Multi-scale Investigation On Plastic Deformation Mechanism Of Polycrystalline Copper Under Uniaxial Compression

Plastic deformation theory of metal materials is of great importance in investigating plastic working of metal materials as well as deformation failure of mechanical structure.Crystal plasticity theory is based on physical mechanism of metal materials such that it is established according to the microstructures of metal materials. In the case of crystal plasticity theory, plastic shear strain is introduced in order to describe the movement of dislocations on the slip system, where based on the idea of statistics, the discontinuous dislocation motion is regarded as continuous plastic deformation so that it is closely related to macroscopic continuum mechanics. As for metal materials with various scales, they exhibit a substantial difference in macroscopic mechanical behavior of plastic deformation, where a strong size effect can occur. In the present study, according to phenomenological plastic constitutive theory based on continuum mechanics as well as crystal plasticity theory, plastic deformation mechanism of polycrystalline copper is investigated in terms of macroscale and mesoscale.The polycrystalline copper is used as the experimental material, where the corresponding compression sample is subjected to compression by 20%, 40% and 60%, respectively. The microstructures and the textures of the compressed copper samples are characterized by means of EBSD. The results show that with the progression of plastic deformation,geometrical necessary dislocation (GND) density is homogeneously distributed in the interior of the grains as well as at the grain boundaries, which plays a significant role in impeding the movement of dislocations as well as increasing the deformation resistance. The as-received copper sample is mainly based on the high angle grain boundaries. When the copper sample is subjected to compression deformation by 60%, the low angle grain boundaries increase in the interior of the grains such that the grains are refined and the number of grain boundaries increases. The cold deformation leads to the rotation of the grains, which contributes to the formation of textures. When the copper sample is subjected to compression deformation by 20%, it possesses the texture of {111}<112>, but when the copper sample is subjected to compression deformation by 60%, it possesses the texture of {111}<110>.Rigid-plastic finite element method based on continuum mechanics is used for simulating uniaxial compression deformation of polycrystalline copper, where stress field, strain field and velocity field are obtained on the basis of various deformation degree. The inhomogeneity of plastic deformation of polycrystalline copper subjected to uniaxial loading at the macroscopic level is revealed based on stress distribution and strain distribution in the different deformation zones.In terms of crystal plasticity constitutive model based on dislocation slip, crystal plasticity finite element model is established according to Voronoi theory, where crystal plasticity finite element simulation parameters, including grain orientation, grain number and element number, are optimized and the corresponding material parameters are fitted. Crystal plasticity finite element method is used to simulate the stress-strain behavior of polycrystalline copper under uniaxial compression, the texture evolution of polycrystalline copper in the case of the different deformation degrees as well as the inhomogeneous plastic deformation of polycrystalline copper. The simulation results indicate that crystal plasticity finite element method is a perfect candidate for simulating the macroscopic stress-strain behavior of polycrystalline copper and capturing the principal characteristic of texture evolution. With the increase in the deformation degree, the fiber texture of <110> is gradually induced and the preferential orientation is formed. In order to meet the requirement for deformation compatibility, the rotation by the different degree occurs along the RD, ND and TD directions between the grains and in the interior of the grain, which reflects the inhomogeneity of plastic deformation at the grain level. The simulated results are in good accordance with the experimetal ones.