Modelling and experimental investigation of geometrically graded NiTi shape memory alloys

Author： Shariat Bashir S Liu Yinong Rio Gerard

ISSN： 0964-1726

Source： Smart Materials and Structures, Vol.22, Iss.2, 2013-02, pp. : 25030-25042

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Abstract

To improve actuation controllability of a NiTi shape memory alloy component in applications, it is desirable to create a wide stress window for the stress-induced martensitic transformation in the alloy. One approach is to create functionally graded NiTi with a geometric gradient in the actuation direction. This geometric gradient leads to transformation load and displacement gradients in the structure. This paper reports a study of the pseudoelastic behaviour of geometrically graded NiTi by means of mechanical model analysis and experimentation using three types of sample geometry. Closed-form solutions are obtained for nominal stress–strain variation of such components under cyclic tensile loading and the predictions are validated with experimental data. The geometrically graded NiTi samples exhibit a distinctive positive stress gradient for the stress-induced martensitic transformation and the slope of the stress gradient can be adjusted by sample geometry design.