Microscopic Simulation Study on Uniaxial Compressive Creep Characteristics of Coal Samples Constrained by Different Numbers of Carbon Fiber Reinforced Polymer Strips

To investigate the influence of carbon fiber reinforced polymer (CFRP) strip with different number on the creep mechanical properties of coal samples under axial compression, a coupled numerical simulation using PFC^3D and FLAC^3D software was conducted, and a hybrid contact model combining the Burger’s model and the Linearpbond model was established. The reliability of the numerical model was validated based on laboratory uniaxial compressive creep tests of unconstrained coal and coal samples constrained with 6 strips of CFRP sheet. The mechanical properties and energy evolution of coal samples constrained with 2 to 7 strips of CFRP sheet under uniaxial compression were studied by numerical simulations. The results show that as the number of strips increases, the initial axial strain of the coal sample tends to increase overall, with a significant increase in axial strain during the accelerated creep stage, and the maximum internal contact force in the hybrid contact model tends to increase overall. The ratio of the contact quantity of Burger’s model to that of Linearpbond model is about 1∶9, and this ratio in the numerical simulation model could reflect the creep mechanical properties of coal samples. Increasing the number of CFRP strips restricts radial deformation, increases the number of shear micro-cracks, causes more severe shear damage within the coal sample, and the failure mode of the coal sample changes from tensile failure to shear failure. As the number of strips increases, the total energy, elastic energy, and dissipated energy all increase, and the change in elastic energy is similar to the change in total energy before the coal sample experiencing creep instability.