A Micro-Contact Model for Boundary Lubrication With Lubricant/Surface Physiochemistry

2002 ◽  
Vol 125 (1) ◽  
pp. 8-15 ◽  
Author(s):  
H. Zhang ◽  
L. Chang ◽  
M. N. Webster ◽  
A. Jackson
Keyword(s):  
Plastic Deformation ◽  
Friction Coefficient ◽  
Oxide Layer ◽  
Contact Pressure ◽  
Friction Force ◽  
Boundary Lubrication ◽  
The State ◽  
Surface Generation ◽  
Contact Friction ◽  
Flash Temperature

A model is developed to study the tribological behavior of sliding micro-contacts. It provides a building block to the modeling of tribo-contacts in boundary lubrication. Three contact variables are calculated at the asperity-level by relating them to the state of contact and the state of asperity deformation. These variables include micro-contact friction force, load carrying capacity and flash temperature. The deformation of the contacting asperity is either elastic, elasto-plastic, or fully plastic. Furthermore, the asperity may be covered by the lubricant/additive molecules adsorbed on the surface, protected by a surface oxide layer or other chemical reaction films, or in direct contact with no boundary protection. The possibility of the contact in each of these three states is represented by a corresponding contact probability. A numerical method is developed to determine the contact state and contact variables in the course of an asperity-to-asperity collision. The asperity flash temperature, which governs the kinetics of lubricant/surface adsorption/desorption, is first calculated by integrating the Jaeger equation over the contact area and in time. Then, the probability of contact covered by an adsorbed film is determined using the Volmer adsorption isotherm, and the probability of contact protected by the oxide layer is estimated using a classical wear theory. For elastic/elasto-plastic deformation of the asperity, the friction coefficient is given by the linear combination of the friction coefficients of the three contact states with their contact probabilities as the weighting factors. For fully plastic deformation of the asperity, the contact pressure and friction force become dependent of each other. The shear stress is approximated by a linear function of the contact probabilities, and the contact pressure and friction coefficient then calculated. Meanwhile, the influence of fresh surface generation due to plastic flow on the contact probabilities is also modeled. Insights are provided into the asperity collision through numerical studies of a sample problem. In addition, parametric studies are carried out to analyze the effects of lubricant and surface parameters on the micro-contact severity and its load capacity.

Experiment and simulation of friction coefficient of polyoxymethylene

2018 ◽  
Vol 70 (2) ◽  
pp. 273-281 ◽  
Author(s):  
Xiaoshuang Xiong ◽  
Lin Hua ◽  
Xiaojin Wan ◽  
Can Yang ◽  
Chongyang Xie ◽  
...  
Keyword(s):  
Mathematical Model ◽  
Friction Coefficient ◽  
Contact Pressure ◽  
Friction Force ◽  
Normal Load ◽  
Fe Model ◽  
Sliding Velocity ◽  
Experiment Data ◽  
Simulation Data ◽  
Content Type

Purpose The purposes of this paper include studying the friction coefficient of polyoxymethylene (POM) under a broad range of normal load and sliding velocity; developing a mathematical model of friction coefficient of POM under a broad range of normal loads and sliding velocities; and applying the model to dynamic finite element (FE) analysis of mechanical devices containing POM components. Design/methodology/approach Through pin-on-disc experiment, the friction coefficient of POM in different normal loads and sliding velocities is investigated; the average contact pressure is between 5 and 15 Mpa and the sliding velocity is from 0.05 to 0.9 m/s. A friction algorithm is developed and embedded in the FE model to simulate the friction of POM in different normal loads and sliding velocities. Findings The friction coefficient of POM against steel declines with the increase of normal loads when the contact pressure is between 5 and 15 Mpa. The friction coefficient of POM against steel increases markedly when the sliding velocity is between 0.05 and 0.15 m/s, it decreases sharply between 0.15-0.45 m/s and then it stabilizes at high sliding velocity between 0.45 and 0.9 m/s. The friction coefficient of POM in different working operations has a significant effect on contact stress and shear stress. The simulation data and experiment data of POM friction force fit very well; therefore, it can be concluded that the friction algorithm and FE model are accurate. Originality/value The friction coefficient of POM under a broad range of normal loads and sliding velocities is investigated. The friction coefficient model of POM is established as a function of normal loads and sliding velocities in the dry sliding condition. A friction algorithm is developed and embedded in the FE model of the friction of POM. The mathematical model of the friction coefficient accurately agrees with the experiment data, and simulation data and experiment data of the POM friction force fit very well.

