽  
Good Agreement

This paper discusses a mixed lubrication model in order to predict the Stribeck curve for starved lubricated line contacts. This model is based on a combination of the contact model of Greenwood and Williamson and the elastohydrodynamic (EHL) film thickness for starved line contacts. The starved solution to be implemented in the EHL component is obtained by using numerical data of Wolveridge, who computed the starved film thickness for smooth line contacts. Calculations are presented for different oil supply layer thickness over roughness values (hoil∕σs). For values of the oil layer thickness over roughness ratio larger than approximately 6, the Stribeck curve and separation between the rough surfaces do not change compared to the fully flooded situation. If the oil layer thickness over roughness ratio is in the range of 6 down to 0.7, friction starts to increase and the film thickness decreases. When the oil layer thickness over roughness ratio is less than approximately 0.7, the Stribeck curve tends to transform into a straight line and separation stays at the same value as in the boundary lubrication regime. Comparison between measurements and calculations is made and a good agreement is found.

Gear Tribology Aspects in Aircraft High-Lift Actuation Systems

2011 ◽  
Author(s):  
Anngwo Wang ◽  
Lotfi El-Bayoumy
Keyword(s):  
Film Thickness ◽  
Boundary Lubrication ◽  
High Lift ◽  
Lubrication Film ◽  
Root Cause ◽  
Lubrication Regime ◽  
Rotary Actuator ◽  
Actuation Systems

Gears are extensively used in aircraft high-lift actuation systems in which the loading is high and the speed is relatively slow. The specific lubrication film thickness falls into the boundary lubrication regime. In case of lubrication failure, it will cause pitch-line pitting, scoring or micropitting. Many tests have been performed to examine the root cause of these problems. The sliding and rolling action between mating gears in a compound planetary rotary actuator is the source of variation in efficiency. This efficiency variation can be smooth or fluctuating depending on the combination and timing of ring, planet and sun gears. The instantaneous efficiency characteristics of synchronous and non-synchronous actuators under forward-driving with opposing load and reverse-driving with aiding load are investigated. These are some of the gear tribological topics discussed in this paper.

Estimation of Minimum Thickness for Line Contacts in the Transition Region between the Isoviscous—Elastic and the Piezoviscous-Elastic Lubrication Regimes

1989 ◽  
Vol 203 (6) ◽  
pp. 379-386 ◽  
Author(s):  
M J Jaffar
Keyword(s):  
Film Thickness ◽  
Transition Region ◽  
Approximate Formula ◽  
Line Contact ◽  
Minimum Thickness ◽  
Lubrication Regimes ◽  
Minimum Film Thickness ◽  
Line Contacts ◽  
Good Agreement

This paper represents a solution for lubricated cylinders in line contact operating in the transition region between isoviscous-elastic and piezoviscous-elastic conditions. The computer solutions are used to generate a formula for the minimum film thickness. The approximate formula is compared with the existing formulae at the boundaries of the lubrication regimes where good agreement is obtained. Also, the influence of the starvation on pressure and film thickness is investigated.

Cylinder Bore Wear Damage Analysis of a Heaving-Buoy Wave Energy Converter With Hydraulic Power Take-Off

2010 ◽  
Author(s):  
Limin Yang ◽  
Torgeir Moan
Keyword(s):  
Dynamic Response ◽  
Film Thickness ◽  
Wave Energy ◽  
Stribeck Curve ◽  
Cylinder Wall ◽  
Hydraulic Power ◽  
Composite Surface ◽  
Lubrication Regime ◽  
Wear Damage ◽  
Cylinder Bore

Wave energy is a non-polluting and renewable source of energy. Among several wave energy converters (WEC), an oscillating body with a hydraulic power take-off (PTO) is commonly used for energy conversion. For such a hydraulic system, the piston ring and cylinder play very important roles in achieving desired energy converting performance and durability. Among the failure modes of the ring-bore components, wear is a prevailing one. Compared with the ring wear, cylinder wear is more important to the manufacturer and user, because cylinders are more expensive to replace than the rings. Since the floating body is exposed to irregular incident waves, the dynamic response of the PTO is also random. The position of maximum accumulated wear damage along the cylinder bore cannot be as easily determined as the engine bores where the maximum wear occurs near the Top Dead Centre (TDC). It is controlled by the characteristic dynamics of the system together with the lubrication of the interface which can be modelled by the well-known Stribeck curve. The purpose of this paper is to establish and apply a method for estimating the wear damage along the cylinder bore. The dynamic response of the WEC system is based on the nonlinear mathematical model established by Yang et al [1]. A particular issue in this research is to calculate the dimensionless film thickness λ (the ratio between the oil film thickness h and the composite surface roughness σ) in the lubricated contacts and then determine the lubrication regime according to the Stribeck curve. Combining the wear coefficient which is related to the lubrication regime and the contact pressure, the bore wear damage along the cylinder wall is predicted. In this paper, the bore wear damage is estimated on the basis of time domain simulations. The results show that the bore wear distribution is affected by two main factors: sea state condition and the nonlinearity of the PTO system. The position of the bore where the maximum accumulated wear occurs is predicted. Finally, the relative contribution of wear damage from different sea states is obtained.

