Fig. 1. Phase structure and transformation behaviour of the Ti-50.86at%Ni alloy. (a): XRD pattern at room temperature. (b): DSC measurement.

Fig. 2. Tensile deformation behaviour of the dog-bone shaped sample.

Fig. 3. DIC analysis of the tensile deformation behaviour of the dog-bone shaped NiTi sample. (a): The εx strain field of the sample at the moment of formation of a Lüders band. In the figure, locations of four local and one global virtual extensometers are indicated. (b): Strain-time variations of the four material points. (c): Comparison of the strain-time variations of P1 and P2 during A→M transformation. (d): Variation of the nominal stress of the sample and the average strain in the austenite region during the Lüders band formation. (e): Local strain drop before the arrival of the Lüders band during its propagation. (f): Local strain surge and relaxation after the passing of the Lüders band.

Fig. 4. The variations of strain along the centreline of the dog-bone shaped NiTi sample and the corresponding strain fields at progressive times during the formation and the propagation of the Lüders band as obtained by DIC.

Fig. 5. The strain variation within the transition zone of austenite and martensite of the dog-bone shaped NiTi sample during the Lüders band propagation of A→M transformation.

Fig. 6. Tensile deformation behaviour of the uniform NiTi strip sample.

Fig. 7. DIC measurements of the uniform NiTi strip sample during tensile deformation. (a): The strain field of the sample upon the Lüders band formation during the reverse M→A transformation and the locations of points of virtual extensometers. (b): The strain-time variations at the observation points. (c): Comparison of the strain-time variations of P1 and P2 during the reverse M→A transformation. (d): Variation of the nominal stress of the sample and the average strain in the martensite region during the Lüders band formation.

Fig. 8. The variations of strain along the centreline of the uniform NiTi strip sample and the corresponding strain fields at progressive times during the formation and the propagation of the Lüders band over the reverse M→A transformation as obtained by DIC.

Fig. 9. The strain variation within the transition zone from the martensite to the austenite of the uniform NiTi strip sample during the Lüders band propagation of the reverse M→A transformation.