Shape Memory Alloys Team:

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Shape Memory Alloys Team High Torque Rotary
Actuator/Motor
Team Members Uri Desai Tim Guenthner J.C.
Reeves Brad Taylor Tyler Thurston Gary
Nickel NASA JSC Mentor Dr. Jim Boyd Faculty
Mentor Reid Zevenbergen Graduate Mentor
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Outline

• Project Goal Fall 2008
• Fundamentals of Shape Memory Alloys
• Design Concepts
• Heat Transfer Analysis
• Comparison and Recommendations
• Future Tasks Spring 2009
• Questions

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Project Goal Fall 2008

• Research and understand SMAs and their
  applications
• Research current conventions Electric motors
• Develop concepts for a Rotary Actuator/Motor
  driven by SMAs
• Evaluate concepts
• Conduct initial analysis of chosen concepts
• Select a baseline design
• Motivation Design a motor that will have a
  higher torque per unit volume and less weight
  than current motors.

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What are Shape Memory Alloys?
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Deformed Martensite

• Converting thermal
• energy to mechanical
• work.

Stress
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4
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Self-Accommodated Martensite
Austenite
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Temperature
Mf
Ms
Af
As
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Applications of SMAs

• Aerospace
• Airfoils, Boeing Chevrons, STARSYS
• Medical
• Stints, Instrumentation
• Other
• Eyeglasses frames, Locking mechanisms,
• Underwires, etc.

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Electric Motors

• Most applications for space utilize electric
  motors.
• Electric motors are very dense and therefore
  there is a weight penalty
• Electric motors operate better at higher speeds
  and lower torque For low torque applications, a
  gear box must be added to the motor, which
  increases the weight.
• Pittman motors have been used, in this case, as
  an example of electric motors with higher than
  average torque densities.
• Highest torque density from Pittman motor
  studied
• 6.83 oz in

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Design Concept 1 Wire Rotary Actuator
Bias Spring
Rack and Pinion
Drive Shaft
SMA Wire
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Modeling Wire Behavior Angular Displacement
Where ?? angle of rotation (rad) etrans
transition strain L length of SMA wire ?x
change in length R respective radii
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Modeling Wire Behavior Moments and Torque
Where F respective forces R respective
radii k spring constant FSMA SMA recovery
force ?x change in length ? efficiency of
gear train n number of SMA wires T torque
generated
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Modeling Wire Behavior SMA Analysis
Where etrans actuation strain eelastic
elastic strain si recovery stress aA
coefficient of thermal expansion for austenite T
-T0 change in temperature EM Youngs Modulus
for martensite EA Youngs Modulus for
austenite dSMA diameter of SMA wire n number
of SMA wires

• Typical actuation stress values 21,755-29,000
  psi

• Substituting above equation into previous moment
  equation

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Results

• Pittman Motor Model GM14X02
• Torque 107 oz in
• Torque Density 6.83 oz/in2
• SMA Wire Application
• 1 wire with diameter of 5mm or 10 wires with
  diameter of .02in (equivalent of 5mm)
• Torque DensityMax 1250 oz/in2 _at_ 5.5
  rotationMin 33.5 oz/in2 _at_ 115.5 rotation

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SMA Wires
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Design Concept 2 Torque Tube Rotary Actuator
Torque Tubes
Casing
Drive Shaft
Bevel Gears
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Mechanism Operation
Torque Tubes
Bevel gear attached to drive shaft
Drive Shaft
Bevel gear attached to torque tube
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Torque Tube Attachment Method
Casing
Torque Tubes
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Torque Tube Analysis
Where T applied torque J polar moment of
inertia c radius of beam G shear modulus L
length of beam f angle of twist
Analyzing a shape memory alloy torque tube
Where ? shear strain ?thermal 0 (for
isotropic material) RM median radius of tube
RM
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Torque Analysis
?trans2
This data based upon G 152,289.625 psi RM 0.2
in L 2 in J 0.0053 in4
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Heat Transfer Overview

• Drives SMA actuation
• Cp varies between 0.32 and 0.6 during actuation
• Material Properties (Nitinol)
• Wire Properties
• Torque Tube Properties

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Heat Transfer Wire

• Resistive Heating
• 4 seconds to heat

• Forced Air Cooling
• 4 seconds to cool

Cycle Time 8 Seconds
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Heat Transfer Torque Tube

• Contact Conductive Heating
• 8 seconds to heat

• Forced Air Cooling
• 10.5 seconds to cool

Cycle Time 18.5 Seconds
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Compare/Contrast and Future Recommendation

• SMA Wire Design

• SMA Torque Tube Design

• Simple and feasible
• Flexibility in altering torque versus output
  rotation Gear Ratios
• Less expensive to manufacture
• Light weight

• Modular design
• Capable of extremely high torque output
• Greater complexity
• Difficult to implement multi-directional rotation
• More expensive to manufacture

Recommendation The SMA Team recommends pursuing
the SMA wire application due to its simplicity,
feasibility and low cost. This design meets our
objective of designing a rotary motor that has
high torque per unit volume while maintaining a
small weight.
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Future Tasks Spring 2009

• Detailed analysis of SMA wire application
• Detailed design of SMA wire application
• Build working prototype
• Test and compare results to theoretical

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Questions?