Abstract:
Carbon fiber reinforced polymer (CFRP) demonstrates promising application prospects in reinforcing protective coal pillars due to its lightweight, high-strength, and corrosion-resistant. To further investigate the mechanical response mechanism of CFRP-confined coal pillars under the dynamic evolution of mining-induced stress fields, particularly under cyclic loading and unloading, both the failure characteristics and energy evolution laws of CFRP-confined coal specimens under cyclic loading and unloading were systematically investigated in the present research. Upon the principle of energy dissipation and employed the acoustic emission RA-AF analysis method. The results indicate that: ① Compared to conventional uniaxial compression, the strengths of coal specimens confined with 0, 1, and 3-layer CFRP under cyclic loading and unloading increased by 2.65%, 10.17%, and 1.22%, respectively. The envelope curve of their stress-strain curves exhibited similarity to the stress-strain curve under uniaxial loading. ② The coal specimens exhibited significant deformation memory characteristics under cyclic loading and unloading. The area and reversal amplitude of the hysteresis loops formed by their stress-strain curves were positively correlated with the number of loading-unloading cycles, while the loop density was negatively correlated with the number of cycles. ③ Both the total accumulated energy and the elastic strain energy density of the coal specimens increased with rising axial stress, exhibiting an exponential functional relationship with axial stress in magnitude. ④ As the number of CFRP layers increased from 0 to 3, the dissipation energy density shifted from a U-shaped distribution to a J-shaped distribution, and the dissipation energy rate changed from an L-shaped distribution to a V-shaped distribution. The proportions of dissipation energy were 6.62%, 31.46%, and 42.56%, respectively, showing a trend of initially rapid increase followed by a slower increase. ⑤ Under cyclic loading and unloading, the proportion of tensile failure in coal specimens varied significantly under different confinement conditions. This experimental study reveals the deformation, failure, and energy evolution characteristics of CFRP-confined coal specimens under cyclic loading and unloading, providing theoretical support for further promoting the industrial application of CFRP in coal pillar reinforcement.