Frictional Packings Research Articles

Shear thickening and hysteresis in dense suspensions: The effect of particle shape

The flow of dense suspension of non-Brownian particles has been considered by various studies affected by their significance in a variety of industries and natural phenomena. In this study, we investigate the effect of polyhedron morphology on shear thickening, shear jamming, and hysteresis characteristics of non-Brownian suspension of acrylate particles. Particles with the same chemical nature and three different shapes of spherical (aspect ratio Γ = 1), elliptical paraboloid (Γ ≈ 1), and boat-shaped (Γ ≈ 3) are fabricated via photopolymerization-based methods. Studied suspensions show the shear-thinning behavior at low shear stresses and shear thickening behavior at the higher range of shear stress. Also, the strength of observed shear thickening is enhanced for the suspensions of polyhedron particles, which can be attributed to the heightened degree of interparticle frictional contacts. Furthermore, it is found that angularity not only shifts the predicted frictionless and frictional jamming packing fractions to lower values but also expands the shear jamming packing fraction range. Finally, a history-dependent hysteresis is observed in all samples due to the different particle spatial structures forming in ascending and descending flow modes. The observed hysteresis loops strongly depend on the volume fraction and diminish near the jamming packing fraction due to the restricted mobility space of particles. In addition, the tumbling of elongated particles also can decrease the hysteresis loop by enhancing viscosity in the ascending flow mode, where the structures are not fully developed.

Understanding slow compression of frictional granular particles by network analysis.

We consider frictional granular packings exposed to quasi-static compression rates, with a focus on systems above the jamming transition. For frictionless packings, earlier work (S. Luding et al., Soft Matter, 2022, 18(9), 1868-1884) has uncovered that the system evolution/response involves smooth evolution phases, interrupted by fast transitions (events). The general finding is that the force networks' static quantities correlate closely with the pressure, while their evolution resembles the kinetic energy for both frictionless and frictional packings. The former represents reversible (elastic) particle deformations with affine and non-affine components, whereas the latter also involves much stronger, irreversible (plastic) rearrangements of the packings. Events are associated with jumps in the overall kinetic energy as well as dramatic changes in the force networks describing the particle micro-structure. The frictional nature of particle interactions affects both their frequency and the relevant time scale magnitude. For intermediate friction, events are often followed by an unexpected slow-down during which the kinetic energy drops below its average value. We find that these slow-downs are associated with a significant decrease in the non-affine dynamics of the particles, and are strongly influenced by friction. Friction modifies the structure of the networks, both through the typical number of contacts of a particle, and by influencing topological features of the resulting networks. Furthermore, friction modifies the dynamics of the networks, with larger values of friction leading to smaller changes of the more stable networks.

Scaling Analysis of Shear Thickening Suspensions

Dense suspensions of particles in viscous liquid often demonstrate the striking phenomenon of abrupt shear thickening, where their viscosity increases strongly with increase of the imposed stress or shear rate. In this work, discrete-particle simulations accounting for short-range hydrodynamic, repulsive, and contact forces are performed to simulate flow of shear thickening bidisperse suspensions, with the packing parameters of large-to-small particle radius ratio δ = 3 and large particle fraction ζ = 0.15, 0.50, and 0.85. The simulations are carried out for volume fractions 0.54 ≤ ϕ ≤ 0.60 and a wide range of shear stresses. The repulsive forces, of magnitude FR, model the effects of surface charge and electric double-layer overlap, and result in shear thinning at small stress, with shear thickening beginning at stresses σ ∼ FRa−2. A crossover scaling analysis used to describe systems with more than one thermodynamic critical point has recently been shown to successfully describe the experimentally-observed shear thickening behavior in suspensions. The scaling theory is tested here on simulated shear thickening data of the bidisperse mixtures, and also on nearly monodisperse suspensions with δ = 1.4 and ζ = 0.50. Presenting the viscosity in terms of a universal crossover scaling function between the frictionless and frictional maximum packing fractions collapses the viscosity for most of the suspensions studied. Two scaling regimes having different exponents are observed. The scaling analysis shows that the second normal stress difference N2 and the particle pressure Π also collapse on their respective curves, with the latter featuring a different exponent from the viscosity and normal stress difference. The influence of the fraction of frictional contacts, one of the parameters of the scaling analysis, and its dependence on the packing parameters are also presented.

