smart+material+by+yunes+sharaf



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" (Rogers, 155). The potential uses for SMAs especially as actuators have broadened the spectrum of many scientific fields. The study of the history and development of SMAs can provide an insight into a material involved in cutting-edge technology. The diverse applications for these metals have made them increasingly important and visible to the world. Video(1) media type="youtube" key="QYp9rIJRM8s" width="425" height="350" align="center"

** It cans called: ** ** (SMA, smart metal, memory metal, memory alloy, muscle wire, smart alloy) ** ** This alloy pre-deformed shape by heating. This material is a lightweight, solid-state alternative to conventional actuators such as hydraulic, pneumatic, and ** motor ** -based systems. ** ** SMA is used in form of wires that can contract up to 8% when heated. **

** Repeated use of the shape-memory effect may lead to a shift of the characteristic transformation temperatures (this effect is known as functional fatigue, as it is closely related with a change of microstructural and functional properties of the material). **

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** Crystal Structures: **

** Exactly what made these metals "remember" their original shapes was in question after the discovery of the shape-memory effect. Dr. Frederick E. Wang, an expert in crystal physics, pinpointed the structural changes at the atomic level which contributed to the unique properties these metals have. (Kauffman and Mayo, 4) ** ** He found that Nitinol had phase changes while still a solid. These phase changes, known as martensite and austenite, "involve the rearrangement of the position of particles within the crystal structure of the solid" (Kauffman and Mayo, 4). Under the transition temperature, Nitinol is in the martensite phase. The transition temperature varies for different compositions from about -50 � C to 166 � C (Jackson, Wagner, and Wasilewski, 1). In the martensite phase, Nitinol can be bent into various shapes. To fix the "parent shape" (as it is called), the metal must be held in position and heated to about 500 � C. The high temperature "causes the atoms to arrange themselves into the most compact and regular pattern possible" resulting in a rigid cubic arrangement known as the austenite phase (Kauffman and Mayo, 5-6). Above the transition temperature, Nitinol reverts from the martensite to the austenite phase which changes it back into its parent shape. This cycle can be repeated millions of times (Jackson, Wagner, and Wasilewski, 1). **

** In this figure, **** ξ **** (T) represents the martensite fraction. The difference between the heating transition and the cooling transition gives rise to [|hysteresis] where some of the mechanical energy is lost in the process. The shape of the curve depends on the material properties of the shape-memory alloy, such as the [|alloying]. [|[2] ] and [|work hardening]. **

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** Types of shape-memory alloys: **

** The three main types of shape-memory alloys are: **

** 1- **** copper-zinc-aluminium-nickel. **

** 2- **** 2- **** copper-aluminum-nickel. **

** 3- **** 3- **** nickel-titanium (NiTi) alloys. **

** but SMAs can also be created by alloying zinc, copper, gold and iron ****. **



** The effects of shape-memory alloys: ** ** Shape-memory alloys have different shape-memory effects. Two common effects are one-way and two-way shape memory. A schematic of the effects is shown below. ** ** The effects of shape-memory alloys: ** ** Shape-memory alloys have different shape-memory effects. Two common effects are one-way and two-way shape memory. A schematic of the effects is shown below. ** ** (I) One-way memory effect ** 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 °Cand 200 °C. ** (II)Two-way memory effect ** 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.

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** History: **

Nickel-titanium alloys have been found to be the most useful of all SMAs. Other shape memory alloys include copper-aluminum-nickel, copper-zinc-aluminum, and iron- manganese-silicon alloys.(Borden, 67) The generic name for the family of nickel-titanium alloys is Nitinol. In 1961, Nitinol, which stands for Nickel Titanium Naval Ordnance Laboratory, was discovered to possess the unique property of having shape memory. William J. Buehler, a researcher at the Naval Ordnance Laboratory in White Oak, Maryland, was the one to discover this shape memory alloy. The actual discovery of the shape memory property of Nitinol came about by accident. At a laboratory management meeting, a strip of Nitinol was presented that was bent out of shape many times. One of the people present, Dr. David S. Muzzey, heated it with his pipe lighter, and surprisingly, the strip stretched back to its original form. (Kauffman and Mayo, 4) ** Future Applications: **

