scholarly journals Dehesion-deformational nature of friction and wear-out

2019 ◽  
Vol 78 (5) ◽  
pp. 303-312
Author(s):  
Dmitriy P. Markov
Keyword(s):  
Friction Force ◽  
Deformation Theory ◽  
Friction Forces ◽  
Actual Contact ◽  
Surface Areas ◽  
Wear And Tear ◽  
Friction Surfaces ◽  
New Compounds ◽  
Solid Bodies ◽  
Irregular Field

Two friction theories are compared: generally recognized adhesion deformation theory and alternative dehision deformation theory, founded by Prandtl and Deryagin. Concepts and peculiarities of effect of adhesion and cohesion forces of interatomic attraction are clarified. The concept of dehesion forces of interatomic repulsion is instroduced; their features are specified. Dehision deformation theory basic provisions are as follows: Compression of solid bodies results in occurrence of the interatomic repulsion forces, which after reaching the unstable equilibrium point (bifurcation point) can be instantaneously replaced with the cohesion attraction forces. Inversion (replacement) of forces forming new compounds are rare during friction, as bifurcation pressure (processes splitting) in the most pairs of substance is higher than the plasticity limit. Friction forces of solid bodies result from engagement of irregularities of the atomic-molecular roughness at the spots of actual contact. The proportionality of friction force to the normal force (Coulomb’s law) is ensured by increase of the depth of engagement of the atomic roughness, and by increase of the area of spots of actual contact. Displacement results in the cut-out of the contact surface areas. The cut-out particles of wear and tear act as the solid bodies; the particles are pressed in solid conglomerates and scratch the surfaces. Dry friction force is determined by the contact pressure, by the interlayer fragments strength, and by the strength of their links between each other and with the friction surfaces. In case of liquid friction, molecules are moved in a barrier-free irregular field of cohesion forces, thereby determining absence of friction of rest and dependence of friction forces on the flow velocity (Newton’s law), in contrast to gas friction resulting from collision of the freely moving molecules (Maxwell’s law). Liquids, which do not include polarized molecules, are pressed out of the friction area and do not affect the friction force. If lubricant includes SAS, then the friction force can change from maximum solid to minimum liquid depending on viscosity, SAS content, pressure, contact area, and slide-to-roll ratio (Stribeck dependence).

Atomistics of Friction

2005 ◽  
Author(s):  
Motohisa Hirano
Keyword(s):  
Friction Force ◽  
Translational Motion ◽  
Static Friction ◽  
System Size ◽  
Dynamic Friction ◽  
Friction Forces ◽  
Internal Motions ◽  
Locking Mechanism ◽  
Roughness Model ◽  
Solid Bodies

The atomistic mechanisms are proposed for the origin of the static and the dynamic friction forces. The mechanism for the origin of the static friction force resembles the mechanical locking mechanism in a surface roughness model. The origin of the dynamic friction force is formulated as a problem of how the given translational kinetic energy dissipates into the internal relative motions of constituent atoms of bodies during sliding. From studying that the available phase space volume of the translational motion becomes negligible small for a large system size, compared with that of the internal motions, it is concluded that the energy dissipation occurs irreversibly from the translational motion to the internal motions. A phenomenon of superlubricity, where two solid bodies move relatively with no resistance, is discussed.

scholarly journals Influence of Nanoscale Textured Surfaces and Subsurface Defects on Friction Behaviors by Molecular Dynamics Simulation

Nanomaterials ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 1617 ◽  
Author(s):  
Ruiting Tong ◽  
Zefen Quan ◽  
Yangdong Zhao ◽  
Bin Han ◽  
Geng Liu
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Friction Force ◽  
Copper Substrate ◽  
Dynamics Simulation ◽  
Textured Surfaces ◽  
Friction Forces ◽  
Subsurface Structures ◽  
Texture Orientation ◽  
Subsurface Defects

In nanomaterials, the surface or the subsurface structures influence the friction behaviors greatly. In this work, nanoscale friction behaviors between a rigid cylinder tip and a single crystal copper substrate are studied by molecular dynamics simulation. Nanoscale textured surfaces are modeled on the surface of the substrate to represent the surface structures, and the spacings between textures are seen as defects on the surface. Nano-defects are prepared at the subsurface of the substrate. The effects of depth, orientation, width and shape of textured surfaces on the average friction forces are investigated, and the influence of subsurface defects in the substrate is also studied. Compared with the smooth surface, textured surfaces can improve friction behaviors effectively. The textured surfaces with a greater depth or smaller width lead to lower friction forces. The surface with 45° texture orientation produces the lowest average friction force among all the orientations. The influence of the shape is slight, and the v-shape shows a lower average friction force. Besides, the subsurface defects in the substrate make the sliding process unstable and the influence of subsurface defects on friction forces is sensitive to their positions.

