The 3D Modeling And Numerical Simulation Analysis For Polycrystalline Metal Under Finite Deformation

Metal materials,which are formed by crystallization,play an irreplaceable role in many engineering fields.Due to the complex crystallization modes which result in the discrepancies between the crystals controlled by different crystal nucleus,so the metal materials are also called polycrystalline metal materials.The complex crystallization modes of polycrystalline materials also make materials display strong geometrical irregularity and complicated deformation mechanism on micro-scale,which further enable the macro mechanical response of polycrystalline materials to be impacted by many factors,such as crystal geometry,crystal orientation and slip systems etc.In this work,aiming at the most widely used ferritic steel in automotive industry,the geometric modeling and material modeling of the polycrystalline microstructure of territic steel at finite deformation are established,and the simulation and analysis of mechanical response are carried out with the finite element method.The main content of this thesis is as follows:First of all,Considering the later homogenization research on the polycrystalline metal materials based on this paper,the finite element simulation and analysis for the polycrystalline materials will be done with FEAP software which has perfect homogenization module.Through the integration and development of FEAP,the secondary development for the user subroutine of St.Venant Kirchhoff crystal model and crystal elastoplastic model are realized,and the finite element analysis platform is integrated and established.Further,the material response model which can characterize cubic lattice system and shear slip deformation mechanism is constructed.In addition,the secondary development for FEAP output file is achieved,through which the model can be visualized in Para View and the problem of stack overflow in postprocessing operations is solved as well.Secondly,in order to construct the polycrystalline microstructure geometric model of metal materials accurately,MATLAB is used to simulate the crystallization process through the Voronoi graph topology method,and the three-dimensional Voronoi polycrystalline geometric model under specific space is then textured.The geometric modeling and meshing are accomplished with ANSYS and ABAQUS.Finally,the 3D Voronoi polycrystalline microstructure geometric model is constructed in FEAP by the translation for the inp.file.In this work,the parametric control of the model for its particle number and regularity is also realized,and a new statistical method to characterize the regularity of the geometric model is proposed.Last,the finite element simulation and analysis of the regular hexahedral single crystal,polycrystal model and the irregular three-dimensional Voronoi polycrystalline microstructure are progressed with Hill model,St.Venant Kirchhoff crystal model and crystal elastoplastic model.The compatibility and advantages of the three material models for the analysis of polycrystalline metal material are compared,through which it can been seen that the finite element simulation based on the crystal elastoplastic model is the most accurate to describe the mechanical properties of polycrystalline metal material.Moreover,the influence of the main material axis of Hill model and the lattice direction of the two crystal models on the stress response of polycrystal model under uniaxial stretch is investigated,in which the influence of the main material axis in Hill model is lowest while the remaining two is higher.The relationship between the lattice direction and the maximum stress value is also obtained.Furthermore,the influence of the geometry and the grain size of the polycrystalline microstructure geometric model on its mechanical properties is evaluated under three material models as well.The simulation results show that the microstructure of polycrystalline metal can not be neglected during the research on the mechanical properties of materials.