scholarly journals To the Development of the Phenomenology of Fast Shear Flows of Grain Materials

2021 ◽  
Vol 27 (4) ◽  
pp. 585-598
Author(s):  
V. N. Dolgunin ◽  
O. O. Ivanov ◽  
S. A. Akopyan
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Granular Materials ◽  
Granular Medium ◽  
Stress Generation ◽  
Shear Stresses ◽  
Plastic Shear ◽  
Unified Approach ◽  
Shear Deformations ◽  
Rate Gradient

Phenomenological approaches to describing the rheological behavior of granular materials under conditions of rapid and quasi-plastic shear deformations are considered. A unified approach to the phenomenological-logical description of the physical parameter, called the temperature of the granular medium, and the mechanisms of shear stress generation is proposed. A description is given of the mechanism for generating shear stresses under the action of a flow of pulses directed along the shear rate gradient and caused by transverse quasi-diffusion of particles. This mechanism is taken into account in the rheological model in addition to the traditional mechanism of generating kinetic shear stresses under the action of tangential shock pulses.

Compaction and flow of potato starch and potato granules Compactación y flujo de almidón de patata y gránulos de patata

1997 ◽  
Vol 3 (5) ◽  
pp. 333-342 ◽  
Author(s):  
P.J. Halliday ◽  
A.C. Smith
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Wall Shear Stress ◽  
Water Content ◽  
Capillary Flow ◽  
Potato Starch ◽  
Slip Flow ◽  
Shear Stresses ◽  
Wall Shear ◽  
Water Contents

Potato starch and potato granules are materials that are often used in extrusion processes. It is important to quantify their rheology for modelling and prediction of process performance. The compaction behaviour of potato starch was examined at water contents of 4-18% wwb (wet weight basis) for pressures between 1 and 85 MPa. The Heckel deformation stress decreased as the water content increased up to 12% but became inaccurate at 18%. This decrease agreed qualitatively with other observations of the decrease in stiffness of starchy materials over this water content range. Potato granules were examined at water contents of 25-45% wwb and aspects of their rheo logical behaviour characterized using different approaches. A first approximation used the shear viscosity-shear rate power law which produced a law exponent for the resulting pastes (0.1-0.2). The classical Benbow equation was used to estimate yield and wall shear stresses in capillary flow. The latter indicates the presence of slip which was examined more fully as a function of wall shear stress. The Mooney technique was used together with a variation of the method where the shear rate for each die was subtracted from that for a non-slip flow, which was approximated using rough dies. A critical wall shear stress for slip was found to be 0.05-0.1 MPa, making it consistent with published results for other materials.

RELATION BETWEEN SHEAR STRESS AND SHEARING TIME IN SELECTED LUBRICANT COMPOSITIONS

Tribologia ◽  
2018 ◽  
Vol 279 (3) ◽  
pp. 25-33 ◽  
Author(s):  
Ryszard CZARNY
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Rheological Properties ◽  
Tribological Properties ◽  
Shear Stresses ◽  
Test Results ◽  
Molybdenum Disulphide ◽  
Lithium Grease ◽  
Lubricant Composition ◽  
Rate Test

The paper presents the results of studies of the influence of fillers introduced into lubricating greases on changes in values of shear stresses in resulting lubricant compositions. These fillers were powders of graphite, molybdenum disulphide, and PTFE. They are added to grease to improve their tribological properties. They also impact the rheological properties of lubricating compositions, especially on the course of the shear stress, whose value decreases with the duration of the flow of these compositions. Knowledge of changes in the value of this stress is essential in designing central lubrication systems in which these compositions may be used. Tests were performed on lithium grease without fillers as well as on a composition of this grease with the fillers mentioned above. Measurements were carried out using a Rheotest 2.1 rheometer by changing the shearing time at selected gradients of shear rate. Test results have shown that both the kind of filler and the shearing time have an impact on the value of shear stress in the tested lubricant composition.

