Characterization of quasi-static and dynamic fracture behaviour of rock-like materials using digital image correlation

Abstract

Rock masses contain geological features which play key role in failure mechanism. Amongst these features are flaws, layers, joints, faults, etc. In this thesis digital image correlation (DIC) is utilized to study crack development behaviour of rock-like materials containing different geological features. 3D printing specimens having pre-existing flaws, layered and bimrock specimens are studied under quasistatic and dynamic impact loadings. Both unfilled and filled flaws are studied in 3D printed specimens. Based on the static testing, it is observed that the flaws configuration have significant effect on the type of cracks. In particular, tensile or shear movement of the flaws controls the type of newly formed cracks. It is observed that filling improves the strength characteristics of the specimens. Filled specimens develop much larger fracture process zone (FPZ) prior to the peak load. Specimens having their filling fractured exhibit an enhancement of the peak load larger than that of the filled specimens without cracking in the fillings. Similar to quasi-static loading, not only the specimens with filled flaws can carry more load than the corresponding unfilled flaw specimens, but also their cracking pattern is different as compared to the unfilled flaw counterpart. However, it is interesting to note that the dynamic peak loads are not dependent on the flaw inclination angle, while the quasi-static peak loads show obvious flaw inclination angle dependence. Moreover, DIC results reveal that under specific flaws configurations, the filling material undergoes shear cracking. In layered specimens, the 0°-30° orientation angles exhibit dominant strain accumulation inside the layers, at 45°-60° mixed tensile-shear cracking is observed in layers and interfaces, and at the layers of 75°-90° only show tensile splitting crack at an interface governs the behaviour. Under dynamic loading, dominate observation is tensile crack development and failure of all the specimens, except that specimens with layers oriented at 60° and 75° showing shear crack initiation in the pre-peak loading stage followed by the development of tensile cracks. In bimrocks the size of blocks remarkably influences the failure trend. Large blocks exhibit both tensile and shear. Moreover, the development of FPZ is highly dependent upon the blocks sizes and the large blocks exhibit obvious development of FPZ.