A multi-scale correlative investigation of ductile fracture

Daly, Michael; Burnett, Timothy L.; Pickering, Ed; Tuck, Olivia C. G.; Léonard, Fabien; Kelley, R. J.; Withers, Philip J.; Sherry, Andrew H.

doi:10.1016/j.actamat.2017.03.028

Cited by 44 publications

(29 citation statements)

References 34 publications

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“…Average Taylor factors (Eqs. 22,24,28) are computed by adaptative quadrature scheme where the integrand function (local Taylor factor) relies on Taylor's minimum shear principle solved through linear programming [70].…”

Section: Coalescence Criterion For Porous Crystalsmentioning

confidence: 99%

A coalescence criterion for porous single crystals

Hure¹

2019

Journal of the Mechanics and Physics of Solids

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Voids can be observed at various scales in ductile materials, frequently of sizes lower than the grain size, leading to porous single crystals materials. Two local deformation modes of porous ductile (single crystals) materials have been identified and referred to as void growth and void coalescence, the latter being characterized by strong interactions between neighboring voids. A simple semi-analytical coalescence criterion for porous single crystals with periodic arrangement of voids is proposed using effective isotropic yield stresses associated with a criterion derived for isotropic materials. An extension of the coalescence criterion is also proposed to account for shear with respect to the coalescence plane. Effective yield stresses are defined using Taylor theory of single crystal deformation, and rely ultimately on the computation of average Taylor factors. Arbitrary sets of slip systems can be considered. The coalescence criterion is assessed through comparisons to numerical limit-analysis results performed using a Fast-Fourier-Transform based solver. A good agreement is observed between the proposed criterion and numerical results for various configurations including different sets of slip systems (Face-Centered-Cubic, Hexagonal-Close-Packed), crystal orientations, void shapes and loading conditions. The competition between void growth and void coalescence is described for specific conditions, emphasizing the strong influence of both crystal orientation and void lattice, as well as their interactions.

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Section: Coalescence Criterion For Porous Crystalsmentioning

confidence: 99%

A coalescence criterion for porous single crystals

Hure¹

2019

Journal of the Mechanics and Physics of Solids

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“…This work expands on previous work, providing additional experimental evidence to highlight the differences in mechanistic ductile fracture between HIP and forged variants of 304L stainless steel, and employs the use of SEM to study the differences in microstructural damage ahead of and surrounding the crack tip of sectioned failed test specimens. This work also expands on the work by Daly et al [15,16], who employed the use of 3D X-ray CT to probe ductile damage in SA508 weld metal in order to improve the calibration of the Gurson, Tvergaard and Needleman [18][19][20] ductile fracture model, by investigating approaches to approximating the fracture surface of cores which exhibit a large depth of fracture process zone.…”

Section: Introductionmentioning

confidence: 86%

“…The immediate surface perimeter of the core was cropped by five voxels to remove the very porous surface as a result of EDM machining of the cores, which may contribute to the inaccurate rendering of voids. The procedure used to segment voids and metal in the X-ray CT reconstructed images is detailed by Daly et al [16]; to which the reader is directed for details. Void segmentation was performed such that any voids in any contact with the fracture surface were assigned to the air surrounding the core.…”

Section: D X-ray Tomographymentioning

confidence: 99%

“…Importantly, X-ray CT allows for the collection of data with 'statistical significance', whereby imaged specimens may contain thousands of measureable voids that have been subjected to a known stress state and/or loading conditions. In recent years, X-ray CT has been employed as a tool to study microvoid coalescence in a variety of alloy systems [13,14], and quantitative X-ray CT has been shown [15][16][17] to be a promising tool for the determination of ductile damage parameters to inform the predictive model for ductile failure developed by Gurson, Tvergaard and Needleman [18][19][20].…”

Section: Introductionmentioning

confidence: 99%

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Ductile Fracture Assessment of 304L Stainless Steel Using 3D X-ray Computed Tomography

