Anisotropie induite par l'endommagement ductile : mécanismes physiques, modélisation et simulation numérique

The objective of this work is to develop a predictive modeling of behavior and ductile fracture of metallic materials with initial anisotropy and induced by the ductile anisotropic damage. Thermodynamics of irreversible processes is used as a framework for the proposed formulation. The model is anisotropic elastoplastic with non-linear isotropic and kinematic hardening under large plastic strains. It is formulated in the framework of the non-associative plasticity theory with associative normality rule and based on quadratic equivalent stress. The anisotropic ductile damage is described by a symmetric second-rank tensor whose evolution is described by Lemaitre /Desmorat type relationships. The strong damage-behavior coupling is done under the assumption of total energy equivalence where the effect of the anisotropic damage is introduced by a fourth-rank symmetric damage-effect tensor of Murakami kind.After an experimental characterization of the main physical mechanisms of anisotropic damage in stainless steel AISI 316L, the behavior model with damage has been identified. Once discretized and implemented in the computer code ABAQUS / Explicit ®, a parametric study and many numerical simulations of anisotropic damage in some metal forming processes have been carried out and discussed in detailL’objectif de ce travail est de développer une modélisation prédictive du comportement et de la rupture ductile des matériaux métalliques à anisotropies initiales et induites par l’endommagement. La thermodynamique des processus irréversibles est utilisée comme cadre pour la formulation proposée. Le modèle de comportement est élastoplastique anisotrope avec écrouissage non linéaire isotrope et cinématique en grandes déformations plastiques, avec une théorie non associée à normalité associée, basée sur des normes de contraintes quadratiques. L’endommagement ductile anisotrope est décrit par un tenseur du second ordre symétrique dont l’évolution est décrites par des relations de type Lemaitre-Desmorat. Le couplage fort comportement-endommagement est réalisé dans le cadre de l’hypothèse de l’équivalence en énergie totale où l’effet de l’endommagement sur le comportement est introduit par un tenseur « effet d’endommagement » d’ordre quatre symétrique de type Murakami. Après une caractérisation expérimentale des mécanismes physiques de l’endommagement dans l’acier AISI 316L, le modèle de comportement avec endommagement a été identifié. Une fois discrétisé et implémenté dans le code de calcul de structures ABAQUS/Explicit®, une étude paramétrique et de nombreuses simulations numériques de l’endommagement anisotrope en mise en forme de quelques structures ont été réalisées et discutées en détai

Ductile damage induced anisotropy : physical mechanisms, modeling and numerial simulation

L’objectif de ce travail est de développer une modélisation prédictive du comportement et de la rupture ductile des matériaux métalliques à anisotropies initiales et induites par l’endommagement. La thermodynamique des processus irréversibles est utilisée comme cadre pour la formulation proposée. Le modèle de comportement est élastoplastique anisotrope avec écrouissage non linéaire isotrope et cinématique en grandes déformations plastiques, avec une théorie non associée à normalité associée, basée sur des normes de contraintes quadratiques. L’endommagement ductile anisotrope est décrit par un tenseur du second ordre symétrique dont l’évolution est décrites par des relations de type Lemaitre-Desmorat. Le couplage fort comportement-endommagement est réalisé dans le cadre de l’hypothèse de l’équivalence en énergie totale où l’effet de l’endommagement sur le comportement est introduit par un tenseur « effet d’endommagement » d’ordre quatre symétrique de type Murakami. Après une caractérisation expérimentale des mécanismes physiques de l’endommagement dans l’acier AISI 316L, le modèle de comportement avec endommagement a été identifié. Une fois discrétisé et implémenté dans le code de calcul de structures ABAQUS/Explicit®, une étude paramétrique et de nombreuses simulations numériques de l’endommagement anisotrope en mise en forme de quelques structures ont été réalisées et discutées en détailThe objective of this work is to develop a predictive modeling of behavior and ductile fracture of metallic materials with initial anisotropy and induced by the ductile anisotropic damage. Thermodynamics of irreversible processes is used as a framework for the proposed formulation. The model is anisotropic elastoplastic with non-linear isotropic and kinematic hardening under large plastic strains. It is formulated in the framework of the non-associative plasticity theory with associative normality rule and based on quadratic equivalent stress. The anisotropic ductile damage is described by a symmetric second-rank tensor whose evolution is described by Lemaitre /Desmorat type relationships. The strong damage-behavior coupling is done under the assumption of total energy equivalence where the effect of the anisotropic damage is introduced by a fourth-rank symmetric damage-effect tensor of Murakami kind.After an experimental characterization of the main physical mechanisms of anisotropic damage in stainless steel AISI 316L, the behavior model with damage has been identified. Once discretized and implemented in the computer code ABAQUS / Explicit ®, a parametric study and many numerical simulations of anisotropic damage in some metal forming processes have been carried out and discussed in detai

