Effect Of Interparticle Friction Research Articles

Granular column collapse: Analysis of inter-particle friction effects

The purpose of this paper is to investigate the effects of inter-particle friction on the granular column collapses via the discrete element method (DEM) while eliminating the particle-size effects. As the inter-particle friction increases, the runout distance decreases, the deposit height increases, the force chains tend to be closer to the vertical upward direction, the percentage of the strong force chains become greater and the granular assembly is less susceptible to the external gravity field, thus making the collapse tend to be toppling-dominant flow. The correlation between the initial height and runout distance of particles at the final deposits becomes stronger when the collapse tends to be more toppling-dominant. The motion patterns of the collapse are governed by the inter-particle friction and initial aspect ratio through dimensional analysis and the effective aspect ratio parameter is proposed to classify granular column collapse into three regimes (sliding-dominant, transition, and toppling-dominant collapse).

Flow of lubricated granular material on an inclined plane

We have studied the gravity driven flow of spherical shaped, millimetric sized granular material coated with aspherical, micron-sized, near frictionless lubricant particles. Experiments were performed on an inclined plane using two different sized particles for varying concentrations of the lubricant. The particle volumetric flow rate exhibits a non-monotonic behavior with increasing lubricant concentration. It shows an increase at lower lubricant concentration followed by a decrease at higher lubricant concentration. The lubricant particles adhere to the granular particle surface thereby reducing the inter-particle friction. However, presence of lubricant particles at higher concentration damps out inter-particle collision thereby reducing the interparticle momentum transfer. Non-monotonicity in the observed behavior is then conjectured to arise due to competing effects of inter-particle friction and inter-particle collision. The present work and the overall observed behavior therein provides a simple experimental system to characterize the effects of added lubricant material in pharmaceutical and other relevant industrial applications.

Effect of inter-particle friction on 3D accordance of stress, strain, and fabric in granular materials

Effect of inter-particle friction on 3D accordance of stress, strain, and fabric in granular materials

On the role of energy dissipation in a dynamically structured fluidized bed

This work explores the effect of interparticle friction on the stability of a structured bubble flow in gas–solid fluidized beds. We provide a detailed quantification of the evolution of bubble properties at varying frequency, comparing experiments with CFD-DEM (computational fluid dynamics – discrete element modeling) simulations. Friction plays a key role. It creates intermittent solid-like regions that restrict the mobility of solids and endow the flow with enough memory to correlate consecutive nucleation events. As friction decreases, solid-like regions widen, allowing the circulation of solids; simultaneously, bubbles grow, move apart and ultimately break up the structure. CFD-DEM reproduces this phenomenon well in a small bed, but shows qualitative differences in bubble shape and acceleration. These deviations propagate into substantial errors at higher frequency or larger domains displaying multiple bubble rows, which stresses the need for further research to understand the effects of other particle properties, polydispersity and the domain size.

Frictional granular flows of rod and disk mixtures with particle shape distributions

Three-dimensional simulations of polydisperse shear flows of rod and disk mixtures are performed using the discrete element method. The effects of particle shape distribution on flow behaviors are investigated assuming that all particles have the same volume and density but different shapes in the simulations. The solid phase stresses and bulk friction coefficients show a strong dependence on the particle alignment and the structural anisotropy of interparticle contacts. The combined effects of interparticle friction and particle shape difference lead to larger stresses for mixtures of different particle shapes than the pure particle species in dense shear flows. For frictionless and frictional flows with particle shape distributions, it is observed that the particle fluctuating velocities follow non-Maxwellian distributions and the fluctuating kinetic energies are unequally partitioned among the different particle species.

Effects of interparticle friction on the response of 3D cyclically compressed granular material

We numerically study the effect of inter-particle friction coefficient on the response to cyclical pure shear of spherical particles in three dimensions. We focus on the rotations and translations of grains and look at the spatial distribution of these displacements as well as their probability distribution functions. We find that with increasing friction, the shear band becomes thinner and more pronounced. At low friction, the amplitude of particle rotations is homogeneously distributed in the system and is therefore mostly independent from both the affine and non-affine particle translations. In contrast, at high friction, the rotations are strongly localized in the shear zone. This work shows the importance of studying the effects of inter-particle friction on the response of granular materials to cyclic forcing, both for a better understanding of how rotations correlate to translations in sheared granular systems, and due to the relevance of cyclic forcing for most real-world applications in planetary science and industry.

