Revealing strain distribution in metallic materials during in-situ SEM mechanical testing via HR-DIC: A review of instrumentation, methodology, and applications

Strain localization is a critical precursor to plastic deformation, fatigue crack initiation, creep damage, and catastrophic failure in metallic materials. High-resolution digital image correlation (HR-DIC) combined with an in-situ scanning electron microscope (SEM) can transform SEM image sequences obtained during mechanical loading into full-field displacement and strain data at the sub-micron scale, providing an essential approach for resolving microstructure-controlled local deformation. This review comprehensively discusses the instrumentation, methodology, and applications of in-situ HR-DIC. First, the integration requirements of tensile and compressive, fatigue, creep, and high-temperature loading systems with SEM imaging platforms are summarized, with a particular emphasis on loading stability, thermal drift, and imaging reliability. Subsequently, key technical procedures are systematically reviewed, including hardware-assisted scan control, fast acquisition, drift compensation, nanoscale speckle patterning, speckle quality assessment, image distortion correction, large-area stitching. Particular attention is given to measurement accuracy and uncertainty quantification, including the spatial-resolution–noise trade-off and the influence of SEM imaging artifacts. Furthermore, the coupling of HR-DIC with electron backscatter diffraction (EBSD), laser scanning confocal microscopy (LSCM), and crystal plasticity simulations is discussed in depth for the analysis of slip identification, grain boundary deformation, out-of-plane displacement, and local stress resolution. Finally, drawing upon typical applications in tensile, fatigue, creep, and high-temperature deformation, future directions regarding three-dimensional mechanistic interpretation, automated analysis, and standardized workflows are outlined.