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Title:Exploration of incompatibility in Al-Li alloys using high energy diffraction microscopy and a crystal plasticity model
Author(s):Tayon, Wesley
Advisor(s):Beaudoin, Armand J.
Department / Program:Mechanical Science and Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):High Energy Diffraction Microscopy (HEDM)
Al-Li alloy
Crystal Plasticity
Geometrically Necessary Dislocations
Abstract:Aluminum-lithium (Al-Li) alloys have inherently desirable properties such as increased specific stiffness and strength. Without question, these alloys would be candidate materials for many aerospace structural designs if it were not for a complicated and confounding mode of fracture termed ‘delamination.’ Delamination is a secondary form of fracture along flat grain boundaries that initiates as a result of highly localized deformation. Currently, designers are reluctant to use Al-Li in structural applications due to concerns over the potential for delamination fracture and the inability to predict/account for it. Recent advancements in technology have enabled more detailed characterizations of delamination fracture with high-speed data collection/analysis. Experimental observations using these improved methods have identified delamination susceptible locations within Al-Li alloy microstructures, revealed preferential (localized) damage accumulation near grain boundaries that exhibit delamination failure, and identified grain boundary shear as a driving force for delamination. The extent of localization may be controlled by precipitates, grain orientation, and grain interactions. The current work leverages in situ High Energy Diffraction Microscopy (HEDM) and polycrystal plasticity simulations to study the local evolution of lattice strains to gain insight into the development of incompatibility. The identification of factors that initiate and drive delamination fracture, such as the development of shear and incompatibility between grain pairs, will be critical for the development of appropriate design criteria and potential processing modifications to eliminate the tendency for delamination fracture in Al-Li alloys. Results from this study highlight the anisotropic response of several grain pairs as indicated through the development of strain and signed dislocation densities in crystal plasticity simulations and experimental testing. Grain pairs that display strong signs of local heterogeneity in mechanical behavior are likely to be more susceptible fracture via delamination.
Issue Date:2012-05-22
Rights Information:Copyright 2012 Wesley Tayon
Date Available in IDEALS:2012-05-22
Date Deposited:2012-05

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