Improving the accuracy of two-fluid sub-grid modeling of dense gas-solid fluidized flows

In gas-solid fluidization highly resolved simulations (HRS) with microscopic two-fluid modeling (mTFM) are frequently employed for deriving sub-grid closures for filtered parameters that are required in filtered formulations useful in large scale simulations of real flows. This work intends to contribute for improving the accuracy of underlying HRS raw data upon which the accuracy of sub-grid closures relies on, particularly regarding dense gas-solid fluidized flows. The accuracy of mTFM is improved by incorporating interparticle frictional effects. The accuracy of correlation to filtered parameters is improved by accounting for macro-scale conditions and by enforcing a three-independent variable approach. HRS were performed in a periodic domain applying the mTFM of MFIX properly modified by the inclusion of a literature trustworthy interparticle friction model. Results showed that accounting for macro-scale conditions and for three independent variables considerably contributes for improving correlation resolution, while the effect of interparticle friction was only marginal.

Inter-particle friction and particle sphericity effects on isotropic compression behavior in real-shaped sand assemblies

A numerical investigation on the effects of inter-particle friction and particle sphericity on isotropic compression in real-shaped sand assemblies is carried out using the discrete element method. Real-shaped sand assemblies are generated in terms of the cumulative distribution of the shape descriptor (sphericity) of real sand particles. The mechanical behaviors of compression are quantified in terms of the volumetric deformation, coordination number, probability distribution of the contact forces, and fabric. The results show that the compression deformation becomes larger with decreasing inter-particle friction, especially for an assembly with frictionless particles. The probability distribution of the coordination number is almost described by a Gaussian distribution, which is somewhat different from that of the monodisperse particles reported in previous studies. Moreover, the inter-particle friction and sphericity have an insignificant effect on the probability distribution of the normalized contact forces, which exhibit a clear exponential decay. Assemblies with lower inter-particle friction and lower sphericity experience greater friction mobilization during compression. The results of the anisotropy of the contact normal force show that all the samples are strongly homogeneous and isotropic, and inter-particle friction and sphericity have substantial effects on the magnitude of the normal contact force.

A rheology-based quasi-static shape retention model for digitally fabricated concrete

The shape retention capability of an extruded filament is of cardinal importance for quality 3D printed concrete elements. Not only is it a prerequisite for surface aesthetics, but it also contributes towards buildability. Optimisation of filament layer height allows for construction time and cost saving possibilities. This research develops the theoretical framework for an analytical shape retention model that predicts the maximum stable filament layer height at which no plastic yielding occurs, based only on the rheology of a material. The Mohr-Coulomb failure criterion is employed and the model simplified by conservatively negating the effect of interparticle friction. A model is also developed that determines whether sufficient friction is present to induce confinement within a filament layer. An experimental verification process via filament extrusion confirms the applicability of the model. A 6.7% difference in stable filament layer height is obtained by comparison with a finite element analysis, proffering as numerical verification for the model.

New insights into the effect of interparticle friction on the critical state friction angle of granular materials

This letter examines the effect of interparticle friction (μ) on the critical state friction angle (φcs) of granular materials via the discrete element method. A series of drained triaxial tests are conducted on multisphere ellipsoids. The results indicate that φcs first increases with μ and then reaches a plateau when μ ≥ 0.3. Anisotropic analysis provides new insights into the underlying mechanisms of the φcs evolution from two perspectives. First, the initial increase of φcs results from the increases of contact normal anisotropy ac, normal contact force anisotropy an and tangential contact force anisotropy at; subsequently, the saturation of φcs is a consequence of the decrease of an being compensated by the increase of at. Second, the relationship between the stress ratio q/p and the contact normal anisotropy within the strong and nonsliding contacts acsn is nearly linear for ellipsoids (i.e., q/p = kacsn). Accordingly, the initial increase of φcs is related to the increase of k and acsn at low μ. The plateau of φcs at high μ can be attributed to the decrease of acsn being compensated by the increase of k.

Effects of particle characteristics and consolidation pressure on the compaction of non-spherical particles

The mechanical strength of compacts depends on particle shape, materials properties as well as compaction conditions. This work presented a numerical study on the effects of interparticle friction, yield pressure of particles and consolidation pressure on the mechanical response of compacts formed of non-spherical particles. Non-convexity of the particle shape and interparticle bonding were explicitly considered in a model based on the Discrete Element Method (DEM). In unconfined uniaxial compression, the results showed that compressive strength of compacts increases with interparticle friction, consolidation pressure but decreases with yield pressure of particles. Larger inter-particle friction and consolidation pressure also lead to a more dispersed and uprising failure zones due to the inhomogeneous structure of compacts formed by die compaction. The non-convexity of particle and consolidation pressure enhanced the role of inter-particle friction in the compressive strength. However, failure mechanism during the unconfined compression showed no dependence on the particle characteristics and operational conditions as most of the bonds were broken by shearing. A large compressive strength was linked to an increased average bond size while a more dispersed bond failure corresponds to an increased proportion of horizontally aligned shear-induced bond failure.

