@misc{10481/41977,
year = {2016},
url = {http://hdl.handle.net/10481/41977},
abstract = {Generally speaking, conventional magnetorheological fluids are colloidal
suspensions of ferromagnetic particles in a non-magnetic continuous
medium. Under the application of an external magnetic field, magnetic
particles align in its direction forming aggregates. The mechanical
properties of magnetorheological fluids under the presence of an external
magnetic field significantly change. In particular, if the particle
concentration and field strength is sufficiently large, it becomes necessary
to overcome a stress threshold, the so-called yield stress for the onset of
flow. Furthermore, under the presence of external fields
magnetorheological fluids become highly viscoelastic. The mechanical
properties of these materials can be easily and rapidly controlled by the
external magnetic field.
Due to their controllable mechanical properties, magnetorheological fluids
are currently used in several commercial applications concerning vibration
control, shock absorbers, precision polishing and even biomedical
applications. Currently, for their proper performance, commercial devices
require higher yield stresses in their operating modes and the use of highly
concentrated magnetorheological fluids.
A careful study of the rheological behavior of these systems under
compression can be of great utility since it has been shown that the yield
stresses under compression are higher than the yield stresses under shear
flow mode at the same concentration. An extensive investigation of the
magnetorheological properties under compression has been carried out in
this dissertation from an experimental point of view, using theoretical developments and performing particle-level simulations. Experimental
results showed that both the normal force and the compressive stress
increase during the compression test. The dependence with the magnetic
field strength was quadratic. The normal force and the yield compressive
stress depend linearly on the particle volume fraction in the dilute case
and quadratic in the concentrated regime.
Due to fact that the magnetic particles employed in the formulation of
commercial magnetorheological fluids are typically polydisperse in size,
the investigation of the effect of polydispersity in the MR performance is
also of interest. Experiments and particle-level simulations were done on
particle size distributions having the same average diameters but different
polydispersity indexes. The results showed that although the microscopic
structure of magnetorheological fluids profoundly changes with the
polydispersity, overall, the yield stress does not significantly changes in
polydisperse systems.},
organization = {Tesis Univ. Granada. Programa Oficial de Doctorado en: Física y Ciencias del Espacio},
organization = {Ministerio de Educación por la ayuda FPU
(AP2010-2144), proyecto del Ministerio de Investigación,
Ciencia e Innovación, MAT 2010-15101; proyecto del Ministerio
de Economía y Competitividad, MAT 2013-44429-R; y a los
proyectos de la Junta de Andalucía P10-RNM-6630, P10-FQM-
5977 y P11-FQM-7074.},
publisher = {Universidad de Granada},
keywords = {Física},
keywords = {Fluidos magnéticos},
keywords = {Reología},
keywords = {Polímeros},
keywords = {Dispersión},
keywords = {Compactación},
title = {Squeeze flow and polydispersity effects in magnetorheology},
author = {Ruiz López, José Antonio},
}