scholarly journals Apparent yield stress in rigid fibre suspensions: the role of attractive colloidal interactions

2016 ◽  
Vol 802 ◽  
pp. 611-633 ◽  
Author(s):  
S. Bounoua ◽  
E. Lemaire ◽  
J. Férec ◽  
G. Ausias ◽  
A. Zubarev ◽  
...  
Keyword(s):  
Yield Stress ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Van Der Waals ◽  
Simple Shear Flow ◽  
Average Particle ◽  
Particle Volume ◽  
Friction Forces ◽  
Aspect Ratios ◽  
Fibre Suspensions

This work is focused on the modelling of the shear and normal stresses in fibre suspensions that are subjected to a simple shear flow in the presence of short-range lubrication forces, van der Waals and electrostatic forces, as well as solid friction forces between fibres. All of these forces are weighed by the contact probability. The theory is developed for attractive fibres with van der Waals interaction dominating over electrostatic repulsion. The model predicts a simple Bingham law for both the shear stress and the first normal stress difference, with the apparent shear and normal yield stresses proportional to the second and the third power of the particle volume fraction respectively. The model is applied to the experimental data of Rakatekar et al. (Adv. Mater., vol. 21, 2009, pp. 874–878) and Natale et al. (AIChE J., vol. 60, 2014, pp. 1476–1487) on suspensions of carbon nanotubes dispersed in a Newtonian epoxy resin. It reproduces well the quadratic dependence of the apparent yield stress on the particle volume fraction $(\unicode[STIX]{x1D70E}_{Y}\propto \unicode[STIX]{x1D719}^{2})$ for average particle aspect ratios of $r=160$ and 1200, while it underpredicts the power-law exponent for $r=80$ (always predicting $\unicode[STIX]{x1D719}^{2}$ behaviour instead of $\unicode[STIX]{x1D719}^{3.2}$).

scholarly journals Hydrodynamics control shear-induced pattern formation in attractive suspensions

2019 ◽  
Vol 116 (25) ◽  
pp. 12193-12198 ◽  
Author(s):  
Zsigmond Varga ◽  
Vincent Grenard ◽  
Stefano Pecorario ◽  
Nicolas Taberlet ◽  
Vincent Dolique ◽  
...  
Keyword(s):  
Shear Flow ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Quantitative Agreement ◽  
Stability Diagram ◽  
Periodic Pattern ◽  
Simple Shear Flow ◽  
Parallel Plates ◽  
Particle Volume ◽  
Hydrodynamic Coupling

Dilute suspensions of repulsive particles exhibit a Newtonian response to flow that can be accurately predicted by the particle volume fraction and the viscosity of the suspending fluid. However, such a description fails when the particles are weakly attractive. In a simple shear flow, suspensions of attractive particles exhibit complex, anisotropic microstructures and flow instabilities that are poorly understood and plague industrial processes. One such phenomenon, the formation of log-rolling flocs, which is ubiquitously observed in suspensions of attractive particles that are sheared while confined between parallel plates, is an exemplar of this phenomenology. Combining experiments and discrete element simulations, we demonstrate that this shear-induced structuring is driven by hydrodynamic coupling between the flocs and the confining boundaries. Clusters of particles trigger the formation of viscous eddies that are spaced periodically and whose centers act as stable regions where particles aggregate to form flocs spanning the vorticity direction. Simulation results for the wavelength of the periodic pattern of stripes formed by the logs and for the log diameter are in quantitative agreement with experimental observations on both colloidal and noncolloidal suspensions. Numerical and experimental results are successfully combined by means of rescaling in terms of a Mason number that describes the strength of the shear flow relative to the rupture force between contacting particles in the flocs. The introduction of this dimensionless group leads to a universal stability diagram for the log-rolling structures and allows for application of shear-induced structuring as a tool for assembling and patterning suspensions of attractive particles.

