Study On Dynamic Behavior Of Granite Under Complex Stress After High Temperature

In this paper,the improved Hopkinson(SHPB) test system is taken as the platform,and the Beishan granite in Gansu is taken as the research object.The Uniaxial Impact Test and the impact test of active confining pressure were carried out on granite specimens heated at different temperatures.The Uniaxial Impact and confining pressure impact tests were carried out for the granite specimens with different compressure(5MPa?10MPa?20MPa)and different temperatures(200??400??600??800??1000?)under three loading rates(striking velocity 8.6m/s?14.6m/s?18.8m/s).The dynamic stress-strain curves of granite after high temperature are studied.The peak stress,peak strain and strain rate of granite under different conditions are analyzed,The failure characteristics of granite under different conditions are analyzed.The effects of different temperature damage,loading rate and confining pressure on the dynamic mechanical properties of granite are summarized.The dynamic damage statistical constitutive model considering the weakening effect of temperature is established.Through the study of this paper.In order to provide some experimental data and theoretical analysis methods for the study of the dynamic mechanical properties and failure reasons of rock materials under complex impact loads,and for the geotechnical engineering after high temperature.The main conclusions are as follows:(1)Under the uniaxial impact load,the granite is a failure mode of tensile splitting.At the same temperature,with the increase of the loading rate,the number of cracks becomes more and more rapidly.Under the same loading rate,When the heating temperature is less than 600 ?,At the same time,the number of cracks is almost equal.The number of cracks and crack growth rate of 800 ? and 1000 ? were significantly improved.When the heating temperature is less than 600 ?,with the increase of loading rate,the particle size becomes smaller and the number increases.When the heating temperature is 800 ? or 1000 ?,the granite specimen is powder.The confining force of the active confining pressure can restrain the expansion of the crack in the specimen,which can restrain the lateral deformation of the specimen and improve the strength of the granite material.(2)The strain rate has a significant effect on the mechanical properties of granite,With the increase of strain rate,At the same temperature,the peak stress of granite specimens increases significantly.However,with the increase of temperature,the strengthening effect is weakened.Under the low loading rate(striking velocity 8.6m/s),the confining pressure has a significant effect on the peak stress,Under the condition of high loading rate(striking velocity 14.6m/s?18.8m/s).,the peak stress of different confining pressures is more obvious than that of uniaxial impact state.(3)Based on statistical theory and damage mechanics,A statistical constitutive equation for dynamic damage of uniaxial impact is established and by using the fitting analysis method,the model parameters are calculated and compared with the experimental stress-strain curves.The rationality of the model and parameters is verified.