Stresses developed by dry cohesionless granular materials sheared in an annular shear cell

1984 ◽  
Vol 142 ◽  
pp. 391-430 ◽  
Author(s):  
S. B. Savage ◽  
M. Sayed
Keyword(s):  
Shear Rate ◽  
Granular Materials ◽  
Volume Fraction ◽  
Particle Diameter ◽  
Shear Stresses ◽  
Normal Stresses ◽  
Shear Cell ◽  
Shear Rates ◽  
Polystyrene Beads ◽  
Annular Shear Cell

Experimental results obtained during rapid shearing of several dry, coarse, granular materials in an annular shear cell are described. The main purpose of the tests was to obtain information that could be used to guide the theoretical development of constitutive equations suitable for the rapid flow of cohesionless bulk solids at low stress levels. The shear-cell apparatus consists of two concentric disk assemblies mounted on a fixed shaft. Granular material was contained in an annular trough in the bottom disk and capped by a lipped annular ring on the top disk. The bottom disk can be rotated at specified rates, while the top disk is loaded vertically and is restrained from rotating by a torque arm connected to a force transducer. The apparatus was thus designed to determine the shear and normal stresses as functions of solids volume fraction and shear rate.Tests were performed with spherical glass and polystyrene beads of nearly uniform diameters, spherical polystyrene beads having a bimodal size distribution and with angular particles of crushed walnut shells. The particles ranged from about ½ to 2 mm in size. At the lower concentrations and high shear rates the stresses are generated primarily by collisional transfer of momentum and energy. Under these conditions, both normal and shear stresses were found to be proportional to the particle density, and the squares of the shear rate and particle diameter. At higher concentrations and lower shear rates, dry friction between particles becomes increasingly important, and the stresses are proportional to the shear rate raised to a power less than two. All tests showed strong increases in stresses with increases in solids concentrations. The ratio of shear to normal stresses showed only a weak dependence upon shear rate, but it increased with decreasing concentration. At the very highest concentrations with narrow shear gaps, finite-particle-size effects became dominant and differences in stresses of as much as an order of magnitude were observed for the same shear rate and solids concentration.

Transversal mass transfer and shear stress formation during rapid gravity flow of a granular medium

2021 ◽  
Vol 6 (3) ◽  
pp. 204-215
Author(s):  
Viktor N. Dolgunin ◽  
Oleg O. Ivanov ◽  
Sergey A. Akopyan
Keyword(s):  
Mass Transfer ◽  
Shear Stress ◽  
Granular Materials ◽  
Granular Media ◽  
Flow Characteristics ◽  
Stress Generation ◽  
Spherical Particles ◽  
Gravity Flow ◽  
Gravity Flows ◽  
Stress Formation

The micro structural models for shear stress generation during rapid gravity flow of granular materials on a rough chute are discussed. The mechanism of the shear stress formation, taking into account the tangential impulse formed under transversal mass transfer of particles, is suggested. The analogy between granular media during rapid shear deformation and dense gases is used to develop the suggested mechanism on the basis of kinetic theory. The total shear stress is determined as the sum of the stress components induced by collisions, transversal mass transfer and contact interactions of uniform cohesionless inelastic spherical particles. The mathematical models describing the components of shear kinetic stresses are developed as the functions of particle properties, structural and kinematical gravity flow characteristics. The equations of impulse and energy conservation in the course of rapid gravity flow of uniform cohesionless particles are formulated. A variant of the formulation of boundary conditions at the flow bottom is proposed for mathematical modeling of the dynamics of rapid gravity flows of granular materials on a rough chute. The variant assumes the displacement of the area with the most intense shear rate inside the flow and into its layers adjacent to the rough chute surface.

scholarly journals Rheology of two-dimensional crushable granular materials

2021 ◽  
Vol 249 ◽  
pp. 07007
Author(s):  
Haruto Ishikawa ◽  
Satoshi Takada ◽  
Yuji Matsumoto
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Discrete Element Method ◽  
Granular Materials ◽  
Power Law ◽  
Fragment Size ◽  
Two Dimensional ◽  
Fragment Size Distribution ◽  
Mean Size ◽  
The Mean

The rheology of two-dimensional crushable granular materials under shear is numerically studied using the discrete element method. We find that the mean fragment size changes as the shear strain increases while the shear stress is almost independent of this mean size. The fragment size distribution is found to follow a power law. In particular, the exponent in the intermediate fragment size regime becomes approximately – 11/6, which is almost independent of the shear rate.

