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

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

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

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)

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

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

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

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

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

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

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

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

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

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.

Texas A&M University Active Materials Laboratory Biomimetic Hydrofoil