To investigate the impact of cyclic stress damage on the dynamic fracture characteristics of coal mass-es,static and dynamic fracture tests were conducted on type Ⅰ single-sided notched beam specimens of coal both prior to and following cyclic stress damage.The test results revealed that the average dynamic mode Ⅰ fracture toughness(KIC)of the coal mass stands at 0.344 MPa·m1/2,with an average mode Ⅰ fracture energy(GC)of 66.99 N/m.These figures are respectively 1.38 and 1.26 times higher than those measured for the static fracture parameters of the coal specimens.After expore to cyclic stress damage,the average static KIC value of the coal specimen was reduced to 0.219 MPa·m1/2,and the average static GC to 44.26 N/m,marking decreases of 12.05％and 16.74％relative to the original specimens.Additionally,the average dynamic KIC and GC values decreased to be 0.279 MPa·m1/2 and 52.72 N/m,respectively,representing reductions of 20.90％and 21.30％compared with the impact fracture test results of the untreated coal specimens.These findings suggest that cyclic stress detrimen-tally affects both the dynamic and static fracture mechanical parameters of coal masses,with dynamic fracture parameters exhibiting a greater degree of degradation.This highlights the enhanced sensitivity of coal mass dy-namic fracture behavior to cyclic stress damage.Furthermore,fractal analysis of the dynamic fracture damage yielded dimensions of 1.32 for untreated specimens and 1.21 for those subjected to cyclic stress damage,indicat-ing a more complex fracture and fragmentation process under impact loading for the former.Numerical calcula-tions based on the cohesive crack model for type Ⅰ dynamic fracture of coal masses align well with experimental results,underscoring the model's effectiveness in capturing the dynamic fracture process of coal masses.These insights provide a reference for coal masses with similar characteristics.
impulse loadfracture toughnessfractal dimensioncohesive crack model
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