smart+materials+-+ibrahim+ahmed

cairo universty aerospace department

 smart materials

by : Ibrahim ahmed salah submit to : d.Mohammed tawfee

smart materials

Smart materials are those that change in response to changing conditions in their surroundings or in the application of other directed influences - such as passing an electric charge through them. Modern products increasingly use them as imaginative designers see the potential they offer. Shirts that change colour with changes in temperature and thermometers that are in the from of printed strips use thermochromic inks whilst Photochromic inks respond to changes in light conditions. Clothing also uses inks that have this characteristic and have patterns that change with altering light conditions. Materials that respond to an electric current might be used as component parts of safety valves or as a part of a functional system that uses the change in shape with current to trigger some other process, These are 'shape memory alloys' (SMA)

Thermoelectric materials again use current but change temperature - in this way cooling or heating can take place and this effect is being used to design innovative.


 * =shape memory alloys=

with one of the most interesting areas being that of shape memory alloys. A shape memory alloy (SMA) can undergo substantial plastic deformation, and then be triggered into returning to its original shape by the application of heat. These properties have led to a proliferation of diverse applications in a variety of industries. From early applications such as greenhouse window openers in which an SMA actuator provided temperature-dependent ventilation, through to plastic-coated mobile phone antennas made from a super-elastic SMA capable of recovering its shape even after an extreme deformation such as dropping the phone, the list of applications has increased enormously throughout the 1990s. Medical applications of SMAs, using their superelastic and shape recovery properties, are particularly interesting and beneficial, and are growing rapidly.

Crystal structures
Many metals have several different crystal structures at the same composition, but most metals do not show this shape-memory effect. The special property that allows shape-memory alloys to revert to their original shape after heating is that their crystal transformation is fully reversible. In most crystal transformations, the atoms in the structure will travel through the metal by diffusion, changing the composition locally, even though the metal as a whole is made of the same atoms. A reversible transformation does not involve this diffusion of atoms, instead all the atoms shift at the same time to form a new structure, much in the way a parallelogram can be made out of a square by pushing on two opposing sides. At different temperatures, different structures are preferred and when the structure is cooled through the transition temperature, the martensitic structure forms from the austenitic phase.

Materials
Alloys of metals having the memory effect at different temperatures and at different percentages of its solid solution contents.
 * Ag-Cd 44/49 at.% Cd
 * Cu-Sn approx. 15 at.% Sn
 * Cu-Zn 38.5/41.5 wt.% Zn
 * Cu-Zn-X (X = Si, Al, Sn)
 * Pt alloys
 * Co-Ni-Al
 * Ni-Ti (~55% Ni)
 * Ni-Ti-Nb
 * Ni-Mn-Ga

Nitinol slug : It is the most famous slug in the industry. Nitinol is available in the form of wire, rod and bar stock, and thin film. Examples of SMA products developed by TiNi Alloy Company include silicon micro-machined gas flow microvalves, non-explosive release devices, tactile feedback device (skin stimulators), and aerospace latching mechanisms. If you are considering an application for shape memory alloys, TiNi Alloy Company can assist you in the design, prototyping, and manufacture of actuators and devices.

Properties of Nitinol Physical Properties of Nitinol • Density: 6.45gms/cc • Melting Temperature: 1240-1310° C • Resistivity (hi-temp state): 82 uohm-cm • Resistivity (lo-temp state): 76 uohm-cm • Thermal Conductivity: 0.1 W/cm-° C • Heat Capacity: 0.077 cal/gm-° C • Latent Heat: 5.78 cal/gm; 24.2 J/gm • Magnetic Susceptibility (hi-temp): 3.8 uemu/gm • Magnetic Susceptibility (lo-temp): 2.5 uemu/gm

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= **//__applications of Nitinlon:__//** =

Vena-cava Filters
Vena-cava filters have a relatively long record of successful in-vivo application. The filters are constructed from Ni-Ti wires and are used in one of the outer heart chambers to trap blood clots, which might be the cause of a fatality if allowed to travel freely around the blood circulation system. The specially designed filters trap these small clots, preventing them from entering the pulmonary system and causing a pulmonary embolism. The vena-cava filter is introduced in a compact cylindrical form about 2.0-2.5mm in diameter. When released it forms an umbrella shape. The construction is designed with a wire mesh spacing sufficiently small to trap clots. This is an example of the use of superelastic properties, although there are also some thermally actuated vena cava filters on the market.

