shape memory alloys- principles and applications
DESCRIPTION
SHAPE MEMORY ALLOYS:FORMATION, PROPERTIES AND TECHNOLOGICAL IMPACT All about shape memory alloys. Principles and applications described brieflyTRANSCRIPT
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SHAPE MEMORY ALLOYS:
FORMATION, PROPERTIES
AND TECHNOLOGICAL IMPACTMuhammed Labeeb
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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
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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.
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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
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Athermal reaction with no diffusion.
PRINCIPLE
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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 )
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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)
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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
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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
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APPLICATIONS
▪ Aeronautics
▪ Wings
▪ Alternatives to hydraulic systems
▪ Medical
▪ Optometry
▪ Self-expandable cardiovascular stent
▪ Piping
▪ Couplings
▪ Robotics
▪ Artificial limbs
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APPLICATIONS
Robots can be given a more fluid movement in joints and limbs
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APPLICATIONS
Plane wings with SMA wires can change shape by inducing voltages in them. This can replace hydraulic and electromechanical actuators.
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APPLICATIONS
Wires have the ability to flex the robotic muscles according to electric pulses sent through the wire.
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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
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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)
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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.
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ADVANTAGES AND DISADVANTAGES OF SHAPE MEMORY ALLOYS
▪ ADVANTAGES
▪ Bio-compatibility
▪ Diverse field of application
▪ Good mechanical properties
▪ DISADVANTAGES
▪ Expensive
▪ Poor fatigue properties
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REFERENCE
▪ http://en.wikipedia.org/wiki/Shape_memory_alloy
▪ http://www.smaterial.com/SMA/sma.html