title: Rotary-bending fatigue characteristics of medical-grade Nitinol wire.
abstract: The rotary bending fatigue properties of medical-grade Nitinol wires were investigated under conditions of 0.5-10% strain amplitudes to a maximum of 10(7) cycles. The results from this study provide insight into the behavior of Nitinol under fully reversed (εmin/εmax=-1) fatigue conditions for three compositions, two surface conditions and three test temperatures. For pseudoelastic conditions there are four distinct regions of the strain-cycle curves that are related to phases (austenite, stress-induced martensite, and R-Phase) and their respective strain accommodation mechanisms. In contrast, there are only two regions for the strain-cycle curves for thermal martensite. It was further observed that the strain amplitude to achieve 10(7)-cycles increases with both decreasing test temperature and increasing transformation temperature. Fatigue behavior was not, however, strongly influenced by wire surface condition. SEM of the fracture surfaces showed that the fatigue fracture area increased with decreasing strain amplitude. Finite element analysis was used to illustrate strain distributions across the wire as well as to calculate the tension-compression contributions to the rotary bending curves. The results from this investigation are discussed with respect to mechanisms of strain accommodation under cyclic tensile and compressive conditions.
authors.affiliation: Nitinol Devices and Components, Inc. 47533 Westinghouse Dr., Fremont, CA 94539, USA. Electronic address: alan.pelton@nitinol.com.
authors.forename: A R
authors.initials: AR
authors.lastname: Pelton
authors.forename: J
authors.initials: J
authors.lastname: Fino-Decker
authors.forename: L
authors.initials: L
authors.lastname: Vien
authors.forename: C
authors.initials: C
authors.lastname: Bonsignore
authors.forename: P
authors.initials: P
authors.lastname: Saffari
authors.forename: M
authors.initials: M
authors.lastname: Launey
authors.forename: M R
authors.initials: MR
authors.lastname: Mitchell
mesh_terms: D004548:Elasticity; D004864:Equipment and Supplies; D008422:Materials Testing; D009532:Nickel; D012399:Rotation; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013718:Tensile Strength; D014025:Titanium
chemical_list: C040654:titanium nickelide; D009532:Nickel; D014025:Titanium
keywords: Fatigue; Nitinol; Pseudoelasticity; Shape memory; Strain amplitude