Integrated correction of optical distortions for global HR-EBSD techniques

Area of Science:

• Materials Science
• Crystallography
• Optical Engineering

Background:

• Camera lens optical distortions impact the precision of elastic strain and lattice rotation measurements in high-angular resolution electron backscatter diffraction (HR-EBSD) and transmission Kikuchi diffraction (HR-TKD) analyses.
• Accurate strain and rotation data are crucial for understanding material deformation mechanisms.

Purpose of the Study:

• To introduce and validate an integrated method for correcting optical distortions in global HR-EBSD/HR-TKD.
• To assess the impact of optical distortions on measurement accuracy and quantify the benefits of the proposed correction.

Main Methods:

• Digital image correlation (DIC) is applied directly to optically distorted patterns, bypassing traditional pre-processing steps.
• The Gauss-Newton algorithm is preserved for numerical efficiency during correction.
• The method's numerical cost is evaluated using a homography-based HR-EBSD approach.

Main Results:

• The correction principle was numerically validated for radial distortion across disorientation angles (0-14°) and elastic strains (0-5×10⁻²).
• Errors from neglecting distortions were quantified, along with the influence of distortion coefficients and pattern/optical center locations.
• The correction is essential even when both reference and target patterns exhibit distortions.

Conclusions:

• An integrated optical distortion correction method for HR-EBSD/HR-TKD is presented and validated.
• The approach maintains numerical efficiency while significantly improving measurement accuracy.
• The study determines the necessary accuracy of distortion parameters for effective correction.