Virtual extensometer based on digital speckle correlation method and its application to deformation field evolution of rock specimen

The virtual extensometer is developed based on digital speckle correlation method (DSCM). To realize the virtual extensometer, the cracks on the specimen are firstly identified and located using the strain fields measured by DSCM. Then, virtual extensometers are installed on the cracks. Finally, the opening and the dislocation of the cracks are calculated through the displacement fields. The principle and realization of the virtual extensometer are introduced. The reliability of virtual extensometer is verified by a specially designed experiment and the resolution of virtual extensometer is calibrated as 0.1 pixels. This virtual extensometer is applied to an experiment to study the failure procedure of a granite specimen containing non-penetrating crack (three-dimensional crack). The type and sequence-by-time of cracks on the specimen are determined based on the measurement results from the virtual extensometer. The failure mechanism of the specimen is then analyzed.