Experimental And Numerical Study On Dynamic Compressive Mechanical Properties Of Heat-treated Granite

Rock materials are widely used.When it comes to complex conditions such as the exploitation of deep ore deposit,the utilization of geothermal resource,the disposal of high radioactive nuclear waste,the reconstruction of tunnel damaged by fire,it is subjected to the combined effect of temperature field and dynamic load.Therefore,it is of importance to carry out the study on the dynamic properties of heat-treated rock.In this paper,the mechanical properties and energy characteristics of the biotite granite after temperature are studied by the experiments and the numerical simulation is supplemented.The main work and related conclusions are as follows:Firstly,the test on heat-treated granite specimen was carried out by using the?50mm straight-cone variable cross-section split Hopkinson pressure bar(SHPB).Based on the test data,the dynamic behavior and failure characteristics of the granite under the coupling action of temperature and impact loading are studied.The results show that the amplitude of incident wave increases with the impact velocity,and the shapes of the transmitted and reflected waves are closely related to the failure state of the specimen.The stress-strain curves for the heat-treated specimens at 700? are obviously different to those at 500? in terms of the slopes for the ascending segment and the peak stress,indicating that there is a temperature threshold between 500? and 700?.Under the same impact velocity,the strain rate decreases slightly and then increases as the temperature increases.At a constant temperature,strain rate increases linearly with the impact velocity.The relationship between elastic modulus and strain rate for the heat-treated specimen obviously tends to have no regularity.Whatever,both peak stress and peak strain exhibit significant strain rate sensitivity.Below 500?,the influence of temperature on peak stress and peak strain is not evident,however,the influence becomes remarkable at 700? and 900?.Secondly,based on the experimental results of SHPB tests and the static compression tests on granite specimens heat-treated by different temperatures,the energy evolution mechanism of heat-treated granite in deformation and failure process was studied.The results show the energy dissipation of granite has a significant loading rate effect.With higher impact velocity in the test and hence higher strain rate in the sample,the energy dissipation is greater.The variations of energy dissipation density and energy utilization ratio with the treated temperature are basically in both the dynamic and static compression tests.For both the dynamic and static compression tests,the energy utilization rate is relatively low,with the maximum of 35%.Finally,the method for determining parameters of Holmquist-Johnson-Cook(HJC)model of granite are given.The SHPB tests of granite are numerically simulated.The simulated stress-strain curves and failure modes of granite are in good agreement with the experimental results,which verifies the reliability of the method for determining the parameters of HJC model and the feasibility of the constitutive model for the description of the dynamic behavior of granite.At the same time,it is found that with the increase of impact velocity,the peak stress and peak strain of granite increase,and the failure degree aggravates.