University of Illinois Urbana-Champaign

Fatigue crack growth (FCG) modeling in the presence of nano-obstacles

Chowdhury, Piyas

Content Files
chowdhury_piyas.pdf

Permalink

https://hdl.handle.net/2142/29530

Description

Title
Fatigue crack growth (FCG) modeling in the presence of nano-obstacles
Author(s)
Chowdhury, Piyas
Issue Date
2012-02-01T00:54:12Z
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
Date of Ingest
2012-02-01T00:54:12Z
Keyword(s)
  • Fatigue crack growth
  • nano-obstacle
  • molecular dynamics
  • twin
  • slip irreversibility
Abstract
A combination of molecular dynamics and dislocation dynamics simulations is performed to model fatigue crack growth (FCG) in a nano-twinned nickel single crystal. Molecular dynamics simulations are employed to investigate the irreversible interaction of crack-tip emitted dislocations with nano-twins in the vicinity of the crack upon cyclic loading. A method is developed to quantify the irreversibility of slip, and calculate it as a function of the twin lamella thickness and crack-tip to twin lamella spacing. Subsequently, atomistically calculated slip irreversibility is utilized in dislocation dynamics crack growth simulations to understand the role of thickness of the nano-twins as well as the crack-tip to twin spacing on da/dN. In molecular dynamics simulations, in order to study the cyclic slip-twin interactions, the nano-twinned single grain specimen is set up such that it favors two separate cases comprising pure screw and pure edge dislocation nucleation from the crack-tip. Both screw and edge dislocations demonstrate a cyclic steady-state interaction mechanism with the nano-twin under strain control loading. The da/dN formulations, based on discrete dislocation dynamics, are derived for the cases ranging from single to multiple screw or edge dislocations emission from the crack-tip over cycles. The molecular dynamics slip irreversibility is incorporated into the dislocation dynamics based da/dN calculations. An implementation of these formulations demonstrates that both for the cases of decreasing nano- twin thickness or lowering of crack-tip to twin spacing, da/dN also decreases complying with some recent experimental findings in literature.
Graduation Semester
2011-12
Permalink
http://hdl.handle.net/2142/29530
Copyright and License Information
Copyright 2011 Piyas Chowdhury

Owning Collections

Graduate Dissertations and Theses at Illinois PRIMARY
Graduate Theses and Dissertations at Illinois
Dissertations and Theses - Mechanical Science and Engineering