Digital Image Correlation for Elastic Strain Evaluation during Focused Ion Beam Ring-Core Milling

The utilization of the focused ion beam digital image correlation (FIB-DIC) technique for measuring in-plane displacements and the employment of the height digital image correlation (hDIC) technique as two-step DIC for determining both in-plane and out-of-plane displacements within the region of interest are detailed in this paper. Consideration is given to the microscopy data’s measurement scale and resolution to confirming the capability of both techniques to conduct micro-scale correlations with nano-scale sensitivity, thereby making it suitable for investigating the residual elastic strains formed due to processing. The sequential correlation procedure of the FIB-DIC technique has been optimized to achieve a balance between accuracy and performance for correlating sequential scanning electron microscope images. Conversely, the hDIC technique prioritizes the accurate correlation of SEM images directly with the reference state without a sequential procedure and offers optimal computational performance through advanced parallel computing tools, particularly suited for correlating profilometry data related to large-scale displacements. In this study, the algorithm of the hDIC technique is applied as two-step DIC to evaluate the elastic strain relaxation on the surface of a ring-core drilled using focused ion beam. Both techniques are utilized to correlate the same scanning electron microscope images collected during the monitoring of the ring drilling process. A comparison of the correlation results of both techniques is undertaken regarding the quantification of the near-surface residual elastic strains, with the analysis conducted to discern the superior accuracy of the hDIC algorithm. Furthermore, the distinctions between the two techniques are delineated and discussed.