Experimental Analysis of the Influence of Soil Composition on Strength Characteristics

This study investigates the influence of soil composition on soil strength by performing direct shear test on various samples, including artificial soil with different components, artificial mixed soil with different amounts, natural soil with different moisture contents, and sandy soil with different sizes. The test results show that soil strength is determined by the joint effect of inter-particle friction and cohesion. Mineral composition and water content are the main factors affecting clay strength. Changes in the mineral composition and water content of clay alter the contact state and connection of its particles, thereby significantly affecting the macroscopic properties of the soil. Different grain compositions modified the shear deformation characteristics by altering the arrangement and intergranular engagement of the particles, consequently affecting the strength. The results of this study provide further insight into the micro and fine mechanism of the soil shear strength characteristics of different components. This study also offers guiding significance in engineering practice.

Effect of Interparticle Friction on the Micromechanical Strength Characteristics of Three Dimensional Granular Media

The role of interparticle friction on the micromechanical strength characteristics of granular assembly subjected to gradual shearing was analyzed. Three dimensional discrete element method (DEM) was applied in the simulation of quasi-static shearing of granular assemblies with varying interparticle frictional coefficients [µ= 0.10, 0.25, 0.50]. From the reported simulation results, analysis of the following was performed for varying interparticle frictional capacities.i. The normal and tangential stress contributions of weak and strong contacts to principal stress components.ii. Contribution of strong and weak contacts to principal and deviator stress.iii. Evolution of mechanical coordination number and fabric anisotropy of strong contact forces.From this analysis, it is safe to conclude that interparticle friction has a direct effect on the major and minor principal stress components in sheared granular assemblies. Consequently, increasing interparticle friction capacity enhances macroscopic shear strength in sheared granular assemblies. Likewise, at the peak shear strength of the sheared granular media, there exists a maximum fabric anisotropy of strong contact forces and this corresponds to a minimum value of mechanical coordination number (minimum possible number of load bearing contacts per particle).

Observed Effects of Interparticle Friction and Particle Size on Shear Behavior of Granular Materials

AbstractThis paper presents an experimental study on the shear behavior of granular materials, focusing on the effects of interparticle friction and particle size, which are of fundamental importance but are not yet well understood. The experimental program consisted of a large number of direct shear tests on glass beads of varying sizes and interparticle friction conditions, performed under a range of packing densities and normal stress levels. Test data were interpreted in terms of the stress–dilatancy relationship and shear strength parameters. The study indicates that under otherwise similar testing conditions, oil-lubricated glass beads tend to have substantially lower shear strength as compared with water-lubricated, water-flooded, and dry glass beads. It has also been found that at similar particle size uniformity, increasing mean particle size (d50) leads to more dilatant shear response and higher shear strength. A generalized stress–dilatancy relation is proposed, which introduces a variable dila...

Microscopic contact model of lunar regolith for high efficiency discrete element analyses

The grains of lunar regolith are characterized with rough surfaces, angular shapes and mutual adhesions due to short-range interactions. These features control the macroscopic mechanical behavior of lunar regolith but have not been completely captured by contact models in previous Discrete Element Method (DEM) analyses. In this paper, a simplified two-dimensional microscopic contact model is proposed for high efficiency DEM analyses of lunar regolith. The model consists of three components in the normal, tangential and rolling directions respectively, plus two new parameters. A shape parameter is used to control the rolling resistance ability at the contact area between two particles to capture the features of grain shape and interlocking. The second parameter, micro-separation, which denotes the nominal minimum distance between the molecules of the two contacting particles, is introduced to account for van der Waals force as the major component of the short-range interactions that contribute to the adhesion of regolith grains in lunar environment conditions. The novel model has been implemented in a two-dimensional DEM code for numerical simulations of biaxial compression tests on lunar regolith. The effects of interparticle friction, grain shape, lunar environment conditions and void ratio on the strength of lunar regolith were numerically investigated. The results show that soils in the simulated lunar environment exhibit greater strength and more apparent strain-softening and shear dilatancy than on the Earth. The proposed model can capture the main features of the mechanical behavior of lunar regolith (apparent cohesion and high peak friction angle) and a wide range of strength indices can be obtained by the contact model.

