The Marriage of Mechanical Testing and Synchrotron Radiation Micro-Diffraction
Dr. Apurva Mehta1, Dr. Nobumichi Tamura2, Mr. Scott Robertson3, Dr. Valentina Imbeni4, Alan Pelton5 and Robert Ritchie3, 1Stanford Synchrotron Radiation Laboratory, 2575 Sandhill Rd, Menlo Park, CA 94025, 2Advanced Light Source, Lawrence Berkeley National Laboratory, 1 Cyclotron Rd., Berkeley, CA 94720, 3Dept of Materials Science and Engineering, Lawrence Berkeley National Laboratory, 1 Cyclotron Rd., Bldg 66-R0200, Berkeley, CA 94720, 4SRI International, 333 Ravenswood Ave., Menlo Park, CA 94025, 5Nitinol Devices & Components, 47533 Westinghouse Dr., Fremont, CA 94539

The use of powerful synchrotron radiation sources, e.g., Stanford Synchrotron Radiation Laboratory and The Advanced Light Source, combined with the recent ability to control those beams to < 1mm2 presents researchers with the unique ability to study highly localized atomistic behavior.  Nitinol, which derives its unique and advantageous mechanical properties from controlled atomic motion in response to applied mechanical loads or temperature changes, is an ideal material for study using these techniques.  Combined with miniaturized, portable versions of mechanical loading devices, we can precisely study the atomistic response, e.g., volume change, stress, strain, and phase transformation, resulting from applied mechanical loads.  This technique allows us to conducted experiments on relevant size scales and in product forms and stress conditions that simulate those biomedical devices.   This paper details: i) the importance for a high-intensity X-ray sources, ii) the value of extremely small beam sizes, and iii) the development of two different miniature test rigs; one that can apply tension and/or torsion to tubular Nitinol, and another that applies tensile loads via pin or compression grips with a stepper motor that can apply displacement rates down to 1 mm/s.  The combination of the two test techniques allows us to study phenomenon such as Luders band-like deformation, the evolution of load-controlled transformations, localized strains at material flaws, and residual stresses and strain-stabilized martensite in fracture surfaces.

Session 2: Materials Characterization and Experimentation

The Preliminary Program for The International Conference on Shape Memory and Superelastic Technologies (May 7-11, 2006)