ABSTRACT:

Here, a shear-tensile crack (STC) model is presented as suitable for Acoustic Emission (AE) events and compared to a traditional MT (Moment Tensor) approach. Experimental data was obtained from a uniaxial compression test performed on a Westerly Granite (WG) specimen using a 14 channel AE monitoring system. The STC is a physical source, which describes anticipated fracture modes: shear-slip and opening/closing tensile crack. It is described by fewer parameters (5 instead of the 6 for MT), which is essential for solving the inverse problem. The presented STC procedure was tested on 38 AE events selected over a range of 50 – 98% for the uniaxial compressive strength. As compared to the MT, the STC model displayed a similar fit for input data while providing far smaller confidence regions. The results indicate a more certain determination for the mechanism orientation and improved reliability for the decomposition components. In addition, use of STC model allowed better distinction between tension and shear type for AE events, which may be a crucial for recognizing an approaching failure. For our experiment, application of the STC model proved to be useful for recognizing the threshold of unstable microcracking.

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