Finite element analysis of laser shock peening of 2050-T8 aluminum alloy

AbstractLaser shock processing is a recently developed surface treatment designed to improve the mechanical properties and fatigue performance of materials, by inducing a deep compressive residual stress field. The purpose of this work is to investigate the residual stress distribution induced by laser shock processing in a 2050-T8 aeronautical aluminium alloy with both X-ray diffraction measurements and 3D finite element simulation. The method of X-ray diffraction is extensively used to characterize the crystallographic texture and the residual stress crystalline materials at different scales (macroscopic, mesoscopic and microscopic).Shock loading and materials’ dynamic response are experimentally analysed using Doppler velocimetry in order to use adequate data for the simulation. Then systematic experience versus simulation comparisons are addressed, considering first a single impact loading, and in a second step the laser shock processing treatment of an extended area, with a specific focus on impact overlap. Experimental and numerical results indicate a residual stress anisotropy, and a better surface stress homogeneity with an increase of impact overlap.A correct agreement is globally shown between experimental and simulated residual stress values, even if simulations provide us with local stress values whereas X-ray diffraction determinations give averaged residual stresses

Mesure des microdéformations dans les tôles minces en cuivre par DRX

L‘objectif de ce travail est de proposer une démarche, mettant en oeuvre la technique de diffraction des rayons X ainsi qu’une approche auto-cohérente, afin d’analyser et mieux comprendre le comportement mécanique du cuivre. L'étude expérimentale vise la caractérisation du comportement mécanique local de ce matériau sous un chargement uniaxial. Pour rendre compte du comportement mécanique du matériau étudié, un modèle polycristallin autocohérent a été adapté et confronté aux expériences menées. La texture cristallographique, les contraintes résiduelles macroscopique et du second ordre ont été prises en compte dans cette analyse

Modélisation micromécanique des polycristaux (couplage plasticité, texture et endommagement)

La méthodologie multi-échelles est mieux adaptée que l approche macroscopique phénoménologique pour une modélisation fine du comportement mécanique des matériaux. Dans ce travail cette approche est utilisée pour modéliser le comportement élastoplastique endommageable des matériaux polycristallins et tenant compte de l évolution de la texture cristallographique. Des travaux expérimentaux comprenant des analyses des textures, des contraintes internes, des caractérisations microstructurales et des essais de traction sont réalisés. L implémentation numérique du modèle développé est faite dans le code de calcul ZéBuLoN. La validation du modèle est réalisée aussi bien avec des calculs de structure par éléments finis que sur des volumes élémentaires représentatifs (VER). Pour le cas du VER la validation a porté sur divers trajets de chargement (traction, laminage, cisaillement, expansion biaxiale) et l exploration, par le biais d une étude paramétrique, de plusieurs aspects tels que l effet de la taille et du choix de l agrégat, l effet de l évolution de la texture, l effet du couplage avec l endommagement. Egalement des validations par comparaison avec les résultats expérimentaux et avec le modèle Auto-Cohérent ont été réalisées. Des calculs de structure éléments-finis ont porté sur la traction où l étude a été focalisée sur les effets de la taille du maillage et du choix de l agrégat, de l évolution de la texture et du couplage avec l endommagement sur l apparition et le développement de bandes de localisationMulti-scales modelling is usually more adequate than the phenomenological macroscopic approach for a fine modelling of the mechanical behavior of materials. In this work, this approach is used to model the elastoplastic behavior coupled with damage of polycrystalline materials and taking into account the crystallographic texture evolution within the framework of finites strains. The modelling is completed by including experimental works including: crystallographic textures and granular stesses analyses by X-ray diffraction and tensile tests. The numerical implementation of the developed model is made in ZéBuLoN Finite Elements code. The model is test on finite elements calculations as well as on local representative elementary volume (REV) calculations. For the case of the REV, diverse loading paths are studied (tensile, shear, rolling, biaxial expansion) and the exploration, through a parametric study, of several aspects such as: the effect of the poly-crystalline aggregate size and choice, the effect of the crystallographic texture evolution and the effect of the damage coupling. Also comparisons with the experimental results and also with Self Consistent model was realized. Finite elements calculations concerned exclusively the tensile test, where the study was focused on the effects of mesh size and the choice of the aggregate, the evolution of the texture and the coupling with the damage on the appearance and the development of localization bandsTROYES-SCD-UTT (103872102) / SudocSudocFranceF

Self consistent intragranular ductile damage modelling in large plasticity for FCC polycrystalline materials

International audienceThis work deals with micromechanical modelling of ductile damage and its effects on the inelastic behaviour of FCC polycrystalline metallic materials such as the evolution of their crystallographic textures. The constitutive equations are written in the framework of rate-dependent polycrystalline plasticity. A strong coupling between plasticity and damage is ensured through a ductile damage variable, which has been introduced at the Crystallographic Slip System (CSS) scale of each FCC grain to describe the material degradation through initiation, growth and coalescence of microdefects inside the aggregate neglecting thermally activated intergranular (or creep) damage. Both the theoretical and numerical (FEA) aspects of the micromechanical coupled model are presented. The model is implemented into a general purpose finite element code in order to analyse the effects of both texture evolution and ductile damage initiation inside the favourably oriented CSSs. The identification of the material parameters is based on experimental results obtained on copper specimens. The ability of the proposed model to predict the plastic strain localization, the induced textural evolution, as well as the effect of the ductile damage occurrence and its evolution until the final macroscopic fracture are investigated

Interaction between ductile damage and texture evolution in finite polycrystalline elastoplasticity

