Thermomechanical testing of thin NiTi yarns for textile applications in combined tension-torsion

Novel hybrid technical textiles with integrated NiTi yarns partially inherit unique thermomechanical functional properties of NiTi wires as shape memory or superelasticity. An essential problem of the underlying R&D is that the NiTi yarns in such textiles are not loaded in uniaxial tension but in combined tension-torsion-bending and we know very little about the thermomechanical responses of NiTi wires under such general loading conditions. Hence, there was a need for appropriate testing equipment and modelling approaches. We have designed and build a first prototype of Avalon Tension-Torsion Universal Tester /ATTUT/ for efficient thermomechanical testing of thin NiTi yarns.  The prototype has already been used to evaluate combine tension-torsion responses of NiTi yarns at constant temperature (from -50^oC to 150^oC), tension-torsion strain responses during cooling-heating cycles under applied combined tension-torsion loads. The results are used for the development of SMA models capable of treating the general loading responses of NiTi yarns in textiles. In this work, the ATTUT equipment will be briefly introduced, experimental results on several superelastic and memory NiTi wires (d<0.1 mm) will be presented and discussed in view of textile applications.