Evaluation of injection molded gas and water atomized 316l stainless steel powder properties

This research investigates the features crucial to injection molding via the rheological behavior, injection molding, debinding, and sintering process of water and gas atomised 316L stainless steel powder utilizing a newly developed locally based binder system containing palm stearin. The critical powder loading for injection molding was 65vol% for gas atomisation and 62vol% for water atomisation. Due to the minimal interparticle friction and high packing density, the gas-atomised powder proved easier to shape. In contrast, the water-atomised powder has a high viscosity of the injection molding feedstock, a high interparticle friction, and a low packing density, all of which impede injection molding. The debinding of the binder was accomplished utilizing solvent and thermal methods. After debinding, samples were sintered in a high-temperature vacuum furnace at 1360 degrees Celsius. Results reveal that water-atomised powder can be sintered to 95% of its theoretical density, whereas gas-atomised powder can be sintered to near full density.

Finding the grain size distribution that produces the densest arrangement in frictional sphere packings: Revisiting and rediscovering the century-old Fuller and Thompson distribution

By means of discrete-element methods, we investigate the joint effects of the grain size distribution (GSD) and contact friction on the structure of three-dimensional samples composed of spherical grains. Specifically, we compress these systems isotropically until jamming and then analyze their structure in terms of density, connectivity, coefficients of uniformity and curvature, and parameters of grading entropy. Our study focuses on power-law GSDs and particularly on the Fuller and Thompson distribution, proposed over a century ago. First, we show that, among the set of GSDs investigated, this particular distribution produces the densest and best-connected systems, falsifying a conjecture recently posed in the literature. Second, we find that the jamming packing fraction can be accurately predicted as a function of simple descriptors of the GSD, but among these descriptors the granular entropy concept proves to be the most useful. This allows for an alternative interpretation of both jamming and grading entropy concepts. Finally, we compare the Fuller and Thompson distribution with two well-known GSDs: that of the Apollonian sphere packing and that towards which granular systems evolve after intensive grain fracturing. Surprisingly, we find that these three GSDs are practically coincident in the limit of large size spans, despite having been introduced or discovered in different scientific contexts (i.e., engineering, mathematics, and earth sciences, respectively).

Friction calculation and packing effect analysis for gravel packing in deepwater horizontal wells

AbstractGravel packing is one of the most commonly used well‐completion methods for controlling sand production in deepwater horizontal gas wells. Both the gravel‐packing mechanisms and the technical difficulties of gravel packing in a horizontal well are discussed in this paper. Subsequently, packing simulations were conducted based on geological data from a well in the LS gas field in the northern South China Sea. The factors influencing the gravel‐packing process were quantitatively analyzed. The influences of the pump rate, carrying fluid leak‐off ratio, and density of gravel on the sand‐dune ratio of the α‐wave, height of the sand dune, packing length of the α‐wave, and packing pressure were analyzed. The results show that the pipe string injection friction is the largest at the slurry injection stage and the α‐wave packing stage. In the β‐wave packing stage, the downhole horizontal flow friction becomes the main pressure loss. The friction increased when the β‐wave packing reached the heel of the horizontal wells. As a result, the packing pressure can easily exceed the formation fracture pressure. Furthermore, the lower the pump rate, the higher the sand‐dune ratio, which would cause premature screen‐out and blockage. Therefore, optimizing the pump rate is essential to ensure that the sand‐dune ratio meets the designed requirements. Under a certain leak‐off rate, the lower the gravel density, the longer the packing length of the α‐wave. For a long horizontal well, the step‐down method can be used to control the packing pressure during the β‐wave packing stage. The results provide technical support for field gravel packing.

Universality of jammed frictional packing

Understanding disordered particle packings is of great significance from both theoretical and engineering perspectives. Establishing a quantitative relationship between nonspherical particle shape and disordered packing properties is generally challenging, due to the complex geometry and topology. Here we resolve this issue by numerically investigating disordered jammed packings of various frictional congruent nonspherical particles, including superellipsoids and polyhedra, over a wide range of friction coefficients. We discover several universal packing characteristics across different particle shapes and frictions. In the infinite friction limit, the coordination numbers for all shapes approach the identical lower bound for jamming. The resulting ``random loose packing'' (RLP) state possesses minimal structural correlations, with the packing fraction as a simple monotonic decreasing function of the orientation-averaged excluded volume for different particle shapes. Packings with finite friction can then be understood via a perturbative approach based on RLP. The nature of RLP can be illuminated by the percolation transition of contacting particle network during the quasistatic densification process. Moreover, the large-scale density fluctuations for all jammed frictional packings are also strongly suppressed, broadening the previous claim of hyperuniformity for the frictionless ones.

