Memoleuven

FP6-515813-2

AVALON Multifunctional textile structures driving new production and organizational paradigms by textile SME interoperation Across highadded-VALue sectOrs for knowledge-based product/service creation

Research Stay Report Memo

TO: Avalon, Integrated project FP6-515813-2 FROM: Ludek HELLER, Institute of Physics, Academy of Sciences of The Czech Republic DATE: May 15, 2006 SUBJECT: Trip to the Department of Metallurgy and Materials Enginerring at KULeuven (MTM KULeuven). From Sunday 2 April to Saturday 29 April 2006.

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Purpose

The one-month stay at MTM KULeuven was planned within the framework of collaboration between MTM KULeuven and Institute of Physics (IoP). Both organizations are involved in the workpackages concerning the mechanical and functional testing of thin NiTi wires. The trip had two main purposes, both included the use of the dynamical mechanical analyser (DMA), which forms a part of MTM KULeuven equipment. The first aim was to conduct an experimental campaign of static tests and the second purpose concerned the assesment of suitability of DMA use for dynamic testing of ultra thin SMA wires.

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Summary Static Tests

The experimental campaign of static tests was performed on superelastic SMA wires of the diameter 0.05mm purchased by MTM KULeuven and denoted as type “C” in the Activity Report of MTM KULeuven covering the period from 2005-03-01 to 2006-03-01. The results of the testing allowed to complete the information about the mechanical and functional behaviour of NiTi wires firstly reported in the previously mentioned Activity Report of MTM KULeuven, which focused on the martensitic NiTi wires. As mentioned above, the tested wires were of the diameter 0.05mm and they had undergone a heat treatment at 450 ‰ for 35 mins. The important property given by such a heat treatment is the presence of the R-phase transition, similarly as in the case of martensitic wires (MTM KULeuven Activity Report). The experimental campaign of static tests consisted of a set of stress-strain-temperature cycles starting always from the austenite phase above Af temperature. The tests were conducted in a wide temperature range starting from −160 ‰ to 160 ‰. All tests were performed in such a way so that the results provide the necessary information for constructing the non-equilibrium stress-temperature diagram which we believe is a useful representation of thermomechanical behaviour of SMA wires. The main results gathered during the stay at MTM KULeuven are presented in the Appendix. These results together with those presented in the Activity Report of MTM KULeuven are to be published for SMST 2006 Conference.

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Dynamic Tests

The DMA experimental equipment provides the facilities allowing to measure the viscoelastic material properties in the frequency range up to 200 Hz. In connection with SMA, the DMA was supposed to be a suitable tool for identification of SMA damping capacities being one of the most important SMA functional properties. A set of dynamic tests was carried out on the “C” wire of the diameter 0.05mm in order to

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asses the applicability of DMA for damping identification of SMA wires. Since many problems had been encountered during these tests it turned out that the damping identification of SMA wires using DMA is highly limited. The main problem encountered was that of the sample slipping at grips. Another problem arised from non-availability of the time response signal which means that one cannot analyse the transfer behaviour of the material to get the basic information about material dynamic behaviour.

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Conclusion

The systematic experimental static tests of thin NiTi wires are to continue at MTM KULeuven and IoP for a deeper understanding of various parameters influence on their behaviour such as the diameter, the heat treatment and the state of the wire surface. For the dynamic tests for which the DMA has failed, the vibration tester being prepared at the Institute of Thermomechanics in Praque will be used. For these purposes the following quantity of SMA wires has been brought back from MTM KULeuven: ˆ superelastic wire “C”

ˆ martensitic wire “H”

– ∅0.024mm − 15m

– ∅0.027mm − 15m

– ∅0.030mm − 15m

– ∅0.035mm − 25m

– ∅0.050mm − 20m

– ∅0.055mm − 20m

– ∅0.1mm − 20m

– ∅0.071mm − 15m – ∅0.095mm − 15m

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Appendix A brief overview of obtained results is given below.

All the tests were performed on the superelastic NiTi wire of the diameter 0.050mm that had undergone the 35mins. heat treatment in argon atmosphere at 450 . The position of transition temperatures had been identified by means of DSC measurement the result of which is shown in Fig.1.

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Fig. 1 Fig.2 illustrates the results of systematic room temperature cyclic pseudoelastic tests carried out to asses the stability of functional properties.

Fig. 2

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The results of cyclic tests at wide range of temperatures are shown in fig.3 and 4. Each of the figures represent the results obtained on a unique sample, with the first cycle starting at 25 . Every temperature increase or decrease consisted of two steps: i) heating above Af and ii) cooling to the given temperature.

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Fig. 3

Fig. 4

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In order to avoid the influence of preceeding cycling on the shape of stress-strain curves, a certain number of tests with the virgin sample for each temperature were performed. These results are summerized in Fig.5 and 6. The second figure reveals one of the important points that is the R-phase transition plateau stress increase when decreasing the temperature.

Fig. 5

Fig. 6

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All gathered results allowed to construct the non-equilibrium stress-temperature diagram shown in Fig.7.

Fig. 7

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