Estimation of elastic strain by integrated image correlation on electron diffraction patterns

Abstract

High-angular-resolution electron backscattered diffraction (HR-EBSD) has been developed to study local elastic strains in crystals. An integrated Digital Image Correlation (DIC) procedure for high resolution diffraction patterns, as recently proposed to bypass several problems of the conventional cross-correlation-based algorithm, was implemented. Through two examples of experimental data where the algorithm was used and compared to conventional means, the current paper illustrates the benefits of the integrated DIC method. It is found that both measurement uncertainty and computation time were simultaneously reduced. Moreover, an enhanced robustness was obtained for relatively high misorientations relative to methods based on cross-correlation. Different computing conditions are explored on experimental data. A number of practical usage conditions are proposed to achieve better precision and speed.

Global DIC approach guided by a cross-correlation based initial guess for HR-EBSD and on-axis HR-TKD

“…As proven by Hardin et al [31], the stress normal to the free surface remains negligible in the absence of stress field sources located near the surface or of large error on the specimen tilt. During this last year, three independent works by Vermeij & Hoefenagels [32], Ruggles et al [33] and Shi et al [34] proposed a 'global' HR-EBSD approach. This method is an 'integrated' Digital Image Correlation (I-DIC) approach [32,34] that correlates EDP signal intensities by using a unique and large ROI.…”

“…During this last year, three independent works by Vermeij & Hoefenagels [32], Ruggles et al [33] and Shi et al [34] proposed a 'global' HR-EBSD approach. This method is an 'integrated' Digital Image Correlation (I-DIC) approach [32,34] that correlates EDP signal intensities by using a unique and large ROI. The relative deformation of the target ROI with respect to the reference ROI is accounted for by eight degrees of freedom, which are the components of b F e .…”

“…The relative deformation of the target ROI with respect to the reference ROI is accounted for by eight degrees of freedom, which are the components of b F e . The deformation gradient is computed iteratively by means of a forward-additive (FA) [32,34] or an inverse-compositional (IC) [33] Gauss-Newton (GN) algorithm in order to solve the non-linear DIC problem, i.e. the minimization of the quadratic difference of intensities between the reference and the warped target ROI.…”

“…the minimization of the quadratic difference of intensities between the reference and the warped target ROI. The 'global' approach shows competitive performance as well as numerous advantages as compared to the 'local' one [33,34]. Bias related to the number of ROI, their location or weights is avoided.…”

Novel remapping approach for HR-EBSD based on demons registration

“…demons registration) [25]. The first demons registration paper was published by Thirion et al [25] as an analogy of Maxwell's demon and has later been widely implemented for many radiotherapy applications [17][18][19][20][21]. The demons registration approach resembles the global image cross-correlation technique in that it also maps the non-rigid transformation of the images.…”