نوع مقاله : علمی - پژوهشی
1 عضو هیات علمی دانشگاه تربیت مدرس
2 دانش آموخته دانشگاه تربیت مدرس
عنوان مقاله [English]
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 research works. However there are lacks of basic information regarding the failure mechanism of rock specimens under the dynamic loadings. Loading rate fundamentally influences on the strength and failure mechanism of rock specimens. In the present study, effect of loading rate on the crack propagation and failure mechanism of specimens containing with five different crack density numerically considered using RFPA2D code. For this purpose, specimen for modeling of uniaxial compression test with 54 mm in diameter and 110 mm in length was simulated. The geo-mechanical properties required for modeling have been derived from some experimental tests which are conducted on Granite specimens. The failure mechanism of simulated specimens was evaluated in three loading rates (0.002, 0.02 and 0.2 mm per steps). The effect of loading rate on the pre-crack growth and failure mode of specimens was considered. Regardless of the loading rate, in the first stage of loading sequences wing cracks initiate from the tips of the pre-existing cracks and tend to propagate parallel to the loading direction. Then secondary cracks usually initiated from tips of the wing cracks. Eventually, the propagation and coalescence of cracks resulted in unstably collapse of specimens. With increasing the loading rate the length of wing cracks decreases so that no wing crack created at loading rate of 0. 2 mm per step. It is shown that the failure modes of specimens under quasi-static compression loading is dominantly diagonal, while the failure mode under dynamic compression loading is “X” shape. This is because with increasing of loading rate to 0.2 mm per step, some second co-planar cracks formed at the tip of the main cracks.