scholarly journals The influence of stick–slip transitions in mixed-friction predictions of heavily loaded cam–roller contacts

2018 ◽  
Vol 233 (5) ◽  
pp. 676-691 ◽  
Author(s):  
Shivam S Alakhramsing ◽  
Matthijn B de Rooij ◽  
Mark van Drogen ◽  
Dirk J Schipper
Keyword(s):  
Friction Coefficient ◽  
Rotational Velocity ◽  
Mixed Lubrication ◽  
Contact Forces ◽  
Contact Friction ◽  
Real Surface ◽  
Asperity Contact ◽  
Roughness Effects ◽  
Friction Mechanism ◽  
Stick Slip

A load-sharing-based mixed lubrication model, applicable to cam–roller contacts, is developed. Roller slippage is taken into account by means of a roller friction model. Roughness effects in the dry asperity contact component of the mixed lubrication model are taken into account by measuring the real surface topography. The proportion of normal and tangential load due to asperity interaction is obtained from a dry contact stick–slip solver. Lubrication conditions in a cam–roller follower unit, as part of the fuel injection equipment in a heavy-duty diesel engine, are analyzed. Main findings are that stick–slip transitions (or variable asperity contact friction coefficient) are of crucial importance in regions of the cam where the acting contact forces are very high. The contact forces are directly related to the sliding velocity/roller slippage at the cam–roller contact and thus also to the static friction mechanism of asperity interactions. Assuming a constant asperity contact friction coefficient (or assuming that gross sliding has already occurred) in highly loaded regions may lead to large overestimation in the minimal required cam–roller contact friction coefficient in order to keep the roller rolling. The importance of including stick–slip transitions into the mixed lubrication model for the cam–roller contact is amplified with decreasing cam rotational velocity.

A Mixed-TEHL Analysis of Cam-Roller Contacts Considering Roller Slip: On the Influence of Roller-Pin Contact Friction

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Shivam S. Alakhramsing ◽  
Matthijn B. de Rooij ◽  
Aydar Akchurin ◽  
Dirk J. Schipper ◽  
Mark van Drogen
Keyword(s):  
Friction Coefficient ◽  
Thermal Effects ◽  
Mixed Lubrication ◽  
Contact Friction ◽  
Sudden Increase ◽  
Low Friction ◽  
Pure Rolling ◽  
Lubrication Performance ◽  
Cam Follower ◽  
Film Lubrication

In this work, a mixed lubrication model, applicable to cam-roller contacts, is presented. The model takes into account non-Newtonian, thermal effects, and variable roller angular velocity. Mixed lubrication is analyzed using the load sharing concept, using measured surface roughness. Using the model, a quasi-static analysis for a heavily loaded cam-roller follower contact is carried out. The results show that when the lubrication conditions in the roller-pin contact are satisfactory, i.e., low friction levels, then the nearly “pure rolling” condition at the cam-roller contact is maintained and lubrication performance is also satisfactory. Moreover, non-Newtonian and thermal effects are then negligible. Furthermore, the influence of roller-pin friction coefficient on the overall tribological behavior of the cam-roller contact is investigated. In this part, a parametric study is carried out in which the friction coefficient in the roller-pin contact is varied from values corresponding to full film lubrication to values corresponding to boundary lubrication. Main findings are that at increasing friction levels in the roller-pin contact, there is a sudden increase in the slide-to-roll ratio (SRR) in the cam-roller contact. The value of the roller-pin friction coefficient at which this sudden increase in SRR is noticed depends on the contact force, the non-Newtonian characteristics, and viscosity–pressure dependence. For roller-pin friction coefficient values higher than this critical value, inclusion of non-Newtonian and thermal effects becomes highly important. Furthermore, after this critical level of roller-pin friction, the lubrication regime rapidly shifts from full film to mixed lubrication. Based on the findings in this work, the importance of ensuring adequate lubrication in the roller-pin contact is highlighted as this appears to be the critical contact in the cam-follower unit.

Numerical Prediction of Surface Wear and Roughness Parameters During Running-In for Line Contacts Under Mixed Lubrication

2018 ◽  
Vol 140 (6) ◽  
Author(s):  
Yazhao Zhang ◽  
Alexander Kovalev ◽  
Noriyuki Hayashi ◽  
Kensuke Nishiura ◽  
Yonggang Meng
Keyword(s):  
Friction Coefficient ◽  
Contact Region ◽  
Mixed Lubrication ◽  
Asperity Contact ◽  
Wear Particles ◽  
Wear Model ◽  
Wear Process ◽  
Line Contacts ◽  
Lubrication Condition ◽  
Initial Line

