scholarly journals Shear thinning in non-Brownian suspensions explained by variable friction between particles

2018 ◽  
Vol 860 ◽  
pp. 682-710 ◽  
Author(s):  
Laurent Lobry ◽  
Elisabeth Lemaire ◽  
Frédéric Blanc ◽  
Stany Gallier ◽  
François Peters
Keyword(s):  
Shear Stress ◽  
Friction Coefficient ◽  
Volume Fraction ◽  
Normal Load ◽  
Shear Thinning ◽  
Particle Volume ◽  
Normal Contact ◽  
Force Coupling ◽  
Applied Shear Stress ◽  
Variable Friction

We propose to explain shear-thinning behaviour observed in most concentrated non-Brownian suspensions by variable friction between particles. Considering the low magnitude of the forces experienced by the particles of suspensions under shear flow, it is first argued that rough particles come into solid contact through one or a few asperities. In such a few-asperity elastic–plastic contact, the friction coefficient is expected not to be constant but to decrease with increasing normal load. Simulations based on the force coupling method and including such a load-dependent friction coefficient are performed for various particle volume fractions. The results of the numerical simulations are compared to viscosity measurements carried out on suspensions of polystyrene particles ($40~\unicode[STIX]{x03BC}\text{m}$in diameter) dispersed in a Newtonian silicon oil. The agreement is shown to be satisfactory. Furthermore, the comparison between the simulations conducted either with a constant or a load-dependent friction coefficient provides a model for the shear-thinning viscosity. In this model the effective friction coefficient$\unicode[STIX]{x1D707}^{eff}$is specified by the effective normal contact force which is simply proportional to the bulk shear stress. As the shear stress increases,$\unicode[STIX]{x1D707}^{eff}$decreases and the jamming volume fraction increases, leading to the reduction of the viscosity. Finally, using this model, we show that it is possible to evaluate the microscopic friction coefficient for each applied shear stress from the rheometric measurements.

scholarly journals Confined flow of suspensions modelled by a frictional rheology

2014 ◽  
Vol 759 ◽  
pp. 197-235 ◽  
Author(s):  
Brice Lecampion ◽  
Dmitry I. Garagash
Keyword(s):  
Shear Stress ◽  
Friction Coefficient ◽  
Normal Stress ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Numerical Predictions ◽  
Dry Granular Flow ◽  
Neutrally Buoyant ◽  
Constitutive Parameters ◽  
Axial Development

AbstractWe investigate in detail the problem of confined pressure-driven laminar flow of neutrally buoyant non-Brownian suspensions using a frictional rheology based on the recent proposal of Boyer et al. (Phys. Rev. Lett., vol. 107 (18), 2011, 188301). The friction coefficient (shear stress over particle normal stress) and solid volume fraction are taken as functions of the dimensionless viscous number $I$ defined as the ratio between the fluid shear stress and the particle normal stress. We clarify the contributions of the contact and hydrodynamic interactions on the evolution of the friction coefficient between the dilute and dense regimes reducing the phenomenological constitutive description to three physical parameters. We also propose an extension of this constitutive framework from the flowing regime (bounded by the maximum flowing solid volume fraction) to the fully jammed state (the random close packing limit). We obtain an analytical solution of the fully developed flow in channel and pipe for the frictional suspension rheology. The result can be transposed to dry granular flow upon appropriate redefinition of the dimensionless number $I$. The predictions are in excellent agreement with available experimental results for neutrally buoyant suspensions, when using the values of the constitutive parameters obtained independently from stress-controlled rheological measurements. In particular, the frictional rheology correctly predicts the transition from Poiseuille to plug flow and the associated particles migration with the increase of the entrance solid volume fraction. We also numerically solve for the axial development of the flow from the inlet of the channel/pipe toward the fully developed state. The available experimental data are in good agreement with our numerical predictions, when using an accepted phenomenological description of the relative phase slip obtained independently from batch-settlement experiments. The solution of the axial development of the flow notably provides a quantitative estimation of the entrance length effect in a pipe for suspensions when the continuum assumption is valid. Practically, the latter requires that the predicted width of the central (jammed) plug is wider than one particle diameter. A simple analytical expression for development length, inversely proportional to the gap-averaged diffusivity of a frictional suspension, is shown to encapsulate the numerical solution in the entire range of flow conditions from dilute to dense.

scholarly journals Rheology of mobile sediment beds in laminar shear flow: effects of creep and polydispersity

