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Static and dynamical functional properties of ultra thin NiTi wires

Ludek Heller 1,2Petr Sittner 1Michal Landa 2Petr Sedlak 2Jan Pilch 1

1. Institute of Physics ASCR, v.v.i., Na Slovance 2, Prague CZ-18221, Czech Republic
2. Institute of Thermomechanics ASCR, vvi, Dolejskova 5, Prague 18200, Czech Republic


2D/3D structures made from ultra thin (<100 μm) NiTi wires are currently considered in engineering applications in textile, medical or robotics field. Thin NiTi wires have several advantages over bulk elements – they are stronger, show enhanced functional properties, they are less prone to failure and able to be actuated with higher frequencies.

The development and design of such novel applications require the knowledge of the thermomechanical behaviour of NiTi ultra thin wires. First, since the material state of the thin NiTi wires is different from that of the bulk NiTi (texture, cold work etc.), their tensile properties cannot be obtained by simply scaling down the results measured on thicker wires but have to be determined experimentally. Second, since the shape set thin NiTi wires in 2D/3D structures deform by combined bending-tension-torsion, such behaviors have to be determined experimentally as well. Third, since many of the introduced applications attempt to take advantage of the unique damping capabilities of NiTi in a form of thin NiTi wires, it is of utmost interest to investigate their dynamical behavior, particularly the influence of temperature, prestress and vibration amplitude on the damping capacity.

In this paper, we will introduce various novel approaches towards termomechanical testing of ultra thin commercially available NiTi wires and simple shape set NiTi structures as helical or snake springs. Basic testing procedures include thermomechanical tensile testing, combined tension-torsion testing realized on a self-made experimental apparatus and forced tensile vibration testing. The experiments involve in-situ measurement of electrical resistance providing feedback information on the micro structural processes in the activated wires. The collected data provide a basis upon which FEM implementable models (related talk by Sedlak et. al.) describing functional thermomechanical behaviors of 2D/3D structures made of thin NiTi wires are built.

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Presentation: Oral at E-MRS Fall Meeting 2007, Symposium E, by Ludek Heller
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-05-14 11:34
Revised:   2009-06-07 00:44