1. Dimitris C.Lagoudas Shape Memory Alloy Research Team Aerospace Engineering Department Texas A&M University Intelligent Systems Laboratory An Introduction to Shape Memory Alloys

2. Texas A&M University Active Materials Laboratory 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 Martensite Low temperature phase Monoclinic Crystal Structure Austenite High temperature phase Cubic Crystal Structure Twinned MartensiteDetwinned Martensite

3. Texas A&M University Active Materials Laboratory Thermally Induced Phase Transformation in SMAs MfMf MsMs AsAs AfAf AusteniteMartensite TEMPERATURE MfMf MsMs AsAs AfAf AusteniteMartensite TEMPERATURE (twinned) Characteristic temperatures: M f =Martensitic Finish M s =Martensitic Start A s =Austenitic Start A f =Austenitic Finish

4. Texas A&M University Active Materials Laboratory Shape Memory Effect: Stress Free Shape Recovery TEMPERATURE STRESS MfMf MsMs AsAs AfAf TEMPERATURE STRESS MfMf MsMs AsAs AfAf Twinned Martensite (unstressed) Detwinned Martensite (stressed - deformed) Detwinned Martensite (unstressed - deformed) Austenite (undeformed)

5. Texas A&M University Active Materials Laboratory The Shape Memory Effect   T Cooling Detwinning Heating/Recovery

6. Texas A&M University Active Materials Laboratory Shape Memory Effect: Shape Recovery Under Stress TEMPERATURE STRESS M f M s Detwinned Martensite (stressed) Austenite A s A f

7. Texas A&M University Active Materials Laboratory The Pseudoelastic Effect STRESS TEMPERATURE M f M s A s A ffssf Austenite Detwinned Martensite (stressed)

8. Texas A&M University Active Materials Laboratory The Pseudoelastic Effect  Mf  Ms  Af  As  

9. Texas A&M University Active Materials Laboratory SMA Demonstrations and Applications Floral Arrangement SMA Actuated Butterfly: SMA Linear Actuator Thermobile ™ Demonstrator: SMA Properties/Thermodynamics

10. Texas A&M University Active Materials Laboratory Where Are SMAs Used?

11. Texas A&M University Active Materials Laboratory SMAs in Bio-medical Devices

12. Texas A&M University Active Materials Laboratory SMA Space Applications Landis G.A., NASA Lewis Research Center, “Materials Adherence Experiment Results from Mars Pathfinder”, 26th Photovoltaic Specialists Conference, 1997 SMA Ribbon Bolt released

13. Texas A&M University Active Materials Laboratory SMAs as Linear Actuators

14. Texas A&M University Active Materials Laboratory 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.

15. Texas A&M University Active Materials Laboratory Biomimetic Hydrofoil