Investigation of the constitutive relationship between energy damage and CFRP layers in axially compressed small coal cylinders: Experiment and simulation

This study investigates the effect of CFRP layer count on the mechanical properties and energy evolution of axially compressed small coal cylinders using uniaxial compression tests and FDM-DEM coupled simulations. The experimental and simulation results exhibit excellent agreement, with the error range is controlled within 10%. This consistency effectively validates the reliability of the research methodology employed. Results show that both unconfined and CFRP-confined small coal cylinders exhibit four stress-strain stages: compaction, elasticity, yielding, and post-peak. CFRP confinement significantly enhances the ductility, with peak stress, peak strain, and elastic modulus increasing by approximately 200%, 250%, and 100%, respectively. Numerical simulations reveal that increasing CFRP layers raises peak stress by 548% and peak strain by 733%, with energy absorption efficiency improving by up to 1051%. However, elastic modulus does not increase monotonically, suggesting a trade-off between strength and stiffness in design. Additionally, CFRP confinement alters the failure mechanism from shear-tensile combined failure to shear failure, with crack distribution becoming more concentrated. Energy and acoustic emission analysis show that CFRP layers enhance energy dissipation, delay crack propagation, and improve residual bearing capacity. Based on these findings, an energy dissipation damage ontology model for small coal cylinders confined by CFRP layers is proposed, providing a useful tool for both theoretical research and engineering practice. • The impact of CFRP layer count on the mechanical properties and energy evolution of coal pillars was studied through uniaxial compression experiments and FDM-DEM coupled simulations. The results indicate that CFRP confinement significantly increases the peak stress, peak strain, and elastic modulus of the coal pillars. • As the number of CFRP layers increases, the peak stress and peak strain of the coal pillars increase by 548% and 733%, respectively, with energy absorption efficiency improving by up to 10.51 times. • CFRP confinement alters the failure mechanism of the coal pillars, shifting from shear-tensile combined failure to shear failure, and delays crack propagation, enhancing residual bearing capacity. • A damage constitutive model based on energy dissipation was proposed, which can accurately reflect the damage evolution process of coal pillars under different CFRP layer confinements.