DEM simulation study on the mechanical and micro-fracture characteristics of jointed coal under direct tensile conditions.

Rock burst events are frequently accompanied by the formation of extensive tensile cracks, with bedding plane dip angles fundamentally determining the tensile strength characteristics, crack propagation, and failure modes of coal measures. This study investigates the influence of bedding plane angles on the tensile mechanical behavior of coal rocks using PFC2D numerical simulations. Models with four distinct bedding angles (0°, 30°, 60°, 90°) were developed to analyze failure mechanisms under tensile loading. The results demonstrate three key findings: (1) both tensile strength and elastic modulus exhibit positive correlations with increasing bedding angle, with tensile strength showing greater sensitivity compared to the more gradual enhancement of elastic modulus. (2) failure patterns evolve characteristically with bedding orientation: (i) 0° specimens fail through horizontal tensile-shear composite fractures, (ii) 30° models display preferential brittle shear failure along bedding planes, (iii) 60° cases show 78% shear-dominated crack propagation parallel to bedding, while (iv) 90° configurations develop multidirectional cracking networks due to constrained bedding-parallel shear. (3) micromechanical analysis reveals that stress transfer mechanisms transition from loading-axis dominance at low angles (0°-30°), through bedding-aligned force chain concentration at intermediate angles (60°), to complex three-dimensional force redistributions at 90° where matrix-bedding interactions dominate.