Since nitinol is a thermally active material—meaning that it moves with response to heat—it is important to build a mathematical model of how it performs.  This means that the stress/strain (force/displacement) curve must be captured at many different temperatures in order to build a temperature dependent model of how the part behaves.  Since nitinol is also hysteretic, the nitinol can have different properties if it was heated to a specific temperature as opposed to cooled to the same temperature. 

        This data is collected with two instruments in the lab: the differential scanning calorimeter (DSC) and the temperature controlled universal testing machine (TCUTM).  The DSC measures the rate of heat absorption by the nitinol, allowing us to identify critical temperatures and latent heat of transformation in a stress-free state.  While the TCUTM cannot measure heat transfer, the TCUTM is able to identify transition temperatures in a stressed state.  This is referred to as active transition temperature measurement.  If your system is operating under stress, it is critical that an active transition temperature test be conducted.  Temperature dependent stress/strain data is required if you intend to use finite element analysis (FEA) to design your system.  Clearly, you will need a higher density of sample data around the critical temperatures and higher data densities will yield a more accurate material definition function (MDF).  Don’t forget that you will need to write the MDF to make allowance for differing properties if the nitinol has cooled to the specified temperature versus warmed to the specified temperature.  We can help you to build the MDF of your nitinol to ensure that you have the best possible results.