Study of an active deformable structure with embedded NiTi shape memory alloy strips

Abstract

The possibility of realising adaptive structures is of great interest in the control/automation fi elds, owing to
the benefi ts related to enhanced performance. To accomplish this, a challenging approach is the employment
of Shape Memory Alloys (SMAs) as active elements, which can recover seemingly permanent strains by
temperature-induced phase transformations whereby the so-called Shape Memory Effect (SME) takes place. This
paper deals with an experimental investigation of the bending recovery performance of a functional structure.
The active material was a near-equiatomic NiTi alloy in the form of strips, which were embedded into a custommade
polymeric matrix. To study the infl uence of heating/cooling rates on the characteristic transformation
temperatures of the NiTi material, several analyses were carried out by means of Differential Scanning Calorimetry
(DSC). Prior to the insertion, the strips were thermo-mechanically treated to memorise a bent shape through
experimentally evaluated shape setting parameters. The martensitic and reverse martensitic transformations were
thermally activated by means of a hot/cold air stream fl ow. Experimental tests enabled the characterisation of the
SME recovery behaviour evolution as well as the shape changes of the structure. Subsequently thermal activations
were considered to assess the stability of the functional structure deformations (polymeric matrix with SMA strips)
whose actual defl ections were evaluated by means of digital image analysis.