Detailed calorimetric investigations of shape memory alloys with all its derived thermodynamic and hysteretic data
"Hysteresis of stress-free martensitic transformations"
"Features of the hysteresis behaviour"
"Thermodynamic parameters of the martensitic transformation of NiTi-X-shape memory alloys"
"The hysteresis loop interior of the thermoelastic martensitic transformation"
"The limiting of the response time of shape memory alloy actuators by transformation rate"
Abstract: The thermal hysteresis of the thermoelastic martensitic transformations monocrystalline Cu-Al-X (X = Zn, Ni, Mn), NiTi, and Mn-Cu and polycrystalline NiTi-X (X = Au, Pt, Pd, Al) shape memory alloys were using calorimetry investigated.
Influence of crystalline interfaces and the skanning rate on the latent hysteresis and on the coefficient of the thermoelasticity (the slope of a transformation trajectory Z(T)) is also examined. The relationship between the thermoelasticity and the hysteresis is discussed.
Characteristics of the thermal and ferroelastic hysteresis as, for example, the memory on the reversal points not only during non complete cycles of the thermo-induced stress-free martensitic transformations (known as a SMART- or TAME-effect), but also during partial cycles of ferroelastic deformation were examined using calorimetry and tensile--compression-deformation tests of different shape memory alloys.
The general behavior of the internal transformation trajectories which is necessary for simulation of the hysteresis and modeling of shape memory properties is summarized based on the experimental investigations.
Experimental results also show that there exists an internal limitation of the conversion rate, so that the increase of the external Skanierungsrate not proportional increase of the internal rate of conversion leads. The calculated from these data limit of the operating frequency of the shape memory actuators is about 1 Hz