The effects of solid shear stress and wall roughness on the simulation of cylindrical hydrocyclone classification

Reasonable numerical conditions are critical for the precision and accuracy of the numerical consequences of hydrocyclones. In this paper, the effects of resistance coefficient, wall roughness, and friction packing limit on particle velocity and distribution as well as the separation behaviors were studied in a cylindrical hydrocyclone using the two-fluid model. The results show that the friction packing limit and wall roughness can significantly influence the numerical results, whereas the effect of the resistance coefficient is negligible. As the friction packing limit increases from 0.4 to 0.55, the cut size gradually decreases with improving separation sharpness, and it reaches the minimum when the friction parking limit is 0.5. The wall roughness monotonously increases the cut size and reduces the separation sharpness. Simulation results were also compared with experimental data, and a reasonable prediction can be obtained with resistance coefficient, friction packing limit, and wall roughness height of 0.95, 0.5, and 50 μm, respectively.

Dynamic analysis of poured packing process of ellipsoidal particles

Packing properties are determined by the dynamic deposition history and affected by many variables. In this work, DEM is used to study the effects of dropping height, deposition intensity and friction coefficient on the dynamic response and stable-state packing properties of ellipsoidal particles. The results demonstrate that with dropping height increasing, packing density increases but the bed becomes less ordered. Dropping height affects the densification process of ellipsoids more significantly than spheres. At high dropping height, the transition period of the orientation angle in the densification process almost disappears for oblate particles, while it becomes longer for prolate particles. With the increase of deposition intensity, packing density decreases significantly, but orientational order changes slightly. With the increase of sliding friction coefficient, packing density and orientational order decrease dramatically. The difference in packing density is mainly caused by dynamic pouring process rather than the densification process.

Stress correlations in frictional granular media

This paper investigates whether in frictional granular packings, like in Hamiltonian amorphous elastic solids, the stress autocorrelation matrix presents long range anisotropic contributions just as elastic Green's functions. We find that in a standard model of frictional granular packing this is not the case. We prove quite generally that mechanical balance and material isotropy constrain the stress auto-correlation matrix to be fully determined by two spatially isotropic functions: the pressure and torque auto-correlations. The pressure and torque fluctuations being respectively normal and hyperuniform force the stress autocorrelation to decay as the elastic Green's function. Since we find the torque fluctuations to be hyper-uniform, the culprit is the pressure whose fluctuations decay slower than normally as a function of the system's size. Investigating the reason for these abnormal pressure fluctuations we discover that anomalous correlations build up already during the compression of the dilute system before jamming. Once jammed these correlations remain frozen. Whether this is true for frictional matter in general or is it the consequence of the model properties is a question that must await experimental scrutiny and possible alternative models.

A study on calculation of friction coefficient and packing stress using static diagnosis test for a balanced globe valve in nuclear power plants

A valve assembly used in nuclear power plants must be qualified and supervised. New technical standards such as ASME QME-1 2007 particularly require detailed qualification using experiment and analysis. Particularly, diagnostic tests and engineering studies are required for qualification of ASME QME-1 2007. Among these studies, the research on the measurement of friction coefficient and packing stress is important. The irregular change of packing stress along the stroke distance occurs because of the abnormal phenomenon, which must be found and studied with quantitative methods. Packing stress should be analyzed conservatively through experimentation and analysis. In this study, various formulas were applied to measure and calculate coefficient of friction and packing stress. This study can be used in relation to qualification and supervision of packing materials. And the calculation using static diagnosis test can be used to find the packing frictional force in dynamic diagnosis test with flow pressure in a pipe. This study has made it possible to reliably consider packing frictional force generated in a valve body. And so, it is believed that more margin can be secured when evaluating the capacity of valve actuator by applying the accurate frictional force generated in the valve assembly.

