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

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.

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

2012

Author dc:creator

• Chowdhury, Piyas

Contributors dc:contributor

• Sehitoglu, Huseyin

• slip irreversibility
• twin
• Fatigue crack growth
• nano-obstacle
• molecular dynamics

Statement dc:rights

• Copyright 2011 Piyas Chowdhury

Language dc:language

en

Handle dc:identifier

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

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/29530