shape+memory+alloys+(m)

Smart materials aren't really smart as they are said to be. They are only materials with weird and exotic properties and features that by chance suited smart engineering needs, that other materials weren't capable of fulfilling. In this article we will introduce you to smart materials,their applications, and what differentiates them from other materials. also you will get to know a brief about the materials history, and you might come across some spotlighting pictures and videos that illustrates how do these materials are put to work.

Historical breif about smart materials:
The term smart materials refers to a class of materials that are highly responsive and have the inherent capability to sense and react according to changes in the environment. Early smart material applications started with magnetostrictive technologies. This involved the use of nickel as a sonar source during World War I to find German U-boats by Allied forces. Piezoceramics, the other main type of smart materials, were initially discovered by Pierre and Jacques Curie. They identified the response that crystals of sugar and Rochelle salt made when subjected to mechanical stress. This development in 1880 began the work in what is now a $600 million dollar industry today. Their initial success, and the corresponding converse effect of strain production by the application of an applied electric field, led the way to the first serious applications of piezoceramic materials, which began during World War I. In addition to nickel sonar transducers, work began in France on the development of an ultrasonic submarine detector that would emit a high frequency "chirp" and measure depth by timing the return echo. The success of sonar then stimulated intense research and development into a variety of piezoelectric formulations and shapes.

what distinguishes sma from other smart materials:
Shape Memory Alloys (SMA): A shape memory alloy is and alloy that remembers its original shape. it can always return to its original shape by heating if deformed.

How does this works:
a shape memory alloy has two distinct crystal structures or phases. temperature determine these phases. martensite exists at lower temperature, and austenite at a high temperature. in the martensetic phase the metal can be easily deformed into any shape. when the alloy is heated and the metal transforms to the austentic phase remembering its original shape before it was deformed. the following graph shows that at low temperature martensite exists and at high temerature austenite exists.



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How Are Shape memory alloys trained:
The **//memory transfer temperature//** is the temperature that the memory alloy changes back to the original shape before deformation. This temperature can be very accurate, within 1 or 2 degrees of the needed temperature.

**Training** Heating is the only way that most memory metals retain their original shape. Since heat is the property that determines the shape of the metal, heat is the first property used for manipulation for formation. If an alloy is subjected to the same heating and deformation, the alloy will begin to acquire two-way training. The treatment for a NiTinol wire is, for example: > 1. The wire is hot/cold worked (stretched) by 3% when it is in the martensite phase > 2. The wire is then heated to austenite finish (AF) to recover its shape > 3. The wire is then cooled to martensite **Memory transfer temperatures can be altered by slight changes in composition, and by slight changes in heat treatment.**

One way and two way memory:
a one way memory alloy when cold (below austenetic phase) can be deformed easily, but when heated again returns to its original shape in the austenite form. a two way memory alloy is an alloy that remembers two different shapes, one at low temperature and one at high temperature. and this is obtained without external force. 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. A shaped, trained object heated beyond a certain point will lose the two-way memory effect, this is known as "amnesia".



Applications:
shape memory alloys are put to use into a wide variety of applications. some of which are: **aircraft** industries, **piping**, **automotive, telecommunication, and robotics.**

limitations**:**
SMAs have poor fatigue properties. While under the same loading conditions such as twisting, bending and compressing, SMA elements may survive for shorter time than a steel component. Moreover, the slow response characteristic of SMA actuators is incompatible with a high speed controller.

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