The Ductile versus Brittle Fracture Behavior Assessed by the Competition between Dislocation Emission and Cleavage at Blunt Crack Tip

2004 ◽  
Vol 274-276 ◽  
pp. 135-140 ◽  
Author(s):  
Ming Xin Huang ◽  
Zhong Hua Li
Keyword(s):  
Brittle Fracture ◽  
Fracture Behavior ◽  
Crack Tip ◽  
Dislocation Emission ◽  
Blunt Crack

Film Effects On Ductile/Brititle Behavior In Stress-Corrosion Cracking

1995 ◽  
Vol 409 ◽  
Author(s):  
Tong-Yi Zhang ◽  
Wu-Yang Chu ◽  
Ji-Mei Xiao
Keyword(s):  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Critical Stress ◽  
Fracture Behavior ◽  
Applied Load ◽  
Crack Tip ◽  
Critical Stress Intensity Factor ◽  
Corrosion Cracking ◽  
Dislocation Emission ◽  
Mode Iii

AbstractThe present work analyzes the effects of a passive film formed during stress corrosion cracking on ductile/brittle fracture behavior, considering the interaction of a screw dislocation with a thin film-covered mode III crack under an applied remote load. Exact solutions are derived, and the results show that the crack stress field due to the applied load is enhanced by a harder film or abated by a softer film. The critical stress intensity factor for dislocation emission from the crack tip is greatly influenced by both the stiffness and thickness of the filn. A dislocation is more easily to be emitted from the crack tip if the covered film has a shear modulus larger than that of the substrate. The opposite is also true, i.e., a softer film makes dislocation emission more difficult. Both phenomena become more significant when the film thickness is smaller.

Continuum Mechanics-Discrete Defect Modeling and Bubble Raft Simulation of Cracked Specimen Response in Nanoscale Geometries

2002 ◽  
Vol 740 ◽  
Author(s):  
Michael J. Starr ◽  
Walter J. Drugan ◽  
Maria d. C. Lopez-Garcia ◽  
Donald S. Stone
Keyword(s):  
Fracture Behavior ◽  
Crack Tip ◽  
Crack Size ◽  
Dislocation Model ◽  
Dislocation Emission ◽  
Crack Location ◽  
Discrete Dislocation ◽  
Emission Behavior ◽  
The Continuum ◽  
Continuum Elasticity

ABSTRACTIn a continuation of prior work, a new group of Bragg bubble model experiments have been performed to explore the effects of nanoscale crack size and nanoscale structural geometry on atomically-sharp crack tip dislocation emission behavior. The experiments have been designed to correspond to the theoretical limits that bound the expected crack tip response. Continuum elasticity analyses of these situations have also been carried out, in which the leading-order terms in the Williams expansion (the K and T terms) are determined, and the predictions of these continuum analyses coupled with discrete dislocation theory are compared with the experimental results. The experiments exhibit fascinating changes in crack tip dislocation emission direction with changing crack and structural size, crack location and loading conditions, as well as substantial changes in the magnitude of the resolved shear stress that drives dislocation emission. These changes are predicted well by the continuum elasticity-discrete dislocation model down to extremely small dimensions, on the order of a few atomic spacings. Preliminary experiments were performed with layered and two-atom basis rafts to establish crucial comparisons between theory and experiment that validate the applicability of continuum elasticity theory to make predictions directly related to nanoscale fracture behavior.

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

2012 ◽  
Vol 05 ◽  
pp. 410-417 ◽  
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.

An atomic simulation of the influence of hydrogen on the fracture behavior of nickel

1992 ◽  
Vol 7 (8) ◽  
pp. 2080-2088 ◽  
Author(s):  
R.G. Hoagland ◽  
H.L. Heinisch
Keyword(s):  
Fracture Behavior ◽  
Crack Surface ◽  
Crack Tip ◽  
Dislocation Emission ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Atomic Simulation ◽  
Crack Tip Opening ◽  
Type Potential ◽  
Hydrostatic Component

A model exploring the effect of the presence of a single hydrogen interstitial on the crack tip configuration of nickel is described. The model is based on a EAM-type potential developed by Daw, Baskes, Bisson, and Wolfer for describing the Ni–Ni, Ni–H, and H–H interactions, and involves the crack tip region of a semi-infinite crack in an infinite solid. Several types of interactions are observed to occur. In a model oriented such that dislocation emission is difficult, hydrogen is observed to increase the crack tip opening displacement (CTOD), exert a force on the crack tip due to interaction between the dilatancy of the defect and the hydrostatic component of the field of the crack, and increase the local tensile stresses. However, the largest contribution to extending the crack derives from the energy released when a hydrogen interstitial escapes to the crack surface. A hydrogen interstitial is also observed to assist dislocation emission in models with an easy emission orientation.

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.

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