Interparticle contact forces in fine cohesive powders. Theory and experiments

AbstractTheory and experiments indicate that ice–bed separation during glacier slip over 2-D hard beds causes basal shear stress to reach a maximum at a particular slip velocity and decrease at higher velocities. We use the sliding theory of Lliboutry (1968) to explore how friction between debris particles in sliding ice and a rock bed affects this relationship between shear stress and slip velocity. Particle–bed contact forces and associated debris friction increase with increasing slip velocity, owing to increased rates of ice convergence with up-glacier facing surfaces. However, debris friction on diminished areas of the bed counteracts this effect as cavities grow. Thus, friction from debris alone increases only slightly with slip velocity, and for sediment particles larger than ~60 mm in diameter, debris friction peaks and decreases with increasing slip velocity. The effect on the sliding relationship is to steepen its rising limb and shift its shear stress peak to a slightly higher velocity. These results, which exclude the effect of debris friction on cavity size and debris concentrations above ~15%, indicate that the effect of debris in ice is to increase basal shear stress but not significantly change the form of the sliding relationship.

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Simulating a direct shear box test by DEM

Canadian Geotechnical Journal ◽

10.1139/t05-097 ◽

2006 ◽

Vol 43 (2) ◽

pp. 155-168 ◽

Cited By ~ 44

Author(s):

S H Liu

Keyword(s):

Contact Angle ◽

Internal Friction ◽

Granular Material ◽

Distinct Element ◽

Contact Forces ◽

Interparticle Contact ◽

Direct Shear ◽

Angle Of Internal Friction ◽

Shear Box ◽

Direct Shear Box Test

Distinct element simulation was performed for direct shear box (DSB) tests on a dense and a loose two-dimensional (2D) sample of 3259 cylinders. Special attention was devoted to the effect that the frictional force between the inside surface of the upper shear box and the sample had on the measured shear strength in the DSB test. Some ways of minimizing this interface frictional force were introduced in the paper. Given that the deformation approximates simple shear within the deforming zone across the sample centre (referred to as the shear zone), a method was proposed to evaluate the overall strains in the DSB test. The numerically simulated data were used to interpret, on a microscopic scale, the angle of internal friction and a 2D stressdilatancy equation for the mobilized plane in granular material. It was found that the angle of internal friction in granular material is not directly related to the interparticle friction angle (ϕµ). Instead, it relates to the average interparticle contact angle ([Formula: see text]) on the mobilized plane and the ratio k/f0, representing the degree of the probability distribution of the interparticle contact forces that is biased toward the positive zone of the contact angle θ (along the shear direction), where k is the slope of the linear distribution of the average interparticle contact forces against the interparticle contact angle; and f0 is the average interparticle contact force.Key words: angle of internal friction, direct shear box test, distinct element method, friction, granular material, stressdilatancy.

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A Biarticulated Robotic Leg for Jumping Movements: Theory and Experiments

Journal of Mechanisms and Robotics ◽

10.1115/1.2963028 ◽

2008 ◽

Vol 1 (1) ◽

Cited By ~ 21

Author(s):

J. Babič ◽

Bokman Lim ◽

D. Omrčen ◽

J. Lenarčič ◽

F. C. Park

Keyword(s):

Numerical Optimization ◽

Frictional Contact ◽

Complex Dynamics ◽

Contact Forces ◽

Jump Performance ◽

Biarticular Muscles ◽

Vertical Jumping ◽

Redundantly Actuated ◽

Robotic Leg ◽

Theory And Experiments

This paper investigates the extent to which biarticular actuation mechanisms—spring-driven redundant actuation schemes that extend over two joints, similar in function to biarticular muscles found in legged animals—improve the performance of jumping and other fast explosive robot movements. Robust numerical optimization algorithms that take into account the complex dynamics of both the redundantly actuated system and frictional contact forces are developed. We then quantitatively evaluate the gains in vertical jumping vis-à-vis monoarticular and biarticular joint actuation schemes and examine the effects of spring stiffness and activation angle on overall jump performance. Both numerical simulations and experiments with a hardware prototype of a biarticular legged robot are reported.

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CORRELATION BETWEEN MICROSTRUCTURE AND YIELD STRESS IN MAGNETICALLY STABILIZED FLUIDIZED BEDS

Journal of Multiscale Modelling ◽

10.1142/s1756973710000400 ◽

2010 ◽

Vol 02 (03n04) ◽

pp. 185-198

Author(s):

J. M. VALVERDE ◽

M. J. ESPIN ◽

M. A. S. QUINTANILLA ◽

A. CASTELLANOS

Keyword(s):

