scholarly journals Effect of Crack Blunting on Subsequent Crack Propagation

1995 ◽  
Vol 408 ◽  
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[l, 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.

scholarly journals Effect Of Crack Blunting On Subsequent Crack Propagation

1995 ◽  
Vol 409 ◽  
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.

Creep behaviour of components containing cracks—a critical review

1978 ◽  
Vol 13 (1) ◽  
pp. 35-51 ◽  
Author(s):  
E G Ellison ◽  
M P Harper
Keyword(s):  
Crack Propagation ◽  
Critical Review ◽  
Elevated Temperatures ◽  
Creep Behaviour ◽  
Crack Tip ◽  
Ductile Materials ◽  
Analysis Techniques ◽  
Reference Stress ◽  
Creep Analysis ◽  
Available Information

The prediction of crack propagation rates at elevated temperatures is important and this paper provides a critical review of available information and models for behaviour. For simplicity, behaviour is divided into three situations. At one extreme, a brittle situation may exist in which the material is brittle and the degree of constraint high, so that substantially plane strain conditions exist and stress redistribution at the crack tip is small; in this situation, the fracture is a local crack tip event and the stress intensity may be of use in correlaiting creep crack propagation data. At the other extreme, ductile behaviour may result if the material is ductile and the constraint is low with plane stress conditions prevailing; in this case, stresses at and near the crack tip will redistribute quickly down to more even values and conventional creep analysis techniques using, say, the reference stress will be most useful, particularly for estimating times to rupture. It is postulated that there is also a large intermediate régime, termed quasi-brittle, in which ductile materials under high constraint exhibit brittle characteristics. A new parameter, C∗, appears to be of more general use in this case and even be extended to other situations. Finally, an attempt is made to survey the information available on the effects of environment on crack propagation at high temperature, though conclusions are necessarily tentative at this time.

Effect of Crack Blunting on the Ductile-Brittle Response of Crystalline Materials

1998 ◽  
Vol 539 ◽  
Author(s):  
D.M. Lipkin ◽  
G.E. Beltz ◽  
L.L. Fischer
Keyword(s):  
Crack Tip ◽  
Dislocation Nucleation ◽  
Crack Advance ◽  
Dislocation Emission ◽  
Crystalline Materials ◽  
Self Consistent ◽  
Crack Blunting ◽  
Cohesive Stresses ◽  
Crack Tip Geometry ◽  
Crack Tip Blunting

AbstractWe propose a self-consistent criterion for crack propagation versus dislocation emission, taking into account the effects of crack-tip blunting. Continuum concepts are used to evaluate the evolving competition between crack advance and dislocation nucleation as a function of crack- tip curvature. This framework is used to classify crystals as intrinsically ductile or brittle in terms of the unstable stacking energy, the surface energy, and the peak cohesive stresses achieved during opening and shear of the atomic planes. We find that ductile-brittle criteria based on the assumption that the crack is ideally sharp capture only two of the four possible fracture regimes. One implication of the present analysis is that a crack may initially emit dislocations, only to reinitiate cleavage upon reaching a sufficiently blunted crack-tip geometry.

Effects of Temperature on Crack Propagation of Nanocrystalline Nickel: A Molecular Dynamics Approach

2014 ◽  
Vol 926-930 ◽  
pp. 98-102
Author(s):  
Zi Qiang Li ◽  
Jin Gui Yu ◽  
Qiao Xin Zhang
Keyword(s):  
Molecular Dynamics ◽  
Crack Propagation ◽  
Great Influence ◽  
Crack Tip ◽  
Md Simulations ◽  
Mode I ◽  
Dislocation Emission ◽  
Nanocrystalline Nickel ◽  
Atomic Lattice ◽  
Effects Of Temperature

The primary purpose of this paper is to study the effects of temperature on crack propagation of nanocrystalline nickel by Molecular Dynamics (MD) simulations. Cracks are loaded in tension mode I. Results show that dislocation emission from a crack tip in nanocrystalline nickel due to the recombination of atomic lattice, then distortion of the crack tip promote crack propagation. The studies we have performed showed that temperature takes a great influence on the crack propagation and the crack shape, and we also found that the crack blunt obviously at high temperature.

Multiscale Simulation of Crack Propagation Based on Molecular Dynamics

2014 ◽  
Vol 941-944 ◽  
pp. 1473-1476
Author(s):  
Gui Xue Bian ◽  
Yue Liang Chen ◽  
Yong Zhang ◽  
Da Zhao Yu
Keyword(s):  
Molecular Dynamics ◽  
Crack Propagation ◽  
Crack Tip ◽  
Multiscale Simulation ◽  
Bond Rupture ◽  
Dislocation Emission ◽  
Atomic Configuration ◽  
Fe Method ◽  
Microcrack Propagation ◽  
Atom Bond

A multiscale simulation approach is developed to investigate mechanism of crack propagation from the atomistic perspective. The finite elements (FE) method has been applied to obtain displacement load of the model. The quadrangle region around the crack tip crack tip has been prepared for the molecular dynamics (MD) model. The displacement load calculated by FE was applied to boundaries of the MD model. The simulation results show that the evolution of atomic configuration of the system includes dislocation emission, atomic disorder, atom bond rupture and microcrack propagation.

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