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

The possibility of realising adaptive structures is of great interest in the control/automation fields, owing to the benefits 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 custom-made polymeric matrix. To study the influence 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 flow. 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 deflections were evaluated by means of digital image analysis.