Abstract
Flaws and discontinuities play a crucial role in the failure process of rocks. To investigate the fracturing mechanism of rock with combined flaws composed of crack and hole, the digital image correlation (DIC) method is used to record and analyze the rock failure behavior. Coupled static and dynamic loads are applied on granite specimens with prefabricated flaws by a modified split Hopkinson pressure bar (SHPB) device. The dynamic mechanical properties of the granite specimens are affected by the flaw inclinations with the loading directions. With the inclination angle increasing, the combined strength and peak strain both decrease first and then increase. Full- and local-field strain evolution of the granite specimens is analyzed in a quantitative way by using DIC technique. The specimens with a flaw angle of 45° are broken relatively evenly with homogenous small particle sizes. The variation trend of fragment sizes is consistent with that of combined strength and absorption energy of the specimens.
Highlights
In recent decades, scholars have carried out numerous tests based on the split Hopkinson pressure bar (SHPB) system, to investigate the mechanism of crack initiation and propagation processes on brittle rock
A contrast group with only circular hole (Group C) and an experimental group with crack unexposed to the hole (Group U) were prepared and tested afterwards. e specific geometrical layout about the test specimen can be seen in Figure 1. e prefabricated combined flaws contain a hole-like flaw and a crack-like flaw 15 mm in length in different inclination angles β. e artificial crack has a minimum distance d of 7 mm from the edge of the internal hole, and the layout is displayed in Figure 2. e prefabricated crack is always tangent to a circle with a radius of 12 mm (R d + r)
There are some limitations for the digital image correlation (DIC) system: (a) measurement accuracy mostly depends on the quality of speckle particle. (b) Measurements are limited to in-plane surface deformation and strain. (c) Once the strain is less than 100 με, DIC is not recommended for any applications [47]
Summary
Scholars have carried out numerous tests based on the SHPB system, to investigate the mechanism of crack initiation and propagation processes on brittle rock. Further study of the fracturing properties of brittle rock materials containing prefabricated hole-crack flaws under coupled static-dynamic loading is essential. Conventional sensors such as strain gauges, extensometers, and accelerometers are widely used to monitor the deformation of rock specimens. The crack initiation and fracturing process of specimens with prefabricated flaws have been investigated with different auxiliary experimental means, such as acoustic emission (AE) technology [34], computerized tomography (CT) scanning [35, 36], and 3-D X-ray computed tomography [37] All those mentioned methods are beneficial to provide inspections for rock failure, especially under static compression tests. The dynamic rock failure analysis by the DIC method will provide some visual observations and proofs for the studies in rock mechanics, for the rocks with natural or artificial flaws
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