Experimental Study of a Variable Pressure Damper on Automotive Valve Motion

1996 ◽  
Author(s):  
Jin-Jang Liou ◽  
Grodrue Huang ◽  
Wensyang Hsu
Keyword(s):  
Experimental Study ◽  
Friction Coefficient ◽  
Friction Force ◽  
High Speed ◽  
Experimental Results ◽  
Variable Pressure ◽  
Friction Forces ◽  
Valve Spring ◽  
Valve Motion

Abstract A variable pressure damper (VPD) is used here to adjusted the friction force on the valve spring to investigate the relation between the friction force and the valve bouncing phenomenon. The friction force on the valve spring is found experimentally, and the corresponding friction coefficient is also determined. Dynamic valve displacements at different speeds with different friction forces are calibrated. Bouncing and floating of the valve are observed when the camshaft reaches high speed. From the measured valve displacement, the VPD is shown to have significant improvement in reducing valve bouncing distance and eliminating floating. However, experimental results indicate that the valve bouncing can not be eliminated completely when the camshaft speed is at 2985 rpm.

scholarly journals Mathematical Modeling of Impact of Possible Shock Dynamic Loads on the Modern Composite Materials

2019 ◽  
Vol 224 ◽  
pp. 02012
Author(s):  
Eugenе Sosenushkin ◽  
Oksana Ivanova ◽  
Elena Yanovskaya ◽  
Yuliya Vinogradova
Keyword(s):  
Composite Materials ◽  
Friction Force ◽  
Equations Of Motion ◽  
Elastic Fiber ◽  
Dynamic Loads ◽  
Friction Forces ◽  
Absolute Value ◽  
A Value ◽  
The Absolute ◽  
The Impact

In this paper, we study the dynamic processes in materials reinforced with fibers, that can be represented as composite rods. There has been developed a mathematical model of wave propagation under the impact of a shock pulse in semi-infinite composite rods. It is believed that the considered composite rod consists of two layers formed by simpler rods of different isotropic materials with different mechanical properties. The cross sections of such rods are considered to be constant and identical. When such composite materials are impacted by dynamic loads, a significant part of the energy is dissipated due to the presence of friction forces between the contact surfaces of the rods. In this regard, we study the propagation of waves in an elastic fiber-rod, the layers of which interact according to Coulomb law of dry friction. The case of instantaneous excitation of rods by step pulses is investigated. The blow is applied to a rod made of a harder material. In the absence of slippage, the friction force gets a value not exceeding the absolute value of the limit. In the absence of slippage, the friction force takes a value not exceeding the absolute value of the limit. Let us consider the value of the friction force constant. Normal stresses and velocities satisfy the equations of motion and Hooke’s law. The problem statement results in the solution of inhomogeneous wave equations by the method of characteristics in different domains, which are the lines of discontinuities of the solution. Solutions are found in all constructed domains. On the basis of the analysis of the obtained solution, qualitative conclusions are made and curves are constructed according to the obtained ratios. From the found analytical solution of the problem it is possible to obtain ratios for stresses and strain rates in composite rods and composite materials.

scholarly journals Prophylaxis protocols and their impact on bracket friction force

2019 ◽  
Vol 89 (6) ◽  
pp. 883-888
Author(s):  
Sérgio Elias Neves Cury ◽  
Silvio Augusto Bellini-Pereira ◽  
Aron Aliaga-Del Castillo ◽  
Sérgio Schneider ◽  
Arnaldo Pinzan ◽  
...  
Keyword(s):  
Sodium Bicarbonate ◽  
Qualitative Analysis ◽  
Friction Force ◽  
Friction Forces ◽  
Debris Accumulation ◽  
Intergroup Comparison ◽  
Group 3 ◽  
Group 2 ◽  
Sliding Mechanics

