澳门2138cn太阳娱乐网站官网-在线登录

Abstract:
The initiation of fracture in rock is associated with a damage zone in the form of a localized region of microcracking. Several techniques such as acoustic emission have been used to characterize features of the damage zone, but limitations of these measurements prevent a detailed description of the zone. Electronic speckle pattern interferometry (ESPI) is an experimental technique which can be used to observe displacements on the order of microns. ESPI involves the comparison of the correlated speckle patterns, which are generated when monochromatic light interacts with an optically rough surface, to obtain information about surface displacements. The fringe pattern can be produced from processing of two speckle patterns with respect to different loading stages during the experiment. Then the information of displacements can be extracted from the fringe pattern.

Mode I fracture experiments are performed using the three-point bending test. The beams with a smooth boundary (no notch) and a center notch are employed to investigate the fracture initiation. A single direction, in-plane ESPI system is constructed to observe the displacements of specimen surface. Through the analysis of displacement field from the measurements, the damage zone of rock can be characterized using ESPI. Two observations can be obtained with ESPI: the length of the damage zone and the amount of crack opening displacement along the zone at various levels of load. These high resolution measurements of the displacement field also demonstrate the utility of ESPI in laboratory testing.