Differential micrograph imaging for visualization of strain localization

Abstract

In this work, we introduce differential micrograph imaging (DMI), a technique developed to reveal subtle microstructural changes associated with strain localization in polished and etched metallic samples subjected to mechanical loading. The method first applies image registration to suppress rigid body motion and global deformation. A pixel-wise subtraction from the undeformed reference micrograph then isolates contrast variations arising from localized strain. DMI does not require speckle patterning and leverages information from every pixel in the micrograph. In contrast, digital image correlation (DIC) relies on surface patterning, and its spatial resolution is fundamentally limited by the subset and speckle size. While DMI is a semi-quantitative technique where heat map intensity correlates with relative strain magnitude, it does not provide exact strain values or directions. Nonetheless, DMI can serve as a complementary technique to DIC by enabling high-resolution visualization of localized microstructural changes, particularly in regions with complex features and subtle deformation-induced microstructure changes.