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Title:Deformation and residual stresses at the intragranular scale – a study using high energy x-ray diffraction and modeling in polycrystalline alloys
Author(s):Chatterjee, Kamalika
Director of Research:Beaudoin, Armand J.
Doctoral Committee Chair(s):Beaudoin, Armand J.
Doctoral Committee Member(s):Johnson, Harley T.; Tortorelli, Daniel A.; Jasiuk, Iwona M.; Miller, Matthew P.; Sangid, Michael D.
Department / Program:Mechanical Sci & Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Ti-7Al alloy
Mesoscale field dislocation mechanics
High energy x-ray diffraction
Residual stress
Subgrain level stress
Strain rate sensitivity
Plasticity bursts
Power-law scaling
High speed detector
Stress gradient
Stress triaxiality
Slip tendency
Abstract:Deformation and internal stress distribution in polycrystalline materials depend upon interactions among neighboring grains and sub-grains (substructure inside a grain). With the advent of high energy x-ray diffraction (HEXD), using synchrotron radiation, it has become possible to probe the bulk of a polycrystalline material in-situ and investigate material deformation with sufficient spatial and temporal resolution. In the current work, the HEXD measurements are used to investigate stress gradients, residual stresses, stress triaxilities, slip system activities, strain rate sensitivities and intermittency in plasticity (jerky motion of dislocations) within individual grains of a Ti-7Al alloy sample so as to interpret the deformation mechanisms and locate any weak spots at that length scale. A high speed mixed mode pixel array detector was utilized to capture diffraction data at rates of 20-500 Hz. Such temporal resolution was necessary for determination of the strain rate sensitivities of individual slip systems and to detect the intermittency in plastic deformation of individual grains in Ti-7Al. In particular cases, a power-law type scaling relationship was established between the size and the probability distribution of the plasticity events. A mesoscale field dislocation mechanics based crystal-plasticity model was employed to demonstrate slip system activity consistent with HEXD data. The experimentally determined grain and sub-grain level characteristics were used to initialize and validate the model. The model was primarily intended to simulate the development of residual stresses at grain or sub-grain scales. The experimental techniques introduced and the results obtained provide insight into the material deformation behavior and hold excellent promise for improving investigation methods and modeling attempts at the crystal-scale.
Issue Date:2017-09-11
Rights Information:Copyright 2017 Kamalika Chatterjee
Date Available in IDEALS:2018-03-13
Date Deposited:2017-12

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