Rheology of magnetofluidized fine powders: The role of interparticle contact forces

2010 ◽  
Vol 54 (4) ◽  
pp. 719-740 ◽  
Author(s):  
M. J. Espin ◽  
J. M. Valverde ◽  
M. A. S. Quintanilla ◽  
A. Castellanos
2020 ◽  
pp. 51-54
Author(s):  
M. A. S. Quintanilla ◽  
A. Castellanos ◽  
J. M. Valverde

2001 ◽  
Vol 64 (3) ◽  
Author(s):  
M. A. S. Quintanilla ◽  
A. Castellanos ◽  
J. M. Valverde

Author(s):  
Lorenzo Garavaglia ◽  
Elena Beretta ◽  
Sandra Strazzer ◽  
Felice Sala ◽  
Morena Delle Fave ◽  
...  

Neuromuscular diseases as a consequence of brain damage are complex phenomena involving disuse, immobility, brain tissue remodeling and cortical function remapping. They may have various causes and strike any part of the population. The vicious circle leading to a worsening of the patients’ conditions proceeds through muscle shortening by contractures, disruption of the normal reflex behavior and sensory problems, development of spasticity [1]. Physical rehabilitation alone or in association with surgery or pharmacological treatments can be useful in limiting those degenerations. Besides manual rehabilitation, splints and braces are prescribed to control the limb posture and obtain stretching of the muscles. The role of those orthoses is to maintain the paretic limb in a set ‘physiological’ position and let it relax into that posture, in an attempt to reduce muscle rigidity and contractures. However applying a fixed constraint to the limb and waiting for relaxation to take place, may cause discomfort, pain, skin rash, and sundry different complications [2]. Also, any residual voluntary movement is prevented by a fixed-angle splinting. In addition, all these negative characteristics limit tolerability and daily application times. This work presents a different way to promote limb repositioning, based on the application of NiTi-alloy-based dynamic splints, which favor mobility and any residual use of the affected limb. Furthermore it suggests that application of mild contact forces prolonged in time has the advantage of feeling less painful and uncomfortable for the patients, improving overall treatment tolerability.


1997 ◽  
Vol 9 (1) ◽  
pp. 65-70 ◽  
Author(s):  
Yoji Yamada ◽  

This paper describes, with reference to related studies, a human-oriented design approach to developing a safe robot system for human-robot coexistence. First, a soft covering made of a visco-elastic material is designed to achieve both effective impact force attenuation and high contact sensitivity within a human pain tolerance limit. Second, a fail-safe robot system is constructed with contact sensing and subsequent emergency stop control capabilities, primarily by using a simple disturbance observer which plays an important role of checking the normal operation of a two-link DD-motor-driven manipulator. Actual human-robot collision experiments verified that the contact forces generated at the collisions were suppressed below the human pain tolerance limit. Moreover, an additional robot speed reduction mechanism was provided to show that the human reflexive motions to avoid a severe contact with the robot within a safeguarding space contribute to enhancing the efficiency of the system to the point of reducing the speed of the robot in a safe manner when the robot comes in contact with the human.


2021 ◽  
Vol 88 (6) ◽  
Author(s):  
Alejandro Roda-Buch ◽  
Valentine A. M. Magnin ◽  
Sandra Guadalupe Maldonado ◽  
Stefano Mischler

Abstract The lubrication regimes of a contact pair escapement-ruby pallet of a Swiss lever escapement have been investigated combining the theory of fluid lubrication with a well-established kinematic and inverse dynamic multibody model. The kinematic analytical results have been confronted with experimental measurements. The developed model allows to easily obtain, for the three operating phases of the Swiss lever escapement, the relative speed and the contact forces and, by considering a hydrodynamic lubrication regime, the lubricant minimum film thickness and the coefficient of friction. The presented formulation allows to study the influence of crucial technical parameters in the Swiss lever escapement lubrication. The spout radii of curvature have been identified as the optimal parameters to control the lubrication regimes in the pallet/escapement contacts. In that sense, an interesting result is that the lubrication regime moves away from the boundary lubrication by increasing these radii.


2006 ◽  
Vol 43 (2) ◽  
pp. 155-168 ◽  
Author(s):  
S H Liu

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 stress–dilatancy 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, stress–dilatancy.


2006 ◽  
Vol 128 (4) ◽  
pp. 828-840 ◽  
Author(s):  
M. Benedetti ◽  
D. Bortoluzzi ◽  
M. Da Lio ◽  
V. Fontanari

The theoretical background and the numerical modeling results of a ground-based verification activity of a critical space mission phase affected by adhesion issues are presented. Tribological models are first reviewed with an emphasis on the contact forces assessment and their relationship to the geometrical, material, and mechanical properties of the contacting metal bodies. An approach based on a finite element analysis of the contact, accounting for the adhesion forces, is then proposed for studying the contact behavior of smooth surfaces in vacuum. Some solutions aimed at reducing adhesion pull-off forces are discussed. Special emphasis is placed on the role of surface roughness in reducing adhesion. To this purpose, a fractal surface theory is used to estimate interaction forces. The obtained results are applied to discuss the role of adhesion on the release of a test mass under zero gravity as well as to suggest an appropriate detachment procedure that finds a specific application in a scientific space mission.


2020 ◽  
Vol 52 (1) ◽  
pp. 121-144 ◽  
Author(s):  
Jeffrey F. Morris

Shear thickening is the increase of the apparent viscosity as shear rate or shear stress increases. This phenomenon is pronounced in concentrated (dense) suspensions of both colloidal-scale and larger particles, with an abrupt form, known as discontinuous shear thickening, observed as the maximum flowable solid fraction is approached. An overview of observed shear thickening behavior is presented, with a discussion of present understanding of the relationship of suspension shear thickening to granular jamming. Mechanistic arguments for the extreme change in rheological properties are outlined, and recent evidence from experiment and simulation for the role of contact forces is presented. Interactions of particles by fluid mechanical lubrication, contact, and steric and electrostatic forces, together with extreme stresses that may lead to solid deformation, require consideration of surface interactions and their tribological consequences in describing shear thickening.


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