Date of Award

11-2020

Document Type

Thesis - Open Access

Degree Name

Master of Science in Aerospace Engineering

Department

Aerospace Engineering

Committee Chair

Dr. Alberto W. Mello

First Committee Member

Dr. Daewon Kim

Second Committee Member

Dr. David J. Sypeck

Comments

The manufacturing and preparation of alloys normally include processes to improve their resistance to crack growth and fatigue endurance for structural application. The benefits of cold expansion are well known, and its application is widely used in new and repaired structures, even in crack arrester holes. When applied in the field, damaged material removal in a cold expansion procedure may be limited to a maximum allowable diameter for reaming and finishing, which may leave small cracks on the strained region. To completely understand the effect of initial cracks as a function of initial plastic deformation level in a cold-worked hole it is necessary to fully evaluate stress/strain distribution during and post cold expansion.

For the completion of this thesis, Al 2024-T3 samples were dimensioned and manufactured following best practices and results from classic plasticity theories. Analytical stress and strain calculations were compared to numerical solutions from elastic-plastic analysis using NX Nastran FEMAP, as well as experimental strain measurements calculated by calibrated Digital Image Correlation with the use of images taken during the cold-working process. The fatigue life was compared between pre-cracked open and cold expanded specimens. The crack growth was monitored using a digital optical microscope. The full analysis and stress/strain maps can help in further development to simulate a typical aerospace application, with test of a cold-worked hole in presence of a galvanic couple under aggressive environment to establish the impact of local residual stress in crack growth acceleration or formation of new cracks.

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