Dental and Orthodontic Applications
Another commercially important application is the use of superelastic and thermal shape recovery alloys for orthodontic applications. Archwires made of stainless steel have been employed as a corrective measure for misaligned teeth for many years. Owing to the limited “stretch” and tensile properties of these wires, considerable forces are applied to teeth, which can cause a great deal of discomfort. When the teeth succumb to the corrective forces applied, the stainless steel wire has to be re-tensioned. Visits may be needed to the orthodontist for re-tensioning every three to four weeks in the initial stages of treatment. Superelastic wires are now used for these corrective measures. Owing to their elastic properties and extendibility, the level of discomfort can be reduced significantly as the SMA applies a continuous, gentle pressure over a longer period. Visits to the orthodontist are reduced to perhaps three or four per year. This continuous, gentle, corrective force illustrates the rather odd elastic properties of superelastic SMAs. A graph showing extension plotted against load produces a straight, horizontal line after initial loading. This shows the alloy to be non-Hookean, unlike carbon steel and other springs and constant forces can be derived from springs made of Ni-Ti alloy. Apart from the tensioned archwires, other superelastic orthodontic devices exist which can move teeth linearly where there is uneven tooth spacing. Movements of 6mm in 6 months are possible with minimum discomfort. Devices also exist that can apply torsional forces in the case of a “twisted” tooth. Orthodontists have modular kits, in which adhesively bonded brackets are attached to the teeth and the arch wire is then attached to and guided by the bracket. Other wire-forms can then be fitted to the brackets to push, pull, twist or force other movements that facilitate corrective measures for cosmetic or clinical reasons. Such dental SMA devices have proved very successful in trials and are being made commercially available in Europe. Other similar SMA devices are also being used for healing broken bones - staples of the shape memory materials are attached to each part of the bone, and these staples then apply a constant, well-defined force to pull the two pieces together as the SMA is warmed by the body and tries to return to its original configuration. This force helps knit the two pieces of bone back together. Such smart ‘healing’ powers are the reason why SMAs are being borne in mind for many applications in the medical, dentistry and other fields in the future.


 * = Piezoelectric =

Piezoelectric crystals are one of many small scale energy sources. Whenever piezoelectric crystals are mechanically deformed or subject to vibration they generate a small voltage, commonly know as piezoelectricity. This form of renewable energy is not ideally suited to an industrial situation. The ability of certain crystals to generate Piezoelectricity in response to applied mechanical stress is reversible in that piezoelectric crystals, when subjected to an externally applied voltage, can change shape by a small amount. This deformation, though only nanometers, has useful applications such as the production and detection of sound. Probably the best-known use of piezoelectric crystals is in the electric cigarette lighter. Here, pressing the button causes a spring-loaded hammer to hit a piezoelectric crystal, the high voltage produced by this ignites the gas as the current jumps over a small spark gap. This technique also applies to some gas lighters used on gas grills or stoves. Another common usage of a piezoelectric crystal energy source is that of creating a small motor; such as that used in a reflex camera to operate the auto focus system. These motors operate by vibration. The two surfaces are forced to vibrate at a phase shift of 90 degrees by a sine wave that has been generated at the motors resonant frequency. This forces a frictional force where the two surfaces meet and as one of the surfaces is fixed the other is forced to move. It has been found that piezoelectric crystals that have been embedded in the sole of a shoe can yield a small amount of energy with each step. This could be applied in a way that the power for instruments such as torches, cell phones or other entertainment devices can be sourced from the movement of the operator.

