Simulation Of The Texture Evolution During Cold Deformation Of FCC Metal With Crystal Plasticity FEM

Crystal plasticity finite element method (CPFEM) model, incorporating the crystal plasticity theory into the framework of the finite element method, has been used to simulate the plastic deformation process at the crystal scale. According to the crystal plasticity theory, the plastic deformation can be described by the dislocation slip and the lattice rotation. Compared with the classic isotropic constitutive law, the constitutive law based on the crystal plasticity provides accurate description of the plastic deformation. Therefore, CPFEM has become a powerful tool in the simulation of texture evolution and material properties during metal forming. This thesis focuses the works on the development of CPFEM software, geometrical modeling of polycrystal and simulation of cold deformation of FCC metal (aluminum). The details are as follows:(1) CPFEM has been implemented in the commercial FEM software, ABAQUS, by developing a user-defined material constitutive law subroutine (UMAT). Bassani-Wu hardening equation has been introduced into the CPFEM model as firstly reported in the literature. The developed CPFEM model has been validated by several experimental results for different deformation processes.(2) The plane strain compression of single crystal aluminum has been simulated by CPFEM. The unknown parameters in the constitutive law has been estimated by fitting the measured stress-strain curve. The obtained parameters have been used to model the tensile deformation of polycrystal aluminum and an accurate stress-strain curve has been predicted. This indicates that these parameters are real material parameters, which are independent of the deformation process and dimension of the deformed sample.(3) The texture evolution during the plane strain compression has been studied. We investigate the effect of the coefficient of friction and reduction. The simulation results show that the lattice mainly rotates around RD when the coefficient of friction is less than 0.15, otherwise the lattice rotation direction is TD. (4) The rolling process of single crystal aluminum with 4 typical textures has been simulated. The results show that the cube orientation and rotated-cube orientation are stable during rolling, while the Goss orientation and Brass orientation are unstable. The lattice mainly rotate around TD during rolling of single crystal aluminum. The simulation results accurately predict 4 deformation bands parallel to the rolling direction. This result has not been reported in the published literature.(5) This thesis has developed methods to build the geometrical model for polycrystal based on the Voronoi diagram approach and to assign the initial textures to each grain in the polycrystalline sample. Two methods, based on Python script and ABAQUS input file respectively, have been proposed to input the geometrical model and the initial textures in ABAQUS CAE.(6) The tensile deformation of polycrystalline aluminum has been investigated. The major simulations have been concentrated on the analysis of the texture evolution and the effect of the grain size. The reason for necking has been analyzed in details.(7) The rolling deformation of polycrystalline aluminum has been simulated. The texture evolution during the deformation and the uneven distribution of the stress and strain have been discussed. The effects of grain boundary and the initial orientation of the grain on the deformation behavior of the grain are analyzed. The simulation results show that the contact pressure and the frictional stress significantly change around the grain boundaries.