ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

Fig. 5. Damage evolution of the three stent designs. The locations where the stent
structure was severely damaged were indicated by circles. The legend is related to the
damage parameter D.
4.2 Corrosion testing of stent sample
After the first day of immersion, the expanded Sample B had several broken points on
struts due to corrosion while the Sample A kept the structural integrity. After 7 days of
immersion, the Sample B had scattered into many pieces while the Sample A just had
several broken points on struts due to corrosion (Fig. 6). From SEM observation it can
be seen that the corrosion of the stent samples was combined with uniform and stress
corrosion. The surfaces of the samples were covered by an oxide layer caused mainly by
uniform corrosion, which were composed of dense small blocks separated by cracks.
Many parts of the oxide layer had been shed from the samples and the matrices were
exposed to be attacked by new uniform corrosion. This "layer by layer" mechanism was
compatible with the simulation on uniform corrosion. The breaks on struts were mainly
caused by stress corrosion, and many locations of the broken points are compatible with
the expected locations from the simulation shown in Fig. 5.
Fig. 6. The SEM observation of Samples A and B after 7 days of corrosion. The red
circles indicate the breaks of struts which are compatible with the expectation in
simulation.