International audienceIn this paper, a multiscale model of ductile damage and its effects on the inelastic behavior of face centered cubic polycrystalline metallic materials, such as the evolution of their crystallographic textures, are investigated. The constitutive equations are written in the framework of rate-dependent polycrystalline plasticity at the microscopic scale. Plasticity and damage are coupled through a ductile damage variable introduced at the scale of the crystallographic slip systems of each grain. When homogenized to the macro-scale, this becomes an approximate phenomenological measure of the macroscopic ductile damage which can describe the material degradation by initiation, growth, and coalescence of micro-defects. In this paper, thermally activated intergranular (or creep) damage is not taken into account. Both theoretical and numerical aspects of the model are presented. The model is implemented into a general-purpose finite element code in order to analyze the effects of texture evolution and ductile damage initiation in the grains with favorably oriented slip systems. The capability of the proposed model to predict the plastic strain localization and the induced textural evolution, as well as the effects of the ductile damage and its evolution up to the final macroscopic failure are studied for a classical tensile loading path, applied to a representative volume element and to a 3D tensile specimen on which a parametric study has been carried out

Self consistent intragranular ductile damage modelling in large plasticity for FCC polycrystalline materials

International audienceThis work deals with micromechanical modelling of ductile damage and its effects on the inelastic behaviour of FCC polycrystalline metallic materials such as the evolution of their crystallographic textures. The constitutive equations are written in the framework of rate-dependent polycrystalline plasticity. A strong coupling between plasticity and damage is ensured through a ductile damage variable, which has been introduced at the Crystallographic Slip System (CSS) scale of each FCC grain to describe the material degradation through initiation, growth and coalescence of microdefects inside the aggregate neglecting thermally activated intergranular (or creep) damage. Both the theoretical and numerical (FEA) aspects of the micromechanical coupled model are presented. The model is implemented into a general purpose finite element code in order to analyse the effects of both texture evolution and ductile damage initiation inside the favourably oriented CSSs. The identification of the material parameters is based on experimental results obtained on copper specimens. The ability of the proposed model to predict the plastic strain localization, the induced textural evolution, as well as the effect of the ductile damage occurrence and its evolution until the final macroscopic fracture are investigated

Micromechanical Polycrystalline Damage-Plasticity Modeling for Metal Forming Processes

International audienceThis chapter deals with the presentation of micromechanical modeling of the elastoplastic material behavior exhibiting ductile damage together with microstructural evolution in terms of grain rotation and phase transformation, under large inelastic strains. A description of the main experimental methods is proposed and multiscale measurements are discussed. For the mesoscopic scale, diffraction techniques are presented as well as microscopy’s results for a specific material. For the macroscopic scale, techniques of tensile test coupled with digital image correlation are described. This allows the damage measurement at different scales. Micromechanical modeling aspects based on the thermodynamics of irreversible processes with state variables defined at different scales are discussed. A non-exhaustive review of several possible models is given. These models depend on the hypothesis for the energy or strain equivalence and on the smallest scale considered. Two particular models are then detailed with their associated constitutive equations and the corresponding numerical aspects. Application is made to two different materials to test the ability of the model to be used for metal forming simulations

Micromechanical Polycrystalline Damage-Plasticity Modeling for Metal Forming Processes

International audienceThis chapter deals with the presentation of micromechanical modeling of the elastoplastic material behavior exhibiting ductile damage together with microstructural evolution in terms of grain rotation and phase transformation, under large inelastic strains. A description of the main experimental methods is proposed and multiscale measurements are discussed. For the mesoscopic scale, diffraction techniques are presented as well as microscopy’s results for a specific material. For the macroscopic scale, techniques of tensile test coupled with digital image correlation are described. This allows the damage measurement at different scales. Micromechanical modeling aspects based on the thermodynamics of irreversible processes with state variables defined at different scales are discussed. A non-exhaustive review of several possible models is given. These models depend on the hypothesis for the energy or strain equivalence and on the smallest scale considered. Two particular models are then detailed with their associated constitutive equations and the corresponding numerical aspects. Application is made to two different materials to test the ability of the model to be used for metal forming simulations

Nanoindentation of dry and aged pultruded composites containing fillers and low profile additives

International audienceIn this article, the distribution through the thickness of both the matrix's modulus and the interfacial shear strength (IFSS) in dry and aged pultruded polyester/glass fiber composites containing fillers and low profile additives are experimentally evaluated, using the nanoindentation test. The obtained results indicate that for the dry composite, both the matrix's modulus and the IFSS are constant across the thickness of that material. As a consequence of the immersion in distilled water at high temperature (65°C), the IFSS was found to exhibit a parabolic trend through the thickness of the aged specimen, with the lowest value at the external surfaces. Such minimum was reached after a short time of immersion. At the saturation time, the IFSS at all layers of the aged specimen reaches lowest value. This was not the case for the matrix's modulus, since the later was found to be not affected by the amount of the absorbed humidity. Similar results were obtained after immersion in sea water at the same temperature. However, the only difference noted was at the external surface of the aged specimen where additional degradation had taken place in the matrix and at the fiber/matrix interface. This was attributed to the accumulation of a large amount of salt molecules at the external surface of the aged specimen during the exposure process. Additional mechanical tests show that after 120 days immersion in hot water the interlaminar shear strength of the material as measured according to the ASTM standard D2344, is reduced by 35%

Study of damage process using self-consistent elastoplastic model

International audienceThe elastoplastic rate-independent self-consistent model has been used to predict influence of damage process on the mechanical behavior of polycrystalline material. In this model, the behavior of a crystal grain inside polycrystalline material under applied stresses is studied. The calculations are performed on two different scales: the macro-scale, where the average elastic and plastic macrostrains are defined, and the grain-scale, on which the behavior of each crystallite under stress is analyzed