Mise en evidence expérimentale de l’anisotropie induite par l’endommagement ductile dans l’acier inoxydable austénitique AISI 316L

International audienceDans ce travail nous nous proposons d’identifier expérimentalement le caractère anisotrope de l’endommagement ductile dans l’acier inoxydable austénitique AISI 316L. L’endommagement est mesuré indirectement, à travers son effet sur le module d’élasticité du matériau, au cours de chargement en traction simple. Un modèle de comportement fortement couplé à l’endommagement a été exploité afin de traduire l’effet anisotrope de la cavitation sur la réponse élastique du matériau. L’endommagement anisotrope est modélisé par un tenseur de second ordre symétrique. Son effet sur le comportement élastique est introduit à travers d’un opérateur effet d’endommagement d’ordre quatre symétrique. Cet opérateur est obtenu dans le cadre du concept de variables effectives avec l’hypothèse d’équivalence en énergie totale. L’évolution de l’endommagement anisotrope est gouvernée par une équation différentielle dans laquelle les tenseurs taux d’endommagement et taux des déformations plastiques sont supposés proportionnels. Les paramètres matériaux qui y interviennent sont identifiés graphiquement pour l’acier AISI 316L. La méthodologie proposée pour la mise en évidence expérimentale de l’anisotropie induite par l’endommagement dans l’acier AISI 316L ainsi que la modélisation comportement-endommagement adoptée peuvent être généralisées pour identifier les paramètres d’endommagement pour tout matériau ductile

Simulation numérique de l'endommagement dans quelques procédés de formage plastique d'un acier de hautes performances

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Caractérisation numérique de l'endommagement ductile d'aciers à hautes performances. Essais d'expansion et de pliage

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An Investigation To Achieve a Good Surface Integrity in WEDM of Ti-6242 Super Alloy

International audienceAbstract Ti-6242 is a super alloy which exhibits the best creep resistance among available titanium alloys and is widely used in the manufacture by WEDM of aircraft engine turbomachinery components. However, the final quality of wire EDMed surface is a great challenge as it is affected by various factors that need optimization for surface integrity and machine efficiency improvement. The aim of this study is to investigate the effect of a set of cutting process parameters such as pulse on time ( T on ), servo voltage ( U ), feed rate ( S ) and flushing pressure ( p ) on surface roughness ( SR ) when machining Ti-6242 super alloy by WEDM process using a brass tool electrode and deionized water as a dielectric fluid. WEDM experiments were conducted, and SR ( Ra ) measurement was carried out using a 3D optical surface roughness-meter (3D–SurfaScan). As a tool to optimize cutting parameters for SR improvement, Taguchi's signal‐to‐noise ratio ( S/N ) approach was applied using L 9 (3^4) orthogonal array and Lower-The-Better (LTB) criteria. Substantially, the findings from current investigation suggest the application of the values 0.9 µs, 100V, 29 mm/min, and 60 bar for T on , U , S and p cutting parameters, respectively, for producing a good surface finish quality. Percent contributions of the machining parameters on SR ( Ra ) assessed based on ANOVA analysis are 62.94%, 20.84%, 11.46% and 4.74% for U , S , T on and p , respectively. Subsequently, accurate predictive model for SR ( Ra ) is established based on response surface analysis (RSA). The contour plots for SR ( Ra ) indicate that when flushing pressure p converges to a critical value (80 bar), a poor-quality surface finish is highly expected with the excessive increase in U and S . Electron microscope scanning (SEM) observations have been performed on machined surface for a wide range of cutting parameters to characterize wire EDMed surface of Ti-6242. SEM micrographs indicate that the machined surface acquires a foamy structure and shows white layer and machining-induced damage that the characteristics are highly dependent on cutting parameters. At high servo-voltage, the decrease in pulse on time T on and feed rate S results in a large decrease in overall machining-induced surface damage. Moreover, for high servo-voltage and feed rate levels, it has been observed that pulse on time could play a role of controlling the surface microcracks density. In fact, the use of a low pulse duration of cut combined with high servo-voltage and feed rate has been shown to inhibit surface microcracks formation giving the material surface a better resistance to cracking than at high pulse duration