ABSTRACT Objective: To evaluate the effect of two different prophylaxis protocols on the friction force in sliding mechanics during in vivo leveling and alignment. Materials and Methods: The sample comprised 48 hemi-arches divided into three groups according to the prophylactic protocol adopted. Group 1 consisted of patients undergoing prophylaxis with sodium bicarbonate, group 2 consisted of patients submitted to prophylaxis with glycine, and group 3 consisted of patients without prophylaxis, as a control. All patients received hygiene instructions and, with the exception of group 3, prophylaxis was performed monthly. After 10 months, the brackets were removed from the oral cavity and submitted to friction force tests and qualitative analysis by scanning electron microscopy. Analysis of variance followed by Tukey tests was performed for intergroup comparison regarding the friction force. Results: The experimental groups presented significantly smaller friction forces than the group without prophylaxis. Accordingly, qualitative analysis showed greater debris accumulation in the group without the prophylactic procedures. Conclusions: Prophylactic blasting with sodium bicarbonate or glycine can significantly prevent an increase of the friction force during sliding mechanics.

Fluid-Hammer Effects on Coiled-Tubing Friction in Extended-Reach Wells

SPE Journal ◽  
2016 ◽  
Vol 22 (01) ◽  
pp. 365-373 ◽  
Author(s):  
Silviu Livescu ◽  
Steven Craig ◽  
Bill Aitken
Keyword(s):  
Friction Force ◽  
Numerical Models ◽  
Laboratory Data ◽  
Friction Reduction ◽  
Friction Modeling ◽  
Radial Vibrations ◽  
Friction Forces ◽  
Planning Stage ◽  
Force Matching ◽  
Coiled Tubing

Summary The lateral reach and residual bottomhole-assembly (BHA) loads in extended-reach wells strongly depend on the coiled-tubing (CT) mechanical friction. Detailed CT-friction modeling becomes crucial in the prejob planning stage to ensure successful job predictability. However, current numerical simulators consider constant coefficients of friction (CoFs) that are determined from similar operations without taking into account the effects of the operational and downhole parameters on the CoF for a specific operation. This study outlines the modeling of CT-friction force, CoF, and axial BHA loads depending on the operational and downhole parameters when a fluid-hammer tool is used. Recent theoretical, laboratory, and field data have established how CoF depends on the downhole parameters (Livescu and Wang 2014; Livescu and Watkins 2014; Livescu et al. 2014a, b; Livescu and Craig 2015). Previously, these effects were not considered in the CT numerical models, leading to significant CoF differences among available commercial simulators. For instance, the default CoFs in the current prejob simulations for cased holes, when no lubricant or friction-reducing tools such as fluid-hammer tools and tractors are used, vary between 0.24 and 0.30 or even higher. This makes it extremely difficult to consistently evaluate and compare the friction-reduction effects of lubricants, fluid-hammer tools, and tractors in extended-reach wells, especially when the field operator may be consulting with several service companies that use different commercial force-modeling software. This study presents the CT-force matching and fundamental physics on the basis of modeled fluid forces, including radial forces, drag forces, and, most importantly, pressure forces on the CT-friction forces caused by fluid-hammer tools. Extending the method of characteristics, regularly used for studying pressure pulses in straight pipes, the perturbations method also accounts for the helical shape of the CT. The new CT fluid-hammer model is validated against laboratory data. This rigorous method for calculating the axial BHA load and reduced CT-friction force caused by radial vibrations can be easily implemented in currently available tubing-force analysis (TFA) software for CT operations. This novel approach, which uses detailed CT mechanical-friction modeling to take into account parameters such as temperature, internal pressure, pumping rate, and others, improves predictions for CT reach in lateral wells. These findings broaden the current industry understanding of the CT mechanical friction modeling in extended-reach wells, and show benefits for the industry when considering variable friction modeling in commercial CT simulators.

Friction Force Measurements Using the Instantaneous IMEP Method and Comparison With RINGPAK Simulations

2005 ◽  
Author(s):  
Myoungjin Kim ◽  
Thomas M. Kiehne ◽  
Ronald D. Matthews
Keyword(s):  
Friction Force ◽  
Piston Ring ◽  
Cost Effective ◽  
Firing Condition ◽  
Force Measurements ◽  
Connecting Rod ◽  
Friction Forces ◽  
Bench Tests ◽  
Ring Assembly ◽  
Analysis System

Even though many researchers have measured the piston/ring assembly friction force over the last several decades, accurate measurement of the piston/ring assembly friction force is a still challenging problem. The floating liner method is not widely used, in spite of its accuracy, due to the substantial modifications required to the engine. On the other extreme, bench tests of the piston/ring assembly cannot completely simulate the real firing condition although bench tests are rapid, consistent, and cost effective. In this study, friction forces of the piston/ring assembly were measured using the instantaneous IMEP method and compared with modeling results using Ricardo’s RINGPAK software. In this research, a flexible flat cable was used to connect the connecting rod strain gage signal to the analysis system instead of using a grasshopper linkage. Therefore, the piston/ring assembly friction force was measured with the minimum change to the engine hardware.

