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Title:Grain-boundary shear in AA7050: an experimental investigation using digital image correlation and finite element techniques
Author(s):Garbaciak, Timothy S
Advisor(s):Beaudoin, Armand J.
Department / Program:Mechanical Science & Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
solid mechanics
digital image correlation
finite element analysis
Abstract:The effects of heat treatment and hot working processes on aluminum alloy 7050 have been well-characterized under standard tensile loading, and shear deformation along grain boundaries has been shown to be a key mechanism for deformation and failure of the material. Using experimental and simulation techniques, the behavior of hot-rolled and aged aluminum alloy 7050 is investigated under direct shear loading parallel and perpendicular to grain boundaries. Digital Image Correlation (DIC) is used to obtain strain measurements on specimen surface during testing, and a validation study of titanium specimens is presented to evaluate its effectiveness at this task. Two specimen geometries for AA7050 are presented, designed to induce pure shear failure under compressive loading; a single-ligament specimen, which is used to obtain the strain field around the ligament and basic material properties; and a three-ligament specimen, which is used to examine the strain-hardening behavior and the plastic work before fracture. The strain fields show a high degree of localization, with high shear strains accompanied by a "peel" strain that complicates analysis of the failure state. Calculations of the shear modulus, shear yield strength and shear ultimate strength show the peak- aged specimens are stronger and stiff er than the over-aged specimens, due to the size of the strengthening precipitates. From a material anisotropy perspective, the rolling and transverse directions prove to be the strongest, due to a combination of textural anisotropy from rolling as well as the effect of coarse precipitates aligned along the roll direction. The 3-ligament specimens show strain hardening on the order of 20 MPa between first and second ligament failure, with a corresponding drop in the amount plastic work observed. The hardness of the peak-aged specimens leads to higher energy dissipation than the over-aged specimens, without a corresponding decrease in strain capacity.
Issue Date:2015-07-20
Rights Information:Copyright 2015 Timothy Stephen Garbaciak
Date Available in IDEALS:2015-09-29
Date Deposited:August 201

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