Cooper

Tuck

Burnett

et al. 2018

The Minerals, Metals &Amp; Materials Series

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Stainless steel manufactured by hot isostatic pressing (HIP) has been shown to exhibit significant differences in ductile fracture behavior when compared to equivalently graded forged steel, due to differences in oxide particle concentration between the two manufacture routes. Herein we analyse and quantify the ductile damage characteristics in the fracture process zone of equivalently graded forged and HIP 304L steel using 3D X-ray computed tomography (CT). Ductile void characteristics have been found to vary in size, shape, and spatial distribution; data which are in agreement with the differences in distribution of initiation particles in HIP and forged steel. Using advanced X-ray CT to characterize ductile damage, experimentally determined data can be employed to calibrate existing well-known ductile failure models, developing both our current understanding of ductile failure as well as a predictive tool to simulate fracture in novel HIP components.

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“…cell simulations [16,17,18]. Homogenized yield criteria for porous single crystals have been developed to account for the effects of crystal orientation [19,20,21,22,23].Most of these homogenized models for porous materials are size-independent, assuming implicitly that only void volume fraction matters irrespectively of void size, although porous materials with voids ranging from micrometric [13] down to nanometric sizes [24,25] are encountered in industrial applications. Moreover, size effects have been predicted from theoretical and numerical studies.…”

mentioning

confidence: 99%

A size-dependent ductile fracture model: Constitutive equations, numerical implementation and validation

Scherer

Hure

2019

European Journal of Mechanics - A/Solids

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Size effects have been predicted at the micro-or nano-scale for porous ductile materials from Molecular Dynamics, Discrete Dislocation Dynamics and Continuum Mechanics numerical simulations, as a consequence of Geometrically Necessary Dislocations or due to the presence of a void matrix interface. As voids size decreases, higher stresses are needed to deform the material, for a given porosity. However, the majority of the homogenized models for porous materials used in ductile fracture modeling are size-independent, even though micrometric or nanometric voids are commonly observed in structural materials. Based on yield criteria proposed in the literature for nanoporous materials, a size-dependent homogenized model for porous materials is proposed for axisymmetric loading conditions, including void growth and coalescence as well as void shape effects. Numerical implementation of the constitutive equations is detailed. The homogenized model is validated through comparisons to porous unit cells finite element simulations that consider interfacial stresses, consistently with the model used for the derivation of the yield criteria, aiming at modeling an additional hardening at the void matrix interface. Potential improvements of the model are finally discussed with respect to the theoretical derivation of refined yield criteria and evolution laws. cell simulations [16,17,18]. Homogenized yield criteria for porous single crystals have been developed to account for the effects of crystal orientation [19,20,21,22,23].Most of these homogenized models for porous materials are size-independent, assuming implicitly that only void volume fraction matters irrespectively of void size, although porous materials with voids ranging from micrometric [13] down to nanometric sizes [24,25] are encountered in industrial applications. Moreover, size effects have been predicted from theoretical and numerical studies. A first kind of size effect, occurring when voids size is lower than the dislocation mean free-path, has been revealed through Discrete Dislocation Dynamics (DDD) simulations [26]. In such situations, dislocations exhaustion can lead to the absence of void growth under mechanical loading. A second kind of size effect is related, in a broad sense, to an additional hardening at or close to the void matrix interface. Strain gradient (crystal-)plasticity models -accounting for the presence of Geometrically Necessary Dislocations [27] to extend conventional plasticity to lower scales -have been used in porous unit cells simulations (see [28,29,30,31] and reference therein), showing a strong effect of the void size on both void growth rate and strength of the porous material, consistently with DDD simulations [32]. Numerous Molecular Dynamics (MD) studies have also been performed to assess the strength of (nano-)porous materials, considering voids in an initially dislocation free matrix material ([33, 34, 35] and references therein). Plasticity occurs through dislocation emission from void matrix interface [36], and an influence...

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A multi-scale correlative investigation of ductile fracture

Cited by 44 publications

References 34 publications

A coalescence criterion for porous single crystals

A coalescence criterion for porous single crystals

Ductile Fracture Assessment of 304L Stainless Steel Using 3D X-ray Computed Tomography

A size-dependent ductile fracture model: Constitutive equations, numerical implementation and validation

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