Study On The Effect Of Joint Characteristics On Impact Crushing Effect Of Rock

The joints in the rock have great influence on its mechanical properties.Meanwhile,as an important component of rock mass,the change of rock mechanical properties will affect the response characteristics of rock mass to external loads.The study on the influence of joint characteristics on the mechanical properties of rock is helpful to improve the stability and safety of rock mass engineering.Based on the similarity theory,specimens with different joint geometry characteristics,such as different angles,different numbers and different penetrations,were prepared by using cement mortar.By means of physical test and numerical simulation,the effects of the geometric characteristics of joints on the dynamic strength,energy absorption,damage development and crack propagation of cement mortar specimens were systematically analyzed.The main research contents and results are as follows:(1)By SHPB impact test under the same pressure,the geometrical characteristics of the joints were studied on the effect of dynamic strength of cement mortar specimen.The stress-strain curves of specimens and the variation characteristics of stress peak with joint angles,joint numbers and joint penetrations were discussed.The results show that the weakening of the dynamic strength of the specimens is caused by the stress concentration at the joint tip,and the geometric characteristics of the joints affect the weakening amplitude of the dynamic strength.(2)The ratio method was used to analyze the variation of energy structure with joint geometry.Based on the equation of energy density per unite time,the energy absorption of the specimens was quantified,and the influence law of joint geometric characteristics on the energy absorption of the specimens was obtained.(3)Nuclear magnetic resonance(NMR)technology was used to study the influence of the geometric characteristics of joints on the damage of microstructure.Using the porosity rate analysis of the damage of the specimens,the relationship between the damage and energy absorption of the specimens was fitted,and the damage evolution mechanism of the specimens with different joint geometric characteristics was revealed.With the increase of joint inclination angle,number and penetration,the damage degree of the specimen presents a parabolic,logarithmic and linear change trend,and the damage has a strong correlation with energy absorption.(4)Based on fracture mechanics,with the help of nuclear magnetic resonance imaging(MRI)and numerical simulation,the failure process of specimens with different geometric characteristics of joints under impact loading was discussed,and the crack propagation law of specimens containing joints was revealed.It is concluded that tensile failure or tensile shear mixed failure leads to the initiation and propagation of the secondary crack,and the crack propagation is accompanied by the change and transfer of the high stress zone.The geometric characteristics of joints determine the failure mode of specimens.