A modified kinetic theory for frictional granular flows in dense and dilute regimes

Continuum modelingof granular and gas-solid flows generally involves the use of a kinetic-theory (KT) model for the particulate phase, and the most widely used KT models have been derived for dilute flows of smooth, frictionless spheres. In reality, however, granular particles are frictional and can achieve dense packing, and these features must be taken into account to improve rheological predictions in these flow scenarios. Existing approaches in the literature for producing closed-form KT-based models employ empirical modifications to adapt the original models for use in dense and frictional systems. In this article, we investigate the capacity for such modifications to improve the rheological predictions of the Garzó–Dufty (GD) KT model[V. Garzó and J. W. Dufty, “Dense fluid transport for inelastic hard spheres,” Phys. Rev. E59, 5895–5911 (1999)]10.1103/PhysRevE.59.5895. On the basis of molecular dynamics simulations of homogeneous, simple shear flows of soft, frictional spheres, we propose a new expression for the radial distribution function at contact as well as modifications to the GD expressions for shear stress and energy dissipation rate. These changes account for dense-regime scalings observed in inertial-number models as well as the effects of interparticle friction while preserving the dynamic nature of the KT model.

Effect of Interparticle Friction on the Cyclic Behavior of Granular Materials Using 2D DEM

This study presents the influence of the interparticle friction angle on the cyclic behavior of granular materials using the two-dimensional (2D) discrete-element method (DEM). The numerical sample was modeled with oval-shaped particles, whereas the isotropically compressed dense sample was prepared from the initial sparse sample using periodic boundaries. Biaxial cyclic shear tests were simulated with different interparticle friction angles. It was noted that the width of the stress-strain cyclic loops becomes thin when the interparticle friction angle increases. It was also noted that the induced fabric anisotropy is more pronounced during unloading than loading. Moreover, a strong correlation between macro- and microquantities was observed for strong contacts during cyclic loading.

The effects of air and particle density difference on segregation of powder mixtures during die filling

Segregation of mono-disperse binary mixtures with different particle densities during die filling in the presence of air was numerically analysed using a coupled discrete element method (DEM) and computational fluid dynamics (CFD) approach. Die filling with powders of different particle density ratios (i.e. the ratio of the heavy particles to the light particles) at various shoe speeds was simulated, in order to explore the effects of air and particle density difference on segregation. For die filling from a stationary shoe, the air can induce significant segregation by hindering the deposition of light particles (i.e., air-sensitive particles). As the particle density ratio increases, the light particles are deposited into the die at even lower speeds compared with the heavy ones due to the effect of air drag, resulting in an increase in the degree of segregation. For die filling with a moving shoe, segregation occurs due to different post-collisional velocities resulting from different particle inertia; and the degree of segregation increases as the particle density ratio increases due to the increasing difference in particle inertia. It is found that, as the shoe velocity increases, the powder flow pattern changes from nose flow dominated to bulk flow dominated and the degree of segregation generally decreases. The effect of air is limited for nose flow dominated die filling because the air can easily evacuate through the gap between the die walls and flowing powder stream. When bulk flow dominates in die filling, the air can be entrapped in the die, which has a significant impact on the powder flow and segregation behaviours. Finally, the effect of interparticle friction on segregation was investigated.

Shear strength of granular materials

ABSTRACT The shear strength properties of granular materials reflect their inherent force and fabric anisotropy. We analyze the role of fabric and force anisotropies with respect to the critical-state shear strength. Then, a model of accessible geometrical states in terms of particle connectivity and contact anisotropy is presented. This model incorporates in a simple way the fact that, due to steric exclusions, the highest levels of connectivity and anisotropy cannot be reached simultaneously, a property that affects seriously the shear strength. We also analyze the force anisotropy in the light of the specific role of weak forces in sustaining strong force chains and thus the main mechanism that underlies anisotropic force patterns. Finally, we briefly discuss the effect of interparticle friction, particle shape, and adhesion.

A study of compaction of composite particles by multi-particle finite element method

We study the compaction of composite mixture of soft and hard micro-/nano-size particles using multi-particle finite element method. In this method, each particle is fully discretized into finite element mesh. Local non-uniform contact deformation and non-uniformity stress chains transmitted through the composite are well illustrated. In this work, we focus on the effect of inter-particle friction and volume fraction of hard particles on compaction pressure. Results of closed die compaction of 400 two-dimensional monosize spherical particles of zero and 40% volume fraction hard particles are presented. The results show that compaction pressure increases with inter-particle friction and volume fraction of hard particles. The predicted compaction pressure curves are in good agreement with experimental data and other models.