COMPUTER MODELING OF CRACKS.
Item
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Title
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COMPUTER MODELING OF CRACKS.
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Identifier
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AAI8302547
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identifier
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8302547
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Creator
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SOM, DILIP KUMAR.
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Contributor
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Arthur Paskin
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Date
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1982
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Language
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English
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Publisher
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City University of New York.
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Subject
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Engineering, Civil
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Abstract
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Brittle fracture is one of the most important properties of solids and yet there is little direct experimental confirmation of the basic models of the underlying atomic mechanisms. In brittle fracture, while there have been some notable experimental confirmations of the basic Griffith approach to fracture, controlled microscopic experiments have not been possible to test these ideas. It is only with the advent of modern computers that theoretical investigations of the pertinent atomic processes have been possible.;The results of a recent molecular dynamic study of a two-dimensional triangular Lennard-Jones system of about 10,000 atoms will be described. Static calculations on this system show very little lattice trapping in contrast to the often quoted results of lattice statics models. It is shown that when lattice statics calculations and hybrid lattice statics calculations are performed using realistic, long-range potentials, lattice trapping is small. Using molecular dynamics, the properties of the system, with and without a crack, are understood sufficiently quantitatively to allow extrapolation to infinite size. With 10,000 atoms size effects are small enough to render the simulation highly reliable.;Dynamic simulations at constant applied load show an intricate interplay between brittle crack propagation and the tendency to form dislocations. At low stresses the behavior is brittle, while dislocation generation and crack blunting are observed at elevated stress.;The velocity of crack propagation was also studied by simulating fracture under constant external displacement. A constant terminal velocity was attained relatively soon after the crack began to propagate. While the constant terminal velocity is in accord with theoretical prediction, the velocity is smaller than expected. Estimates indicate that the finite size of the sample is responsible for the lower value of the terminal velocity.;Brittle fracture is known to occur in normally ductile metals under the influence of certain specific external environments. This effect is commonly termed stress corrosion cracking and/or hydrogen embrittlement. Simulating a crack coated with an elastically hard film, brittle fracture was observed in various computer simulations. A model was developed for how the environment can trigger such a brittle behavior in a material that is inherently ductile.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
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Program
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Physics
