Explicit incorporation of deformation twins into crystal plasticity finite element models

Abstract

Highlights• Morphology and crystallography of deformation twinning are implemented in crystal plasticity finite element models.• Intrinsic twinning transformation shear strain is enforced to correspond to the plastic strain accommodated by the twin lamella.• Heterogeneities in spatial mechanical fields are correlated with microstructural changes during twin formation and thickening.• Multiple thin twin lamellae are predicted to be more favorable than a single thick twin lamella in uranium. AbstractDeformation twinning is a subgrain mechanism that strongly influences the mechanical response and microstructural evolution of metals especially those with low symmetry crystal structure. In this work, we present an approach to modeling the morphological and crystallographic reorientation associated with the formation and thickening of a twin lamella within a crystal plasticity finite element (CPFE) framework. The CPFE model is modified for the first time to include the shear transformation strain associated with deformation twinning. Using this model, we study the stress-strain fields and relative activities of the active deformation modes before and after the formation of a twin and during thickening within the twin, and in the parent grain close to the twin and away from the twin boundaries. These calculations are carried out in cast uranium (U), which has an orthorhombic crystal structure and twins predominantly on the {130} <310> systems under ambient conditions. The results show that the resolved shear stresses on a given twin system on the twin-parent grain interface and in the parent are highly inhomogeneous. We use the calculated mechanical fields to determine whether the twin evolution occurs via thickening of the existing twin lamella or formation of a second twin lamella. The analysis suggests that the driving force for thickening the existing twin lamella is low and that formation of multiple twin lamellae is energetically more favorable. The overall modeling framework and insight into why twins in U tend to be thin are described and discussed in this paper.

Texture formation in orthorhombic alpha-uranium under simple compression and rolling to high strains

“…The geometry of the predominant slip/twin systems has been depicted in Refs. [2,3]. Like most metals, possessing a lowsymmetry crystal structure [4e6], activation barriers of these modes are not equivalent.…”

Anisotropic modeling of structural components using embedded crystal plasticity constructive laws within finite elements

“…At the meso-scale, we use multiple types of constitutive laws, ranging from simple isotropic elasticity to a complex, polycrystal model. At the microscale, for activating plastic slip within each crystal within the polycrystal model, we used an extended Voce type [65] hardening model for Cu [66] and a dislocation density-hardening model for α-U [13,67,68]. For twinning, we use a different model that incorporates both the lattice reorientation and shear provided by the twin.…”

Twinning behavior of polycrystalline alpha-uranium under quasi static compression

“…Recently, Ardeljan et al [32] reported a model within an explicit finite element framework to calculate the stress fields upon twin formation and propagation in cast uranium. Their simulation is able to relate spatially resolved field of stress and strain with evolution of deformation twin.…”