Modeling the mechanical response of polycrystals deforming by climb and glide (original) (raw)
Related papers
In this work microstructure evolution in a columnar polycrystal of pure aluminum is studied using a microstructure sensitive crystal plasticity finite element model (CPFEM). In the model, based upon the kinematics of crystal deformation and dislocation interaction laws, dislocation generation and annihilation are modeled. Dislocation densities evolve in the form of closed loops and are tracked as state variables, leading to spatially inhomogeneous dislocation densities that show patterning in the dislocation structures. The hardening law is based on the strength of junctions between dislocations on specific slip systems. The CPFEM model is able to show the anisotropic hardening behavior of aluminum single crystals. The measures of accumulated plastic strain in the experiment and the simulation are compared with varying degrees of success.
Single crystal deformation of Aluminium
polymer substrates. The type of conductive filler considerably determines the characteristics of nucleation, growth and the electroforming of the product microstructures.
International Journal of Plasticity, 2008
This is a study of plastic strain localization, surface roughening and of the origin of these phenomena in polycrystals. An oligocrystal aluminum sample with a single quasi-2D layer of coarse grains is plastically deformed under uniaxial tensile loading. During deformation, the history of strain localization, surface roughening, microstructure and in-grain fragmentation is carefully recorded. Using a crystal plasticity finite element model, corresponding high-resolution simulations are conducted. A series of comparisons identifying aspects of good and of less good match between model predictions and experiments is presented. The study suggests that the grain topology and microtexture have a significant influence on the origin of strain heterogeneity. Moreover, it suggests that the final surface roughening profiles are related both to the macro strain localization and to the intra-grain interaction. Finally slip lines observed on the surface of the samples are used to probe the activation of slip systems in detail. The study concludes with an assessment of the limitations of the crystal plasticity model.
Physical Mesomechanics, 2010
The paper briefly considers the structure of internal variable constitutive relations. The mesoscale model required for determination of macroscale internal variables is taken to be one of the crystal plasticity (Lins model), in which critical shear stress along slip systems assumes great importance. In this work, evolution equations for critical shear stress that take into account dislocation annihilation and reactions with the formation of Lomer Cottrell barriers are proposed thus making possible description of the Bauschinger effect and additional hardening under complex loading. The potentialities of the model are demonstrated by numerical simulation of monotonic and cyclic uniaxial loading of polycrystals.
Effects of grain interactions on deformation and local texture in polycrystals
Acta Metallurgica Et Materialia, 1995
Detailed simulations of grain deformation and crystal orientation evolution in a small region at the interior of polycrystal have been performed. The finite element model accounts for deformation by crystallographic slip and for crystal lattice rotation with deformation. The initial shapes and orientations of the grains and the crystal hardening relations were determined from polycrystalline aluminum samples. The results clearly demonstrate the effects of grain interaction on local deformation and texture evolution. A comparison of the predicted lattice orientations with results from plane strain compression experiments shows good agreement for some of the grains and little agreement for others. Part of the discrepancy results from kinematic restrictions which were necessary to model the 3D microstrueture with 2D models. The model shows very nonuniform strain fields and provides detailed information on grain interactions.
Deformation Behaviour of Aluminium-Bicrystals
2003
Introduction: Grain boundaries are natural obstacles to the motion of dislocations during plastic straining of crystalline matter. As such, they may be the cause of grain-scale heterogeneity in terms of the mismatch of the elastic±plastic strain rate, internal stress, and crystallographic reorientation rate fields.
Plastic deformation and latent strain energy in a polycrystalline aluminum model
International Journal of Solids and Structures, 1974
A crystalline aggregate model of aluminum is evaluated for nearly uniaxial stressing. Progression of crystallographic slip, a hysteresis effect in a strain cycle, and heat generated and latent strain energy stored during plastic deformation are investigated. Close correspondence is found between calculated and experimental results for percentages of heat and latent energy. A proof is included that total mechanical energy dissipated is absolutely less than macroscopic plastic work for all paths. 2. REVIEW OF THE BASIC THEORY AND MODEL The following is taken from [IO]. At the outset we define a microscopic continuum pointof-view wherein a crystal material "point" has dimensions of order 10e3 mm (i.e. > lo3 lattice spacings). This is consistent with the minimum level at which a continuum mechanics description of plastic deformation in metats can be judged physically meaningful (see, for 853 US 5'01 10 No 8-B
Multiscale modeling of the plasticity in an aluminum single crystal
International Journal of Plasticity, 2009
This paper describes a numerical, hierarchical multiscale modeling methodology involving two distinct bridges over three different length scales that predicts the work hardening of face centered cubic crystals in the absence of physical experiments. This methodology builds a clear bridging approach connecting nano-, micro-and meso-scales. In this methodology, molecular dynamics simulations (nanoscale) are performed to generate mobilities for dislocations. A discrete dislocations numerical tool (microscale) then uses the mobility data obtained from the molecular dynamics simulations to determine the work hardening. The second bridge occurs as the material parameters in a slip system hardening law employed in crystal plasticity models (mesoscale) are determined by the dislocation dynamics simulation results. The material parameters are computed using a correlation procedure based on both the functional form of the hardening law and the internal elastic stress/plastic shear strain fields computed from discrete dislocations. This multiscale bridging methodology was validated by using a crystal plasticity model to predict the mechanical response of an aluminum single crystal deformed under uniaxial compressive loading along the [4 2 1] direction. The computed strain-stress response agrees well with the experimental data.
45th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics & Materials Conference, 2004
In this paper, a multiscale modelling strategy is used to study the effect of grain-boundary sliding on stress localization in a polycrystalline microstructure with an uneven distribution of grain size. The development of the molecular dynamics (MD) analysis used to interrogate idealized grain microstructures with various types of grain boundaries and the multiscale modelling strategies for modelling large systems of grains is discussed. Both molecular-dynamics and finiteelement (FE) simulations for idealized polycrystalline models of identical geometry are presented with the purpose of demonstrating the effectiveness of the adapted finite-element method using cohesive zone models to reproduce grain-boundary sliding and its effect on the stress distribution in a polycrystalline metal. The yield properties of the grain-boundary interface, used in the FE simulations, are extracted from a MD simulation on a bicrystal. The models allow for the study of the load transfer between adjacent grains of very different size through grain-boundary sliding during deformation. A large-scale FE simulation of 100 grains of a typical microstructure is then presented to reveal that the stress distribution due to grain-boundary sliding during uniform tensile strain can lead to stress localization of two to three times the background stress, thus suggesting a significant effect on the failure properties of the metal.
Proceedings of the Royal Society a Mathematical Physical and Engineering Sciences, 2006
By combining the theory of mixtures with continuous diversity with Liu's method of Lagrange multipliers, a thermodynamically consistent constitutive theory is derived for large polycrystalline masses made up of transversely isotropic crystallites. The media under study are supposed to be incompressible and subjected to strain-induced anisotropy and recrystallization effects. Owing to the fabric (texture) changes caused by lattice rotation and polygonization, the polycrystal and its composing grains are modelled as polar media. Among other results of the theory, the existence of a dislocation potential is inferred, which represents for polycrystals the counterpart to the chemical potential of physical chemistry. Furthermore, exploitation of the dissipation inequality gives rise to the notion of a driving pressure for grain boundary migration. Besides, the vanishing of the Voigt couple stress is analysed together with the existence of internal stresses and couples responsible for the bending/twisting of crystallites by polygonization and heterogeneous strain.