Dissertation•
Caractérisation à la rupture de matériaux ductiles par approche locale
24 Feb 2019-
TL;DR: In this paper, a review on the ductile fracture divided in two main parts is presented, the first part concerns the elastic plastic fracture mechanics that is represented by the J-Integral.
Abstract: This thesis is a contribution to the study of the ductile fracture phenomenon of porous materials. Firstly, a review on the ductile fracture divided in two main parts is presented. The first part concerns the elastic plastic fracture mechanics that is represented by the J-Integral. The other part is dedicated to the micromechanical approach of the ductile fracture. A numerical and experimental study of the AISI 304L thin sheets is proposed. Firstly, the ductile fracture phenomenon is simulated using the GTN and Rousselier models. An hybrid approach combining experimental tests on CT specimens and simulations using the GTN model in order to assess the fracture toughness is proposed. The EWF method is also used with a numerical validation using a cohesive zone modeling. In the third chapter, an identification method for the GTN model parameters identification is proposed. The method is based on the hierarchy of the void volume fraction parameters evolution until the final fracture. In the fourth chapter, the mechanical response of porous materials is studied using the numerical homogenization. The GTN model is extended to take into account a wide range of porous materials. Finally, an experimental validation is proposed.
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Journal Article•
TL;DR: Sandia National Laboratories, in partnership with US National Science Foundation and Naval Surface Warfare Center Carderock Division, launched a computational challenge in mid-summer, 2012 to predict crack initiation and propagation in a simple but novel geometry fabricated from a common off-the-shelf commercial engineering alloy as mentioned in this paper.
Abstract: Existing and emerging methods in computational mechanics are rarely validated against problems with an unknown outcome. For this reason, Sandia National Laboratories, in partnership with US National Science Foundation and Naval Surface Warfare Center Carderock Division, launched a computational challenge in mid-summer, 2012. Researchers and engineers were invited to predict crack initiation and propagation in a simple but novel geometry fabricated from a common off-the-shelf commercial engineering alloy. The goal of this international Sandia Fracture Challenge was to benchmark the capabilities for the prediction of deformation and damage evolution associated with ductile tearing in structural metals, including physics models, computational methods, and numerical implementations currently available in the computational fracture community. Thirteen teams participated, reporting blind predictions for the outcome of the Challenge. The simulations and experiments were performed independently and kept confidential. The methods for fracture prediction taken by the thirteen teams ranged from very simple engineering calculations to complicated multiscale simulations. The wide variation in modeling results showed a striking lack of consistency across research groups in addressing problems of ductile fracture. While some methods were more successful than others, it is clear that the problem of ductile fracture prediction continues to be challenging. Specific areas of deficiency have been identified through this effort. Also, the effort has underscored the need for additional blind prediction-based assessments.
95 citations
06 Feb 2013
TL;DR: In this article, the authors used results of FE simulations of crack extension in panels by the cohesive model to validate analytical procedures for determining J -integral values at large crack extension from measurable quantities, namely the force vs displacement records.
Abstract: The concept of R -curves has been adopted to characterise stable crack extension and predict residual strength of thin-walled structures particularly in the aircraft industry. The present contribution uses results of FE simulations of crack extension in panels by the cohesive model to validate analytical procedures for determining J -integral values at large crack extension from measurable quantities, namely the force vs. displacement records. The numerically determined J -integral is taken as the benchmark for the outcome of the analytical formulas. The geometry dependence of J and CTOD based R -curves is investigated and alternative concepts like CTOA and dissipation rate at crack extension are discussed.
18 citations
01 Jan 2000
TL;DR: In this paper, the influence of thickness on the fracture toughness of aluminum 6082T0 thin plates of 1-6 mm thicknesses was investigated experimentally and numerically from tensile testing of cracked DENT specimens.
