A. Runciman, R. O. Ritchie, University of California, Berkeley, CA; A. R. Pelton, Nitinol Devices and Components, Fremont, CA
Nitinol stents are subjected to complex multiaxial loading conditions in vivo, including axial tension and compression, radial compression, pulsatile, bending, and torsion. Fatigue lifetime prediction analyses for Nitinol, however, are invariably based on uniaxial loading and thus may fall far short of accurately predicting the safe life of stents under the multiaxial loading conditions experienced physiologically. While there has been considerable research done on Nitinol in uniaxial tension, there remains a lack of fatigue life data in several other loading conditions, particularly torsion. In this work, thin-walled Nitinol tubes were fatigue tested in torsion to investigate the torsional hysteresis and fatigue behavior of Nitinol under these loading conditions, and to develop a fatigue life-prediction model for torsional loading. Equivalent fatigue testing was done on samples under uniaxial tensile loading for comparison with the torsional fatigue life data. The constitutive and fatigue life data obtained were used to try and develop a more comprehensive fatigue life-prediction model for Nitinol.
Summary: Nitinol tubing was fatigue tested in torsion to investigate the torsional hysteresis and fatigue behavior of Nitinol under torsional loading. The data was used to develop a fatigue life-prediction model for torsional loading. Equivalent fatigue testing was done on samples under uniaxial tensile loading for comparison with the torsional fatigue life data. The constitutive and fatigue life data obtained in both torsion and uniaxial tension were used to try and develop a more comprehensive fatigue life-prediction model for Nitinol.