Studies on the Adhesion of Oxide Layer Formed on Steel Long-Term Operated at an Elevated Temperature

2015 ◽  
Vol 227 ◽  
pp. 389-392
Author(s):  
Monika Gwoździk
Keyword(s):  
Elevated Temperature ◽  
Friction Coefficient ◽  
Oxide Layer ◽  
Friction Force ◽  
Flue Gas ◽  
Applied Pressure ◽  
Oxide Layers ◽  
Steam Pipeline

The paper contains results of studies into the formation of oxide layers on steel long-term operated at an elevated temperature. The material studied comprised specimens of steel taken from an steam pipeline and on the flue gas side. The oxide layer adhesion tests were carried out on an automated Revetest XPress Plus instrument using a diamond Rockwell indenter. The adhesion of oxide layers, friction force, friction coefficient, scratching depth were determined as well as the force at which the layer was delaminated. It has been found that the oxide layer formed under the influence of applied pressure is more degradation in the areas where are a pores and cracks.

A new asperity interaction model considering transient flash temperature and inhomogeneous distribution of oil viscosity

2016 ◽  
Vol 231 (3) ◽  
pp. 347-356
Author(s):  
Jun Liu ◽  
Zhinan Zhang ◽  
Bo Zhao ◽  
Youbai Xie
Keyword(s):  
Friction Coefficient ◽  
Boundary Lubrication ◽  
Interaction Model ◽  
Asperity Contact ◽  
Inhomogeneous Distribution ◽  
Sliding Velocity ◽  
Flash Temperature ◽  
Oil Viscosity ◽  
Temperature Characteristics ◽  
Simulation Results

A momentary contact of asperities will generate transient flash temperature phenomena in boundary lubrication. According to the viscosity–temperature characteristics of lubricant, the inhomogeneous distribution of temperature during the process of asperity contact would cause the inhomogeneous distribution of oil viscosity. This paper proposes a coupled Eulerian–Lagrangian based approach to analyze the influence of inhomogeneous distribution of viscosity on the friction coefficient of an asperity junction. The asperity interaction in boundary lubrication with different sliding velocities and different degrees of overlap of the undeformed surfaces were taken into account. Simulation results showed that the friction coefficient is proportional to the overlap and inversely proportional to sliding velocity. The results also showed that the influence of inhomogeneous distribution of oil viscosity on friction coefficient in boundary lubrication is limited.

A Quantitative Theory for the Computation of Tire Friction Under Severe Conditions of Sliding

1986 ◽  
Vol 14 (1) ◽  
pp. 44-72 ◽  
Author(s):  
C. M. Mc C. Ettles
Keyword(s):  
Friction Coefficient ◽  
Flash Temperature ◽  
Contact Conditions ◽  
Quantitative Form ◽  
Heating Effects ◽  
Rubber Friction ◽  
Viscoelastic Effects ◽  
Tire Friction ◽  
Pavement Friction ◽  
Metal Polymer

Abstract It is proposed that tire-pavement friction is controlled by thermal rather than by hysteresis and viscoelastic effects. A numerical model of heating effects in sliding is described in which the friction coefficient emerges as a dependent variable. The overall results of the model can be expressed in a closed form using Blok's flash temperature theory. This allows the factors controlling rubber friction to be recognized directly. The model can be applied in quantitative form to metal-polymer-ice contacts. Several examples of correlation are given. The difficulties of characterizing the contact conditions in tire-pavement friction reduce the model to qualitative form. Each of the governing parameters is examined in detail. The attainment of higher friction by small, discrete particles of aluminum filler is discussed.

