smart+materials+by+ahmedkhairy

//**Shape Memory Alloys :**//
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.

//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.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. 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.

//Manufacture// :

There are various ways to manufacture Nitinol. Current techniques of producing nickel-titanium alloys include vacuum melting techniques such as electron-beam melting, vacuum arc melting or vacuum induction melting. "The cast ingot is press-forged and/or rotary forged prior to rod and wire rolling. Hot working to this point is done at temperatures between 700 ° C and 900 ° C.

There is also a 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".

//Applications ://

in Aircraft, Piping , Automotive , Telecommunication , Robotics , Medicine and Dentistry.

this video shows how a SMA regains its shape when heated ,

[|SMA]

References : [] []

**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** It 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, 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).

**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).


 * Some Applications**

//1-Piezoelectric sensors//

Piezoelectric sensor are devices using the piezoelectric effect to measure acceleration, pressure, strain or force and converting them to an electrical signal. Piezoelements are suitable for the detection of dynamic processes. In static applications the piezoelectric charges are too small, in order to be detected. An amplifier is used to convert the piezoelectric charges into a measurable electrical tension.

2- //Piezoelectric motors//

A piezo motor is based on the change in mechanical shape of a piezoelectric material when an tension is applied. The material produces ultrasonic or acoustic vibrations and produces a linear or rotary motion. A few design exists currently: > According to manufacturers, precision can be of a few nanometers.
 * Locking mechanisms
 * Stepping Actions
 * Single Action With a fast response of the material (up to 5Mhz), it is possible to obtain a linear speed of 800mm/second.

3- //Other Applications//


 * High-voltage sources
 * In lighters or portable sparkers with a piezo fuze a sudden and strong pressure is used in order to produce a short high voltage. The spark then ignites the gas.
 * Frequency standard
 * Reduction of vibrations
 * Piezoelements are used in music for acoustic instruments. They are inserted in stringed instruments such as guitar, violin or Mandoline. The dynamic deformation of the instrument (vibration of the cords) is converted into a small alternating voltage.

Video demonstration of Piezoelectricity []

Piezoelectric effect in action []

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