Title: Shape Memory Alloys Team:
1Shape 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
2Outline
- Project Goal Fall 2008
- Fundamentals of Shape Memory Alloys
- Design Concepts
- Heat Transfer Analysis
- Comparison and Recommendations
- Future Tasks Spring 2009
- Questions
3Project 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.
4What are Shape Memory Alloys?
1
2
3
4
5
2
Deformed Martensite
- Converting thermal
- energy to mechanical
- work.
Stress
3
4
1
Self-Accommodated Martensite
Austenite
5
Temperature
Mf
Ms
Af
As
5Applications of SMAs
- Aerospace
- Airfoils, Boeing Chevrons, STARSYS
- Medical
- Stints, Instrumentation
- Other
- Eyeglasses frames, Locking mechanisms,
- Underwires, etc.
6Electric 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
7Design Concept 1 Wire Rotary Actuator
Bias Spring
Rack and Pinion
Drive Shaft
SMA Wire
8Modeling Wire Behavior Angular Displacement
Where ?? angle of rotation (rad) etrans
transition strain L length of SMA wire ?x
change in length R respective radii
9Modeling 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
10Modeling 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
11Results
- 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
12SMA Wires
Company Transformation Temperature Sizing Strain
Dynalloy Flexinol Af 70 - 100C Nitinol Af 80 - 90C Flexinol 0.001-0.02 Nitinol 0.004-0.01 4-5
SMA, Inc. Pseudoelastic Af -25-125C Wire 0.012-0.25 4-5
Small Parts Varying Af 70 - 90C Wire 0.006-0.1 3-5
13Design Concept 2 Torque Tube Rotary Actuator
Torque Tubes
Casing
Drive Shaft
Bevel Gears
14Mechanism Operation
Torque Tubes
Bevel gear attached to drive shaft
Drive Shaft
Bevel gear attached to torque tube
15Torque Tube Attachment Method
Casing
Torque Tubes
16Torque 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
17Torque Analysis
?trans Max Torque (oz-in) Torque (f 8) (oz-in)
2 10558.6 3069.4
3 15837.9 8348.7
4 21117.2 13627.9
5 26396.5 18907.3
6 31675.8 24186.6
?trans2
This data based upon G 152,289.625 psi RM 0.2
in L 2 in J 0.0053 in4
18Heat Transfer Overview
- Drives SMA actuation
- Cp varies between 0.32 and 0.6 during actuation
- Material Properties (Nitinol)
- Wire Properties
- Torque Tube Properties
Density Resistivity Cp Activation Relaxation
Austenite 6.45 g/cc 76 µOcm 0.322 J/gC 78 C -
Martensite - 82 µOcm 0.322 J/gC - 42 C
Trans. - - 0.6 J/gC 68 C 52 C
Radius 1 Radius 2 Length Voltage Power Conv. Coeff. Tempa
0 cm 0.05 cm 10 cm 0.2 V 0.44 W 0.01 W/cc K 20 C
Radius 1 Radius 2 Length Exterior Heat Conv. Coeff. Tempa
0.3 cm 0.5 cm 5 cm 110 W 70 W 0.1 W/cc K 20 C
19Heat Transfer Wire
- Resistive Heating
- 4 seconds to heat
- Forced Air Cooling
- 4 seconds to cool
Cycle Time 8 Seconds
20Heat Transfer Torque Tube
- Contact Conductive Heating
- 8 seconds to heat
- Forced Air Cooling
- 10.5 seconds to cool
Cycle Time 18.5 Seconds
21Compare/Contrast and Future Recommendation
- 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.
22Future Tasks Spring 2009
- Detailed analysis of SMA wire application
- Detailed design of SMA wire application
- Build working prototype
- Test and compare results to theoretical
23Questions?