F.E. elastoplastic damaged model with 2D adaptive remeshing procedure for fracture prediction in metal forming simulation

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Metaheuristic Solution for Stability Analysis of Nonlinear Systems Using an Intelligent Algorithm with Potential Applications

In this article, we provide a metaheuristic-based solution for stability analysis of nonlinear systems. We identify the optimal level set in the state space of these systems by combining two optimization phases. This set is in a definite negative region of the time derivative for a polynomial Lyapunov function (LF). Then, we consider a global optimization problem stated in two phases. The first phase is an external optimization to search for a definite positive LF, whose derivative is definite negative under linear matrix inequalities. The candidate LF coefficients are adjusted using a Jaya metaheuristic optimization algorithm. The second phase is an internal optimization to ensure an accurate estimate of the attraction region for each candidate LF that is optimized externally. The key idea of the algorithm is based mainly on a Jaya optimization, which provides an efficient way to characterize accurately the volume and shape of the maximal attraction domains. We conduct numerical experiments to validate the proposed approach. Two potential real-world applications are proposed

Multi-criteria/comparative analysis and multi-objective optimization of a hybrid solar/geothermal source system integrated with a carnot battery

Among the different electrical energy storage technologies, the Carnot batteries are promising options with low specific cost that do not suffer from geographical limitations and power-capacity coupling. In addition to power balancing, this approach can also be unique for multi-vector energy management. A comprehensive evaluation (thermodynamic design and exergoenvironmental and exergoeconomic evaluations), comparison, and multi-objective optimization of four Carnot battery configurations based on solar-electric energy and a geothermal source is presented. Geothermal energy can simultaneously improve the thermodynamic and environmental performances of the Carnot battery. The main structure of all configurations is based on electrical energy obtained from PV and captured thermal energy from a geothermal source. The four Brayton, heat pump, flash, and organic Rankine cycle (ORC) units are periodically integrated. The outcomes point out that the discharging process is based on an ORC unit and a flash-heat pump cycle (F-HPC)-based charging process makes more optimal heat-to-power efficiency. Moreover, the Carnot battery based on the regenerative-Brayton cycle (R-BC) unit has a higher investment cost rate compared to the ORC unit (in the discharging process). When integrating the geothermal, the third configuration (R-HPC/R-BC) experiences the greatest improvement (5.3-fold) due to the increase in thermal energy received from the geothermal source

Thermocapillary and buoyancy driven convection analysis for a hybrid nanofluids enclosed in a cavity with heated obstacle

Two-dimensional numerical simulations are performed to investigate the problem of thermocapillary, and buoyancy driven convection. A hybrid MWCTN-Fe$$_3$$O$$_4$$-thermal oil nanofluid was used in an enclosed cavity equipped with a hot obstacle. The entire set of equations associated with the convective heat transfer phenomena in a hybrid nanofluid layer with a free surface are solved numerically using the blocked-off region method of Patankar. A parametric study varying the position, the size of the obstacle, the Marangoni number, the Rayleigh number, the volume fraction of the nanofluid has been performed. The results concern the flow profile, the temperature profile and the evolution of the Nusselt number under different conditions. It was shown that an enhancement of the convective heat transfer of more than 170% can be achieved on the cold wall just by switching the position of the obstacle from the bottom to the top