A stochastic model for predicting the evolutions of wear profile and surface height probability density function (PDF) of initial line contacts during running-in under mixed lubrication condition is presented. A numerical approach was developed on the basis of stochastic solution of mixed lubrication, which combined the Patir and Cheng's average flow model for calculation of the hydrodynamic pressure and the Kogut and Etsion's (KE) rough surface contact model for calculation of the asperity contact pressure. The total friction force was assumed to be the sum of the boundary friction at the contact asperities and the integration of viscous shear stress in the hydrodynamic region. The wear depth on the contact region was estimated according to the modified Archard's wear model using the asperity contact pressure. Sugimura's wear model was modified and used to link the wear particle size distribution and the variation of surface height PDF during wear. In the wear process, the variations of profile and surface height PDF of initial line contacts were calculated step by step in time, and the pressure distribution, friction coefficient, and wear rate were updated consequently. The effect of size distribution of wear particles on the wear process was numerically investigated, and the simulation results showed that the lubrication condition in which small wear particles are generated from the asperity contact region is beneficial to reduce friction coefficient and wear rate, and leads to a better steady mixed lubrication condition.

Mixed Lubrication of “Parallel” Plane Sliders

1972 ◽  
Vol 39 (1) ◽  
pp. 36-40
Author(s):  
D. S. Bedi ◽  
M. J. Hillier
Keyword(s):  
Theoretical Model ◽  
Friction Coefficient ◽  
Critical Speed ◽  
Mixed Lubrication ◽  
Parallel Plane ◽  
Stick Slip ◽  
Lubrication Conditions ◽  
Film Lubrication ◽  
Slip Phenomenon ◽  
Fluid Film Lubrication

A theoretical model for the friction coefficient indicates two critical speeds of sliding. The lower critical speed corresponds to a change-over from boundary to mixed lubrication conditions, the higher critical speed a transition to full fluid-film lubrication at angles of inclination less than 0.01 deg. The first critical speed appears to be associated with the “stick-slip” phenomenon.

scholarly journals Multiscale Analysis of the Roughness Effect on Lubricated Rough Contact

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
Ibrahim Demirci ◽  
Sabeur Mezghani ◽  
Mohammed Yousfi ◽  
Mohamed El Mansori
Keyword(s):  
Friction Coefficient ◽  
Point Contact ◽  
Friction Reduction ◽  
Real Surface ◽  
Surface Geometry ◽  
Roughness Effects ◽  
Multiscale Decomposition ◽  
Lubricated Contact ◽  
Major Factors ◽  
Film Lubrication

Determining friction is as equally essential as determining the film thickness in the lubricated contact, and is an important research subject. Indeed, reduction of friction in the automotive industry is important for both the minimization of fuel consumption as well as the decrease in the emissions of greenhouse gases. However, the progress in friction reduction has been limited by the difficulty in understanding the mechanism of roughness effects on friction. It was observed that micro-surface geometry or roughness was one of the major factors that affected the friction coefficient. In the present study, a new methodology coupling the multiscale decomposition of the surface and the prediction of the friction coefficient by numerical simulation was developed to understand the influence of the scale of roughness in the friction coefficient. In particular, the real surface decomposed in different roughness scale by multiscale decomposition, based on ridgelets transform, was used as input into the model. This model predicts the effect of scale on mixed elastohydroynamic point contact. The results indicate a good influence of the fine scale of surface roughness on the friction coefficient for full-film lubrication as well as a beginning of improvement for mixed lubrication.

Piston ring-cylinder liner tribology investigation in mixed lubrication regime: part I-correlation with bench experiment

2015 ◽  
Vol 67 (6) ◽  
pp. 520-530 ◽  
Author(s):  
Lin Ba ◽  
Zhenpeng He ◽  
Lingyan Guo ◽  
Young Chiang ◽  
Guichang Zhang ◽  
...  
Keyword(s):  
Friction Coefficient ◽  
Sudden Change ◽  
Mixed Lubrication ◽  
Friction Reduction ◽  
Asperity Contact ◽  
Film Rupture ◽  
Frictional Loss ◽  
Content Type ◽  
Oil Film ◽  
Ring Sample

