TEXTURE INFORMED CRYSTAL PLASTICITY FINITE ELEMENT MODELING OF POLYCRYSTALLINE MATERIAL DEFORMATION

Zhe Leng

Metallic materials, such as aluminum, ferrite, magnesium, are used in a wide variety of applications such as structure components of automobiles and plane industry, due to its high strength and low density. It is of great importance to understand the mechanical behavior of these structure metals, such as the relationship between the microstructure and the local deformation and stress state. In this study, a dislocation density based crystal plasticity finite element model has been developed and applied to aluminum and ferrite, respectively. The dislocation is represented as a square loop and its density and other related quantities is tracked explicitly as state variables, based on the crystal kinematics and dislocation related mechanisms. The dislocation generation and annihilation is modeled, in addition, the dislocation flux which is caused by the density gradient is also included in the model. The simulation is then conducted on both single and polycrystalline metallic materials using the initial measured sample texture. Both the experiment and the simulation results indicated localized plastic strain and dislocation patterning, which were controlled by the individual crystallite orientations and the grain boundary effects. The results also revealed that the level of concentrated stress at the grain boundaries depends on misorientation of the interface, besides, grain boundaries and triple junctions had higher hardening effects than the grain interiors. The interaction between the dislocation and the grain boundaries is also incorporated in the model. For the near grain boundary regions, particular consideration and finite element formula is applied to account for the additional activation energy term as well as the geometric compatibility of the grain boundary during dislocation penetration events, both of the energy term and the geometric barrier depend on the grain boundary character. The formulations applied here provide a reasonable methodology to understand how the interactions between dislocation and grain boundary affect the overall mechanical behavior and the microstructure, and quantitative comparisons of predicted geometrically necessary dislocation distributions with the those determined experimentally indicates a reasonable agreement, further analysis also indicates that stress concentration, as well as the dislocation patterning, depends highly on the grain boundary characters.

TEXTURE INFORMED CRYSTAL PLASTICITY FINITE ELEMENT MODELING OF POLYCRYSTALLINE MATERIAL DEFORMATION

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