Abstract: The influence of thickness on the fracture toughness of aluminium 6082T0 thin plates of 1-6 mm thicknesses was investigated experimentally and numerically from tensile testing of cracked DENT specimens. The critical J-integral, J(c), critical CTOD, delta(CTODc), and essential work of fracture, w(e), are found to increase with thickness and to constitute equivalent measures of fracture toughness at small thickness. For larger thickness, J(c) and delta(CTODc) increase non-linearly with thickness and reach a maximum for 5-6 mm thickness Whereas iv, keeps increasing linearly with thickness. This difference is related to a more progressive development of the necking zone in front of the crack tip when thickness increases: at large thickness, cracking initiates well before the neck has developed to its stationary value during propagation, w(e) is more directly related to the steady-state crack growth resistance. A linear regression on the fracture toughness/thickness curve allows further separation of the two contributions of the essential work of fracture: the necking work and the fracture work spent for damaging. The maximum of the stress triaxiality ratio is shown to constitute a pertinent parameter for characterising how constraint affects cracking initiation in the present context where out-of-plane constraint dominates in-plane constraint. It allows justifying the shape of the J(c)/thickness relationship and results in the proposal of a 3D J(c)/thickness/triaxiality fracture locus. As fracture profiles are macroscopically flat with microscopic dimples and with only very small shear lips along the edges, a local criterion based on the growth and coalescence of voids has been used in order to predict fracture initiation. (C) 1999 Elsevier Science Ltd. All rights reserved.
4 citations
01 Jan 2011
TL;DR: In this article, a fiber-reinforced composite material is modelled via an approach employing a Representative Volume Element with periodic boundary conditions, where a finite number of fibres are randomly distributed within the representative periodic cell.
Abstract: In this article a fibre-reinforced composite material is modelled via an approach employing a Representative Volume Element with periodic boundary conditions. The effective elastic moduli of the material are thus derived. In particular, the method of asymptotic homogenization is used where a finite number of fibres are randomly distributed within the representative periodic cell. The study focuses on the efficacy of such an approach in representing a macroscopically random (hence transversely isotropic) material. Of particular importance is the sensitivity of the method to cell shape, and how this choice affects the resulting (configurationally averaged) elastic moduli. The averaging method is shown to yield results that lie within the Hashin-Shtrikman variational bounds for fibre-reinforced media and compares well with the multiple scattering and (classical) self-consistent approximations with a deviation from the latter in the larger volume fraction cases. Results also compare favourably with well-known experimental data from the literature.
3 citations
01 Jan 2008
TL;DR: In this article, the effect of load history on ductile fracture initiation in a typical fracture mechanics Compact Tension (CT) specimen was investigated and the benefits of applying such models to situations where events in the plant loading history can have a significant effect on crack driving force for typical defects that subsequently develop during service.
Abstract: Local Approach methods provide alternative routes for carrying out fracture mechanics assessments. These methods use a finite element analysis of the cracked component that incorporates a micro-mechanical model of material behaviour in the region of the crack tip. The development of damage, and eventual failure of the material for particular loading conditions, is calculated directly by the micro-mechanical model. A potential advantage of such models is that they can automatically incorporate the effects of loss of constraint and load history. This paper describes studies that compare the predictions of the Gurson-Tvergaard-Needleman (GTN) local approach model of ductile fracture with traditional fracture mechanics parameters. The model is used to consider the effect of load history on ductile fracture initiation in a typical fracture mechanics Compact Tension (CT) specimen. The aim is to investigate the benefits of applying such models to situations where events in the plant loading history can have a significant effect on crack driving force for typical defects that subsequently develop during service. It is anticipated that the results will be used to make improvements to the accuracy of the traditional assessment procedures. The results show that in certain circumstances, for instance where residual stresses are present in the vicinity of a defect, load excursions on the specimen can have a beneficial effect on global load carrying capacity and that load history effects can be captured by adopting the local approach for the assessment of ductile fracture. It is also noted that the trends observed in other local parameters, e.g. J and CTOD, must be treated with caution, probably due to near crack-tip softening associated with the implementation of the GTN model in a region of high stress concentration.Copyright © 2008 by British Crown/MOD
3 citations
References
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TL;DR: In this paper, it is shown that to answer several questions of physical or engineering interest, it is necessary to know only the relatively simple elastic field inside the ellipsoid.
