Effect of nanotwin and dislocation pileup at twin boundary on dislocation emission from a semi-elliptical blunt crack tip in nanocrystalline materials

This paper establishes a theoretical model to explore the coupled effect of grain boundary (GB) sliding deformation and crack tip dislocation emission on the critical stress intensity factor (SIF) for crack growth in ultrafine-grained and nanocrystalline materials (NCMs). The model postulates that the stress concentration near a crack tip initiates GB sliding. It is found that GB sliding leads to the formation of wedge disclination dipole at the triple junctions of grain boundaries. Under the external load and stress fields produced by wedge disclinations, dislocations are emitted from crack tips but will stop at the opposite GBs. The influence of the wedge disclination dipole and the dislocation emitted from crack tip on the critical SIF for crack growth is investigated. The model prediction shows that the critical SIF varies with the decrement of grain size, and that there is a critical grain size corresponding to a minimum value of SIF. Compared with the pure brittle fracture in NCMs at the grain sizes of tens of nanometers, the combined deformation mechanisms can bring an increase of the critical SIF for crack growth.

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COMPARISON OF FRACTURE BEHAVIOR OF SHARP WITH BLUNT CRACK TIP IN NANOCRYSTALLINE MATERIALS BY MOLECULAR DYNAMICS SIMULATION

International Journal of Modern Physics Conference Series ◽

10.1142/s2010194512002292 ◽

2012 ◽

Vol 05 ◽

pp. 410-417 ◽

Cited By ~ 2

Author(s):

MOVAFFAQ KATEB ◽

KAMRAN DEHGHANI

Keyword(s):

Molecular Dynamics ◽

Nanocrystalline Materials ◽

Fracture Behavior ◽

Md Simulation ◽

Crack Tip ◽

Dislocation Nucleation ◽

Dynamics Simulation ◽

Blunt Crack ◽

Pile Up ◽

Fracture Behaviors

Molecular Dynamics (MD) simulation was used to figure out the fracture behaviors of nanocrystalline materials (NCM). The simulation was based on more than 13 thousand atoms considered for two systems with sharp and blunt crack tip in NCM. Their atomic level resolution provides novel insights into the fracture behavior of NCM. The results show semi brittle manner for both sharp and blunt tips. Dislocation nucleation and pile up at grain boundary (GB), lead to forming voids at GB. Merging mechanism of voids ahead of crack tip causes crack growth.

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Dislocation emission criterion from a blunt crack tip

Journal of the Mechanics and Physics of Solids ◽

10.1016/j.jmps.2004.03.003 ◽

2004 ◽

Vol 52 (9) ◽

pp. 1991-2003 ◽

Cited By ~ 52

Author(s):

Mingxin Huang ◽

Zhonghua Li

Keyword(s):

Crack Tip ◽

Dislocation Emission ◽

Blunt Crack

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Effect of nanoscale amorphization on dislocation emission from a semi-elliptical surface crack tip in nanocrystalline materials

Mathematics and Mechanics of Solids ◽

10.1177/10812865211045108 ◽

2021 ◽

pp. 108128652110451

Author(s):

Fujun Jiang ◽

Min Yu ◽

Xianghua Peng ◽

P.H. Wen

Keyword(s):

Numerical Analysis ◽

Crack Length ◽

Surface Crack ◽

Nanocrystalline Materials ◽

Crack Tip ◽

Emission Angle ◽

Curvature Radius ◽

Complex Method ◽

Dislocation Emission ◽

The Impact

An impact analysis model is built to describe the effect of nanoscale amorphization on dislocation emission from a surface semi-elliptical crack tip in nanocrystalline materials. The nanoscale amorphization is formed by the splitting transformation of grain boundary(GB)disclinations caused by the motion of GBs. The analytical solution of the model is obtained by using the complex method, and the influence of nanoscale amorphization, dislocation emission angle, crack length, and curvature radius of surface crack tip on the critical stress intensity factor (SIF) of the first dislocation emission is investigated through numerical analysis. The numerical analysis shows that the impact of nanoscale amorphization on the critical SIF corresponding to dislocation emission depends on the dislocation emission angle, the position and the size of the nanoscale amorphous, the curvature radius, and the length of surface crack. As the curvature radius of surface crack tip and the crack length increase, the normalized critical SIF increases. When the nanoscale amorphization size is small, it has a great impact on the critical SIF for dislocation, but when the size is relatively large, the effect becomes small. The effect of the increasing strength of the nanoscale amorphization on dislocation emission from the surface crack tip is related to the distance between the nanoscale amorphization and the crack tip, and there is a critical crack-junction for which the increase of dislocation strength has little effect on dislocation emission.

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Effect of wedge disclination dipole on dislocation emission from a surface crack tip in nanocrystalline materials

Theoretical and Applied Fracture Mechanics ◽

10.1016/j.tafmec.2015.11.005 ◽

2016 ◽

Vol 81 ◽

pp. 25-31 ◽

Cited By ~ 2

Author(s):

Z.P. Wang ◽

H. Feng ◽

F. Liu ◽

Q.H. Fang ◽

Y.W. Liu ◽

...

Keyword(s):

Surface Crack ◽

Nanocrystalline Materials ◽

Crack Tip ◽

Dislocation Emission ◽

Disclination Dipole ◽

Wedge Disclination

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Nanoscale rotational deformation effect on dislocation emission from an elliptically blunted crack tip in nanocrystalline materials

International Journal of Solids and Structures ◽

10.1016/j.ijsolstr.2013.10.008 ◽

2014 ◽

Vol 51 (2) ◽

pp. 352-358 ◽

Cited By ~ 9

Author(s):

H. Feng ◽

Q.H. Fang ◽

Y.W. Liu ◽

C.P. Chen

Keyword(s):

Nanocrystalline Materials ◽

Crack Tip ◽

Dislocation Emission ◽

Deformation Effect ◽

Rotational Deformation

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Effect Of Crack Blunting On Subsequent Crack Propagation

MRS Proceedings ◽

10.1557/proc-409-95 ◽

1995 ◽

Vol 409 ◽

Cited By ~ 6

Author(s):

J. SchiØtz ◽

A. E. Carlsson ◽

L. -M. Canel ◽

Robb Thomson

Keyword(s):

Crack Propagation ◽

Brittle Material ◽

Crack Tip ◽

Dislocation Emission ◽

Dislocation Source ◽

Blunt Crack ◽

Ductile Materials ◽

Noticeable Increase ◽

Greens Function ◽

Crack Blunting

AbstractTheories of toughness of materials depend on an understanding of the characteristic instabilities of the crack tip, and their possible interactions. In this paper we examine the effect of dislocation emission on subsequent cleavage of a crack and on further dislocation emission. The work is an extension of the previously published Lattice Greens Function methodology[1, 2, 3]. We have developed a Cavity Greens Function describing a blunt crack and used it to study the effect of crack blunting under a range of different force laws. As the crack is blunted, we find a small but noticeable increase in the crack loading needed to propagate the crack. This effect may be of importance in materials where a dislocation source near the crack tip in a brittle material causes the crack to absorb anti-shielding dislocations, and thus cause a blunting of the crack. It is obviously also relevant to cracks in more ductile materials where the crack itself may emit dislocations.

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