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.

Atomistic simulation for configuration evolution and energetic calculation of crack in body-centered-cubic iron

2006 ◽  
Vol 21 (10) ◽  
pp. 2542-2549 ◽  
Author(s):  
Li-Xia Cao ◽  
Chong-Yu Wang
Keyword(s):  
Low Temperatures ◽  
Crack Tip ◽  
Dislocation Nucleation ◽  
Effect Of Temperature ◽  
Body Centered Cubic ◽  
Partial Dislocations ◽  
Higher Temperature ◽  
Crack Blunting ◽  
Increasing Temperature ◽  
Extended Dislocation

The molecular dynamics method has been used to simulate mode I cracking in body-centered-cubic iron. Close attention has been paid to the process of the atomic configuration evolution of the cracks. The simulation shows that at low temperatures, partial dislocations are emitted before the initiation of crack propagation, subsequently forming the stacking faults or multilayer twins on {112} planes, and then brittle cleavage and extended dislocation nucleation are observed at the crack tip accompanied by twin extension. These results are in agreement with the experimental observation that twinning and fracture processes cooperate at low temperatures. Furthermore, an energetics analysis has been made on the deformation behavior observed at the crack tip. The effect of temperature on the fracture process is discussed. At the higher temperature, plastic deformation becomes easier, and crack blunting occurs. With increasing temperature, the fracture resistance increases, and the effect of the lattice trapping can be weakened by thermal activation.

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

1997 ◽  
Vol 55 (10) ◽  
pp. 6211-6221 ◽  
Author(s):  
J. Schiøtz ◽  
L. M. Canel ◽  
A. E. Carlsson
Keyword(s):  
Crack Tip ◽  
Dislocation Emission ◽  
Crack Tip Geometry

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.

scholarly journals Effect of Crack Geometry on Dislocation Nucleation and Cleavage Thresholds

1998 ◽  
Vol 539 ◽  
Author(s):  
L.L. Fischer ◽  
G.E. Beltz
Keyword(s):  
Continuum Model ◽  
Crack Tip ◽  
Critical Energy ◽  
Dislocation Nucleation ◽  
Mode I ◽  
Critical Mode ◽  
Critical Energy Release Rate ◽  
Material Behaviors ◽  
Mode I Loading ◽  
Crack Tip Blunting

AbstractA 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.

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.

Atomistic Study of Cleavage and Dislocation Emission in NiAl

1994 ◽  
Vol 364 ◽  
Author(s):  
M. Ludwig ◽  
P. Gumbsch
Keyword(s):  
Finite Element ◽  
Mixed Mode ◽  
Crack Tip ◽  
Mode I ◽  
Crack Plane ◽  
Dislocation Emission ◽  
Dislocation Generation ◽  
Embedded Atom ◽  
Atomistic Study ◽  
Eam Potential

AbstractThe atomistic processes during fracture of NiAl are studied using a new embedded atom (EAM) potential to describe the region near the crack tip. To provide the atomistically modeled crack tip region with realistic boundary conditions, a coupled finite element - atomistic (FEAt) technique [1] is employed. In agreement with experimental observations, perfectly brittle cleavage is observed for the (110) crack plane. In contrast, cracks on the (100) plane either follow a zig-zag path on (110) planes, or emit dislocations. Dislocation generation is studied in more detail under mixed mode I/II loading conditions.

Crack-tip dislocation emission arrangements for equilibrium—III. Application to large applied stress intensities

1992 ◽  
Vol 40 (11) ◽  
pp. 2883-2894 ◽  
Author(s):  
P.G. Marsh ◽  
W. Zielinski ◽  
H. Huang ◽  
W.W. Gerberich
Keyword(s):  
Applied Stress ◽  
Crack Tip ◽  
Dislocation Emission
Sign in / Sign up

Export Citation Format

Share Document