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

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.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Mechanical Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2010

Author dc:creator

• Oyelakin, John O.

Contributors dc:contributor

• Sehitoglu, Huseyin

• Fatigue
• Fatigue Crack Growth
• Nanocrystalline
• Nickel Cobalt
• Alloy
• Digital Image Correlation (DIC)
• Electrodeposit
• Effective Stress Intensity Factor Range
• Barrier
• Twin Boundary
• Slip

Statement dc:rights

• Copyright 2010 John O. Oyelakin

Language dc:language

en

Handle dc:identifier

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

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/16165