Experimental study on dynamic strength and crack evolution of rocks under different strain rates

PAN Tao; LIU Xiao

doi:10.13347/j.cnki.mkaq.20250941

Abstract：The study on the dynamic mechanical characteristics of rocks under impact loading holds significant theoretical guiding significance for achieving controlled blasting during roof cutting blasting.Based on a split Hopkinson pressure bar(SHPB)test sys-tem,sandstone from the roof of Dingji Coal Mine in Huainan city was tested.By varying impact velocities to achieve different strain rates,the stress-strain relationship of sandstone under impact loading at different strain rates was obtained.The strength characterist-ics of sandstone specimens under different strain rates were analyzed and internal crack evolution and fractal dimension changes were investigated by CT scanning.The results indicate that stress-strain curves under varying strain rates comprise four stages,namely:the primary fracture compaction stage with concave sections,the approximately elastic linear deformation stage with differ-ent slopes,the yield stage with nonlinear increase of stress,and the softening failure stage with significant decrease of stress as de-formation increases.The dynamic peak stress,dynamic elastic modulus and strain rate show a significant positive correlation.The in-crease of strain rate can enhance the ultimate bearing capacity of the specimen.The dynamic strength growth coefficient of the speci-men increases with the increase of strain rate,but there exists a critical strain rate state.Under the action of impact dynamic loading,the cracks in sandstone specimens expand from the outside to the inside,tangential to radial,and interpenetrate each other,present-ing the characteristics of tensile splitting failure evolution.With the increase in the number of impacts,the specimen as a whole shows an increase in the number of cracks,an increase in the volume and area of cracks,and a slow to significant increase trend in the volume and area of cracks,while the fractal dimension shows a significant to slow increase trend.