S. Zhang, ev3 Endovascular Inc, Plymouth, MN; E. Young, A. Mukherjee, Edwards LifeSciences, Irvine, CA
Uniaxial Mechanical Characterization of Nitinol Tubing
Sean Zhang, Ernie Young and Avijit Mukherjee
Edwards LifeSciences, One Edwards Way, Irvine, CA 92614
Abstract
Uniaxial mechanical test provides the most important material data for device design and numerical modeling. Nitinol material has its unique behavior under loading, such as the stress-induced phase transformations, different elastic moduli between austenite and martensite, hysteresis between loading and unloading, the effect of loading cycles, the orientation dependent and localized phase transformation, etc. In this study, the focuses are: 1) How to define the Young’s moduli of martensite; 2) how the loading cycles affect the phase transformation; 3) how the deformation level affects the reversed phase transformation and the hysteresis. Answering these questions help to understand the material, develop new devices and develop better material model for numerical simulation.
Summary: In this study three different cyclic tests were conducted to investigate the cyclic response of Nitinol tubing: cyclic test under a constant strain, ascending cyclic test and descending cyclic test. The results indicate that the evolution of the loading/unloading yield stresses, loading/unloading plateaus and the hysteresis loops are not only related with the number of cycles, but more importantly are related with the deformation levels. Applying these results in material model for numerical simulation will help for more accurate computer modeling and therefore help for new device development.
