New Modelling Approach for Micromechanical Modelling of the Elastoplastic Behaviour (original) (raw)
Related papers
Acta Mechanica, 2015
A self-consistent scheme taking into account the intragranular microstructure is applied for the micromechanical modelling of the elastoplastic material behaviour during monotonic and sequential loading paths. The intragranular description used in the model is initially based on experimental observations of the dislocations evolution in body-centred cubic polycrystals. We have extended this description to face-centred cubic materials. For each crystallite, three internal variables are introduced to describe the microstructural features allowing to determine the mechanical characteristics of the grain. Next, a meso-macro transition using an elastoplastic self-consistent model is used to deduce the polycrystal behaviour from the grain one. A correct agreement is observed between simulations and experimental results at the mesoscopic and the macroscopic levels.
Materials Science Forum, 2006
A two-level homogenisation approach is applied to the micro-mechanical modelling of the elasto-plasticity of polycrystalline materials during various strain-path changes. The model is tested by simulating the development of intragranular strains during different complex loads. Mechanical tests measurements are used as a reference in order to validate the model. The anisotropy of plastic deformation in relation to the evolution of the dislocation structure is analysed. The results demonstrate the relevance of this approach for FCC polycrystals.
Prediction of intergranular strains in cubic metals using a multisite elastic-plastic model
Acta Materialia, 2002
A novel approach is adopted for determining the elastic and plastic strains of individual grains within a deformed polycrystalline aggregate. In this approach, termed "multisite modeling", the deformation of a grain does not merely depend on the grain lattice orientation. It is also significantly influenced by the interaction with one or several of the surrounding grains. The elastic-plastic constitutive law is integrated by identifying iteratively which dislocation slip systems are activated within the grains, and the local stress tensor is shown to be the solution of a linear equation set. Several micro-macro averaging schemes are considered for the distribution of the macroscopic load over the polycrystalline aggregate. These averaging schemes are tested by simulating the development of intergranular strains during uniaxial tension of MONEL-400 as well as commercial purity aluminium. Neutron diffraction measurements of the elastic lattice strains are used as a reference in order to discriminate between the various predictions. The results demonstrate the relevance of "multisite" grain interactions in f.
Modelling of elastoplastic polycrystals and aspects of applications
Computational Materials Science, 1997
A micromechanical approach is developed to study the formation of induced dislocation cell structure and the effects on the mechanical behavior of metals starting from the Helmholtz free energy and the dissipation of an elastoplastic solid containing moving surfaces of plastic strain discontinuity. The results are applied to an evolving two phase microstructure representing the dislocation cell structure induced by plastic straining. In this way, the internal variables are reduced to the plastic strain of each mechanical phase, the volume fraction and the morphology of the ellipsoidal inclusion describing the cell structure. We obtain the conjugate forces according to the formalism of irreversible thermodynamics.
Modeling the evolution of dislocation populations under non-proportional loading
International Journal of Plasticity, 2014
The two-phase composite approach of describes an evolving dislocation cell structure with dislocation populations for cell walls and the interior. enhanced the model to capture the effects of hydrostatic pressure and temperature during severe plastic deformation. The main goal of the present study is to extend this microstructural model to non-proportional deformation in order to develop a framework suitable for the simulation of dislocation density evolution upon load path changes. Thereby, the two-phase composite approach is examined carefully. Both physical and numerical drawbacks are revealed and possible solutions are presented. Here, a special aim is to ensure that values of the dislocation densities remain within a physically reasonable range. Moreover, some improvements concerning reliable parameter identification are suggested as well. The material parameters are identified for an aluminum alloy using TEM cell size measurements. The extension to non-proportional deformation aims to predict the experimentally observed dissolution of cells and reduction of total dislocation density shortly after load path change. In order to capture these effects, some tensor-valued state variables are introduced which couple the refined micro model with the macroscopic viscoplasticity framework proposed by . As a result, a new system of constitutive equations is obtained. In order to demonstrate the framework's capability to respond to load path changes, load cases as typical for Equal Channel Angular Pressing (ECAP) are considered. The obtained evolution of dislocation populations differs significantly depending on which ECAP route is applied.
