Homogeneity-dependent fracture behavior and instability mechanism of composite coal-rock: Insights from three-point bending tests

• Composite coal-rock exhibits a three-stage mechanical response (weak contact, strong contact, post-peak) with distinct crack evolution patterns. • Lithological homogeneity positively correlates with tensile crack proportion, influencing fracture behavior. • Peak frequency (PF) of acoustic emission shows clear lithology-dependent characteristics, unlike average frequency (AF). • Mathematical relationships between fracture strength, crack propagation angle, fractal dimension, and homogeneity coefficient are established.