Study On Mechanical Properties And Numerical Simulation Of Granite Under Uniaxial Impact Load

Compared with the static characteristics of rock,its dynamic characteristics are complex and changeable.At present,the dynamic characteristics and failure mode of rocks are involved in mine excavation and hydropower construction.Moreover,in actual engineering,rocks are often unstable and destroyed under multiple impact loads.This paper focuses on laboratory experiments,supplemented by numerical simulation to study the dynamic characteristics of granite.The main work and conclusions are as follows:Firstly,the experimental study on the mechanical properties and energy dissipation of the biotite granite under single and cyclic impact loads was carried out using the modified split-Hopkinson pressure bar.The results show that the maximum strain,peak stress,dynamic strength growth factor and unit volume absorption energy have a good linear relationship with the average strain rate under different single impact loads.With the increase of incident energy,the proportion of incident energy that absorbed energy will gradually increase,and its proportion will gradually exceed the proportion of incident energy that transmitted energy accounts for;As the average strain rate increases,the degree of sample breakage gradually increases,and the rebound phenomenon on the stress-strain curve gradually disappears.Under different levels of cyclic impact loads,the mechanical characteristics of rock samples mainly show three changes:?i?The mechanical properties of rock samples deteriorate rapidly during impact;?ii?The rock sample was in a compaction process during the previous impacts,and the mechanical properties were first enhanced and then deteriorated;?iii?The mechanical properties of rock samples are basically unchanged.Then,based on the Weibull distribution,a statistical damage constitutive model of granite was developed,and the influence of various parameters on the constitutive relationship was discussed.Research shows that the parameters E_a,E_band D?will affect the slope and peak stress of the loading section of the stress-strain curve.The increase of the parameter F₀will correspondingly increase the peak stress and the stress value in the unloading phase.The change of the parameter m mainly affects the magnitude of the peak stress,and the change of the parameter?will only slightly affect the stress-strain curve as a whole.It is found by comparison that the fitting results of the model are in good agreement with the experimental data.And the improved model can also better describe the constitutive relationship of rock samples under confined pressure.Finally,on the basis of the existing Holmquist-Johnson-Cook?HJC?model parameters,a set of parameters of the granite HJC model under study is obtained through trial adjustment.And The ANSYS/LS-DYNA software was used to numerically simulate the test results of the rock under a single impact load.The study found that the HJC model can better characterize the mechanical behavior and failure characteristics of granite under a single impact load,and the parameter determination method used is feasible and accurate;After performing sensitivity analysis on the HJC parameters,it was found that when simulating impact problems,the parameters A,B,N,and f_chave a greater influence on the peak stress.In addition,only the influence of parameter B on the maximum strain exceeds 10%.Compared with blasting simulations,changes in HJC parameters have less impact on the impact simulation results,and the number of parameters with strong sensitivity is also less.