Triological Aspects and Fluidity of Dense Granular Flow

Tribology ◽  
2005 ◽  
Author(s):  
Kevin Lu ◽  
Emily E. Brodsky ◽  
H. Pirouz Kavehpour
Keyword(s):  
Grain Size ◽  
Shear Stress ◽  
Shear Rate ◽  
Granular Flow ◽  
Granular Layer ◽  
Plastic Material ◽  
Powder Layer ◽  
Mixed Regime ◽  
Applied Torque ◽  
Inertial Regime

A key difficulty in describing the fluid-like behavior of granular materials is the transitional regime between the fully dynamic regime, i.e. the grain-inertial regime, to a quasi-static one. In the present investigation, we aim to establish a constitutive relation between stress and strain rate for a granular layer over a range of deformation rates within the transition/mixed regime. Our objective is to understand the relationship between granular flow and tribological-related issues, such as friction and stress behaviors, in terms of dependences on packing density, shear rate, and grain size. For the experimental setup, we utilize a Tribo-Rheometer to infer shear stress directly from the applied torque through steps of constant velocities. The configuration is a torsional-plane-shear geometry between two plates and the granular layer is confined laterally by a self-lubricating Teflon cylindrical sleeve. To analyze granular motion, we consider the powder layer as a compressible, frictional, athermal, and elasto-plastic material with solid, fluid, and gas-like properties. The granular flow regimes, defined by the dominant mode of interaction, are then analyzed as a function of different dimensionless parameters to illustrate the process that is controlling the tribological behavior. We find that shear stress and normal stress both decrease with increasing shear rate within the transition regime between the two limiting regimes. Also, the granular flow up to the grain-inertial regime shows a Coulomb-like friction behavior with no correlation to shear rate. However, the granular sample displays a quadratic rate-dependence of friction coefficient leading into and within the grain-inertial regime. A decrease in grain-size results in a dramatic increase in friction at the boundary.

scholarly journals Breakdown of Scaling and Friction Weakening in Intermittent Granular Flow

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
A. Baldassarri ◽  
M. A. Annunziata ◽  
A. Gnoli ◽  
G. Pontuale ◽  
A. Petri
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Natural Hazards ◽  
Granular Flow ◽  
Granular System ◽  
Average Behavior ◽  
Self Similar ◽  
Symmetric Profile ◽  
Dynamical Origin ◽  
Low Shear

AbstractMany materials are produced, processed and stored as grains, while granularity of matter can be crucial in triggering potentially catastrophic geological events like landslides, avalanches and earthquakes. The response of grain assemblies to shear stress is therefore of utmost relevance to both human and natural environment. At low shear rate a granular system flows intermittently by distinct avalanches. In such state the avalanche velocity in time is expected to follow a symmetrical and universal average behavior, whose dependence on the slip size reduces to a scale factor. Analyzing data from long lasting experiments, we observe a breakdown of this scaling: While in short slips velocity shows indeed a self-similar and symmetric profile, it does not in long slips. The investigation of frictional response in these different regimes evidences that this breakdown can be traced back to the onset of a friction weakening, which is of dynamical origin and can amplify instabilities exactly in this critical state, the most frequent state for natural hazards.

scholarly journals Quantification of shear viscosity and wall slip velocity of highly concentrated suspensions with non-Newtonian matrices in pressure driven flows

2021 ◽  
Author(s):  
Patrick Wilms ◽  
Jan Wieringa ◽  
Theo Blijdenstein ◽  
Kees van Malssen ◽  
Reinhard Kohlus
Keyword(s):  
Shear Stress ◽  
Liquid Phase ◽  
Shear Rate ◽  
Shear Viscosity ◽  
Slip Velocity ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Wall Slip ◽  
Flow Index ◽  
Concentrated Suspensions

AbstractThe rheological characterization of concentrated suspensions is complicated by the heterogeneous nature of their flow. In this contribution, the shear viscosity and wall slip velocity are quantified for highly concentrated suspensions (solid volume fractions of 0.55–0.60, D4,3 ~ 5 µm). The shear viscosity was determined using a high-pressure capillary rheometer equipped with a 3D-printed die that has a grooved surface of the internal flow channel. The wall slip velocity was then calculated from the difference between the apparent shear rates through a rough and smooth die, at identical wall shear stress. The influence of liquid phase rheology on the wall slip velocity was investigated by using different thickeners, resulting in different degrees of shear rate dependency, i.e. the flow indices varied between 0.20 and 1.00. The wall slip velocity scaled with the flow index of the liquid phase at a solid volume fraction of 0.60 and showed increasingly large deviations with decreasing solid volume fraction. It is hypothesized that these deviations are related to shear-induced migration of solids and macromolecules due to the large shear stress and shear rate gradients.