** There are many possible applications for SMAs. Future applications are envisioned to include engines in cars and airplanes and electrical generators utilizing the mechanical energy resulting from the shape transformations. Nitinol with its shape memory property is also envisioned for use as car frames. (Kauffman and Mayo, 7) Other possible automotive applications using SMA springs include engine cooling, carburetor and engine lubrication controls, and the control of a radiator blind ("to reduce the flow of air through the radiator at start-up when the engine is cold and hence to reduce fuel usage and exhaust emissions") (Turner, 299). ** ** SMAs are "ideally suited for use as fasteners, seals, connectors, and clamps" in a variety of applications (Borden, 67). Tighter connections and easier and more efficient installations result from the use of shape memory alloys (Borden, 72). **

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** Conclusion: ** 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. ** Works Cited: ** Borden, Tom. "Shape-Memory Alloys: Forming a Tight Fit." Mechanical Engineering Oct. 1991: 67-72. Falcioni, John G. "Shape Memory Alloys." Engineering Apr. 1992: 114. Jackson, C.M., H.J. Wagner, and R.J. Wasilewski. 55-Nitinol- -The Alloy With a Memory: Its Physical Metallurgy, Properties, and Applications: A Report. Washington: NASA, 1972. Kauffman, George, and Isaac Mayo. Memory Metal." Chem Matters Oct. 1993: 4-7. Rogers, Craig. "Intelligent Materials." Scientific American Sept. 1995: 154-157.  Stoeckel, Dieter, and Weikang Yu. "Superelastic Nickel- Titanium Wires." Available from Raychem Corporation, Menlo Park, CA.  Turner, J.D. "Memory-metal Actuators for Automotive Applications." Proceedings of the Institution of Mechanical Engineers 208 (1994): 299-302. = =

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= =﻿= = = = = = Piezoelectricity =

Is the charge which accumulates in certain solid materials (notably [|crystals], certain [|ceramics] , and biological matter such as bone, [|DNA] and various [|proteins] ) in response to applied mechanical [|stress]. The word //piezoelectricity// means electricity resulting from pressure. It is derived from the [|Greek] //piezo// or //piezein//, which means to squeeze or press, and //electric// or //electron// , which stands for [|amber] , an ancient source of electric charge. [|[2]] Piezoelectricity is the direct result of the piezoelectric effect.

** the history and Discovery **** : **

Piezoelectricity was discovered in 1880 by Jacques and Pierre Curie when studying how pressure generates electrical charge in crystals (such as quartz and tourmaline). Its use in submarine sonar in World War 1 generated intense development interest in piezoelectric devices. The pyroelectric effect, where a material generates an electric potential in response to a temperature change, was studied by Carl Linnaeus and Franz Aepinus in the mid-18th century. Drawing on this knowledge, both René Just Haüy and Antoine César Becquerel posited a relationship between mechanical stress and electric charge; however, experiments by both proved inconclusive.

The first demonstration of the direct piezoelectric effect was in 1880 by the brothers Pierre Curie and Jacques Curie. They combined their knowledge of pyroelectricity with their understanding of the underlying crystal structures that gave rise to pyroelectricity to predict crystal behavior, and demonstrated the effect using crystals of tourmaline, quartz, topaz, cane sugar, and Rochelle salt (sodium potassium tartrate tetrahydrate). Quartz and Rochelle salt exhibited the most piezoelectricity. examples of piezoelectric Some materials are given in table 1.

** Table 1. ** Piezoelectric constants of materials. ** Key Properties ** The ability to produce a strain output (or deformation) in response to an applied
 * The ability to produce a voltage output in response to an applied stress

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A piezoelectric disk generates a voltage when deformed (change in shape is greatly exaggerated) The Curies, however, did not predict the converse piezoelectric effect. The converse effect was mathematically deduced from fundamental thermodynamic principles by Gabriel Lippmann in 1881.[4] The Curies immediately confirmed the existence of the converse effect, and went on to obtain quantitative proof of the complete reversibility of electro-elasto-mechanical deformations in piezoelectric crystals. For the next few decades, piezoelectricity remained something of a laboratory curiosity. More work was done to explore and define the crystal structures that exhibited piezoelectricity. This culminated in 1910 with the publication of Woldemar Voigt's Lehrbuch der Kristallphysik (textbook on crystal physics), which described the 20 natural crystal classes capable of piezoelectricity, and rigorously defined the piezoelectric constants using tensor analysis.

