Methodology for microscale deformation measurement of free-standing thin films

摘要

Deformation measurement at macro/microscale can be fulfilled by a variety of methods with the development of experimental measuring techniques. However, the measurement of free-standing thin films is still difficult, especially for full-field measurement. The difficulty is the fabrication of the deformation markers (such as gratings or speckles) on the free-standing thin films. A grating fabrication technique based on focused ion beam (FIB) deposition is introduced in our previous works, and the superiority of this technique is minimal damage to the surface of the specimen. We adopted this FIB deposition technique to fabricate a frequency of 2000 line/mm gratings on the free-standing metallic films with a thickness of 2 μm. Notches of 10 μm length and 2 μm width are prepared by the FIB etching at the edge of the films. An in situ tensile test is operated in the scanning electronic microscope system. At the crack initiation stage, the displacement field is measured from the deformation of the gratings. The fracture parameter J integral is characterized for the 2-μm metallic films. The results demonstrate that the full-field measurement of the free-standing thin films at microscale can be realized successfully by this method.