Doctoral Dissertations

Abstract

"Micro-slotting, a micro-scale relaxation residual stress measurement technique, has been shown in recent years to be a reliable method for measuring local residual stresses in metallic materials. This technique employs an SEM-focused ion beam system for milling and imaging, digital image correlation software to track displacements due to residual stress relaxation, and finite element analysis for interpolation of the original local stress state. In this research, a micro-slotting procedure was established using finite element models and was used to obtain sub-surface residual stress measurements on machined and shot peened planar Ti-6Al-4V samples. These measurements were compared to macro-scale XRD residual stress measurements, and discrepancies between the results of the two techniques were discussed. The measurement procedure was then applied to as-drilled and cold-expanded holes for near-edge measurement of residual hoop stresses. Comparison of the measured residual stress distributions with plastic strain data obtained using EBSD allowed for interpretation of fatigue life differences and crack growth behavior. Next, a grid of measurements was performed in a sub-surface region of the shot peened sample, and EBSD was used to acquire microstructure information in the measurement regions. Comparison of the measured displacements and interpolated residual stress values with the local microstructure allowed for novel qualitative observations regarding residual stress orientation and microstructure effects on the measured residual stress relaxation. Last, the use of the micro-slotting technique was demonstrated for measurement of local residual stress in additive manufactured components. Series of measurements were performed across two interfaces in a complex Ti-6Al-4V build, and post-measurement optical microscopy allowed for analysis of the residual stress data at the microstructural level"--Abstract, page iv.

Advisor(s)

Newkirk, Joseph William

Committee Member(s)

Zhou, Caizhi
Bartlett, Laura
Wen, Haiming
Castle, James

Department(s)

Materials Science and Engineering

Degree Name

Ph. D. in Metallurgical Engineering

Comments

The funding support for this work was provided by the Air Force Research Lab-managed Metals Affordability Initiative (MAI) consortium and Boeing Research & Technology.

Publisher

Missouri University of Science and Technology

Publication Date

Fall 2018

Journal article titles appearing in thesis/dissertation

  • Micro-slotting technique for reliable measurement of sub-surface residual stress in Ti-6Al-4V
  • Micro-slotting residual stress measurement technique for understanding fatigue performance of open-hole Ti-6Al-4V samples
  • Qualitative evaluation of local microstructure effects on micro-slotting residual stress measurements in Ti-6Al-4V
  • Micro-scale residual stress measurements across interfaces in a LFMT Ti-6Al-4V build

Pagination

xvii, 131 pages

Note about bibliography

Includes bibliographical references.

Rights

© 2018 Elizabeth Anne Burns, All rights reserved.

Document Type

Dissertation - Open Access

File Type

text

Language

English

Thesis Number

T 11989

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Included in

Metallurgy Commons

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