Proceedings Article | 18 April 2007
KEYWORDS: Magnetorheological finishing, Foam, Actuators, Magnetism, Iron, Particles, Polymers, Prototyping, Lymphatic system, Composites
Magneto-rheological fluid (MRF) was first developed in the late 1940s. MRF consists of iron or other ferrous particles,
typically on the order of 1 - 10 μm characteristic dimension, dispersed in a host carrier fluid, usually oil or water. In the
presence of a magnetic field, the alignment of the iron particles along field lines results in the effective rheological
properties of the composite fluid to be modified. In the "off" state (no field applied), the fluid has similar viscous
properties to the host fluid. In the "on" state (field applied), the viscosity and yield stress can be significantly modified.
Recently, MRF has been of interest in a number of novel devices, for example, for variable damping such as in
automotive shock absorbers. In the present work, we briefly describe our initial investigations into variable damping
MRF/foam devices. Open-cell polymer foam blocks were infused with commercial MRF and subjected to magnetic
fields of various strengths. Drop tests were conducted by dropping a small indenter from a fixed platform and
observing the rebound height as a function of applied field strength. The difference in rebound height can be directly
related to loss of energy through damping. In the tests conducted, the energy absorbed by the MRF/foam increased
from about 60% in the off-state device to over 90% in the on-state device. One of the difficulties encountered in
performing the drop tests and providing credible data interpretation was that the MRF/foam itself changed dimensions
under applied field. The iron particles in the fluid were attracted to the magnet and thus caused constriction of the foam
block.
Peristalsis is the process of involuntary and successive wave-like muscular contractions by which food is moved
through the digestive tract. The esophagus, stomach, and intestines all move and/or mix food and liquid by peristalsis.
Peristalsis is also used to move lymph through the lymphatic system. Inspired by biological peristalsis, peristaltic
pumps in industry are common for a variety of material handling applications, particularly involving the movement of
sterile fluids (for example, blood). The peristaltic pump is usually circular in configuration, relying on external rollers
to move fluid within a tube. Some linear configuration pumps have been proposed and developed, however they are
complicated than their circular counterparts.
In the remaining part of the present work, we discuss the development of a linear peristaltic actuator based upon the
deformation of MRF/foam. The actuator consists of an open-cell polymer foam substrate infused with MRF. To one
side of the foam substrate resides a translating magnet, such that a magnetic field can be propagated down its length.
The linear peristaltic action is generated as the transversely propagating field shapes the MRF/foam substrate in a
corresponding way. Experimental results are discussed, an outline of on-going theoretical modeling is presented, and
conclusions are provided.
