Date of Award

12-1995

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Aeronautics and Astronautics

First Advisor

Shankar Mall, PhD

Abstract

More and more aircraft, both commercial and military, are being called upon to fly well beyond their economic and structural service lives. Budget cuts and dwindling new aircraft development has forced the United States Air Force (USAF) to look toward more reliable structural repairs. One of these repair techniques, which was the subject of this study, is the repair of metallic aircraft structures using high strength composite materials. This study investigated the fatigue response of a precracked, 508x1 52x1 mm, 2024-T3 aluminum panel repaired with a partially bonded, unidirectional, three-ply boron/epoxy composite reinforcement with ply lengths of 68, 56 and 50 mm and a width of 50 mm. Intentional disbonds were created in the bondline of the repair using teflon inserts to simulate defects seen in real applications due to service conditions or during manufacturing. The repaired panels were subjected to constant amplitude fatigue testing at a peak load of 120 MPa to study the damage and fatigue tolerance of partially bonded composite reinforcements to cracked aluminum panels. The effects of various disbond locations and sizes were investigated and compared to each other as well as to panels repaired with a completely bonded reinforcement and to cracked panels without any reinforcement. Five disbond locations were investigated. Also, the effect of disbond size varying from 5 to 20% of the total bond area for a few cases of disbond location was investigated. It was found that disbonds around the crack resulted in greater crack growth rates and reduced specimen life. The amount of patch efficiency reduction was a function of how much of the crack was covered by the disbond during growth within the patch as well as the size of the disbond perpendicular to the crack.

AFIT Designator

AFIT-GAE-ENY-95D-7

DTIC Accession Number

ADA306361

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