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.

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.

Investigation of Patterned Textures in Ball-on-Disk Lubricated Point Contacts

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
Wang Wenzhong ◽  
Shen Dian ◽  
Zhang Shengguang ◽  
Zhao Ziqiang
Keyword(s):  
Friction Coefficient ◽  
Film Thickness ◽  
Contact Region ◽  
Point Contact ◽  
Friction Reduction ◽  
Hertzian Contact ◽  
Rheological Parameters ◽  
Boundary Edge ◽  
Optimal Distribution ◽  
Wide Range

The numerical simulations of surface textures in point-contact lubrication are conducted based on the unified Reynolds equation model. The textures are numerically produced on one of the interacting surfaces. The lubricant rheological parameters used in the simulations are calibrated by experiments. The numerical results show good agreements with those from experiments. The friction reduction mechanism is investigated by systemically analyzing the periodic change of friction coefficient of textures. It is illustrated that the transient friction coefficient is minimal when the dent moves to the front boundary edge of the Hertzian contact zone. A local film enhancement region will be formed on the trail of the dent within the Hertzian contact region. The results suggest that a bigger local film enhancement area will offer stronger film thickness enhancement as well as a lower friction coefficient. Different pattern distributions are also studied to find the optimal distribution of patterned textures, which not only achieves a lower friction coefficient, but also offers stronger film thickness enhancement; moreover, the optimal distribution is numerically proved to be applicable for a wide range of working conditions.

scholarly journals A thermal resistances-based approach for thermal-elastohydrodynamic calculations in point contacts

2017 ◽  
Vol 232 (11) ◽  
pp. 2088-2102 ◽  
Author(s):  
Eduardo de la Guerra Ochoa ◽  
Javier Echávarri Otero ◽  
Enrique Chacón Tanarro ◽  
Benito del Río López
Keyword(s):  
Friction Coefficient ◽  
Film Thickness ◽  
Thermal Effects ◽  
Good Accuracy ◽  
Computational Cost ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Point Contacts ◽  
New Approach ◽  
Ball On Disc

This article presents a thermal resistances-based approach for solving the thermal-elastohydrodynamic lubrication problem in point contact, taking the lubricant rheology into account. The friction coefficient in the contact is estimated, along with the distribution of both film thickness and temperature. A commercial tribometer is used in order to measure the friction coefficient at a ball-on-disc point contact lubricated with a polyalphaolefin base. These data and other experimental results available in the bibliography are compared to those obtained by using the proposed methodology, and thermal effects are analysed. The new approach shows good accuracy for predicting the friction coefficient and requires less computational cost than full thermal-elastohydrodynamic simulations.

Predicting the wear coefficient and friction coefficient in dry point contact using continuum damage mechanics

2018 ◽  
Vol 233 (3) ◽  
pp. 447-455 ◽  
Author(s):  
Sahar Ghatrehsamani ◽  
Saleh Akbarzadeh
Keyword(s):  
Friction Coefficient ◽  
Damage Mechanics ◽  
Point Contact ◽  
Continuum Damage Mechanics ◽  
Continuum Damage ◽  
Wear Coefficient ◽  
Mechanics Model ◽  
Pin On Disk ◽  
Disk Test ◽  
The Continuum

Wear coefficient and friction coefficient are two of the key parameters in the performance of any tribo-system. The main purpose of the present research is to use continuum damage mechanics to predict wear coefficient. Thus, a contact model is utilized that can be used to obtain the friction coefficient between the contacting surfaces. By applying this model to the continuum damage mechanics model, the wear coefficient between dry surfaces is predicted. One of the advantages of using this model is that the wear coefficient can be numerically predicted unlike other methods which highly rely on experimental data. In order to verify the results predicted by this model, tests were performed using pin-on-disk test rig for several ST37 samples. The results indicated that the wear coefficient increases with increasing the friction coefficient.

An articular cartilage contact model based on real surface geometry

2005 ◽  
Vol 38 (1) ◽  
pp. 179-184 ◽  
Author(s):  
Sang-Kuy Han ◽  
Salvatore Federico ◽  
Marcelo Epstein ◽  
Walter Herzog
Keyword(s):  
Articular Cartilage ◽  
Contact Model ◽  
Real Surface ◽  
Surface Geometry ◽  
Model Based

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.

