Moreover, strain time dependence can be described once the heat exchange phenomena and the effect of the Martensitic-Austenitic transformation are evaluated.

In this work, an experimental-numerical approach, used to study the thermo-mechanical behaviour of NiTi wire.

Tests were carried out heating, by an electrical power, wires having diameters of 80 and 150 mm and loaded by constant stresses of different values.

The numerical code integrates the ordinary differential equation describing the volumetric wire heating and cooling transients assuming that the electrical power is the only external heating source. Temperature distribution in the wire is considered uniform and its change in time depends on wire specific heat, latent heat of the Martensitic-Austenitic transformation, free convection heat exchange coefficient and total emissivity of the surface wire.

Numerical simulations, aimed to reproduce the experimental wire temperature and strain histories, allow to obtain information regarding heat exchange coefficient defining the heat loss by convection and the influence of the latent heat of the Martensitic-Austenitic transformation on the wire temperature and strain time dependence.

The results indicate that the wire heating rate mainly depends on the applied electrical power, latent heat of the Martensitic-Austenitic transformation, the wire total emissivity and the convection heat exchange coefficient.

In the cooling transient, the capability to decrease the wire temperature to reach the ambient value is effected by the curve representing the heat released during the Austenitic-Martensitic transformation, by a different convection heat exchange coefficient and the wire total emissivity.

Finally, resuslts obtained adopting different experimental configurations (horizontal or vetrical wire) are discussed to indicate the influence of the wire position on the convection heat exchange coefficient.