High-precision full-field measurement of dynamic shear rupture by digital image correlation using novel transmissive femtosecond laser-etched speckle patterns

Accurate characterization of deformation fields near the shear rupture tip is essential in dynamic friction and earthquake mechanics investigations. Under ultrahigh-speed conditions, the geometric dimensions, distribution of the speckle and illumination intensity in the imaging are key factors that limit the accurate measurement of the deformation fields by digital image correlation. In this study, we propose a novel femtosecond laser-etched speckle fabrication method on transparent PMMA substrates. Integrated with a transmissive optical configuration, the micro-cavities fabricated and precisely filled with black ink yield speckle patterns with controllable size, high stability, excellent repeatability, and exceptional optical contrast under ultrahigh-speed imaging conditions. The transmissive optical configuration significantly enhances illumination efficiency, resolving synchronization challenges inherent in traditional flash illumination systems. Results from different fields of view indicate that accurate strain measurements in the rupture tip singular zone can be achieved at a spatial resolution corresponding to a pixel size of approximately 13.4 µm. Furthermore, when the spatial resolution of speckle images is reduced to 3 µm pixel size, the deformation field within the rupture tip process zone can also be quantified in detail. In summary, the presented method significantly enhances experimental capabilities for studying dynamic rupture with different spatial resolutions. The experimental data will enrich our understanding of dynamic rupture mechanics and laboratory-scale earthquake phenomena.