Piezoelectric generators work due to the piezoelectric effect. This is the ability of certain materials to create electrical potential when responding to mechanical changes. To put it more simply, when compressed or expanded or otherwise changing shape a piezoelectric material will output some voltage. This effect is also possible in reverse in the sense that putting a charge through the material will result in it changing shape or undergoing some mechanical stress. These materials are useful in a variety of ways. Certain piezoelectric materials can handle high voltage extremely well and are useful in transformers and other electrical components. It is also used to make motors, reduce vibrations in sensitive environments, and relevant to our interests it can be used as an energy collector. Let’s examine some of the ways it can be used for energy. Some of the most obvious applications of piezoelectric materials for energy collection are personal energy generators that are enough to power phones, MP3 players, etc. The sole of your shoe could be constructed of piezoelectric materials and every step you took would begin to generate electricity. This could then be stored in a battery or used immediately in personal electronics devices. One new idea that is gaining traction is to use the vibrations created by sound reverberating through piezoelectric materials to generate electricity. This means that while you’re driving your car listening to the radio, sitting outside in a park, or doing anything you could be converting sound to electricity. Have a look at this video showing the piezoelectric effect in action. When the board hits the material it outputs enough energy to power the lights for a moment.

Piezoelectricity has hopeful future as a personal electrical generator. A few companies have even produced and sold charging devices already. It won’t be long before your MP3 player charges itself from the noise in the room or your morning jog. Many devices and technologies already use piezoelectricity though. Having a solid material that can transform shape when it becomes electrically charged is quite useful. As is a material that can generate that same charge when mechanically altered. For example, on the right you can see a piece from an alarm that passed a charge through a piezoelectric material wrapped around a metal disk. This would allow for a buzzing sound when the charge was rapidly cycled. Piezoelectrical charges are a new technology but one that will surely be invaluable to us in the near future.

appelication

sensors. The principle of operation of a piezoelectric sensor is that a physical dimension, transformed into a force, acts on two opposing faces of the sensing element. Depending on the design of a sensor, different "modes" to load the piezoelectric element can be used: longitudinal, transversal and shear.

Detection of pressure variations in the form of sound is the most common sensor application, e.g. piezoelectric microphones (sound waves bend the piezoelectric material, creating a changing voltage) and piezoelectric pickups for Acoustic-electric guitars. A piezo sensor attached to the body of an instrument is known as a contact microphone.

Piezoelectric sensors especially are used with high frequency sound in ultrasonic transducers for medical imaging and also industrial nondestructive testing (NDT).

For many sensing techniques, the sensor can act as both a sensor and an actuator – often the term transducer is preferred when the device acts in this dual capacity, but most piezo devices have this property of reversibility whether it is used or not. Ultrasonic transducers, for example, can inject ultrasound waves into the body, receive the returned wave, and convert it to an electrical signal (a voltage). Most medical ultrasound transducers are piezoelectric.

piezo generator
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 * =Magnetorheological fluid=

Magnetorheological fluid or MR fluid is a special material used for building smart structures that can withstand earthquakes. The Magnetorheological fluid can change from liquid to solid and vice versa. It makes the buildings of which it is a component particularly flexible so they can adapt to external force that would have made other more rigid buildings snap.

The Need for Smart Structures
Traditional belief in structural engineering dictates that the more rigid a building is, the better it will be able to stand up to strong earthquakes and strong winds. As science and technology advanced, it was realized that this doctrine is not necessarily true. As a case in point, an earthquake does not do damage because it shakes the ground; destruction happens as a result of resonance or energy being released at frequencies that the structure is not equipped to handle. A rigid structure is more susceptible to damage because it does not 'adapt' to the forces exerted on it during earthquakes or high winds.

Smart Structures
The solution to this problem is the use of dampers or structures built to absorb the resonant waves (or 'shock waves') caused by earthquakes. Modern dampers adapt to the force of an earthquake, shifting with each shockwave to reduce the impact on the building's structure, in effect "dampening" the overall effect on the building.Modern dampeners are constructed with the Magnetorheological fluid which can change from liquid to solid with the application of a magnetic field. 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 'smart' structure which adapts instead.

