University of Illinois Urbana-Champaign

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

Oyelakin, John O.

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https://hdl.handle.net/2142/16165

Description

Title
On the fracture and fatigue crack growth of thin sheets of nanocrystalline metal alloys
Author(s)
Oyelakin, John O.
Issue Date
2010-05-19T18:39:28Z
Director of Research (if dissertation) or Advisor (if thesis)
Sehitoglu, Huseyin
Department of Study
Mechanical Sci & Engineering
Discipline
Mechanical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
M.S.
Degree Level
Thesis
Keyword(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.
Graduation Semester
2010-5
Permalink
http://hdl.handle.net/2142/16165
Copyright and License Information
Copyright 2010 John O. Oyelakin

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