Fatigue-crack growth properties of thin-walled superelastic austenitic Nitinol tube for endovascular stents

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review

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Author(s)

Detail(s)

Original languageEnglish
Pages (from-to)685-691
Journal / PublicationJournal of Biomedical Materials Research - Part A
Volume81
Issue number3
Online published22 Dec 2006
Publication statusPublished - 1 Jun 2007
Externally publishedYes

Abstract

Over the past 10 years, the supereleastic nickel-titanium alloy Nitinol has found widespread application in the manufacture of small-scale biomedical devices, such as self-expanding endovascular stents. Although conventional stress/strain-life (S/N) analyses are invariably used as the primary method for design against fatigue loading and for predicting safe lifetimes, fracture mechanics-based methodologies provide a vital means of assessing the quantitative effect of defects on such lifetimes. Unfortunately, fracture mechanics studies on fatigue in Nitinol are scarce, and most results do not pertain to the (thin-walled tube) product forms that are typically used in the manufacture of endovascular stents. In the current work, we document the basic fatigue-crack growth properties of flattened thin-walled (∼400 μm thick) Nitinol tubing in a 37°C air environment. Crack-growth behavior is characterized over a wide range of growth rates (∼6 orders of magnitude) and load ratios, that is, as a function of the alternating and maximum stress intensities, at 50 Hz. Limited experiments at both 5 and 50 Hz were also performed in 37°C air and simulated body fluid to determine whether the cyclic frequency affects the fatigue behavior. Fatigue-crack growth-rate properties in such thin-walled Nitinol tube are found to be quite distinct from limited published data on other (mainly bulk) product forms of Nitinol, for example, bar and strip, both in terms of the relative fatigue thresholds and the variation in steady-state growth rates.

Research Area(s)

  • Crack growth, Fatigue, Frequency effects, Load ratio effects, Nitinol, Stents

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