Purpose – The purpose of this paper is to improve the environment and save energy, friction reduction, lower oil consumption and emissions demand that are the chief objectives of the automotive industry. The piston system is the largest frictional loss source, which accounts for about 40 per cent of the total frictional loss in engine. In this paper, the reciprocating tribometer, which is updated, was used to evaluate the friction and wear performances. Design/methodology/approach – An alternate method is introduced to investigate the effect of reciprocating speed, normal load, oil pump speed and ring sample and oil temperature on friction coefficient with the ring/liner of a typical inline diesel engine. The orthogonal experiment is designed to identify the factors that dominate wear behavior. To understand the correlations between friction coefficients and wear well, different friction coefficient results were compared and explained by oil film build-up and asperity contact theory, such as the friction coefficient over a long period and averaged the friction coefficient over one revolution. Findings – The friction coefficient changes little but fluctuates with a small amplitude in the stable stage. The sudden change of frequency, load and stroke will lead to the oil film rupture. The identification for the factors that dominates the wear loss is ranged as F (ring sample) > , E (oil sample) > , B (stroke) > , D (temperature) > , A (load) > , G (liner) > and C (frequency). Originality/value – This paper develops and verifies a methodology capable of mimicking the real engine behavior at boundary and mixed lubrication regimes which can minimize frictional losses, wear, reduce much work for the experiment and reduce the cost. The originality of the work is well qualified, as very few papers on a similar analysis have been published, such as: The friction coefficient values fluctuating in the whole stage may be caused by the vibration of the system; suddenly, boundary alternation may help the oil film to form the lubrication; and weight loss mainly comes from the contribution of the friction coefficient value fluctuation. The paper also found that the statistics can gain more information from less experiment time based on a design of experiment.

scholarly journals Sliding Interaction for Coated Asperity with Power-Law Hardening Elastic-Plastic Coatings

Materials ◽  
2019 ◽  
Vol 12 (15) ◽  
pp. 2388
Author(s):  
Bin Zhao ◽  
Hanzhang Xu ◽  
Xiqun Lu
Keyword(s):  
Friction Coefficient ◽  
Yield Strength ◽  
Young’S Modulus ◽  
Contact Force ◽  
Young's Modulus ◽  
Contact Forces ◽  
Geometrical Parameters ◽  
Asperity Contact ◽  
Strength Ratio ◽  
Modulus Ratio

Sliding between asperities occurs inevitably in the friction pair, which affects the efficiency and reliability in both lubricated and non-lubricated conditions. In this work, the contact parameters in the coated asperity sliding process are studied, and the universal expressions of the average contact force and the friction coefficient are obtained. The effect of the interference between asperities, the material and geometrical parameters including the Young’s modulus ratio and yield strength ratio of the coating and substrate, and the hardening exponent and thickness of the coating on the average contact forces and friction coefficient is considered. It shows both normal and tangential contact forces increase with the increasing interference, increasing Young’s modulus ratio, decreasing yield strength ratio, and decreasing coating thickness; while the trend is different for the effect of the hardening exponent of the coating. The normal force increases and the tangential force decreases as the hardening exponent increases. Based on this, the influence of these parameters on the effective friction coefficient is obtained further. It reveals that the friction coefficient increases as the interference and Young’s modulus ratio enlarge and decreases as the yield strength ratio, the coating’s hardening exponent, and thickness increase. The universal expressions for the contact force and friction coefficient in the sliding process are obtained. This work might give some useful results to help choose the optimum coatings for specific substrates to reduce friction in cases where the asperity contact exists, especially in the focused field of the journal bearing in the marine engine under poor lubrication conditions.

scholarly journals Contact stiffness and damping of spiral bevel gears under transient mixed lubrication conditions

Friction ◽  
2021 ◽  
Author(s):  
Zongzheng Wang ◽  
Wei Pu ◽  
Xin Pei ◽  
Wei Cao
Keyword(s):  
Contact Stiffness ◽  
Mixed Lubrication ◽  
Asperity Contact ◽  
Spiral Bevel Gears ◽  
Bevel Gears ◽  
Dry Contact ◽  
Spiral Bevel ◽  
Stiffness And Damping ◽  
Lubrication Conditions ◽  
Film Lubrication

AbstractExisting studies primarily focus on stiffness and damping under full-film lubrication or dry contact conditions. However, most lubricated transmission components operate in the mixed lubrication region, indicating that both the asperity contact and film lubrication exist on the rubbing surfaces. Herein, a novel method is proposed to evaluate the time-varying contact stiffness and damping of spiral bevel gears under transient mixed lubrication conditions. This method is sufficiently robust for addressing any mixed lubrication state regardless of the severity of the asperity contact. Based on this method, the transient mixed contact stiffness and damping of spiral bevel gears are investigated systematically. The results show a significant difference between the transient mixed contact stiffness and damping and the results from Hertz (dry) contact. In addition, the roughness significantly changes the contact stiffness and damping, indicating the importance of film lubrication and asperity contact. The transient mixed contact stiffness and damping change significantly along the meshing path from an engaging-in to an engaging-out point, and both of them are affected by the applied torque and rotational speed. In addition, the middle contact path is recommended because of its comprehensive high stiffness and damping, which maintained the stability of spiral bevel gear transmission.

