Generalized Constitutive Model Considering Particle Crushing For Granular Materials And Its Realization On FEM Programs

A generalized constitutive model considering particle crushing for granular materials is proposed.The 3D elastoplastic finite element program based on the constitutive model is also developed.The main research work is about the following three aspects:the development of the transformed stress method,proposing the constitutive model considering particle crushing and the development of the elastoplastic finite element program.Development of the transformed stress method:Based on the existed transformed stress method,it is realized that the critical state of anisotropic constitutive models is combined with the transformed stress method.It is applied in the generalizations of the isotropic and anisotropic constitutive models,then the characteristics of yield surfaces in the normal stress space and the transformed stress space are analyzed,by which the reasonableness and validity of the transformed stress method is displayed.Taking the Modified Cam-Clay model and the K₀-MCC model as examples,the characteristics and deficiencies of the other methods for generalizing constitutive models are analyzed.The transformed stress method are compared with the widely used g(?)method by generalizing the isotropic and anisotropic constitutive models.It is seen from the comparison between the model predictions and the test results that the transformed stress method is much better than other existing methods for generalizing constitutive models,it solves the difficulty of the generalization of the anisotropic models,and it can reasonably describe the material behaviors in general stress state.The tangent stiffness matrix of the generalized constitutive model is given,so it is very convenient to apply the transformed stress method into the finite element analysis.Constitutive model considering particle crushing for granular materials:Based on the test characteristics of the sand and rockfill under high stress level,which contain the mechanical behaviors under the isotropic compression,the strength on the p-q plane and the stress dilatancy,the plastic potential function,the hardening parameter and the yield function of a constitutive model considering particle crushing for granular materials are proposed.There are 7 material parameters in this model,and all of which can be determined by the isotropic consolidated test and the common triaxial compression test.The method for determine the material parameters is given detailedly.This model is generalized from the triaxial compression to the 3D stress condition using the transformed stress method.The proposed model is validated by the predicting the triaxial tests results for sand and rockfill under high stress level.It is seen from the comparison between the model predictions and the test results that the proposed model can reasonably describe the stress-strain relation and strength behavior for materials existing particle crushing.Development of the finite element program:Based on the proposed constitutive model considering particle crushing and the existed overconsolidated soil constitutive model,a 3D elastoplastic finite element calculating(TEPFEC)program is developed with Fortran language.The pre and post processes of the finite element analysis are realized on the software Patran.The Fortran program of the TEPFEC is open.The deformation and stress field of the triaxial sample under general stress state is analyzed using the TEPFEC program based on the proposed constitutive model,by which the influence of particle crushing on materials behaviors is simulated.The stress and displacement of the foundations of the Olympic Forest Park project are calculated using the TEPFEC program based on overconsolidated soil constitutive model.It is realized from the development of the TEPFEC program that the generalized constitutive model considering particle crushing for granular materials and the overconsolidated soil constitutive model could be applied into the calculation and analysis for practical engineerings.