Investigation on the Rheological Behavior of Polyamide6/Montmorillonite Nanocomposites by Reactive Extrusion

2011 ◽  
Vol 233-235 ◽  
pp. 1998-2001 ◽  
Author(s):  
Ming Zhao ◽  
Xiao Zhong Lu ◽  
Kai Gu ◽  
Xiao Min Sun ◽  
Chang Qing Ji
Keyword(s):  
Activation Energy ◽  
Shear Stress ◽  
Shear Rate ◽  
Rheological Behavior ◽  
Reactive Extrusion ◽  
Shear Thinning ◽  
Experimental Results ◽  
Montmorillonite Nanocomposites

The rheological behavior of PA6/montmorillonite(MMT) by reactive extrusion was investigated using cone-and-plate rheometer. The experimental results indicated that PA6/MMT exhibited shear-thinning behavior. The shear stress of both neat PA6 and PA6/MMT increased with the increase in the shear rate. The reduction of the viscous activation energy with the increase of shear stress reflected PA6/MMT can be processed over a wider temperature.

Are the dynamic response characteristics of brachial artery flow-mediated dilation sensitive to the magnitude of increase in shear stimulus?

2008 ◽  
Vol 105 (1) ◽  
pp. 282-292 ◽  
Author(s):  
K. E. Pyke ◽  
J. A. Hartnett ◽  
M. E. Tschakovsky
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Dynamic Response ◽  
Phase I ◽  
Brachial Artery ◽  
Flow Mediated Dilation ◽  
Final Phase ◽  
Stimulus Magnitude ◽  
Brachial Artery Diameter ◽  
Response Characteristics

The purpose of this study was to determine the dynamic characteristics of brachial artery dilation in response to step increases in shear stress [flow-mediated dilation (FMD)]. Brachial artery diameter (BAD) and mean blood velocity (MBV) (Doppler ultrasound) were obtained in 15 healthy subjects. Step increases in MBV at two shear stimulus magnitudes were investigated: large (L; maximal MBV attainable), and small (S; MBV at 50% of the large step). Increase in shear rate (estimate of shear stress: MBV/BAD) was 76.8 ± 15.6 s−1 for L and 41.4 ± 8.7 s−1 for S. The peak %FMD was 14.5 ± 3.8% for L and 5.7 ± 2.1% for S ( P < 0.001). Both the L (all subjects) and the S step trials (12 of 15 subjects) elicited a biphasic diameter response with a fast initial phase (phase I) followed by a slower final phase. Relative contribution of phase I to total FMD when two phases occurred was not sensitive to shear rate magnitude ( r2 = 0.003, slope P = 0.775). Parameters quantifying the dynamics of the FMD response [time delay (TD), time constant (τ)] were also not sensitive to shear rate magnitude for both phases (phase I: TD r2 = 0.03, slope P = 0.376, τ r2 = 0.04, slope P = 0.261; final phase: TD r2 = 0.07, slope P = 0.169, τ r2 = 0.07, slope P = 0.996). These data support the existence of two distinct mechanisms, or sets of mechanisms, in the human conduit artery FMD response that are proportionally sensitive to shear stimulus magnitude and whose dynamic response is not sensitive to shear stimulus magnitude.

Effect of Shear Surface Boundaries on Stress for Shearing Flow of Dry Metal Powders—An Experimental Study

1987 ◽  
Vol 109 (2) ◽  
pp. 232-237 ◽  
Author(s):  
K. Craig ◽  
R. H. Buckholz ◽  
G. Domoto
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Normal Stress ◽  
Particle Diameter ◽  
Surface Boundary ◽  
Metal Powders ◽  
Shear Surface ◽  
Shear Cell ◽  
Shearing Flow ◽  
Solids Content

This paper studies the rapid simple shearing flow of dry cohesionless metal powders contained between parallel rotating plates. In this study, an annular shear cell test apparatus was used; the dry metal powders are rapidly sheared by rotating one of the shear surfaces while the other shear surface remains fixed. Such a flow geometry is of interest to tribologists working in the area of dry or powder lubrication. The shear stress and normal stress on the stationary surface are measured as a function of the following parameters: shear surface boundary material and roughness, the shear-cell gap thickness, the shear-rate and the fractional solids content. Both the fractional solids content and the gap thickness are kept at prescribed values during stress measurements. In this experiment the metal powder tested is different from the shear transmission surface material; the effect on the measured normal and shear stress data are reported. The results show the dependence of the normal stress and the shear stress on the shear-rate, particle density and particle diameter. Likewise, a significant stress dependence on both the fractional solids content and the shear-cell gap thickness was observed.