Abstract: It is supposed that a region within an isotropic elastic solid undergoes a spontaneous change of form which, if the surrounding material were absent, would be some prescribed homogeneous deformation. Because of the presence of the surrounding material stresses will be present both inside and outside the region. The resulting elastic field may be found very simply with the help of a sequence of imaginary cutting, straining and welding operations. In particular, if the region is an ellipsoid the strain inside it is uniform and may be expressed in terms of tabulated elliptic integrals. In this case a further problem may be solved. An ellipsoidal region in an infinite medium has elastic constants different from those of the rest of the material; how does the presence of this inhomogeneity disturb an applied stress-field uniform at large distances? It is shown that to answer several questions of physical or engineering interest it is necessary to know only the relatively simple elastic field inside the ellipsoid.
11,784 citations
"Caractérisation à la rupture de mat..." refers background in this paper
...Elle se base sur l'extension des résultats établis par Eshelby pour une inclusion singulière [252]....
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...La première tentative est la loi des mélanges et des méthodes bien plus avancées ont vu le jour depuis la dernière théorie d'Eshelby [252]....
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Book•
01 Jan 1950
TL;DR: In this paper, the solution of two-dimensional non-steady motion problems in two dimensions is studied. But the solution is not a solution to the problem in three dimensions.
Abstract: 1. Introduction 2. Foundations of the thoery 3. General theorems 4. The solution of plastic-elastic problems I 5. The solution of plastic-elastic problems II 6. Plane plastic strain and the theory of the slip-line field 7. Two-dimensional problems of steady motion 8. Non-steady motion problems of steady motion 9. Non-steady motion problems in two dimensions II 10. Axial symmetry 11. Miscellaneous topics 12. Platic anisotropy
7,810 citations
Additional excerpts
...[108] R. Hill, "The Mathematical Theory of Plasticity," Oxford, Clarendon Press, 1950....
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...Le terme VER à été expliqué par Hill [233] et détaillé par Hashin [234, 235]....
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...Une matrice qui obéit au critère de Hill [108] contenant des vides sphériques est considérée....
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...[247] R. Hill, "Theory of mechanical properties of fibre-strengthened materials - III....
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...La première application du modèle de zone cohésive au comportement à la rupture a été réalisée par Hillerborg et al. [129] qui a utilisé ce modèle pour décrire le comportement endommageable du béton....
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TL;DR: In this paper, an integral is exhibited which has the same value for all paths surrounding a class of notches in two-dimensional deformation fields of linear or non-linear elastic materials.
Abstract: : An integral is exhibited which has the same value for all paths surrounding a class of notches in two-dimensional deformation fields of linear or non-linear elastic materials. The integral may be evaluated almost by inspection for a few notch configurations. Also, for materials of the elastic- plastic type (treated through a deformation rather than incremental formulation) , with a linear response to small stresses followed by non-linear yielding, the integral may be evaluated in terms of Irwin's stress intensity factor when yielding occurs on a scale small in comparison to notch size. On the other hand, the integral may be expressed in terms of the concentrated deformation field in the vicinity of the notch tip. This implies that some information on strain concentrations is obtainable without recourse to detailed non-linear analyses. Such an approach is exploited here. Applications are made to: Approximate estimates of strain concentrations at smooth ended notch tips in elastic and elastic-plastic materials, A general solution for crack tip separation in the Barenblatt-Dugdale crack model, leading to a proof of the identity of the Griffith theory and Barenblatt cohesive theory for elastic brittle fracture and to the inclusion of strain hardening behavior in the Dugdale model for plane stress yielding, and An approximate perfectly plastic plane strain analysis, based on the slip line theory, of contained plastic deformation at a crack tip and of crack blunting.
