Effects of Contact Force Model and Size Distribution on Microsized Granular Packing

2014 ◽  
Vol 136 (2) ◽  
Author(s):  
Xin Dou ◽  
Yijin Mao ◽  
Yuwen Zhang
Keyword(s):  
Particle Size ◽  
Contact Force ◽  
Van Der Waals ◽  
Van Der Waals Force ◽  
Particle Packing ◽  
Force Model ◽  
Size Distributions ◽  
Structure Variation ◽  
Packing Structure ◽  
Granular Packing

Granular packing of microsized particles with different size distributions and contact force models is studied using discrete element method (DEM). Three kinds of size distributions, monosized, uniform, and Gaussian, with mean diameter of 50, 60, and 70 μm are studied. Two aspects of microscale particle packing issues are addressed: one is the importance of van der Waals force when the particle size approaching to microscale, the other one is the structure variation caused by different contact force models. The results indicate that compared with contact force, the van der Waals force contributes very insignificantly to the final packing structure. The packing structures obtained using two different force models are similar to each other. The effects of particle size and its distribution on the packing structure are more significant than the force model.

scholarly journals Analysis of Cohesive Microsized Particle Packing Structure Using History-Dependent Contact Models

2015 ◽  
Vol 138 (4) ◽  
Author(s):  
Raihan Tayeb ◽  
Xin Dou ◽  
Yijin Mao ◽  
Yuwen Zhang
Keyword(s):  
Particle Size ◽  
Coordination Number ◽  
Gaussian Distribution ◽  
Packing Density ◽  
Mean Value ◽  
Distribution Functions ◽  
Particle Packing ◽  
Size Distributions ◽  
Packing Structure ◽  
Contact Models

Granular packing structures of cohesive microsized particles with different sizes and size distributions, including monosized, uniform, and Gaussian distribution, are investigated by using two different history dependent contact models with discrete element method (DEM). The simulation is carried out in the framework of liggghts, which is a DEM simulation package extended based on branch of granular package of widely used open-source code LAMMPS. Contact force caused by translation and rotation, frictional and damping forces due to collision with other particles or container boundaries, cohesive force, van der Waals force, and gravity is considered. The radial distribution functions (RDFs), force distributions, porosities, and coordination numbers under cohesive and noncohesive conditions are reported. The results indicate that particle size and size distributions have great influences on the packing density for particle packing under cohesive effect: particles with Gaussian distribution have the lowest packing density, followed by the particles with uniform distribution; the particles with monosized distribution have the highest packing density. It is also found that cohesive effect to the system does not significantly affect the coordination number that mainly depends on the particle size and size distribution. Although the magnitude of net force distribution is different, the results for porosity, coordination number, and mean value of magnitude of net force do not vary significantly between the two contact models.

Textural and Acidic Properties of Mixed Alumina-Silica Oxides Prepared with Commercially Available Sols

1997 ◽  
Vol 497 ◽  
Author(s):  
Steven J. Monaco ◽  
Edmond I. Ko
Keyword(s):  
Particle Size ◽  
Mixed Oxides ◽  
Building Blocks ◽  
Particle Packing ◽  
Atomic Scale ◽  
Size Distributions ◽  
Particle Size Distributions ◽  
Acidic Properties ◽  
Fixed Composition ◽  
Insight Into

ABSTRACTIn this study we have used commercially available preformed sols as building blocks to systematically explore the effects of composition, particle size, and packing on the textural and acidic properties of alumina-silica. We have prepared single oxides and alumina-silica mixed oxides with varying Al:Si atomic ratios using commercial sols from Vista Chemical Co. (alumina) and Eka Chemicals, Inc. (silica). Simple particle packing models based on the structure and experimentally determined particle size distributions of the sols explain the textural and acidic properties of both the single and mixed oxides. Comparisons with aerogels prepared from alkoxides show that materials with different atomic-scale homogeneity can be obtained. This continuum of precursor sizes from monomer through colloid allows a measure of control over textural and acidic properties in the mixed oxides, even at a fixed composition. These results show that systematic studies using preformed sols add insight into the effect of preparation upon catalytic materials.

Analysis of Pressure Distribution on Head Disk Air Bearing Slider Involved Van der Waals Force

2013 ◽  
Vol 419 ◽  
pp. 111-116
Author(s):  
Hong Rui Ao ◽  
Ming Dong ◽  
Xi Chao Wang ◽  
Hong Yuan Jiang
Keyword(s):  
Pressure Distribution ◽  
Van Der Waals ◽  
Disk Drive ◽  
Van Der Waals Force ◽  
Flying Height ◽  
Force Model ◽  
Air Bearing ◽  
Analysis Process ◽  
Before And After ◽  
Bearing Force

This paper focuses on the pressure distribution on the surface of slider in hard disk drive when its flying height is in nanoscale. The gas rarefaction effect and van der Waals force are involved in the analysis process. Here the air bearing force model is based on F-K model and we establish the equation of van der Waals force between the head and disk. Using the finite element method, the modified Reynolds equation and the van der Waals force were obtained. The air bearing force on slider before and after the van der Waals force involved were compared. The results illustrate that the effect of van der Waals force on the air bearing force is different according to the slider shapes and flying heights. As a result, van der Waals force plays an important role when the flying height of slider is below 10 nm.

