Smart get darker when exposed to sunlight.SMA are


Smart materials in manufacturingMaterials technology has had such a profound impact on the evolution of human civilization that historians have characterized periods in that evolution by such terms as the stone age the bronze age and the Iron age synthetic materials age and smart materials age.Smart materials are those materials that respond to external factors like changing condition or surrounding or other directed influences like passing electric current among them or emitting sunlight to them. Nowadays using smart materials is developing day by day. They are used in all industries fields such as automotive, Surgery, electronic, Manufacturing. There is several kinds of smart materials. For example Piezoelectric,shape memory alloys, thermochromic, photochromic and etc. In this essay we will familiar to smart materials and some of their properties. Then we will figure it out how can use smart materials for design better and more reliable goods. (smart materials and structure,1992) Piezoelectrics are materials which applying a mechanical stress to them can produce electrical current. for instance in a cheap lighter when you press the button a piezoelectric material charge and generate sufficient current for create a sparkle.Shape memory materials are materials which after deformation, they remember their original shape  and return back to it, when heated.for example there is one shape memory alloy (SMA) called nitinol (a metal alloy of nickel and titanium) which has been used in extremely resilient glasses frames. Thermochromic: an input of thermal energy (heat) to the material alters its molecular structure.the new molecular structure has a different spectral reflectivity then does the original structure; as a result, the materials colour (is reflected radiation in the visible range of the electromagnetic spectrum) changes. They have been used in bath plugs that change color in red when the water getting too hot. Photochromic  are similar to thermochromic though they change color in response to changes in light conditions.the best example is photochromic glasses which get darker when exposed to sunlight.SMA are the most famous and applicable smart materials in the industry.besides their unique property as a smart material they have other fantastic physical properties that makes them an excellent  alternative for regular metals and alloys. They have high yield strength and coefficient of thermal expansion.their electrical and thermal conductivity are low therefore they are good conductors.for example nitinol’s yield strength and electrical and thermal conductivity are:690 Mpa, 82×10?6 ?·cm, 0.18 w/cm.k respectively (engineering aspects of shape memory alloys, 1990). According to these marvelous properties SMAs can use instead of aluminum or steel in industries. For example: comercial and the most useful alloys of steel only has yield strength around 330 Mpa. It is half of the nitinol’s.nitinol and zinc, copper, gold and iron alloys are very popular in industries. The first steps in discovering of shape-memory effect has been taken in 1930 decade. Professor Otsuka from university of Tsukuba and professor Wayman from university of illinois discovered the elastic behaviour of gold-cadmium alloy in 1932. After that about six years later scientists observed  the formation and fadeaway of martensite phase by performing heat to copper-zinc alloy. Nitinol first time discovered in US naval lab between 1962-1963. The main properties of this alloy discovered accidentally. Today shape memory polymers have been developed and are commercially available.phase transformation plays the key role in the SMA’s unique behaviour. The martensitic transformation converts the material between two particular phases, namely austenite and martensite. Austenite is the high temperature or ‘parent’ phase and exhibits a cubic crystalline structure whereas martensite is the low temperature phase that exhibits a tetragonal or monoclinic crystalline structure. The martensitic transformation is a shear-dominant, diffusionless transformation that occurs via the nucleation and growth of the martensitic phase from the parent austenitic phase. The transformation from austenite to martensite may lead to twinned martensite in the absence of internal and external stresses or detwinned martensite if such stresses exist at a sufficient level. Because the transformation from austenite to twinned martensite results in negligible macroscopic shape change, twinned martensite is often referred to as self-accommodated martensite. The reorientation of twinned martensite into detwinned martensite can take place under the application of sufficient stress. From the early ‘thermal engines, engineers and other designers in many fields have been developed ways to convert thermal energy to mechanical work by using  the crystallographic phase change of SMAs, which have now been used in real-world applications for several decades. One of the most well-known of these early applications were the hydraulic tubing coupling used in the F-14 in 1971. Since that time, designers have continued to use both the shape memory and pseudoelastic effects of SMAs in solving engineering problems in the aerospace industry. Such implementations of SMA technology has spanned the areas of fixed wing aircraft, rotorcraft, and spacecraft; work continues in all three of these areas. The following section describes some of the more recently explored aerospace applications of SMAs and then briefly summarizes the challenges facing the designers of such systems.Applications which apply specifically to the propulsion systems and structural configurations of fixed wing aircraft will first be considered. Perhaps two of the most well-known fixed-wing projects of the past are the Smart Wing program and the Smart Aircraft and Marine Propulsion System demonstration (SAMPSON). The Smart Wing program was intended to develop and demonstrate the use of active materials, including SMAs, to optimize the performance of lifting bodies . The project was split into two phases with the first being the most SMA-intensive..we will see that many smart materials may also actually act as sensors or actuators.in this kind of role, a smart material answer to a change in its surrounding by generating a perceivable response. Hence a thermochromic material could be used directly as a device for sensing a change in the temperature of an environment via its colour response capabilities. Other materials, such as piezoelectric crystals, could also be used as actuators by passing an electric current through the material to create a force.many common sensors and actuators are based on the use of smart materials. In the use of type two materials as a sensor or actuator, there are also different kinds of electronic systems that are integral to the system to amplify, modify, transmit, or interpret generated signals. Logic capabilities provided via micro processors or other computer-based systems are similarly common.

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