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Molecular-dynamics Simulation-based Cohesive Zone Representation of Intergranular Fracture Processes in AluminumA traction-displacement relationship that may be embedded into a cohesive zone model for microscale problems of intergranular fracture is extracted from atomistic molecular-dynamics simulations. A molecular-dynamics model for crack propagation under steady-state conditions is developed to analyze intergranular fracture along a flat 99 [1 1 0] symmetric tilt grain boundary in aluminum. Under hydrostatic tensile load, the simulation reveals asymmetric crack propagation in the two opposite directions along the grain boundary. In one direction, the crack propagates in a brittle manner by cleavage with very little or no dislocation emission, and in the other direction, the propagation is ductile through the mechanism of deformation twinning. This behavior is consistent with the Rice criterion for cleavage vs. dislocation blunting transition at the crack tip. The preference for twinning to dislocation slip is in agreement with the predictions of the Tadmor and Hai criterion. A comparison with finite element calculations shows that while the stress field around the brittle crack tip follows the expected elastic solution for the given boundary conditions of the model, the stress field around the twinning crack tip has a strong plastic contribution. Through the definition of a Cohesive-Zone-Volume-Element an atomistic analog to a continuum cohesive zone model element - the results from the molecular-dynamics simulation are recast to obtain an average continuum traction-displacement relationship to represent cohesive zone interaction along a characteristic length of the grain boundary interface for the cases of ductile and brittle decohesion. Keywords: Crack-tip plasticity; Cohesive zone model; Grain boundary decohesion; Intergranular fracture; Molecular-dynamics simulation
Document ID
20080014337
Acquisition Source
Langley Research Center
Document Type
Preprint (Draft being sent to journal)
Authors
Yamakov, Vesselin I. (National Inst. of Aerospace Hampton, VA, United States)
Saether, Erik (NASA Langley Research Center Hampton, VA, United States)
Phillips, Dawn R. (Lockheed Martin Space Operations Hampton, VA, United States)
Glaessgen, Edward H. (NASA Langley Research Center Hampton, VA, United States)
Date Acquired
August 24, 2013
Publication Date
January 1, 2006
Publication Information
Publication: Journal of the Mechanics and Physics of Solids
Volume: 54
Issue: 9
Subject Category
Atomic And Molecular Physics
Funding Number(s)
CONTRACT_GRANT: NCC-1-02043
CONTRACT_GRANT: NAS1-00135
OTHER: 23-064-20-32
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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