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** Applications: ** Applications Currently, industrial and manufacturing is the largest application market for piezoelectric devices, followed by the automotive industry. Strong demand also comes from medical instruments as well as information and telecommunications. The global demand for piezoelectric devices was valued at approximately US$14.8 billion in 2010. The largest material group for piezoelectric devices is piezocrystal, and piezopolymer is experiencing the fastest growth due to its light weight and small size.[16] Piezoelectric crystals are now used in numerous ways: ** High voltage and power sources ** Direct piezoelectricity of some substances like quartz, as mentioned above, can generate potential differences of thousands of volts. The best-known application is the electric cigarette lighter: pressing the button causes a spring-loaded hammer to hit a piezoelectric crystal, producing a sufficiently high voltage electric current that flows across a small spark gap, thus heating and igniting the gas. The portable sparkers used to light gas grills or stoves work the same way, and many types of gas burners now have built-in piezo-based ignition systems. ** Sensors: **

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**Piezoelectric disk used as a guitar pickup ** **Many rocket-propelled grenades used a piezoelectric fuze. For example: RPG-7[22] ** **Main article: Piezoelectric sensor ** **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. **

Metal disk with piezoelectric disk attached, used in a buzzer As very high electric fields correspond to only tiny changes in the width of the crystal, this width can be changed with better-than-µm precision, making piezo crystals the most important tool for positioning objects with extreme accuracy - thus their use in actuators. Multilayer ceramics, using layers thinner than100 µm, allow reaching high electric fields with voltage lower than 150 V. These ceramics are used within two kinds of actuators: direct piezo actuators andAmplified piezoelectric actuators. While direct actuator's stroke is generally lower than 100 µm, amplified piezo actuators can reach millimeter strokes. " Loudspeakers: Voltage is converted to mechanical movement of a piezoelectric polymer film. **Frequency standard: ** The piezoelectrical properties of quartz are useful as standard of frequency. " Quartz clocks employ a crystal oscillator made from a quartz crystal that uses a combination of both direct and converse piezoelectricity to generate a regularly timed series of electrical pulses that is used to mark time. The quartz crystal (like any elastic material) has a precisely defined natural frequency (caused by its shape and size) at which it prefers to oscillate, and this is used to stabilize the frequency of a periodic voltage applied to the crystal.

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**Piezoelectric motors: ** Types of piezoelectric motor include: 1- The traveling-wave motor used for auto-focus in reflex cameras 2- Inchworm motors for linear motion 3- Rectangular four-quadrant motors with high power density (2.5 watt/cm3) and speed ranging from 10 nm/s to 800 mm/s. 4- Stepping piezo motor, using stick-slip effect. All these motors, except the stepping stick-slip motor work on the same principle. Driven by dual orthogonal vibration modes with a phase difference of 90°, the contact point between two surfaces vibrates in an elliptical path, producing a frictional force between the surfaces. Usually, one surface is fixed causing the other to move. In most piezoelectric motors the piezoelectric crystal is excited by a sine wave signal at the resonant frequency of the motor. Using the resonance effect, a much lower voltage can be used to produce a high vibration amplitude

Video(5) media type="youtube" key="SQ7Qx3dPXsw" width="425" height="350" **The piezoelectric effect: ** The piezoelectric effect describes the relation between a mechanical stress and an electrical voltage in solids. It is reversbile: an applied mechanical stress will generate a voltage and an applied voltage will change the shape of the solid by a small amount (up to a 4% change in volume). In physics, the piezoelectric effect can be described as the the link between electrostatics and mechanics

**<span style="color: #0000ff; font-family: 'Arial','sans-serif'; font-size: 17.3333px;">The piezoelectric effect: ** <span style="display: block; font-family: 'Arial','sans-serif'; font-size: 150%; text-align: left;">The piezoelectric effect describes the relation between a mechanical stress and an electrical voltage in solids. <span style="display: block; font-family: 'Arial','sans-serif'; font-size: 150%; text-align: left;">It is reversbile: an applied mechanical stress will generate a voltage and an applied voltage will change the shape of the solid by a small amount (up to a 4% change in volume). <span style="display: block; font-family: 'Arial','sans-serif'; font-size: 150%; text-align: left;">In physics, the piezoelectric effect can be described as the the link between electrostatics and mechanics

