Study Of Rock Dynamic Damage Model Based On Unified Strength Theory

Rock dynamic damage model plays an important role in solving rock dynamic problems such as blasting and impact,as well as the study of rock dynamic problems.At present,a number of of rock dynamic damage models are reported,as their validity is affected by their deficiencies and defects to a certain degree.Therefore,it appears necessary and significant to develop a new rock dynamic damage model and avoid the shortcomings of these reported models.In this paper,first of all,according to the deficiencies and defects the present commonly used rock dynamic damage models have,based on the elastic-plastic mechanics and damage mechanics,using the unified strength theory as the yield criterion,set up a new rock dynamic damage model;Then,in order to facilitate the application of rock dynamic damage model,Fortran language is adopted to program the dynamic damage model of rock blasting and make its numerical implementation.At last,the rock dynamic model is applied,that is,the dynamic NSCB test and rock blasting under different in-situ stress conditions are simulated based on the rock dynamic damage model,and then the two typical rock dynamic problems are studied.The research contents and conclusions of this paper mainly include the following aspects:(1)Establishment of rock dynamic damage model.Based on the unified strength theory,the constitutive relation of rock dynamic damage model is deduced,and a rock dynamic damage model is established.The model takes into account the Lode angle effect,strain rate effect of rock,confining pressure effect of rock,hardening behavior of rock under tension and compression conditions,damage evolution law of rock under tension and compression-shear conditions.The unreasonable expression of volumetric strain in HJC model is modified,and a solution to the singularity of yield surface in the unified strength theory is given.(2)Numerical implementation and validation of rock dynamic damage model.In this section,firstly,the constitutive model is programmed by Fortran language through the user-defined interface(Umat)of LS-DYNA,a large-scale general finite element software.A new LS-DYNA solver is generated by using Intel(R)Fortran Complier,a Fortran language compiler,to make the rock dynamic damage model.It is embedded in LS-DYNA.Then the concrete determination methods of rock dynamic damage model parameters are given from four aspects:basic parameters,strength parameters,hardening parameters and damage parameters.Finally,four typical examples are given,namely,rock uniaxial compression test,rock triaxial compression test,rock uniaxial tension test and rock SHPB test.The test results show that the new LS-DYNA solver is stable and the rock dynamic damage model can describe the mechanical behavior of rock under quasi-static and dynamic loading conditions.(3)Sensitivity analysis of main parameters of rock dynamic damage model.Based on the single element test method and the sensitivity analysis method of local parameters,the sensitivity analysis of the main parameters of the rock dynamic damage model is carried out qualitatively and quantitatively.Their sensitivity is in order from large to small:?m?D1??0???Pcrush??crush?b1??lock?Plock?D2?K1.K2 and K3 have no influence on the quasi-static mechanical behavior of rocks.(4)Numerical simulation of rock dynamic NSCB test.Based on the rock dynamic daruage model,the numerical simulation of dynamic NSCB test is carried out.The effects of loading rate on damage evolution,failure morphology and energy evolution of NSCB rock specimens are studied respectively.The results show that loading rate has an important influence on the damage range,failure morphology and energy evolution of NSCB rock specimens.The larger the loading rate is,the larger the damage range of NSCB is,the worse the flatness of crack is and the greater the final stability value of internal energy is.According to the ratio of internal energy to total energy,the whole process of rock deformation to failure in NSCB test can be divided into five stages,which can contribute to a better understanding of rock dynamic fracture.(5)Numerical simulation of rock blasting under different in-situ stress conditions.Based on the rock dynamic damage model,the numerical simulation of rock blasting under different in-situ stress conditions is carried out.Combining with theoretical analysis,the damage evolution,crack propagation and energy evolution of rock blasting under different in-situ stress are studied.The results show that the larger the hydrostatic pressure is,the smaller the damage range of rock is.The smaller the energy utilization ratio of rocks is,the larger the energy effective utilization ratio of explosives is;the lateral pressure coefficient of in-situ stress k has certain influence on the damage range,crack propagation and energy evolution of rocks.With the increase of lateral pressure coefficient of in-situ stress k,the damage range of rocks tends to decrease,and the energy utilization ratio of rocks and explosives tends to increase.Cracks mainly extend along the direction of maximum stress,and the lateral pressure coefficient of in-situ stress mainly affects the crack growth in the direction of the minimum stress.