scholarly journals VISCOMETRY OF NANODISPERSE MAGNETIC LIQUIDS AND LUBRICATING OILS. 1. INSTRUMENTATION FOR RHEOLOGICAL STUDIES OF MAGNETIC NANODISPERSE LIQUID MEDIA

2021 ◽  
pp. 44-55
Author(s):  
Александр Николаевич Болотов ◽  
Ольга Олеговна Новикова
Keyword(s):  
Magnetic Field ◽  
Shear Stress ◽  
Shear Rate ◽  
Viscosity Coefficient ◽  
Structural Features ◽  
Shear Stresses ◽  
Low Viscosity ◽  
Wide Range ◽  
Magnetic Nanofluids ◽  
The Magnetic Field

Анализ литературных источников показывает, что существующие вискозиметры не всегда и не полностью могут обеспечить комплексные исследования магнитных наножидкостей для научных и практических целей. Разработана конструкция магнитного ротационного вискозиметра, на котором исследования могут проводиться в широком диапазоне значений индукции магнитного поля. Магнитное поле в приборе направлено ортогонально напряжению сдвига и может изменяться от нуля до 1,7·10 А/м. Прибор имеет два измерительных зазора заполненных жидкостью, что повышает точность результатов исследований маловязких жидкостей. Вискозиметр позволяет измерять стандартные характеристики магнитных наножидкостей (коэффициент вязкости, пластическая вязкость, предельное напряжение сдвига и др.), а также изучать структурные особенности жидкостей при сдвиговых напряжениях. Скорость сдвига в жидкости может стабильно поддерживаться в широком диапазоне (1 ÷5)·10 с. Вязкость исследуемых жидкостей может изменяться от 10 Па·с до ≈ 10 Па·с. Для исследований на вискозиметре требуется небольшое количество магнитной наножидкости объемом около 3,5 см. Математическое описание процесса ламинарного течения жидкости в кольцевом зазоре вискозиметра позволило оптимизировать его геометрические размеры и получить формулы для расчета коэффициента вязкости, напряжения сдвига и скорости сдвига, используя экспериментальные данные. Analysis of the literature sources shows that the existing viscometers are not always and not completely able to provide comprehensive studies of magnetic nanofluids for scientific and practical purposes. Design has been developed of a magnetic rotary viscometer which makes it possible to carry out investigations in a wide range of the magnetic field induction. The magnetic field in the device is directed orthogonally to the shear stress and can vary from zero to 1,7·10 A/m. The device has two measuring gaps filled with liquid, that increases the accuracy of the results of studies of low-viscosity liquids. The viscometer allows you to measure the standard characteristics of magnetic nanofluids (viscosity coefficient, plastic viscosity, ultimate shear stress, etc.), as well as to study the structural features of liquids under shear stresses. The shear rate in the liquid can be stably maintained in a wide range of (1÷5)·10 c. The viscosity of the studied liquids can vary from 10 Pa·s to ≈10 Pa·s. For studies on a viscometer, a small amount of magnetic nanofluid with a volume of about 3,5 cm is required. Using experimental data, the mathematical description of the process of laminar fluid flow in the annular gap of the viscometer made it possible to optimize its geometric dimensions and obtain formulas for calculating the viscosity coefficient, shear stress and shear rate.

scholarly journals Calculations of the rigidity and the strength of concrete filled steel deck diaphragms

2021 ◽  
Vol 274 ◽  
pp. 03014
Author(s):  
Oleg Efimov ◽  
Linur Gimranov ◽  
Alsou Fattakhova
Keyword(s):  
Shear Stress ◽  
Shear Stresses ◽  
Horizontal Load ◽  
Joint Work ◽  
Shear Deformations ◽  
Floor Slabs ◽  
Frame Buildings ◽  
Steel Frame Buildings ◽  
Two Sides ◽  
Steel Deck

Calculations of horizontal loads such as wind are required even for low-rise buildings. With stores number increasing their influence increases. The horizontal loads are perceived by the flooring discs. Steelreinforced concrete floors with profiled decking are most often used in steel frame buildings. Floor slabs and frame’s joint work is ensured by shear studs. The article discusses a shear studs’ stress determining method from horizontal load. There are different slab supporting variants: slap supported on two sides and along slab's perimeter. The goal was to determine shear stress in each flexible stop. The tasks were solved by calculating and by computing. Then the results were compared. Therefore, the resulting formula allows determining shear stresses not only in square slab but in rectangular ones too. Shear stress knowledge in the studs allows to determinate frames’ displacements by horizontal loads. Frame displaces relative to the floor slab due to studs shear and flexibility. The derived displacements determining formula takes into account shear deformations and anchor compliance in different directions. Herewithin the article, proposed displacements formula is not checked, but only the components determining a method is proposed.

