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Abstract
Metallic components go through a complex sequence of deformation processes during manufacturing. The purpose of a structural component dictates the use of specific metallic material with a given set of mechanical properties. In order to predict material behavior and microstructural evolution during deformation on a computer rather than in a workshop, computationally efficient models have been developed over the past several decades. Mean-field plasticity models like viscoplastic self-consistent (VPSC) and elastoplastic self-consistent (EVPSC) models are popular for their efficiency in terms of computational time compared to full-field models but lack in accuracy due to the consideration of only mean field properties neglecting higher order statistics in the microstructure. Recent extension of VPSC model by the introduction of higher order field fluctuation (FF) terms has made significant improvement to VPSC model leading to as accurate texture prediction as full-field models during deformation and recrystallization. In this dissertation, higher order FF calculation is implemented in mean-field incremental EVPSC model. The model is named as FF-ΔEVPSC which calculates the second moment of stress, lattice spin, intragranular misorientations. Based on the implemented intragranular misorientation spreads, grain fragmentation and static recrystallization models are incorporated in FF-ΔEVPSC model. A dislocation density based recovery model is also implemented in the model. FF-ΔEVPSC is applied to interpret and predict ex-situ and in-situ thermo-mechanical and neutron diffraction datasets pertaining to deformation, recovery, and static recrystallization behavior of pure Ta. Next, the FF-VPSC model is utilized to predict grain size evolution during high pressure torsion (HPT) of pure Cu and aluminum alloy AA5182-O based on grain fragmentation model. The FF-VPSC is coupled with commercial finite element (FE) software package ABAQUS through user material (UMAT) subroutine and a sequence of rolling, recrystallization, and cup drawing is simulated for aluminum alloy AA6022-T4. Then, the present version of FF-VPSC model is extended to account for twinning in hexagonal close packed (hcp) materials by extending the FF calculation for twinned grains and a dynamic recrystallization model is developed that considers nucleation of new grains in both parent and twinned grains. The model is applied to simulate thermo-mechanical response and texture evolution dictated by dynamic recrystallization of Mg alloy AZ31. Finally, strain-gradient (SG) plasticity model based on geometrically necessary dislocation (GND) density is implemented in VPSC. FF formulations are utilized for the SG implementation in VPSC, and we call this model SG-VPSC. SG-VPSC is first applied to predict the mechanical response and grain size effect of high purity α-Ti and then applied to predict the evolution of GND density for aluminum alloy AA6016-T4.
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