2021 ◽  
Vol 932 ◽  
Author(s):  
Christoph Rettinger ◽  
Sebastian Eibl ◽  
Ulrich Rüde ◽  
Bernhard Vowinckel
Keyword(s):  
Friction Coefficient ◽  
Shear Flow ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Rheological Behaviour ◽  
Spherical Particles ◽  
Particle Volume ◽  
Two Phase ◽  
Transport Modelling ◽  
Static State

Classical scaling relationships for rheological quantities such as the $\mu (J)$ -rheology have become increasingly popular for closures of two-phase flow modelling. However, these frameworks have been derived for monodisperse particles. We aim to extend these considerations to sediment transport modelling by using a more realistic sediment composition. We investigate the rheological behaviour of sheared sediment beds composed of polydisperse spherical particles in a laminar Couette-type shear flow. The sediment beds consist of particles with a diameter size ratio of up to 10, which corresponds to grains ranging from fine to coarse sand. The data was generated using fully coupled, grain resolved direct numerical simulations using a combined lattice Boltzmann–discrete element method. These highly resolved data yield detailed depth-resolved profiles of the relevant physical quantities that determine the rheology, i.e. the local shear rate of the fluid, particle volume fraction, total shear and granular pressure. A comparison against experimental data shows excellent agreement for the monodisperse case. We improve upon the parameterization of the $\mu (J)$ -rheology by expressing its empirically derived parameters as a function of the maximum particle volume fraction. Furthermore, we extend these considerations by exploring the creeping regime for viscous numbers much lower than used by previous studies to calibrate these correlations. Considering the low viscous numbers of our data, we found that the friction coefficient governing the quasi-static state in the creeping regime tends to a finite value for vanishing shear, which decreases the critical friction coefficient by a factor of three for all cases investigated.

scholarly journals Research on a mechanical model of magnetorheological fluid different diameter particles

2021 ◽  
Vol 11 (1) ◽  
pp. 158-166
Author(s):  
Jun Qiu ◽  
Yiping Luo ◽  
Yuqing Li ◽  
Jiao Luo ◽  
Zhibin Su ◽  
...  
Keyword(s):  
Experimental Data ◽  
Shear Stress ◽  
Mechanical Model ◽  
Volume Fraction ◽  
Silicone Oil ◽  
Theoretical Data ◽  
Magnetorheological Fluid ◽  
Average Error ◽  
Shear Strain Rate ◽  
Particle Volume

Abstract In this paper, the chain structure of magnetorheological fluid (MRF) magnetic particles was studied and analyzed, the mechanical model of MRF with different diameter ferromagnetic particles was established, silicone oil-based MRF with different particle volume fractions was prepared, the shear properties of the MRF were tested, and the theoretical and experimental data were compared. The experimental results show that the shear stress is stable with the increase of shear strain rate under the action of the magnetic field, and it has a shear thinning effect. The shear stress increases linearly with the increase of particle volume fraction. The shear stress increases with the increase of magnetic induction intensity. After data analysis and in the case of control variables, the average error of improved theoretical data and experimental data is lower than that of previous theoretical data and experimental data, which verifies that the improved theory (mechanical model) has a certain accuracy.

Static Friction Model for Rough Surfaces With Asymmetric Distribution of Asperity Heights

2004 ◽  
Vol 126 (3) ◽  
pp. 626-629 ◽  
Author(s):  
Ning Yu, ◽  
Shaun R. Pergande, and ◽  
Andreas A. Polycarpou
Keyword(s):  
Friction Coefficient ◽  
Normal Load ◽  
Static Friction ◽  
Friction Model ◽  
Published Data ◽  
Asymmetric Distribution ◽  
Adhesion Forces ◽  
Normal Contact ◽  
Static Friction Coefficient ◽  
Gaussian Case

The CEB static friction model is extended to include asymmetric distributions of asperity heights, using the normalized one-parameter Weibull distribution. The normal contact, tangential (friction), and adhesion forces are calculated for different skewness values, and are used to obtain the static friction coefficient. It is predicted that surfaces with negative skewness experience higher static friction coefficient compared to the Gaussian case, under the same external normal load, which agrees with published data. This effect is magnified for lower external loads, as is commonly encountered in microtribological applications.