Experimental study of the sedimentation of dilute and semi-dilute suspensions of fibres

1999 ◽  
Vol 384 ◽  
pp. 133-158 ◽  
Author(s):  
BENJAMIN HERZHAFT ◽  
ÉLISABETH GUAZZELLI
Keyword(s):  
Aspect Ratio ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Complex Function ◽  
Orientation Distribution ◽  
Particle Volume ◽  
Mean Velocity ◽  
Aspect Ratios ◽  
Dilute Suspensions ◽  
Orientation Distributions

Steady-state velocity and orientation distributions of sedimenting fibres were measured as a function of particle concentration and aspect ratio. Two different regimes of sedimentation were clearly identified. For dilute suspensions, the fibres tend to align in the direction of gravity with occasional flipping and clump together to form packets. In this regime, the vertical mean sedimentation speed is not hindered and can be larger than the Stokes' velocity of an isolated vertical fibre. Its scaling is a complex function of particle volume fraction and aspect ratio. As the concentration is increased, the fibres still tend to orient in the direction of gravity. The mean velocity becomes hindered and scales with particle volume fraction. The velocity fluctuations were found to be large and anisotropic. They were found to increase with increasing volume fraction. A similar substantial anisotropy of the orientation distribution was observed for all particle concentrations and aspect ratios studied.

Rheological Study of Micro Particle Laden Polymeric Thermal Interface Materials: Part 2 — Modeling

2002 ◽  
Author(s):  
Ravi S. Prasher ◽  
Jim Shipley ◽  
Suzana Prstic ◽  
Paul Koning ◽  
Jin-Lin Wang
Keyword(s):  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Yield Stress ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Thermal Interface Materials ◽  
Particle Volume ◽  
Thermal Interface ◽  
Complete Set ◽  
Interface Materials

Currently there are no models to predict the thickness or the bondline thickness (BLT) of particle laden polymeric thermal interface materials (TIM) for parameters such as particle volume fraction and pressure. TIMs are used to reduce the thermal resistance. Typically this is achieved by increasing the thermal conductivity of these TIMs by increasing the particle volume fraction, however increasing the particle volume fraction also increases the BLT. Therefore, increasing the particle volume fraction may lead to an increase in the thermal resistance after certain volume fraction. This paper introduces a model for the prediction of the BLT of these particle laden TIMs. Currently thermal conductivity is the only metric for differentiating one TIM formulation from another. The model developed in this paper introduces another metric: the yield stress of these TIMs. Thermal conductivity and the yield stress together constitute the complete set of material parameters needed to define the thermal performance of particle laden TIMs.

Microstructure and Mechanical Properties of High Strength Al2O3p/6061Al Composites

2007 ◽  
Vol 353-358 ◽  
pp. 1390-1393
Author(s):  
Bai Feng Luan ◽  
Gao Hui Wu ◽  
Qing Liu ◽  
Niels Hansen ◽  
Ting Quan Lei
Keyword(s):  
Mechanical Properties ◽  
Yield Stress ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Hot Extrusion ◽  
High Strength ◽  
Dispersion Strengthening ◽  
Particle Volume ◽  
Microstructure And Mechanical Properties ◽  
Before And After

An experimental study of microstructure and mechanical properties in the Al2O3 particulate reinforced 6061 Aluminum composites has been used to determine the effect of extrusion and particle volume fraction (20, 26, 30, 40, 50, 60%Vf) in deformed metal matrix composites. The microstructure of Al2O3 /6061Al composite before and after hot extrusion is investigated by TEM and SEM. Results show that dislocation and subgrain generated after hot extrusion as well as the particle distribution of composite become more uniform with extrusion ratio of 10:1. The ultimate strength, yield strength and elongation of the composite also increase after hot extrusion. Dispersion strengthening and subgrain boundary strengthening is discussed and also the effect of precipitate introduced by heat treatment both after casting and after extrusion. The yield stress (0.2% offset) of the composites has been calculated and predicted using a standard dislocation hardening model. Whilst the correlation between this and the measured value of yield stress obtained in previous experimental test is reasonable.

scholarly journals Effect of coarse particle volume fraction on the yield stress and thixotropy of cementitious materials

2008 ◽  
Vol 38 (11) ◽  
pp. 1276-1285 ◽  
Author(s):  
Fabien Mahaut ◽  
Samir Mokéddem ◽  
Xavier Chateau ◽  
Nicolas Roussel ◽  
Guillaume Ovarlez
Keyword(s):  
Yield Stress ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Cementitious Materials ◽  
Coarse Particle ◽  
Particle Volume

scholarly journals Effect of Coarse Particle Volume Fraction on the Yield Stress of Muddy Sediments from Marennes Oléron Bay

2010 ◽  
Vol 2010 ◽  
pp. 1-6 ◽  
Author(s):  
A. Pantet ◽  
S. Robert ◽  
S. Jarny ◽  
S. Kervella
Keyword(s):  
Yield Stress ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Fine Fraction ◽  
General Description ◽  
Measurement Sensitivity ◽  
Particle Volume ◽  
Fine Sediments ◽  
Sandy Material ◽  
Muddy Sediments

