Effect of Test Sample Model On Finite Element Analysis of Nitinol

Finite Element Analysis (FEA) is a standard tool for design and optimization of implants. Mechanical property data are typically generated using uniaxial tensile tests. The shape of the tensile test samples and their processing effect the obtained properties and consequently the data fed into the material model for the FEA. While in the past mechanical properties of semi-finished materials such as tubes, sheets and wires were used for the material model, recent trends towards tensile test samples, which are designed closer to finished device structures, can be seen. This is carried out to achieve a closer match between the material model for the FEA and the real device properties.

In this study the role of test sample geometry and processing on tensile test properties was investigated. Samples with different shapes were produced using various processing routes and subjected to uniaxial tensile testing. Subsequently, FEA Nitinol material models were calculated using the measured mechanical properties. Nitinol stent radial force test characteristics were calculated for each material model using FEA. In parallel, Nitinol stent samples with defined properties and shapes matching the FEA models were manufactured and subjected to radial force testing. Experimentally determined radial force test results were compared to simulation results.

This study provides an assessment of the tensile test sample model used as input for Finite Element Simulation. The presentation shows which model fits best to real radial deformation behaviour of a Nitinol stent.