7,468 citations
TL;DR: In this paper, a method of calculating the average internal stress in the matrix of a material containing inclusions with transformation strain is presented. But the authors do not consider the effects of the interaction among the inclusions and of the presence of the free boundary.
7,000 citations
"Caractérisation à la rupture de mat..." refers background in this paper
...Les propriétés moyennes deviendraient alors des propriétés effectives [229, 234, 235, 246-249]....
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...Pour prendre en considération l'interaction entre les inclusion par moyennisation, d'autres hypothèses ont été introduites comme le schéma de Mori-Tanaka [248] ou bien le schéma self-consistant [253]....
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TL;DR: In this article, a relation between extent of plastic yielding and external load applied was investigated, and panels containing internal and edge slits were loaded in tension and lengths of plastic zones were measured.
Abstract: Y ielding at the end of a slit in a sheet is investigated, and a relation is obtained between extent of plastic yielding and external load applied. To verify this relation, panels containing internal and edge slits were loaded in tension and lengths of plastic zones were measured.
6,830 citations
"Caractérisation à la rupture de mat..." refers background in this paper
...42 Figure I.17) Modes de coalescence : a) par striction interne, b) par cisaillement interne 42 Figure I.18) Prédiction de la déchirure ductile en utilisant R&T et R&T modifié par Taktak et al. 44 Figure I.19) Modèle d'unité sphérique proposé par Gurson 45 Figure I.20) Evolution de la fraction volumique effective du vide 46 Figure I.21) Forme de vides : a) oblate, b) prolate 47 Figure I.22) Influence des paramètres du modèle de Rousselier : a) 0f , b) Cf , C) 1 50 Figure I.23) Identification des paramètres par optimisation non-linéaire 51 Figure I.24) Le modèle de Dugdale 51 Figure I.25) Le modèle de Barenblatt 52 Figure I.26) Les lois de traction-séparation utilisées 52 Figure I.27) Modèle de zone cohésive : représentation du processus d‘endommagement physique par séparation des interfaces d‘épaisseur nulle 53 Chapitre II Figure II.1) Maillage de l'éprouvette de traction 58 Figure II.2) Evolution de l‘état de contrainte lors de la sollicitation de l‘éprouvette de traction 58 Figure II.3) Comparaison entre expérimental et numérique pour l‘éprouvette de traction 59 Figure II.4) Maillage de l'éprouvette CT 59 Figure II.5) Evolution de la contrainte dans l‘éprouvette CT 60 Figure II.6) Courbes de capacité (éprouvette CT) 60 Figure II.7) Courbes R (éprouvette CT) 60 Figure II.8) Courbe contrainte-déformation en traction de l'acier inoxydable AISI 316L 62 Figure II.9) Contrainte de von Mises dans l'éprouvette CT 63 Figure II.10) Déformation du maillage après essai 63 Figure II.11) Courbe force-déplacement CT0....
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...De cette manière, la zone plastique à été remplacée par une zone de processus de rupture Figure I.24) Le modèle de Dugdale [41] Chapitre I Revue bibliographique sur la rupture ductile Figure I.25) Le modèle de Barenblatt [128] La dégradation et la séparation du matériau est concentrée dans un plan discret représentée par les éléments cohésifs qui sont intégrés dans des éléments continus représentés par l‘éprouvette testée ou l‘élément de structure....
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...l‘idée d‘une force cohésive qui prévient la propagation des fissures est introduite par Dugdale [41]....
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...Kobayashi et al. [40] ont évalué ICJ en utilisant plusieurs éprouvettes CCT par le biais du modèle de Dugdale [41]....
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...[41] D. S. Dugdale, "Yielding of steel sheets containing slits," Journal of Mechanics and Physics of Solids, vol. 8, pp. 1-8, 1960....
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