shape memory alloys

SOUTH DAKOTA STATE UNIVERSITY

MECHANICAL ENGINEERING

TERM PROJECT ON SHAPE MEMORY ALLOYS (SMAs)

BY SURESH DARAVATH

7346212

INSTRUCTURE Fereidoon Delfanian

OUTLINE

Introduction of shape memory alloys History of shape memory alloys Types of shape memory alloys Characteristic of SMA Types of SMA behavior Properties of SMA Advantages of SMA Disadvantages of SMA Future scope applications Conclusion References

INTRODUCTION OF SMA

Shape memory alloy is an alloy.SMA a is one the type of smart materials.Shape Memory Alloys are materials that “remember” their original

shape. If deformed, they recover their original shape upon heating.They can take large stresses without undergoing permanent deformation.They can be formed into various shapes like bars, wires, plates and rings

thus serving various functions.

HOW DO THEY WORK

• We all know the most common phase changes:• SMAs shape changes based on a solid state phase transformation. The transition from one form of crystalline structure to another creates the mechanism by which the shape change occurs in SMAs. This change involves transition from a monoclinic crystal form (martensitic) to an ordered cubic crystal form (austenite).

HISTORY OF SHAPE MEMORY ALLOYS 1938: Arne Olande observed shape and recovery ability of Au-Cd alloy.1938: Greninger and Mooradian observed the formation and disappearance of martensitic phase by varying the temperature of a Cu-Zn alloy.1962-63: William j.Buehler and Frederic. Wang observed the shape memory effect in Nickel and Titanium alloy at the United States Naval Ordnance Laboratory. Nitinol – Nickel Titanium Naval Ordnance Laboratories. where the two elements are present in roughly equal atomic percentages e.g. Nitinol 55, Nitinol 60.

TYPES OF SHAPE MEMORY ALLOYS

There two main families of alloys Based on Copper(Cu): cu-al-ni and cu-zn-al are used for narrow hysteresis and adaptability to two shape

memory. Based on Nickel (Ni): Ni-Ti-ternary(x) Now way days NI-Ti-X are used more than 90% of new SMA applications, NI-Ti alloys are more expensive to melt and produced than copper alloy, but they are preferred for their corrosion resistance, biocompatibility, and higher electrical resisting for resistive heating in actuator application.

CHARACTERISTICS SHAPE MEMORY ALLOYS It exhibits two main characteristic:1. Shape memory effect2. Superelasticity effect Shape memory effect: Is based on martensitic phase transformation taking place without diffusion. Martensitic phase transformation that occurs as a result of stress or temperature change

THERMALLY INDUCED PHASE TRANSFORMATION IN SMA

MECHANICAL DEFORMATION

Shape memory effect behavior:Two types of shape memory behavior One-way shape memory: Transformation to the desired shape occurs only upon heating, i.e., memory is with the austenite phase.

Two-way shape memory: The deformed shape is remembered during cooling, in addition to the original shape being remembered during heating, i.e., memory is with both austenite and martensitic phases.

Superelasticity shape memory (Pseudoelasticity):

It is an elastic (reversible) response to an applied stress. Occurs without temperature change. This property allows the SMA’s to bear large amounts of stress without undergoing permanent deformation. Temperature of SMA is maintained above transition temperature

Load is increased until austenite transforms to martensitic.

When loading is decreased, martensitic transforms back of austenite.

SMA goes back to original shape as temperature is still above transition temperature.

PROPERTIES OF SMAThe copper-based and Ni-Ti-based shape-memory alloys are considered to be engineering materials.These compositions can be manufactured to almost any shape and size. The yield strength of shape-memory alloys is lower than that of conventional steel, but some

compositions have a higher yield strength than plastic or aluminum. The yield stress for Ni Ti can reach 500 MPa.  The maximum recoverable strain these materials can hold without permanent damage is up to 8% for

some alloys. This compares with a maximum strain 0.5% for conventional steels.

ADVANTAGES OF SMA Very high power/weight ratio comparatively Accessible voltages can accomplish Thermo elastic transformation Higher strain recovery Higher strengthCompactness, allowing for reduction in overall actuator size. Noiseless and silent operation High corrosion resistance

LIMITATIONS OF SMA Heat Dissipation, need Mechanism for cooling

Less Stiffness / high Flexibility

Relatively expensive to manufacture and machine compared to other materials such as steel and

aluminum.

Most SMA's have poor fatigue properties ( a steel component may survive for more than one

hundred time more cycles than an SMA element. )

APPLICATIONS OF SMA Aircraft To reduces engine noise, some designers installs chevrons onto engines to mix the flow of exhaust

gases and reduces engine noise.Automotive

Robotics Recently, a prosthetic hand was introduced by Loh et al. that can almost replicate the

motions of a human hand

Civil Structures SMAs find a variety of applications in civil structures such as bridges and buildings.

One such application is Intelligent Reinforced Concrete (IRC), which incorporates SMA wires embedded within the concrete.

Another application is active tuning of structural natural frequency using SMA wires to dampen vibrations.

Piping The first consumer commercial application was a shape-memory coupling for piping, e.g. oil

line pipes for industrial applications, water pipes. Use of memory alloys for coupling tubing: A memory alloy coupling is expanded (a) so it fits over the

tubing (b). When the coupling is reheated, it shrinks back to its original diameter (c), squeezing the tubing for a tight fit.

Medicine Stent- A reinforced grafts for vascular application to replace or repair damaged arteries (25mm diameter)

Optometry

Eyeglass frames made from titanium-containing SMAs are marketed under the trademarks Flexon and TITANflex. These frames are usually made out of shape-memory alloys that have their transition temperature set below the expected room temperature. This allows the frames to undergo large deformation under stress, yet regain their intended shape once the metal is unloaded again.

FUTURE SCOPE APPLICATION

There are many possible applications for SMAs. Future applications are envisioned to include engines in cars and airplanes and electrical generators

utilizing the mechanical energy resulting from the shape transformations.Nitinol with its shape memory property is also envisioned for use as car frames.Other possible automotive applications using SMA springs include engine cooling, carburetor and

engine lubrication controls, and the control of a radiator blind ("to reduce the flow of air through the radiator at start-up when the engine is cold and hence to reduce fuel usage and exhaust emissions")

CONCLUSION The many uses and applications of shape memory alloys ensure a bright future for these metals. Research is currently carried out at many robotics departments and materials science departments. With the innovative ideas for applications of SMAs and the number of products on the market using

SMAs continually growing, advances in the field of shape memory alloys for use in many different fields of study seem very promising.

REFERENCES • Shape Memory Alloy, BTP Report by Saurabh Maghade and Sahil Agarwal.• http://www.stanford.edu/~richlin1/sma/sma.html• www.wikipedia.org• Hodgson DE, Wu MH, Biermann RJ. (1990) Shape memory alloys. ASM Handbook: ASM

International. pp. 897–902• Wilkes, K. E.; Liaw, P. K.; Wilkes, K. E. (2000). "The fatigue behavior of shape-memory

alloys". JOM 52 (10): 45• Wu, S; Wayman, C (1987). "Martensitic transformations and the shape-memory effect in

Ti50Ni10Au40 and Ti50Au50 alloys". Metallography 20 (3): 359.

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