Date of Award

6-2005

Document Type

Thesis

Degree Name

Master of Science in Astronautical Engineering

Department

Department of Aeronautics and Astronautics

First Advisor

Shankar Mall, PhD

Abstract

This research focuses on investigating the mechanical behavior of cracked aluminum panels repaired with bonded boron/epoxy composite patches. The effects of crack initiation and growth on the residual strength of the repaired panels are characterized. This research establishes a correlation between damage modes, residual strength and evolution of strain within as well as outside the patch. Monotonic tensile tests on specimens with a perfectly bonded patch were used to determine the base line strength. Likewise, fatigue tests on specimens with a perfectly bonded patch served to establish baseline fatigue life. In addition, several specimens with a perfectly bonded patch were subjected to different fractions of the expected fatigue life, introducing damage, which were quantified by NDE techniques. These specimens were then subjected to a monotonic tensile test to failure in order to characterize the residual strength and the evolution of strain within and outside the patch, and the correlation between the disbonds and strain measurements at various locations on the specimen. This research looks to help in extending the service life of military and commercial aging aircraft, by using bonded composite patches on developing cracks in the structure. Bonded composite patches may be able to replace the crack patching technique of using bolted joints, which have the disadvantage of requiring holes to be machined in the metallic structure, which decreases its load-carrying capacity, creating stress concentrations and sites for crack initiation. In this study it was learned how the strain values increase as the crack grows. And despite differing crack growth rates, the strain values followed the growth of the crack closely throughout all the tests. The effects of overload situations were seen, and how this produces a retardation effect in the rate of growth of the crack.

AFIT Designator

AFIT-GA-ENY-05-J01

DTIC Accession Number

ADA438420

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