Finite-element study of Existent medical stent

 existent1The analysis goals are to calculate the stress-strain fields that develops during the various stages of stent deployment into a blood vessel and to calculate the fatigue behavior and safety factor of the stent under in vivo conditions.

The FE model of the stent contained the smallest repeating pattern of the struts under appropriate symmetry conditions. Figure 1 shows the geometry of the model. In order to simulate the physical conditions as closely as possible, FEA was carried out in 6 stages:

Stage 1: Crimping. The stent was radially compressed to reduce its diameter until all struts were in tight contact and gaps were eliminated. The solution was obtained by solving a contact problem between a rigid cylinder surface (initially the outer diameter of the stent) and the outer surface of the stent.
Stage 2: Spring-back. The crimping surface was gradually removed by increasing its diameter and letting the stent assume its equilibrium, load-free configuration. The unloaded (recoiled) configuration was then obtained.
Stage 3: Inflation. The stent balloon was inflated to its final shape (inner diameter at 110% of the nominal diameter). Solving a contact problem between the balloon and the inner surface of the stent simulated inflation in the FE model.
Stage 4: Recoil. The inflation surface was gradually removed, allowing the stent to recoil to its equilibrium state. The unloaded configuration was obtained.
Stage 5: The stent was recoiled to a 3% reduction of its maximum expanded diameter.
Stage 6: Alternating load. The solution of Stage 5 was loaded by an inner pressure level that matches the maximum level of pressure existing in a blood vessel.