Abstract
The use of shape memory alloys (SMA) as smart structures and other modern applications require a previous evaluation of its performance under load as well as a training procedure. In general, these requirements lead to the design and assembly of a specific test bench. In this work, an experimental set-up was specially designed to perform the electro-thermomechanical characterization of SMA wires. This apparatus was used to determine the strain-temperature (epsilon - T) and electrical resistance-temperature (R - T) hysteretic characteristics curves of a Ti-Ni shape memory wire (90 mm in length and 150 µm in diameter) under mechanical load. The SMA wire is loaded by means of constant weights and a controlled system for injection of electrical power allows performing the heating-cooling cycles. The obtained hysteretic epsilon - T and R - T characteristics curves for some levels of applied loads are used to determine important shape memory parameters, like martensitic transformation temperatures, temperature hysteresis, temperature slopes and shape memory effect under load. These parameters were in accord with the ones found in literature for the studied SMA wires.
Highlights
Shape memory alloys (SMA) are active metallic materials classified nowadays as “smart” or “intelligent” materials along with piezoelectric ceramic and polymers, eletroactive plastics, electro-rheological and magneto-rheological fluids and others
The experimental set-up illustrated in Figure 1 allows to measure at the same time the strain (ε) and electrical resistance (R) of the shape memory alloys (SMA) wire as a function of electrical current i(t)
Electrical current can be directly converted to temperature of the SMA wire using Equation 2
Summary
Shape memory alloys (SMA) are active metallic materials classified nowadays as “smart” or “intelligent” materials along with piezoelectric ceramic and polymers, eletroactive plastics, electro-rheological and magneto-rheological fluids and others These materials are naturally considered as sensor-actuator elements demonstrating large possibilities for applications in high technology smart systems. The heating and cooling of SMA by direct passage of electrical current through the wire sample accompanied of electrical resistance and strain measurements, is a challenge that was not yet fully explored. In this case, when the SMA wire sample is very thin, direct measurement of SMA temperature becomes difficult.
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