A Film Thickness Analysis for Line Contacts Under Pure Rolling Conditions With a Non-Newtonian Rheological Model

1981 ◽  
Vol 103 (2) ◽  
pp. 305-313 ◽  
Author(s):  
B. Gecim ◽  
W. O. Winer
Keyword(s):  
Shear Stress ◽  
Film Thickness ◽  
High Viscosity ◽  
Low Viscosity ◽  
Limiting Shear Stress ◽  
Lubrication Regime ◽  
Pure Rolling ◽  
Reasonable Range ◽  
Line Contacts ◽  
Rolling Elements

The non-Newtonian constitutive equation proposed by Winer and Bair [1] is applied in a conventional isothermal film thickness analysis of line contact lubrication of rolling elements. The present analysis provides four different dimensionless film thickness equations for four different regimes of lubrication. Due to the formulation technique used in deriving the governing pressure-gradient equation, the present study is recommended for high viscosity, high rolling speed, and low limiting shear stress cases where Newtonian models fail to match the experimental data. Comparison of the present film thickness equations with the Newtonian correspondences in each lubrication regime shows a considerable difference, but the analysis suffers from the fact that the limiting shear stress parameters of these high viscosity lubricants need to be determined experimentally. The present analysis assumes a reasonable range of limiting shear stress which is smaller than the corresponding values for low viscosity lubricants which are predominantly Newtonian in behavior (unless severe rolling and/or sliding with high loads is applied).

scholarly journals An improved contact model considered the effect of boundary lubrication regime on piston ring-liner contact for the two-stroke marine engines from the perspective of the Stribeck curve

2021 ◽  
pp. 095440622110272
Author(s):  
Lyu Xiuyi ◽  
Bowen Jiao ◽  
Yuechang Wang ◽  
Abdullah Azam ◽  
Xiqun Lu ◽  
...  
Keyword(s):  
Contact Pressure ◽  
Boundary Lubrication ◽  
Piston Ring ◽  
Cylinder Liner ◽  
Work Conditions ◽  
Stribeck Curve ◽  
Regime Transition ◽  
Lubrication Regime ◽  
Lubrication Performance ◽  
Marine Engines

The prediction of lubrication performance is required to be the basement of friction optimization for marine engines. This paper simulates the lubrication performance of marine engines based on statistical models which have the advantages of fast, efficient, and macroscopic fault location. Boundary lubrication exists in the piston ring-cylinder liner (PRCL) of two-stroke marine engines because of the harsher load, lower speed, and larger structure. It has been proposed that there would be tribofilm under boundary lubrication which has a significant influence on the contact. To understand the boundary lubrication, it is necessary to study the lubrication regime transition. In this paper, firstly, the coefficient of friction curve combined with the thickness ratio embodies the lubrication regime transition process of two-stroke engines under work conditions. However, the phenomenon that the coefficients under boundary lubrication are smaller than that of other regimes shows the non-objectivity of this curve. Therefore, the Stribeck curve is introduced for objectively evaluating the transition. Then, the calculation of asperities contact pressure under boundary lubrication, which Wen proposed, is introduced into the classic Greenwood-Williamson model, the problem that the original model cannot reflect the boundary lubrication regime in the form of the Stribeck curve is improved. Finally, the results are compared before and after modifying the model to verify this study’s practicability. It provides more precise asperities contact pressure for the tribofilm growth calculation from the perspective of the Stribeck curve under the PRCL statistical model in future work.

scholarly journals STRIBECK AND TRACTION CURVES FOR ELLIPTICAL CONTACTS: ISOTHERMAL FRICTION MODEL

2014 ◽  
Vol 4 (2) ◽  
Author(s):  
R.I. Popovici ◽  
D.J. Schipper
Keyword(s):  
Film Thickness ◽  
Rough Surface ◽  
Boundary Lubrication ◽  
Friction Model ◽  
Mixed Lubrication ◽  
Rigid Surface ◽  
Volume Conservation ◽  
Line Contacts ◽  
Highly Loaded ◽  
Model Approach

This paper deals with the prediction of the Stribeck and traction curves, by proposing a mixed lubrication model for highly loaded elliptical contacts. The model represents an extension on the mixed lubrication model of Gelinck and Schipper and comprehends both the asperity component or the so called boundary lubrication component (BL) and the elastohydrodynamic component (EHL). The asperity component is calculated from a fully deterministic contact perspective, where an equivalent rough surface is in contact with a smooth and rigid surface. In EHL regime, the film thickness is calculated according to Nijenbanning et al. and the separation for the asperity component is derived from Johnson, with a small adaptation, which was possible due to the deterministic contact model approach. In this way, the separation is calculated from the volume conservation theory of Johnson and even if this can be negative, the film thickness remains above zero permitting the calculation of highly loaded contacts. For the traction curve calculation, an elastic-plastic approximation for BL micro-contacts as proposed by Gelinck and Schipper for line contacts is used.