**<span style="color: #0000ff; font-family: 'Arial','sans-serif'; font-size: 17.3333px;">Drawing for electric effect on a Piezoelectricity: **



<span style="color: #000000; font-family: 'Arial','sans-serif'; font-size: 13.3333px;">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. <span style="color: #000000; font-family: 'Arial','sans-serif'; font-size: 13.3333px;">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. = = Video(1) media type="custom" key="10836025" =How it works:= <span style="color: #000000; font-family: 'Arial','sans-serif'; font-size: 150%;">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

<span style="color: #000000; font-family: 'Arial','sans-serif'; font-size: 12.6667px;">

<span style="color: #000000; font-family: 'Arial','sans-serif'; font-size: 12.6667px;">When a magnetic field is applied, however, the microscopic particles (usually in the 0.1–10 µm range) align themselves along the lines of [|magnetic flux], see below. When the fluid is contained between two poles (typically of separation 0.5–2 mm in the majority of devices), the resulting chains of particles restrict the movement of the fluid, perpendicular to the direction of flux, effectively increasing its viscosity. Importantly, mechanical properties of the fluid in its “on” state are [|anisotropic]. Thus in designing a magnetorheological (or MR) device, it is crucial to ensure that the lines of flux are perpendicular to the direction of the motion to be restricted.



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= Modes of operation: = <span style="color: #000000; font-family: 'Times New Roman','serif'; font-size: 16px;">An MR fluid is used in one of three main modes of operation, these being flow mode, shear mode and squeeze-flow mode. These modes involve, respectively, fluid flowing as a result of pressure gradient between two stationary plates; fluid between two plates moving relative to one another; and fluid between two plates moving in the direction perpendicular to their planes. In all cases the magnetic field is perpendicular to the planes of the plates, so as to restrict fluid in the direction parallel to the plates



= The Applications of above operation : = The applications of these various modes are numerous. Flow mode can be used in dampers and shock absorbers, by using the movement to be controlled to force the fluid through channels, across which a magnetic field is applied. Shear mode is particularly useful in clutches and brakes - in places where rotational motion must be controlled. Squeeze-flow mode, on the other hand, is most suitable for applications controlling small, millimeter-order movements but involving large forces. This particular flow mode has seen the least investigation so far. Overall, between these three modes of operation, MR fluids can be applied successfully to a wide range of applications. =Applications:=
 * = v Mechanical engineering =
 * = v Military and defense =
 * = v Optics =
 * = v Automotive and aerospace =

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= Abstract: = <span style="color: #0000ff; font-family: 'Arial','sans-serif'; font-size: 111%;">Magnetorheological (MR) fluids is very promising intelligent materials and it can rapidly by changed from a liquid state to a solid state in a magnetic field. Various industries are full of potential MR fluids applications, but current MR fluids have the limitation that their yield stresses are not strong enough to meet some industrial requirements. The crucial problem is how to enhance the yield stress of MR fluids. Electrorheological (ER) fluids, similar to MR fluids, can be achieved high strength under squeeze mode, which proposed a method to achieve high-efficiency MR fluids by study of shear after compression. The performance of MR fluids under squeeze-shear mode was inveatigated. Magnetic fields being generated by two coils carrying different magnitudes of DC electrical current were applied on the MR fluids when shearing after compression were carried out on a self-constructed test system. For each trail the current in the coil and the compressive force were kept constant and the instantaneous yield stress was recorded. The relations of compression stress versus compression strain, yield stress versus compression stress were studied under different applied currents. The ploting of compressive stress against compressive strain has been observed to have three regions: the first and third regions has a linear relationship and the second region has a zero increasing. The slope of the curve was found to be larger when the applied current was larger. The SG MRF2035 without compression process has a yield stress about 53kPa at most even if increasing the applied current. But after compression, the yield stress increase with the increasing compressive stress under the different applied currents. And some promising results are obtained, for example, when the applied current is 2.5A and the compressive stress is 2.0MPa, the yield stress exceeds 1100kPa. It showed that the yield stress of MR fluids after compression was much stronger than that of uncompressed MR fluids under the same applied current. The enhanced yield stress of MR fluids can be utilized to design the MR clutch and brake for new structure and will make MR fluids technology attractive for many applications.



