Influence of the loading path on the mechanical behavior of metallic materials

Commercial finite element software packages are widely used for the numerical simulation of sheet metal forming processes. However, most of existing software packages present some limitations. In particular, they are essentially based on phenomenological constitutive models and, accordingly, they do not precisely account for physical mechanisms of plasticity that take place at finer scales, or the associated microstructure evolution. In this context, we propose to couple the Abaqus finite element code and the LAM3 code with micromechanical simulation techniques based on crystal plasticity and a self-consistent scale-transition scheme. This coupling strategy will be applied to the simulation of rolling processes in order to assess the influence of the loading path on the evolution of the mechanical properties of the material. By following some appropriately selected strain paths along the rolling process, one can predict the texture evolution of the material as well as other parameters related to its microstructure. Our numerical results are compared with experimental data in the case of ferritic steels elaborated by the steel maker ArcelorMittal.LabEx DAMA

A multiscale approach for the vibration analysis of heterogeneous materials: Application to passive damping

International audienceThis paper presents a multiscale numerical technique for vibration analysis of hetero-geneous materials. In this procedure, the unknownmacroscopic constitutive relationship is searched by solving a local finite element problem at the microscale. Since the inertia effects areneglected at the microscopic level, this approach is limited to problems in which microstructure characteristic length is smaller than thewavelength. Numerical examples are limited to free vibration analysis of viscoelastic materials with a constant complex modulus. Theseexamples allow one to validate the multiscale approach and to study the influence of different parameters on the passive damping of thestructure. These parameters concern the morphology, the stiffness ratio and the inclusion volume fraction

Multiscale finite element simulation of forming processes based on crystal plasticity

For the numerical simulation of sheet metal forming processes, the commercial finite element software packages are among the most commonly used. However, these software packages have some limitations; in particular, they essentially contain phenomenological constitutive models and thus do not allow accounting for the physical mechanisms of plasticity that take place at finer scales as well as the associated microstructure evolution. In this context, we propose to couple the Abaqus finite element code with micromechanical simulations based on crystal plasticity and a selfconsistent scale-transition scheme. This coupling strategy will be applied to the simulation of rolling processes, at different reduction rates, in order to estimate the evolution of the mechanical properties. By following some appropriately selected strain paths (i.e., strain lines) along the rolling process, one can also predict the texture evolution of the material as well as other parameters related to its microstructure. Our numerical results are compared with experimental data in the case of ferritic steels produced by ArcelorMittal.French program “Investment in the future” operated by the National Research Agency (ANR)-11-LABX-0008-01, LabEx DAMAS (LST)

Latent and Manifested flatness predictions in thin strip cold rolling using a general rolling FEM model

International audienceFlatness defects in thin strip cold rolling are a consequence of roll thermo-elastic deformation and the resulting heterogeneous strip plastic deformation. But in the case of on-line, manifested flatness defects, buckling reorganizes the stress field in the pre- and post-bite areas, which might impact strain and stress fields in the bite or at its ends. Such effects have always been neglected in the past. The purpose of the present paper is to present two coupled approaches to examine to what extent such potential in-bite / out-of-bite feedback determines the in-bite fields and the flatness of the strip. Using both methods and comparing with the standard case where buckling is not accounted for, it has been shown that (i) taking buckling into account results in completely different stress fields and fits correctly the measured on-line residual stresses under tension ("stress-meter rolls"); (ii) coupling buckling in the post-bite area and the rolling model, whatever the technique, changes little the in-bite fields; differences, if any, concentrate in the immediate vicinity of the bite exit; (iii) but in the case where manifested flatness defects occur, these tiny interactions (namely, through the exit velocity transverse profile) are essential for the precise description of the residual stresses and for accurate flatness prediction

Automatic solver for non-linear partial differential equations with implicit local laws: Application to unilateral contact

International audienceIn general, non-linear continuum mechanics combine global balance equations and local constitutive laws. In this work, frictionless contact between a rigid tool and a thin elastic shell is considered. This class of boundary value problems involves two non-linear algebraic laws: the first one gives explicitly the stress field as a function of the strain throughout the continuum part, whereas the second one is a non-linear equation relating the contact forces and the displacement at the boundary.Given the fact that classical computational approaches sometimes require significant effort in implementation of complex non-linear problems, a computation technique based on automatic differentiation of constitutive laws is presented in this paper. The procedure enables to compute automatically the higher-order derivatives of these constitutive laws and thereafter to define the Taylor series that are the basis of the continuation technique called asymptotic numerical method. The algorithm is about the same with an explicit or implicit constitutive relation. In the modelling of forming processes, many tool shapes can be encountered. The presented computational technique permits an easy implementation of these complex surfaces, for instance in a finite element code : the user is only required to define the tool geometry and the computer is able to obtain the higher-order derivatives