Linear Friction Damper Consisted of Cylindrical Block and Inclined Lever (Improvement to Avoid Sprag-Slip Problem and Analytical Model to Verify Cause)

2011 ◽  
Author(s):  
Hideya Yamaguchi ◽  
Hidehisa Yoshida
Keyword(s):  
Analytical Model ◽  
Friction Force ◽  
Friction Damper ◽  
Friction Forces ◽  
Constant Friction ◽  
Linear Friction ◽  
New Type ◽  
Passive Isolation ◽  
Isolation Systems ◽  
Cylindrical Block

For the passive isolation systems, the ordinary friction damper of constant friction force has performance limitations. This is, because the isolation characteristic declines and the displacement remains apart from the equilibrium position after the disturbance disappears, when the friction force is large. It is known that the above drawbacks are improved when the friction force varies depending on the displacement. The authors have proposed a new type of friction damper in our previous paper. This friction damper uses an inclined lever, which contacts the cylindrical block by means of a rotational spring. The angle of inclination of the lever varies together with the displacement of the cylindrical block. Then, the normal and friction forces on the contact surface vary depending on the displacement. However, “Sprag-slip” vibration occurred in some cases in the experiments. This paper investigates the cause of the vibration and a design to prevent it. Then, an analytical model is proposed to simulate the problem and to estimate the effect of improvement.

Experimental Study of Friction in a Pneumatic Actuator at Constant Velocity

1993 ◽  
Vol 115 (3) ◽  
pp. 575-577 ◽  
Author(s):  
Lee E. Schroeder ◽  
Rajendra Singh
Keyword(s):  
Experimental Study ◽  
Experimental Method ◽  
Friction Force ◽  
Constant Velocity ◽  
Sliding Friction ◽  
Pneumatic Actuator ◽  
Friction Forces ◽  
Friction Models ◽  
Semi Empirical ◽  
Force Data

This paper describes an experimental method of determining sliding friction forces in a pneumatic actuator. Several empirical and semi-empirical friction models are evaluated using measured friction force data. A repeatability study is also performed to qualitatively assess friction randomness and a change in friction regimes.

A STUDY OF THE INFLUENCE OF FRICTION FORCES ON THE TRANSMISSION OF SOIL VIBRATION ON GAS PIPELINES

Tribologia ◽  
2017 ◽  
Vol 272 (2) ◽  
pp. 49-58 ◽  
Author(s):  
Wacław GAWĘDZKI ◽  
Jerzy TARNOWSKI
Keyword(s):  
Friction Force ◽  
Field Experiments ◽  
Tensile Force ◽  
Variable Parameter ◽  
Gas Pipeline ◽  
Vibration Acceleration ◽  
Friction Forces ◽  
Acceleration Signal ◽  
Acceleration Signals ◽  
Pipe Vibration

The article presents the influence of friction force values during the contact of a gas pipeline with sand pack on the transmission of soil vibrations on a tested pipe section. Field experiments were carried out on standard gas pipeline insulations subjected to dynamic interactions. The load sources comprised artificially generated soil vibrations with an impulsive character. Within the course of experiments, soil and pipe vibration acceleration signals were registered for different values of friction forces in its contact with the soil. The value of friction forces being a variable parameter during experiments were applied by the change of values of the tension static force of the gas pipeline section. The analysis of the registered soil and pipe vibration acceleration signals were conducted based on the time-domain signal decomposition method, Hilbert-Huang Transform (HHT). This method enables one to decompose the non-stationary vibration acceleration signal into narrowband components. For each component, a course of instantaneous values for frequency and amplitude was specified. The dependence of the pipe vibration acceleration amplitude on the pipe tensile force and friction force of the pipe in the contact with the soil was demonstrated.

Sign in / Sign up

Export Citation Format

Share Document