The superelasticity in shape memory alloys has been widely promoted as a phenomenon to be used for passive damping purposes. This superelastic damping (SD) is commonly evidenced by the area of stress-strain loop observed during one quasi static superelastic cycle. However, the relevance of such a demonstration is questionable with regard to dynamic conditions the damping applications are subjected to. Although the martensitic transformation (MT) is considered as a rate independent process, the deformation rate affects SD owing to heat effects (HEs) accompanying MT. The presented work is aimed to evaluate those HEs with regard to SD.
To characterize the role of HEs in SD, a phenomenological 1D model of SMA (RLOOP) is extended by a lumped-capacity heat equation including the latent heat generation/absorption, convective heat transfer and irreversible heat production during the phase transition. The effect of all those respective HEs on SD is analyzed with respect to the deformation rate, temperature, amplitude and prestrain. The predicted exponential SD decrease with deformation rate demonstrates unambiguously the unfavorable consequences of HEs.
To confront the conclusions provided by the model with experimental data, a dedicated self-designed vibrational tester is used. The system allows for a tensional harmonic excitation of a prestrained NiTi element in a wide frequency, strain amplitude and temperature ranges.
All collected experimental data clearly show the presence of HEs whose effect becomes more and more pronounced when increasing the loading frequency. The destroying impact the HEs have on SD is also demonstrated in agreement with predicted data.