G. Siekmeyer, A. Schuessler, ADMEDES SCHUESSLER GmbH, Pforzheim, Germany; M. Quellmalz, Admedes Schuessler GmbH, Pforzheim, Germany
Self expanding vascular implants are largely manufactured from Nitinol tubing. It is well known that the mechanical properties of those devices can be tuned during the thermal shape setting process by altering annealing time and temperature for example. However, it is less know that tube manufacturing history, such as cold work and annealing also may affect mechanical properties of finished devices.
Nitinol micro tensile test samples were laser cut from tubes of different ingots and tubing vendors and underwent different thermo-mechanical processing. Processing was geared towards achieving a comparable radial force between different tube materials. The fatigue life of these were tested by using accelerated fatigue tests based on a diamond shape model.
Tensile testing was performed at 37°C to determine mechanical properties, such as elastic modulus, tensile strength, and plateau strengths. Differential scanning calorimetry, metallographical and TEM investigations were performed to assess the impact of cold work and final annealing steps of tubing as well as the thermal shape-setting. All different results were put into a matrix in order to correlate the fatigue results with the thermo-mechanical impact such as nucleated precipitations, inclusion sizes and densities and fracture morphology.
Summary: Nitinol micro tensile test samples were laser cut from tubes of different ingots and tubing vendors. Samples underwent different thermo-mechanical processing in order to achieve a comparable radial force between different tube materials. Data from fatigue and tensile testing at 37°C will be presented and compared. Differential scanning calorimetry, metallographical and TEM investigations were performed to assess the impact of cold work and final annealing steps of tubing as well as the thermal shape-setting.
