In recent years the characterization and modelling of shape memory behaviour of NiTi

alloys are the targets of many research programs, in order to optimize, control and design

SMA sensors and actuators. SMAs offer great potential as active material in a variety of

different applications ranging through micro-robot manipulation, aircraft wing shape control

and micro-system precision control, but present significant difficulties for controlling due to

their hysteretic behaviour.

The present paper reports the results of a thermo-mechanical characterization of a Ni-51 at.

% Ti alloy. In particular the two way shape memory effect (TWSME), induced through a

proper thermo-mechanical treatment (training), was reported. One training cycle involves

a tensile load step until a fixed deformation value (training deformation), a successive

unloading, a heating up to Af (Austenite finish temperature) and a cooling down to Mf

(Mertensite finish temperature).

In order to analyze the hysteretic behaviour and the stability of TWSME, some trained

specimens, prepared by electro discharge machining, were subjected to thermal cycles

between characteristic transformation temperatures (Af and Mf). The experimental results

were used in order to develop a numerical model which is capable in simulating the complex

hysteretic behaviour of this class of materials; furthermore a systematic comparison of

numerical and experimental results was carried out.