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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.