Fatigue and asymmetric deformation of nitinol shape memory alloys

Nickel titanium (NiTi) shape memory alloys, also referred to as Nitinol, have been used in various medical applications owing to their ability to recover large stratins and their relatively strong chemical and mechanical bio-compatibility. Amongst other things, it is critical to fully understand the mechanical behavior of NiTi shape memory alloys in order to successfully use them in design. In the present paper we discuss the fatigue and highly asymmetric (tension-compression) deformation of NiTi shape memory alloys, both of which are important factors for device design. Particular emphasis is placed on understanding the underlying structure that drives these effects, with a secondary emphasis on methods to design the material structure and ensuing devices with these effects in mind.