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Modeling superelastic NiTi wire structures
|Petr Sedlak 1, Petr Sittner 2, Michal Landa 1, Miroslav Frost 1, Ludek Heller 1,2|
1. Institute of Thermomechanics ASCR, vvi, Dolejskova 5, Prague 18200, Czech Republic
Research on the possibility to produce textile structures using superelastic NiTi wires is currently in progress. NiTi knitted self-expanding stents can be mentioned as a well-known example. Less known is that thin NiTi wires are considered for production of knitted and woven smart textiles with unique thermomechanical properties promising a wide range of new engineering applications. Optimal design of NiTi textiles requires reliable knowledge and modeling of superelastic behaviour of NiTi wire structures, composed from not just straight wires but generally from curved shape set wires. This appears to be a new area for SMA experimentation and modeling.
In the present contribution, we describe a newly proposed SMA model describing superelastic behavior of NiTi wires in tension and compression at constant temperature developed particularly for the purpose of simulating superelastic behaviour of NiTi 2D wire structures. The model describes the internal state with three internal variables: the martensite volume fraction, R-phase volume fraction and return points. The proposed model fulfils four basic requirements given on it:
·It captures the strains due to multiple deformation mechanisms taking place in NiTi transforming though B2-R-B19’sequences (the presence of R-phase dramatically affects mechanical behaviour of shape set NiTi structures).
·It reliably describes the closed shapes of entire and partial superelastic loops in stress – strain space including the return-point memory phenomenon (reliable modeling of partial loops is of key importance for shape set NiTi structures) .
·It captures asymmetric behavior in tension and compression (essential to simulate bending).
·It can be easily implemented into finite element models (essential to simulate nonhomogeneous deformations in shape set NiTi structures).
For demonstration, the experimental and simulated superelastic behavior of knitted self-expanding stent and NiTi “snake yarn” is presented and discussed.
Presentation: Oral at E-MRS Fall Meeting 2007, Symposium E, by Petr Sedlak
See On-line Journal of E-MRS Fall Meeting 2007
Submitted: 2007-05-14 11:03 Revised: 2009-06-07 00:44