Effect of shape/size and distribution of microgeometries of textures on tribo-performance of crankpin bearing

2021 ◽  
pp. 135065012110105
Author(s):  
Nguyen Van Liem ◽  
Wu Zhenpeng ◽  
Jiao Renqiang
Keyword(s):  
Friction Coefficient ◽  
Friction Force ◽  
Contact Force ◽  
Distribution Density ◽  
Hydrodynamic Lubrication ◽  
Operating Conditions ◽  
Asperity Contact ◽  
Combined Model ◽  
Obvious Effect ◽  
Area Density

The effect of the shape/size and distribution of microgeometries of textures on improving the tribo-performance of crankpin bearing is proposed. Based on a combined model of the slider-crank mechanism dynamic and hydrodynamic lubrication, the distribution density, area density, and shape of spherical textures, square-cylindrical textures, wedge-shaped textures, and a hybrid between spherical texture and square-cylindrical texture on the crankpin bearing's tribo-performance are investigated under different operating conditions of the engine. The tribological characteristic of the crankpin bearing is then evaluated via the indexes of the oil film pressure p, asperity contact force, friction force, and friction coefficient of the crankpin bearing. The research results show that the distribution density with n = 12 and m = 6, and area density with α = 30% of various microtextures have an obvious effect on ameliorating the crankpin bearings tribo-performance. Concurrently, at the mixed lubrication region, the shape of the square-cylindrical texture on improving the tribo-performance is better than the other shapes of the spherical texture, wedge-shaped texture, and spherical and square-cylindrical texture. Particularly, all the average values of the asperity contact force, friction force, and friction coefficient with a square-cylindrical texture are significantly reduced by 14.6%, 19.5%, and 34.5%, respectively, in comparison without microtextures. Therefore, the microtextures of the spherical texture applied on the bearing surface can contribute to enhance the durability and decrease the friction power loss of the engine.

Numerical and experimental study on the effect of surface texture with roughness orientation considered under a mixed lubrication state

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Junru Wang ◽  
Quandai Wang ◽  
Yueyan Li ◽  
Meiling Guo ◽  
Pengyang Li ◽  
...  
Keyword(s):  
Surface Texture ◽  
Surface Texturing ◽  
Mixed Lubrication ◽  
Laser Surface ◽  
Geometric Parameters ◽  
Laser Surface Texturing ◽  
Textured Surface ◽  
Asperity Contact ◽  
Content Type ◽  
Texture Parameters

Purpose The purpose of this paper is to investigate the effects of surface texture with roughness orientation considered on tribological properties under a mixed lubrication state numerically and experimentally. Design/methodology/approach Based on the average Reynolds equation and asperity contact model, the impacts of surface texture parameters and roughness orientation on lubrication properties have been calculated using finite difference method. Tin–bronze samples with various prescribed surface texture geometric parameters and roughness orientation were fabricated by laser surface texturing technique, and the tribology performance of the textured surface was studied experimentally. Findings The effects of surface geometric parameters and roughness orientation parameters have been discerned. The experimental observations are in good agreement with the numerical prediction, which suggests that the numerical scheme adopted in this work is suitable in capturing the surface texture and roughness effect under mixed lubrication state. Originality/value By meticulously controlling the surface roughness and surface texture geometric characteristics based on the laser surface texturing process, samples with prescribed surface texture parameters and roughness orientation consistent with that in theoretical studies were fabricated and the theoretical model and results were verified experimentally.

Numerical Modeling of Mixed Lubrication and Flash Temperature in EHL Elliptical Contacts

2007 ◽  
Vol 130 (1) ◽  
Author(s):  
Neelesh Deolalikar ◽  
Farshid Sadeghi ◽  
Sean Marble
Keyword(s):  
Surface Deformation ◽  
Elastohydrodynamic Lubrication ◽  
Mixed Lubrication ◽  
Asperity Contact ◽  
Lubrication Regime ◽  
Predicting Performance ◽  
Pure Rolling ◽  
Rolling Element ◽  
Contact Pressures ◽  
Film Lubrication

Highly loaded ball and rolling element bearings are often required to operate in the mixed elastohydrodynamic lubrication regime in which surface asperity contact occurs simultaneously during the lubrication process. Predicting performance (i.e., pressure, temperature) of components operating in this regime is important as the high asperity contact pressures can significantly reduce the fatigue life of the interacting components. In this study, a deterministic mixed lubrication model was developed to determine the pressure and temperature of mixed lubricated circular and elliptic contacts for measured and simulated surfaces operating under pure rolling and rolling/sliding condition. In this model, we simultaneously solve for lubricant and asperity contact pressures. The model allows investigation of the condition and transition from boundary to full-film lubrication. The variation of contact area and load ratios is examined for various velocities and slide-to-roll ratios. The mixed lubricated model is also used to predict the transient flash temperatures occurring in contacts due to asperity contact interactions and friction. In order to significantly reduce the computational efforts associated with surface deformation and temperature calculation, the fast Fourier transform algorithm is implemented.

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