Study On Constitutive Model And Damage Law Of Hard Rock Under Microwave

In order to solve the problem of lack of theory in microwave-assisted rock breaking research at the present stage.It was very important to establish the damage evolution equation and constitutive model of hard rock under microwave action.In this paper,rock damage theory,statistics theory and rock micro-element strength theory were fused to establish the damage evolution equation and constitutive model of hard rock under microwave action.The characteristics of damage change,temperature change,cracking and mechanical properties change under microwave irradiation were analyzed by microwave irradiation test and mechanical properties test of two kinds of granite.The experimental data are used to verify the constitutive model of hard rock under the action of microwave and force,and the theoretical stress-strain curve obtained from the model is compared with the stress-strain curve obtained from the test,and the advantages and disadvantages of the constitutive model are discussed.The main conclusions of this study are as follows:(1)Assuming that the rock is composed of elastic elements,the microwave damage evolution equation with the power of microwave irradiation as the only variable under microwave action is obtained.Furthermore,the damage variables under the combined action of microwave and force were defined and the damage evolution equation was established based on the micro-element strength theory and the three-parameter Weibull distribution.Generalized Hooke's law is introduced to establish the constitutive model of hard rock under the action of microwave and force,and the formula for determining each parameter in the model is obtained;(2)Two kinds of granite samples,sesame ash and yellow rust stone,were taken as examples to carry out microwave irradiation tests.Observation and analysis of the apparent damage showed that the microwave power was 2.66kW at the beginning of cracks in sesame ash and 4.66kW at the beginning of cracks in yellow rust stone.The damage of the two kinds of granite is more obvious with the increase of microwave power,and the sesame ash rock is more sensitive to microwave.According to the changing characteristics of temperature and ultrasonic wave velocity,it is found that different rocks have different microwave absorption capacities.The microwave power corresponding to the fastest absorption rate is not fixed.The damage of sesame ash begins at a very small microwave power,and the damage of yellow rust stone is greater than that of sesame ash;(3)Uniaxial compression tests were carried out on the samples irradiated by microwave,and the stress-strain curves of each rock sample were analyzed according to the four stages of rock compression failure.With the increase of microwave power,the compaction stage becomes significantly longer,which proves that with the increase of microwave power,the internal cracks of rock samples increase significantly.The elastic stage is obviously shorter,which proves that the elastic energy storage capacity of rock is reduced.The failure stage obviously changes from linear descent to slow descent,which indicates that the failure mode of rock gradually changes from brittle failure to ductile failure with the increase of microwave power;(4)Based on the experimental data,the theoretical constitutive curves of sesame ash granite under the action of microwave and force were obtained under three microwave powers.Through the comparison between the model and the test curve,it is proved that the constitutive model fits well and can describe the constitutive relationship of rock under various microwave power irradiation well.Due to the adoption of D-P criterion and relatively conservative assumptions,the model is conservative as a whole.The influence law and physical significance of each parameter were explored by means of control variables.A and B represented the rock compaction rate and initial defect before the threshold.After the threshold value,F represents the compressive strength of rock and determines the size of the stress peak;m determines the compressive deformation rate of rock and indirectly affects the peak value;? determines the slope of the model curve after the peak value and represents the form of rock failure.