Determination of mechanical properties and full-field strain measurements of rock material under dynamic loads

摘要

We present a detailed experimental procedure for the quantitative determination of mechanical properties and full-field strain measurement of rock material under dynamic loads. Three kinds of testing methods, i.e., notched semi-circular bending, Brazilian disc, and uniaxial compression, were conducted using a split Hopkinson pressure bar (SHPB) system. Experimental setup, data acquisition-and interpretation were described in detail. The digital image correlation (DIC) technique in conjunction with high-speed (HS) photography was adopted for the measurement of surface deformation characteristics (e.g., strain localization and evolution, and onset of fracture) of rock specimens. To verify the accuracy of this technique, comparative tests were performed in which the strains in the specimens were simultaneously determined using on-specimen strain gauges. Strain gauges were also used to determine the time-to-fracture and crack propagation velocity. Specifically, the scanning electron microscope (SEM) imaging technique was used to investigate the brittle failure micromechanisms of white belt initiated and developed prior to observable cracks in specimens. Experimental results show that dynamic crack initiation toughness, dynamic tensile strength and dynamic uniaxial compressive strength can be well determined, and the HS-DIC technique provides reliable full-field strain fields in the specimens under dynamic loads.