Domain interfaces and fatigue failure of niti polycrystalline strips

Lüders-like band is an important deformation feature in a stretched pseudoelastic NiTi polycrystalline strip and its formation/evolution can influence the fatigue life of the NiTi strips significantly. For "elastic" fatigue tests on the specimens with unchanged domain/band patterns (immobile domain interfaces), it is normally expected that the fatigue failure would occur at the band front (the interface separating the Martensite and the Austenite domains); however, it was revealed recently that the fatigue failure can happen inside the Martensite domain. To further understand this phenomenon, the "elastic" fatigue tests and in-situ highresolution recording of the interface morphology were conducted on NiTi strips of different thicknesses. It is found that the strip's thickness can influence the morphology of the domain interface so as to affect the strip's fatigue life. Moreover, the fatigue failure can occur at the domain interfacial zone or inside Martensite domain, depending on the morphology of the domain interface which depends on the strip's thickness. It is implied that the domain interface could be a key feature governing the fatigue failure of NiTi strips.