scholarly journals Investigation of the Sedimentation Property of Backfill Material on the Basis of Rheological Test: A Case Study of Iron Tailings

2018 ◽  
Vol 2018 ◽  
pp. 1-9 ◽  
Author(s):  
Yong Wang ◽  
Aixiang Wu ◽  
Lianfu Zhang ◽  
Hongjiang Wang ◽  
Fei Jin
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Mass Concentration ◽  
Filling Material ◽  
Quantitative Characterization ◽  
Filling Materials ◽  
Characterization Studies ◽  
Rheological Test ◽  
Sedimentation Property

Sedimentation of filling materials could cause pipe blocking accident in mines. However, few quantitative characterization studies have investigated the sedimentation characteristics of filling materials. In this study, the sedimentation property of iron tailings with a cement-sand ratio of 1 : 4 and mass concentration of 73%∼82% was investigated based on rheology measurements. Results showed that shear stress increased as shear rate rose from 0 s−1to 120 s−1. The shear stress increased as the filling material concentration increased as well. However, when the shear rate was reversed from 120 s−1to 0 s−1, the shear stress presented an increase-constant-decrease change pattern as the mass concentration increases in the rheological curve. Accordingly, the sedimentation performance of iron tailings filling material was divided into three types: intense sedimentation (the ascending rheological curve) in the mass concentration range of 73%∼76%, slight sedimentation (the constant rheological curve) in the mass concentration range of 77%∼79%, and almost no sedimentation (the descending rheological curve) in the mass concentration range of 80%∼82%. The associated mechanism involving slurry mass concentration-rheological curves-sedimentation performance was illustrated. A correlation between the pipeline rheology and filling material sedimentation performance was established, which provides a practical guide to avoid pipeline blocking while transporting the filling material.

ENTROPY INFLUENCE ON THE DEPENDENCE OF THE NANOFLUIDS VISCOSITY ON TEMPERATURE AND SHEAR RATE

2021 ◽  
Vol 7 (3) ◽  
pp. 89-105
Author(s):  
Lyudmila P. SEMIKHINA ◽  
Daniil D. Korovin
Keyword(s):  
Activation Energy ◽  
Shear Stress ◽  
Shear Rate ◽  
Viscous Flow ◽  
High Reliability ◽  
Narrow Particle Size Distribution ◽  
Disperse Systems ◽  
Rotational Viscometer ◽  
Surfactant Micelles ◽  
Dispersed Systems

A Brookfield DV-II + Pro rotational viscometer was used to study the viscosity of 7 samples of concentrated nanodispersed systems (nanofluids) with a similar viscosity (6-22 mPa ∙ s), the particles of the dispersed phase in which are nanosized surfactant micelles and conglomerates from them. It was found that for 5 out of 7 studied reagents, there is a decrease in viscosity typical for dispersed systems with an increase in the shear rate, and their flow curves, that is, the dependence of the shear stress on the shear rate, correspond to the ideal plastic flow of non-Newtonian fluids. Moreover, with high reliability, R2 ≥ 0.999 is described by the Bingham equation with a small value of the limiting shear stress (less than 0.2 Pa). It is shown that all the studied reagents are also characterized by an increase in the activation energy of a viscous flow Е with an increase in the shear rate. As a result, a decrease in viscosity with an increase in shear rate, typical for disperse systems, including nanofluids, is provided by a more significant increase in entropy changes ΔS compared to Е. It has been substantiated that, depending on the ratio between the activation energy of viscous flow Е and the change in entropy ΔS, the viscosity of concentrated micellar dispersed systems with an increase in the shear rate can decrease, remain unchanged, and increase. The last two cases, not typical for disperse systems and nanofluids, were identified and studied using the example of two demulsifiers, RIK-1 and RIK-2, with a maximum of a very narrow particle size distribution at 160 ± 5 nm, corresponding to the size of a special type of very stable micelles Surfactant — vesicle.

