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.

The Influence of Base Oil and Thixotropy on Magnetorheological Property of MRF

2013 ◽  
Vol 320 ◽  
pp. 19-24
Author(s):  
Jian Jian Yang ◽  
Hua Yan ◽  
Zhi De Hu ◽  
Shi Xiang Xu
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Magnetorheological Fluid ◽  
Mineral Oil ◽  
Dispersed Phase ◽  
Zero Field ◽  
Rotational Viscometer ◽  
Base Oil ◽  
Low Shear

Adopting carbonyl iron powder and silicone/mineral oil as suspend phase and dispersed phase separately,and silica, kaolin as lubricant additives,magnetorheological (MR) fluid was prepared by ball milling. The apparent viscosity of base oil and shear stress were measured on a modified rotational viscometer. The experimental results demonstrated that an appropriate viscosity of base oil contributed to the rheology of MRF. Adding a small amount of thixotropy into MRF had little influence on zero-field viscosity, which facilitated the application of MRF to maintain adequate liquidity. Under low shear rate conditions, the shear stress was improved by adding thixotropy to some extent, especially in the mineral oil-based magnetorheological fluid, in which the role of silica was superior to kaolin.

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 Rheological Properties of Kaolin/PolyetherSulfone(PESf) Used in Hollow Fiber Fabrication: Effects of Content Ratio

2014 ◽  
Vol 660 ◽  
pp. 244-248
Author(s):  
Mohd Suffian Misaran ◽  
Rossalam Sarbatly ◽  
Md Mizanur Rahman
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Rheological Properties ◽  
Rate Of Change ◽  
Flow Index ◽  
Polymeric Liquid ◽  
Polyether Sulfone ◽  
Fiber Fabrication ◽  
Content Ratio ◽  
Low Shear

In the present work, the rheological properties in terms of shear stress and viscosity of Kaolin/Polyether-Sulfone (PESf) of varying ratio were investigated by a rotating rheometer. The shear rate of Kaolin/PESf sample was measured at increasing interval shear rate. By assuming that the fluid behaves like a typical Non-newtonian polymeric liquid, the consistency index, K and flow index, n were able to be determined. Thus, the rheology behaviors of the kaolin/PESf suspension could be investigated at a wider range of shear rate. The shear stress was found to increase with increasing shear rate, with the rate of change quite apparent at low shear rate. At higher shear rate, the shear stress increases definitively with the increase of kaolin content. On the other hand, the viscosity decreased at a faster rate initially and slows down to monotonous rate as the shear rate increases. Evidently at increasing shear rate, the viscosity tends to become constant as the deviation become smaller which is also known as zero shear rate viscosity region.

Viscosity Function for Yield-Stress Liquids

2004 ◽  
Vol 14 (6) ◽  
pp. 296-302 ◽  
Author(s):  
Paulo R. Souza Mendes ◽  
Eduardo S. S. Dutra
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Yield Stress ◽  
Power Law ◽  
Drilling Fluid ◽  
Oil Emulsion ◽  
Viscosity Function ◽  
Coating Formulation ◽  
Low Shear

Abstract A viscosity function for highly-shear-thinning or yield-stress liquids such as pastes and slurries is proposed. This function is continuous and presents a low shear-rate viscosity plateau, followed by a sharp viscosity drop at a threshold shear stress value (yield stress), and a subsequent power-law region. The equation was fitted to data for Carbopol aqueous solutions at two different concentrations, a drilling fluid, an water/oil emulsion, a commercial mayonnaise, and a paper coating formulation. The quality of the fittings was generally good.

Force-Balance Capillary Rheometry at Low Shear Rates

1980 ◽  
Vol 53 (5) ◽  
pp. 1117-1123
Author(s):  
J. P. Chalifoux ◽  
E. A. Meinecke
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Pressure Drop ◽  
Thermoplastic Elastomer ◽  
Force Balance ◽  
Exit Plane ◽  
Capillary Rheometry ◽  
Shear Rates ◽  
Entrance Pressure ◽  
Low Shear

Abstract The validity and accuracy of force-balance rheometry have been demonstrated by comparing data with readily available methods. At low speeds of extrusion the entrance pressure drop accounts for a very small portion of the overall pressure drop. This situation permitted us to show the equivalence between τwa and the true τw derived from equation (5) or the slopes in the Fe−Lb/D graph. Bagley plots confirmed that the effective τw and results from bottom-top dies yield comparable values over a decade of shear rate. Using flow birefringence techniques, Han and Drexler observed an exit effect at shear rates lower than 10 sec−1, but the data obtained with this thermoplastic elastomer indicated that the velocity profile rearranges only when the exit plane is reached. The wall shear stress was also shown to be independent of L/D.

Thixotropic effect of some biochemical factors in ischaemic stroke

2018 ◽  
Vol 87 (1) ◽  
pp. 7-10
Author(s):  
Piotr Kowal ◽  
Anna Marcinkowska-Gapinska
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Ischaemic Stroke ◽  
Acute Ischaemic Stroke ◽  
Stroke Patients ◽  
Blood Fluidity ◽  
Apolipoprotein A ◽  
Reversible Loss ◽  
Low Shear

Background. Yield shear stress (YSS) well characterizes the thixotropic status of blood, that exemplifies a reversible loss of blood fluidity due to a low shear rate. At the stable haematocrit ratio YSS depends mainly on the fibrinogen level.Aim. Since the role of other biochemical factors in the YSS phenomenon in cerebral ischaemia has not been well known, we have undertaken this problem in a group of stroke patients. Material and Methods. The study was carried out in 36 patients with acute ischaemic stroke and in 12 controls. YSS was estimated by means of microviscometric method. In all subjects the concentration of the following biochemical factors were assayed: albumin, IgG, IgA, IgM, apolipoprotein A, and B, cholesterol, triglycerides, LDL, HDL and fibrinogen. Then the thixotroipic effect of all biochemical factors and their correlations to fibrinogen were estimated by means of mathematical formulas.Results. We found a positive correlation in relation to the following thixotropic effects: for all subjects and separately for patients’ group: Alb(YSS) (p < 0.001), ApoA(YSS) (p < 0.001), ApoB(YSS) (p < 0.05), chol(YSS) (p < 0.01), HDL(YSS) (p < 0.05); for patients group without additional diseases: Alb(YSS) (p < 0.05), ApoA(YSS) (p < 0.005), chol(YSS) (p < 0.05), HDL(YSS) (p < 0.02), LDL(YSS) (p < 0.05). There were not any significant correlations in controls.Conclusions. Results of the study indicated that in the interaction between the red cells and fibrinogen some additional factors appearing or activating during ischaemic process may play a role.

scholarly journals Epitaxial Crystallization of Poly(ε-caprolactone) on Reduced Graphene Oxide at a Low Shear Rate by In Situ SAXS/WAXD Methods

ACS Omega ◽  
2020 ◽  
Vol 5 (49) ◽  
pp. 31535-31542
Author(s):  
Weijun Miao ◽  
Feng Wu ◽  
Shiman Zhou ◽  
Guibin Yao ◽  
Yiguo Li ◽  
...  
Keyword(s):  
Graphene Oxide ◽  
Shear Rate ◽  
Reduced Graphene Oxide ◽  
Epitaxial Crystallization ◽  
Reduced Graphene ◽  
Low Shear

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.

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