Coastal erosion results from a combination of various factors, both natural and humaninduced, which have different time and space patterns. In addition, uncertainties still remain about the interactions of the forcing agents, as well as on the significance of non-local causes of erosion. We focused about the surface sediments in the Marennes Oléron bay, after a general description of the site that has many various activities. The superficial sediments show a mechanical behavior, mainly depends on the fine fraction for a composition that contains up to 60% of sandy material. Fine sediments fraction has a typical yield stress depending naturally of concentration or water content. This yield could be modified slightly or significantly by adding silt or sand. As a result, the rheological measurement sensitivity allows us to characterize five typical sediments that correlate with solid fraction and fine fraction.

scholarly journals Cold Forming of Al-TiB2 Composites Fabricated by SPS: A Computational Experimental Study

Materials ◽  
2020 ◽  
Vol 13 (16) ◽  
pp. 3456 ◽  
Author(s):  
Elad Priel ◽  
Nissim U. Navi ◽  
Brigit Mittelman ◽  
Nir Trabelsi ◽  
Moshe Levi ◽  
...  
Keyword(s):  
Yield Stress ◽  
Damage Mechanics ◽  
Mechanical Response ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Continuum Damage Mechanics ◽  
Tib2 Particle ◽  
Particle Volume ◽  
Cold Forming ◽  
Effective Yield

The mechanical response and failure of Al-TiB2 composites fabricated by Spark Plasma Sintering (SPS) were investigated. The effective flow stress at room temperature for different TiB2 particle volume fractions between 0% and 15% was determined using compression experiments on cylindrical specimens in conjunction with an iterative computational methodology. A different set of experiments on tapered specimens was used to validate the effective flow curves by comparing experimental force–displacement curves and deformation patterns to the ones obtained from the computations. Using a continuum damage mechanics approach, the experiments were also used to construct effective failure curves for each material composition. It was demonstrated that the fracture modes observed in the different experiments could be reproduced in the computations. The results show that increasing the TiB2 particle volume fraction to 10% results in an increase in material effective yield stress and a decrease in hardening. For a particle volume fraction of 15%, the effective yield stress decreases with no significant influence on the hardening slope. The ductility (workability) of the composite decreases with increasing particle volume fraction.

scholarly journals Collective diffusion in sheared colloidal suspensions

2008 ◽  
Vol 597 ◽  
pp. 305-341 ◽  
Author(s):  
ALEXANDER M. LESHANSKY ◽  
JEFFREY F. MORRIS ◽  
JOHN F. BRADY
Keyword(s):  
Volume Fraction ◽  
Hard Spheres ◽  
Particle Volume Fraction ◽  
Strain Tensor ◽  
Density Fluctuations ◽  
Hydrodynamic Interactions ◽  
Simple Shear Flow ◽  
Particle Volume ◽  
Simulation Results ◽  
Sheared Suspensions

Collective diffusivity in a suspension of rigid particles in steady linear viscous flows is evaluated by investigating the dynamics of the time correlation of long-wavelength density fluctuations. In the absence of hydrodynamic interactions between suspended particles in a dilute suspension of identical hard spheres, closed-form asymptotic expressions for the collective diffusivity are derived in the limits of low and high Péclet numbers, where the Péclet number ${\it Pe}\,{=}\,\gamdot a^2/D_0$ with $\gamdot$ being the shear rate and D0 = kBT/6πη a is the Stokes–Einstein diffusion coefficient of an isolated sphere of radius a in a fluid of viscosity η. The effect of hydrodynamic interactions is studied in the analytically tractable case of weakly sheared (Pe ≪ 1) suspensions.For strongly sheared suspensions, i.e. at high Pe, in the absence of hydrodynamics the collective diffusivity Dc = 6 Ds∞, where Ds∞ is the long-time self-diffusivity and both scale as $\phi \gamdot a^2$, where φ is the particle volume fraction. For weakly sheared suspensions it is shown that the leading dependence of collective diffusivity on the imposed flow is proportional to D0 φPeÊ, where Ê is the rate-of-strain tensor scaled by $\gamdot$, regardless of whether particles interact hydrodynamically. When hydrodynamic interactions are considered, however, correlations of hydrodynamic velocity fluctuations yield a weakly singular logarithmic dependence of the cross-gradient-diffusivity on k at leading order as ak → 0 with k being the wavenumber of the density fluctuation. The diagonal components of the collective diffusivity tensor, both with and without hydrodynamic interactions, are of O(φPe2), quadratic in the imposed flow, and finite at k = 0.At moderate particle volume fractions, 0.10 ≤ φ ≤ 0.35, Brownian Dynamics (BD) numerical simulations in which there are no hydrodynamic interactions are performed and the transverse collective diffusivity in simple shear flow is determined via time evolution of the dynamic structure factor. The BD simulation results compare well with the derived asymptotic estimates. A comparison of the high-Pe BD simulation results with available experimental data on collective diffusivity in non-Brownian sheared suspensions shows a good qualitative agreement, though hydrodynamic interactions prove to be important at moderate concentrations.