Experiments and Simulations on the micromechanics of single- and polycrystalline metals
Crystallographic slip, i.e.movement of dislocations on distinct slip planes, is the main source of plastic deformation of most metals. The Crystal Plasticity FEM combines this basic process with the Finite Element Method by assuming that the plastic velocity gradient is composed out of the shear contributions of all slip systems. To apply the method to forming simulation of "real" parts suffered from the fact, that a huge number of single orientations is needed to approximate the crystallographic texture of such parts. This problem was recently solved by the introduction of the Texture Component Crystal Plasticity FEM(TCCP-FEM),which uses orientation distributions (texture components) for the texture approximation instead of single orientations. Excellent agreement of experiments and numerical simulations for different forming operations has shown the feasibility of this idea. Most crystal plasticity codes use simple empirical constitutive equations. However, as crystal plasticity is build on dislocation movement it was an obvious idea to introduce a constitutive model based on dislocation densities (internal state variables) instead of strain (external variable) into the crystal plasticity. The dislocation model used is based on five main ingredients: 1) For every slip system mobile and immobile dislocations are distinguished. 2) A scaling relation between mobile and immobile dislocations is derived. 3) The immobile dislocations are divided into parallel and forest dislocations for every slip system. 4) The Orowan equation is used as kinetic equation. 5) Rate equations for the immobile dislocation densities are formulated based on distinct dislocation processes, e.g. lock formation or annihilation by dislocation climb. For a wide range of temperature and strain rate the constitutive behavior of single and polycrystals is studied and simulation results are checked by comparison with experiments.
Materials Science and Engineering: A, 2002
A new approach to the modeling of work hardening during plastic deformation of f.c.c.-metals and alloys has been recently proposed by the present authors. The model is based on a statistical approach to the problem of athermal storage of dislocations. By combining the solution for the dislocation storage problem with models for dynamic recovery of network dislocations and sub-boundary structures, a general internal state variable description is obtained. The model includes effects due to variations in: (i) stacking fault energy, (ii) grain size, (iii) solid solution content, and (iv) particle size and volume fraction. The result is a work hardening model, which in principle is capable of providing the stress-strain behavior for a given metal or solid solution alloy under condition ranging from deformation in the ambient temperature range to high temperature creep. It will be demonstrated that the model predictions, in terms of microstructure evolution and associated properties, in general, are in good agreement with experimental observations.
An attempt for a unified description from dislocation dynamics to metallic plastic behaviour
Le Journal de Physique IV, 2001
This paper introduces a unified description of metallic polycrystal plasticity based on the individual behaviour of dislocations. It starts at the level of the elementary mechanisms involved in plastic deformations of pure face-centred cubic metals. Every significant step that allows linking an upper scale with the previous one is reviewed. Specific relations that have been previously used in literature for single crystal plasticity are then justified. Finally, the use of these relations in a global model of polycrystalline plasticity is detailed. Tensile tests on Aluminium multicrystals with 99.99% purity for deep-drawing applications provide the experimental data for this study. The successfUl comparison between experimental and simulated data validates the whole procedure. reference shear strain rate. The athermal shear stress 7 ; ' depends on the dislocation density p'P' on each
International Journal of Plasticity, 2003
In this work, a model, based on a representation of the dislocation cell microstructures by a non-local two-phase material with evolving microstructures, is proposed for the elastic-plastic behavior of metals under monotonic and sequential loading. The first phase represents the cell interior and the second one, the cell walls. The evolution of the microstructure is taken into account considering the cell-wall interfaces as free boundaries. Finally, the accumulation within walls of dislocations crossing the cells defines a non-local hardening process. Assuming a piecewise uniform plastic strain field and assuming ellipsoidal cells, the free energy of the system is calculated. The driving and critical forces associated with the plastic flow of the twophases and the morphology of the cells are established. In a third part, numerical results are presented for monotonic and sequential loading. The results show an overall softening related to the destabilization of the dislocation microstructures which occurs in sequential as well as monotonic paths.