Effect Of Crack Blunting On Subsequent Crack Propagation

Schiøtz, Jakob; Carlsson, Anders; Canel, L. M.; Thomson, Robb

doi:10.1557/proc-409-95

Cited by 7 publications

(4 citation statements)

References 10 publications

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“…The jog may act as a local nucleation site for dislocations, favoring ductile behavior 12,13 . But even without introducing inhomogeneities the detailed atomic configuration may significantly change the behavior of the crack: In a recent paper 14 we demonstrated that the emission of dislocations becomes favored if the crack tip is blunt at the atomic level. In this paper this effect is investigated further.…”

Section: Introductionmentioning

confidence: 99%

Effects of crack tip geometry on dislocation emission and cleavage: A possible path to enhanced ductility

1997

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We present a systematic study of the effect of crack blunting on subsequent crack propagation and dislocation emission. We show that the stress intensity factor required to propagate the crack is increased as the crack is blunted by up to thirteen atomic layers, but only by a relatively modest amount for a crack with a sharp 60 • corner. The effect of the blunting is far less than would be expected from a smoothly blunted crack; the sharp corners preserve the stress concentration, reducing the effect of the blunting. However, for some material parameters blunting changes the preferred deformation mode from brittle cleavage to dislocation emission. In such materials, the absorption of preexisting dislocations by the crack tip can cause the crack tip to be locally arrested, causing a significant increase in the microscopic toughness of the crack tip. Continuum plasticity models have shown that even a moderate increase in the microscopic toughness can lead to an increase in the macroscopic fracture toughness of the material by several orders of magnitude. We thus propose an atomic-scale mechanism at the crack tip, that ultimately may lead to a high fracture toughness in some materials where a sharp crack would seem to be able to propagate in a brittle manner.When the crack is loaded in mode II, the load required to emit a dislocation is affected to a much higher degree by the blunting, in agreement with the estimates from continuum elasticity. In mode II the emission process is aided by a reduction of the free surface area during the emission process. This leads to emission at crack loadings which are lower than predicted from the continuum analysis of Rice.

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Section: Introductionmentioning

confidence: 99%

Effects of crack tip geometry on dislocation emission and cleavage: A possible path to enhanced ductility

1997

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“…Results from various groups in the atomistic community suggest that crack tip geometry can have a substantial quantitative effect on the energies of nucleation and cleavage [8,9,10,11]. Physically speaking, an atomically sharp crack is rare, and this is motivation enough to study the effects of crack geometry using continuum analyses.…”

Section: Introductionmentioning

confidence: 99%

Effect of Crack Geometry on Dislocation Nucleation and Cleavage Thresholds

Fischer

Beltz

1998

MRS Proc.

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A continuum model based upon the Peierls-Nabarro description of a dislocation ahead of a crack is used to evaluate the critical mode I loading for dislocation nucleation at the tip of a finite, pre-blunted crack. A similar approach is used to evaluate the critical mode I loading for atomic decohesion. Results are presented for various crack tip root radii (a measure of bluntness), for several crack lengths. It is shown that increasing the crack length increases the critical energy release rate for both material behaviors. Increasing the bluntness of a crack tip always increases the required loading for atomic decohesion but nucleation thresholds are initially decreased by very small increases in crack tip bluntness. Nucleation thresholds are later increased after reaching significant crack tip blunting. Implications for ductile versus brittle competition are discussed by comparing the ongoing competition between these two different material behaviors.

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“…The physical reality of a blunted crack configuration has motivated limited attempts at evaluating its effect and determining to what extent its stress fields differ from the sharp crack stress fields. Schiøtz [3,4] has tackled this problem using a conformal mapping technique. Using the Schwarz-Christoffel transformation, a simple 60 • blunted crack tip can be mapped to the upper complex half plane with z = x 1 + ix 2 .…”

Section: Introductionmentioning

confidence: 99%

“…However, this process is extremely calculation intensive and expensive if one wants to study a configuration of reasonable size. Recent work done on atomistic models developed by Schiøtz and co-workers [3,4], Gumbsch and co-workers [6,7], and Thomson [8] have provided partial motivation for the development of the model and specific geometry discussed in this paper.…”

Section: Introductionmentioning

confidence: 99%

Continuum mechanics of crack blunting on the atomic scale: elastic solutions

Fischer¹,

Beltz²

1997

Modelling Simul. Mater. Sci. Eng.

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In order to improve upon continuum models for understanding the origins of ductile versus brittle response in materials, an accurate assessment of the stress fields near a crack tip must be developed. Existing continuum models have considered the crack tip to be perfectly sharp in order to use convenient analytical solutions for the stress fields around the crack tip. Numerous experimental observations have indicated that an atomically sharp crack is very rare and that crack tip blunting can precede or accompany crack propagation. A two-dimensional finite element model has been developed to evaluate the stress fields at a blunted crack tip subjected to loading. Stress fields have been calculated for mode I loading as well as for the self-stress due to the presence of a dislocation near a crack tip. These calculated stress fields have been compared with analytical solutions for appropriate limiting cases.

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Effect Of Crack Blunting On Subsequent Crack Propagation

Cited by 7 publications

References 10 publications

Effects of crack tip geometry on dislocation emission and cleavage: A possible path to enhanced ductility

Effects of crack tip geometry on dislocation emission and cleavage: A possible path to enhanced ductility

Effect of Crack Geometry on Dislocation Nucleation and Cleavage Thresholds

Continuum mechanics of crack blunting on the atomic scale: elastic solutions

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