Friction Force and Stresses Analysis for Contact of Assembled Details

2006 ◽  
Vol 113 ◽  
pp. 334-338
Author(s):  
Z. Dreija ◽  
O. Liniņš ◽  
Fr. Sudnieks ◽  
N. Mozga
Keyword(s):  
Mechanical Properties ◽  
Surface Roughness ◽  
Plastic Deformation ◽  
Friction Force ◽  
Sliding Friction ◽  
Friction Model ◽  
Contact Interface ◽  
Finite Element Program ◽  
Elastic Plastic ◽  
Element Program

The present work deals with the computation of surface stresses and deformation in the presence of friction. The evaluation of the elastic-plastic contact is analyzed revealing three distinct stages that range from fully elastic through elastic-plastic to fully plastic contact interface. Several factors of sliding friction model are discussed: surface roughness, mechanical properties and contact load and areas that have strong effect on the friction force. The critical interference that marks the transition from elastic to elastic- plastic and plastic deformation is found out and its connection with plasticity index. A finite element program for determination contact analysis of the assembled details and due to details of deformation that arose a normal and tangencial stress is used.

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.

Influence of the contact with friction on the deformation behavior of advanced high strength steels in the Nakajima test

2021 ◽  
pp. 030932472110212
Author(s):  
Mohammad Mehdi Kasaei ◽  
Marta C Oliveira
Keyword(s):  
Finite Element ◽  
Friction Coefficient ◽  
Strain Rate ◽  
Contact Pressure ◽  
Deformation Behaviour ◽  
High Strength Steels ◽  
High Strength ◽  
Advanced High Strength Steels ◽  
Deformation Mechanics ◽  
Nakajima Test

This work presents a new understanding on the deformation mechanics involved in the Nakajima test, which is commonly used to determine the forming limit curve of sheet metals, and is focused on the interaction between the friction conditions and the deformation behaviour of a dual phase steel. The methodology is based on the finite element analysis of the Nakajima test, considering different values of the classic Coulomb friction coefficient, including a pressure-dependent model. The validity of the finite element model is examined through a comparison with experimental data. The results show that friction affects the location and strain path of the necking point by changing the strain rate distribution in the specimen. The strain localization alters the contact status from slip to stick at a portion of the contact area from the pole to the necking zone. This leads to the sharp increase of the strain rate at the necking point, as the punch rises further. The influence of the pressure-dependent friction coefficient on the deformation behaviour is very small, due to the uniform distribution of the contact pressure in the Nakajima test. Moreover, the low contact pressure range attained cannot properly replicate real contact condition in sheet metal forming processes of advanced high strength steels.

scholarly journals Comparison Between the Action of Nano-Oxides and Conventional EP Additives in Boundary Lubrication

Lubricants ◽  
2020 ◽  
Vol 8 (5) ◽  
pp. 54
Author(s):  
Valdicleide Silva Mello ◽  
Marinalva Ferreira Trajano ◽  
Ana Emilia Diniz Silva Guedes ◽  
Salete Martins Alves
Keyword(s):  
Friction Coefficient ◽  
Boundary Lubrication ◽  
Friction And Wear ◽  
Film Formation ◽  
Environmental Issues ◽  
Protective Film ◽  
Extreme Pressure ◽  
Extreme Pressure Additives ◽  
Environmental Requirements ◽  
Lubrication Conditions