Measurement and Characterization of Stiction Force in Microstructures With Tapered Features

2011 ◽  
Author(s):  
Christopher Pelzmann ◽  
Laxman Saggere
Keyword(s):  
Plane Surface ◽  
Van Der Waals ◽  
Theoretical Models ◽  
Adhesive Force ◽  
Van Der Waals Force ◽  
Curved Surface ◽  
Force Model ◽  
Curved Surfaces ◽  
Surface Geometry ◽  
Adhesive Forces

Modeling and measurement of stiction or adhesion due to van der Waals force between microstructures and micro-gripper tools are important for contact-based manipulation and assembly of microstructures. Microfabricated structures commonly feature rough tapered curved surfaces due to undercutting and surface alterations inherent in the microfabrication processes. While several theoretical models exist for calculating adhesive forces between microstructures featuring spherical, cylindrical and flat surfaces, a model for estimating adhesive forces between microstructures featuring tapered curved surfaces is lacking in the literature. This paper presents experimentally measured values of adhesion or pull-off force between a rough tapered curved microstructure from a rough plane surface using a custom micro-cantilever beam as a force sensing mechanism. The paper also introduces an approach to estimate adhesive force between a tapered curved surface and a flat surface by considering the tapered curved surface as a frustum of a cone bound between two cylinders and using the van der Waals force model for cylinders. It is shown that the experimentally measured adhesive force values lie within the upper and lower values of the theoretically estimated van der Waals force values for the two cylinders that define the tapered curved surface geometry.

Processing of Optimized Cements and Concretes Via Particle Packing

MRS Bulletin ◽  
1993 ◽  
Vol 18 (3) ◽  
pp. 45-49 ◽  
Author(s):  
D.M. Roy ◽  
B.E. Scheetz ◽  
M.R. Silsbee
Keyword(s):  
Particle Size ◽  
Discrete Systems ◽  
Particle Packing ◽  
Particle Sizes ◽  
Size Distributions ◽  
Particle Size Distributions ◽  
Small Particles ◽  
Fresh Material ◽  
Simple Cubic ◽  
Packing Efficiency

It has been well-recognized for many years that the particle-size distributions of the cement and the grading of the aggregates play an important role in determining the properties and characteristics of cement and concrete products. DSP (densified with small particles) type cements and concretes, to a certain extent, MDF (macro-defect-free) cements, and optimized concretes are recently recognized outstanding examples of the application of this principle. The preset characteristics of the cementitious slurry are also strongly influenced by these factors. Both the workability of the fresh material, and the microstructure development are controlled to a considerable extent by these geometric parameters.Two seminal works in the areas of continuous particle size distributions and particle packing are those of Andreason and Furnas, respectively. Furnas deals mainly with discrete systems and Andreason with continuous distributions. As early as 1907, the concept of idealized particle packing was being used to optimize cements and concretes. Figure 1a shows an idealized cross section of a simple cubic packing of monodispersed spheres. This system has a maximum packing density of 0.65%. In an ideally packed system of discrete size ranges, the size of the next smallest particles would be such that they just fit in the gaps between the largest size particles, and so on for subsequent particle sizes; this system is represented schematically in Figure 1b. Not only the sizes but also the relative numbers of particles are important; Figures 1c and 1d show systems where some fraction of the smaller and larger particle sizes, respectively, are missing. Figure 1e shows a system where the size of the second largest particles is too large to fit into the gaps between the largest particles, resulting in a lower packing efficiency. Thus, both the particle size and fractions are important when considering packing efficiency.

Simulation of Random Packing of Spherical Particles With Different Size Distributions

2006 ◽  
Author(s):  
Yu Shi ◽  
Yuwen Zhang
Keyword(s):  
Particle Size ◽  
Size Distribution ◽  
Spherical Particles ◽  
Gravity Potential ◽  
Size Distributions ◽  
Packing Structure ◽  
Loose Packing ◽  
Packing Process ◽  
Physical Background

A numerical model for a loose packing process of spherical particles is presented. The simulation model starts with randomly choosing a sphere according to a pre-generated continuous particle-size distribution, and then dropping the sphere into a dimension-specified box, and obtaining its final position by using dropping and rolling rules which are derived from similar physical process of spheres dropping in the gravitational field to minimize its gravity potential. Effects of three different particle-size distributions on the packing structure were investigated. Analysis on the physical background of the powder-based manufacturing process is additionally applied to produce optimal packing parameters of bimodal and Gaussian distributions to improve the quality of the fabricated parts. The results showed that higher packing density can be obtained using bimodal size distribution with particle-size ratio from 1.5 to 2.0 and the mixture composition around n2:n1=6:4. For particle size with a Gaussian distribution, the particle radii should be limited in a narrow range around 0.67 to 1.5.

254. A Comparison of the Particle Size Distributions for Aerosols Generated During Wet Grinding and Dry Deburring of Beryllium

1999 ◽  
Author(s):  
K.K. Ellis ◽  
R. Buchan ◽  
M. Hoover ◽  
J. Martyny ◽  
B. Bucher-Bartleson ◽  
...  
Keyword(s):  
Particle Size ◽  
Size Distributions ◽  
Particle Size Distributions ◽  
Wet Grinding
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