Date of Award

3-2003

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Aeronautics and Astronautics

First Advisor

Anthony N. Palazotto, PhD

Abstract

Many military and commercial aircraft are being called upon to fly well beyond their original intended service lives. This has forced the United States Air Force (USAF) to increasingly rely on structural repairs to address fatigue induced damage and to extend aircraft useful life. The focus of this research is the use of a high-strength composite patch technique to repair a fatigue crack on an aluminum aircraft structure. This study investigates the thermal residual strains that occur as a direct result of the coefficient of thermal expansion (CTE) mismatch between the repair patch and the underlying cracked metallic structure to which the patch is bonded. This research examines the response of a precracked 24 inches x 6 inches x 0.125 inch 7075-T6 aluminum panel repaired with a 15-ply graphite/epoxy patch. Two adhesives: EA 9696 and FM 73M were used with varying cure cycles. The hypothesis is that by reducing cure temperatures the CTE mismatch will be less dramatic thus yielding a more robust repair with a comparable fatigue crack growth rate. The research concluded that reducing the cure cycle temperature could decrease the thermal residual strains by as much as 26.5% between the graphite/epoxy composite patch and structure when FM 73M adhesive is used to bond them together and 7.4% when EA 9696 is used. The research also concluded that a lower cure cycle temperature did not detrimentally affect the panels' fatigue crack growth rates.

AFIT Designator

AFIT-GAE-ENY-03-11J

DTIC Accession Number

ADA415693

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