Additives are essential in lubricant development, improving their performance by the formation of a protective film, thus reducing friction and wear. Some such additives are extreme pressure additives. However, due to environmental issues, their use has been questioned because their composition includes sulfur, chlorine, and phosphorus. Nanoparticles have been demonstrated to be a suitable substitute for those additives. This paper aims to make a comparison of the tribological performance of conventional EP additives and oxides nanoparticles (copper and zinc) under boundary lubrication conditions. The additives (nanoparticles, ZDDP, and sulfur) were added to mineral and synthetic oils. The lubricant tribological properties were analyzed in the tribometer HFRR (high frequency reciprocating rig), and during the test, the friction coefficient and percentual of film formation were measured. The wear was analyzed by scanning electron microscopy. The results showed that the conventional EP additives have a good performance owing to their anti-wear and small friction coefficient in both lubricant bases. The oxides nanoparticles, when used as additives, can reduce the friction more effectively than conventional additives, and displayed similar behavior to the extreme pressure additives. Thus, the oxide nanoparticles are more environmentally suitable, and they can replace EP additives adapting the lubricant to current environmental requirements.

Experimental and Theoretical Study of the Contact Mechanics of Five Total Knee Joint Replacements

1995 ◽  
Vol 209 (4) ◽  
pp. 225-231 ◽  
Author(s):  
T Stewart ◽  
Z M Jin ◽  
D Shaw ◽  
D D Auger ◽  
M Stone ◽  
...  
Keyword(s):  
Plastic Deformation ◽  
Knee Joint ◽  
Contact Pressure ◽  
Contact Stress ◽  
Linear Elasticity ◽  
Contact Area ◽  
Elasticity Analysis ◽  
Joint Replacements ◽  
Total Knee ◽  
Maximum Contact

The tibio-femoral contact area in five current popular total knee joint replacements has been measured using pressure-sensitive film under a normal load of 2.5 kN and at several angles of flexion The corresponding maximum contact pressure has been estimated from the measured contact areas and found to exceed the point at which plastic deformation is expected in the ultra-high molecular weight polyethylene (UHMWPE) component particularly at flexion angles near 90°. The measured contact area and the estimated maximum contact stress have been found to be similar in magnitude for all of the five knee joint replacements tested. A significant difference, however, has been found in maximum contact pressure predicted from linear elasticity analysis for the different knee joints. This indicates that varying amounts of plastic deformation occurred in the polyethylene component in the different knee designs. It is important to know the extent of damage as knees with large amounts of plastic deformation are more likely to suffer low cycle fatigue failure. It is therefore concluded that the measurement of contact areas alone can be misleading in the design of and deformation in total knee joint replacements. It is important to modify geometries to reduce the maximum contact stress as predicted from the linear elasticity analysis, to below the linear elastic limit of the plastic component.

A novel technique for modeling friction behavior in knitted fabric simulation

2017 ◽  
Vol 29 (6) ◽  
pp. 776-792
Author(s):  
Vajiha Mozafary ◽  
Pedram Payvandy
Keyword(s):  
Friction Coefficient ◽  
Uniform Distribution ◽  
Friction Force ◽  
Experimental Result ◽  
Knitted Fabric ◽  
Friction Behavior ◽  
Content Type ◽  
Novel Technique ◽  
Fabric Structure ◽  
Fabric Surface

Purpose Fabric-object friction force is a fundamental factor in cloth simulation. A large number of parameters influence the frictional properties of fabrics such as fabric structure, yarn structure, and inherent properties of component fibers. The purpose of this paper is to propose a novel technique for modeling fabric-object friction force in knitted fabric simulation based on the mass spring model. Design/methodology/approach In this technique, unlike other studies, distribution of friction coefficient over the fabric surface is not uniform and depends on the fabric structure. The main reason for considering non-uniform distribution is that in various segments of fabric, contact percent of fabric-object is different. Findings The proposed technique and common methods based on friction coefficient uniform distribution are used to simulate the frictional behavior of knitted fabrics. The results show that simulation error values for proposed technique and common methods are 2.7 and 9.4 percent as compared with the experimental result, respectively. Originality/value In the existing methods of the friction force modeling, the friction coefficient of fabric is assumed uniform. But this assumption is not correct because fabric does not have an isotropic structure. Thus in this study, the friction coefficient distribution is considered based on fabric structure to achieve more of realistic simulations.

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