Anisotropic ductile fracture

Benzerga, A. Amine; Besson, Jacques; Pineau, A.

doi:10.1016/j.actamat.2004.06.019

Cited by 229 publications

(145 citation statements)

References 19 publications

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“…The present problem of damage evolution inside the weak zone of a weld involves a significant change of stress triaxiality during deformation and requires a model that takes into account void shape changes. [10][11][12][13] An extra complexity also came from the observation that, in AA 6056 alloys, submicron secondary voids played a key role in setting the value of the ductility by affecting the onset of coalescence between primary voids ( Figure 2). [14] It was thus found essential, in order to build a quantitative model for the ductility, to introduce the effect of this second population of voids using a recent extension of the void coalescence condition by internal necking.…”

Section: Introductionmentioning

confidence: 98%

Multiscale Analysis of the Strength and Ductility of AA 6056 Aluminum Friction Stir Welds

Gallais

Simar

Fabrègue

et al. 2007

Metall Mater Trans A

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The number of parameters affecting the friction stir welding process, the subsequent forming operations, and the structural integrity is very large: chemical composition of the two welded materials, welding parameters and thermal history, initial microstructure, flow properties of each alloy, etc. A multiscale analysis based on macro-and micromechanical tests has been conducted in order to determine and quantify the phenomena controlling the mechanical properties of joints made by welding AA 6056 Al alloys in a T4 or T78 state and to construct a predictive model for plasticity and fracture. Small tensile test samples were machined inside the various zones of the welds and parallel to the welding direction to identify the local plastic and fracture properties. Macrotensile tests using samples machined transverse to the welding direction and strain maps obtained by digital image correlation (DIC) provided information about the overall strength, plastic strain localization, and fracture of the joint. Three-dimensional (3-D) finite element (FE) analysis of the deformation of the welded samples loaded transverse to the welding line based on J 2 flow plasticity theory and on the parameters identified on the small test samples was used to quantify the effects of the geometrical, microstructural, and mechanical factors affecting the plastic flow localization process and the evolution of the constraint in the weak zone, which controls the damage rate. Uniform plastic flow is controlled not only by the yield strength mismatch between the weak zone and its surrounding but also by the strain hardening mismatch, both related to the precipitation of the Q phase. The ductility was addressed using a micromechanics-based damage model. A key ingredient of the model was to account for both large primary voids nucleated early on intermetallic particles and small secondary voids nucleated on dispersoı¨ds, which have a first-order effect on the fracture of the AA 6056 Al alloy. The model is shown to capture very well the drop of the overall ductility in the welded joints.

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Section: Introductionmentioning

confidence: 98%

Multiscale Analysis of the Strength and Ductility of AA 6056 Aluminum Friction Stir Welds

Gallais

Simar

Fabrègue

et al. 2007

Metall Mater Trans A

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“…Although the field of ductile fracture has received attention for more than 50 years, continually striving for more reliable damage models and localization criteria, the field is rich with new challenges. These include capitalizing on recent experimental and theoretical developments related to stress state dependence [15][16][17][18], development of computational models capable of predicting both crack initiation and crack advance [7][8][9][10][11][19][20][21][22], applications to extensive tearing of plates and sheets [23][24][25][26], further progress in void growth and coalescence models [27][28][29][30][31][32] and the challenge of localization and fracture under distinctly non-proportional straining and stressing histories such as those often encountered in forming processes. last two stages of void nucleation, growth and coalescence.…”

Section: Introductionmentioning

confidence: 99%

On localization and void coalescence as a precursor to ductile fracture

Tekoğlu

Hutchinson

Pardoen

2015

Phil. Trans. R. Soc. A.

130

110

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Two modes of plastic flow localization commonly occur in the ductile fracture of structural metals undergoing damage and failure by the mechanism involving void nucleation, growth and coalescence. The first mode consists of a macroscopic localization, usually linked to the softening effect of void nucleation and growth, in either a normal band or a shear band where the thickness of the band is comparable to void spacing. The second mode is coalescence with plastic strain localizing to the ligaments between voids by an internal necking process. The ductility of a material is tied to the strain at macroscopic localization, as this marks the limit of uniform straining at the macroscopic scale. The question addressed is whether macroscopic localization occurs prior to void coalescence or whether the two occur simultaneously. The relation between these two modes of localization is studied quantitatively in this paper using a three-dimensional elastic-plastic computational model representing a doubly periodic array of voids within a band confined between two semi-infinite outer blocks of the same material but without voids. At sufficiently high stress triaxiality, a clear separation exists between the two modes of localization. At lower stress triaxialities, the model predicts that the onset of macroscopic localization and coalescence occur simultaneously.

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“…In particular, the ligament between voids often may break in one of two directions: (a) perpendicular to the loading directions (intervoid ligament necking) and (b) in the localized shear direction (void shearing). The coalescence starts when the size of the voids and the ligament between voids becomes nearly equal [10,11].…”

Section: Introductionmentioning

confidence: 99%

Development of a Microscopic Damage Model for Low Stress Triaxiality

Achouri

Germain

Santo

et al. 2011

KEM

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is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. Abstract. This work deals a contribution to ductile damage of High-Strength Low-Alloy (HSLA) steel steels under low stress triaxiality. This work is based on micrographics observations and in situ shear tests to examine the evolution of microstructure in this kind of loading and to identify the damage process associated. Numerical simulations by finites elements has been performed to simulate the material behavior of nucleation mechanism and the interaction between cavities during the coalescence phase, as well as the effect of the relative position of the inclusions in the shear plane. The model used as a reference in this work is the Gurson-Tvergaard-Needleman (GTN) model. It has been recently improved in order to take into account the effects of low triaxiality during shearing. The implementation of this model in a finite element code is in progress.

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Anisotropic ductile fracture

Cited by 229 publications

References 19 publications

Multiscale Analysis of the Strength and Ductility of AA 6056 Aluminum Friction Stir Welds

Multiscale Analysis of the Strength and Ductility of AA 6056 Aluminum Friction Stir Welds

On localization and void coalescence as a precursor to ductile fracture

Development of a Microscopic Damage Model for Low Stress Triaxiality

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