shape memory alloys- principles and applications

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SHAPE MEMORY ALLOYS: FORMATION, PROPERTIES AND TECHNOLOGICAL IMPACT Muhammed Labeeb

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SHAPE MEMORY ALLOYS: FORMATION, PROPERTIES AND TECHNOLOGICAL IMPACT All about shape memory alloys. Principles and applications described briefly

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Page 1: SHAPE MEMORY ALLOYS- PRINCIPLES AND APPLICATIONS

SHAPE MEMORY ALLOYS:

FORMATION, PROPERTIES

AND TECHNOLOGICAL IMPACTMuhammed Labeeb

Page 2: SHAPE MEMORY ALLOYS- PRINCIPLES AND APPLICATIONS

SMA

▪ Shape memory alloys are metal alloys that “remember” their original shapes and having the ability to return to original shape after being deformed by heating

▪ A class of smart materials

▪ The most effective and widely used alloys are NiTi, CuZnAl, and CuAlNi

▪ SMAs have two stable phases - the high-temperature phase, called austenite and the low-temperature phase, called martensite

▪ The shape change involves a solid state phase change involving a molecular rearrangement between Martensite and Austenite

▪ SMA also exhibits superelastic (pseudoelastic) behavior

Page 3: SHAPE MEMORY ALLOYS- PRINCIPLES AND APPLICATIONS

A BRIEF HISTORY

▪ 1932 - A. Ölander discovers the pseudoelastic properties of Au-Cd alloy.

▪ 1949 - Memory effect of Au-Cd reported by Kurdjumov & Kandros.

▪ 1967 – At Naval Ordance Laboratory, Beuhler discovers shape memory effect in nickel titanium alloy, Nitinol (Nickel Titanium Naval Ordance Laboratory), which proved to be a major breakthrough in the field of shape memory alloys.

▪ 1970-1980 – First reports of nickel-titanium implants being used in medical applications.

▪ Mid-1990s – Memory metals start to become widespread in medicine and soon move to other applications.

Page 4: SHAPE MEMORY ALLOYS- PRINCIPLES AND APPLICATIONS

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

▪ detwinned

▪ A phase transformation which occurs between these two phases upon heating/cooling is the basis for the unique properties of the SMAs

Page 5: SHAPE MEMORY ALLOYS- PRINCIPLES AND APPLICATIONS

Athermal reaction with no diffusion.

PRINCIPLE

Page 6: SHAPE MEMORY ALLOYS- PRINCIPLES AND APPLICATIONS

PRINCIPLE

▪ Upon cooling in the absence of applied load the material transforms from austenite into twinned martensite. (no observable macroscopic shape change occurs)

▪ Upon heating the material in the martensitic phase, a reverse phase transformation takes place and as a result the material transforms to austenite.

▪ If mechanical load is applied to the material in the state of twinned martensite (at low temperature) it is possible to detwin the martensite.

▪ Upon releasing of the load, the material remains deformed. A subsequent heating of the material to a temperature above the austenite finish temperature (Af) will result in reverse phase transformation (martensite to austenite) and will lead to complete shape recovery.

(Af: temperature at which transformation of martensite to austenite is complete )

Page 7: SHAPE MEMORY ALLOYS- PRINCIPLES AND APPLICATIONS

PRINCIPLE

TEMPERATURE

ST

RE

SS

Mf Ms As Af

TEMPERATURES

TR

ES

S

Mf Ms As Af

Twinned Martensite (unstressed)

Detwinned Martensite (stressed - deformed)

Detwinned Martensite (stressed - deformed)

Austenite (undeformed)

Twinned Martensite (unstressed)

Page 8: SHAPE MEMORY ALLOYS- PRINCIPLES AND APPLICATIONS

PRINCIPLE

▪ SMA remembers the shape when it have austenitic structure.

▪ So if we need SMA to remember and regain/recover certain shape, the shape should be formed when structure is austenite

▪ Reheating the material will result in complete shape recovery

Page 9: SHAPE MEMORY ALLOYS- PRINCIPLES AND APPLICATIONS

PSEUDOELASTIC BEHAVIOR

ST

RE

SS

TEMPERATURE

M f Ms As Aff s s f

Austenite

Detwinned Martensite(stressed)

▪ Occurs when an alloy is completely in the Austenite phase

▪ Is not dependent on temperature

▪ When the load is increased to a point, the alloy transitions from the Austenite phase to the detwinned Martensite phase

▪ Once the load is removed, the alloy returns to the it original Austenite shape

▪ Rubber like effect

Page 10: SHAPE MEMORY ALLOYS- PRINCIPLES AND APPLICATIONS

APPLICATIONS

▪ Aeronautics

▪ Wings

▪ Alternatives to hydraulic systems

▪ Medical

▪ Optometry

▪ Self-expandable cardiovascular stent

▪ Piping

▪ Couplings

▪ Robotics

▪ Artificial limbs

Page 11: SHAPE MEMORY ALLOYS- PRINCIPLES AND APPLICATIONS

APPLICATIONS

Robots can be given a more fluid movement in joints and limbs

Page 12: SHAPE MEMORY ALLOYS- PRINCIPLES AND APPLICATIONS

APPLICATIONS

Plane wings with SMA wires can change shape by inducing voltages in them. This can replace hydraulic and electromechanical actuators.

Page 13: SHAPE MEMORY ALLOYS- PRINCIPLES AND APPLICATIONS

APPLICATIONS

Wires have the ability to flex the robotic muscles according to electric pulses sent through the wire.

Page 14: SHAPE MEMORY ALLOYS- PRINCIPLES AND APPLICATIONS

APPLICATIONS

©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.

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

Page 15: SHAPE MEMORY ALLOYS- PRINCIPLES AND APPLICATIONS

APPLICATIONS▪ Nanomuscles

▪ Surgical instruments

▪ Tissue Spreader

▪ Stents (angioplasty)

▪ Coronary Probe

▪ Brain Spatula

▪ Endoscopy: miniature zoom device, bending actuator

▪ Force sensor

▪ Smart skin (wing turbulence reduction)

Page 16: SHAPE MEMORY ALLOYS- PRINCIPLES AND APPLICATIONS

APPLICATIONS

▪ The most common commercial application involves the pseudo-elastic property during it’s high temperature state.

▪ This includes eye-glasses, cell phone antennas, and so on, which are experiencing their high temperature state at room temperature.

Page 17: SHAPE MEMORY ALLOYS- PRINCIPLES AND APPLICATIONS

ADVANTAGES AND DISADVANTAGES OF SHAPE MEMORY ALLOYS

▪ ADVANTAGES

▪ Bio-compatibility

▪ Diverse field of application

▪ Good mechanical properties

▪ DISADVANTAGES

▪ Expensive

▪ Poor fatigue properties

Page 18: SHAPE MEMORY ALLOYS- PRINCIPLES AND APPLICATIONS

REFERENCE

▪ http://en.wikipedia.org/wiki/Shape_memory_alloy

▪ http://www.smaterial.com/SMA/sma.html