THERMOMECHANICAL TESTING MACHINE CONCEIVED FOR THE STUDY OF SHAPE-MEMORY ALLOYS - APPLICATION TO THE TRAINING AND TESTING OF THE 2-WAY MEMORY EFFECT

An electrohydraulic testing machine dedicated to the study of shape me mory alloys has been developed. A complete computer control of force ( resolution +/-1 N), elongation (sensitivity +/-10 mu m) and temperatur e (precision 1 K) has been built. The machine is able to work in a sof t mode, i.e. force controlled, or a hard mode i.e. deformation control led and in a range of temperatures from 173 K to 473 K. The performanc es of the system have been checked by studying the two-way shape memor y effect induced by thermomechanical cycling in Cu-Zn-Al alloys. The t raining cycles consist of cooling down to the Mf temperature under a u niaxial tensile stress of 35 MPa followed by heating up to Af at zero stress. The cycling procedures are completely automatic. A comparison of the two-way memory effect in single crystals (nominal Ms of 273 K) and polycrystals (nominal Ms of 230 K) is reported. A study in compres sion of tensile educated crystals shows the aptitude of these specimen s to produce work.