Study On Impact Compression Experiment And Numerical Simulation Of Granite Under Confining Pressure

The mechanical properties of rock under dynamic loading and confining pressure relate to many fields such as the development of underground engineering structures,deep rock bursts,and rock bursts of brittle rock masses under high ground stress.At present,there are still relatively few studies on the mechanical properties of rock under the coupling of dynamic loading and confining pressure.and its theoretical development has some limitations.This article is based on the basic theory of rock dynamics to carry out indoor experimental,combined with numerical simulation techniques,the work carried out and the conclusions are as follows:Firstly,the split hopkinson pressure bar(SHPB)was used to carried out the impact compression test of granite specimens under different confining pressures to investigate the mechanism of granite strength,deformation characteristics and energy dissipation.The strength,deformation,energy characteristics,failure modes and mechanism of granite under dynamic loading were discussed.The results show that the strength of rock sample is enhanced obviously with the increase of confining pressure and strain rate,and the effect of energy dissipation density on rock specimen strength is similar to strain rate.The plastic deformation of the granite under high confining pressure increases,and a clear plastic yielding platform appears.The strain rate effect of the dynamic strength in the Mohr-Coulomb criterion is mainly manifested by the continuous increase of the cohesive,and the fitting effect of the three-parameter power function criterion is the best.The strain rate and energy dissipation density of granite have a good linear relationship with the incident energy under certain confining pressure.The strain rate and energy dissipation density both decrease with the increase of confining pressure under same incident energy.Both the crack propagation velocity and the damage degree of the granite are increasing with the energy dissipation density,and the failure of tensile fracture with the low confining stress turn to compression-shear failure under the high confining pressure.Then,a constitutive model with high strain rate and confining pressure of granite was established based on the damage statistics theory and mechanics components,The influence of various parameters on the stress-strain curve of the model was discussed.It was found that when E_a increases,the slopes of the loading and unloading sections increase;the parameter E_b only affects the curve before yield strength.The parameters m and?have a significant effect on the stress-strain curve after the yield phase,where the parameter m between 3 and 6,and?is proportional to the confining pressure and strain rate.The viscosity coefficient?affects the complete stress-strain curve at the range of 0.1 and 0.5.Finally,thephysicalmeaningofvariousparametersof Holmquist-Johnson-Cook(HJC)constitutive are introduced in detail and the HJC parameters suitable for the granite in this paper are finally determined according to the previous achievements.Afterwards,the numerical simulation of the impact test process carried out by using ANSYS/LS-DYNA.It is concluded that under the impact loading,the granite specimens were the first to tearing strain damage and then turned into axial splitting damage,and some were crushed.The HJC model can well characterize the stress-strain relationship and failure modes of rock materials under the conditions of large deformation,high strain rate and confining pressure.The numerical simulation is in good agreement with the experimental results.