Perpustakaan Digital ITB

A new microscale visualization experimental system is proposed for in-situ measurement of microcracking and microdeformation behaviour of macroscopic specimens during real-time loading. A series of three-point bending experiments were conducted on sandstone beam specimens containing a Mode I pre-crack. The newly developed microscopic experimental system and two other traditional experimental techniques, including acoustic emission (AE) monitoring and macroscopic charge coupled device (CCD) monitoring, were applied together to capture and measure the cracking process and deformation characteristics around the pre-crack tip in real-time. The results show that the crack initiation determined by the proposed microscopic monitoring system was earlier than that determined by AE monitoring and macroscopic CCD monitoring. The microscopic monitoring system observed that the cracks initiated at multiple locations at the pre-crack tip, and they continuously propagated, opened, and coalesced with each other to eventually form a main crack in a zigzag and irregular way, which is significantly different from the macroscopic CCD monitoring observations that suggested that the crack only initiated from the pre-crack tip and rapidly extended upwards along the pre-crack length direction in a relatively simple way. Furthermore, the full-field deformation characteristics at the pre-crack tip were quantitatively obtained by the macrograph-based digital image correlation (DIC) and the micrograph-based DIC calculations. The results indicate that the calculated localized strain zones from the micrograph-based DIC were narrower than those calculated from the macrograph-based DIC. The former had a very similar morphology to realistic microscopic cracks, whereas the latter was wider and longer than the induced macroscopic cracks. The average critical crack opening displacement (COD) calculated using the micrograph-based DIC was approximately 1.3 times larger than that calculated using the macrograph-based DIC.