Thermomechanical Testing Machine Conceived for the Study of Shape Memory Alloys. Application to the Training and Testing of the Two-Way Memory Effect

Abstract

An electrohydraulic testing machine dedicated to the study of shape memory alloys has been developed. A complete computer control of force (resolution ±1 N), elongation (sensitivity ±10 μm) and temperature (precision 1 K) has been built. The machine is able to work in a soft mode, i.e. force controlled, or a hard mode i.e. deformation controlled and in a range of temperatures from 173 K to 473 K. The performances of the system have been checked by studying the two-way shape memory effect induced hy thermomechanical cycling in Cu-Zn-Al alloys. The training cycles consist of cooling down to the Mf temperature under a uniaxial 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 compression of tensile educated crystals shows the aptitude of these specimens to produce work.