THE+SMARTEST+MATERIALS

What is MR fluid?
=A **magnetorheological fluid** (MR fluid) is a type of [|smart fluid] in a carrier fluid, usually a type of oil. When subjected to a [|magnetic field], the fluid greatly increases its [|apparent viscosity], to the point of becoming a [|viscoelastic] solid. Importantly, the yield stress of the fluid when in its active ("on") state can be controlled very accurately by varying the magnetic field intensity. The upshot of this is that the fluid's ability to transmit force can be controlled with an [|electromagnet], which gives rise to its many possible control-based applications.=

MR fluid is different from a [|ferrofluid] which has smaller particles. MR fluid particles are primarily on the [|micrometre]-scale and are too [|dense] for [|Brownian Motion] to keep them suspended (in the lower density carrier fluid). [|Ferrofluid] particles are primarily [|nanoparticles] that are suspended by [|Brownian Motion] and generally will not settle under normal conditions. As a result, these two fluids have very different applications.

= How it works ? =

The magnetic particles, which are typically [|micrometer] or [|nanometer] scale spheres or ellipsoids, are suspended within the carrier oil are distributed randomly and in suspension under normal circumstances, as below.

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=﻿THE DESCRIPTION AND BEHAVIOUR OF THE MR FLUIDS := =﻿= fluids are such that they have a low viscosity in the absence of an applied magnetic field, but become quasi-solid with the application of such a field. In the case of MR fluids (and [|ER]), the fluid actually assumes properties comparable to a solid when in the activated ("on") state, up until a point of yield (the [|shear stress] above which shearing occurs). This yield stress (commonly referred to as apparent yield stress) is dependent on the magnetic field applied to the fluid, but will reach a maximum point after which increases in [|magnetic flux density] have no further effect, as the fluid is then magnetically saturated. The behavior of a MR fluid can thus be considered similar to a [|Bingham plastic], a material model which has been well-investigated. However, a MR fluid does not exactly follow the characteristics of a Bingham plastic. For example, below the yield stress (in the activated or "on" state), the fluid behaves as a [|viscoelastic] material, with a [|complex modulus] that is also known to be dependent on the magnetic field intensity. MR fluids are also known to be subject to [|shear thinning], whereby the viscosity above yield decreases with increased shear rate. Furthermore, the behavior of MR fluids when in the "off" state is also [|non-Newtonian] and temperature dependent, however it deviates little enough for the fluid to be ultimately considered as a Bingham plastic for a simple analysis. Thus our model of MR fluid behavior becomes: ==Where τ = shear stress; τ//y// = yield stress; //H// = Magnetic field intensity η = Newtonian viscosity; is the velocity gradient in the z==

APPLICATIONS OF THE MR :
o Vehicle Suspension Dampers o The MR damper has a built-in MR valve across which the MR fluid is forced. The piston of the MR damper acts as an electromagnet with the required number of coils to produce the appropriate magnetic field. Also the M R damper has a run-through shaft to avoid an accumulator. Modern dampeners are constructed with the Magnetorheological fluid which can change from liquid to solid with the application of a. The Magnetorheological fluid inside modern dampeners are kept solid in normal conditions, but change to liquid and back as sensors activate and deactivate a magnetic field during an earthquake, allowing the dampeners to absorb the shockwaves and reducing damage to the structure. The Magnetorheological fluid inside the dampeners changes a building from a rigid structure that must absorb the shockwaves to a &apos;smart&apos; structure which adapts instead SOME PHOTOS FOR THE MR FLUID:

[|www.youtube.com/watch?v=AeaAN8VF8wI]

=﻿piezo electric material :=

is the charge which accumulates in certain solid materials in response to applied mechanical.
 * Piezoelectric**

Discovery and early research
The first demonstration of the direct piezoelectric effect was in 1880 by the brothers piere and jacques.

the behaviour :
This material is affected from the electric field. It's volume change when it be in an electric field.

Applications :
the piezo electric materials is used in making sensors,piezo electric motors.

Photos and vidios for piezo electric materials :








[|www.youtube.com/watch?v=ozoLuPUuAMw]

-- =SHAPE MEMORY ALLOYS :=

This material is a kind of materials which has amemory of its first phase. This material is a lightweight, solid-state alternative to conventional actuators such as hydraulic, pneumatic, and motor-based systems.

Description and behaviour of the material :
When a shape-memory alloy is in its cold state (below //As//), the metal can be bent or stretched and will hold those shapes until heated above the transition temperature. Upon heating, the shape changes to its original. When the metal cools again it will remain in the hot shape, until deformed again. With the one-way effect, cooling from high temperatures does not cause a macroscopic shape change. A deformation is necessary to create the low-temperature shape. On heating, transformation starts at //As// and is completed at //Af// (typically 2 to 20 °C or hotter, depending on the alloy or the loading conditions). //As// is determined by the alloy type and composition and can vary between −150 °C and 200 °C. The two-way shape-memory effect is the effect that the material remembers two different shapes: one at low temperatures, and one at the high-temperature shape. A material that shows a shape-memory effect during both heating and cooling is called two-way shape memory. This can also be obtained without the application of an external force (intrinsic two-way effect). The reason the material behaves so differently in these situations lies in training. Training implies that a shape memory can "learn" to behave in a certain way. Under normal circumstances, a shape-memory alloy "remembers" its high-temperature shape, but upon heating to recover the high-temperature shape, immediately "forgets" the low-temperature shape. However, it can be "trained" to "remember" to leave some reminders of the deformed low-temperature condition in the high-temperature phases. There are several ways of doing this.[|[][|4][|]] A shaped, trained object heated beyond a certain point will lose the two-way memory effect, this is known as "amnesia.

Applications by this material :
The shape memory alloys is used in making :
 * aircrafts
 * telecommunications
 * piping
 * robotics
 * automotives

Some photos and vidios for shape memory alloys :




[|www.youtube.com/watch?v=fsBHF_j2FJ4] [|www.youtube.com/watch?v=QYp9rIJRM8s]