Prediction of grain boundary stress fields and microcrack initiation induced by slip band impingement

Sauzay, Maxime; Moussa, Mohamed Ould

doi:10.1007/s10704-013-9878-4

Cited by 31 publications

(20 citation statements)

References 84 publications

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“…However, there remains the possibility for an intermediary (multiscale?) approach for better calculations of the continuum energy contributions in a similar manner to that adopted by Sangid [20] for the MD-calculated energy contribution, utilising, for example, the modelling techniques recently developed by Sauzay [21,22].…”

Section: Slip Localisation and Persistent Slip Bands (Psbs)mentioning

confidence: 99%

“…Clearly, a number of fatigue crack nucleation criteria have already been introduced above [16,18,21,47] at differing length scales and for relevant microstructural features. Nucleation criteria addressed in this section are CP-based but seek to utilise fatigue indicator parameters which capture microstructural sensitivity.…”

Section: Nucleation Criteria and Microcracksmentioning

confidence: 99%

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Fatigue crack nucleation: Mechanistic modelling across the length scales

Dunne

2014

Current Opinion in Solid State and Materials Science

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This paper presents an assessment of recent literature on the mechanistic understanding of fatigue crack nucleation and the associated modelling techniques employed. In particular, the important roles of (a) slip localisation and persistent slip band formation, (b) grain boundaries, slip transfer and interfaces, (c) microtexture and twins, and (d) nucleation criteria and microcracks are addressed in the context of the three key modelling techniques of crystal plasticity (CP), discrete dislocation (DD) plasticity and molecular dynamics (MD) where appropriate. In addition, the need for computational fatigue crack nucleation methodologies which incorporate mechanistic understanding is addressed. Key challenges identified include (i) the overall need for multiscale models for fatigue crack nucleation which are continuum-based but mechanistically informed; (ii) full (3D) crystal slip models to capture slip localisation at a DD level; (iii) MD modelling methodologies for slip transfer to inform DD models; and (iv) rigorously validated dislocation structure models at the DD and CP levels.

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Section: Slip Localisation and Persistent Slip Bands (Psbs)mentioning

confidence: 99%

Section: Nucleation Criteria and Microcracksmentioning

confidence: 99%

Fatigue crack nucleation: Mechanistic modelling across the length scales

Dunne

2014

Current Opinion in Solid State and Materials Science

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“…In the case of brittle fracture, the fracture energy is defined as the two fresh free surface energy values minus the GB energy. A close-from expression giving the remote tensile stress to GB fracture is then deduced [6,7]. Finally, GB fracture of pre-irradiated SS (dose > 10 dpa) loaded in either inert or pressurized water reactor (PWR) environment is predicted for comparison with the existing experimental results obtained in similar conditions.…”

mentioning

confidence: 98%

“…1b). Analytical formulae are deduced from the numerous FE results, accounting for channel thickness, grain size, channel density and crystal / GB orientations [6,7]. Grain boundary fracture is simulated using a double criterion based on both critical normal stress and fracture energy as deduced from atomistic computations of GB fracture.…”

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confidence: 99%

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Effect of Clear Bands on Intergranular Stresses and IASCC Early Damage

Sauzay

Moussa

Diawara

et al. 2016

EPJ Web of Conferences

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Slip localization is a common feature in post-irradiated metallic poly-crystals undergoing tensile straining. This effect takes place for instance in the form of thin slip bands called channels or clear bands, formed after the local vanishing of irradiation defects induced interactions with gliding dislocations [1][2][3]. Channel impingement towards grain boundaries (GBs) should induce local stress concentrations along GBs, in the quasi-elastic surrounding matrix. It has been shown extensively that this trigger GB crack initiation [2][3].Since the fifties, the clear band stress fields have been modeled using the dislocation pile-up theory, which leads to stress singularities similar to the LEFM ones [4]. But such theory does not allow fair predictions of GB fracture, neither in inert or PWR environment [5]. In practice, channel thickness is at least 50 nm depending on material, temperature and loading conditions. As a matter of fact, many slip planes are plastically activated through the channel thickness. Numerous crystalline finite element (FE) computations have been carried out using microstructure inputs varying in broad ranges (slip band aspect ratio and spacing). Slip bands (low critical resolved shear stress) are embedded in a matrix or small aggregates (high CRSS). Microstructure inputs as well as plasticity parameters are evaluated based on TEM observations and dislocation dynamics computation results. High local stress fields are highlighted (Fig. 1a) but they are nevertheless considerably lower than the ones deduced from the pile-up theory (Fig. 1b). Analytical formulae are deduced from the numerous FE results, accounting for channel thickness, grain size, channel density and crystal / GB orientations [6,7]. Grain boundary fracture is simulated using a double criterion based on both critical normal stress and fracture energy as deduced from atomistic computations of GB fracture. The critical stress is deduced from the fracture energy using the universal-binding-energy relationship (UBER). In the case of brittle fracture, the fracture energy is defined as the two fresh free surface energy values minus the GB energy. A close-from expression giving the remote tensile stress to GB fracture is then deduced [6,7]. Finally, GB fracture of pre-irradiated SS (dose > 10 dpa) loaded in either inert or pressurized water reactor (PWR) environment is predicted for comparison with the existing experimental results obtained in similar conditions. Centre of Excellence for Nuclear MaterialsIn the case of inert environment, free surface and GB energy values are easily found in literature. The predicted remote tensile stress to GB fracture is then equal to the yield stress in agreement with various experimental data (Fig. 2a). In the case of PWR environment, GBs are assumed to be oxidized up to a depth of a few µm due to Cr depletion induced by the strong RIS observed at high irradiation dose [2]. Either literature data have been used (iron oxides [8]) or they have been computed by the DFT method for various GBs and by...

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Coupling a discrete twin model with cohesive elements to understand twin-induced fracture

2021

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The interplay between twinning and fracture in metals under deformation is an open question. The plastic strain concentration created by twin bands can induce large stresses on the grain boundaries. We present simulations in which a continuum model describing discrete twins is coupled with a crystal plasticity finite element model and a cohesive zone model for intergranular fracture. The discrete twin model can predict twin nucleation, propagation, growth and the correct twin thickness. Therefore, the plastic strain concentration in the twin band can be modelled. The cohesive zone model is based on a bilinear traction-separation law in which the damage is caused by the normal stress on the grain boundary. An algorithm is developed to generate interface elements at the grain boundaries that satisfy the traction-separation law. The model is calibrated by comparing polycrystal simulations with the experimentally observed strain to failure and maximum stress. The dynamics of twin and crack nucleation have been investigated. First, twins nucleate and propagate in a grain, then, microcracks form near the intersection between twin tips and grain boundaries. Microcracks appear at multiple locations before merging. A propagating crack can nucleate additional twins starting from the grain boundary, a few micrometres away from the original crack nucleation site. This model can be used to understand which type of texture is more resistant against crack nucleation and propagation in cast metals in which twinning is a deformation mechanism. The code is available online at https://github.com/TarletonGroup/CrystalPlasticity. Graphic Abstract

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Prediction of grain boundary stress fields and microcrack initiation induced by slip band impingement

Cited by 31 publications

References 84 publications

Fatigue crack nucleation: Mechanistic modelling across the length scales

Fatigue crack nucleation: Mechanistic modelling across the length scales

Effect of Clear Bands on Intergranular Stresses and IASCC Early Damage

Coupling a discrete twin model with cohesive elements to understand twin-induced fracture

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