Experimental investigation and discrete element modeling of acoustic emission characteristics, crack evolution, and energy variation in shale specimens during uniaxial compression

• Tensile cracks dominate failure (tensile-to-shear crack ratio = 2.8), driving AE surges and peak energy release. • Elastic modulus has a far greater impact on crack generation (61.89% increase when doubled) than bond strength (1.2% increase when doubled). • Numerical model’s crack initiation (70% of peak strength) and damage strengths (90% of peak strength) are 15–20% higher than specimens with natural microcracks. • Provides guidance for shale gas extraction (focus on high-elastic-modulus formations) and geo-mechanical stability monitoring. Elucidating the deformational attributes and mechanical properties of shale is crucial for shale gas exploitation. Based on laboratory tests (displacement-controlled loading, 0.1 mm/min) and acoustic emission (AE) tests, combined with two-dimensional particle flow code simulations (loading rate, 0.6 mm/min), the AE evolution, energy conversion and crack propagation laws were analyzed under three different operating conditions. The average macro-mechanical parameters are as follows: peak strength of 41.38 MPa, elastic modulus of 10.6 GPa, Poisson's ratio of 0.30 and porosity of 3.23%. Key findings are as follows: low-strength specimens have 23.78% fewer cumulative ring-down counts in the first three AE stages than high-strength specimens, whereas the incremental ring-down count of high-strength specimens in the fourth stage is 6 times that of low-strength specimens. In the model, the first tensile crack initiates at 70% of peak strength (crack initiation strength), and massive cracking occurs at 90% of peak strength (damage strength); both strengths are 15–20% higher than laboratory specimens with natural microcracks, as natural microcracks induce stress concentrations and lower strength thresholds. Tensile cracks dominated failure: the average tensile-to-shear crack ratio across three conditions was 2.8. AE surges are driven by tensile crack propagation/coalescence, consistent with peak energy release. Elastic modulus has a greater impact on crack generation than bond strength: doubling elastic modulus increased cracks by 61.89%, while doubling bond strength increased cracks by only 1.2%, emphasizing attention to high-elastic-modulus formations in shale gas extraction. This work enhances understanding of AE-crack-meso-property coupling and provides guidance for safety monitoring and engineering design.