Self-expandable Nitinol stent has seen its application in peripheral artery disease. Fracture resistance evaluation is an active research area in recent years due to reported fracture from clinical studies. Constitutive models that describe Nitinol material behavior make it possible to simulate the stress-strain behavior of Nitinol devices under various loading conditions, which allows researchers to use various fatigue models to predict fracture resistance of Nitinol devices. Nitinol devices are commonly designed to accommodate large deformation during deployment and under clinical application. It is possible that buckling occurs during either bench top-testing or clinical condition. However, publication on Nitinol device analysis has been scarce due to technical difficulties to perform such analysis.

In this study, a linear buckling analysis was first performed to obtain the mode shapes and natural frequency of a Nitinol stent of a specified length. The lowest frequency mode shape was selected to introduce a perturbation for subsequence nonlinear buckling analysis. Typically, RIKS analysis is employed with implicit code to achieve convergent solutions for post buckling process that involved structure instability.

In nonlinear buckling analysis, on-site of buckling occurs as the load displacement curve show a drop with negative stiffness. FEA result of force displacement curve of Nitinol stent under axial compression  indicated that the stent buckles at about half way of the loading curve.  Deformed shape of the stent at on-site of the buckle, which is different from the symmetric deformation typically seen in models without buckling. It is very important to note that the strain distribution in buckled structure is highly localized. This is very different from the analysis without considering buckling where the high strain locations are generally quite evenly distributed amongst different struts as long as the stent has certain degree of symmetry.