Flow Properties of Utah Shale Oils

1981 ◽  
Vol 21 (06) ◽  
pp. 679-686 ◽  
Author(s):  
W.H. Seitzer
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Pour Point ◽  
Water Solution ◽  
Shale Oil ◽  
Concentric Cylinder ◽  
Long Distance ◽  
Time Calibration ◽  
The Difference ◽  
Cylinder Viscometer

Abstract In a concentric cylinder viscometer. Utah shale oils have different characteristics, both at equilibrium flow and during start-up from rest, depending on whether the wax has crystallized as needles or spherulites. Compared with waxy crude oils, which are thixotropic, shale oil had the added rheological property of being antithixotropic. Introduction The most likely liquid synthetic fuel to be produced initially in the U.S. will be raw shale oil from western oil shale. This abundant resource is located principally in the western Rocky Mountain states of Colorado. Utah. and Wyoming (Fig. 1). Ultimate commercial production probably will be transported to marketing, distribution, and refining centers by pipeline. It has been reported that Utah shale oils produced by the Union "B" and Paraho DH retorting processes gave similar physical and chemical properties. Some properties of the two Utah shale oils are given in Table 1. The only major difference is that the Union shale oil has a pour point of - 1 degree C compared with a pour point of 25 degrees C for the Paraho oil. Wax Crystallization The difference in the pour points of the oils from the Utah shale retorted by Union Oil Co of California and Paraho is caused mainly by the difference in how the wax in the respective oils crystallizes. In the high- pour-point (25 degrees C) Paraho DK oil, the wax, under a microscope, appears as fine (1 to 10 m) needles, as expected for normal paraffins. However, the wax in the low-pour-point (−1 degrees C) Union oil forms small spherulites.Wax spherulites have not been reported before: however, this type of crystal is seen commonly in polymer. Spherulites show up as round areas containing a maltese cross when observed between crossed polars under a microscope.Photomicrographs of these crystals are shown in Figs. 2 and 3. The former, showing spherulites, is of the Union oil. In contrast, they are very different from the customary needles as typified by the Paraho oil in the latter micrograph. Presumably, these highly ordered spheres are made up of wax needles grown out radially from the center as described by Hartshorne and Stuart. The polarized light is scattered only by those needles not parallel nor perpendicular to the plane of polarization. Viscometer Measurements To understand the effect of these spherulites on the flow characteristics of raw shale oil at flow conditions expected in a long-distance pipeline, typical stress-rate measurements were made in a rotating cylinder viscometer, the Haake Rotovisco RV3 with MK500 measuring head and MVI coaxial cylinder sensor having an 82-mm cup and radii ratio of 0.95. This equipment has provisions for varying shear rate continuously at selected values down to 23.4 sec(−1)/min and can produce and record shear stress as a function of either shear rate or time. Calibration of the sensor was verified with a sucrose/water solution at several temperatures.Changes in temperature always were made from lower to higher to keep the sensor full of oil. Also, the shear-stress/ shear-rate curves were obtained by starting at high shear, down to zero, and then back up. SPEJ P. 679^

Effects of grain size and grain shape in granular flow simulations

2014 ◽  
pp. 1453-1458
Author(s):  
S Moriguchi ◽  
K Terada ◽  
J Kato ◽  
S Takase ◽  
T Kyoya
Keyword(s):  
Grain Size ◽  
Granular Flow ◽  
Grain Shape ◽  
Flow Simulations

scholarly journals Shear-rate dependence of thermodynamic properties of the Lennard-Jones truncated and shifted fluid by molecular dynamics simulations

2021 ◽  
Author(s):  
Martin P. Lautenschlaeger ◽  
Hans Hasse
Keyword(s):  
Molecular Dynamics ◽  
Shear Stress ◽  
Shear Rate ◽  
Molecular Dynamics Simulations ◽  
Local Structure ◽  
Rate Dependence ◽  
Lennard Jones ◽  
Fluid Properties ◽  
Dynamics Simulations ◽  
Shear Rate Dependence

It was shown recently that using the two-gradient method, thermal, caloric, and transport properties of fluids under quasi-equilibrium conditions can be determined simultaneously from nonequilibrium molecular dynamics simulations. It is shown here that the influence of shear stresses on these properties can also be studied using the same method. The studied fluid is described by the Lennard-Jones truncated and shifted potential with the cut-off radius r*c = 2.5σ. For a given temperature T and density ρ, the influence of the shear rate on the following fluid properties is determined: pressure p, internal energy u, enthalpy h, isobaric heat capacity cp, thermal expansion coefficient αp, shear viscosity η, and self-diffusion coefficient D. Data for 27 state points in the range of T ∈ [0.7, 8.0] and ρ ∈ [0.3, 1.0] are reported for five different shear rates (γ ̇ ∈ [0.1,1.0]). Correlations for all properties are provided and compared with literature data. An influence of the shear stress on the fluid properties was found only for states with low temperature and high density. The shear-rate dependence is caused by changes in the local structure of the fluid which were also investigated in the present work. A criterion for identifying the regions in which a given shear stress has an influence on the fluid properties was developed. It is based on information on the local structure of the fluid. For the self-diffusivity, shear-induced anisotropic effects were observed and are discussed.

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