Structures
The pulsed-field structure of an emulsion of monodisperse, magnetizable oil droplets is investigated via optical microscopy. By permitting droplet diffusion in the field-off state, a pulsed field allows minimization of energy through structural rearrangement. For droplets with a magnetic susceptibility of χ = 2.2 and radius //a// ≥ 0.32 μm, we find that rearrangement into ellipsoidal aggregates occurs in response to a pulsed magnetic field. The ellipsoid ends are composed of chainlike projections at low pulse frequencies and conical spikes at high pulse frequencies. The conical spikes appear to be energetically favored but cannot form at low pulse frequencies due to the large diffusion distance of the droplets in the field-off state. The eccentricity of the ellipsoids is invariant with field strength in strong fields, but in weak fields we find that the ellipsoids become more elongated as the field strength is lowered. This elongation in weak fields coincides with the formation of more dilute aggregates and gives information about the change in surface structure as field strength decreases.

Magnetorheological Fluid Components
Magnetorheological fluid is composed of three ingredients: carbonyl iron particles, 'soft' iron particles which are only 3-5 micrometers in diameter (or 0.0003 to 0.0005 millimeters); a 'carrier' liquid, usually hydrocarbon oil; and additives which enhance lubricity, modifies the fluid's thickness or viscosity, keeps the particles suspended in the liquid, and slows down the gravitational setting of the iron particles. The carbonyl iron particles provide the means for changing the fluid into solid; applying a magnetic field to the Magnetorheological fluid forces the particles to line up so the liquid becomes solid. The solidity of the fluid is influenced by the strength of the magnetic field – the stronger the field, the 'harder' the Magnetorheological fluid becomes. Removing the magnetic field unlocks the particles and turns the solid back to liquid. Magnetorheological fluid has been around since the 1940s. However, the technology that controls the magnetic field – required to adjust the Magnetorheological fluid's solidity to the level of force it is adapting to – has been developed only since the 1990s. Magnetorheological fluids are also being used in exercise machines, washing machines, car shock absorbers, and artificial legs..

simple MR fluid
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 * = Auxetic =

//that is Negative Poisson's ratio materials//
"Poisson's ratio, also called the Poisson coefficient, is the ratio of transverse contraction strain to longitudinal extension strain in a stretched bar. Since most common materials become thinner in cross section when stretched, Poisson's ratio for them is positive. The reason is that inter-atomic bonds realign with deformation. Stretching of normal honeycomb, shown on the right, illustrates the concept. Normal polymer foams or cellular solids, above left, have a positive Poisson's ratio.



Auxetics are materials that have a negative Poisson's ratio. When stretched, they become thicker perpendicular to the applied force. Auxetic materials can be created from particular structures of macroscopic matter. Such materials are expected to have mechanical properties such as high energy absorption and fracture resistance. Auxetics may be useful in applications such as body armor, packing material, knee and elbow pads, robust shock absorbing material, and sponge mops. The term auxetic derives from a Greek word which means "that which tends to increase", This terminology was coined by Ken Evans of the University of Exeter.



=Polyester Fibers= Initial work at Bolton successfully fabricated auxetic polypropylene fiber using a novel thermal melt-spinning technique. This paper reports in detail both the methods and principles involved in screening polyester powder and also the manufacturing method for successful production of auxetic polyester fibers. Videoextensometry along with micro-tensile testing were used to measure the Poisson’s ratio of the fiber. The Poisson’s ratio of the polyester fiber was found to vary between -0.65 and -0.75.

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=Refrences=

1- http://en.wikipedia.org/wiki/Smart_material 2- http://www.design-technology.info/alevelsubsite/page11.htm 3- http://en.wikipedia.org/wiki/Piezoelectric 4- http://jap.aip.org/resource/1/japiau/v108/i2/p023513_s1?isAuthorized=no 5- http://arxiv.org/abs/0909.4174 6- http://en.wikipedia.org/wiki/Auxetics 7- http://www.seminarprojects.com/Thread-magnetorheological-fluid-full-report 8- http://en.wikipedia.org/wiki/Magnetorheological_fluid 9- http://www.britannica.com/EBchecked/topic/460053/piezoelectricity 10- http://science.howstuffworks.com/engineering/structural/smart-structure1.htm