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Auxetic hexagon, becoming more square as it is stretched

Auxetics are materials that have a negative Poisson's ratio. When stretched, they become thicker perpendicular to the applied force. This occurs due to their hinge-like structures, which flex when stretched. Auxetic materials can be single molecules or a particular structure 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.

Auxetics can be illustrated with an inelastic string wound around an elastic cord. When the ends of the structure are pulled apart, the inelastic string straightens while the elastic cord stretches and winds around it, increasing the structure's effective volume.

The term auxetic derives from the Greek word ????????? (auxetikos) which means "that which tends to increase" and has its root in the word ???????, or auxesis, meaning "increase" (noun). This terminology was coined by Professor Ken Evans of the University of Exeter.[1]

Scientists have known about auxetic materials for over 100 years,[2] but have only recently given them special attention. The earliest published example of a synthetic auxetic material was in Science in 1987, entitled "Foam structures with a Negative Poisson's Ratio" [3] by R.S. Lakes from the University of Iowa. The use of the word auxetic to refer to this property probably began in 1991.[citation needed]

Typically, auxetic materials have low density, which is what allows the hinge-like areas of the auxetic microstructures to flex

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= The applications: =

Biomedical Industry
Key areas of application are seen in the biomedical field. Prosthetic materials, surgical implants, suture/muscle/ligament anchors and a dilator to open up blood vessels during heart surgery are all possible. Another area relates to the use of auxetic materials in piezoelectric sensors and actuators. Auxetic metals could be used as electrodes sandwiching a piezoelectric polymer, or piezoelectric ceramic rods could be embedded within an auxetic polymer matrix. These are expected to increase piezoelectric device sensitivity by at least a factor of two, and possibly by ten or a hundred times. The development of auxetic materials for micro- and nano-mechanical and electromechanical devices is also being investigated. =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.




 * Figure 1. Schematic of particulate de-fouling capabilities of non-auxetic and auxetic materials **

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=Auxetic Fibres=

The breakthrough development of a continuous process to produce auxetic materials in fibrous form has created the opportunity to apply their unique characteristics in a wide range of applications previously not possible. Fibres can be used in single or multiple filament structures and can be used to produce a woven structure. Typical performance characteristics expected of auxetic fibres and structures are detailed in the table of applications, (table 1), together with a list of the applications in which these characteristics could offer significant benefits. For example, by analogy with the filter de-fouling scenario of figure 4, biomedical fibrous drug-release materials could be made from auxetic fibres. Extending the fibres opens the micropores and a specific dose of drug is released.

Advanced auxetic fibres will include multi-filament yarns in which an auxetic filament is wrapped with one or more other yarns, perhaps high stiffness/strength, dyeable or conductive filaments, so that the benefits of the auxetic material are combined with other beneficial properties for smart technical textiles applications. This will lead to the possibility of hierarchical composites displaying auxetic behaviour at more than one lengthscale. Current research on auxetic composites is concentrated on the use of non-auxetic constituents and so benefits due to the impact energy and acoustic energy absorption, to be achieved at the microstructural level. auxetic effect occur at a macrostructural level. Employing auxetic fibres as the reinforcement will enable benefits, such as

=Auxetic Fibre Reinforced Composites=

Auxetic fibre reinforcements should also enhance the failure properties of composites. Fibre pull-out is a major failure mechanism in composites. A unidirectional composite loaded in tension will undergo lateral contraction of both the matrix and fibre materials, leading to failure at the fibre/matrix interface. Auxetic fibres, on the other hand, allow the possibility of maintaining the interface by careful matching of the Poisson's ratios of the matrix and fibre, figure 2.

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= The Future of Auxetics: =

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.

**<span style="color: #0000ff; font-family: 'Agency FB','sans-serif';"> Reference : ** > >
 * <span style="color: #17375e; font-family: 'Arial Black','sans-serif'; font-size: 24px;">Harper, Douglas. [|"piezoelectric"] . // [|Online Etymology Dictionary] //.
 * <span style="color: #17375e; font-family: 'Arial Black','sans-serif'; font-size: 24px;"> [|"Mechanical properties of magnetorheological fluids under squeeze-shear mode" by Wang, Hong-yun; Zheng, Hui-qiang; Li, Yong-xian; Lu, Shuang]
 * ** [|HowStuffWorks "How Smart Structures Will Work"]  **
 * ** [|HowStuffWorks "How Smart Structures Will Work"]  **