Magnetic Field ◽

Tensile Strength ◽

Gas Flow ◽

Fine Particles ◽

Contact Forces ◽

Interparticle Contact ◽

Gas Velocity ◽

Jamming Transition ◽

Interparticle Contacts ◽

Different Response

A magnetofluidized bed consists of a bed of magnetizable particles subjected to a gas flow in the presence of an externally applied magnetic field. In the absence of magnetic field, there is a given gas velocity at which naturally cohesive fine particles can form a network of permanent interparticle contacts capable of sustaining small stresses. This gas velocity marks the jamming transition of the fluidized bed. For gas velocities above the jamming transition, the bed resembles a liquid. Below the jamming transition, the bed behaves as a weak solid and it has a nonvanishing tensile strength. In the absence of magnetic field, the tensile strength of the solidlike stabilized bed has its only origin in nonmagnetic attractive forces acting between particles. In the presence of a magnetic field, the gas velocity at the jamming transition and the tensile strength of the bed depend on the field strength as a consequence of the magnetostatic attraction induced between the magnetized particles. In this work we present experimental measurements on the jamming transition and tensile strength of magnetofluidized beds of linearly magnetizable fine powders. It is shown that powders with similar magnetic susceptibility but different strength of the nonmagnetic forces show a different response to the magnetic field. This finding can be explained by the influence of the nonmagnetic natural forces on the network of contacts. Thus, our experimental results reported in this paper reinforce the role of short-ranged interparticle contact forces on the behavior of the system, which contrasts with the usual modeling approach in which the magnetofluidized bed is viewed as a continuum medium and a fundamental assumption is that the fields can be averaged over large distances as compared with particle size.

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Correlation between bulk and interparticle contact forces for fine powders

Powders and Grains 2001 ◽

10.1201/9781003077497-15 ◽

2020 ◽

pp. 51-54

Author(s):

M. A. S. Quintanilla ◽

A. Castellanos ◽

J. M. Valverde

Keyword(s):

Contact Forces ◽

Interparticle Contact ◽

Fine Powders

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Correlation between bulk stresses and interparticle contact forces in fine powders

Physical Review E ◽

10.1103/physreve.64.031301 ◽

2001 ◽

Vol 64 (3) ◽

Cited By ~ 56

Author(s):

M. A. S. Quintanilla ◽

A. Castellanos ◽

J. M. Valverde

Keyword(s):

Contact Forces ◽

Interparticle Contact ◽

Fine Powders

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A Computational Mechatronics Approach for the Analysis, Synthesis and Design of a Simple Active Biped Robot: Theory and Experiments

Applied Bionics and Biomechanics ◽

10.1155/2006/289145 ◽

2006 ◽

Vol 3 (2) ◽

pp. 121-130

Author(s):

L.-I. Lugo-Villeda ◽

V. Parra-Vega

Keyword(s):

Biped Robot ◽

Contact Forces ◽

Human Beings ◽

Biped Walking ◽

Modeling And Control ◽

Complex Process ◽

Three Degree Of Freedom ◽

And Control ◽

Support Leg ◽

Theory And Experiments

Biped walking is a quite complex process that has been mastered only by human beings. Transferring this skill to a robot requires implementing advanced techniques in every aspect. To this end, a computational mechatronics platform was integrated to run the scheme for the analysis, synthesis and design to achieve planar biped walking. The result is an advanced computational tool that integrates advanced modeling and control as well as path planning techniques along with hardware-in-the-loop for perhaps the simplest biped robot. An experimental underactuated three-degree-of-freedom (two active and one passive) active biped robot yields encouraging results; that is, achieving biped walking with this simple device requires adding a telescopic support leg. Considering a more complete dynamic model to take into account frictional and contact forces.

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Simultaneous Prey Encounters by Optimally Foraging Predators: Theory and Experiments

Comments® on Theoretical Biology ◽

10.1080/08948550302441 ◽

2003 ◽

Vol 8 (1) ◽

pp. 1-36 ◽

Cited By ~ 14

Author(s):

Ludeˇk Berec

Keyword(s):

Theory And Experiments

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Modeling of Tread Block Contact Mechanics Using Linear Viscoelastic Theory3

Tire Science and Technology ◽

10.2346/1.2965832 ◽

2008 ◽

Vol 36 (3) ◽

pp. 211-226 ◽

Cited By ~ 9

Author(s):

F. Liu ◽

M. P. F. Sutcliffe ◽

W. R. Graham

Keyword(s):

High Speed ◽

Slip Rate ◽

Material Model ◽

Contact Forces ◽

Block Modeling ◽

Rate Dependent ◽

Linear Viscoelastic Material ◽

Linear Viscoelastic ◽

The Impact ◽

Good Agreement

Abstract In an effort to understand the dynamic hub forces on road vehicles, an advanced free-rolling tire-model is being developed in which the tread blocks and tire belt are modeled separately. This paper presents the interim results for the tread block modeling. The finite element code ABAQUS/Explicit is used to predict the contact forces on the tread blocks based on a linear viscoelastic material model. Special attention is paid to investigating the forces on the tread blocks during the impact and release motions. A pressure and slip-rate-dependent frictional law is applied in the analysis. A simplified numerical model is also proposed where the tread blocks are discretized into linear viscoelastic spring elements. The results from both models are validated via experiments in a high-speed rolling test rig and found to be in good agreement.

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