15 July 2002 Simple thermal actuator using R-phase transformation of Nitinol
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R<-->A phase transformation in NiTi alloy is associated with a very small recoverable strain of the order of 0.5% compared to that of 6-8% recoverable strain of M<-->A transformation. The stability of R<-->A transformation against large number of thermal cycles is an attractive feature for an application of SMA. A spring of NiTi is designed and fabricated, using 40% prior cold worked nitinol wire of dia 1mm, with appropriate heat-treatment such that martensitic transformation takes place through two stage A-->R-->M. The transformation behaviors of this wire are studied using DSC and electrical resistivity measurements. Further, the spring has been subjected to thermo-mechanical treatment for getting a two-way memory, viz:, while heating the spring gets contracted and while cooling it gets elongated. This spring has been used as an thermal actuator and temperature variation is confined between 50-65 degree(s)C to utilize only R<-->A transformation. Linear stroke of 4cm by the spring is used to rotate a platform carrying a load of 2 kg. The efficiency and reliability of the spring is tested over a million thermal cycles.
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Jayagopal Uchil, Jayagopal Uchil, Kumara K. Ganesh, Kumara K. Ganesh, K.K. Mahesh, K.K. Mahesh, } "Simple thermal actuator using R-phase transformation of Nitinol", Proc. SPIE 4701, Smart Structures and Materials 2002: Smart Structures and Integrated Systems, (15 July 2002); doi: 10.1117/12.474680; https://doi.org/10.1117/12.474680

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