Effects of crack arresting delaminations in aluminum-lithium alloys

Hernquist, Mark W.

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Description

Title

Effects of crack arresting delaminations in aluminum-lithium alloys

Author(s)

Hernquist, Mark W.

Issue Date

2010-05-19T18:38:20Z

Director of Research (if dissertation) or Advisor (if thesis)

Beaudoin, Armand J.

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)

• aluminum
• lithium
• fracture
• delamination

Abstract

Aluminum‐lithium alloys have been studied extensively in the last century for their low densities and increased stiffness over conventional high strength aluminum alloys. Combined with cryogenic strength and toughness properties exceeding those at room temperatures, Al‐Li alloys are an appealing choice in astronautics. However, along with these beneficial properties comes a propensity for limited ductility contributing to an unconventional fracture mechanism known as delamination, a secondary fracture along a grain boundary interface similar to the separation within a laminated composite. In this study, mechanical experimentation was coupled with computer simulation to investigate the causes and effects of delaminations occurring along grain boundaries perpendicular to the direction of a Mode I primary crack. Fracture toughness samples were tested with concurrent in situ Digital Image Correlation to obtain a means for validation of the two finite element models. The models were devised to capture the bulk response of the sample immediately prior to and after the delamination event. A crystal plasticity framework with rate‐independent kinematic hardening was then used to determine the local behavior of the crystallographic orientations prone to delamination.

Graduation Semester

2010-5

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http://hdl.handle.net/2142/16132

Copyright and License Information

Copyright 2010 Mark W. Hernquist

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