Properties of Nickel Titanium Shape Memory Alloys


  • Shape memory alloys (SMAs) are widely used as actuators in many high tech applications from heart stints to aircraft.  Recently the ASL discovered a previously unreported property of Nickel Titanium SMAs that could make them even more useful in more applications.  The ASL is continuing research to explain the nature and origion of the property.
  • Shape memory alloys can under go large, recoverable deformations in their low temperature, martensitic state.  When heated the materials undergo a reversible phase transformation to an austenite crystalline structure and try to return to their parent geometry.  When cooled back to a martensite state the SMA will stay in its parent geometry unless loaded to deform again.  The ASL discovered that, when a SMA is mechanically constrained from returning to its parent geometry in the austenite state, and cooled to its martensite state, it will produce a “post constrained recovery residual stress” (PCRRS) that does not depend upon continued thermal actuation.


  • Explore and understand the origin and nature of PCRRS.
  • Create new theory to explain PCRRS.




This research has been supported by:

  • Funds provided by The University of Wisconsin – Milwaukee