HS DIC-system application for strain and displacement measurements under static-dynamic coupling loading

To study the deformation and fracture of sandstone under static-dynamic coupled load, a cylindrical specimen under pre-static axial and confining pressure was dynamically loaded using an improved split Hopkinson pressure bar (SHPB). Through the application of a special shape striker, stress equilibrium and nearly constant strain rate in specimen were achieved. During dynamic tests, the failure process of the specimen was completely monitored (7 frames at a time resolution of 25 s) by a high speed (HS) camera. Furthermore, the recorded images were matched with the loading steps through a specified trigger mode, based on which both full-field displacement values and the corresponding surface in-plane strain were obtained via digital image correlation (DIC) system. Finally, analysis on the surface deformation and failure mode of specimen shows that the sample presents an interaction of tension-shear failure and expansion failure under the axial static pressure of 72 MPa, which reflects the effect of axial static pressure on the dynamic fracture mode of the sample surface.