Smart+Mateiel+by+Salah+Ahmed+Morsi

= =

= __//Smart Materials//__ =

Science and technology have made amazing developments in the design of electronics and machinery using standardmaterials, which do not have particularly special properties (i.e.steel, aluminum, gold).Imagine the range of possibilities, which exist for specialmaterials that have properties scientists can manipulate. Somesuch materials have the ability to change shape or size simplyby adding a little bit of heat, or to change from a liquid to asolid almost instantly when near a magnet; these materials arecalled smart materials.

=  shape memory alloys : nitinol =

the alloy is a metal that is made up of two or more metallic substances that have been combined. shape memory alloys (SMAs) are metals that "remember" their original shapes. SMAs are useful for such things as actuators which are materials that "change shape, stiffness, position, natural frequency, and other mechanical characteristics in response to temperature or electromagnetic fields. The first reported steps towards the discovery of the shape-memory effect were taken in the 1930s. According to Otsuka and Wayman  SMA wire is sometimes called ‘Nitinol’, as it is a composed of nickel and titanium. On first site this special wire looks like ordinary wire and even has many of the same properties. It can be folded to form complex shapes quite easily and it conducts electricity. However, it is very expensive when compared to ordinary steel or even copper wire. However, it has properties that make it very special:
 * **2.** The material can also be ‘programmed’ to remember a shape. This can be achieved by folding the wire to a particular shape and clamping it in position. The wire is then heated for a approximately five minutes at precisely 150 degrees or pass an electric current through the SMA wire. If the wire is now folded into another shape and then placed in hot water it returns to the original ‘programmed’ shape. ||||   ||
 * The diagram below shows a steel jig. This is used to fold the SMA wire to shape. A battery is then connected and current is passed through it. The wire has now been ‘programmed’ to its new shape. ||
 * media type="youtube" key="WREwKx0qF7o" width="295" height="244" align="right"
 * media type="youtube" key="WREwKx0qF7o" width="295" height="244" align="right"

Properties :
The  properties of Nitinol are particular to the exact composition of the metal and the way it was processed. The physical properties of Nitinol include a melting point around 1240 ° C to 1310 ° C, and a density of around 6.5 g/cm³ (Jackson, Wagner, and Wasilewski, 23). Various other physical properties tested at different temperatures with various compositions of elements include electrical resitivity, thermoelectric power, Hall coefficient, velocity of sound, damping, heat capacity, magnetic susceptibility, and thermal conductivity (Jackson, Wagner, and Wasilewski, 23-55). Mechanical properties tested include hardness, impact toughness, fatigue strength, and machinability (Jackson, Wagner, and Wasilewski, 57-73). The large force generated upon returning to its original shape is a very useful property. Other useful properties of Nitinol are its "excellent damping characteristics at temperatures below the transition temperature range, its corrosion resistance, its nonmagnetic nature, its low density and its high fatigue strength" (Jackson, Wagner, and Wasilewski, 77). Nitinol is also to an extent impact- and heat-resistant (Kauffman and Mayo, 4). These properties translate into many uses for Nitinol.

Conclusion :
The many uses and applications of shape memory alloys ensure a bright future for these metals. Research is currently carried out at many robotics departments and materials science departments. With the innovative ideas for applications of SMAs and the number of products on the market using SMAs continually growing, advances in the field of shape memory alloys for use in many different fields of study seem very promising.

= piezoelectric : sensor actuator = Simply stated, piezoelectric materials produce a voltage in response to an applied force, usually a uniaxial compressive force. Similarly, a change in dimensions can be induced by the application of a voltage to a piezoelectric material. In this way they are very similar to electro-strictive materials. A mechanical deformation (such as a compressive force) can decrease the separation between the cations and anions which produces an internal field or voltage.

 As u can see the above pictures, when we compress the material, deflection can be seen in the voltmeter which indicates there is some potential difference in material. Transducers : Piezoelectric materials are used in electromechanical devices. In the case of a microphone transducer, sound of a particular frequency results in a strain in the material, which in turn induces an electric field. Similarly in speakers, a voltage input into the piezoelectric material can be converted into a mechanical strain, such as in a speaker transducer.

media type="youtube" key="Xuw9frP1GNo" align="center" width="425" height="350"

Other Applications :
__In radios, piezoelectric devices can be used in tuners, where the correct strain in the crystal will amplify only the desired frequency.__

Magnetorheological fluids : MRF Magnetorheological fluids (MRF) are suspensions of fine, magnetic particles (carbonyl iron powder with particle diameters of a few microns) in an oil based carrier fluid. Under the influence of a magnetic field the particles form chains in the direction of the magnetic flux, which changes the flow resistance of the MRF highly dynamic and almost linearly. The hardening process takes around twenty thousandths of a second. . This effect can be used to design and we can see the change in this video : Magnetorheological fluid computer simulation and you can see how the magnetic field arrange the particule on the screen.
 * controllable dampers or
 * clutches and brakes.

