Fracture Process Zone Features of Three Granites Under Mode I Loading: Insights from Acoustic Emission and Thin-section Observation
Tianyang GUO#+, Louis WONG, Xinyu XIAO
The University of Hong Kong, Hong Kong SAR

Fracture process zones (FPZs) often develop in front of crack tips preceding the initiation of macrocracks subjected to loading in rocks. However, the effects of mineralogy and texture of granites on the FPZ features are very complex and not entirely understood. In this study, we experimentally study the FPZ features of three granites of comparable mineral composition, but with different grain sizes, namely fine-, medium- and coarse-grained granites (gf, gm, and gc respectively) in mode I semi-circular bending tests. The development of FPZs is monitored by continuously recording the acoustic emission (AE) during the test. The fully-developed FPZs (FD-FPZs), which refer to the FPZ status immediately before the initiation and propagation of macrocracks, are characterized by the spatial distributions of AE events. To investigate the microcracks features, a postmortem microscopic study is conducted on the thin-section samples of the specimens after loading tests quantitatively. The results show that for the FD-FPZs of the gf and gm, the AE event number decreases exponentially with the distance away from the notch central plane along the principal tension stress direction, and the AE event number decreases nonlinearly with the distance for the gc. The locations of the maximum AE event points are consistent with those of the maximum microcrack density along the same direction for the gm. In terms of the energy distribution of the AE events characterizing the FD-FPZs, the gf is comparable with that of gc, which is different from the energy distribution of the gm. This experimental study reveals the complex effects of mineralogy and texture on the FD-FPZ development of granite under mode I loading.