Acoustic emission characteristics and energy mechanism of CFRP-jacketed coal specimens under uniaxial compression

Fiber-reinforced polymer (FRP) wrapping is a potentially attractive coal-pillar reinforcement technique. To study the effect of carbon fiber-reinforced polymer (CFRP) jacketing on mechanical properties, crack evolution, and energy dissipation mechanism of coal specimens, a series of uniaxial compression tests with acoustic emission (AE) monitoring were conducted on coal specimens with 0–2 CFRP-jacket layers. The results showed that the CFRP jacket had visible effects on the core failure process of coal specimens. (1) With an increase in the number of CFRP-jacketed layers, the specimens showed stronger strain-softening characteristics in the unstable crack growth stage, and the damage stress threshold increased significantly. (2) The correlation analysis between average frequency (AF) and rise angle (RA) demonstrated that with an increase in the number of CFRP-jacketed layers, the tendency of crack classification to change from tensile mode to shear mode increased. (3) The spatiotemporal evolution of AE event locations showed that CFRP jackets changed the AE event location concentration mode from a longitudinal distribution along the coal specimen to a distribution near the fracture. Moreover, the strain energy density evolution of coal specimens with 0–2 layers of CFRP jacketing was analyzed based on the mechanical equilibrium and energy conservation of CFRP-jacketed coal specimens. The dissipation strain energy ratio was introduced to define the damage variable, and the damage constitutive model with regards to CFRP jackets was constructed; the model describes the CFRP-jacketed coal specimen stress–strain relationship for strain-hardening, strain-softening, and sudden failure.