Effect of Transfer Films on Friction of PTFE/PEEK Composite

2020 ◽  
Vol 143 (4) ◽  
Author(s):  
Shuren Qu ◽  
King Him Lo ◽  
Su Su Wang
Keyword(s):  
Solid State ◽  
Friction Coefficient ◽  
Friction Theory ◽  
Subsequent Investigation ◽  
Transfer Films ◽  
Constituent Material ◽  
Peek Composite ◽  
Theoretical Predictions ◽  
Film Development ◽  
Film Lubrication

Abstract This paper investigates the effect of transfer films on friction coefficient of polytetrafluoroethylene (PTFE)/polyetheretherketone (PEEK) composite. Friction experiments were carried out first to investigate transfer-film development during sliding contact of PTFE/PEEK composite with different PTFE volume fractions on a steel counterface. Quantitative relationships between PTFE/PEEK composite friction coefficient and constituent material mechanical properties are then established to facilitate the subsequent investigation of friction mechanisms and influence of transfer films on the composite friction. A micromechanics-based friction theory is developed for predicting PTFE/PEEK composite friction coefficient. The effect of transfer films on composite friction is accounted for based on two distinctly different mechanisms—one with solid-state film lubrication and the other with PTFE as a solid-state lubricant on the top surface of transfer films. The friction theory is first validated through the excellent agreement obtained between the theoretical predictions and the in-house experimental results on PTFE/PEEK composite with up to 20% PTFE (by volume). The validity of the theory is further demonstrated by comparing the theoretical predictions with the test data reported by other researchers in the literature.

scholarly journals Tribology Properties of Synthesized Multiscale Lamellar WS2 and Their Synergistic Effect with Anti-Wear Agent ZDDP

2019 ◽  
Vol 10 (1) ◽  
pp. 115 ◽  
Author(s):  
Na Wu ◽  
Ningning Hu ◽  
Jinhe Wu ◽  
Gongbo Zhou
Keyword(s):  
Friction Coefficient ◽  
Synergistic Effect ◽  
Solid Phase ◽  
Friction Reduction ◽  
Lubricating Oil ◽  
Solid Phase Reaction ◽  
Phase Reaction ◽  
Wear Properties ◽  
Base Oil ◽  
Electron Probe Micro Analyzer

The microscale/nanoscale lamellar-structure WS2 particles with sizes of 2 µm and 500 nm were synthesized by solid-phase reaction method and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The synergies between microscale/nanoscale WS2 particles and ZDDP as lubricating oil additives was evaluated by means of UMT-2 tribometer at room temperature. The wear scars were examined with SEM and electron-probe micro-analyzer (EPMA). The results show that the anti-wear properties were improved and the friction coefficient was greatly decreased with the simultaneous addition of WS2 particles and ZDDP, and the largest reduction of friction coefficient was 47.2% compared with that in base oil. Moreover, the presence of ZDDP additive in the lubricant further enhances the friction-reduction and anti-wear effect of microscale/nanoscale WS2. This confirms that there is a synergistic effect between WS2 particles and ZDDP.

Tribological Investigation of Nanographite Platelets as Additive in Anti-Wear Lubricant: A Top-Down Approach

2014 ◽  
Vol 136 (3) ◽  
Author(s):  
Flavio A. C. Vidal ◽  
Antonio F. Ávila
Keyword(s):  
Friction Coefficient ◽  
Friction Reduction ◽  
Wear Properties ◽  
Top Down ◽  
Base Oil ◽  
Graphene Layers ◽  
Sliding Mechanism ◽  
Wear And Friction ◽  
Different Types ◽  
Mineral Base

A top-down approach is employed to investigate the tribological effect of adding nanographite platelets (NGPs) to mineral base oil (MBO). The performance of the NGP-modified MBO was evaluated by examining the friction and anti-wear properties. Four different types of NGPs produced by two different processes were employed. The optimal NGP-modified MBO attained a significant wear and friction reduction when compared with the MBO without NGPs. The process used to exfoliate the graphite nanoplatelet samples provided better wear properties because of the graphene layers' smoother sliding mechanism. Graphene layers seeped inside the groove marks to keep the friction coefficient low.

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