Transcript An Introduction to Shape Memory Alloys

Intelligent
Systems
Laboratory
An Introduction to
Shape Memory
Alloys
Dimitris C.Lagoudas
Shape Memory Alloy Research Team
Aerospace Engineering Department
Texas A&M University
What are Shape Memory Alloys?
•Shape Memory Alloys
(SMAs) are metallic
alloys that undergo a
solid-to-solid phase
transformation which
can exhibit large
recoverable strains.
Example: Nitinol
Austenite
• High temperature phase
•Cubic Crystal Structure
Martensite
•Low temperature phase
•Monoclinic Crystal Structure
Twinned Martensite
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Detwinned Martensite
Active Materials Laboratory
Thermally Induced Phase Transformation in
SMAs
Martensite
(twinned)
Martensite
(twinned)
TEMPERATURE
Mf
Ms
As
Af
TEMPERATURE
Mf
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Ms
As
Af
Austenite
Characteristic
temperatures:
Mf=Martensitic Finish
Ms=Martensitic Start
As=Austenitic Start
Af=Austenitic Finish
Austenite
Active Materials Laboratory
Detwinned Martensite
(stressed - deformed)
Mf
STRESS
STRESS
Shape Memory Effect:
Stress Free Shape Recovery
Ms
As
Twinned Martensite
(unstressed)
TEMPERATURE
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Af
Detwinned Martensite
(stressed - deformed)
Mf
Detwinned Martensite
(unstressed - deformed)
Ms
As
Af
TEMPERATURE
Austenite
(undeformed)
Active Materials Laboratory
The Shape Memory Effect
s
Detwinning
e
Cooling
Heating/Recovery
T
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STRESS
Shape Memory Effect: Shape
Recovery Under Stress
Detwinned Martensite
(stressed)
Mf
Ms
Austenite
As
Af
TEMPERATURE
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Active Materials Laboratory
The Pseudoelastic Effect
STRESS
Detwinned Martensite
(stressed)
Mf
Ms
As
Af
TEMPERATURE
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Austenite
Active Materials Laboratory
The Pseudoelastic Effect
s
s Mf
s Ms
s As
s Af
e
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Active Materials Laboratory
SMA Demonstrations and Applications
Floral Arrangement SMA Actuated
Butterfly: SMA Linear Actuator
Thermobile™ Demonstrator:
SMA Properties/Thermodynamics
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Where Are SMAs Used?
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SMAs in Bio-medical Devices
(a)
(b)
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SMA Space Applications
SMA Ribbon
Bolt released
Landis G.A., NASA Lewis Research Center, “Materials
Adherence Experiment Results from Mars Pathfinder”,
26th Photovoltaic Specialists Conference, 1997
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Active Materials Laboratory
SMAs as Linear Actuators
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Miniaturized Walking Robot
The implementation of SMA
wires coupled with a simple
DC control system can be
used to drive small objects
without the addition of
relatively heavy motors,
gears, or drive mechanisms.
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Active Materials Laboratory
Biomimetic Hydrofoil
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Active Materials Laboratory