Theoretical modeling and numerical simulation of dynamic contact characteristics of a spherical pump with variable friction coefficient

2021 ◽  
pp. 135065012110162
Author(s):  
Dong Guan ◽  
Li Jing ◽  
Xue Han ◽  
Lihui Wang ◽  
Junjie Gong
Keyword(s):  
Friction Coefficient ◽  
Contact Force ◽  
Structural Parameters ◽  
Dynamic Contact ◽  
Cylinder Block ◽  
Normal Contact ◽  
Variable Friction ◽  
Resistance Performance ◽  
The Relationship ◽  
Maximum Contact

In this paper, the dynamic contact characteristics between a piston system and a cylinder block in a spherical pump are studied theoretically and numerically. The theoretical contact model between a piston and a cylinder is established based on its structural and operational properties, to obtain the maximum contact force quantitatively. The effects of different structural parameters and working pressures on the contact force are analyzed and discussed. The relationship between friction coefficient and rotation speed is presented. The contact pairs are modeled numerically using the finite-element method and augmented Lagrange algorithm to obtain both the tangential and normal contact characteristics. Both static and dynamic contact characteristics of the piston are analyzed and discussed. These proposed studies can provide practical suggestions on improving the wear resistance performance and durability of the spherical pump.

Modeling of Friction Induced Vibration due to Third-Body Effects

2001 ◽  
Author(s):  
David S. Xu ◽  
Hooshang Heshmat
Keyword(s):  
Friction Coefficient ◽  
Normal Load ◽  
System Response ◽  
Viscous Damping ◽  
Third Body ◽  
The Third ◽  
Damping Material ◽  
Variable Friction ◽  
Semi Empirical ◽  
Friction Induced Vibration

Abstract Friction induced vibration at contact interfaces is still a big challenging problem and not well understood how to affect the high cycle fatigue (HCF) failures in gas turbine engine and other machinery. Most researchers conducted on the subject of only two bodies in contact with the Coulomb’s friction law only. In this paper, the interface friction phenomena and induced vibration are investigated by means of the improved third-body composite interface micro-slip model which includes a variable friction coefficient and a flexible contact, represented as effective stiffness and equivalent viscous damping elements. The third-body considered herein is almost always present at contacting interfaces and is comprised of generated wear debris or a soft intermediate anti-fretting coating applied to the mating surfaces. This kind of third-body can be viewed as a thin factional damping material layer to provide shear energy dissipation in order to mitigate the destructive effects of high frequency vibrations in components with highly stressed contacts. A properly engineered third-body can also play the role of both a damping material and a lubricant to decrease wear rate. For the study presented, a semi-empirical formula for the third-body powder properties was employed, depending on the experimental data and the non-linear regression approach. The experimental powder TiO2 data included density, shear strength, frictional coefficients, loss factor as a function of normal load, shear strain, speed and frequency. The results in this paper indicate that the third body semi-empirical equivalent stiffness / viscous damping representation of a flexible contact with variable friction coefficient does indeed have merit and does have influence on overall system response. It has been shown that the third body effects should be considered in the friction and damping induced vibration on the contact interfaces. Such a model may be used to assess designs and material coating approaches to counter fretting in highly stressed contacts as well as assessing the interaction of contact kinematics on HCF failures. Further experimental investigation of specified friction contact configuration of the components needs to be conducted in order to evaluate their friction characteristics and move this technology toward a practical engineering applications.

Properties Analysis of Disk Spring with Effects of Asymmetric Variable Friction

2021 ◽  
Author(s):  
Renzhen Chen ◽  
Xiaopeng Li ◽  
Jinchi Xu ◽  
Zemin Yang ◽  
Hexu Yang
Keyword(s):  
Friction Coefficient ◽  
Vibration Isolation ◽  
Normal Load ◽  
Static Friction ◽  
Primary Objective ◽  
Friction Model ◽  
Computational Accuracy ◽  
Static Friction Coefficient ◽  
Disk Spring ◽  
Variable Friction

The primary objective of this fundamental research is to investigate the mechanical properties of the disk spring when the friction at the contact edges is asymmetric and varies with the load. The contact mechanics study shows that the static friction and static friction coefficient on fractal surfaces change depending on the normal load. In this paper, a fractal contact model based on the W-M function is used to explore the connection between the static friction and the normal load. Subsequently, taking into account the asymmetry of the contact surface at the edge, the variable static friction coefficient is brought into the existing model to obtain an improved static model of the disk spring. Different fractal dimensions, frictional states and free heights are considered under quasi-static loading condition, the relative errors between this paper and the method using Coulomb friction are also calculated, and experimental validation was performed. The static stiffness and force hysteresis of the disk spring for different forms of asymmetric variable friction are discussed. It is shown that using the variable friction model can improve the computational accuracy of the disk spring model under small loads and help to improve the design and control accuracy of preload and vibration isolation equipment using the disk spring as a component.

