According to the recently issued ASTM standard, F2516-05: Standard Test Method for Tension Testing of Nickel-Titanium Superelastic Materials, strain measurement for nitinol specimens can be determined by machine crosshead motion or an extensometer.

A video extensometer is non-contacting extensometer that can measure one-dimensional deformation of a specimen by tracking the movement of two attached markers.  Typical Stress-Strain diagrams of Superelastic Nitinol will be compared between three different strain measurement techniques: a video extensometer, a clip-on extensometer and crosshead motion.  Gauge length and crosshead speed will be varied per the ASTM F2516.  Discussion will address features and limitations of each strain measurement technique.