Methodology and some results of studying the influence of frequency on functional properties of pseudoelastic SMA

Abstract

The mechanical loading frequency affects the functional properties of shape memory alloys (SMA). Thus, it is necessary to study the effect of frequency in order to use successfully these materials in real structures. Based on the pseudoelastic cyclic behavior, the experimental methodology that allows testing of NiTi wires in stress controlled mode is proposed. Cyclic tensile tests are carried out using universal testing machine STM-100 at room temperature with loading frequencies of 0.1 Hz and 10 Hz. The functional dependencies are determined based on the experimentally obtained hysteresis loops. These functional dependencies comprise dissipated energy and damping factor. It iis found that the increase of loading frequency results in the worsening of functional properties, namely, to the decrease of dissipated energy and damping factor. This is caused by the fact that the regions of austenitic and martensitic transformation under the high loading frequency are absent. That is, the transformation of austenite into martensite does not occur, that stands for the pseudoelasticity effect. Nevertheless, it should be noted that the increase of loading frequency in 100 times augments the lifetime of pseudoelastic wire made of NiTi alloy roughly by 30%. It is determined that the increase of loading frequency results in the decrease of maximum strain in two times in the first loading cycle, and practically in 5 times after 200 cycles of loading.