SEMINAR ON SHAPE MEMORY ALLOYS SUBMITTED BY: PRABHAT KUMAR SINGH 1012240072 MECHANICAL-53

Definition of a Shape Memory Alloy Shape Memory Alloys (SMAs) are a class of metal alloys that can recover apparent permanent strains when they are heated above a certain temperature. They can retain their properties at high temp.

History Of SMA’s Discovered in 1932 By Chang and Read In 1938, Brass (CuZn) In 1951, Gold Cadmium (AuCd) Buehler and co-workers discovered Nickel-Titanium (NiTi).(1962)

Basic working principle SMAs have two stable phases - the high-temperature phase, called austenite and the low-temperature phase, called martensite. the martensite can be in one of two forms: twinned and detwinned, as shown in Figure 1. A phase transformation which occurs between these two phases upon heating/cooling is the basis for the unique properties of the SMAs.

 

Selection Criteria of SMA’S Range Sensitivity Repeatability Linearity and Accuracy Impedance Nonlinearities Static and Coulomb Friction Frequency Response

Properties: A Shape Memory Alloy may be stretched up to 8% more than their original length without permanently stretching or damaging the material.

Types Of Shape Memory Alloys One-way Shape Memory Alloy Two-way Shape Memory Alloy Types Of Alloys NITINOL Copper Based

Ni-Ti Alloy (NITINOL) NITINOL means Nickel Titanium Naval Ordnance Laboratory and it is discovered in 1965. Its composition is about 56% Nickel and 44% Titanium. Nitinol “remembers” its original shape and springs back up to temperatures up to 500 degrees C. Can be strained 8 to 10 times more than spring steel without permanent deformation.

Physical Properties of Nitinol Density-6.45gms/cc Melting temperature-1240-310ºc Resistivity: 82uhom-cm Thermal conductivity:.1wW/cm-ºc Latent heat:5.78cal/gm Heat capacity:0.077cal/gm-ºc Magnetic succeptibility:3.8uemu/gm

Mechanical Properties of Nitinol Ultimate tensile strenth: 754-960mpa Typical elongation:15.5% Yield strenth(hi temp):560 Yield strenth (low temp):100 Poission ‘s ratio:0.3 Energy conversion efficiency:5% Work output:1 joule/gm

Current Application of Nitinol It has similar properties to human hair. Nitinol’s amazing properties allows surgeons to perform life saving operations. Nitinol is used to:- Seal holes in the heart Patch up faulty blood vessels Attach tendons to bone

Application of Nitinol The ICEmobile A Nitinol heat engine, called the Icemobile has a loop of Nitinol which you immerse in warm water, to make it spin (which then cuts up ice cubes).

Future application of Nitinol Engines in cars and airplanes Car frames Engine cooling Carburetor Engine lubrication

LIMITATIONS OF SMA’S Heat Dissipation Stiffness/Flexibility Relatively expensive to manufacture and machine compared to other materials such as steel and aluminum. Most SMA's have poor fatigue properties; this means that while under the same loading conditions (i.e. twisting, bending, compressing) a steel component may survive for more than one hundred times more cycles than an SMA element.

ABNORMAL BEHAVIOUR OF SMA SMA also exhibits superelastic (pseudoelastic) behavior. SMAs deformed above a critical temperature show a large reversible elastic deformation (recoverable strains up to 10%. much exceeding the elasticity) as a result of stress-induced martensitic transformation.

APPLICATION OF NANOMUSCLES An advantage to this new shape memory alloy is its’ efficiency. No other alloy or polymer can compare to its’ strength and efficiency to weight ratio. Nanomuscles weigh just one gram but can lift 140 grams, and are preferred to electric motors as they are far cheaper to produce.

Application in aircraft Active Control and reduction of noise and vibrations in external parts. • control of aero-acoustic excitations. active suspension of equipment. Shape control of aerodynamic surfaces. • Active fluid dynamics. • Integrated antennas and electromagnetic structures.

CONCLUSION Shape memory alloys provide wide range of alloys which can be used in every field. They allow to avoid shock loading, have simple design and are easy to operate. IT can also used in carburetor, automobiles,engines and in aircrafts. They are also used in combustion chamber.

REFERENCE Shape Memory Applications Inc. Shape Memory Alloys. Hodgson, Darel E.; Ming H. Wu, Memory Technologies; Robert J. Biermann, Harrison Alloys, Inc. http://www.sma-inc.com/SMAPaper.html Nickel-Titanium Shape Memory Alloys. Azom.com. http://www.azom.com/details.asp?articleID Shape Memory Alloys. TiNi Aerospace Inc <http://www.tiniaerospace.com/html/ShapeMemoryAlloys>

REFERENCE CONTINUED……. http://www.cs.ualberta.ca/~database/MEMS/sma_mems/sma.html http://smart.tamu.edu/ http://www.abc.net.au/science/news/stories/s832821.htm Shape memory alloy micro-actuators for medical applications; J. Peirs, D. Reynaerts, H. Van Brussel, K.U.Leuven - P.M.A. Celestijnenlaan 300B, 3001 Heverlee

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