This is an overview talk being given at Parker Hannifin in an effort to begin new collaboration, given by the NASA GRC Shape Memory Alloy (SMA) Team

Padula, Santo, II

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GENERAL BACKGROUND ON 
SHAPE MEMORY ALLOYS
Santo Padula, II
High Temperature and Smart Alloys Branch
Materials and Structures Division
NASA Glenn Research Center
https://ntrs.nasa.gov/search.jsp?R=20180004683 2019-08-31T15:31:52+00:00Z
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NASA GRC Shape Memory Alloy (SMA) Team
• Othmane Benafan
• Glen Bigelow 
• Chris Dellacorte
• Malcolm Stanford
• Fransua Thomas
• Santo Padula II 
• Darrell Gaydosh
• Anita Garg
• Timothy Halsmer
• Ron Noebe
Branch Chief: Bob Carter
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Shape Memory Alloys (SMAs): An Introduction
ü Metal alloys that have a “memory.”
ü These materials have the ability to remember and 
recover their original shapes against significant 
externally applied loads.
ü SMAs exhibit a solid-to-solid, reversible phase 
transformation that can be induced by the 
application of force or temperature.
ü NiTi most common alloy – highest work 
output/energy density.
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Basic Differences between Conventional Metals and 
Shape Memory Alloys (SMA)
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Conventional Material Deformation
qRequire imposed forces/stresses only generate ELASTIC deformation.
Elastic deformations
ü Distort the material lattice through bond stretch.
ü Deformations are REVERSIBLE.
Undeformed Crystal
Elastic
Deformation
t
Inelastic deformations - Plasticity
ü Distort the material lattice through microstructural 
rearrangement (metallic materials - slip).
ü Deformations are IRREVERSIBLE.
ü Can only dissipate energy.
Undeformed Crystal
Elastic & Plastic
Deformation
t
q If imposed forces/stresses create deformations that can’t be accommodated 
by ELASTIC distortion of lattice – PLASTIC deformation (bond breakage).
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Shape Memory Alloys:   An Introduction
Austenite Martensite Deformation
Heating 
Austenite Martensite 
Simplified 2D
a b
c
e1
e2
e3
Variant selection 
q How? 
ü Bain strain → (lattice deformation) 
ü Lattice invariant shear → (accommodation)
ü Inelastic deformation (transient twinning) → REVERSIBLE
Austenite Martensite
Microstructure
Courtesy of A. Garg
q Don’t accommodate deformations through elastic bond 
stretch.
q SMAs exhibit a solid-to-solid, reversible phase 
transformation.
q Transformation capable of storing over 30x the 
deformation that can be done in an elastic bond stretch.
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Mechanical Component Design Constructs
Conventional Design SMA Design
0.3 % Reversible Strain 7 - 8 % Reversible Inelastic Strain
Design so that component
remains elastic
Design so that component
takes advantage of inelastic
Shape Memory Alloys (SMAs) allow for  > 10 times the strain to be accommodated in the 
component, allowing designs that could never be contemplated with conventional materials
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Practical Example of Difference between 
Conventional Material and Shape Memory Alloys
Brass
Plastic Buckling & Fracture
Stainless Steel
Plastic Deformation
Shape Memory Alloy
Reversible Pseudoelasticity
The reversible, solid-state phase transformation that occurs in Shape Memory Alloys 
(SMAs) is capable of storing over 30x the deformation that can be done in a material 
required to accommodate the deformation solely through elastic bond stretch.
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Different Modes of Operation When Using 
Shape Memory Alloys (SMA)
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Alloy Chemistry Alters Temperature at Which 
Phase Transformation Happens
Solid-state Phase Transformation
between two phases
Temperature
AfAsMf Ms
Below Mf
Temp:
Martensite
Phase is stable
Above Af
Temp:
Austinite
Phase is stable
Martensite Finish: Mf
Martensite Start: Ms
Austenite Start: As
Austenite Finish: Af
Temperatures
AfAsMf Ms
Below Mf
Temp:
Martensite
Phase is stable
Above Af
Temp:
Austinite
Phase is stable
Alloy #2
Alloy #1
RT = 25 oC
Actuator Behavior (SME)
Pseudoelastic / Superelastic Behavior
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Examples of Shape Memory Alloys in Action
Thermally Induced Transformation
Actuator Behavior (SME)
Mechanically Induced Transformation
(Pseudoelastic / Superelastic Behavior)
Loa
din
g
Un-Loading
Austinite Austinite
Martensite
Martensite Martensite
Austinite
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§ SMA actuators can generate motion in one dimension (wire form), two dimensions (bending of a bar) 
or even motion in a more complex three dimensions(springs, honeycombs, panels)
§ Functionality: Tension (e.g., wires, springs), compression (e.g., rods, springs), bending (e.g., beams, 
plates),  torsion (e.g., rods, tubes, and springs)
Examples of the Two Transformation Types
Courtesy of UCF
Thermally Induced TransformationMechanically Induced Transformation
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Work Being Conducted by
Shape Memory Alloy (SMA) Team at GRC
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• WIDEN TEMPERATURE range over which 
they can be used.
• Improving WORK capability.
• Create materials that have BETTER 
STABILITY (REPEATABLE PERFORMANCE).
• BETTER WEAR and CORROSION 
RESITANCE.
• HIGHER DURABILITY and LONGER LIFE.
Research Driven Approach to Product Development
10-10 10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2
nm µm mmÅ m
10-1 100
STRUCTURAL SCALE
(COMPONENTS) 
MICRO-SCALE 
(MICROSTRUCTURES) 
ATOMIC SCALE
(NANOMATERIALS)
0
200
400
600
800
0 5 10 15 20
st
re
ss
 (M
Pa
)
strain (%)
15% 
10% 
5% 
8% 
13% 
18% 
 (b)
0% 
0
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0
0
8
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0
0
1
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0
0
2
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0
0
3
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0
0
4
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0
0
5
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0
0
6
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0
0
7
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0
0
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Examples of NASA Applications Using
Shape Memory Alloys (SMA)
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Shape Memory Alloy (SMA)
Non-Pneumatic Tires
qUtilization of Nickel-titanium (NiTi), “psuedoelastic” Shape Memory Alloy (SMA).
qCompliant tire technology:
ü Carry significant load
ü Envelop obstacles without permanent deformation or damage
q Two types of construction currently available:
ü Spring Tire
ü Radially Stiffened Tire
• Can carry much higher loads than coiled designs
• More easily scalable for changes in load and tire size requirements
Generation 2  – 2200 N (~500 lbf.)
Generation 1  – 890 N (~200 lbf.)
Generation 3  – 8900 N (~2000 lbf.)
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Shape Memory Alloy (SMA)
Non-Pneumatic Tires
Generation 1  – Spring Tire Generation 3  – Radially-Stiffened Tire
Non-pneumatic tire designs have the potential to open the door to thinking about 
wheel and brake assemblies in a way never before possible.
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Wing-tip actuation using SMAs  (Ground test)
Wings up
+75°
Wings down
-75°
Wings at
0°
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Wing-tip actuation using SMAs  (Flight test)
Wings up
+75°
Wings down
-75°
Wings at
0°
https://www.youtube.com/watch?v=9y1kkG2_QpE
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Wing-tip actuation using SMAs
(Close-up Demo)
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Questions?


General Background on Shape Memory Alloys

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