scholarly journals Puzzling Low-Temperature Behavior of the Van Der Waals Friction Force between Metallic Plates in Relative Motion

Universe ◽  
2021 ◽  
Vol 7 (11) ◽  
pp. 427
Author(s):  
George Dedkov
Keyword(s):  
Friction Force ◽  
Relative Motion ◽  
Van Der Waals ◽  
Tangential Force ◽  
Perfect Crystal ◽  
Crystal Lattices ◽  
Friction Forces ◽  
Residual Resistance ◽  
Distance Dependence ◽  
Metallic Plates

This paper presents the results of calculating the van der Waals friction force (dissipative fluctuation-electromagnetic force) between metallic (Au) plates in relative motion at temperatures close to 1 K. The stopping tangential force arises between moving plates along with the usual Casimir force of attraction, which has been routinely measured with high precision over the past two decades. At room temperatures, the former force is 10 orders of magnitude less than the latter, but at temperatures T<50 K, friction increases sharply. The calculations have been carried out in the framework of the Levin-Polevoi-Rytov fluctuation electromagnetic theory. For metallic plates with perfect crystal lattices and without defects, van der Waals friction force is shown to increase with decreasing temperature as T-4. In the presence of residual resistance ρ0 of the metal, a plateau is formed on the temperature dependence of the friction force at T→0 with a height proportional to ρ0-0.8. Another important finding is the weak force-distance dependence ~a-q (with q<1). The absolute values of the friction forces are achievable for measurements in AFM-based experiments.

Experimental Validation of Friction Models for Rotor-Rubbing

2019 ◽  
Author(s):  
Juan Jauregui ◽  
Oscar De Santiago Duran
Keyword(s):  
Friction Force ◽  
Cross Correlation ◽  
Tangential Force ◽  
Nonlinear Behavior ◽  
Experimental Results ◽  
Friction Forces ◽  
Rotating Speed ◽  
Friction Models ◽  
The Cross ◽  
Set Up

Abstract The work presented here is a continuation of a set of experiments that were designed for predicting friction forces during rotor rubbing. The experimental set up consisted of a rotor rubbing a fixed surface. The surface had two force sensors, one aligned with the tangential force, and the other aligned in the radial direction. This set up allowed us to measure the friction component and the normal force. The measurements were complemented with a couple of accelerometers mounted on the bearings, and the accelerations and the friction force were measured simultaneously. All the data were analyzed using the Continuous Wavelet Transform (CWT) and the cross-correlation function. The CWT produces a spectrogram that is useful for identifying the nonlinear behavior of the phenomenon. The cross-correlation is used to measure the similarities between the friction force and the acceleration measurements. At low friction levels, experimental results show a sub-synchronous vibration at half of the rotating speed. This pattern is always present regardless of the friction source, but it is impossible to reproduce this effect using current friction models. The experimental results were compared to numerical results, these results were computed with the Muszynska’s model that is based on the physics of the phenomenon, but their predictions differ significantly from the experimental results. One of the reasons for these discrepancies lay on the fact that rotor-rubbing models consider the friction as an external force instead of modifying the system parameters.

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.

Analysis of Motion of the Impact-Dry-Friction Pair of Bodies and its Application to the Investigation of the Impact Dampers Dynamics

1999 ◽  
Author(s):  
František Peterka
Keyword(s):  
Analytical Solution ◽  
Numerical Simulations ◽  
Mechanical System ◽  
Relative Motion ◽  
Dry Friction ◽  
Friction Pair ◽  
Strong Nonlinearity ◽  
Friction Forces ◽  
The Impact ◽  
Analysis Of Motion

Abstract The motion with impacts and dry friction forces appears in some mechanical systems as mechanisms with clearances, (e.g., in gearings, pins, slots, guides, valve gears etc.), impact dampers, relays, forming and mailing machines, power pics etc. Such mechanisms include one or more pairs of impacting bodies, which introduce the strong nonlinearity into the system motion. The motion of the general pair of bodies with the both-sides impacts and dry friction forces is assumed (Fig.1). It can be the part of a more complex chain of masses in the mechanical system. Dead zones in the relative motion of bodies can be caused by assumed nonlinearities. The mathematical conditions controlling the numerical simulations or analytical solution of the motion are introduced. The application of this method is explained by the study of the influence of dry friction force on amplitude-frequency characteristics of four types of dynamical and impact dampers with optimised parameters.

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.

Force Analysis of the Film in a COF Chip Mounter’s Loader

2004 ◽  
Author(s):  
Dein Shaw ◽  
H. C. Lin
Keyword(s):  
Friction Force ◽  
Relative Motion ◽  
Lower Layer ◽  
Axial Direction ◽  
Tension Force ◽  
Force Distribution ◽  
Force Analysis ◽  
Transportation Vehicle

In this study, the tension force distributions in the film of COF cartridge are studied. It is noted that if the tension force on the film is too high, the interface between chip and film cracked. If the force is too low, there is no enough friction force to keep the COF in fix position when the cartridge is on the transportation vehicle. The relative motion between the chips of lower layer and the film of upper layer will cause the fatigue of interface of chips and film. It is also important to note that due to the friction the tension force at any section of the film is different. To fine the force distribution, a method to determine the tension force is developed and only effect of axial direction is considered. The assumption makes the film behave like a string. The results show that the forces on the film are different whenever the film passes a chip underneath.

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