AE-based classification and fracture process analysis of flawed marble with stress intensity factor validation

The stability of rock masses is critically influenced by pre-existing cracks, yet the micro-mechanisms governing cracks evolution under varying crack geometries remain inadequately quantified. This work introduces a novel, rock-specific acoustic emission (AE) classification criterion for marble, established through integrated notched semi-circular bend (NSCB) and straight-notched Brazilian disc (SNBD) tests. The proposed criterion for both tensile cracks (AF > 40 RA + 30) and shear cracks (AF < 20 RA + 30) provides a quantitative and material-adapted method for real-time crack-type discrimination. Combining AE monitoring with stress intensity factor (SIF) analysis, 9 groups of uniaxial compression tests were conducted on marble specimens with crack inclinations (15°, 30°, 45°, 60°, 75°, 90°) and lengths (5 mm, 10 mm, 15 mm). The synchronous evolution of SIF and AE parameters across four loading stages validates the AE-based classification. The test results reveal that crack inclination governs the tensile-to-shear transition, while crack length accelerates damage accumulation. It is demonstrated that the coupled AE-SIF analysis captures micro-mechanical crack evolution and bridges microscopic fracture processes with macroscopic failure modes. This study offers a reliable framework for early warning of rock instability.