smart+materials-ahmed+salah

smart materials   smart materils are materials which have properties that can be significantly changed in a controlled fashion by external stimuli, such as stress, temperature, electric and magnetic fields.

There are many types of smart materials such as :

1. shape memory alloys :

Shape memory alloy is a metal which remember its original shape. SMA change its shape, stiffness, position, natural frequency, and other mechanical characteristics in response to temperature or electromagnetic fields.it is very useful as actuators such as hydraulic and pneumatic. The study of the history and development of SMAs can provide an insight into a material involved in cutting-edge technology.

History of SMA:

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- m s : anganese-silicon alloys. 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.

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the ways to manufacture Nitinol :

process of cold working of Ni-Ti alloys. The procedure is similar to titanium wire fabrication. Carbide and diamond dies are used in the process to produce wires ranging from 0.075mm to 1.25mm in diameter. Cold working of Nitinol causes "marked changes in the mechanical and physical properties of the alloy". These processes of the production of Nitinol are described in greater detail in Jackson, Wagner, and Wasilewski's report (15-22)

How Shape Memory Alloys Work:

The two unique properties described above are made possible through a solid state phase change, that is a molecular rearrangement, which occurs in the shape memory alloy. Typically when one thinks of a phase change a solid to liquid or liquid to gas change is the first idea that comes to mind. A solid state phase change is similar in that a molecular rearrangement is occurring, but the molecules remain closely packed so that the substance remains a solid. In most shape memory alloys, a temperature change of only about 10 C is necessary to initiate this phase change. The two phases, which occur in shape memory alloys, are Martensite, and Austenite



Martensite, is the relatively soft and easily deformed phase of shape memory alloys, which exists at lower temperatures. The molecular structure in this phase is twinned which is the configuration shown in the middle of Figure 2. Upon deformation this phase takes on the second form shown in Figure 2, on the right. Austenite, the stronger phase of shape memory alloys, occurs at higher temperatures. The shape of the Austenite structure is cubic, the structure shown on the left side of Figure 2. The un-deformed Martensite phase is the same size and shape as the cubic Austenite phase on a macroscopic scale, so that no change in size or shape is visible in shape memory alloys until the Martensite is deformed.

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The temperatures at which each of these phases begin and finish forming are represented by the following variables: Ms, Mf, As, Af. The amount of loading placed on a piece of shape memory alloy increases the values of these four variables as shown .The initial values of these four variables are also dramatically affected by the composition of the wire

2.Piezoelectric materials:

Introduction: 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.



History

The piezoelectric effect was discovered in 1880 by the Jacques and Pierre Curie brothers. They found out that when a mechanical stress was applied on crystals such as tourmaline, tourmaline, topaz, quartz, Rochelle salt and cane sugar, electrical charges appeared, and this voltage was proportional to the stress.

First applications were piezoelectric ultrasonic transducers and soon swinging quartz for standards of frequency (quartz clocks).

An everyday life application example is your car's airbag sensor. The material detects the intensity of the shock and sends an electricla signal which triggers the airbag.



Piezoelectric materials The piezoelectric effect occurs only in non conductive materials. Piezoelectric materials can be divided in 2 main groups: crystals and cermaics. The most well-known piezoelectric material is quartz (SiO2).

JAPANESE DEVELOPMENTS 1965 - 1980 In contrast to the "secrecy policy" practiced among U.S. piezoceramic manufacturers at the outset of the industry, several Japanese companies and universities formed a "competitively cooperative" association, established as the Barium Titanate Application Research Committee, in 1951. This association set an organizational precedent for successfully surmounting not only technical challenges and manufacturing hurdles, but also for defining new market areas.

Beginning in 1965 Japanese commercial enterprises began to reap the benefits of steady applications and materials development work which began with a successful fish-finder test in 1951. From an international business perspective they were "carrying the ball," i.e., developing new knowledge, new applications, new processes, and new commercial market areas in a coherent and profitable way.

Persistent efforts in materials research had created new piezoceramic families which were competitive with Vernitron's PZT, but free of patent restrictions. With these materials available, Japanese manufacturers quickly developed several types of piezoceramic signal filters, which addressed needs arising in television, radio, and communications equipment markets; and piezoceramic igniters for natural gas/butane appliances.

As time progressed, the markets for these products continued to grow, and other similarly valuable ones were found. Most notable were audio buzzers (smoke alarms, TTL compatible tone generators), air ultrasonic transducers (television remote controls and intrusion alarms) and SAW filter devices (devices employing Surface Acoustic Wave effects to achieve high frequency signal filtering).

By comparison to the commercial activity in Japan, the rest of the world was slow, even declining. Globally, however, there was still much pioneering research work taking place as well as device invention and patenting.media type="youtube" key="wIcqHKGJPwA" width="677" height="560"