CHARACTERISTICS OF A YIELD STRESS SCALING FUNCTION FOR ELECTRORHEOLOGICAL FLUIDS

2002 ◽  
Vol 16 (17n18) ◽  
pp. 2636-2642 ◽  
Author(s):  
H. J. CHOI ◽  
J. W. KIM ◽  
M. S. CHO ◽  
C. A. KIM ◽  
M. S. JHON
Keyword(s):  
Field Strength ◽  
Electric Field ◽  
Electric Field Strength ◽  
Yield Stress ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Critical Evaluation ◽  
Particle Volume ◽  
Scaling Equation ◽  
Er Fluids

The electrorheological (ER) fluids exhibit a drastic change in rheological and electrical properties. Among these properties, yield stress is one of the critical evaluation parameters of the performance of ER devices. The published experimental data of yield dependence on the electric field strength and particle volume fraction are inconsistent due to the time dependence of material properties and measuring conditions. In this paper, we present a universal function, descriptive of the normalized yield stress, via scaling of the applied electric field strength. This scaling equation hybridizes both the polarization and conductivity models. Yield stress data for various ER fluids are collapsed onto a single curve for a broad range of electric field strengths, suggesting that the proposed scaling equation is adequate for predicting the ER property. Furthermore, the yield stresses, obtained from two different measuring techniques (static and dynamics methods), were also examined.

scholarly journals Multicomponent Water Effects on Rotating Machines Disk Erosion

Water ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 757
Author(s):  
Chunxia Yang ◽  
Shanshan Hou ◽  
Junhui Xu ◽  
Yuquan Zhang ◽  
Yuan Zheng ◽  
...  
Keyword(s):  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Particle Diameter ◽  
Operating Conditions ◽  
Particle Model ◽  
Average Particle ◽  
Rotating Machines ◽  
Rotating Disc ◽  
Particle Volume ◽  
Inlet Velocity

When sand particles are entrained into carrier flow, such as liquid, a strong interaction occurs with the surface of the metallic material, resulting in serious erosion damage. However, the effect of the physical properties of particles and materials on erosion characteristics has not been well studied. In this paper, the erosion-wear behavior of a rotating disc surface under the action of solid–liquid two-phase flow was studied by using the discrete particle model (DPM). The wear effects on the surface of sample due to particle diameter (d = 0.1 mm, d = 0.2 mm, d = 0.3 mm, d = 0.4 mm), particle volume fraction (CV = 2%, CV = 3%, CV = 4%, CV = 5%), and particle inlet velocity (v = 1.05 m/s, v = 2.05 m/s, v = 3.05 m/s, v = 4.05 m/s) were analyzed using representative values of operating conditions of rotating machines. The results show that the wear amount increases exponentially with the radius, whilst the maximum wear amount increases faster than the average wear amount with the particle volume fraction. The surface wear grows inversely with the particle diameter but slightly with the particle inlet velocity. A case study of stainless steel samples at different radius positions on the surface of rotating disc is carried out using a mixed velocity of sand and water of 2.05 m/s, an average particle size of 0.1 mm, and a concentration of CV = 2.5%. The experiments show the wear amount increases with the radius on the surface of the rotating disc, just as predicted by the numerical simulation. Two important findings emerge from the study: (1) the wear morphology of the specimen surface develops from two to three regions; (2) when the basal body is rotating at high speed, the wear degree is influenced more by the circumferential than particle inlet velocity. The wear morphology was observed by using a scanning electron microscope (SEM). It exhibited a mixture of fine and coarse scratches and pits, and the distribution of these varied according to the radial distance of the disc.

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