Direct numerical simulation of wave propagation in saturated random granular packings using coupled LBM-DEM

Poroelasticity theory predicts wave velocities in a saturated porous medium through a coupling between the bulk deformation of the solid skeleton and porous fluid flow. The challenge emerges below the characteristic wavelengths at which hydrodynamic interactions between grains and pore fluid become important. We investigate the pressure and volume fraction dependence of compressional- and shear-wave velocities in fluid-saturated, random, isotropic, frictional granular packings. The lattice Boltzmann method (LBM) and discrete element method (DEM) are two-way coupled to capture the particle-pore fluid interactions; an acoustic source is implemented to insert a traveling wave from the fluid reservoir to the saturated medium. We extract wave velocities from the acoustic branches in the wavenumber-frequency space, for a range of confining pressures and volume fractions. For random isotropic granular media the pressure-wave velocity data collapse on a single curve when scaled properly by the volume fraction.

Time scales and rheology of visco-cohesive granular flows

In the presence of viscous and cohesive interactions between particles, a granular flow is governed by several characteristic time and stress scales that determine its rheological properties (shear stress, packing fraction, effective viscosities). In this paper, we revisit and extend the scaling arguments used previously for dry cohesionless granular flows and suspensions. We show that the rheology can be in principle described by a single dimensionless control parameter that includes all characteristic times. We also briefly present simulation results for 2D sheared suspensions and 3D wet granular flows where the effective friction coefficient and packing fraction are consistently described as functions of this unique control parameter.

Influence of frictional packing limit on hydrodynamics and performance of gas-solid fluidized beds

The influence of frictional packing limit (FPL) on prediction of hydrodynamics and performance of fluidized bed reactors was studied. Dense gas-solid flows in non-reactive (under isothermal cold and at elevated temperatures) and reactive atmospheres (fluidized bed gasifier) were simulated using Eulerian-Eulerian methodology considering a range of values for FPL. Simulations under cold flow conditions were conducted to establish a range of FPL values that provides physically realistic predictions. It is noticed that bed pressure drop increases with increasing value of FPL when superficial gas velocity (U) is less than or equal to the minimum fluidization velocity. For larger values of U, predicted pressure drop is unaffected by the choice of value of FPL. However, in these cases, the distribution of particles, their velocities and bubbling behavior are significantly affected by FPL. Effect of FPL at elevated temperatures is similar to the one observed at cold flow conditions. It is further noticed that FPL not only affects the predictions on bed hydrodynamics but also has profound influence on reactive flow characteristics such as bed temperature and product gas composition. Sensitivity analysis under cold flow conditions could reveal better predictions when the ratio of FPL to close packing limit is chosen between 0.9 and 0.97.

Rheology and granular texture of viscoinertial simple shear flows

By means of extensive particle dynamics simulations in a three-dimensional model, we analyze the rheology and granular texture in the steady-state of the viscoinertial granular flow. The interactions between dry particles are added by the theoretical description of the capillary cohesion forces and viscous forces due to the presence of the viscous liquid bridge. We show that the rheology of such flow characterized by the apparent friction coefficient and packing fraction can be nicely described as a function of the viscoinertial number combining the particle inertia and viscous stress of the liquid bridge by keeping the constant value of the liquid-vapor surface tension. Furthermore, the flow behavior can alternatively be described by the effective viscosities (normal and shear components) as a function of the imposed volume fraction, which is in good agreement with previous numerical simulations of particles immersed in a viscous fluid and experiments in dense suspensions. Interestingly, the granular texture characterized by the fabric and force anisotropies and the bond coordination number is also well-described by this modified inertial number. Remarkably, the stress transmission ratio reflects the intermediate relationship between microstructure and mechanical behavior of wet granular flow, expressed as a function of the viscoinertial number. We also find that shearing leads to variations of the compressive and tensile interactions between neighboring particles.

Rigidity percolation control of the brittle-ductile transition in disordered networks

In ordinary solids, material disorder is known to increase the size of the process zone in which stress concentrates at the crack tip, causing a transition from localized to diffuse failure. Here, we report experiments on disordered 2D lattices, derived from frictional particle packings, in which the mean coordination number $\langle z \rangle$ of the underlying network provides a similar control. Our experiments show that tuning the connectivity of the network provides access to a range of behaviors from brittle to ductile failure. We elucidate the cooperative origins of this transition using a frictional pebble game algorithm on the original, intact lattices. We find that the transition corresponds to the isostatic value $\langle z \rangle = 3$ in the large-friction limit, with brittle failure occurring for structures vertically spanned by a rigid cluster, and ductile failure for floppy networks containing nonspanning rigid clusters. Furthermore, we find that individual failure events typically occur within the floppy regions separated by the rigid clusters.

