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 JC will do the introduction of the team. 1

Outline Project Goal: Fall 2008 Fundamentals of Shape Memory Alloys Design Concepts Heat Transfer Analysis Comparison and Recommendations Future Tasks: Spring 2009 Questions JC will quickly run through the outline of the presentation.

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. JC will explain the goals of this semester and briefly expand on a few points.

What are Shape Memory Alloys? 1 2 3 5 4 Deformed Martensite 2 Converting thermal energy to mechanical work. Stress Uri will discuss what SMAs are, what they do, and how they do it. 3 4 1 Self-Accommodated Martensite Austenite 5 Temperature Mf Ms As Af

Applications of SMAs Aerospace: Medical Other Airfoils, Boeing Chevrons, STARSYS Medical Stints, Instrumentation Other Eyeglasses frames, Locking mechanisms, Underwires, etc. Tim

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 Tim

Design Concept #1: Wire Rotary Actuator Bias Spring Rack and Pinion Drive Shaft SMA Wire Tyler will describe how the mechanism works, including the advantages of the ratchet system.

Modeling Wire Behavior: Angular Displacement Where: Δθ = angle of rotation (rad) εtrans = transition strain L = length of SMA wire Δx = change in length R = respective radii Tyler will then discuss how we obtained the final equation of output shaft rotation as a function of wire contraction.

Modeling Wire Behavior: Moments and Torque Where: F = respective forces R = respective radii k = spring constant FSMA = SMA recovery force Δx = change in length η = efficiency of gear train n = number of SMA wires T = torque generated Brad will continue by discussing the equations leading to the calculation of output torque.

Modeling Wire Behavior: SMA Analysis Where: εtrans = actuation strain εelastic = elastic strain σi = recovery stress αA: coefficient of thermal expansion for austenite T -T0: change in temperature EM: Young’s Modulus for martensite EA: Young’s 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 Brad continued

Results Pittman Motor: Model GM14X02 SMA Wire Application 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 Density: Max: 1250 oz/in2 @ 5.5° rotation Min: 33.5 oz/in2 @ 115.5 ° rotation Brad

Transformation Temperature SMA Wires Company Transformation Temperature Sizing Strain Dynalloy Flexinol:: Af: 70° - 100°C Nitinol:: Af: 80° - 90°C Flexinol:: 0.001”-0.02” Nitinol:: 0.004”-0.01” ~4-5% SMA, Inc. Pseudoelastic Af: -25°-125°C Wire:: 0.012”-0.25” Small Parts Varying Af: 70° - 90°C Wire: 0.006”-0.1” ~3-5% Uri will discuss viable option of obtaining SMA wires

Design Concept #2: Torque Tube Rotary Actuator Torque Tubes Casing Drive Shaft Bevel Gears Uri will describe the setup of the torque tube mechanism

Mechanism Operation Torque Tubes Bevel gear attached to drive shaft Uri will further explain, in detail, how the system functions. Bevel gear attached to torque tube

Torque Tube Attachment Method Casing Uri will describe how we plan on overcoming the problem of attaching the torque tubes Torque Tubes

Torque Tube Analysis Where: T = applied torque J = polar moment of inertia c = radius of beam G = shear modulus L = length of beam φ = angle of twist Analyzing a shape memory alloy torque tube: Where: γ = shear strain γthermal= 0 (for isotropic material) RM = median radius of tube RM

Torque Analysis γtrans Max Torque (oz-in) Torque (φ = 8°) 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 ηtrans=2% This data based upon: G = 152,289.625 psi RM= 0.2 in L = 2 in J = 0.0053 in4

Heat 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 μΩcm 0.322 J/g°C 78 °C - Martensite 82 μΩcm 42 °C Trans. 0.6 J/g°C 68 °C 52 °C Tim 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

Heat Transfer: Wire Cycle Time: 8 Seconds Resistive Heating 4 seconds to heat Forced Air Cooling 4 seconds to cool Tim Cycle Time: 8 Seconds

Heat Transfer: Torque Tube Contact Conductive Heating 8 seconds to heat Forced Air Cooling 10.5 seconds to cool Tim Cycle Time: 18.5 Seconds

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 Tyler 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.

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 JC will explain the future tasks to be completed next semester.

Questions? We will open the floor up for questions from the audience.