Analysis of the Yielding Behavior of Electrorheological Suspensions by Controlled Shear Stress Experiments

2006 ◽  
Vol 16 (1) ◽  
pp. 14-18 ◽  
Author(s):  
Vladimír Pavlínek ◽  
Petr Sáha ◽  
José Pérez-González ◽  
Lourdes de Vargas ◽  
Jaroslav Stejskal ◽  
...  
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Yield Stress ◽  
Silicone Oil ◽  
Stress Measurement ◽  
Chain Structure ◽  
Shear Stresses ◽  
Initial Rupture ◽  
Yielding Behavior ◽  
Electrorheological Suspensions

Abstract The yielding behavior of two model electrorheological suspensions of uncoated silica particles and silica coated with polyaniline base in silicone oil using controlled shear rate and controlled shear stress experiments has been analyzed. The results demonstrate that unlike the uncertain dynamic yield stress values estimated from the results obtained in the former mode by extrapolation of the unsteady shear stresses to zero shear rate, the controlled shear stress measurement permits to detect sensitively the region starting from the initial rupture of particle chain structure in the electric field at rest corresponding to a static yield stress τy and ending in total breakage of suspension structure at a breaking stress τb.. The latter quantity can be detected with a good accuracy and proved to be a reliable criterion of the stiffness of ER structure.

Dynamic Association between Artery Shear flow Condition and Platelet Cytosolic Free Ca2+ Concentration in Human Hypertension

1990 ◽  
Vol 79 (6) ◽  
pp. 613-618 ◽  
Author(s):  
Jaime Levenson ◽  
Marie-Aude Devynck ◽  
Isabelle Pithois-Merli ◽  
Kim Hanh Le Quan Sang ◽  
Vincenzo Filitti ◽  
...  
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Vascular Endothelial Cells ◽  
Cell Metabolism ◽  
Shear Stresses ◽  
Double Blind ◽  
Wide Range ◽  
Membrane Stretching ◽  
Positive Correlations

1. Blood cells and vascular endothelial cells are subjected to a wide range of haemodynamically generated shear stress forces. In vitro, membrane stretching or shear stress have been observed to activate ion channels and cell metabolism and to facilitate erythrocyte and platelet aggregation. 2. The present study was designed to evaluate the participation of shear stresses in the control of apparent platelet cytosolic free Ca2+ concentration in hypertensive patients. 3. Shear conditions and platelet cytosolic free Ca2+ concentration in vitro were studied after a dynamic perturbation induced by 3 months of double-blind treatment with one of two β-antagonists, carteolol and atenolol. Brachial artery wall shear rate and stress were estimated by means of a pulsed Doppler velocimeter, and blood viscosity was measured by a co-axial viscometer at a shear rate of 96 s−1. Platelet cytosolic free Ca2+ concentration was simultaneously measured by using the Quin-2 fluorescent chelator. The direct effect of atenolol and carteolol on platelet cytosolic free Ca2+ concentration in vitro was also measured after addition of the β-blockers to plateletrich plasma. 4. Atenolol and carteolol decreased blood pressure similarly but their effects on shear rate (P < 0.02), shear stress (P < 0.01) and platelet cytosolic free Ca2+ concentration (P < 0.05) differed after 3 months of therapy. In contrast, neither of the drugs significantly altered platelet cytosolic free Ca2+ concentration, in vitro per se. 5. In the overall population, strong positive correlations existed not only between changes in platelet cytosolic free Ca2+ concentration and those in shear rate (r = 0.81, P < 0.001) and shear stress (r = 0.83, P < 0.001), but also between their absolute values, suggesting a possible haemodynamic shear-dependent modulation of transmembrane Ca2+ transport.

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