Incorporation of deformation twinning in crystal plasticity models (original) (raw)

Explicit incorporation of deformation twins into crystal plasticity finite element models

Computer Methods in Applied Mechanics and Engineering, 2015

Deformation 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 < > 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.

A crystal plasticity model for twinning-and transformation-induced plasticity

A dislocation density-based crystal plasticity model incorporating both transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP) is presented. The approach is a physically-based model which reflects microstructure investigations of ε-martensite, twins and dislocation structures in high manganese steels. Validation of the model was conducted using experimental data for a TRIP/TWIP Fe-22Mn-0.6C steel. The model is able to predict, based on the difference in the stacking fault energies, the activation of TRIP and/or TWIP deformation mechanisms at different temperatures.

Role of Deformation Twinning on Strain Hardening in Cubic and Hexagonal Polycrystalline Metals

Advanced Engineering Materials, 2003

Besides crystallographic slip, deformation twinning is the most prevalent mechanism of plastic deformation in many materials. Novel experiments were conducted in cubic and hexagonal metals to elucidate the effect of deformation twins on subsequent mechanical response. Orientation Imaging Microscopy TM (OIM) and indentation techniques were employed in conjunction with conventional mechanical testing and optical microscopy to obtain new insights. Here, we show direct and clear evidence for hardening of the material by deformation twinning due to both a reduction of the effective slip length (Hall±Petch effect) and an increase in hardness of the twinned regions (Basinski mechanism), as well as softening due to lattice reorientation of the twinned regions. These results appear to explain the seemingly contradictory results that have been reported previously on the strengthening effects of twins.

On the Deformation Heterogeneities Described By Crystal Plasticity

2015

The deformation fields within grains in polycrystalline materials are generally highly heterogeneous and can be the precursors to the nucleation of micro-cracks or cavities. Such behavior is conditioned by microstructural features, such as grain structure, texture, morphology, size, etc. The understanding of such complex phenomena is crucial to enable structural integrity assessments of engineering components, since it constitutes the physical bases on which to describe the local mechanisms of deformation and failure to be incorporated into structural integrity codes. This work provides a brief overview of the different continuum mechanics approaches used to describe the deformation behavior of either single crystals or individual grains in polycrystalline metallic materials. The crucial role played by physics based local and non-local crystal plasticity approaches in the prediction of heterogeneous deformation is discussed. Representative examples are given regarding the use of dis...

Effects of constraints on lattice re-orientation and strain in polycrystal plasticity simulations

Computational Materials Science, 2009

Employing a rate-dependent crystal plasticity model implemented in a novel and fast algorithm, two instantiations of an OFHC copper microstructure have been simulated by FE modelling to 11% tensile engineering strain with two different sets of boundary conditions. Analysis of lattice rotations, strain distributions and global stress-strain response show the effect of changing from free to periodic boundary conditions to be a perturbation of a response dictated by the microstructure. Average lattice rotation for each crystallographic grain has been found to be in fair agreement with Taylor-constraint simulations while fine scale element-resolved analysis shows large deviations from this prediction. Locally resolved analysis shows the existence of large domains dominated by slip on only a few slip systems. The modelling results are discussed in the light of recent experimental advances with respect to 2-and 3-dimensional characterization and analysis methods.

Modeling of twinning-induced plasticity using crystal plasticity and thermodynamic framework

Acta Mechanica, 2019

In many applications of steels, especially in aerospace and petroleum industry, large deformation is required in order to achieve complex shape and geometry of finished products. In these, advanced highstrength steels play a vital role by attaining favorable amalgamation of high strength and ductility. Among all second-generation steels, twinning-induced plasticity contains a significant percentage of austenite phase, shows outstanding tensile strength and ductility. The primary cause of having these outstanding properties is found to be stress-assisted austenite to martensite phase transformation, commonly described as twinning. In this paper, a micromechanical model is developed in the thermomechanical framework to investigate elasticplastic deformation of twinning-induced plasticity steel. It is assumed that plastic deformation is caused due to slip and mechanical twinning under given loading conditions. Firstly, a micromechanical constitutive model, considering slip and mechanical twinning as sources of permanent deformation, is developed by kinematic decomposition of an austenite crystal into intermediate configurations. Secondly, a thermodynamic framework is used to formulate driving potentials for slip and twinning mechanisms. Thirdly, the developed model is numerically implemented into finite element software ABAQUS by a user-defined material subroutine. Finally, the deformation behavior of single and polycrystalline austenite are predicted by numerical simulations in tension compression, and simple shear loading conditions. It is found that in tension twin deformation plays a dominant role, while the reverse is observed in compression. In simple shear, on an activation of twin mode, slip systems encounter higher slip resistance due to slip-slip and slip-twin interactions.

A new crystal plasticity constitutive equation based on crystallographic misorientation theory

2011

Since plastic deformation of polycrystal sheet metal is greatly affected by its initial and plastic deformed textures, multi-scale finite element (FE) analysis based on homogenization with considering micro-polycrystal morphology is required [1]. We formulated a new crystal plasticity constitutive equation to introduce not only the effect of crystal orientation distribution, but also the size of crystal grain and/or the effect of crystal grain boundary for the micro-FE analysis. The hardening evolution equation based on strain gradient theory [2], [3] was modified to introduce curvature of crystal orientation based on crystallographic misorientation theory. We employed two-scale structure, such as a microscopic polycrystal structure and a macroscopic elastic/plastic continuum. Our analysis

Influence of grain size and stacking-fault energy on deformation twinning in fcc metals

Metallurgical and Materials Transactions A, 1999

This article investigates the microstructural variables influencing the stress required to produce deformation twins in polycrystalline fcc metals. Classical studies on fcc single crystals have concluded that the deformation-twinning stress has a parabolic dependence on the stacking-fault energy (SFE) of the metal. In this article, new data are presented, indicating that the SFE has only an indirect effect on the twinning stress. The results show that the dislocation density and the homogeneous slip length are the most relevant microstructural variables that directly influence the twinning stress in the polycrystal. A new criterion for the initiation of deformation twinning in polycrystalline fcc metals at low homologous temperatures has been proposed as ( tw Ϫ 0 )/G ϭ C(d/b) A , where tw is the deformation twinning stress, 0 is the initial yield strength, G is the shear modulus, d is the average homogeneous slip length, b is the magnitude of the Burger's vector, and C and A are constants determined to have values of 0.0004 and Ϫ0.89, respectively. The role of the SFE was observed to be critical in building the necessary dislocation density while maintaining relatively large homogeneous slip lengths.