Nanometric metrology by FIB-SEM-DIC measurements of strain field and fracture separation on composite metallic material

Abstract

Currently, kinematic field measurements for studying the mechanical behavior of materials and structures use common optical methods, such as mark tracking techniques, grid methods and correlation techniques. These techniques are employed over a region of interest ranging from micro to millimeter scale. However, when studies need to be conducted on even smaller scales such as sub-micrometric scale, the use of more complex means of observation is required. In this case, the work can be achieved using the scanning electron microscope (SEM), and the Focused-Ion-Beam (FIB) as marking technique. An adaptation of Digital Image Correlation (DIC) method Heaviside-based Digital Image Correlation (H-DIC) is chosen to investigate the mechanical behavior and taking into account local fractures. As the studied problem is to extract strains from a fractured material using a displacement field measurement method, derivative computation for strain determination is not well adapted. The proposed approach consists in extracting the residual strains from local first gradients of H-DIC, which are less perturbed by the fractures. Various tests were performed to evaluate the validity of this new proposed approach. An application to study the mechanical behavior of a metallic composite (Al/ω-Al-Cu-Fe) is proposed. A particular exploitation of all field lies in the good separation of the strain fields and the cracked part. A discussion that focus on the comparison between a conventional DIC analysis and its extension was presented on the zones without or with fractures.

Keywords

• Fracture
• FIB-SEM-DIC
• Image correlation
• Residual strains