Numerical Simulation On Copper Foil Rolling Process Based On Crystal Plasticity FEM

In recent years,metal foils(i.e.copper foils,etc.)are wide applied in the fields of electronics industry,microelectromechanical systems,medical and new energy resources,the needs to metal foil is increasing,and the requirement to its quality is becoming strict.The characteristic geometrical sizes of those micro-parts decrease to the same ones of micro-structures(i.e.grains).At this scale,the constraint from grains leads to the significant size-dependent behavior.The deformation behavior of a polycrystalline metal is influenced largely by the internal state of materials,such as morphology and orientation of grains,etc.However,due to the microscale effect,the previous constitutive theories and the relevant calculation methods are not applied to describe the deformation of materials at the microscale directly.And moreover,by the way of numerical simulation,more detailed information can be got than experiment.The mechanical properties of the microstructure are embodied in the constitutive framework of polycrystalline plasticity theory.Deformation behavior of the metal foil such as plastic anisotropy at the microscopic level is derived from averaged grain microscopic responses.According to the crystal plasticity theory,the plastic deformation can be described by the dislocation slip and the lattice rotation.Compared with the classical isotropic constitutive law,the constitutive law based on the crystal plasticity provides accurate description of the plastic deformation.By using theoretic analysis,numerical simulation and experiment verification,the influence of crystallographic orientation,grain structure,heterogeneous plastic deformation at grain level and active slip system on plastic deformation behavior of foil rolling have been investigated,and the microscale effect of foil rolling has also sharply studied.Motivated by this background,the employed methods and results of this thesis are introduced as follows:1.CP-FEM has been implemented in the commercial FEM software,ABAQUS,by developing a user-defined material constitutive law subroutine to simulate foil rolling process.Bassani-Wu hardening equation has been introduced into the CP-FEM model.The uniaxial tension of polycrystalline pure copper foil has been simulated by CP-FEM.The unknown parameters in the constitutive law have been estimated by fitting the measured stress-strain curve.The developed CP-FEM model has been validated by several experimental results for different foil rolling deformation process.2.New algorithm of the generation of polycrystalline structures has been developed based on the Voronoi diagram approach and meshing of these structures has also been proposed.In this algorithm,the generation and meshing of polycrystals were automatically executed according the parameters given.The proposed algorithm was extraordinary convenient and rapid.The original orientation of each grain was generated with random lattice orientation or typical texture based on the orientation distribution function.The finite element model of polycrystalline foil rolling,based on the ABAQUS input file INP,has been proposed to input the geometrical model and the initial texture in ABAQUS/CAE.3.To analyze the plastic deformation behavior of single layer grain in foil rolling,a finite element model for rolling of FCC single layer grain was established,in which each grain was given a different orientation,and the grain boundary constraint was simulated by grain misorientation of the neighbor grains.The major simulation has been concentrated on the analysis of the influence of grain orientation,rolling process parameters and texture types on the deformation behavior in single layer grain microstructure foil rolling.It is showed that the grain orientation,rolling process parameters,active slip system were the important factors which affect the intergranular and intragranular behavior of inhomogeneous deformation and the plastic deformation behavior.The plastic deformation of single layer grain in foil rolling and its' evolution can be described well,and the relationship between microstructure characteristics and plastic deformation behavior can be established by crystal plasticity finite element model in mesoscale,that is:the earlier activation of slip system in nearby grain boundaries and grain surface than other regions,and with further deformation,these activation areas were spread into grains.The active system of different parts in a same grain were different due to the different grain orientation and texture,and the grain-scale inhomogeneous plastic deformation,then the changing of contact characteristics between roll and foil was induced.4.2-D crystal plasticity finite element model(CP-FEM)on polycrystal was used to study and analysis the thickness size-dependent behavior of polycrystalline ultra-thin strip.The results showed that,for single layer grain ultra-thin strip,the active region of the grain surface was increases with decreases thickness and the intracrystalline shear deformation was changed from the several narrow slip bands which parallel to the rolling direction to a single sharp slip band penetrating the grain.That is:the thinner the more easily slip.These size-dependent behaviors were originated from the active region of the grain surface.For multilayer grain ultra-thin strip,the influence of grain orientation on roll force and stress were greatly increased and the fluctuation of roll force was also significantly increased and accumulative plastic slipping was gradually transferred from interior grain boundaries to the surface grains with the decreases thickness.That is:the thinner the more easily slip of the surface grains.The active slip systems in ultra-thin strip reveal that these different size-dependent behaviors were originated from the softing effect of surface grains.5.To analyze the statistical grain size effect in foil rolling,the grain size-dependent behavior of poly crystalline copper foil rolling and the intrinsic mesoscale deformation behavior were explored.The result showed that,for single layer grain copper foil,the stress concentration gradually shift from grain boundaries to grain interior and the intracrystalline shear deformation was changed from a single sharp shear band penetrating the thickness direction to several narrow shear bands which parallel to the rolling direction with the decreases distance of adjacent vertical grain boundaries.That is:the greater distance of adjacent vertical grain boundaries the more easily slip.These different size-dependent behaviors were originated from the number of grain boundaries in deformation zone,and the active region of grain surface and grain boundary.For multilayer grain copper foil,the roll force increases,the impact of grain orientation on roll force and stress decreases,and the fluctuation of its roll force decreases significantly with the increase the number of grains through the thickness.The rotation angle and the scatter of the grain orientation of the surface grains were greater than interior grains.The number of active slip systems were remain unchanged which the slip can be extended to the entire range of surface grains,and the number of active slip systems were increased which the slip can be extended to the entire range of interior grains with the decreases grain size.These size-dependent behaviors were originated from the increased of active region of the grain boundary with the decreases grain size.It is showed that the influences of grain structure and active region of the grain boundary were described effectively by using crystal plasticity finite element model,and the mesomechanism of the microscale effect was well interpreted by analyzed the property of active slip systems.