Failure Mode Analysis of Nitinol Medical Devices: Fractography of Stent Structures

For the production of Nitinol stent structures there are two major manufacturing techniques established: Laser Tube Cutting and Wire Braiding or Winding. It is well known that both techniques can cause material fractures during and after their processing. The interaction of specific process parameters and product design parameters may cause such a failure mode. Therefore, a certain variety of root causes for material fracture is identified and a Nitinol fracture pattern characterization is performed for the cause of this study.

Standard tests on laser cut struts and wires with different loading conditions (tensile, torsion, kinking, shear, cyclic) lead to different fracture patterns (overload, fatigue, overload+fatigue) and their individual characteristics. Those standard test patterns, which will be presented primarily, are baseline for the following characterization of process-related fractures of Nitinol stent structures.

All fracture patterns (standard tests & process-related) will be investigated by Scanning Electron Microscopy (SEM) and correlated to their individual root cause.