Numerical Simulation Of The Technique Of Red Sandstone With Coupled Static-dynamic Loading

In view of the shortcomings of the actual rock impact test,such as not easy to repeat,high cost and end face error,this paper uses ANSYS/LS-DYN A software to conduct numerical simulation of the rock with coupled static-dynamic loading test,and compares the simulation calculation results with the actual test results to verify the feasibility and accuracy of numerical simulation.This paper carries out numerical simulation of the test,and its advantages are as follows: on the one hand,the failure process of rock can be obtained by using post-processing software,which improves the failure mechanism of rock with coupled static-dynamic loading;On the other hand,based on the characteristics of the laboratory test device,the corresponding finite element model can be established to analyze the influence of the external device on the rock stress wave shape,which provides a convenient and effective research means to analyze the rock stress wave propagation law under three-dimensional static load.Firstly,the corresponding finite element model was established according to the component size of the actual laboratory test.Taking red sandstone as the research object,the material model parameters and contact relations were set reasonably,and the method of implicit to explicit analysis was adopted to realize the combined dynamic and static loading of rock.The results show that the wave width and amplitude obtained by numerical simulation are obviously larger than the actual test.This is because in the indoor rock impact test,the impact velocity of the spindle punch will be affected by friction and air resistance,resulting in less than the set value.The rock failure modes of numerical simulation and test are similar.At the same time,the microsecond failure process of rock can be obtained by numerical simulation.According to the rock failure cloud map,regardless o f the existence of initial static stress,the rock failure mode is split failure,and its failure trend presents a change characteristic from the edge of the rock to the axis.Secondly,in order to improve the accuracy of numerical simulation of rock dynamic and static combination test,RHT constitutive model was selected as red sandstone material model in this paper,and relevant model parameters were determined by theoretical calculation,experimental measurement and other methods.For difficult to determine the parameters in the model,combining with the actual test results,with uncertain parameters as independent variables,to reflect wave width and stress amplitude difference of correlation rate as well as the stress-strain curve as the dependent variable,multiple regression equation is used to calculate the interaction effect of undetermined parameters and main effect,as well as parameters change in response to the amount of contribution,the sensitivity of the undetermined parameters.The results show that the significant degree of interaction effects of most parameter combinations is greater than 0.05,that is,the interaction effects of the undetermined parameters are not obvious,but the main effect of the undetermined parameters is nonlinear.By analyzing the sensitivity of each undetermined parameter,this paper redefines the parameters of the RHT model,and the accuracy of the numerical simulation results is obviously improved after calculation and testing.Finally,in order to study the influence of external device on stress wave shape in rock dynamic and static combined test,the finite element model of external device was established on the basis of the original model and combined with the characteristics of the actual test device,and the stress wave propagation test was simulated to obtain the simulated stress wave shape and the stress cloud map of steel rod.The results show that the external device has little effect on the incident wave and reflected wave on the steel rod,but has great effect on the transmitted wave when there is no initial static load and rock specimen.When the test condition is three-dimensional static load and rock specimen,the research results are as follows: without the device,the falling edge of the incident wave e xceeds the initial strain value and reaches around the "0" scale line.After the stress wave reflection,the tail end of the waveform does not return to the initial strain value.When there is an external device,the steel rod is still in compression state due to its constraint,and the end of the stress wave returns to the initial strain value.