Rheology and shear jamming of frictional ellipses

Understanding and predicting dense granular flows is of importance in geology and industrial applications. Still, most theoretical work has been limited to flows and packings composed of discs or spheres, a narrow subset of all possible packings. To advance our understanding of more realistic flows we here study the granular rheology of ellipses in steady-state flow with a focus on the effects of elongation and interparticle friction. We carry out novel numerical simulations of amorphous granular flows in a shear cell under confining pressure, at constant shear rate and at various aspect ratios. Both frictionless and frictional particles are considered. The various rheological curves follow the semi-empirical constitutive relations previously found for granular flows composed of discs or spheres. At the shear jamming point one finds well-defined packings, all characterised by their own set of critical parameters such as critical packing fraction, effective friction, etc. Packings composed of frictionless or almost frictionless particles are found to have a non-monotonic dependence of the macroscopic friction but a monotonic increase in packing fraction as the aspect ratio increases. For packings composed of particles with high interparticle friction the reverse is found. While frictionless packings are found to be hypostatic (except in the disc limit) frictional packings are remarkably close to the isostaticity point of having three contacts per particle. Both frictional and frictionless packings are found to have an increasing nematic ordering as the aspect ratio increases. The onset of a rolling, rather than sliding, motion between very frictional particles diminish this nematic ordering substantially. These findings put new and previously unknown bounds on the packing ratios and yield criteria for these amorphous packings at shear jamming.

Comparison of two-fluid and discrete particle modeling of gas-particle flows in micro fluidized beds

The formation of a more porous zone in the near wall region has been commonly suggested to be one of the main mechanisms of the delayed onset of fluidization in micro fluidized beds (MFBs). If such geometrical effect still plays a major role once the bed is fluidized, it will challenge the applications of Two-Fluid Model (TFM) to simulate micro fluidized beds. In this work this issue is assessed by taking the simulation results of the Computational Fluid Dynamics coupled with the Discrete Element Method (CFD-DEM) as the benchmark data. Both the delayed onset of fluidization and the advanced onset of turbulent fluidization predicted by CFD-DEM simulations are successfully captured by the TFM simulations. The radial profiles of solids volume fraction and solids axial velocity predicted by TFM and CFD-DEM simulations are also in well agreement. Such results demonstrate that TFM can be appropriately used to model micro fluidized beds systems. Parameter analyses show that TFM simulation results are closely related to the input parameter setting. The minimum bubbling velocity predicted by TFM simulations closely depends on the chosen value of frictional packing limit. And the specularity coefficient has a significant impact on the predicted solids flow behavior.

A microscale analytical study on the strength of two-dimensional frictional granular materials

We introduce an analytical study of the links between macroscopic strength and the grain-to-grain interactions in two-dimensional frictional granular packings. This study consists of two main parts that are developed and connected progressively. First, we obtain explicit expressions that enable us to relate microscale parameters such as contact forces and fabric to macroscopic stress and strength. Second, physical connections and interpretations between the aforementioned micro-parameters, micro-mechanisms, fabric anisotropy and macroscopic strength are derived. Furthermore, throughout this theoretical study, some fundamental physics related to a packing’s strength as well as contact buckling is extracted, providing a better understanding of the micro-mechanics that furnishes and builds up the macroscopic strength of this kind of materials.

Viscoinertial regime of immersed granular flows.

By means of extensive coupled molecular dynamics-lattice Boltzmann simulations, accounting for grain dynamics and subparticle resolution of the fluid phase, we analyze steady inertial granular flows sheared by a viscous fluid. We show that, for a broad range of system parameters (shear rate, confining stress, fluid viscosity, and relative fluid-grain density), the frictional strength and packing fraction can be described by a modified inertial number incorporating the fluid effect. In a dual viscous description, the effective viscosity diverges as the inverse square of the difference between the packing fraction and its jamming value, as observed in experiments. We also find that the fabric and force anisotropies extracted from the contact network are well described by the modified inertial number, thus providing clear evidence for the role of these key structural parameters in dense suspensions.