Un modèle éléments finis général pour la prédiction des défauts de planéité en laminage des tôles fines

Titre du résumé en anglais joint : Manifested flatness predictions in thin strip cold rolling using a general rolling FEM modelNational audienceL'objectif du présent travail est de développer un modèle de laminage capable de prédire avec précision les défauts de planéité des tôles laminées. Ainsi, on a couplé itérativement un modèle éléments finis 3D de calcul de l'écrasement de la tôle dans l'emprise, un modèle semi-analytique de calcul de la déformation des cylindres de la cage et un modèle éléments finis de flambement de coques donnant les défauts de planéité. Le modèle de laminage obtenu prédit des champs de contraintes en bon accord avec les mesures expérimentales et est capable de simuler les défauts de planéité en laminage des tôles.See http://hal.archives-ouvertes.fr/docs/00/59/26/08/ANNEX/r_690NC59B.pd

Modélisation du flambage des tôles laminées sous contraintes résiduelles

978-2-11-098374-9National audienceLa modélisation des défauts de planéité occupe une position prioritaire parmi les axes de recherche pour les producteurs des tôles métalliques. Par ailleurs, on dispose d'un logiciel Lam3/Tec3 dédié pour la simulation de laminage des tôles qui présente certaines limitations dans sa version standard, surtout quand il s'agit des cas de laminage des tôles pour les quels le flambage, d'où des défauts de planéité, peut se produire. De ce fait, il a été complété durant les présents travaux par un modèle de flambage des plaques afin de combler ses insuffisances

Une méthode de perturbation pour les problèmes de plasticité en grandes déformations

Dans ce travail, on propose une nouvelle technique de régularisation pour résoudre des problèmes élastoplastiques dans le cadre de la MAN en grandes déformations. En effet, le comportement élastoplastique présente de fortes non linéarités et combine deux conditions unilatérales. Deux régularisations sont alors introduites; la première permet le passage du domaine élastique au domaine plastique et dépend du champ des contraintes. La deuxième, quant à elle, permet de prendre en compte la décharge élastique et dépend à la fois de la contrainte et de sa dérivée par rapport au temps. Une application sur des structures discrétisées par éléments finis est alors présentée pour évaluer l'efficacité de l'algorithme

Understanding the material flow path of friction stir welding process using unthreaded tools

Material flow during friction stir welding is very complex and not fully understood. Most of studies in literature used threaded pins since most industrial applications currently use threaded pins. However, initially threaded tools may become unthreaded because of the tool wear when used for high melting point alloys or reinforced aluminium alloys. In this study, FSW experiments were performed using two different pin profiles. Both pins are unthreaded but have or do not have flat faces. The primary goal is to analyse the flow when unthreaded pins are used to weld thin plates. Cross-sections and longitudinal sections of welds were observed with and without the use of material marker (MM) to investigate the material flow. Material flow with unthreaded pin was found to have the same features as material flow using classical threaded pins: material is deposited in the advancing side (AS) in the upper part of the weld and in the retreating side (RS) in the lower part of the weld; a rotating layer appears around the tool. However, the analysis revealed a too low vertical motion towards the bottom of the weld, attributed to the lack of threads. The product of the plunge force and the rotational speed was found to affect the size of the shoulder dominated zone. This effect is reduced using the cylindrical tapered pin with flats

Investigation des conditions aux limites thermiques pour la modélisation du FSW : étude paramétrique

Le but de notre travail est d'étudier l'influence des conditions aux limites thermiques sur les résultats de simulation du procédé de soudage par friction et malaxage « FSW ». Généralement, les dimensions des pièces à souder peuvent être très importantes et une zone très réduite autour de l'outil de soudage est modélisée pour l'étude thermomécanique de ce procédé. Nous proposons dans cette étude une stratégie numérique qui permet de déterminer les conditions aux limites thermiques sur cette zone et de réduire le temps de calcul de façon significative