Numerical durability evaluation of Nitinol stent
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Date
2012
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Technická Univerzita v Liberci
Technical university of Liberec, Czech Republic
Technical university of Liberec, Czech Republic
Abstract
Shape memory alloys, such as binary NiTi alloy, have
gained the attention of researchers, thanks to their
remarkable properties. In comparison with other usually
used materials, they exhibit large reversible strains
(pseudoelasticity) and especially a heat-induced regaining
of their original shape even in the case of significantly
large deformations (shape memory effect) (Yahia 2000;
Lagoudas 2008).
Even though many articles have been written on
account of these materials (Duerig et al. 1999;
Kleinstreuer et al. 2008; Nayan et al. 2009), only a few
deal with their fatigue properties. The need to know and
understand the behaviour of the material under cyclic
loading came from a project which deals with coronary
Nitinol stent grafts. Stents (Figure 1), which form a
skeleton of an implant, are made up of NiTi wires. After an
implantation of a stent graft into a blood vessel, it is
subjected to cyclic change of its diameter due to the
alternation between the systolic and diastolic blood
pressure.
The aim of this study was to carry out fatigue analysis
of a Nitinol stent, subjected to a cyclic crush test, and to
reveal critical areas of its construction. In previous work,
the dependency of stress amplitude versus number of
cycles until the failure of a specimen was evaluated
experimentally. This dependency is called Wo¨hler’s or the
S –N curve, and is one of the basic indicators that define
the fatigue properties of a material.
Thanks to our knowledge of the S –N curve of NiTi
alloy, we were able to predict the life of a Nitinol stent
with the support of data gained from a crush test of a stent
performed using the finite element method (FEM) in MSC
Marc software.
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1476-8259