media type="youtube" key="u9bvl3bK1lI" width="425" height="350" align="center"

applications Because the state of MR materials can be controlled by the strength of an applied magnetic field, it is useful in applications where variable performance is desired. Microprocessors, sensor technologies and increasing electronic content and processing speeds have created real-time control possibilities of smart systems used MR devices. Beginning of the commercialization of MR technology was year 1995 and use of rotary brakes in aerobic exercise equipment. From this moment application of magnetorheological material technology in real-world systems has grown steadily. media type="youtube" key="toPsSqwxOG4" width="425" height="350" align="right"

conclusion Science and technology in the 21st century will rely heavily on the development of new materials that are expected to respond to the environmental changes and manifest their own functions according to the optimum conditions. The development of smart materials will undoubtedly be an essential task in many fields of science and technology such as information science, microelectronics, computer science, medical treatment, life science, energy, transportation, safety engineering and military technologies. Materials development in the future, therefore, should be directed toward creation of hyperfunctional materials which surpass even biological organ in some aspects. The current materials research is to develop various pathways that will lead the modern technology toward the smart system. These fluids can reversibly and instantaneously change from a free-flowing liquid to a semi-solid with controllable yield strength when exposed to a magnetic field. In the absence of an applied field, MR fluids are reasonably well approximated as Newtonian liquids. For most engineering applications, a simple Bingham plastic model is effective in describing the essential, field-dependent fluid characteristics. MR technology has moved out of the laboratory and into viable commercial applications for a diverse spectrum of products. Applications include automotive primary suspensions, truck seat systems, control-by-wire/tactile-feedback devices, pneumatic control, seismic mitigation and human prosthetics. In contrast to conventional electro-mechanical solutions, MR technology offers: * Real-time, continuously variable control of
 * Damping
 * Motion and position control
 * Locking
 * Haptic feedback
 * High dissipative force independent of velocity
 * Greater energy density
 * Simple design (few or no moving parts)
 * Quick response time (10 milliseconds)
 * Consistent efficacy across extreme temperature variations (range of 140C to 130 C)
 * Minimal power usage (typically 12V, 1 Amp max current; fail-safe to battery backup, which can fail-safe to passive damping mode)
 * Inherent system stability (no active forces generated)
 * MR fluids can be operated directly from low-voltage power supplies. MR technology can provide flexible, reliable control capabilities in designs

= auxetic materials =

Auxetics are materials that have a negative Poisson ratio — when they are stretched, they get fatter instead of thinner. This is possible because of their underlying structure. One might imagine a foam made out of millions of tiny bow-tie shaped cells, connected to one another. If someone pulls on the sides of the material, the bow ties expand into squares, expanding on the transverse plane as well as the plane parallel to the stretching action. This phenomenon is caused by the macrostructure or microstructure of the material and not the chemical composition of the material itself, so many common materials can be put into auxetic arrangements, although materials that are flexible and stretchy work best.media type="youtube" key="vdkYuLsT7Sc" width="425" height="350" align="right"

Put simply, such a material becomes thicker widthwise when stretched lengthwise, and thinner when compressed. This is counter to the response of many common materials, which become thinner when stretched.

What advantages do auxetic materials offer?
> auxetic materials show enhanced mechanical properties such as:
 * __increased shear stiffness__
 * __increased plane strain fracture toughness__
 * __increased indentation resistance__

Filters Auxetic foam and honeycomb filters offer enhanced potential for cleaning fouled filters, for tuning the filter effective pore size and shape, and for compensating for the effects of pressure build-up due to fouling. These benefits rely on the pores opening up both along and transverse to the direction of a tensile load applied to an auxetic filter. The pores of a non-auxetic filter open up in the stretching direction but close up in the lateral direction, leading to poorer filter performance, figure 1. However, stretching an auxetic filter improves performance by opening pores in both directions. The effect of stretching on the de-fouling of an auxetic polymeric honeycomb fouled with glass beads has been investigated. For the particular honeycomb studied the value of n is dependent on the stretching direction. The studies clearly demonstrate that defouling is enhanced when the filter is loaded in the direction with the largest negative n.

Production of Auxetic Materials
It is clear that auxetic materials have beneficial properties, so the next step is to produce them, and there are as many different routes as there are materials. Some routes rely on transforming non-auxetic materials into an auxetic form (foams), whereas others employ standard techniques but with novel material architecture to achieve the auxetic effect (honeycombs and fibre-reinforced composites). Still others require novel development of existing processing routes for conventional materials to produce auxetic functionality. As an example of this latter scenario, take the processing of auxetic microporous polymers. The key is to produce a three-dimensional version in the polymer of the two-dimensional schematic in figure 1, i.e. to achieve nodules interconnected with fibrils. The route used to achieve this complex microstructure, for UHMWPE, is a batch process based on conventional polymer powder processing techniques of sintering and extrusion, but adapted so that there is only partial melting of the starting powder, which gives rise to fibrillation. An additional initial compaction stage can be used solely to impart some degree of structural integrity to the extrudates. This means the properties of the polymers can be tailored to fit the applications required and, by varying certain processing parameters, to produce everything from structural auxetic polymers with a Young's modulus of 0.2GNm-2, down to very auxetic, low modulus polymers.

The Future So what does the future hold for auxetics? Despite the very significant developments to date we have only scratched the surface of this exciting and multi-disciplinary field. The successful synthesis and development of molecular and multi-functional auxetics represent key opportunities for the future. In addition to leading to materials with extreme properties such as high modulus and strength, these advanced materials will have potential in sensor, drug-release and separations applications. By accepting a negative Poisson's ratio as a positive property we are truly expanding the applications of these fascinating materials || [] http://www.azom.com [] [] [] []
 * __ references : __ ||  ||