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On the fracture and fatigue crack growth of thin sheets of nanocrystalline metal alloys

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Title: On the fracture and fatigue crack growth of thin sheets of nanocrystalline metal alloys
Author(s): Oyelakin, John O.
Advisor(s): Sehitoglu, Huseyin
Department / Program: Mechanical Sci & Engineering
Discipline: Mechanical Engineering
Degree Granting Institution: University of Illinois at Urbana-Champaign
Degree: M.S.
Genre: Thesis
Subject(s): Fatigue Fatigue crack growth nanocrystalline nickel cobalt alloy digital image correlation (DIC) electrodeposit effective stress intensity factor range barrier twin boundary slip
Abstract: Fatigue crack growth was investigated in thin sheets of electrodeposited nickel–1.6% cobalt (Ni-Co) and rolled Inconel 718. Digital image correlation (DIC) was used to determine the crack opening displacement profiles, and the entire crack displacement fields. These parameters were then used to determine the magnitude of the crack tip stress intensity factor, and virtual extensometers were used to establish precisely the crack opening stress levels. The use of DIC enhanced the processing of experimental data and images, and gave detailed view of the crack tip stress intensity evolution with increasing crack length, transcending the limitations of previous measurement techniques. The Ni-Co alloy exhibits planar slip, has a nanocrystalline grain structure and high density of nanotwins as shown with extensive transmission electron microscopy. The crack growth rate exponent is less than 1.5 and the growth rates are finite stress intensity ranges as high as 100. We relate the fatigue crack growth resistance in the Ni-Co to slip-twin interactions, and the difficulty of slip to penetrate grain boundaries and annealing twins.
Issue Date: 2010-05-19
URI: http://hdl.handle.net/2142/16165
Rights Information: Copyright 2010 John O. Oyelakin
Date Available in IDEALS: 2010-05-19
Date Deposited: May 2010
 

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