An Experimental Investigation of Grease-Lubricated Journal Bearings

2006 ◽  
Vol 129 (1) ◽  
pp. 84-90 ◽  
Author(s):  
Xiaobin Lu ◽  
M. M. Khonsari
Keyword(s):  
Elastohydrodynamic Lubrication ◽  
Mixed Lubrication ◽  
Stribeck Curve ◽  
Grease Lubrication ◽  
Lubrication Regime ◽  
Bearing Load ◽  
Line Contacts ◽  
The Coefficient Of Friction ◽  
Mixed Lubrication Regime ◽  
Basic Characteristics

A series of experimental results is presented to explore the frictional characteristics of a grease-lubricated journal bearing. Load, grease type, and bushing material are varied to examine their effects on the friction coefficient. The results attest to the existence of distinctive regimes in grease lubrication akin to the oil-lubricated Stribeck curve. A mixed elastohydrodynamic lubrication model for line contacts is employed to estimate the coefficient of friction in mixed lubrication regime. The simulation results capture the basic characteristics of mixed lubrication.

Enhanced Photoyield with Decreasing Film Thickness on Metal-Semiconductor Structures

1996 ◽  
Vol 448 ◽  
Author(s):  
V. Hoffmann ◽  
M. Brauer ◽  
M. Schmidt
Keyword(s):  
Quantum Yield ◽  
Film Thickness ◽  
Layer Thickness ◽  
Experimental Results ◽  
Experimental Result ◽  
Model Calculations ◽  
Hot Carrier ◽  
Semiconductor Structures ◽  
Carrier Scattering ◽  
Good Agreement

AbstractExperimental results of the internal quantum yield Yi associated with the internal photoemission on Au/n-Si structures are presented. The samples were prepared on Si(100) and Si(111) substrates with photoemitter layer thicknesses ranging from 5 nm to 50 nm. The Yi was measured at temperatures between 165 K and 300 K with the photoexciting energy varying from 0.72 eV to 1.07 eV. It was found that the Yi increases with decreasing Au layer thickness with a strong enhancement (40 times) in regard to the conventional Fowler theory. This experimental result is in good agreement with model calculations taking account of hot carrier scattering in the photoemitter layer. Barrier energies are larger than deduced from the Fowler plot.

Combined Effects of Shear Thinning and Viscous Heating on EHL Characteristics of Rolling/Sliding Line Contacts

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Punit Kumar ◽  
M. M. Khonsari
Keyword(s):  
Film Thickness ◽  
Thermal Effect ◽  
Fluid Model ◽  
Elastohydrodynamic Lubrication ◽  
Shear Thinning ◽  
Viscous Heating ◽  
Shear Thinning Fluids ◽  
Line Contacts ◽  
Power Law Index ◽  
Good Agreement

The combined influence of shear thinning and viscous heating on the behavior of film thickness and friction in elastohydrodynamic lubrication (EHL) rolling/sliding line contacts is investigated numerically. The constitutive equation put forward by Carreau is incorporated into the model to describe shear thinning. An extensive set of numerical simulations is presented. Comparison of the film thickness predictions with published experiments reveals good agreement, and it is shown that thermal effect plays an important role in the precise estimation of EHL film thickness and friction coefficient. Parametric simulations show that thermal effect in shear-thinning fluids is strongly affected by the power-law index used in the Carreau equation. Comparisons of prediction of the Newtonian fluid model are presented to quantify the degree to which it overestimates the film thickness.

The Deformation of an Erythrocyte Under the Radiation Pressure by Optical Stretch

2006 ◽  
Vol 128 (6) ◽  
pp. 830-836 ◽  
Author(s):  
Yong-Ping Liu ◽  
Chuan Li ◽  
Kuo-Kang Liu ◽  
Alvin C. K. Lai
Keyword(s):  
Radiation Pressure ◽  
Experimental Situation ◽  
Numerical Data ◽  
Shear Stiffness ◽  
Cell Deformation ◽  
Membrane Properties ◽  
Optimization Approach ◽  
Bending Modulus ◽  
Average Shear ◽  
Good Agreement

In this paper, the mechanical properties of erythrocytes were studied numerically based upon the mechanical model originally developed by Pamplona and Calladine (ASME J. Biomech. Eng., 115, p. 149, 1993) for liposomes. The case under study is the erythrocyte stretched by a pair of laser beams in opposite directions within buffer solutions. The study aims to elucidate the effect of radiation pressure from the optical laser because up to now little is known about its influence on the cell deformation. Following an earlier study by Guck et al. (Phys. Rev. Lett., 84, p. 5451, 2000; Biophys. J., 81, p. 767, 2001), the empirical results of the radiation pressure were introduced and imposed on the cell surface to simulate the real experimental situation. In addition, an algorithm is specially designed to implement the simulation. For better understanding of the radiation pressure on the cell deformation, a large number of simulations were conducted for different properties of cell membrane. Results are first discussed parametrically and then evaluated by comparing with the experimental data reported by Guck et al. An optimization approach through minimizing the errors between experimental and numerical data is used to determine the optimal values of membrane properties. The results showed that an average shear stiffness around 4.611×10-6Nm−1, when the nondimensional ratio of shear modulus to bending modulus ranges from 10 to 300. These values are in a good agreement with those reported in literature.

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