Experimental studies on cracking processes and failure in marble under dynamic loading

Abstract

The loading conditions influence not only the strength but also the cracking behaviors of rocks. The crack behavior study in various rock types containing artificially created flaws under the quasi-static loading condition has been extensively studied in the past. In the present study, the research of cracking processes in a natural rock is extended to dynamic loading conditions, which are then compared with the quasi-static results. Carrara marble specimens containing a single pre-existing open flaw are tested. The dynamic loadings are generated by the Split Hopkinson Pressure Bar (SHPB) system with the high-speed data acquisition subsystem and the high-speed video subsystem. Firstly, the influences of the flaw inclination angle on the compressive strength of the marble specimens are discussed and compared under these two loading conditions. Secondly, the cracking processes of marble are analyzed, which are found to consist of two stages—the development of white patches and the growth of macro-cracks. In the first stage, under these two loading conditions, the white patch patterns are generally similar with only minor differences. Significant differences with respect to the macro-crack types and the failure modes are found in the second stage. Under the quasi-static compression, the tensile wing and anti-wing white patches evolve into the closed tensile wing cracks (only for low flaw inclination angle specimens) and the open anti-wing cracks, subsequently leading to the specimen failure. In contrast, under dynamic compression, only the anti-wing and shear patches evolve into two symmetrical pairs of shear cracks, which result in the specimen failure. The flaw inclination angle appears not to influence the shape and orientation of the shear crack trajectories far away from the flaw tips. Therefore, the failure mode under quasi-static compression is dominantly diagonal, while the failure mode under dynamic compression is “X” shape regardless of the flaw inclination angle.