Pre-Yield Shearing Regimes of Magnetorheological Fluids

2012 ◽  
Author(s):  
Waad Nassar ◽  
Xavier Boutillon ◽  
José Lozada
Keyword(s):  
Magnetic Field ◽  
Shear Stress ◽  
Shear Strain ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Initial Response ◽  
Magnetic Pole ◽  
Particle Volume ◽  
Average Shear ◽  
The Magnetic Field

We analyzed experimentally the pre-yield regime of some MRFs. The hearing response is ruled by two successive regimes and limited by an interfacial phenomenon. The initial response is pseudo-elastic and independent from the magnetic field and of the particle volume fraction. The shear-stress limit of this regime is proportional to the square of the magnetic field and to the particle volume fraction. In the next regime, the shear strain is not uniform in the fluid. The increase in average shear stress varies linearly with the increase in average shear strain. The variation coefficient is proportional to the square of the magnetic field and decreases with the particle volume fraction. Finally, a loss of adhesion of the magnetic aggregates with the shearing plate or the magnetic pole occurs. The corresponding shear stress is proportional to the square of the magnetic field and to the particle volume fraction.

scholarly journals CFD Study for the Flow Behaviour of Nanofluid Flow over Flat Plate

2020 ◽  
Vol 14 ◽  
Keyword(s):  
Heat Transfer ◽  
Shear Stress ◽  
Heat Transfer Coefficient ◽  
Friction Coefficient ◽  
Wall Shear Stress ◽  
Base Fluid ◽  
Volume Fraction ◽  
Skin Friction Coefficient ◽  
Average Heat Transfer Coefficient ◽  
Average Heat

Computation fluid dynamics (CFD) modelling of laminar heat transfer behaviour of three types of nanofluids over flat plate are studied. In the modelling the two dimensional under laminar model is used. The base fluid is pure water and the volume fraction of nanoparticles in the base fluid is 0, 1, 2, 3, and 4%. The applied Reynolds number range considered is 997.1 ≤ Re ≤ 9971. For modelling of the physical properties of the nanofluid, single phase approach is used. The effect of the volume fraction and the type of nanoparticles on the physical properties has been evaluated and presented. Then, the analysis the flow behaviour of these three nanofluids is conducted by presenting the effect of increasing the nanoparticles concentration on the velocity profile, wall shear stress, skin friction coefficient, and average heat transfer coefficient. The results show that the type of nanoparticles is an important parameter for the heat transfer enhancement as each type has shown dissimilar behaviour in this study. Moreover, a polynomial correlation has been obtained to present the relation of the wall shear stress, skin friction coefficient and average heat transfer coefficient as a function of the volume fraction for the three nanofluids.

scholarly journals Analysis of Sheet Metal Forming (Warm Stamping Process): A Study of the Variable Friction Coefficient on 6111 Aluminum Alloy

Metals ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1189
Author(s):  
Shasha Dou ◽  
Xiaoping Wang ◽  
Jason Xia ◽  
Lisa Wilson
Keyword(s):  
Aluminum Alloy ◽  
Friction Coefficient ◽  
Normal Load ◽  
Thickness Distribution ◽  
Simulation Software ◽  
Spring Back ◽  
Sliding Speed ◽  
Test Measurement ◽  
Variable Friction

Aluminum alloy materials have been widely used in automobile, aerospace and other fields because of their low density, high specific strength and corrosion resistance. The process of the warm forming of aluminum alloy improves the formability of aluminum alloy sheets, reduces the deformation resistance and spring-back and improves the forming accuracy and quality of parts. For these reasons, it is frequently used. In this work, the effects of temperature, sliding speed and normal load on the friction coefficient of 6111 aluminum alloy were studied by using a CFT-I (Equipment Type) friction tester under boundary lubrication conditions. The surface morphology of the sample after the friction test was observed by optical microscopy. The results show that the surface quality of aluminum alloy is better at 200 °C, which was used as the temperature in the experiments. According to the test measurement results, the friction coefficient increases with the increase in temperature and decreases with the increase in sliding speed and normal load. Variable friction coefficient models of sliding speed and normal load were established. Using the optimal parameter combination as the simulation parameter, the established variable friction coefficient models were input into numerical simulation software, and two sets of comparative simulations were established. The thickness distribution of the sheet material obtained through the simulation was compared with the actual test measurement. Further verification was carried out through the amount of spring-back. The results show that the thickness distribution and spring-back of the sheet obtained by the variable friction coefficient model are closer to the actual measurements (the error of the spring-back angle decreased from more than 20% to less than 10%), which verifies the reliability and accuracy of the variable friction coefficient model.

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